ALBERT

Description: This paper presents a compact planar tunable quadrature coupler with improved phase responses. Wide coupling-tuning ratio is achieved by using two varactors loaded on the center of the transmission lines of the modified coupler. Closed-form equations are derived for design parameters. For verification, a 1-GHz tunable coupler is designed and measured. The measured results agree well with the simulated ones. The measured power-dividing ratio can be tuned in a range from 16.2 to −35 dB (from 42 to 3.2E-4) with better than 20-dB return loss and isolation, while the phase imbalance is smaller than 10°. The coupler size is $0.21lambda text{g},,times ,,0.08lambda text{g}$ and reduced by 73.1% compared with the conventional branch-line coupler. The theoretical analysis shows that the phase imbalance and insertion loss are mostly caused by the loss from varactors. Then, a tunable coupler with improved phase and loss responses is proposed, where the additional phase difference and insertion loss resulting from the varactors are compensated for by introducing a negative resistance from the negative impedance converter. Measured results of a demonstrative 1-GHz coupler show a power-dividing ratio tuning range from 24.4 to −22.2 dB (from 275.4 to 6E-4) while maintaining 20-dB return loss and isolation. The phase imbalance is smaller than 1° and the insertion loss is improved by 1 dB and nearly close to theoretical values across the tuning range.

Description: This paper presents a new kind of highly flexible frequency-agile bandpass filters (FA-BPFs) based on the novel synchronously tuned dual-mode resonator (STDR). The bandwidth (BW), BW variation tendency, passband selectivity (stopband rejection level), and frequency tuning range of the filter can be predefined individually. Benefiting from the unique characteristics of the STDR, the FA-BPF with very simple and highly flexible design/control procedures is achieved. Due to the proposed geometry, two self-adaptive transmission zeros are introduced and move with the passband. The predefined mechanism is investigated in detail, and the simple design and predefined procedures are summarized. Then, three 0.75–1.7 GHz single-band examples with elliptic response are developed to achieve three predefined absolute BWs (ABW). The design techniques and filter superiority are confirmed by the experiments. Moreover, aiming at China 2G/3G/4G cellular wireless/mobile communication system (up to band 40:0.825–2.65 GHz), a novel intrinsically switchable single-/dual-band FA-BPF is presented based on the proposed STDR. An example with a constant ABW 1 dB and a fractional bandwidth 1 dB (FBW 1 dB is designed to validate the theory and analysis. The FA-BPF is able to operate as a highly selective dual-band FA-BPF with 0.76–1.78 GHz/1.61–2.63 GHz tuning ranges, and also can be switched to single-band operation with the continuous tuning range of 0.76–2.63 GHz.

Description: For the first time, the 6-port quadrature and rat-race couplers with balanced–unbalanced-hybrid ports are proposed. The corresponding design methodology is presented, which is capable of designing the proposed couplers with arbitrary power divisions and terminated resistances. In this paper, four types including quadrature and rat-race couplers are fully analyzed, covering all the application configurations of the balanced/unbalanced ports. Besides, the design equations are rigorously derived, with the final design procedures presented. Eventually, prototypes of the four coupler types are fabricated and experimentally measured. The final results sufficiently validate the proposed methodology.

Description: This paper presents the design and characterization of a load modulated balanced amplifier for telecom base station applications adopting a novel mode of operation. The theory of operation is described explaining the main differences compared to Doherty amplifiers, in particular the RF bandwidth advantages and, on the other hand, the intrinsic nonlinear behavior. The specific design strategy that adopts prematching for back-off broadband matching is explained in detail. A prototype, based on 25-W GaN packaged devices, has been fabricated and measured with single tone CW and modulated signal stimulus. For CW conditions, on the 1.7–2.5-GHz band, the peak output power is between 63 and 78 W, with power added efficiency higher than 48%, 43%, and 39% at saturation, 6- and 8-dB output power back-off, respectively. With a modulated signal for Long Term Evolution the amplifier provides an average output power of around 10 W, with efficiency higher than 40%, and can be linearized by adopting a low complexity predistorter. If compared to previously published power amplifiers targeting similar power and bandwidth, the measurement shows very good performance, demonstrating the potential of this novel technique in the field of efficiency enhanced transmitters.

Description: A new type of K-band high-Q frequency-tunable waveguide filters is proposed in this paper. The presented filter structure adopts a new technique for tuning the resonant frequency of each resonator. A dielectric plate is inserted in each resonator and rotating it leads to the frequency tuning. Unlike the conventional frequency tuning methodologies for tunable waveguide cavity filters, the new frequency tuning technique alleviates the electrical grounding issue for tuning devices. In addition, we demonstrate a new design method that allows the filter to have an absolute constant bandwidth in the frequency tuning range without using tunable coupling structures.

Description: This paper reports on a broadband high-power amplifier (HPA) millimeter-wave integrated circuit (MMIC) covering the extended W-band (65–125 GHz). The MMIC is based on the Fraunhofer IAF 50-nm gate-length metamorphic high-electron-mobility transistor (mHEMT) technology. The HPA consists of two parallelized unit amplifiers. Each unit amplifier (UA) utilizes four stacked-HEMT unit power cells (UPCs) and four-way power combiners at the input and output. The UPCs stack four transistors with a gate width of $4times 40~mu text{m}$ per HEMT. The UA achieves an average small-signal gain of 19.4 dB and an average saturated output power of 21.6 dBm at least from 70 to 110 GHz. The HPA yields an average small-signal gain of 16.8 dB and an average saturated output power of 22.5 dBm at least from 68 to 110 GHz. A peak output power of 24.1 dBm is achieved at an operating frequency of 75 GHz.

Description: The general coupling matrix representation of bandpass filter (BPF) circuits is a widely used technique that has simplified the analysis and optimization of complex microwave filters. In this paper, we demonstrate a novel application of the general coupling matrix for modeling wireless power-transfer (WPT) systems based on the BPF model of magnetically coupled resonators. Compared to other methods of WPT analysis, our model simplifies accommodation of complex loads and provides direct expressions for impedance matching (IM) in WPT systems. Using this tool, we achieve optimal IM for two resonator systems with a complex load, thus achieving the greatest possible power-transfer efficiency (PTE). Furthermore, our model reveals additional design constraints for optimizing PTE in coupled resonator systems exhibiting low quality factor and small interresonator coupling. Overall, this paper introduces a new, versatile framework for the analysis and optimization of coupled resonator WPT systems. Experimental results are presented, verifying the optimal IM design process.

Description: In this paper, we present a new architecture for implementation of millimeter-wave (mm-wave) and terahertz (THz) radiator arrays based on standing-wave properties. This structure is a continuous distributed coherent array that avoids lossy and parasitic coupling networks. Moreover, it can be scaled simply by extending the size of the structure and replicating the unit cell. The absence of coupling parasitics in addition to the unique characteristics of standing waves allows us to extend the tuning range without using varactors. The 0.34-THz four-element radiator array is designed and fabricated in a 130-nm SiGe BiCMOS process using microstrip transmission lines as the standing-wave mediums and on-chip patch antennas to radiate the desired fourth harmonic of the oscillation. The circuit was measured with no post processing or silicon lens and has 5.9% frequency tuning range (332.5–352.8 GHz) with less than 6-dB output power variation across the band. It consumes 425-mW power from 1.8-V supply and the radiated power is −10.5 dBm at center frequency with −98.2 dBc/Hz phase noise at 10-MHz offset frequency.

Description: This paper presents an extension of synthetic aperture radar (SAR) techniques to enable simultaneous radar imaging, sensor tag localization, and backscatter-based data uplink from multiple sensor tags in a cluttered environment. A unified system model is presented that leverages coherent processing of backscattered signals gathered over the synthetic aperture for all three of these purposes. The proposed approach, using balanced orthogonal codes for SAR-based localization as well as the backscatter data uplink, is shown to have several favorable properties, including straightforward tag-vs-clutter discrimination, straightforward multiple access among tags, and improved signal-to-noise ratio during localization. A proof-of-principle indoor experiment is presented in the X-band (10–13 GHz) using two custom-designed backscatter tags interrogated by a vector network analyzer functioning as an FMCW radar. The proposed system model is validated by simultaneous imaging of a cluttered scene, tag localization with a maximum range error of 9 mm, and data demodulation from both tags telemetering temperature changes at a rate of 1 bit/s at ranges of 4.4 m and 4.7 m. The resulting point-spread functions of tags demonstrate a range resolution of 4.7 cm and a cross-range resolution of 9.1 cm.

Description: A two-stage, high-power symmetric Doherty power amplifier (PA) at 15 GHz is presented. The PA is implemented in 45 nm CMOS silicon on insulator and achieves more than 23 dB power gain with 25.7 dBm saturated output power and 31% peak power added efficiency (PAE). The 6 dB back-off PAE is 25%, which is a 64% improvement compared to ideal class B PA back-off performance. High output power is obtained by employing four-stack multigate devices at the output stage; driver stages employ two-stack devices. A simple analog predistortion linearizer is proposed that effectively corrects the AM–AM response of the Doherty PA and extends the P1dB from 23 to 25.1 dBm. The PA also exhibits excellent AM–PM response. The amplifier has compact dimensions and occupies only 1 mm 2 chip area, including pads.

