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  • Articles  (3,695)
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  • International Journal of Antennas and Propagation  (1,465)
  • 97415
  • Electrical Engineering, Measurement and Control Technology  (3,695)
  • 1
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    High-Precision Spotlight SAR Imaging with Joint Modified Fast Factorized Backprojection and Autofocus (2020)
    Hindawi
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    Publication Date: 2020-08-25
    Description: Fast factorized backprojection (FFBP) takes advantage of high accuracy of time-domain algorithms while also possessing high efficiency comparable with conventional frequency domain algorithms. When phase errors need to be compensated for high-resolution synthetic aperture radar (SAR) imaging, however, neither polar formatted subimages within FFBP flow nor the final Cartesian image formed by FFBP is suitable for phase gradient autofocus (PGA). This is because these kinds of images are not capable of providing PGA with a clear Fourier transform relationship (FTR) between image domain and range-compressed phase history domain. In this paper, we make some essential modifications to the original FFBP and present a scheme to incorporate overlapped-subaperture frame for an accurate PGA processing. The raw data collected by an airborne high-resolution spotlight SAR are used to demonstrate the performance of this algorithm.
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  • 2
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    Frequency Diverse Array Target Localization Based on IPSO-BP (2020)
    Hindawi
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    Publication Date: 2020-08-27
    Description: For the traditional target localization algorithms of frequency diverse array (FDA), there are some problems such as angle and distance coupling in single-frequency receiving FDA mode, large amount of calculation, and weak adaptability. This paper introduces a good learning and predictive method of target localization by using BP neural network on FDA, and FDA-IPSO-BP neural network algorithm is formed. The improved particle swarm optimization (IPSO) algorithm with nonlinear weights is developed to optimize the neural network weights and biases to prevent BP neural network from easily falling into local minimum points. In addition, the decoupling of angle and distance with single frequency increment is well solved. The simulation experiments show that the proposed algorithm has better target localization effect and convergence speed, compared with FDA-BP and FDA-MUSIC algorithms.
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  • 3
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    Prediction Model of In-Band Blocking Interference under the Electromagnetic Radiation of Dual-Frequency Continuous Wave (2020)
    Hindawi
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    Publication Date: 2020-07-15
    Description: Two hypotheses for the blocking effect mechanisms under the electromagnetic radiation are presented, and the corresponding dual-frequency interference prediction models are proposed, which can be used to predict the working state of equipment under the condition that the single-frequency susceptibility is known. By taking a radar and a communication radio as the EUT, the experiments of dual-frequency continuous wave electromagnetic radiation are designed and carried out to verify the prediction models. The test results show that the sensitive bandwidth of blocking interference effect for the tested radar and the communication station is consistent with their working bandwidth, respectively. By substituting the test data into the proposed prediction models, the prediction errors of the models are less than 13%. Moreover, it can be found that the tested radar is more sensitive to the peak value of electric field, and the tested communication station is more sensitive to the effective value of electric field.
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  • 4
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    An UHF RFID Reader Antenna with Multitag Identification for Extremely Low-Temperature Medical Systems (2020)
    Hindawi
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    Publication Date: 2020-07-10
    Description: A radio frequency identification reader antenna having multitag identification for medical systems is presented, which consists of four PIFAs, two hybrid couplers, and four power dividers. The high isolation is achieved by the symmetric design of the antenna geometry and four power dividers, which are fed by two hybrid couplers. The experimental results show an isolation of more than 40 dB in the North American (902–928 MHz), Korean (917–923.5 MHz), and Japanese (916.7–923.5 MHz) RFID frequency bands.
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  • 5
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    Central DOA Estimation Method for Exponential-Type Coherent Distributed Source Based on Fourth-Order Cumulant (2020)
    Hindawi
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    Publication Date: 2020-07-11
    Description: The performance of direction-of-arrival (DOA) estimation for sparse arrays applied to the distributed source is worse than that applied to the point source model. In this paper, we introduce the coprime array with a large array aperture into the DOA estimation algorithm of the exponential-type coherent distributed source. In particular, we focus on the fourth-order cumulant (FOC) of the received signal which can provide more useful information when the signal is non-Gaussian than when it is Gaussian. The proposed algorithm extends the array aperture by combining the sparsity of array space domain with the fourth-order cumulant characteristics of signals, which improves the estimation accuracy and degree of freedom (DOF). Firstly, the signal-received model of the sparse array is established, and the fourth-order cumulant matrix of the received signal of the sparse array is calculated based on the characteristics of distributed sources, which extend the array aperture. Then, the virtual array is constructed by the sum aggregate of physical array elements, and the position set of its maximum continuous part array element is obtained. Finally, the center DOA estimation of the distributed source is realized by the subspace method. The accuracy and DOF of the proposed algorithm are higher than those of the distributed signal parameter estimator (DSPE) algorithm and least-squares estimation signal parameters via rotational invariance techniques (LS-ESPRIT) algorithm when the array elements are the same. Complexity analysis and numerical simulations are provided to demonstrate the superiority of the proposed method.
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  • 6
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    Conformal Array Pattern Synthesis and Activated Elements Selection Strategy Based on PSOGSA Algorithm (2015)
    Hindawi
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    Publication Date: 2015-08-12
    Description: The pattern synthesis and activated element selection for conformal array is investigated based on hybrid particle swarm optimization-gravitational search algorithm (PSOGSA) in this paper. With the introduction of PSOGSA algorithm which is a novel hybrid optimization technique, the element excitations are optimized to obtain the desired pattern for conformal array in the case of considering uncoupled and coupled element pattern. Numerical simulation and full-wave electromagnetic calculation verify the advantage and efficiency of our method. Then, a novel strategy of activated element selection based on PSOGSA algorithm is proposed for saving the energy consumption in conformal array.
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  • 7
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    A Compact Experimental Planar Antenna with a USB Connector for Mobile Phone Application (2015)
    Hindawi
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    Publication Date: 2015-08-04
    Description: A practical antenna design combined with a universal serial bus (USB) connector in close vicinity is proposed. In the proposed arrangement, the antenna unit consisted of two planar inverted F antennas (PIFAs) placed on the two sides of the USB connector. The antenna is located at the bottom of the mobile phone to avoid the crowded space on the top side of the phone where various mobile phone accessories are usually assigned. A diplexer is incorporated in the unit to alleviate the adverse effect of the metal USB connector on the radiating efficiency of the antenna. A prototype antenna was fabricated and tested and showed good coverage for GSM850/900/1800/1900, UMTS2100, and LTE700/2500 multibands operation. The overall performances demonstrated the good design of the proposed unit for mobile phone application.
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  • 8
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    A Building-Block Favoring Method for the Topology Optimization of Internal Antenna Design (2015)
    Hindawi
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    Publication Date: 2015-08-03
    Description: This paper proposes a new design technique for internal antenna development. The proposed method is based on the framework of topology optimization incorporated with three effective mechanisms favoring the building blocks of associated optimization problems. Conventionally, the topology optimization of antenna structures discretizes a design space into uniform and rectangular pixels. However, the defining length of the resultant building blocks is so large that the problem difficulty arises; furthermore, the order of the building blocks becomes extremely high, so genetic algorithms (GAs) and binary particle swarm optimization (BPSO) are not more efficient than the random search algorithm. In order to form tight linkage groups of building blocks, this paper proposes a novel approach to handle the design details. In particular, a nonuniform discretization is adopted to discretize the design space, and the initialization of GAs is assigned as orthogonal arrays (OAs) instead of a randomized population; moreover, the control map of GAs is constructed by ensuring the schema growth based on the generalized schema theorem. By using the proposed method, two internal antennas are thus successfully developed. The simulated and measured results show that the proposed technique significantly outperforms the conventional topology optimization.
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  • 9
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    Radio Capacity Estimation for Millimeter Wave 5G Cellular Networks Using Narrow Beamwidth Antennas at the Base Stations (2015)
    Hindawi
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    Publication Date: 2015-08-19
    Description: This paper presents radio frequency (RF) capacity estimation for millimeter wave (mm-wave) based fifth-generation (5G) cellular networks using field-level simulations. It is shown that, by reducing antenna beamwidth from 65° to 30°, we can enhance the capacity of mm-wave cellular networks roughly by 3.0 times at a distance of 220 m from the base station (BS). This enhancement is far much higher than the corresponding enhancement of 1.2 times observed for 900 MHz and 2.6 GHz microwave networks at the same distance from the BS. Thus the use of narrow beamwidth transmitting antennas has more pronounced benefits in mm-wave networks. Deployment trials performed on an LTE TDD site operating on 2.6 GHz show that 6-sector site with 27° antenna beamwidth enhances the quality of service (QoS) roughly by 40% and more than doubles the overall BS throughput (while enhancing the per sector throughput 1.1 times on average) compared to a 3-sector site using 65° antenna beamwidth. This agrees well with our capacity simulations. Since mm-wave 5G networks will use arbitrary number of beams, with beamwidth much less than 30°, the capacity enhancement expected in 5G system when using narrow beamwidth antennas would be much more than three times observed in our simulations.
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  • 10
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    A Three-Component Model Based on Macropropagation Phenomena Approach for Complex Building Scattering (2015)
    Hindawi
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    Publication Date: 2015-08-24
    Description: Multipaths represent a common predominant and uncontrolled component on channel impairments for all terrestrial and Land Mobile Satellite systems. Without restrictions w.r.t mobile terrestrial applications, the addressed multipath problematic in this paper is focused on Land Mobile Satellite applications where delayed signal replicas are highly impacting performances on communication systems while they induce strong positioning errors for navigation systems. The actual trend in propagation channel modelling is to improve the multipath characterisation and representation by using semideterministic and hybrid physical-statistical models into channel simulators instead of narrow-band empirical approaches. In this context, this paper presents a new simplified model, called 3CM (3-Component Model) to reproduce building scattering in an efficient way which strongly improves computation performances. This model is based on asymptotic methods, namely, PO (Physical Optics) which allows the 3CM to be frequency scalable, polarimetric, and dielectric materials oriented. Note that the proposed model and the retained approach can be integrated into more complex tools such as existing ray tracers. However, this issue is not discussed in this paper.
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  • 11
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    Full-Wave Analysis of Stable Cross Fractal Frequency Selective Surfaces Using an Iterative Procedure Based on Wave Concept (2015)
    Hindawi
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    Publication Date: 2015-08-18
    Description: This work presents a full-wave analysis of stable frequency selective surfaces (FSSs) composed of periodic arrays of cross fractal patch elements. The shapes of these patch elements are defined conforming to a fractal concept, where the generator fractal geometry is successively subdivided into parts which are smaller copies of the previous ones (defined as fractal levels). The main objective of this work is to investigate the performance of FSSs with cross fractal patch element geometries including their frequency response and stability in relation to both the angle of incidence and polarization of the plane wave. The frequency response of FSS structures is obtained using the wave concept iterative procedure (WCIP). This method is based on a wave concept formulation and the boundary conditions for the FSS structure. Prototypes were manufactured and measured to verify the WCIP model accuracy. A good agreement between WCIP and measured results was observed for the proposed cross fractal FSSs. In addition, these FSSs exhibited good angular stability.
