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  • Artikel  (1.326)
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  • Elektrotechnik, Elektronik, Nachrichtentechnik  (1.326)
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  • 1
    Publikationsdatum: 2020-08-25
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2020-08-27
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2020-07-15
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2020-07-10
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2020-07-11
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2013-09-26
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2013-09-13
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2013-09-13
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2013-09-20
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2013-09-20
    Beschreibung: 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.
    Print ISSN: 1687-5869
    Digitale ISSN: 1687-5877
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Publiziert von Hindawi
    Standort Signatur Erwartet Verfügbarkeit
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