Description: In this paper, a novel design theory of two-section two-resistor Wilkinson power divider (WPD) is introduced. By selecting two different physical lengths of two-section transmission lines (TLs), two arbitrary frequency band WPD can be achieved. Compared with the former work, the designable frequency ratio range $u$ can be extremely extended from $1 〈 u 〈 3$ to $1 〈 u 〈 infty$ , general design equations for characteristic impedances, physical lengths, absorption resistors, and frequency ratio ranges are newly derived and proved from even- and odd-mode analysis. Because of no capacitors or inductors, the proposed WPD can be used for high-frequency applications. Spurious band of $S_{21}$ appears between two passbands under the condition of two different physical lengths; therefore, a $Pi$ -type dual-band transformer is newly introduced to replace single TL for spurious band suppression. We proved that $Pi$ -type structure could effectively suppress spurious band of $S_{11}$ , maintain two arbitrary frequency passband of $S_{21}$ , and provide an extra isolation band of $S_{32}$ at center frequency. Finally, three proposed WPD examples with $Pi$ -type structure are selected with diffe- ent frequency ratios, where frequency ratio $u = 4$ in Example A, $u = 6$ in Example B, and $u = 20$ in Example C are designed and fabricated in the experiment. Measured results show good agreement with the theoretical results.

Description: In this paper, a technique to extend the linearity and to improve the efficiency of power amplifiers (PAs) is analyzed. The method avoids complex topologies, often affecting the radio-frequency performance and increasing the power consumption, chip area, and costs. In contrast, this approach can be implemented by a simple, but sophisticated design of the input biasing network. In this case, the input biasing network works in such a way that the dc current consumption adapts inherently to the demanded output power while ensuring high linearity. The large-signal behavior is analyzed, and analytical equations for the optimum parameter of the bias network are derived. For integration reason, the network is extended to a compact solution, which also includes the source resistance. According to these theoretical considerations, a PA is implemented in a 0.25- $ {mu }text{m}$ SiGe BiCMOS process. The analytical solutions are verified by the measured output-referred 1-dB compression point of 23.6 dBm. To estimate the improvement by using optimum values of the elements, simulations reveal an increase of the input-referred compression point by 2 dB and by 7% of power-added efficiency.

Description: In this paper, a receiver architecture is presented which is capable of handling angle-of-arrival (AOA) detection as well as data communication. The architecture of the proposed multifunction receiver is based on the multiport interferometer technique, and it integrates two previously reported six-port-based system functions that were realized as two distinct six-port receivers (SPRs). This unification of two SPRs is mainly achieved through a new configuration of RF/local oscillator (LO) signals at input ports, a new phase processing of the input signals within a structured eight-port passive network and a complementary postprocessing of the signals at the output of detectors. Using two RF input ports and two LO input ports that are switched in two consecutive time slots, the proposed multiport-based receiver (MPR) can estimate the AOA with a simple signal-processing algorithm. The plurality of the RF input ports can cause self-interference for the received communication signals. Therefore, a phasing network within the proposed eight-port wave correlator is devised such that the incoming quadrature modulated RF carriers are demodulated in an orthogonal manner at four output ports. It is found that receiving communication signal from a nonzero AOA makes imbalance between demodulated components. To this end, the proposed MPR can first find the angular position of the other unit and then recover the demodulation components through data fusion and postprocessing. The mathematical model for the developed MPR is derived along with the development of an appropriate calibration technique, and its principal functionality is theoretically analyzed. In addition, a transceiver architecture based on this MPR is implemented, and prototyped for operation around 77 GHz. The techniques for hybrid millimeter-wave system integration are explained in this paper. The proposed concept is proven and concluded with satisfactory measurements for both functions. This unified multifunction M- R can find applications in the future vehicle-to-vehicle radios and joint radar-communication systems.

Description: The transmitter (TX)-induced interference due to power amplifier nonlinearities poses severe desensitization problems to the receiver chain in frequency-division duplexing transceivers. Due to nonlinear signal process involved, a high sampling rate is normally required in the existing digital suppression approaches, which can result in high cost and high power consumption in wideband systems. In this paper, a new digital suppression model is proposed to cancel the TX leakage at baseband with a low sampling rate. The cancellation model is based on the modified decomposed vector rotation model. With the addition of cross-term products, the enhanced model is capable of eliminating the aliasing effect arising from the reduced sampling rate. Theoretical analysis of aliasing elimination is presented, and the algorithm is subsequently verified by both simulation and experiment results, confirming the effectiveness and feasibility of the proposed cancellation technique for TX leakage suppression. Compared with conventional solutions, the new approach uses much less hardware resource and consumes much lower power while achieving comparable performance.

Description: In this paper, we propose an experimental approach for determining the internal electric field for exposure evaluation of wireless power transfer (WPT) systems by using measured magnetic near-field data. Two WPT systems are fabricated and used in the measurements: one without ferrite tiles, and the other with ferrite tiles and a metal plate. The amplitude and phase of the magnetic near field in the vicinity of the WPT systems are then measured by using in-house magnetic-field probes and a near-field measurement system. Numerical dosimetry of human exposure is performed using the measured near field as an incident field in the impedance method to derive the internal electric field strength inside numerical human models. Validation of the proposed approach has been demonstrated by comparing measurement results with those obtained from numerical simulations. Additionally, the coupling factor, which represents the relationship between the incident magnetic field and the induced electric field in the human body, at different distances is derived for realistic exposure scenarios.

Description: In this paper, a new method to design a digitally assisted and spurious-free direct carrier mixerless modulator based on the six-port correlator is proposed. The calibration of the modulator based on modified Cartesian memory polynomial (MCMP) is used to linearize and mitigate hardware impairment of the whole system. The modulation and the up conversion are performed by using the variable loads controlled by the differential in-phase and quadrature-phase baseband voltages together with common-mode voltages. The proposed MCMP is able to compensate for nonlinearity, frequency responses, residual carrier leakage, crosstalk between the in-phase and the quadrature-phase data. The proof-of-concept of digitally assisted mixerless modulator is developed and its performance is assessed at 2.6 GHz with modern communication signals. The error vector magnitudes between the input ideal baseband signals and the up-converted radio frequency signals are all between 2% and 4%. The residual carrier leakage, which remains present after imperfect suppression through hardware means, degrades the overall system performance and it can be suppressed completely by means of the proposed memory polynomial model.

Description: Real-time spectrum sensing refers to searching for possible signals at a specific time and location, which is applicable to cognitive radio for primary signal detection. The simplicity and low sensing time of phaser-based spectrum sensors, implemented in a discrete manner previously, provided the incentive for this paper. In this paper, an integrated CMOS wideband real-time spectrum sensor with a novel on-chip phaser in 57–354-MHz band, as part of VHF/UHF TV broadcast bands, is presented. The proposed approach provides a fast, simple, area-efficient analog solution for real-time spectrum sensing with low noise figure and power consumption. The integrated chip has been fabricated in a standard 0.18- $mu text{m}$ CMOS IBM technology and has achieved a sensing time of as low as 2.5 $mu text{s}$ for 27-MHz frequency resolution.

Description: A compact asymmetric orthomode transducer (OMT) with high isolation between the vertical and horizontal Ports is developed for the X-band synthetic aperture radar application. The basic idea of the design is to deploy the combined E- and H-plane bends within the common arm. Moreover, an offset between each polarization axis is introduced to enhance the isolation and decrease the size to be around one-third of most of the existing asymmetric OMTs. The OMT achieves better than 22.5-dB matching level and 65-dB isolation level between the two modes. Good agreement is obtained between measurements and full-wave simulations.

Description: For the practical implementation of RF and microwave impedance matching networks, a widely employed solution—alternative to the use of classical impedance transformers—is based on tapered lines. This paper shows a simple method to design smooth tapers that take into account the dispersion of the line and the required design bandwidth simultaneously. A planar taper has been designed in microstrip technology with the same length of classical ones but improving their performances. A waveguide prototype has also been designed with similar performance to a commercial one but with one third of its length. Both tapered structures have been obtained through the optimization of very few parameters using the same design strategy. As a result, the reflection coefficient of the tapers can be optimally adapted to a given specific mask using the prescribed value of physical length. Experimental results for both tapers are included for the validation of the proposed topologies and the related design method.

Description: A coupled-line coupling structure is proposed for the design of quasi-elliptic bandpass filters (BPFs). The coupled-line structure functions as the input coupling structure for a BPF and introduces one pair of symmetrical transmission zeros at around the cutoff frequencies. Equivalent circuit models play an important role in the design of microwave filters. Accordingly, this paper undertakes a major effort to develop the equivalent circuit of the coupling structure. The equivalent circuit is in a form that can be readily used in combination with a given direct-coupled filter. The coupling structure can serve as a basic building block for the design of quasi-elliptic BPFs. As demonstrated by the theoretical and experimental treatment, the coupling structure can be used to transform a Chebyshev filter into a quasi-elliptic filter.

Description: This paper presents a W-band phased array receive front end in 32-nm CMOS silicon-on-insulator technology. The architecture is based on cascode low-noise amplifiers and passive switched LC 5-bit phase-shifters and with root-mean-square (rms) phase error of <3.5° at 88–93 GHz. The 4-bit equivalent (11°) rms phase error bandwidth is 88–98 GHz. An average system noise figure (NF) of 5.3 dB is obtained at 93–97 GHz with 18-dB gain and input $P_{mathrm{ 1dB}}$ of −25 dBm. The low-noise amplifier and phase-shifter front end consumes 24.3 mW including bias circuits. To the author’s knowledge, the front-end NF and power consumption are state of the art for silicon-based phased array receivers at W-band frequencies, and compares well with indium phosphide (InP) and gallium arsenide (GaAs) pseudomorphic high electron mobility transistor front ends.