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  • 12
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    Ray Tracing RF Field Prediction: An Unforgiving Validation (2015)
    Hindawi
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    Publication Date: 2015-08-13
    Description: The prediction of RF coverage in urban environments is now commonly considered a solved problem with tens of models proposed in the literature showing good performance against measurements. Among these, ray tracing is regarded as one of the most accurate ones available. In the present work, however, we show that a great deal of work is still needed to make ray tracing really unleash its potential in practical use. A very extensive validation of a state-of-the-art 3D ray tracing model is carried out through comparison with measurements in one of the most challenging environments: the city of San Francisco. Although the comparison is based on RF cellular coverage at 850 and 1900 MHz, a widely studied territory, very relevant sources of error and inaccuracy are identified in several cases along with possible solutions.
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  • 13
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    Integral Equation Analysis of EM Scattering from Multilayered Metallic Photonic Crystal Accelerated with Adaptive Cross Approximation (2015)
    Hindawi
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    Publication Date: 2015-08-05
    Description: A space-domain integral equation method accelerated with adaptive cross approximation (ACA) is presented for the fast and accurate analysis of electromagnetic (EM) scattering from multilayered metallic photonic crystal (MPC). The method directly solves for the electric field in order to easily enable the periodic boundary condition (PBC) in the spatial domain. The ACA is a purely algebraic method allowing the compression of fully populated matrices; hence, its formulation and implementation are independent of integral equation kernel (Green’s function). Therefore, the ACA is very well suited for accelerating integral equation analysis of periodic structure with the integral kernel of the periodic Green’s function (PGF). The computation of the spatial-domain periodic Green’s function (PGF) is accelerated by the modified Ewald transformation, such that the multilayered periodic structure can be analyzed efficiently and accurately. An effective interpolation method is also proposed to fast compute the periodic Green’s function, which can greatly reduce the time of matrix filling. Numerical examples show that the proposed method can greatly save the frequency sweep time for multilayered periodic structure.
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  • 14
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    Study of the Colocated Dual-Polarized MIMO Capacity Composed of Dipole and Loop Antennas (2015)
    Hindawi
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    Publication Date: 2015-06-04
    Description: The colocated dual-polarized dipole (DPD) and dual-polarized loop (DPL) MIMO channel performances are compared. Computation results show that, for the ideal electric and magnetic dipoles, the dual-polarized MIMO systems have identical channel capacity. But the contour plots of the capacity gain of the realistic DPD and DPL are different, due to the difference in antenna patterns. The cumulative distribution function (CDF) of the capacity gain in the two-mirror (TM) channel shows that, for small distance, the capacity gain obtained by the DPD is obviously smaller than that of the DPL, but, with the increase of the distance, the difference gets smaller. A DPL with low mutual coupling is fabricated. Measured results show that high MIMO capacities can be obtained by this DPL in both the anechoic chamber (AC) and the realistic office room. The capacity gain of the DPL antenna is 1.5–1.99, which basically coincides with the theoretical and numerical results. Furthermore, the capacity of the virtual DPL antenna with no mutual couplings is also investigated. It is shown that, in the AC, the mutual coupling will generally decrease the dual-polarized MIMO capacity; however, in the office room, the effect of mutual coupling is not always negative.
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  • 15
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    Novel Base Station MIMO Antennas with Enhanced Spectral Efficiencies Using Angular Reuse (2015)
    Hindawi
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    Publication Date: 2015-06-05
    Description: The true polarization diversity (TPD) technique is combined with the spatial diversity technique in novel MIMO antenna array geometries with a large number of elements. The use of a large number of elements requires some angular reuse within the array for polarization diversity. With designs compatible with existing base station antenna array configurations, the novel geometries with combining diversity schemes are shown to be able to achieve near the maximum spectral efficiencies. True polarization diversity (TPD) schemes are found to be an excellent complement to more conventional spatial diversity schemes for obtaining optimum MIMO array performance in base station antennas.
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  • 16
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    An Efficient Full-Wave Electromagnetic Analysis for Capacitive Body-Coupled Communication (2015)
    Hindawi
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    Publication Date: 2015-06-05
    Description: Measured propagation loss for capacitive body-coupled communication (BCC) channel (1 MHz to 60 MHz) is limitedly available in the literature for distances longer than 50 cm. This is either because of experimental complexity to isolate the earth-ground or design complexity in realizing a reliable communication link to assess the performance limitations of capacitive BCC channel. Therefore, an alternate efficient full-wave electromagnetic (EM) simulation approach is presented to realistically analyze capacitive BCC, that is, the interaction of capacitive coupler, the human body, and the environment all together. The presented simulation approach is first evaluated for numerical/human body variation uncertainties and then validated with measurement results from literature, followed by the analysis of capacitive BCC channel for twenty different scenarios. The simulation results show that the vertical coupler configuration is less susceptible to physiological variations of underlying tissues compared to the horizontal coupler configuration. The propagation loss is less for arm positions when they are not touching the torso region irrespective of the communication distance. The propagation loss has also been explained for complex scenarios formed by the ground-plane and the material structures (metals or dielectrics) with the human body. The estimated propagation loss has been used to investigate the link-budget requirement for designing capacitive BCC system in CMOS sub-micron technologies.
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  • 17
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    Compressive Sensing for High-Resolution Direction-of-Arrival Estimation via Iterative Optimization on Sensing Matrix (2015)
    Hindawi
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    Publication Date: 2015-07-30
    Description: A novel compressive sensing- (CS-) based direction-of-arrival (DOA) estimation algorithm is proposed to solve the performance degradation of the CS-based DOA estimation in the presence of sensing matrix mismatching. Firstly, a DOA sparse sensing model is set up in the presence of sensing matrix mismatching. Secondly, combining the Dantzig selector (DS) algorithm and least-absolute shrinkage and selection operator (LASSO) algorithm, a CS-based DOA estimation algorithm which performs iterative optimization alternatively on target angle information vector and sensing matrix mismatching error vector is proposed. The simulation result indicates that the proposed algorithm possesses higher angle resolution and estimation accuracy compared with conventional CS-based DOA estimation algorithms.
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  • 18
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    A Novel Miniaturized Dual Slant-Polarized UWB Antenna Array with Excellent Pattern Symmetry Property for MIMO Applications (2015)
    Hindawi
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    Publication Date: 2015-07-30
    Description: A novel miniaturized 1 × 10 uniform linear dual slant-polarized UWB antenna array for MIMO base station is presented. The antenna array operates in the frequency band from 1710 to 2690 MHz with a 17.3–18.7 dBi gain in a size of 105 × 1100 × 37 mm. The array element is composed of two single-polarized dipoles evolved from bow-tie antenna with slots on them, which miniaturize the size of the antenna. The 10 array elements are fed through an air dielectric strip-line power splitter. Two parameters, the beam tracking and the beam squint, are presented to quantitatively describe the pattern symmetry property of the antenna. The simulated and measured radiation performances are studied and compared. The results show that the pattern symmetry property of the single antenna element has been improved about 24% compared with the former study, and the antenna array also provides excellent pattern symmetry property.
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  • 19
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    Smart Wireless Power Transfer Operated by Time-Modulated Arrays via a Two-Step Procedure (2015)
    Hindawi
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    Publication Date: 2015-08-05
    Description: The paper introduces a novel method for agile and precise wireless power transmission operated by a time-modulated array. The unique, almost real-time reconfiguration capability of these arrays is fully exploited by a two-step procedure: first, a two-element time-modulated subarray is used for localization of tagged sensors to be energized; the entire 16-element TMA then provides the power to the detected tags, by exploiting the fundamental and first-sideband harmonic radiation. An investigation on the best array architecture is carried out, showing the importance of the adopted nonlinear/full-wave computer-aided-design platform. Very promising simulated energy transfer performance of the entire nonlinear radiating system is demonstrated.
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  • 20
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    Dual-Polarized Planar Phased Array Analysis for Meteorological Applications (2015)
    Hindawi
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    Publication Date: 2015-08-07
    Description: This paper presents a theoretical analysis for the accuracy requirements of the planar polarimetric phased array radar (PPPAR) in meteorological applications. Among many factors that contribute to the polarimetric biases, four factors are considered and analyzed in this study, namely, the polarization distortion due to the intrinsic limitation of a dual-polarized antenna element, the antenna pattern measurement error, the entire array patterns, and the imperfect horizontal and vertical channels. Two operation modes, the alternately transmitting and simultaneously receiving (ATSR) mode and the simultaneously transmitting and simultaneously receiving (STSR) mode, are discussed. For each mode, the polarimetric biases are formulated. As the STSR mode with orthogonal waveforms is similar to the ATSR mode, the analysis is mainly focused on the ATSR mode and the impacts of the bias sources on the measurement of polarimetric variables are investigated through Monte Carlo simulations. Some insights of the accuracy requirements are obtained and summarized.
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  • 21
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    Dual Circularly Polarized Omnidirectional Antenna with Slot Array on Coaxial Cylinder (2015)
    Hindawi
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    Publication Date: 2015-08-07
    Description: A dual circularly polarized (CP) omnidirectional antenna based on slot array in coaxial cylinder structure is presented in this paper. It is constructed by perpendicular slot pairs around and along the axis of the coaxial cylinder to realize the omnidirectional CP property, and two ports are assigned in its two sides as left hand circularly polarized (LHCP) port and right hand circularly polarized (RHCP) port, respectively. The proposed antenna achieves a bandwidth of 16.4% ranging from 5.05 to 5.95 GHz with an isolation higher than 15 dB between the two CP ports, and the return loss (RL) is higher than 10 dB within the bandwidth in both of the two ports. From the measured results, the average axial ratio (AR) of the proposed antenna in omnidirectional plane is lower than 1.5 dB.
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  • 22
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    Creeping Ray Tracing Algorithm for Arbitrary NURBS Surfaces Based on Adaptive Variable Step Euler Method (2015)
    Hindawi
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    Publication Date: 2015-08-13
    Description: Although the uniform theory of diffraction (UTD) could be theoretically applied to arbitrarilyshaped convex objects modeled by nonuniform rational B-splines (NURBS), one of the great challenges in calculation of the UTD surface diffracted fields is the difficulty in determining the geodesic paths along which the creeping waves propagate on arbitrarilyshaped NURBS surfaces. In differential geometry, geodesic paths satisfy geodesic differential equation (GDE). Hence, in this paper, a general and efficient adaptive variable step Euler method is introduced for solving the GDE on arbitrarilyshaped NURBS surfaces. In contrast with conventional Euler method, the proposed method employs a shape factor (SF) to efficiently enhance the accuracy of tracing and extends the application of UTD for practical engineering. The validity and usefulness of the algorithm can be verified by the numerical results.
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  • 23
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    A Wideband Dual-Polarized Antenna Using Planar Quasi-Open-Sleeve Dipoles for Base Station Applications (2015)
    Hindawi
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    Publication Date: 2015-08-13
    Description: A wideband dual-polarized antenna for WLAN, WiMAX, and LTE base station applications is presented in this paper. The proposed antenna consists of two pairs of orthogonal planar quasi-open-sleeve dipoles along the centerlines, a balanced feeding structure and a square ground plane. The planar quasi-open-sleeve dipole comprises a pair of bowtie-shaped planar dipoles with two parallel curve parasitic elements. The introduced parallel curve parasitic elements change the path of the current of the original bowtie-shaped planar dipoles at high frequencies and hence wideband characteristic is achieved. Two pairs of the planar quasi-open-sleeve dipoles placed orthogonally further broaden the bandwidth of the antenna with dual-polarization characteristics. The proposed antenna achieves a 10-dB return loss bandwidth from 2.32 to 4.03 GHz (53.9% bandwidth) using the planar quasi-open-sleeve dipole structures. The isolation between the two ports remains more than 32 dB in the whole bandwidth. Measured results show that the proposed antenna keeps the cross-polarization under −33 dB and the front-to-back ratio better than 15 dB in the operating band. The antenna has an area of 0.3λ  × 0.3λ at 2.32 GHz making it easy to be extended to an array element.