Description: A 0.1-THz input coupler for HE 04 mode confocal gyrotron traveling-wave amplifiers is presented. A high-order HE 04 mode in confocal waveguide is efficiently excited from a TE 10 mode. The coupler consists of a Y-type power-divider and a mode-converting section. The wave is coupled with the confocal waveguide via two nonstandard rectangular apertures to maximize the coupling efficiency. The mode-converting section is enclosed with mode-selective grooves to suppress the unwanted modes and thus achieve a high efficiency over a broad frequency band. The prototype is fabricated and measured. Measurements are conducted utilizing two identical back-to-back connected couplers, and the measured performances show excellent agreement with the numerical one. Experimental results show that the coupler achieves a transmission of better than −3 dB in the frequency band from 92 to 110 GHz and a maximum transmission of −1 dB. The coupler exhibits high conversion efficiency, broad bandwidth, and flat transmission throughout the 1-dB bandwidth, which can also be used as a mode converter in cold test experiments of the interaction circuits.

Description: In this contribution, a novel method to design broadband nonreciprocal phase shifters (NRPS) is illustrated: this new topology is based on the combination of two directive-distributed amplifiers with a four-port phase-shifting network. The presented approach includes explicit design formulae allowing for arbitrary differential-phase implementation. Extensive design description of a 180° NRPS, acting as broadband differential-phase inverter, is also provided. The $3.5 times 3.4$ mm 2 demonstrator, realized in 0.5 $mu text{m}$ GaN HEMT technology, has an average zero insertion loss up to 25 dBm of input power, 180° ± 2° differential-phase shift, and good port matching over the 3–7-GHz operating bandwidth.

Description: This paper reports on the investigation, design, and fabrication of single-pole double-throw (SPDT) millimeter-wave integrated circuit (MMIC) switches for applications with an operating frequency of up to 330 GHz. An analysis of the well-established millimeter-wave (mmW) switch topology ( $lambda /4$ -shunt SPDT switch) is done to achieve wideband performance and high isolation simultaneously. Using a standard technology parameter ( $R_{mathrm{scriptscriptstyle ON}}$ ), this theory allows a performance estimation of switch MMICs before a wafer run and can support the design of mmW switches. Based on this analysis, a novel switch topology, with an improved isolation, is introduced. Additionally, this paper demonstrates three SPDT switch MMICs (SPDTs 1–3), the first two of which are targeting the W-band, whereas the latter is targeting the H-band frequency range. All MMICs were fabricated on the Fraunhofer Institute for Applied Solid State Physics 50-nm gate length metamorphic high-electron-mobility transistor process. SPDT 1 achieves a bandwidth of 52–168 GHz. The average insertion loss (IL) and the isolation are 3.1 and 42.1 dB, respectively. The peak performance is 2.1 and 52 dB. SPDT 2 utilizes the novel switch topology and yields the average IL and isolation of 4.5 and 56.4 dB, respectively. The operating bandwidth is 75–170 GHz. The peak performance is 3 and 65 dB. The 1-dB compression points ( $P_{mathrm {in1,dB}}$ ) of SPDTs 1 and 2 are 19 dB and 14 dBm, respectively. SPDT 3 operates from 122 to 330 GHz and achieves the average IL and isolation of 2.2 and 17.4 dB, respectively. The peak performance is 1.5 and 22.8 dB.

Description: In this paper, a 210-GHz triple-push voltage-controlled oscillator consisting of two antiparallel inductor–capacitor ring oscillators with shared inductors is presented. By properly designing the sizes of the ring oscillators and a symmetrical layout, the power of the third harmonic and its phase noise are optimized. A codesign of the inductors, the output combiner, and the pad provides a low-loss signal path at third harmonic and natural filtering at all other harmonics. A prototype of the proposed oscillator is implemented in a 90-nm standard CMOS process. The oscillator achieves a low phase noise of −88 dBc/Hz at 1-MHz offset and −111.5 dBc/Hz at 10-MHz offset with a peak output power of −6 dBm at 210 GHz. The resulting figure of merit is −179.7 dBc/Hz at 1-MHz offset and −183.4 dBc/Hz at 10-MHz offset. The oscillator consumes 28.6 mW of dc power from a 1.1-V supply voltage and occupies a compact area of 0.17 mm 2 due to the simplicity of the architecture. The oscillator covers a frequency range from 204.3 to 215 GHz.

Description: In this paper, an asymmetric drain biased postmatching Doherty power amplifier (DPA) using harmonic injection is proposed for further back-off extension. The injected harmonic components are generated by the two active devices. Aided by the proposed harmonic injection network, drain waveform amplitude modulation for both devices can be achieved at saturation, which results in enhanced saturated power for both carrier and peaking devices, while carrier back-off power remains unchanged. As a consequence, the back-off region is extended. Moreover, the power utilization factor of the asymmetric drain biased DPA is also improved. A DPA for wideband code-division multiple access systems was designed and fabricated based on commercially available gallium nitride HEMT (Cree CGH 40010F) devices to validate the proposed technique. Measured results of the proposed DPA demonstrated that operation at 10-dB back off is possible between 1.6 and 1.9 GHz, with efficiency better than 46%.

Description: In this paper, we report the design, fabrication, and demonstration of a compact, V-band, zero-bias, and linear-in-dB power detector based on our in-house metal–insulator–graphene diode fabricated on a glass substrate. The presented circuit is optimized for the frequency band of 40–75 GHz. The measured prototype shows a repeatable measured dynamic range of at least 50 dB with down to −50 dBm sensitivity on 500- $mu text{m}$ -thick quartz substrate. It also shows input return loss better than −9.5 dB over the entire design bandwidth. The measured tangential responsivity for the fabricated circuit on glass is 168 V/W at 2.5 GHz and 15 V/W at 60 GHz. The obtained results together with the robust device fabrication based on chemical vapor deposition graphene promote the proposed scheme and device for repeatable, statistically stable millimeter-wave, and submillimeter-wave applications.

Description: The well-known cavity perturbation method, in which a cavity resonator is partially filled with a material sample is used to determine material parameters (permittivity, electrical conductivity, and permeability) at microwave frequencies. These parameters are inferred from the differences in resonant behavior between the empty cavity and the material-loaded cavity. When applying the method, one has to couple the cavity to external measuring equipment (e.g., a vector network analyzer) to obtain the ${S}$ -parameters of the cavity. The insertion of a coupling device (e.g., a thin stub) detunes the cavity. If the cavity is loaded with a large sample or if one has no access to the empty cavity—both cases may occur in in-process monitoring applications—one must remove the detuning effect from measured ${S}$ -parameters to produce accurate estimates of the sample material parameters. Several methods for this de-embedding have been proposed in the literature. They work well for loose or not-too strong coupling, but less so for strong coupling, which may occur in in-process monitoring situations. We have examined the known de-embedding procedures with respect to their ability for coping with strong coupling by thin stubs and propose a method that works in this case.

Description: Limited sensitivity and sensing range are arguably the greatest challenges in microwave sensor design. Recent attempts to improve these properties have relied on metamaterial (MTM)-inspired open-loop resonators coupled to transmission lines (TLs). Although the strongly resonant properties of the resonator sensitively reflect small changes in the environment through a shift in its resonance frequency, the resulting sensitivities remain ultimately limited by the level of coupling between the resonator and the TL. This paper introduces a novel solution to this problem that employs negative-refractive-index TL MTMs to substantially improve this coupling so as to fully exploit its resonant properties. A MTM-infused planar microwave sensor is designed for operation at 2.5 GHz, and is shown to exhibit a significant improvement in sensitivity and linearity. A rigorous signal-flow analysis of the sensor is proposed and shown to provide a fully analytical description of all salient features of both the conventional and MTM-infused sensors. Full-wave simulations confirm the analytical predictions, and all data demonstrate excellent agreement with measurements of a fabricated prototype. The proposed device is shown to be especially useful in the characterization of commonly available high-permittivity liquids as well as in sensitively distinguishing concentrations of ethanol/methanol in water.

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Description: A general numerical scheme is proposed for the waveport modeling and scattering-parameter (S-parameter) extraction of inhomogeneous waveports with the discontinuous Galerkin time-domain method. In this scheme, the waveports are truncated with perfectly matched layers with a hybrid mesh automatically extruded from the mesh of the physical device to be simulated. The waveports are then excited by a total-field/scattered-field technique, with which the incident and scattered waves can be obtained for an accurate calculation of the S-parameters. A novel eigenmode solver is also developed to calculate the required modal profiles for the eigenmodes in both homogeneous and inhomogeneous waveports. Special attention is paid to the S-parameter extraction for evanescent modes, which has been a difficult task for time-domain simulations. Numerical examples are given to validate the proposed numerical scheme.

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Description: This paper discusses a novel optimization technique for broadband reflective-type phase shifters (RTPS). The performance characteristics of an RTPS, including its achievable maximum phase shift and the corresponding average loss, are calculated on the basis of simulated or measured varactor data. In addition, the root-mean-square (rms) errors are evaluated to determine the broadband performance of the device. To extract the characteristics, a reciprocal, lossless matching network with arbitrary output impedance is connected in series to the varactor. The results are plotted on Smith charts, which yield an intuitive representation of the matching network area to achieve the design goals. The technique is verified by realizing a WR-3 band (220–325 GHz) RTPS microwave monolithic integrated circuit realized in a 50-nm metamorphic high electron mobility transistor InGaAs technology. The measured phase shift is 118° at the center frequency of 240 GHz with a bandwidth of 62 GHz. The rms phase and amplitude errors are lower than 5.6° and 0.67 dB, respectively.

Description: Perfect electromagnetic absorption in an array of thin resonators is analyzed by means of the quality factor involving separately the contribution of losses and a coupling with free space. An equivalent electrical circuit based on an open-resonator model is introduced for an absorber made of dielectric cubes arranged in a square lattice deposited onto a metallic ground plane. From full-wave simulations, two regimes depending on the lattice period are pointed out. A quadratic dependence of the radiative quality factor is shown for largest periods, whereas the radiative $Q$ -factor is governed by a coupling between resonators at small periods. It results that an optimal period for obtaining a unitary absorption can be deduced from a single simulation and that a maximal absorption bandwidth emerges from a tradeoff between these two regimes. Finally, the radiative $Q$ -factor concept is applied to analyze an absorber made of patch resonators with the goal to broaden the absorption bandwidth. Particularly, the performances of a multisized patch absorber are experimentally evaluated in the W-band (75–110 GHz) with a good agreement when compared to simulations. Such an analysis of $Q$ -factor appears as a powerful tool for designing single-sized and multisized resonator absorbers targeting a specific absorption spectrum.

Description: This paper presents the development of a comprehensive distributed circuit model to account for the existing nonlinear effects in bulk acoustic wave (BAW) resonators. The comprehensiveness of the model and its distributed implementation allow for the inclusion of the nonlinear effects occurring in any layer of the BAW configuration, not only the piezoelectric layer. The model has been applied to evaluate the nonlinear contribution of the piezoelectric layer and silicon dioxide (SiO 2 ) layer in the Bragg reflector. The nonlinear manifestations are a function of the frequency of the driving fundamental tones. Accurate measurements of state-of-the-art resonators validate the model proposed and confirm the contribution of the SiO 2 layer in the overall nonlinear performance.

Description: A direct matrix approach is presented for the first time to synthesize high selectivity in-line topology filters where multiple transmission zeros are generated and independently controlled by a set of frequency-variant couplings. As the resultant network only involves resonators cascaded one by one without any auxiliary elements (such as cross-coupled or extracted-pole structures), this paper provides the best synthesis solution in configuration simplicity for narrowband filters. Considering both the couplings and capacitances of a traditional low-pass prototype, a generalized transformation on the admittance matrix is introduced as the basis of the synthesis, which allows more than one cross-coupling to be annihilated in a single step, while generating a frequency-variant coupling simultaneously. It is then shown that the in-line topology as well as some other unique topologies can be determined by applying a specific sequence of the transformations. For the validation, a group of examples with synthesis as well as experimental results are demonstrated.

Description: By virtue of the strong confinement of surface-wave fields that it provides, the transverse corrugated conducting rod is an important structure in the fields of plasmonics and metasurfaces, finding applications in focusing, sensing, imaging, spectroscopy, and subwavelength optics, among others. This paper presents an analytical modal method for treating such grated rods with generally dielectric-filled grooves, one which offers rapid yet accurate surface-wave modal solutions. Based on the asymptotic corrugation boundary conditions, the formulation is simple and elegant, providing not only the dispersion relationship between the frequency and wavenumber but also the explicit functional forms of the fields. Dispersion and modal field results obtained by the proposed method are validated with an independent full-wave solver. Because of its candidacy for microwave applications at high powers and high frequencies, as well as transmissions over long distances, studies of dielectric and conductor losses are also carried out, for both the grooved rod and its likewise corrugated circular waveguide counterpart. Parametric studies are conducted on three aspects, namely, the degree of field localization on the surface of the rod, as well as attenuation due to dielectric and metal losses. Measurements of dispersion and field decay properties conducted on a manufactured rod that concur with theory are also reported.

Description: This paper proposes a unified synthesis methodology and the related architecture for fully passband-tunable dual-mode filters with wide tuning range. The methodology and architecture relate the well-developed frequency-fixed synthesis technologies to tunable filters, and can be applied to any tunable filter design and analysis by an element-variable coupling matrix. This general methodology accounts for bandwidth (BW), center frequency (CF), and return loss (RL) (passband ripple or stopband rejection) tuning, and helps to implement the passband-tunable filter. For validation, a novel tunable dual-mode bandpass filter (BPF) based on the architecture is presented. The proposed filter has the ability to arbitrarily construct the two-pole passband within the frequency tuning range as predicted. In addition, three transmission zeros (TZs) are generated by the proposed structure, which results in a highly selective passband and a reconfigurable stopband. A tunable filter with a tuning range from 0.8 to 1.2 GHz is designed and fabricated. The measured filter presents an elliptic response during the frequency tuning. The 50% CF tuning range (0.8–1.42 GHz) with a constant absolute BW 1 dB and a BW 1 dB tuning range from 50 to 500 MHz at the fixed CF are measured. Good agreement among matrix calculation, circuit model simulation and measurement demonstrates the validity of the proposed method and structure. In addition, different states of the stopband with the same passband are obtained to further broaden its application.

Description: The 2-D/3-D hybrid discontinuous Galerkin time-domain (DGTD) method is efficient to deal with structures that contain elements capable of 2-D simplification. To separate 2-D elements from 3-D ones, a criterion for approximation error manipulation is required. However, in the latest reported technique, this kind of criterion is derived from the causality principle and the Courant–Freidrichs–Lewy constraint, and thus is indirect and inessential to 2-D simplification. As a result, some elements capable of 2-D simplification are unnecessarily flagged as 3-D ones, deteriorating efficiency dramatically. Moreover, controlling absolute error, the traditional criterion is not flexible for structures with complex mode distribution. In this paper, a novel criterion is proposed. Compared with the traditional one, this new criterion controls comparative error instead of absolute error, thus enhancing accuracy and flexibility. Besides, for the time-adaptive updating algorithm, the proposed criterion is derived directly from the discretized matrix equations of the DGTD method, rendering it straightforward and efficient. Finally, the 2-D/3-D DGTD with the proposed criterion is integrated with the modified nodal analysis technique for the analysis of power-ground plate pairs with decoupling capacitors. The accuracy, flexibility, and efficiency enhancement of the proposed criterion are demonstrated by comparison with commercial software and the traditional method.

Description: VoxHenry, a fast Fourier transform (FFT)-accelerated integral-equation-based simulator for extracting frequency-dependent inductances and resistances of structures discretized by voxels, is presented. VoxHenry shares many features with the popular inductance extractor, FastHenry. Just like FastHenry, VoxHenry solves a combination of the electric volume integral equation and the current continuity equation, but with three distinctions that make VoxHenry suitable and extremely efficient for analyzing voxelized geometries: 1) it leverages a carefully selected set of piecewise-constant and piecewise-linear basis functions; 2) it exploits FFTs to accelerate the matrix–vector multiplications during the iterative solution of system of equations; and 3) it employs a sparse preconditioner to ensure the rapid convergence of iterative solution. VoxHenry is capable of accurately computing frequency-dependent inductances and resistances of arbitrarily shaped and large-scale structures on a desktop computer. The accuracy, efficiency, and applicability of VoxHenry are demonstrated through inductance analysis of various structures, including square and circular coils as well as arrays of RF inductors (situated over ground planes).

Description: This paper reports on the design and optimization of MEMS-tunable evanescent-mode cavity-based bandpass filters with continuously variable center frequency within an octave tuning range. The devised filters are manufactured using silicon-micromachining techniques that enable their actualization for frequencies located in the millimeter-wave (30–100 GHz) regime. An RF design methodology that takes into consideration all microfabrication-induced constrains—e.g., nonvertical wall profiles and finite MEMS deflection—enables high unloaded factor ( $Q_{u}$ ) and also minimizes bandwidth (BW) variation within the octave tuning range is reported. Furthermore, a new passively compensating package-integrated input/output feeding structure that enables optimal impedance matching over the entire tuning range is also presented. In order to evaluate the devised RF design methodology, a filter prototype was manufactured and measured at Ka-band. It exhibits a measured frequency tuning between 20 and 40 GHz (2:1 tuning range), relative BW between 1.9 and 4.7%, insertion loss between 3.1 and 1.1 dB, and input reflection below 15 dB. This paper also explores important tradeoffs between mechanical stability and insertion loss by comparing creep-resistant to pure-Au tuning diagrams.

Description: This paper presents the extraction of microwave properties of low-temperature cured inorganic composite materials based on barium titanate (BaTiO 3 ). These composite materials exhibit attractive features such that when the volume fraction of the filler contents varied, its electrical properties of high permittivity and moderately low loss tangent can be manipulated to suit different areas of applications. For the extraction of the permittivity and the loss tangent, three different ink particles were developed and printed on the top of interdigital-shaped microwave capacitor. The properties of the inks were extracted from measured results through computer simulations. The obtained results were verified with several types of interdigital capacitor structures of different fingers and linewidths. The effect of the thickness of the ink layer materials on the top of the capacitor structures was likewise investigated. The results show relative permittivity ( $varepsilon _{r}$ ) values of 30, 25, and 27 for composite layers printed using inks with Pr. A shape at 67.4 wt% (percentage by weight), Pr. B shape at 66.3 wt%, and Pr. C shape at 67.1 wt% of BaTiO 3 , respectively, at 2 GHz. Corresponding loss tangents (tan $delta $ ) were 0.065, 0.040, and 0.025. The dielectric properties of the composite materials are influenced by the thickness variation of the ink layers on the capacitor structures. This novel capacitor composite materials would be a promising candidate for printed application in mobile telecommunication operations, especially in the frequency range of 0.5–3 GHz.