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  • 24
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    Backward Surface Wave Propagation and Radiation along a One-Dimensional Folded Cylindrical Helix Array (2015)
    Hindawi
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    Publication Date: 2015-09-11
    Description: Wave propagation along a closely spaced folded cylindrical helix (FCH) array is investigated for the purpose of designing compact array for energy transport and antenna radiation. It is found that the height of this surface wave guiding structure can be decreased from 0.24 to 0.06 by replacing the monopole element with the FCH. Both the propagation constant and the mode distribution of the dominant wave mechanism are extracted by ESPRIT algorithm, which indicates that a backward propagating surface wave is supported by the array structure. A compact backfire FCH antenna array is designed and measured based on the identified dominant wave mechanism.
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    Transponder Designs for Harmonic Radar Applications (2015)
    Hindawi
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    Publication Date: 2015-09-15
    Description: This work presents a review on the concept of harmonic or secondary radar, where a tag or transponder is used to respond at a harmonic multiple of the incoming interrogation signal. In harmonic radar, the tag is called a harmonic transponder and the necessary frequency multiplication is implemented using a nonlinear element, such as a Schottky diode. Different applications and operating frequencies of harmonic transponders are presented, along with various tag design aspects. The designer may have to deal with certain tradeoffs during the design with respect to a number of transponder properties, and the role of these tradeoffs is also considered. Additionally, techniques usable for characterization of harmonic transponders are discussed.
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    Synthesis of Circular Array Antenna for Sidelobe Level and Aperture Size Control Using Flower Pollination Algorithm (2015)
    Hindawi
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    Publication Date: 2015-09-16
    Description: Sidelobe level suppression is a major problem in circular array antenna (CAA) synthesis. Many conventional numerical techniques are proposed to achieve this which are time consuming and often fail to handle multimodal problems. In this paper, a method of circular array synthesis using nature inspired flower pollination algorithm (FPA) is proposed. The synthesis technique considered here adapts one and two degrees of freedom, namely, amplitude only and amplitude spacing. The effectiveness of the FPA is studied by comparing the results with genetic algorithm (GA) and uniform circular array antenna (UCAA) with uniform spacing. Also the effect of additional degree of freedom on the aperture size and the computational time is analyzed. A relative side lobe level (SLL) of −25 dB is achieved using the algorithm under both no beam scanning (0°) and beam scanning (15°) conditions for 20 and 40 elements of CAA.
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    On the Capacity of Densely Packed Arrays with Mutual Coupling and Correlated Noise (2015)
    Hindawi
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    Publication Date: 2015-09-18
    Description: Capacity of a wireless link can be enhanced by increasing the number of receive antennas. However, imposed receiver physical size constraints necessitate that the antenna elements be in close proximity, which typically reduces the overall link capacity of the wireless channel. Counterintuitively, under certain conditions the capacity of the overall link can be enhanced by decreasing antenna spacings. The focus of this paper is that of identifying the fundamental mechanisms and the conditions that give rise to this excess capacity. Closed-form expressions that directly quantify this capacity gain are derived based on a representative circuit theoretic model. Interesting insights are developed about the impact of different noise and interference sources and the limiting effect of heat losses in the antenna system. The capacity analysis is subsequently generalized to encompass the effect of antenna current deformation and load mismatch due to mutual coupling, based on the standard Method of Moments (MoM) analysis, demonstrating similar capacity enhancement behavior as predicted by the closed-form expressions.
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    Dual Band and Beam-Steering Antennas Using Reconfigurable Feed on Sierpinski Structure (2015)
    Hindawi
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    Publication Date: 2015-09-21
    Description: Fractal patch antennas based on the Sierpinski structure are studied in this paper. The antennas operate at dual bands (around 2 and 5 GHz) and are designed to steer the beam directions at around 5 GHz band (the first harmonic). The antennas use reconfigurable triple feeds on the same antenna plane to have three beam directions. The same scale factor defines the geometrical self-similarity of the Sierpinski fractal. The proposed antennas are fabricated through three iterations from 1st order to 3rd order and utilize FR-4 (εr = 4.4) for the microwave substrate. The performances of the antennas, such as reflection coefficients and radiation patterns are verified by simulation and measurement. The results show that the properties of the proposed antennas in three orders are similar.
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    A MIMO Reversed Antenna Array Design for gsm1800/td-scdma/lte/wi-max/wiLan/wifi (2015)
    Hindawi
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    Publication Date: 2015-09-21
    Description: A triband MIMO antenna used for gsm1800/td-scdma/lte/wi-max/wiLan/wifi has been proposed in this paper. The design with the size of 32 m 73.6 mm is fabricated on FR4 substrate (thickness is 1.6 mm). This antenna consists of two reversed monopole meandered radiators and defected ground structure which work together to achieve impedance match and enhance isolation for all operating bands. According to the subsequent measured results, the working frequency domains are at gsm1800 (1.71 GHz–1.88 GHz), td-scdma (1.88 GHz–2.025 GHz), lte (2.1–2.35, 2.48–2.51), wi-max (3.5 GHz, 5.5 GHz), wiLan (5.725 GHz–5.8 GHz), and wifi (5.8 GHz–5.88 GHz) approximately. Besides, the measured radiation patterns (gain total) are also well at these working frequency domains and the omnidirectional performance has been achieved for the reversed MIMO antenna array. Furthermore, the realized isolation is more than 15 dB, 24.2 dB, and 22 dB at the first, the second, and the third working frequency band, respectively.
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    A Compact Two-Level Sequentially Rotated Circularly Polarized Antenna Array for C-Band Applications (2015)
    Hindawi
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    Publication Date: 2015-11-24
    Description: A compact circular polarized antenna array with a convenient gain/bandwidth/dimension trade-off is proposed for applications in the C-band. The design is based on the recursive application of the sequential phase architecture, resulting in a 4 × 4 array of closely packed identical antennas. The 16 antenna elements are disc-based patches operating in modal degeneration, tuned to exhibit a broad while imperfect polarization. Exploiting the compact dimension of the patches and a space-filling design for the feeding network, the entire array is designed to minimize the occupied area. A prototype of the proposed array is fabricated with standard photoetching procedure in a single-layer via less printed board of overall area 80 × 80 mm2. Adequate left-hand polarization is observed over a wide bandwidth, demonstrating a convenient trade-off between bandwidth and axial ratio. Satisfying experimental results validate the proposed design, with a peak gain of 12.6 dB at 6.7 GHz maintained within 3 dB for 1 GHz, a very wide 10 dB return loss bandwidth of 3 GHz, and a 4 dB axial ratio bandwidth of 1.82 GHz, meaning 31% of fractional bandwidth.
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    Direction of Arrival Estimation Accuracy Enhancement via Using Displacement Invariance Technique (2015)
    Hindawi
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    Publication Date: 2015-08-26
    Description: A new algorithm for improving Direction of Arrival Estimation (DOAE) accuracy has been carried out. Two contributions are introduced. First, Doppler frequency shift that resulted from the target movement is estimated using the displacement invariance technique (DIT). Second, the effect of Doppler frequency is modeled and incorporated into ESPRIT algorithm in order to increase the estimation accuracy. It is worth mentioning that the subspace approach has been employed into ESPRIT and DIT methods to reduce the computational complexity and the model’s nonlinearity effect. The DOAE accuracy has been verified by closed-form Cramér-Rao bound (CRB). The simulation results of the proposed algorithm are better than those of the previous estimation techniques leading to the estimator performance enhancement.
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    A Multibeam Dual-Band Orthogonal Linearly Polarized Antenna Array for Satellite Communication on the Move (2015)
    Hindawi
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    Publication Date: 2015-10-28
    Description: The design and simulation of a 10 × 8 multibeam dual-band orthogonal linearly polarized antenna array operating at Ku-band are presented for transmit-receive applications. By using patches with different coupling methods as elements, both perpendicular polarization in 12.25–12.75 GHz band and horizontal polarization in 14.0–14.5 GHz band are realized in a shared antenna aperture. A microstrip Rotman lens is employed as the beamforming network with 7 input ports, which can generate a corresponding number of beams to cover −30°–30° with 5 dB beamwidth along one dimension. This type of multibeam orthogonal linearly polarized planar antenna is a good candidate for satellite communication (SatCom).
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    Electromagnetic Field Interference on Transmission Lines due to On-Board Antenna (2015)
    Hindawi
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    Publication Date: 2015-06-01
    Description: As the available space in the board of a mobile device becomes smaller and more compact, circuit elements and transmission lines are arranged in very close proximity, especially from the antennas which are usually installed on the same board. Due to the various on-board antennas which are designed in small space, the transmission lines on the board are electromagnetically interfered, resulting in the performance degradation of the circuit. So the engineers and circuit designers should find the least interfered place for the transmission lines and components to minimize the electromagnetic interferences. This paper discusses and presents a methodology to find the least sensitive position in the induced current distribution as well as in the noise power delivered from the antenna. For this purpose some vertical, horizontal, and bent transmission lines with antenna on the same board are designed and fabricated with and without common ground, and the transferred powers to the transmission lines were measured and were also simulated using a full-wave simulator. The results predicted by the EM simulation model were successfully confirmed through the measurement of S-parameters in the experimental setup, which shows the validness of the suggested analysis method.
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    Bistatic High Frequency Radar Ocean Surface Cross Section for an FMCW Source with an Antenna on a Floating Platform (2016)
    Hindawi
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    Publication Date: 2016-07-18
    Description: The first- and second-order bistatic high frequency radar cross sections of the ocean surface with an antenna on a floating platform are derived for a frequency-modulated continuous wave (FMCW) source. Based on previous work, the derivation begins with the general bistatic electric field in the frequency domain for the case of a floating antenna. Demodulation and range transformation are used to obtain the range information, distinguishing the process from that used for a pulsed radar. After Fourier-transforming the autocorrelation and comparing the result with the radar range equation, the radar cross sections are derived. The new first- and second-order antenna-motion-incorporated bistatic radar cross section models for an FMCW source are simulated and compared with those for a pulsed source. Results show that, for the same radar operating parameters, the first-order radar cross section for the FMCW waveform is a little lower than that for a pulsed source. The second-order radar cross section for the FMCW waveform reduces to that for the pulsed waveform when the scattering patch limit approaches infinity. The effect of platform motion on the radar cross sections for an FMCW waveform is investigated for a variety of sea states and operating frequencies and, in general, is found to be similar to that for a pulsed waveform.
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    A Parasitic Array Receiver for ISAR Imaging of Ship Targets Using a Coastal Radar (2016)
    Hindawi
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    Publication Date: 2016-07-15
    Description: The detection and identification of ship targets navigating in coastal areas are essential in order to prevent maritime accidents and to take countermeasures against illegal activities. Usually, coastal radar systems are employed for the detection of vessels, whereas noncooperative ship targets as well as ships not equipped with AIS transponders can be identified by means of dedicated active radar imaging system by means of ISAR processing. In this work, we define a parasitic array receiver for ISAR imaging purposes based on the signal transmitted by an opportunistic coastal radar over its successive scans. In order to obtain the proper cross-range resolution, the physical aperture provided by the array is combined with the synthetic aperture provided by the target motion. By properly designing the array of passive devices, the system is able to correctly observe the signal reflected from the ships over successive scans of the coastal radar. Specifically, the upper bounded interelement spacing provides a correct angular sampling accordingly to the Nyquist theorem and the lower bounded number of elements of the array ensures the continuity of the observation during multiple scans. An ad hoc focusing technique has been then proposed to provide the ISAR images of the ships. Simulated analysis proved the effectiveness of the proposed system to provide top-view images of ship targets suitable for ATR procedures.