Description: This paper presents a new systematic and efficient method for the design of high-power varactor-based impedance tuners. By incorporating the varactor losses and voltage handling capabilities, the method allows the impedance tuning range to be maximized and losses to be minimized under high-power operating conditions. A 2.2-GHz large-signal double-stub tuner has been designed using the proposed methodology and SiC varactor diodes. Using comprehensive large-signal measurements, a 25-W input power handling is demonstrated up to $Gamma _{max } approx ~0.8$ . Two-tone linearity measurements show an input third-order intercept point exceeding 50 dBm for most impedances. These results clearly demonstrate the feasibility of the proposed technique for the design of high-performance large-signal tuners.

Description: A new methodology for the prediction of oscillator phase dynamics under the effect of an interference signal is presented. It is based on a semianalytical formulation in the presence of a noisy or modulated interferer, using a realistic oscillator model extracted from harmonic-balance simulations. The theoretical analysis of the phase process enables the derivation of key mathematical properties, used for an efficient calculation of the interfered-oscillator spectrum. The resulting quasi-periodic spectrum is predicted, as well as the impact of the interferer phase noise and modulation over each spectral component, in particular over the one at the fundamental frequency. It is demonstrated that under some conditions, the phase noise at this component is pulled to that of the interference signal. Resonance effects at multiples of the beat frequency are also predicted. In addition, the effects of interferer phase and amplitude modulation on the oscillator phase dynamics have been studied and compared. For that analysis, efficient simulation techniques have been developed. The analyses have been validated with experimental measurements in an FET-based oscillator at 2.5 GHz, obtaining excellent agreement.

Description: This paper presents for the first time the design, fabrication, and demonstration of a dielectric waveguide (DWG)-based ortho-mode sub-THz interconnect channel for planar chip-to-chip communications. By combining the proposed new transition of microstrip line with DWG orthogonally, the ortho-mode transition is constructed to form an ortho-mode channel. The measured minimum insertion losses for the $E_{y11}$ mode and the $E_{x11}$ mode are 6.6 dB with 20.3-GHz 3-dB bandwidth and 6.5 dB with 55.2-GHz 3-dB bandwidth, respectively. The simulation and measurement results agree well with each other.

Description: This paper presents the analytical design of transmission-type arbitrary prescribed wideband flat group delay (GD) circuits (type-I and type-II) using $lambda $ /4 coupled lines. The GD circuit type-I consists of two sections of coupled lines, whereas the GD circuit type-II consists of $lambda $ /4 transmission lines (TLs) at input and output, in addition to coupled lines. The additional $lambda $ /4 TLs at input–output ports in GD circuit type-II provide more freedom to obtain larger GD, as compared to type-I, without fabrication difficulties. The analytical analysis shows that the wideband flat GD response can be obtained by selecting the appropriate even- and odd-mode impedances of coupled lines and the characteristic impedance of TLs. To obtain the arbitrary prescribed wideband flat GD response, the closed-form analytical design equations are provided. For experimental validation of the proposed structures, prototypes of GD circuits (type-I and type-II) are designed and fabricated at the center frequency of 2 GHz. The measurement results agree well with the simulation and theoretical predicted results.

Description: A stability and bifurcation analysis of multi-element non-Foster networks is presented, illustrated through its application to non-Foster transmission lines. These are obtained by periodically loading a passive transmission line with negative capacitors, implemented with negative-impedance converters (NICs). The methodology takes advantage of the possibility to perform a stability analysis per subintervals of the perturbation frequency. This will allow an independent analytical study of the low-frequency instability, from which simple mathematical criteria will be derived to prevent bias-network instabilities at the design stage. Then, a general numerical method, based on a combination of the Nyquist criterion with a pole-zero identification of the individual NIC, will be presented, which will enable the detection of both low- and high-frequency instabilities. A bifurcation analysis of the multi-element non-Foster structure will also be carried out, deriving the bifurcation condition from a matrix-form formulation of the multi-element structure. The judicious choice of the observation ports will enable a direct calculation of all the coexisting bifurcation loci, with no need for continuation procedures. These bifurcation loci will provide useful insight into the global-stability properties of the whole NIC-loaded structure.

Description: This paper proposes a topology of a broadband Wilkinson power divider based on the segmented structure. The segmented structure is formed by many transmission line segments in shunt with grounded capacitors and series resistor–capacitor networks. Each transmission line segment has the length of a fraction of a quarter of the wavelength (or $lambda $ /4) and the summed length of all segments remains $lambda $ /4. The segmented structure resembles a multiorder matching network and can extend the operation bandwidth through concurrent matching at multiple frequencies. Theoretically, the operation bandwidth can keep increasing with the increased number of segments. Practically, the widest achievable bandwidth is limited by the implementable component values. The theoretical background of the proposed broadband topology is explained. The guideline of designing the proposed power divider is provided. A power divider prototype with the structure of three segments is designed and fabricated. The measurement results, matching the simulations, show the state-of-the-art −20-dB operation bandwidth of 101%, if compared with all the published Wilkinson power dividers having a total length of $lambda $ /4.

Description: The need for a flexible coupler topology to support a wide variety of coupling coefficients and robust suppression of harmonics often results in severely increased insertion loss, system size, and fabrication complexity. In this paper, we propose a two-section branch-line coupler (BLC) topology that simultaneously achieves a wide bandwidth, reconfigurable coupling coefficient, and harmonic suppression. Closed-form equations and a design methodology are provided. To verify the proposed technique, a BLC prototype operating at 3 GHz was designed, fabricated, and measured. The circuit can work under four configurations providing the coupling coefficients of 4, 6, 8, and 10 dB. The prototype achieved a 15-dB harmonic suppression up to 7.5 GHz. The measured fractional bandwidth, defined by 1-dB amplitude imbalance and 5° phase stability, is 30% from 2.55 to 3.45 GHz, the widest of reported reconfigurable couplers.

Description: This paper proposes a new theory for harmonically tuned power amplifiers (PAs) with maximally flat waveforms, Class-X PAs. This class has been developed to achieve maximally flat waveforms. In this class, the relationship between the fundamental load impedance and the independently set second- and third-harmonic load impedances is established to maintain constant output power with constant efficiency. This relationship sets an optimum fundamental load design space when the second- and third-harmonic impedances are varied simultaneously and independently of each other. By varying the second- and third-harmonic impedances independently, higher flexibility in the design of broadband PAs is obtained. The theory of Class-X PA and its broadband characteristics were validated with an experimental design example using a Cree’s 10-W Gallium Nitride (GaN) device. This design showed a measured drain efficiency higher than 70% and output power within 3-dB variation over more than one-octave bandwidth.

Description: This paper presents a new method for designing multiband bandpass filters (BPFs). The filter consists of low-pass filter and two open stub-loaded shorted stubs. Multiple transmission zeros (TZs) are produced by the open stub-loaded shorted stub, and multiple passbands can be realized. For the first time, different numbers of open stubs are used to realize multiband BPFs with two to seven passbands. The center frequencies and the last passband bandwidth can be tuned in a certain range by adjusting the TZs and transmission poles. First, a wideband BPF is presented to introduce the design concept. Theoretical analysis is done to illustrate the design principle. Then, a wide single-band BPF and a dual-band BPF are designed to demonstrate the design method. The design procedure is summarized to guide the design process. Finally, tri-/quad-/quint-/sext-/sept-band BPFs are designed according to the design principle. All the BPFs are manufactured. Measured results show good agreement with simulated ones.

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Description: This paper presents the design, fabrication, and characterization of a zero-bias quasi-optical terahertz detector based on monolithically integrated heterostructure backward diodes (HBDs) for operation at G-band. The reported detectors consist of HBDs with $0.7 times 0.7 ~mu text{m}^{2}$ active device area and submicrometer-scale airbridges, integrated with lens-coupled high-impedance planar folded dipole antennas. Measurements of the HBD detector show that a peak-measured detector sensitivity of approximately 2400 V/W and a minimum noise equivalent power (NEP min ) of 2.14 pW/ $surd $ Hz have been obtained at 170 GHz. If an antireflection coating was used on the lens, a sensitivity of approximately 3500 V/W and NEP min of 1.48 pW/ $surd $ Hz is projected. The radiation patterns of the quasi-optical detector in both $E$ - and $H$ -planes have been measured, and good agreement has been achieved between simulation and measurement. The performance of this detector can be further improved by scaling the HBD device active area. The reported approach using monolithically integrated heterostructure backward tunneling diodes and submicrometer airbridges is promising for developing high performance and compact detectors and focal-plane arrays for millimeter-wave and terahertz sensing and imaging applications.

Description: Differences in the material reflection are required for any contrast in microwave- and millimeter-wave (mm-wave) imaging systems. Therefore, the dielectric properties, which determine the reflection of materials, need to be characterized. The characterization of skin and other biological tissue is, therefore, necessary, to apply imaging systems for instance in cancer diagnosis. In this paper, short, coherent mm-wave pulses (wavelets) are generated and their reflection on dispersive materials is studied. The reflections of wavelets on porcine skin and water are examined in time and frequency domain. A first-order Debye model is fitted to the reflection coefficient in frequency domain to quantify material dispersion. The frequency-dependent reflection on dispersive materials causes a distortion of the wavelets in the time domain. The startup behavior of the pulses is examined by simulation and measurements. The rise time of the pulses is identified as a feature in time domain for wavelets reflected on dispersive media. Together with other features characteristic for a pulse, for instance the wavelet amplitude, this enables identification of dispersive materials by reflectometry measurements, making it suitable for applications in mm-wave imaging systems.

Description: A measurement technique to emulate coupling between power amplifiers (PAs) such as that in an antenna array is presented. The case that the technique aims to emulate is referred to as the target array. The technique provides emulation of the distorted output signal for each PA under the coupling effect without the requirement for constructing the target physical coupling network or antenna array. Furthermore, given that the target array contains identical elements or PAs, transmitting either identical or different signals, the technique merely requires one PA as the device-under-test (DUT) to produce all output signals. The technique has direct connection to active load–pull, and aims to present the output of the DUT with corresponding time-varying impedances of each transmission path in the target array. The emulated output signals can then be analyzed, for example, in terms of adjacent channel power ratio, error vector magnitude, and normalized mean square error. Such measurement technique provides insight into the distortion and the impairment generated in the target array without the requirement to realize an actual array, and can be used, as an example, during the design stage of an array. The technique is theoretically motivated. The procedure is thoroughly described. The technique is experimentally demonstrated and verified under various usage cases and scenarios. Subsequent comparison to conventional active load–pull is provided.

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Description: The use of multisine signals to improve the efficiency of wireless power transfer (WPT) for low average received power was proposed recently. Several measurement-based studies illustrated the gain that can be achieved for different circuit or waveform instances, focusing on the impact of a time-varying amplitude on the rectifying efficiency. This paper first establishes a model enabling a thorough analysis of the multisine-based WPT system focusing on the bandwidth of the signal and the rectifier. This model enables a codesign of signal and rectifier for optimal WPT. The proposed model provides insight into the output voltage and power, as a function of the input waveform for different circuit models. By including the input matching and the clamper, our model is generic and can include a wide range of rectifiers with different voltage multiplication approaches. The key insight gained from our analysis is that there is a tradeoff between the frequency spacing of the tones of the multisine signal and the cut-off frequency of the low-pass RC filter, as a main property of the rectifier circuit. Our model predicts the measured power conversion efficiency and voltage with an error below 0.1 and 0.2 V, respectively.

Description: In this paper, an analytical coupling matrix extraction scheme is proposed for parallel-connected dual-passband coupled-resonator filters for the first time. Model-based vector fitting technique is adopted to fit the measured responses of the dual-passband filter (DPBF) with a set of rational functions, from which a transversal coupling matrix can be constructed. A novel coupling matrix transformation strategy is developed to transform the transversal coupling matrix to the one corresponding to the topology of a parallel-connected DPBF. A practical filter is used as a test example to demonstrate the extraction procedure. In diagnosing the coupling matrix of the test filter, two kinds of ambiguity problems are discussed in detail and are solved by a perturbation technique. This paper provides a general theoretic framework for computer-aided tuning of a parallel-connected dual-passband or multiple-passband filter.

Description: This work presents a full two-port, i.e., double input-double output, behavioral modeling approach suitable for radio frequency power amplifiers (PAs) in the presence of dynamic load modulation (DLM). The formulation of the model, based on a first-order approximation of a modified Volterra series, accounts for the nonlinear distortion determined by large-signal operation under mismatched conditions, and also for the memory effects stimulated by a modulated PA input signal, or by the dynamic variations of the PA load. By following an exhaustive procedure defined in the frequency domain, the model of a general purpose commercial PA is extracted over 160 MHz of modulation bandwidth (BW) with nonlinear vector network analyzer measurements. Validation results under 20-MHz BW multisine excitation and injected 80-MHz BW multisine load modulation show improved prediction capabilities with respect to quasi-static or single-input descriptions, allowing for reliable system-level simulations in the presence of DLM.

Description: This paper investigates the back-gating effects due to traps, and presents a new nonlinear trap modeling approach suitable for gallium nitride (GaN) high electron mobility transistors (HEMTs). It is shown that the traps have nonidentical influence on the channel compared with the gate. The potential due to trapped electrons in the buffer and the gate–source voltage need to be differentiated to model their respective influence on conductivity of the 2-D electron gas. Hence, the back-gating potential due to traps cannot be included in the transistor model by directly offsetting the gate–source voltage. A new modulation factor is therefore introduced to create an effective back-gating potential, and thereby improve the modeling of trapping effects. The proposed nonlinear trap model is shown to accurately predict the trapping behavior for a large voltage operating region. A detailed procedure is presented to derive the model parameters from basic device measurements. The model is experimentally validated and shown to accurately predict dc-, pulsed-IV, and large-signal waveform performance for a commercial GaN HEMT.

Description: In this paper, a model for the input impedance of a hot-wire electro-explosive device (EED) based on differential-mode measurements is proposed. The model represents the EED using three transmission line segments in cascade. The characteristics of each segment are estimated according to data reported in the literature and to measurements of the differential-mode input impedance of actual EEDs in the ultrahigh frequency range. The experimental procedure and model are presented in detail. In addition, the impedance measurements and the predictions of the proposed model are compared with previous results reported in the literature.

Description: This paper presents a new simple model for representing and characterizing the loss effect introduced by the roughness of the metal-to-dielectric interface on the conductor attenuation of substrate integrated waveguides. The proposal allows for the parameter determination using simple linear regressions which can be implemented directly from S-parameter data and avoids the use of data corresponding to structures with perfectly smooth conductors. In fact, no previous knowledge of the metal surface profile is required to obtain the model parameters. Excellent agreement between full-wave simulations and experimental data at several tens of gigahertz is achieved.

Description: The visualization of carbon fibers polyether ether ketone (PEEK) composite material heating for a grounded coplanar waveguide and a stepped impedance low-pass filter by the thermal camera is performed. The purpose of such visualization is to characterize electromagnetic field influence on the diagonally anisotropic composite material and find out its application opportunity. COMSOL Multiphysics simulation has been done in order to understand heating principles and origin. Experimental results were in a good agreement with simulations and they showed that the characteristics of the microstrip structures can be modulated/tuned by simple rotation of the composite material. Finally, a tunable application by the carbon/PEEK composite material for the microstrip low-pass filter was developed due to the microwave absorption selectivity dependence on the composite material orientation.

Description: This paper provides the guidelines for the practical development of novel advanced test beds for passive intermodulation (PIM) measurements. The proposed test beds show high performance and are flexible, allowing for the measurement of several PIM signals of different orders, with two or more input carriers. In contrast to classic test beds for satellite hardware, based on the cascaded connection of several elements, an integrated solution involving the minimum number of hardware pieces is proposed. The result is a lower number of flanged interconnections, thus reducing residual PIM level and insertion losses. In addition, return loss degradation and harmful spurious generation in the interconnections are also avoided. Measurement test beds for conducted and radiated PIM, in both transmitted and reflected directions, are discussed, highlighting the benefits and drawbacks of each configuration. Design guidelines for the key components are fully discussed. Illustrative application examples are also reported. Finally, excellent experimental results obtained from low-PIM measurement setups, working from C-band to Ka-band, are shown, thus fully confirming the validity of the proposed configurations.

Description: In this paper, a new design method for bridged-T coil (BTC) is proposed such that it can be made equivalent to two different transmission line sections at two different frequencies. In this way, on-chip dual-band branch-line coupler and dual-band power divider designs with very compact circuit sizes can be made possible through the use of BTCs. Specifically, the proposed 2.45/5.8-GHz dual-band branch-line coupler realized using the integrated passive device (IPD) process features a compact circuit size of only $2.8~text {mm} times 1.4$ mm while the proposed 2.4/5.5-GHz dual-band power divider in IPD exhibits a very small circuit size of only $1.8~text {mm} times 1.7$ mm. To the best of our knowledge, the proposed dual-band branch-line coupler is the smallest one ever reported while the circuit size of the proposed dual-band power divider is comparable to the smallest in the literature.

Description: A new planar filter design technique with constant and frequency mappings has been proposed for multifrequency wideband bandpass filters (BPFs). The constant mapping treats components in the $LC$ circuit (e.g., frequency invariant admittances, capacitors, and ideal inverters) as frequency dependent. It is consistent with practical planar circuits and caters to a wide frequency range. Following the classic single-to-multiband transformation, a new frequency mapping function is proposed by incorporating this constant mapping idea. With these two mapping functions, a direct relation between the $LC$ circuit and its microstrip counterpart is established. Therefore, the multifrequency wideband BPF is readily designed from a lowpassing $LC$ circuit to the transmission line circuit. A ladder-type Chebyshev filter and a trisection filter with the general Chebyshev response have been designed as examples. The first one is a dual-band case exhibiting a wide bandwidth for each passband. The second filter is a triple-band one showing a large frequency ratio between the first and third passband. Both examples experimentally validate the proposed constant and frequency mapping technique.

Description: This paper presents a frequency- and bandwidth-tunable bandstop filter using substrate-integrated wave- guide (SIW) resonators. For designing such a filter, this paper also presents a tunable coupling structure between a microstrip line and an SIW resonator for obtaining the bandwidth tuning capability. The coupling structure has two coupling slots between the microstrip line and the resonator, and the phase shift between the two slots determines the overall external coupling value of the resonator. This external coupling value can be controlled by making use of a phase shifter, which in turn makes it possible to adjust the bandwidth of a bandstop filter. A thorough mathematical analysis is shown using the equivalent circuit model of the presented coupling structure, and it has been verified by measuring an SIW resonator containing the presented structure. The presented tunable coupling structure has also been applied to a design of bandstop filter that can be tuned from 2.8 to 3.4 GHz. The measured results at 3.1 GHz show that the bandwidth can be tuned from 0 (all-pass) to 96 MHz reaching the attenuation level of 44 dB.

Description: This paper presents a design strategy to enhance the bandwidth of three-stage Doherty power amplifier (DPA) with operation upto 12-dB back-off. Based on the proposed strategy, a broadband 48-W DPA is designed and implemented using packaged CREE GaN transistors. The measured drain efficiency of 50%–61.8% at 12-dB back-off and 51.9%–66.2% at 6-dB back-off is obtained over the frequency range of 600–900 MHz. Over this 300-MHz band, the drain efficiency is between 51.1% and 78% at saturation. This corresponds to 40% fractional bandwidth. The three-stage DPA is also linearized with a three carrier 15-MHz WCDMA signal with a PAPR of 10.6 dB at various frequencies within operating band and shows the output signal qualifies spectral mask specifications.