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    Miniaturized Dielectric Resonator Antenna Array for GNSS Applications (2016)
    Hindawi
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    Publication Date: 2016-07-15
    Description: The increase in global navigation satellite systems (GNSS) availability and services is fostering a new wave of applications related to satellite navigation. Such increase is also followed by more and more threats, aiming at signal disruption. In order to fully exploit the potentialities of precise and reliable navigation, being able at the same time to counteract threats such as interference, jamming, and spoofing, smart antenna systems are being investigated worldwide, with the requirements of multiband operation and compactness. In order to answer such need, the present work proposes a miniaturized dielectric resonator antenna (DRA) 2 × 2 array able to operate at E5/L5, L2, and E6 bands, with an overall footprint of only 3.5′′ (89 mm).
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    A Wideband Antenna with Circular and Rectangular Shaped Slots for Mobile Phone Applications (2016)
    Hindawi
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    Publication Date: 2016-07-18
    Description: A wideband slot antenna for mobile phone applications is proposed. The antenna has two slots with open ends etched on the opposite edges of the ground plane. The main slot, of total length of 59 mm, is composed of a rectangle connected to a circle having radius of 5 mm. Another slot, having a rectangular shape with width of 2.8 mm and length of 26 mm, is employed to enhance the antenna bandwidth. The slots are fed by means of a rectangular monopole connected to a circular patch joined to a bent 50 Ω microstrip transmission line forming two right angles. To obtain a wideband impedance matching, the upper edge of the monopole and a part of the feeding line evolve along the top edge of the two slots. To reduce the antenna size, the upper part of the board above the slot (just 3 mm from the slot) is folded vertically to the ground plane. The measured bandwidth of the antenna is 0.698–1.10 GHz and 1.64–2.83 GHz covering LTE700/2300/2500, GSM850/900/1800/1900, and UMTS bands.
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    An Approximation Mathematical Formula of Pattern Analysis for Distorted Reflector Antennas considering Surface Normal Vector Variation (2016)
    Hindawi
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    Publication Date: 2016-07-26
    Description: An approximation mathematical formula to compute the distorted radiation pattern for reflector antennas is presented. In this approximation formula, besides the phase error caused by the structural deformation being added in the far field integral, the surface normal vector variation is also taken into consideration. The formula is derived by expanding the surface normal vector into a first-order Taylor series and the phase error into a second-order Taylor series. By assembling the integrals including the contributions of both surface normal vector variation and phase error, the far field electrical vector expressed as a function of structural nodal displacements is further obtained in a matrix form. Simulation results of a distorted reflector show the application of this formula.
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    Study of Ocean Waves Measured by Collocated HH and VV Polarized X-Band Marine Radars (2016)
    Hindawi
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    Publication Date: 2016-07-27
    Description: The significant wave height (SWH) retrieved from collocated HH and VV polarized X-band marine radars under different sea states is studied. The SWH are retrieved from different principal components of X-band marine radar image sequence. As compared with the SWH measured by a buoy, the root-mean-square errors of the SWH are 0.32–0.45 m for VV polarization, and they are 0.37–0.60 m for HH polarization. At the wind speeds of 0–5 m/s, the SWH can be derived from VV polarized radar images, while the backscatter of HH polarized radar is too weak to contain wave signals at very low wind speeds (~0–3 m/s). At the wind speeds of 5–18 m/s, the SWH retrieved from VV polarization coincide well with the SWH measured by the buoy, while the SWH retrieved from HH polarization correspond with the changes of the wind speed. At the wind speeds of 18–26 m/s, the influence of wave breaking on HH polarization is more important than that on VV polarization. This indicates that the imaging mechanisms of HH polarized X-band marine radar are different from those of VV polarized X-band marine radar.
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    Recent Advances in Design and Signal Processing for Antenna Arrays (2016)
    Hindawi
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    Publication Date: 2016-08-01
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    Evolutionary Algorithm Geometry Optimization of Optical Antennas (2016)
    Hindawi
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    Publication Date: 2016-06-21
    Description: Printed circuit antennas have been used for the detection of electromagnetic radiation at a wide range of frequencies that go from radio frequencies (RF) up to optical frequencies. The design of printed antennas at optical frequencies has been done by using design rules derived from the radio frequency domain which do not take into account the dispersion of material parameters at optical frequencies. This can make traditional RF antenna design not suitable for optical antenna design. This work presents the results of using a genetic algorithm (GA) for obtaining an optimized geometry (unconventional geometries) that may be used as optical regime antennas to capture electromagnetic waves. The radiation patterns and optical properties of the GA generated geometries were compared with the conventional dipole geometry. The characterizations were conducted via finite element method (FEM) computational simulations.
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    Effect of Antenna Parameters on the Field Coverage in Tunnel Environments (2016)
    Hindawi
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    Publication Date: 2016-05-06
    Description: Radio wave propagation in confined spaces is consequent upon the reflections of boundaries; thus, the radiation characteristics of the antenna have significant influence on the field coverage in the confined space. This paper investigates the effects of antenna parameters on field coverage characteristics in a tunnel environment. A modified modal method is proposed to analyse the wave propagation properties along the tunnel. The relationships between the amplitudes of modes and the antenna parameters, including the beam width, beam direction, and antenna location, are analysed. The results indicate that by properly selecting the antenna parameters, optimum field coverage in tunnel environments can be realized.
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    A Small Planar Antenna for 4G Mobile Phone Application (2016)
    Hindawi
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    Publication Date: 2016-05-10
    Description: The analysis and design of a small planar multiband antenna operating in the 4G frequency bands are presented. The numerical and experimental results demonstrated that the proposed antenna satisfies the requirement of 6 dB return loss for the impedance bandwidth of the LTE700/LTE2300/LTE2500 and WiMAX3500 bands. The gains at 750 MHz/2.3 GHz/2.6 GHz/3.5 GHz are 2.1 dBi/4.9 dBi/4.7 dBi/4.3 dBi, respectively. The measured radiation patterns verify the suitability of the antenna to be employed in mobile phones. The dimensions of the radiant patch are 49 × 10 mm2. The proposed antenna can be easily fabricated and customized to various 4G mobile phones as a compact internal antenna.
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    Millimeter Wave Fabry-Perot Resonator Antenna Fed by CPW with High Gain and Broadband (2016)
    Hindawi
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    Publication Date: 2016-05-11
    Description: A novel millimeter wave coplanar waveguide (CPW) fed Fabry-Perot (F-P) antenna with high gain, broad bandwidth, and low profile is reported. The partially reflective surface (PRS) and the ground form the F-P resonator cavity, which is filled with the same dielectric substrate. A dual rhombic slot loop on the ground acts as the primary feeding antenna, which is fed by the CPW and has broad bandwidth. In order to improve the antenna gain, metal vias are inserted surrounding the F-P cavity. A CPW-to-microstrip transition is designed to measure the performances of the antenna and extend the applications. The measured impedance bandwidth of less than −10 dB is from 34 to 37.7 GHz (10.5%), and the gain is 15.4 dBi at the center frequency of 35 GHz with a 3 dB gain bandwidth of 7.1%. This performance of the antenna shows a tradeoff among gain, bandwidth, and profile.
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    Location Optimization for Square Array Antennas Using Differential Evolution Algorithm (2016)
    Hindawi
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    Publication Date: 2016-05-11
    Description: In recent works thinned arrays giving minimum peak sidelobe levels for planar square antenna arrays are obtained using Hadamard difference sets. In the current work thinned array configurations giving lower peak sidelobe levels than those given in the literature are obtained for square arrays of , , , and elements. Differential evolution algorithm is used in the determination of the antenna locations.
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    A Dual-Band Printed End-Fire Antenna with DSPSL Feeding (2016)
    Hindawi
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    Publication Date: 2016-05-27
    Description: A novel dual-band printed end-fired antenna with double-sided parallel-strip line (DSPSL) feeding is presented. The DSPSL acts in wideband transition using balanced transmission. Two different modes of the parasitic patches allow the antenna to work in different bands. The printed antenna is designed as a quasi-Yagi structure to achieve directivity in the lower band, and the parallel rectangular patches serve as the parasitic director. These patches act as radiation patches with end-fire direction characteristics in the upper band. The measured bandwidths were 18.3% for the lower frequency band (2.28–2.74 GHz) and 12.6% for the upper frequency band (5.46–6.2 GHz).
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    A Novel Compact Dual-Polarized Antenna (2016)
    Hindawi
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    Publication Date: 2016-05-27
    Description: A novel compact dual-polarized antenna is proposed. The antenna has a 1.43% impedance bandwidth which is from 1801 MHz to 1827 MHz for return loss larger than 10 dB. The isolation between the two ports is above 28 dB in the bandwidth, and the gain is 6.6 dBi. The proposed antenna not only consists of a full-planar structure, but also is easy to be fabricated for its simple structure. Additionally, a section of slots and slits is cut on the radiation patch to reduce the area of it to 54% compared with the conventional square patch.
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    Brush-Painting and Photonic Sintering of Copper Oxide and Silver Inks on Wood and Cardboard Substrates to Form Antennas for UHF RFID Tags (2016)
    Hindawi
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    Publication Date: 2016-05-13
    Description: Additive deposition of inks with metallic inclusions provides compelling means to embed electronics into versatile structures. The need to integrate electronics into environmentally friendly components and structures increases dramatically together with the increasing popularity of the Internet of Things. We demonstrate a novel brush-painting method for depositing copper oxide and silver inks directly on wood and cardboard substrates and discuss the optimization of the photonic sintering process parameters for both materials. The optimized parameters were utilized to manufacture passive ultra high frequency (UHF) radio frequency identification (RFID) tag antennas. The results from wireless testing show that the RFID tags based on the copper oxide and silver ink antennas on wood substrate are readable from ranges of 8.5 and 11 meters, respectively, and on cardboard substrate from read ranges of 8.5 and 12 meters, respectively. These results are well sufficient for many future wireless applications requiring remote identification with RFID.
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    Pilot Design for Sparse Channel Estimation in Large-Scale MIMO-OFDM System (2016)
    Hindawi
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    Publication Date: 2016-05-13
    Description: The pilot design problem in large-scale multi-input-multioutput orthogonal frequency division multiplexing (MIMO-OFDM) system is investigated from the perspective of compressed sensing (CS). According to the CS theory, the success probability of estimation is dependent on the mutual coherence of the reconstruction matrix. Specifically, the smaller the mutual coherence is, the higher the success probability is. Based on this conclusion, this paper proposes a pilot design algorithm based on alternating projection and obtains a nonorthogonal pilot pattern. Simulation results show that applying the proposed pattern gives the better performance compared to applying conventional orthogonal one in terms of normalized mean square error (NMSE) of the channel estimate. Moreover, the bit error rate (BER) performance of the large-scale MIMO-OFDM system is improved.
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    Composite GPS Patch Antenna for the AR Bandwidth Enhancement (2016)
    Hindawi
    Details
    Publication Date: 2016-02-08
    Description: A composite Global Positioning System (GPS) patch antenna with a quadrature 3 dB hybrid coupler was designed and implemented for working RHCP and had a broadband axial ratio (AR) bandwidth. We designed two patches as a FR-4 patch and 1.5 mm thickness thin ceramic patch with a quadrature 3 dB hybrid coupler. A CP radiation pattern was achieved, and the AR bandwidth improved by incorporating a quadrature 3 dB hybrid coupler feed structure in a micro-strip patch antenna. SMD by chip elements was applied to the quadrature 3 dB hybrid coupler. For the composite FR-4 and ceramic patch antennas, the VSWR measurement showed a 2 : 1 ratio over the entire design band, and the 3 dB AR bandwidth was 295 and 580 MHz for the FR-4 patch and ceramic patch antennas, respectively. The antenna gains for the composite FR-4 and ceramic patch antennas were measured as 1.36–2.75 and 1.47–2.71 dBi with 15.11–25.3% and 19.25–28.45% efficiency, respectively.
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    Beam Performance Optimization of Multibeam Imaging Sonar Based on the Hybrid Algorithm of Binary Particle Swarm Optimization and Convex Optimization (2016)
    Hindawi
    Details
    Publication Date: 2016-05-13
    Description: It should be noted that the peak sidelobe level (PSLL) significantly influences the performance of the multibeam imaging sonar. Although a great amount of work has been done to suppress the PSLL of the array, one can verify that these methods do not provide optimal results when applied to the case of multiple patterns. In order to suppress the PSLL for multibeam imaging sonar array, a hybrid algorithm of binary particle swarm optimization (BPSO) and convex optimization is proposed in this paper. In this algorithm, the PSLL of multiple patterns is taken as the optimization objective. BPSO is considered as a global optimization algorithm to determine best common elements’ positions and convex optimization is considered as a local optimization algorithm to optimize elements’ weights, which guarantees the complete match of the two factors. At last, simulations are carried out to illustrate the effectiveness of the proposed algorithm in this paper. Results show that, for a sparse semicircular array with multiple patterns, the hybrid algorithm can obtain a lower PSLL compared with existing methods and it consumes less calculation time in comparison with other hybrid algorithms.
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    Cell Curvature and Far-Field Superconvergence in Numerical Solutions of Electromagnetic Integral Equations (2016)
    Hindawi
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    Publication Date: 2016-05-13
    Description: Two curved targets are used to explore far-field superconvergence effects arising in numerical solutions of the electric-field and magnetic-field integral equations. Three different orders of basis and testing functions are used to discretize these equations, and three different types of target models (flat facets, quadratic-curved facets, and cubic-curved facets) are employed. Ideal far-field convergence rates are only observed when the model curvature is one degree higher than the basis order.
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    Robust Adaptive Beamforming Using a Low-Complexity Steering Vector Estimation and Covariance Matrix Reconstruction Algorithm (2016)
    Hindawi
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    Publication Date: 2016-07-11
    Description: A novel low-complexity robust adaptive beamforming (RAB) technique is proposed in order to overcome the major drawbacks from which the recent reported RAB algorithms suffer, mainly the high computational cost and the requirement for optimization programs. The proposed algorithm estimates the array steering vector (ASV) using a closed-form formula obtained by a subspace-based method and reconstructs the interference-plus-noise (IPN) covariance matrix by utilizing a sampling progress and employing the covariance matrix taper (CMT) technique. Moreover, the proposed beamformer only requires knowledge of the antenna array geometry and prior information of the probable angular sector in which the actual ASV lies. Simulation results demonstrate the effectiveness and robustness of the proposed algorithm and prove that this algorithm can achieve superior performance over the existing RAB methods.
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    An OPMA for Robust Mutual Coupling Coefficients Estimation of URA with Single Snapshot in MIMO HF Sky-Wave Radar (2016)
    Hindawi
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    Publication Date: 2016-07-21
    Description: Due to the fluctuation of the signal-to-noise ratio (SNR) and the single snapshot case in the MIMO HF sky-wave radar system, the accuracy of the online estimation of the mutual coupling coefficients matrix of the uniform rectangle array (URA) might be degraded by the classical approach, especially in the case of low SNR. In this paper, an Online Particle Mean-Shift Approach (OPMA) is proposed, which is to get a relatively more effective estimation of the mutual coupling coefficients matrix with the low SNR. Firstly, the spatial smoothing technique combined with the MUSIC algorithm of URA is introduced for the DOA estimation of the multiple targets in the case of single snapshot which are taken as coherent sources. Then, based on the idea of the particle filter, the online particles with a moderate computational complexity are used to generate some different estimation results. Finally, the mean-shift algorithm is applied to get a more robust estimate of the equivalent mutual coupling coefficients matrix. The simulation results demonstrate the validity of the proposed approach in terms of the success probability, the statistics of bias, and the variance. The proposed approach is more robust and more accurate than the other two approaches.
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    Minimum Redundancy MIMO Array Synthesis by means of Cyclic Difference Sets (2013)
    Hindawi
    Details
    Publication Date: 2013-09-26
    Description: Antenna array synthesis is an important issue in MIMO radars. By judiciously designing antenna positions, one can create a very long virtual array steering vector with a small number of antennas and therefore achieve very high spatial resolution at a small cost. This paper presents a combinatorial methodology based on cyclic difference sets (CDSs) for minimum redundancy (MR) MIMO array synthesis which seeks to maximize the virtual array aperture for a given number of antennas. First, the key features of CDSs and the CDS-based MR-MIMO layouts are described. Then, the analytical expression of the maximum contiguous virtual array aperture is derived. Further, based on this expression, an enumerative shifting procedure is developed for identifying the optimal CDS-based MR-MIMO layout. Selected examples are analyzed to point out the computational effectiveness of the CDS-based MR-MIMO array synthesis.
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    Full-Wave Analysis of Microstrip Antennas in Three-Layered Spherical Media (2013)
    Hindawi
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    Publication Date: 2013-09-13
    Description: A model of three-layered spherical microstrip antenna has been analyzed based on Rao-Wilton-Glisson (RWG) triangular basis functions using mixed potential integral equation (MPIE). Firstly, the model of antenna and the dyadic Green’s function in spherical microstrip antennas are given at the beginning of this paper. Then, due to the infinite series convergence problem, asymptotic extraction approach is presented to accelerate the Green’s functions convergence speed when source and field points are located in the same layer and different layers. The convergence speed can be accelerated observably by using this method. Finally, in order to simplify impedance matrix elements calculation at the junction of the probe and patch, a novel division fashion of pair of triangles is adopted in this paper. The input impedance result obtained shows the validity and effectiveness of the analysis method comparing with published data.
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    Frequency-Adjustable Small Zeroth-Order Resonant Antenna with Capacitor-Loaded Rectangular Slot on Ground Plane (2013)
    Hindawi
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    Publication Date: 2013-09-13
    Description: A capacitor-loaded electrical small zeroth-order resonant (ZOR) antenna is proposed. The proposed antenna is designed on the basis of a mushroom structure for zeroth-order resonance. To obtain a compact size, the proposed antenna has a rectangular slot on the ground plane, and the chip capacitor is mounted on the slot. The resonant frequency is easily controlled from 2.82 GHz to 2.29 GHz by changing the capacitance from 1 pF to 7 pF, respectively. Therefore, the proposed antenna has the advantages of a small antenna size as well as easy frequency adjustment.
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    Time-Domain Physical Optics Method for the Analysis of Wide-Band EM Scattering from Two-Dimensional Conducting Rough Surface (2013)
    Hindawi
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    Publication Date: 2013-09-20
    Description: Time-domain physical optics (TDPO) method is extended to investigate electromagnetic (EM) scattering from two-dimensional (2D) perfectly electrically conducting (PEC) rough surface in both time domain and frequency domain. The scheme requires relatively small amounts of computer memory and CPU time, and has advantage over the Kirchhoff Approximation (KA) method in obtaining transient response of rough surface by a program run. The 2D Gaussian randomly rough surface is generated by Monte Carlo method and then is partitioned into small triangle facets through the meshing preprocess. The accuracy of TDPO is validated by comparing the numerical results with those obtained by the KA method in both backward and specular directions. The transient response and its frequency distribution of radar cross section (RCS) from rough surface is shown, respectively. The scattering results from rough surface with different size in the specular direction are given. The influence of the root mean square height (σ) and correlation length () on electromagnetic scattering from PEC rough surface is discussed in detail. Finally, the comparisons of backscattering results at different incident angles are presented and analyzed.
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    Zero Index Metamaterial for Designing High-Gain Patch Antenna (2013)
    Hindawi
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    Publication Date: 2013-09-20
    Description: A planar wideband zero-index metamaterial (ZIM) based on mesh grid structure is studied. It is demonstrated that the real part of the index approaches zero at the wideband covering from 9.9 GHz to 11.4 GHz. Two conventional patch antennas whose operating frequencies are both in the range of zero-index frequencies are designed and fabricated. And then, the ZIM is placed in the presence of the conventional patch antennas to form the proposed antennas. The distance between the antenna and the ZIM cover is investigated. Antenna performances are studied with simulations and measurements. The results show that the more directional and higher gain patch antennas can be obtained. The measured results are in good agreement with the simulations. Compared to the conventional patch antenna without the ZIM, it is shown that the beamwidth of antenna with the ZIM cover becomes more convergent and the gain is much higher.
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    A Novel Segmented Modeling Method of Via including the Effect of Power/Ground Plane Pair (2013)
    Hindawi
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    Publication Date: 2013-10-01
    Description: This paper focuses on the modeling method of common interconnects which act as coupling channels in the analysis of PCB immunity. Fast modeling and parameters extraction of power/ground plane pair are realized using cavity resonance method. The calculated results of the model match with the simulation results of HFSS within 9 GHz, which demonstrates the effectiveness of the modeling method. Besides, segmented via modeling method including the effect of power/ground plane pair is proposed. In this modeling method, via structure is decomposed into three parts, and each part is modeled, respectively. The modeling of single via and differential vias in single plane pair and multilayer is completed using this method. High accuracy is reached due to the adoption of the effect of power/ground plane pair and the adoption of second-order circuit model of capacitance and inductance, where the parameters can be gotten from analytic formulas. Finally, considering an actual signal network, for example, the equivalent circuit model of the network, is established, and every part of the equivalent circuit model is imported into Designer for cosimulation. The results are consistent with the simulation results of HFSS within 9 GHz.
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    Broadband Multilayered Array Antenna with EBG Reflector (2013)
    Hindawi
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    Publication Date: 2013-10-01
    Description: Most broadband microstrip antennae are implemented in the form of slot structure or laminate structure. The impedance bandwidth is broadened, but meanwhile, the sidelobe of the directivity pattern and backlobe level are enlarged. A broadband stacked slot coupling microstrip antenna array with EBG structure reflector is proposed. Test results indicate that the proposed reflector structure can effectively improve the directivity pattern of stacked antenna and aperture coupled antenna, promote the front-to-back ratio, and reduce the thickness of the antenna. Therefore, it is more suitable to be applied as an airborne antenna.