Description: In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage. Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA. When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution. The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance. This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA. A broadband CM-DPA working over 1.6–2.7 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories. The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode. Under continuous wave excitation, experimental results show the drain efficiencies of 46.5%–63.5% at 6-dB output back-off power levels and 56%–75.3% at peaking power levels. The maximum output power of this DPA is 43.8–45.2 dBm with a gain of 9.4–11.5 dB across the whole working band. Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 7.4 dB is also applied to the fabricated CM-DPA at 2.2 GHz. At an average output power of 37.5 dBm, measurement results show the adjacent channel power ratios of −30.2 and −50.1 dBc before and after digital predistortion, respectively.

Description: This paper presents a compact and wideband millimeter-wave antenna-coupled detector, with a Schottky diode directly integrated across the feeding terminals of a planar dipole. An integrated wideband dipole is proposed, as a radiator as well as a radio frequency choke. It contains a pair of folded strips for broadening the bandwidth and a pair of U-slot resonators for sidelobe reduction, both of which facilitate the compact design. To form unidirectional radiation with a low profile, a hybrid reactive impedance surface is presented, which can simultaneously enhance the gain and impedance bandwidths covering the full Ka-band. An equivalent circuit model is provided to illustrate the operating mechanism of this antenna-coupled detector, and the mounting effect caused by the diode is examined. A Ka-band prototype with dimensions of about $1.12lambda _{0}times 1.12lambda _{0}times 0.08lambda _{0}$ is fabricated and characterized, exhibiting a responsivity between 1500 and 3800 V/W over the full Ka-band. The proposed design has the advantages of broad bandwidth, low profile, small footprint, and mechanically stable structure. It can be fabricated using low-cost printed circuit technology, and can easily be configured into a planar 2-D array, making it suitable for low-cost sensing and imaging applications based on small unmanned aerial vehicles.

Description: To address the challenging needs of small size, wide bandwidth, and low-frequency applicability, a novel phase shifter implementation is introduced that utilizes tunable active differential inductors within all-pass networks. The inductor tuning is used to achieve phase shifts up to 180°. A switchable active balanced-to-unbalanced transition (balun) circuit is included in front of the all-pass network to complement its phase shift capability by another 180°. In addition, the all-pass network is followed by a variable-gain amplifier to correct for gain variations among the phase shifting states and act as an output buffer. Although active inductors have previously been used in the design of various components, to the best of our knowledge this is the first time that they have been used in an all-pass phase shifter. The approach is demonstrated with an on-chip design and implementation exhibiting wideband performance for S- and L-band applications by utilizing the 0.5- $mu text{m}$ TriQuint pHEMT GaAs monolithic microwave integrated circuits (MMIC) process. Specifically, the presented phase shifter $1 times 3.95~ text {mm}^{2}$ die area and operates within the 1.5–3-GHz band (i.e., 2:1 bandwidth) with 10-dB gain, less than 1.5-dB root-mean-square (rms) gain error and less than 9° rms phase error. Comparison with the state-of-the-art MMIC phase shifters operating in S- and L-bands demonstrates that the presented phase shifter exhibits a remarkable bandwidth performance from a very compact footprint with low-power consumption. Consequently, it presents an alternative for the implementation of wideband phase shifters where all-passive implementations will consume expensive die real estate.

Description: This paper reports for the first time, the dielectric characterization of a new, electronically tuneable electrochromic (EC) thin-film material over the frequency range 1–67 GHz, at temperatures of 7 °C, 23 °C, and 50 °C. Test cells composed of a microstrip line terminated with coplanar waveguide (CPW) transitions were fabricated to facilitate on-wafer RF measurements and the application of different bias voltages using a standard CPW probe station. A precise curve-fitting technique based on full-wave simulations was used to extract the permittivity and loss tangent values of the material. The validity of the dielectric extraction technique was first demonstrated by employing a known material, silicon dioxide (SiO 2 ). It is shown that the dielectric tunability of the EC material varies between 11.3% (1 GHz) and 7.5% (67 GHz) at 23 °C, and the measured loss tangent varies between 0.012 (OFF, 0 V, state) and 0.025 (ON, 6 V, state). Above room temperature, the devices exhibit higher values of dynamic tunability and a small increase in insertion loss. The results obtained for this first generation of tuneable EC material are encouraging, and many of the dielectric properties are shown to compare favourably with other, more mature bulk tuneable media, such as liquid crystals.

Description: This paper presents an in-depth, systematic study of the impact of input and output harmonics in the design of high-efficiency power amplifiers (PAs). The study evaluates the performance of harmonically tuned amplifiers, tackling concurrently both input and output harmonics. The proposed theory starts with deriving an altered input voltage waveform under the impact of input nonlinearity. Intrinsic drain voltage and drain current components are formulated as a function of the conduction angle $alpha $ considering both source and load terminations. Output power and drain efficiency are then computed as a function of input nonlinearity, $alpha $ , and output loading conditions. The derived formulations allow to investigate the design sensitivity to input nonlinearity and its impact on fundamental design space. The impact of source harmonics is evaluated using harmonic source pull under different output loading conditions. Thereafter, PA design and implementation has been carried out using NXP 1.95 mm die to confirm the distinctive behavior of class GF and GF −1 amplifiers with respect to the input harmonic terminations. For practical validation, four different design cases with different second harmonic source impedances are investigated. At 2.6 GHz, drain efficiencies ranging between 76% and 83% were exhibited depending on the source and load harmonic tuning for each design case. Measurement results confirm the theoretical findings reported in this paper.

Description: This paper presents a novel general design method of frequency varying impedance matching. The method is applied to design of a broadband high-efficiency power amplifier (PA). The proposed method defines the optimal impedance regions of a PA at several frequency sections over the operational frequency band. These regions contain the impedances that can achieve a high output power and a high-power added efficiency (PAE) simultaneously. A low-pass $LC$ -ladder circuit is selected as the matching network (MN). The element values of the MN can be obtained using a synthesizing method based on stochastic reduced order models and Voronoi partition. The MN provides desired impedance in the predefined optimal impedance region at each frequency section. Thus, optimal output power and PAE of the PA can be achieved. To validate the proposed method, two eighth-order low-pass $LC$ -ladder networks are designed as the input and output MNs, respectively. A gallium nitride (GaN) HEMT from Cree is employed as the active device. Packaging parasitic of the transistor has been taken into account. A PA is designed, fabricated, and measured. The measurement results show that the PA can achieve P1 dB PAE of better than 60% over a fractional bandwidth of 160% (0.2–1.8 GHz). The output power is 42–45 dBm (16–32 W), and the gain is 12–15 dB. The performance of the PA outperforms existing broadband high-efficiency PAs in many aspects, which demonstrates the excellence of the proposed method.

Description: A method is presented to accurately assess the uncertainty of calibrated one-port vector network analyzers (VNAs), using various techniques necessary to minimize systematic errors in the uncertainty analysis. Methods to experimentally quantify connector pin-gap discontinuity errors are presented and validated. Furthermore, we present a simplified equivalent air-line measurement model together with a multivariate optimization algorithm suitable for determining the model parameters. The unique strength of this algorithm is that it only requires two-port scattering parameter data of the airline and avoids extensive dimensional characterization. Experimental verification measurements confirm that a significant enhancement in VNA measurement accuracy is achieved by the combined use of offset discs to avoid measurement reference plane errors together with the air-line model to account for device imperfections. It is proven that using this approach, VNA uncertainty levels can be reached by industrial calibration laboratories that so far only were achievable at national measurement institutes via very extensive and cumbersome mechanical measurements.

Description: In this paper, we devise a position-invariant method for unique and accurate complex permittivity ( $varepsilon _{r}$ ) determination of low-loss samples from transmission and shorted-reflection scattering (S-) parameter measurements while mitigating the effect around Fabry–Perot frequencies. For this goal, we derived a metric function in terms of propagation factor $T$ only and utilized a branch-index-independent expression for unique $varepsilon _{r}$ by eliminating multiple solutions problem. We measured S-parameters of two low-loss samples with substantial thickness, which both introduced a Fabry–Perot effect in the frequency range, and the measurements were conducted to validate our method and compare its accuracy with the accuracy of similar methods in the literature. We also performed an uncertainty analysis to evaluate and improve the accuracy of our method.

Description: Provides instructions and guidelines to prospective authors who wish to submit manuscripts.

Description: The IEEE MTT-S International Conference on Numerical Electromagnetic Modeling and Optimization for RF, Microwave, and Terahertz Applications (NEMO) is an annual international conference founded by the IEEE Microwave Theory and Techniques Society (MTT-S) in 2014. The idea of NEMO conference originated from the need to give special attention to the topics related to computational electromagnetics, advanced numerical techniques, and optimization algorithms and strategies. NEMO conferences are expected to be ideal venues to share new ideas on numerical techniques for electromagnetic/multiphysics modeling, propose efficient design algorithms and tools, and anticipate the modeling needs of future technologies and applications.