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    Suppression of Repeat-Intensive False Targets Based on Temporal Pulse Diversity (2013)
    Hindawi
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    Publication Date: 2013-10-02
    Description: This paper considers the problem of suppressing the repeat-intensive false targets produced by a deception electronic attack (EA) system equipped with a Digital Radio Frequency Memory (DRFM) device. Different from a conventional repeat jammer, this type of jamming intensively retransmits the intercepted signal stored in a DRFM to the victim radar in a very short time-delay interval relative to a radar pulse wide. A multipeak matched-filtering output is then produced other than the merely expected true target. An electronic protection (EP) algorithm based on the space time block code (STBC) is proposed to suppress the adverse effects of this jammer. By transmitting a pulse sequence generated from the STBC in succession and the following cancellation process applied upon the received signal, this algorithm performs successfully in a single antenna system provided that the target models are nonfluctuating or slow fluctuating and the pulse repetition frequency (PRF) is comparatively high. The performance in white and correlated Gaussian disturbance is evaluated by means of Monte Carlo simulations.
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    Design of Multilayer Dielectric Cover to Enhance Gain and Efficiency of Slot Arrays (2013)
    Hindawi
    Details
    Publication Date: 2013-06-11
    Description: An effective design procedure, based on the Elliot synthesis method, is proposed to investigate the properties of waveguide slot arrays with multilayer dielectric cover. Then, the features of the designed arrays are analyzed by means of a FEM commercial software, namely, Ansys HFSS 13. We show how a proper choice of the dielectric cover configuration allows increasing the array gain and aperture efficiency, while taking advantage of the properties of the radome structure, in terms of insulation, protection, and pressurization of the radiating waveguides. Therefore, a significant outcome of the optimal choice of the multilayer dielectric cover is the reduction of the number of slots with respect to an array radiating into free space with the same gain and efficiency, with a consequent reduction of the production cost.
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    Performance Analysis of a Two-Hop MIMO Mobile-to-Mobile via Stratospheric-Relay Link Employing Hierarchical Modulation (2013)
    Hindawi
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    Publication Date: 2013-06-13
    Description: Next generation wireless communication networks intend to take advantage of the integration of terrestrial and aerospace infrastructures. Besides, multiple-input multiple-output (MIMO) architecture is the key technology, which has brought the wireless gigabit vision closer to reality. In this direction, high-altitude platforms (HAPs) could act as relay stations in the stratosphere transferring information from an uplink to a downlink MIMO channel. This paper investigates the performance of a novel transmission scheme for the delivery of mobile-to-mobile (M-to-M) services via a stratospheric relay. It is assumed that the source, relay, and destination nodes are equipped with multiple antennas and that amplify-and-forward (AF) relaying is adopted. The performance is analyzed through rigorous simulations in terms of the bit-error rate (BER) by using a recently proposed 3D geometry-based reference model in spatially correlated flat-fading MIMO channels, employing a hierarchical broadcast technique and minimum mean square error (MMSE) receivers.
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    A Reconfigurable Triple-Notch-Band Antenna Integrated with Defected Microstrip Structure Band-Stop Filter for Ultra-Wideband Cognitive Radio Applications (2013)
    Hindawi
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    Publication Date: 2013-06-13
    Description: A printed reconfigurable ultra-wideband (UWB) monopole antenna with triple narrow band-notched characteristics is proposed for cognitive radio applications in this paper. The triple narrow band-notched frequencies are obtained using a defected microstrip structure (DMS) band stop filter (BSF) embedded in the microstrip feed line and an inverted π-shaped slot etched in the rectangular radiation patch, respectively. Reconfigurable characteristics of the proposed cognitive radio antenna (CRA) are achieved by means of four ideal switches integrated on the DMS-BSF and the inverted π-shaped slot. The proposed UWB CRA can work at eight modes by controlling switches ON and OFF. Moreover, impedance bandwidth, design procedures, and radiation patterns are presented for analysis and explanation of this antenna. The designed antenna operates over the frequency band between 3.1 GHz and 14 GHz (bandwidth of 127.5%), with three notched bands from 4.2 GHz to 6.2 GHz (38.5%), 6.6 GHz to 7.0 GHz (6%), and 12.2 GHz to 14 GHz (13.7%). The antenna is successfully simulated, fabricated, and measured. The results show that it has wide impedance bandwidth, multimodes characteristics, stable gain, and omnidirectional radiation patterns.
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    A Compact Microstrip Spiral Antenna Embedded in Water Bolus for Hyperthermia Applications (2013)
    Hindawi
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    Publication Date: 2013-04-10
    Description: This paper presents the design, simulation, fabrication, and measurement of a circular spiral microstrip antenna embedded in distilled water bolus. The antenna is mainly designed to operate at 434 MHz ISM band to be used for a hyperthermia applicator. The performance of the antenna is compared to a conventional patch antenna also embedded in water bolus. The results show that spiral antenna has significant narrower radiation pattern and is capable to operate at multiple frequencies as well. Narrow beam of the antenna is desired to design a multiantenna arrangement with less coupling and a better focusing resolution which can be crucial for deep regional hyperthermia applications. The option of other frequencies is desirable to have a better control over the penetration depth versus focusing depending on the application region.
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    Modified Dual-Band Stacked Circularly Polarized Microstrip Antenna (2013)
    Hindawi
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    Publication Date: 2013-04-09
    Description: A novel high-performance circularly polarized (CP) antenna is proposed in this paper. Two separate antennas featuring the global positioning system (GPS) dual-band operation (1.575 GHz and 1.227 GHz for L1 band and L2 band, resp.) are integrated with good isolation. To enhance the gain at low angle, a new structure of patch and two parasitic metal elements are introduced. With the optimized design, good axial ratio and near-hemispherical radiation pattern are obtained.
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    Metamaterials (2013)
    Hindawi
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    Publication Date: 2013-03-31
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    Balance Analysis of Microstrip-to-CPS Baluns and Its Effects on Broadband Antenna Performance (2013)
    Hindawi
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    Publication Date: 2013-04-01
    Description: Amplitude and phase balances of two types of microstrip-(MS-) to-coplanar stripline (CPS) baluns have been analyzed through simulations and measurements, and their effects on broadband antenna performance are investigated. The impedance bandwidth of the balun determined by a back-to-back configuration can sometimes overestimate the balun operating bandwidth. With the conventional balun with a 180° phase delay line, it is observed that the balun balance over the operating frequencies becomes much more improved as the CPS length increases to over 0.1 . As compared with the conventional balun, the proposed MS-to-CPS balun demonstrated very wideband performance from 5 to over 20 GHz. With the proposed balun, amplitude and phase imbalances are within 1 dB and ±5°, respectively. Effects of the balun imbalance on overall broadband antenna performance are also discussed with a quasi-Yagi antenna and a narrow beamwidth tapered slot antenna (TSA).
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    Rotating Parabolic-Reflector Antenna Target in SAR Data: Model, Characteristics, and Parameter Estimation (2013)
    Hindawi
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    Publication Date: 2013-04-04
    Description: Parabolic-reflector antennas (PRAs), usually possessing rotation, are a particular type of targets of potential interest to the synthetic aperture radar (SAR) community. This paper is aimed to investigate PRA’s scattering characteristics and then to extract PRA’s parameters from SAR returns, for supporting image interpretation and target recognition. We at first obtain both closed-form and numeric solutions to PRA’s backscattering by geometrical optics (GO), physical optics, and graphical electromagnetic computation, respectively. Based on the GO solution, a migratory scattering center model is at first presented for representing the movement of the specular point with aspect angle, and then a hybrid model, named the migratory/micromotion scattering center (MMSC) model, is proposed for characterizing a rotating PRA in the SAR geometry, which incorporates PRA’s rotation into its migratory scattering center model. Additionally, we in detail analyze PRA’s radar characteristics on radar cross-section, high-resolution range profiles, time-frequency distribution, and 2D images, which also confirm the models proposed. A maximal likelihood estimator is developed for jointly solving the MMSC model for PRA’s multiple parameters by optimization. By exploiting the aforementioned characteristics, the coarse parameter estimation guarantees convergency upon global minima. The signatures recovered can be favorably utilized for SAR image interpretation and target recognition.
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    Analysis for Resolution of Bistatic SAR Configuration with Geosynchronous Transmitter and UAV Receiver (2013)
    Hindawi
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    Publication Date: 2013-04-04
    Description: Bistatical SAR with geosynchronous illuminator and unmanned aerial vehicle receiver (GEO-UAV BiSAR) has significant potential advantages in the field of continuous local observation under a dangerous environment within nearly 24 h. Due to the extreme platform velocity differences, the ellipse orbital movement of GEOSAR makes this BiSAR configuration not like the conventional spaceborne BiSAR. In this paper, based on the orbital kinetic characteristic of GEOSAR, we theoretically analyze the variations of bistatic configuration effect on common azimuth coverage and coherent accumulated time. In addition, two-dimension the resolution is deduced by geometrical configuration on the basis of gradient method. The simulations show that the appropriate selection of initial bistatic configuration can restrain from the appearance of the dead zone in common coverage. And the image results are obtained by frequency domain RD based on Method of Series Reversion (MSR). It is shown that GEO-UAV BiSAR has the high resolution ability.
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    Sparse Planar Array Synthesis Using Matrix Enhancement and Matrix Pencil (2013)
    Hindawi
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    Publication Date: 2013-04-04
    Description: The matrix enhancement and matrix pencil (MEMP) plays important roles in modern signal processing applications. In this paper, MEMP is applied to attack the problem of two-dimensional sparse array synthesis. Firstly, the desired array radiation pattern, as the original pattern for approximating, is sampled to form an enhanced matrix. After performing the singular value decomposition (SVD) and discarding the insignificant singular values according to the prior approximate error, the minimum number of elements can be obtained. Secondly, in order to obtain the eigenvalues, the generalized eigen-decomposition is employed on the approximate matrix, which is the optimal low-rank approximation of the enhanced matrix corresponding to sparse planar array, and then the ESPRIT algorithm is utilized to pair the eigenvalues related to each dimension of the planar array. Finally, element positions and excitations of the sparse planar array are calculated according to the correct pairing of eigenvalues. Simulation results are presented to illustrate the effectiveness of the proposed approach.
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    Wideband, Multiband, Tunable, and Smart Antenna Systems for Mobile and UWB Wireless Applications (2013)
    Hindawi
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    Publication Date: 2013-09-10
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    A Novel Method for Recognition of Bioradiolocation Signal Breathing Patterns for Noncontact Screening of Sleep Apnea Syndrome (2013)
    Hindawi
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    Publication Date: 2013-09-10
    Description: A novel method for recognition of breathing patterns of bioradiolocation signals breathing patterns (BSBP) in the task of noncontact screening of sleep apnea syndrome (SAS) is proposed and implemented on the base of wavelet transform (WT) and neural network (NNW) applications. Selection of the optimal parameters of WT includes determination of the proper level of wavelet decomposition and the best basis for feature extraction using modified entropy criterion. Selection of the optimal properties of NNW includes defining the best number of hidden neurons and learning algorithm for the chosen NNW topology. The effectiveness of the proposed approach is tested on clinically verified database of BRL signals corresponding to the three classes of breathing patterns: obstructive sleep apnea (OSA); central sleep apnea (CSA); normal calm sleeping (NCS) without sleep-disordered breathing (SDB) episodes.
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    Improved Pilot-Aided Channel Estimation for MIMO-OFDM Fading Channels (2013)
    Hindawi
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    Publication Date: 2013-09-12
    Description: An improved pilot-aided channel estimation scheme is proposed to enhance the channel estimation accuracy of multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) fading channels. Based on the adaptive path number selection mechanism, the number of paths can be scalable and adaptively changed with the characteristics of MIMO-OFDM fading channels. The fine channel estimation formulas for all data subcarriers are derived. The space-frequency block code-OFDM (SFBC-OFDM) system and a six-path fading channel model are considered as an example of the high mobility MIMO-OFDM wireless communications system. Through simulations it is shown that SFBC-OFDM system using the proposed approach can satisfy the performance requirements over frequency selective and frequency nonselective fast fading channels.
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    Power Management in Multiuser Adaptive Modulation Transmission under QoS Requirements (2013)
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    Publication Date: 2013-09-17
    Description: A transmitter power management mechanism is presented in this paper where Multiple-Input Multiple-Output (MIMO) Multiuser Random Beamforming with Adaptive Modulation strategy is performed by the system. The objective of the proposed mechanism is quality of service (QoS) satisfaction for the scheduled user. The QoS is represented by the application demanded data rate and symbol error rate. The power outage problem is considered and a practical method to minimize the outage probability is proposed. The obtained results are encouraging as they show a great decrease in the system power budget. The multiuser system capability is also exploited to achieve larger power saving values and smaller probability of power outage by scheduling the user with the best channel characteristics at each time instant. The amount of saved power and the power outage probability are both presented through closed-form expressions. These theoretical results are compared to computer simulations, which show very good agreement in performance.
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    Modelling and Design of HF RFID Passive Transponders with Additional Energy Harvester (2013)
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    Publication Date: 2013-09-19
    Description: The huge progress in electronics technology and RFID technique gives the opportunity to implement additional features in transponders. It should be noted that either passive or semipassive transponders are supplied with energy that is derived from the electromagnetic field generated by the read/write device and its antenna. This power source is used to conduct radio-communication process and excess energy could be used to power the extra electronic circuits, but the problem is to determine the additional power load impact on the RFID system proper operation and size of interrogation zone. The ability to power the supplementary electronic blocks applied in the HF passive transponders is discussed in detail this paper. The simulation model and test samples with a harvester that recovers energy from the electromagnetic field of read/write device and its antenna have been developed in order to conduct investigations. The harvested energy has been utilized to supply a microprocessor acquisition block for LTCC pressure sensor developed in research previously described by authors.
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    Narrowband-to-Narrowband Frequency Reconfiguration with Harmonic Suppression Using Fractal Dipole Antenna (2013)
    Hindawi
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    Publication Date: 2013-09-23
    Description: Harmonic suppressed fractal antenna with switches named TMFDB25 is developed to select desired frequency band from 400 MHz to 3.5 GHz. The radiating element length is changed to tune the operating frequency while the stub is used to eliminate the undesired harmonic frequency. The balun circuit is reduced by 75% from the original size. The antenna is built on a low loss material. It has the ability to select a single frequency out of fifteen different bands and maintain the omnidirectional radiation pattern properties. Furthermore, the antenna is designed, built, and tested. Simulation and measurement results show that the antenna operates well at the specific frequency range. Therefore, the antenna is suitable to be used for switching frequencies in the band of TV, GSM900/1800, 3G, ISM 2.4 GHz, and above.
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    A Model of Double-Directional Indoor Channels for Multiterminal Communications (2013)
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    Publication Date: 2013-09-23
    Description: We propose a model of double-directional indoor nonline of sight (NLOS) channels for multiterminal communications. We derive a simple channel matrix that describes input-output relationship for such channels. The multiterminal systems may consist of several terminals that act as amplify-and-forward (AF) relays, where source, relays, and destination have arbitrary numbers of antennas. We complete our model by characterizing the parameters of double-directional channel impulse response of such channels through measurements in indoor environment using 3D synthetic array antenna at 2.5 GHz band. To find out the relation between spatial characteristic of channels in each hop, we observe the direction of arrival (DOA) and direction of departure (DOD) of multipath component signals at the terminal that acts as relay. We find that there are several closely matched azimuths of DOAs and azimuths of DODs which follow uniform distribution in the range of −180° to 180° for elevation around the broadside direction of vertical omnidirectional elements of arrays.
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    Cross Beam STAP for Nonstationary Clutter Suppression in Airborne Radar (2013)
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    Publication Date: 2013-09-27
    Description: A novel space-time adaptive processing (STAP) method for nonstationary clutter suppression is proposed. The developed method forms a multibeam along the cross line to participate in adaptive processing, which sufficiently utilizes the spatial information both in azimuth and elevation and guarantees the least system degrees of freedom (DOFs). The characteristics of this structure help to suppress the short-range clutter which is the primary component of nonstationary clutter. Therefore, this method provides favorable clutter suppression performance when clutter range dependence exists. Approach analysis and simulation results are given to demonstrate the effectiveness of the method.
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    Analysis of an Underground Horizontal Electrically Small Antenna (2015)
    Hindawi
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    Publication Date: 2015-05-04
    Description: This work is about a horizontal electrically small wire antenna located underground, which transmits electromagnetic signals to the ground. To solve this problem, the expressions of the magnetic vector potential and the electric field are derived. Further, a quasi-static situation is considered in the condition of extremely low frequency (ELF) or super low frequency (SLF) to make an approximation on Sommerfeld integral for easy calculation. The method of moments (MOM) is used to solve the current distribution along the antenna surface at different frequencies, which lays a good foundation for obtaining the electric field of the antenna. Then the three components of the electric field along the radial distance at different polar angles on the ground are investigated, as well as the voltage received on the ground. Furthermore, some influence factors of the antenna are analyzed in order to know the operating characteristics of the antenna better. The results indicate that the antenna length and relative permittivity have a positive correlation with the radial component of the electric field magnitude, while the buried depth, frequency, and conductivity have a negative correlation with that. The influence of these factors on electric field is obvious except the relative permittivity.
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    Analysis of Power Transfer Efficiency of Standard Integrated Circuit Immunity Test Methods (2015)
    Hindawi
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    Publication Date: 2015-05-11
    Description: Direct power injection (DPI) and bulk current injection (BCI) methods are defined in IEC 62132-3 and IEC 62132-4 as the electromagnetic immunity test method of integrated circuits (IC). The forward power measured at the RF noise generator when the IC malfunctions is used as the measure of immunity level of the IC. However, the actual power that causes failure in ICs is different from forward power measured at the noise source. Power transfer efficiency is used as a measure of power loss of the noise injection path. In this paper, the power transfer efficiencies of DPI and BCI methods are derived and validated experimentally with immunity test setup of a clock divider IC. Power transfer efficiency varies significantly over the frequency range as a function of the test method used and the IC input impedance. For the frequency range of 15 kHz to 1 GHz, power transfer efficiency of the BCI test was constantly higher than that of the DPI test. In the DPI test, power transfer efficiency is particularly low in the lower test frequency range up to 10 MHz. When performing the IC immunity tests following the standards, these characteristics of the test methods need to be considered.
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    The Fast Simulation of Scattering Characteristics from a Simplified Time Varying Sea Surface (2015)
    Hindawi
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    Publication Date: 2015-05-11
    Description: This paper aims at applying a simplified sea surface model into the physical optics (PO) method to accelerate the scattering calculation from 1D time varying sea surface. To reduce the number of the segments and make further improvement on the efficiency of PO method, a simplified sea surface is proposed. In this simplified sea surface, the geometry of long waves is locally approximated by tilted facets that are much longer than the electromagnetic wavelength. The capillary waves are considered to be sinusoidal line superimposing on the long waves. The wavenumber of the sinusoidal waves is supposed to satisfy the resonant condition of Bragg waves which is dominant in all the scattered short wave components. Since the capillary wave is periodical within one facet, an analytical integration of the PO term can be performed. The backscattering coefficient obtained from a simplified sea surface model agrees well with that obtained from a realistic sea surface. The Doppler shifts and width also agree well with the realistic model since the capillary waves are taken into consideration. The good agreements indicate that the simplified model is reasonable and valid in predicting both the scattering coefficients and the Doppler spectra.
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    EIRP Characterization of Electrically Large Wireless Equipment with Integrated Signal Generator in a Compact Environment (2015)
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    Publication Date: 2015-05-11
    Description: We describe a measurement technique to characterize the equivalent isotropically radiated power (EIRP) of electrically large wireless equipment in a compact environment. A modified phase-measurement method was proposed and, thus, the separation of the signal generator and radiating element was not required during the measurement. A Fresnel-to-far-field transformation was used for the fast measurement time in a compact anechoic chamber. An experimental verification of the method was carried out in a compact anechoic chamber, where the source-detector separation was approximately 1/5 of the far-field distance. The measured magnitude and phase pattern exhibited only a small error. The EIRP obtained using a Fresnel-to-far-field transformation was compared with a reference value, and the error was within 0.5 dB.
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    Application of Support Vector Machines for Estimating Wall Parameters in Through-Wall Radar Imaging (2015)
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    Publication Date: 2015-05-14
    Description: In through-wall radar imaging (TWRI), ambiguities in wall characteristics including the thickness and the relative permittivity will distort the image and shift the imaged target position. To quickly and accurately estimate the wall parameters, an approach based on a support vector machine (SVM) is proposed. In TWRI problem, the nonlinearity is embodied in the relationship between backscatter data and the wall parameters, which can be obtained through the SVM training process. Measurement results reveal that once the training phase is completed, the technique only needs no more than one second to estimate wall parameters with acceptable errors. Then through-wall images are reconstructed using a back-projection (BP) algorithm by a finite-difference time-domain (FDTD) simulation. Noiseless and noisy measurements are discussed; the simulation results demonstrate that noisy contamination has little influence on the imaging quality. Furthermore, the feasibility and the validity are tested by a more realistic situation. The results show that high-quality and focused images are obtained regardless of the errors in the wall parameter estimates.
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    A Hybrid Solvers Enhanced Integral Equation Domain Decomposition Method for Modeling of Electromagnetic Radiation (2015)
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    Publication Date: 2015-05-15
    Description: The hybrid solvers based on integral equation domain decomposition method (HS-DDM) are developed for modeling of electromagnetic radiation. Based on the philosophy of “divide and conquer,” the IE-DDM divides the original multiscale problem into many closed nonoverlapping subdomains. For adjacent subdomains, the Robin transmission conditions ensure the continuity of currents, so the meshes of different subdomains can be allowed to be nonconformal. It also allows different fast solvers to be used in different subdomains based on the property of different subdomains to reduce the time and memory consumption. Here, the multilevel fast multipole algorithm (MLFMA) and hierarchical (H-) matrices method are combined in the framework of IE-DDM to enhance the capability of IE-DDM and realize efficient solution of multiscale electromagnetic radiating problems. The MLFMA is used to capture propagating wave physics in large, smooth regions, while H-matrices are used to capture evanescent wave physics in small regions which are discretized with dense meshes. Numerical results demonstrate the validity of the HS-DDM.
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    Measurement of Coherence Bandwidth in UHF Radio Channels for Narrowband Networks (2015)
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    Publication Date: 2015-05-05
    Description: This paper presents results of investigation on the coherence bandwidth of narrowband radio channels in 430 MHz band. The coherence bandwidth values were estimated from a power delay profile obtained by recording CDMA2000 forward channel signals during real-field measurements in various environments: medium city, flat terrain, and hilly terrain in northern Poland. The results of measurements are compared with characteristic parameters of UHF radio channel models defined for exemplary narrowband digital system from the TETRA standard. In all of the tested environments, the coherence bandwidth values during most of an observation time were much higher than 25 kHz. Therefore, the fading in tested UHF narrowband channels should be classified as flat fading.
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    Experimental Characterization and Correlation Analysis of Indoor Channels at 15 GHz (2015)
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    Publication Date: 2015-05-06
    Description: The indoor radio channels at 15 GHz are investigated based on measurements. The large- and small-scale fading behaviors as well as the delay dispersion characteristics are discussed. It is found that the large-scale fading, Ricean -factor, and delay spread can be described by log-normal distributions. Furthermore, both autocorrelation and cross correlation properties of the above parameters are analyzed and modeled. These parameters characterize fading and delay behaviors as well as their mutual dependency and can be used as empirical values for future wireless system design and simulation in 15 GHz short-range indoor channels.
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    Effects of Erroneous CSI on the Performance of Multiple-Transmit Antenna Selection (2015)
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    Publication Date: 2015-05-06
    Description: The paper assumes that the channel state information (CSI) is available at the receiver and is known partially at the transmitter through a feedback channel. The bit error rate (BER) performance of multiple transmit antenna selection (MTAS) for the multiple-input and single-output (MISO) system with STBC (MTAS/MISO-STBC) will be investigated in detail. Meanwhile, the selection criterion that maximizes the channel Frobenius norm or minimizes the error probability of MTAS/MISO-STBC system is employed. In two cases of erroneous CSI (ECSI) and inerrable CSI (ICSI), wireless channels of the MTAS systems are modeled and their analytical expressions are derived. For the case of ICSI, the exact BER expressions of the Chernoff upper bound (CUB) for both the MISO-STBC system of full complexity and MTAS system are evaluated, respectively. Next, for the ECSI case, a comprehensive analytical expression of BER CUB for the same system is derived in detail. Finally, extensive Monte-Carlo simulations are presented to support and validate our numerical analysis proposed in this paper. Both the simulating results and the numerical results show that MTAS can reduce effectively the effect of the erroneous CSI.
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    Energy-Efficient Resource Allocation in Uplink Multiuser Massive MIMO Systems (2015)
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    Publication Date: 2015-05-06
    Description: Energy-efficient communications, namely, green communications, has attracted increasing attention due to energy shortage and greenhouse effect. Motivated by this, we consider the uplink energy-efficient resource allocation in multiuser massive multiple-input multiple-output (MIMO) systems. Specifically, we consider that both the number of antenna arrays at the base station (BS) and the transmit data rate at UE are adjusted adaptively to maximize the energy efficiency. Firstly, we demonstrate the existence of a unique resource allocation solution that is globally optimal by exploiting the properties of objective function. Then we develop an iterative algorithm to solve it. By transforming the originally fractional optimization problem into an equivalent subtractive form using the properties of fractional programming, we develop another efficient iterative resource allocation algorithm. Simulation results have validated the effectiveness of the proposed two algorithms and have shown that both algorithms can fast converge to a near-optimal solution in a small number of iterations.
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    On the MIMO Capacity for Distributed System under Composite Rayleigh/Rician Fading and Shadowing (2015)
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    Publication Date: 2015-05-07
    Description: Wireless channels are commonly affected by short-term fading and long-term fading (shadowing). The shadowing effects must be taken into account also when mobility is present in the wireless scenario. Using a composite fading model, the total channel capacity can be studied for a scenario with short-term Rayleigh fading along with shadowing. This work provides quantitative results for these kinds of scenarios with Rayleigh fading and shadowing, considering also multiple-input and multiple-output systems, which have not been previously reported. In addition, the channel capacity has been studied in depth in its relation with the shadowing level, signal to noise ratio, and the number of elements in the multiple-input and multiple-output system. Moreover, the channel performance with shadowing has been compared to the one without it. Furthermore, Rician model with shadowing is studied and its results are reported. In addition, correlated and experimental results are provided. It is identified that the distributed MIMO systems can benefit from shadowing in Rician channels. This advantage has not been reported previously. This type of fading is proposed for massive MIMO by others and our results open the door to emulate massive MIMO on a reverberation chamber.
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    Low Sidelobe Sparse Concentric Ring Arrays Optimization Using Modified GA (2015)
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    Publication Date: 2015-05-08
    Description: To minimize the peak sidelobe level (PSLL) of sparse concentric ring arrays, this paper presents an optimization method of grid ring radii of these arrays. The proposed method is based on modified real genetic algorithm (MGA); it makes grid ring radii as optimal variables and makes elements more reasonably distributed on the array aperture. Also, it can improve the PSLL of the sparse concentric ring arrays and can meanwhile control the computational cost. The simulated results confirming the efficiency and the robustness of the algorithm are provided at last.
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    Design of a Small Modified Minkowski Fractal Antenna for Passive Deep Brain Stimulation Implants (2014)
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    Publication Date: 2014-11-05
    Description: A small planar modified Minkowski fractal antenna is designed and simulated in dual frequency bands (2.4 and 5.8 GHz) for wireless energy harvesting by deep brain stimulation (DBS) devices. The designed antenna, physically being confined inside a miniaturized structure, can efficiently convert the wireless signals in dual ISM frequency bands to the energy source to recharge the DBS battery or power the pulse generator directly. The performance metrics such as the return loss, the specific absorption rate (SAR), and the radiation pattern within skin and muscle-fat-skin tissues are evaluated for the designed antenna. The gain of the proposed antenna is 3.2 dBi at 2.4 GHz and 4.7 dBi at 5.8 GHz; also the averaged SAR of the antenna in human body tissue is found to be well below the legally allowed limit at both frequency bands. The link budget shows the received power at the distance of 25 cm at 2.4 GHz and 5.8 GHz are around 0.4 mW and 0.04 mW, which can empower the DBS implant. The large operational bandwidth, the physical compactness, and the efficiency in wireless signal reception make this antenna suitable in being used in implanted biomedical devices such as DBS pulse generators.
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    Enhancement of Cross-Borehole Pulse Radar Signature on a Partially Water-Filled Tunnel (2014)
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    Publication Date: 2014-12-17
    Description: Cross-borehole pulse radar has been employed to detect a deeply located empty tunnel. In this paper, effects of underground water collected in the bottom of an empty tunnel on cross-borehole pulse radar signatures are analyzed numerically. B-scan images, stacks of received pulses, are calculated by applying the finite-difference time-domain (FDTD) method for 6 different heights of water from the bottom to the half height inside an empty tunnel. The most important features of an empty tunnel, the fastest time of peak (TOP) and time of arrival (TOA) extracted from the B-scan images, are slowed considerably depending on the increased height of water inside the tunnel. To compensate the weak TOP like that of an empty tunnel, a relation curve is formulated only utilizing measurable parameters of the fastest TOP and the fastest TOA. Then, a unified curve including the effects of two granites with the low and high dielectric properties is derived to cover widely varied dielectric properties of underground rocks. Based on the fastest TOP of an empty tunnel, the average difference between the fastest TOP of an empty tunnel and that of a partially water-filled tunnel decreases from 22.92% to 2.59% after enhancement.
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    Statistical Analysis of Radio Propagation Channel in Ruins Environment (2015)
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    Publication Date: 2015-04-02
    Description: The cellphone based localization system for search and rescue in complex high density ruins has attracted a great interest in recent years, where the radio channel characteristics are critical for design and development of such a system. This paper presents a spatial smoothing estimation via rotational invariance technique (SS-ESPRIT) for radio channel characterization of high density ruins. The radio propagations at three typical mobile communication bands (0.9, 1.8, and 2 GHz) are investigated in two different scenarios. Channel parameters, such as arrival time, delays, and complex amplitudes, are statistically analyzed. Furthermore, a channel simulator is built based on these statistics. By comparison analysis of average excess delay and delay spread, the validation results show a good agreement between the measurements and channel modeling results.
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    An Optimal Transmission Strategy for Joint Wireless Information and Energy Transfer in MIMO Relay Channels (2015)
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    Publication Date: 2015-02-06
    Description: An optimal resource allocation strategy for MIMO relay system is considered in simultaneous wireless information and energy transfer network, where two users with multiple antennas communicate with each other assisted by an energy harvesting MIMO relay that gathers energy from the received signal by applying time switching scheme and forwards the received signal by using the harvesting energy. It is focused on the precoder design and resource allocation strategies for the system to allocate the resources among the nodes in decode-and-forward (DF) mode. Specifically, optimal precoder design and energy transfer strategy in MIMO relay channel are firstly proposed. Then, we formulate the resource allocation optimization problem. The closed-form solutions for the time and power allocation are derived. It is revealed that the solution can flexibly allocate the resource for the MIMO relay channel to maximize the sum rate of the system. Simulation results demonstrated that the performance of the proposed algorithm outperforms the traditional fixed method.
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    Broadband DOA Estimation Based on Nested Arrays (2015)
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    Publication Date: 2015-04-29
    Description: Direction of arrival (DOA) estimation is a crucial problem in electronic reconnaissance. A novel broadband DOA estimation method utilizing nested arrays is devised in this paper, which is capable of estimating the frequencies and DOAs of multiple narrowband signals in broadbands, even though they may have different carrier frequencies. The proposed method converts the DOA estimation of multiple signals with different frequencies into the spatial frequency estimation. Then, the DOAs and frequencies are pair matched by sparse recovery. It is possible to significantly increase the degrees of freedom (DOF) with the nested arrays and the number of sources can be more than that of sensor array. In addition, the method can achieve high estimation precision without the two-dimensional search process in frequency and angle domain. The validity of the proposed method is verified by theoretic analysis and simulation results.
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    Design of a Novel UWB Omnidirectional Antenna Using Particle Swarm Optimization (2015)
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    Publication Date: 2015-04-08
    Description: A UWB E-plane omnidirectional microwave antenna is designed and fabricated for IEEE 802.11a communication system and microwave magnetron source system as a radiation monitor. A cooptimization method based on particle swarm optimization (PSO) algorithm and FDTD software is presented. The presented PSO algorithm is useful in many industrial microwave applications, such as microwave magnetron design and other techniques with a high power level. The maximum measured relative bandwidth of 65% is achieved for the proposed antenna after a rapid and efficient optimization. Furthermore, the measured antenna polarization purity reaches about 20 dB at the communication C band. The PSO algorithm is a powerful candidate for microwave passive component design.
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    Scan Performance and Reconfigurability of Agile Radiating Matrix Antenna Prototype (2015)
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    Publication Date: 2015-04-08
    Description: This paper is dedicated to different experimental validations concerning a novel concept of beam forming and beam steering antenna. The working principle of the antenna is based on the equivalent radiating surface approach and inspired from an electromagnetic band gap antenna. The theoretical aspect and some numerical validations have been already published in the work of Abou Taam et al. (2014). Different electromagnetic behaviors have been demonstrated, such as low mutual coupling, and high gain preservation for high scanning angles values. In this paper, some of these electromagnetic behaviors will be proven experimentally by the means of two different feeding configurations.
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    The Simulation and Experiment of a Non-Cross-Feeding Printed Log-Periodic Antenna (2015)
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    Publication Date: 2015-04-08
    Description: A non-cross-fed printed log-periodic antenna is simulated and studied experimentally. To avoid complex feeding with long coaxial line, the non-cross-feeding structure is applied in this antenna. The software CST Microwave Studio is employed to simulate the proposed antenna, and the optimized antenna model is obtained. According to the simulation results, the antenna prototype is produced and measured. Simulation and measured results show that the antenna is with  dB in band of 4.2–9.2 GHz. And the radiation pattern and gain vary steadily in this band, which achieves requirements for wideband antenna. This antenna design can be extended to the design of the antenna integrated in communication circuit.
    Print ISSN: 1687-5869
    Electronic ISSN: 1687-5877
    Topics: Electrical Engineering, Measurement and Control Technology
    Published by Hindawi
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