Description: This paper presents a novel algorithm for the analysis of piecewise homogeneous, possibly lossy, waveguide circuits. The algorithm is based on the segmentation technique to split the circuit into homogeneous building blocks, combined with the representation of the generalized admittance matrix (GAM) of each block by the boundary integral-resonant mode expansion (BI-RME) method. The GAMs are then recombined by a circuital cascading procedure. The core of the method is the calculation of the quasi-static Green’s function of a rectangular box, which is required to determine the terms of the BI-RME pole-expansion of the GAM. The expressions of the quasi-static Green’s function, manipulated by Ewald’s technique to improve the convergence, are fully described, and numerical considerations for their efficient and accurate calculation are provided, with a particular focus on the proper selection of the splitting parameter. To demonstrate the correctness of the given formulas, the algorithm is developed and applied in the limited case of circuits segmentable into boxed building blocks. Numerical examples demonstrate the accuracy and efficiency of the proposed technique.

Description: Thin-sheet models are essential to allow shielding effectiveness of composite enclosures and vehicles to be modeled. Thin dispersive sheets are often modeled using surface-impedance models in finite-difference time-domain (FDTD) codes in order to deal efficiently with the multiscale nature of the overall structure. Such boundary conditions must be applied to collocated tangential electric and magnetic fields on either side of the surface; this is usually done on the edges of the FDTD mesh cells at the electric field sampling points. However, these edge-based schemes are difficult to implement accurately on stair-cased surfaces. Here, we present a novel face-centered approach to the collocation of the fields for the application of the boundary condition. This approach naturally deals with the ambiguities in the surface normal that arise at the edges on stair-cased surfaces, allowing a simpler implementation. The accuracy of the new scheme is compared to edge-based and conformal approaches using both planar sheet and spherical shell canonical test cases. Staircasing effects are quantified and the new face-centered scheme is shown have up to 3-dB lower error than the edge-based approach in the cases considered, without the complexity and computational cost of conformal techniques.

Description: Numerical methods are widely used to analyze and design microwave components for communication applications. In the implementation of any numerical technique, however, there are always a set of parameters that must be properly adjusted in order to obtain, at the same time, computational efficiency and numerical accuracy of the results. In this context, therefore, we focus in this paper on the multimode equivalent network formulation for waveguide devices, and we propose a more intuitive and efficient strategy for choosing these parameters. Following our approach, setting only one global numerical variable is sufficient to adjust automatically the specific convergence parameters of each discontinuity to give a specific level of numerical accuracy of the results. As a consequence, the computational efficiency is significantly increased. In addition, the user experience is significantly improved since our approach eliminates all lengthy convergence tests previously needed to assure good numerical accuracy. In addition to theory, we discuss in this paper a number of numerical results that clearly demonstrate how the new strategy is very effective, thereby fully validating the theoretical formulation.

Description: Presents the table of contents for this issue of this publication.

Description: Provides a listing of current staff, committee members and society officers.

Description: The physical mechanism of the experimentally observed dependence of passive intermodulation (PIM) in printed circuits on conductor surface roughness is studied. It is shown that electrothermal (ET) nonlinearity, arising due to heating of imperfect conductors by high-power carriers in a multicarrier system, is correlated with conductor surface roughness and has a unique signature. Carriers modulate the conductor resistivity, skin depth, and surface impedance which generate PIM products. The detailed analysis demonstrates that ET-PIM depends on the conductor resistivity, shape, and roughness profile and also on the electric and thermal properties of the substrate. Their effects on PIM are illustrated by examples of uniform microstrip lines with different conductor and substrate materials, and periodically perturbed and meandered microstrip lines.

Description: With rapidly increasing switching speeds and surge current requirements, placement of local decoupling capacitors is becoming critically important in high-speed low-power designs. In this paper, utilizing the driving-point impedance (viewed from the device pin) as a metric, a new method is presented for the placement of decoupling capacitors in parallel-plate power ground pairs of high-speed circuits. In the proposed approach, instead of using the traditional trial-and-error method to identify an appropriate placement distance, the process is formulated in the form of a transcendental function. The resulting function is solved using Newton–Raphson (N-R) iterations to give a direct solution for the distance. Also, an analytical representation based on Hankel functions for the driving point impedance and its derivatives is developed to speed up the N-R iterations. The proposed method is validated by comparing the results with the full-wave electromagnetic simulations.

Description: In this paper, we show a simulation strategy for composite dispersive thin-panels, starting from their microscopic characteristics and ending into a time-domain macroscopic model. In a first part, we revisit different semianalytic methods that may be used to obtain the S-parameter matrices. The validity of them is assessed with numerical simulations and experimental data. We also include some formulas that may be used to tailor the shielding effectiveness of panels in a design phase. In a second part, we present an extension to dispersive media of a subgridding hybrid implicit–explicit algorithm finite difference time domain (FDTD) devised by the authors to deal with that kind of materials. The method, here presented and applied to the FDTD method, is a robustly stable alternative to classical impedance boundary condition techniques. For this, a previous analytical procedure allowing to extract an equivalent effective media from S-parameters is presented, thus making this road map able to simulate any kind of dispersive thin layer. A numerical validation of the algorithm is finally shown by comparing with experimental data.

Description: This paper presents the design and implementation of a novel class of substrate-integrated waveguide (SIW) filters, based on partially air-filled cavity resonators. Removing the dielectric in a portion of the SIW cavity allows obtaining dual-mode cavities: such cavities represent a doublet, used as the building blocks in the design of filters. A thorough modal analysis of the air-filled resonant cavity based on transmission lines’ representation and a detailed study of the doublet permit to demonstrate a full control of the operation frequency, pass bandwidth, spurious-free region, and position of the transmission zeros of the filter. This paper presents the design, fabrication, and measurement of several two-pole filters based on this concept, with the aim to show the capabilities of the proposed structure and of the design technique. A five-pole filter is also presented, to describe the extension of the proposed approach to higher order filters.

Description: The generation of terahertz radiation using photoconductive antennas is becoming very popular. Several experimental and simulation studies have been performed to study the characteristics of the photoconductive antenna (PCA). Although various methods have been proposed to increase the radiated power from it, the radiated power remains very low. In this paper, we present an analytical study of improving the radiated power from a large aperture PCA using an external magnetic field source. The transit time behavior of the carriers is computed using the basic semiconductor carrier dynamics model, including the transient mobilities with the dependencies on the electric field and carrier’s concentration. Analytical studies show that substantial enhancement in the radiated field can be achieved when such external magnetic field is applied. Furthermore, the polarity of the radiated field depends on the orientation of the applied magnetic field. The results obtained from analytical calculations exhibit similar behavior as reported in some experimental results.

Description: This paper addresses the robust mode computation of the metallic hollow cylindrical waveguide with parabolic contour. Although this waveguide can be solved by separation of variables, it has not been fully characterized in a systematic way in the past. This is not only due to its challenging manufacture, which nowadays can be addressed by modern techniques, but also because of its more complex resolution, involving root finding in a pair of coupled functions with two variables. In order to solve this system, this paper proposes the use of a recently published algorithm for bivariate problems, which is applied for the first time to waveguide mode computation. The method, properly combined with the even and odd Taylor functions, allows obtaining the modes in a systematic and robust way, avoiding, in comparison with previous works, graphical means and the use of starting points from which to iterate. All the modal solutions for symmetrical and asymmetrical cases are solved at once over a wide domain of search with proven high accuracy (relative difference with respect to results from a finite-element method in the order of $10^{-5}$ for more than 1600 modes).

Description: Compact balanced bandpass filters based on a combination of multisection mirrored stepped-impedance resonators and interdigital capacitors are presented in this paper. The considered filter topology is useful to achieve wide bandwidths for the differential mode, with broad stop bands for that mode, as well as very efficient common-mode suppression. By conveniently adjusting the transmission zeros for both operation modes, the differential- and common-mode stopbands can be extended up to significantly high frequencies. Filter size and this differential- and common-mode stopband performance are the main relevant characteristics of the proposed balanced filters. The potential of the approach is illustrated by the design of a prototype order-5 balanced bandpass filter, with central frequency $f_{0} = 1.8$ GHz, 48% fractional bandwidth (corresponding to 55.4% −3-dB bandwidth), and 0.04-dB ripple level. The filter is automatically synthesized by means of an aggressive space-mapping software tool, specifically developed, and two (pre- and post-) optimization algorithms, necessary to determine the transmission-zero frequencies. The designed filter is as small as $0.48lambda _{g} times 0.51lambda _{g}$ , where $lambda _{g}$ is the guided wavelength at the central filter frequency, and the differential-mode stopband extends up to at least 6.5 GHz with more than 22-dB rejection. The common-mode suppression is better than 28 dB from dc up to at least 6.5 GHz.

Description: An improvement in the energy transfer in a cavity-type microwave plasma source (MPS) operated at 915 MHz by a better design of the device, capable of ensuring a high microwave power coupling from the supply line to the sustained plasma was a goal of this paper. Our approach was twofold. First, numerical simulations of an electromagnetic field distribution inside a typical cavity-type MPS were carried out. The standard model of homogeneous plasma generated by the MPS and the two-port method was combined. This enabled estimating the concentration $n_{e}$ and collisions frequency $nu $ of electrons in the plasma. Based on these data, a more energy efficient MPS could be designed. Second, to verify the numerical prediction, a modified version of the MPS was built and the improvement in the MPS energy efficiency was proved experimentally.

Description: Superluminal pulse propagation has been observed in past investigations. Conventional methods rely on resonance-based gain/absorption line materials, inevitably inducing significant pulse distortion. Motivated by the negative reactance slope of the non-Foster circuits, we investigated superluminal propagation based on a non-Foster loaded waveguide. Superluminal square-wave pulse transmission with negligible distortion has been observed in time-domain measurements. In addition, the propagation distance limitation for a non-Foster-based superluminal waveguide is derived by analyzing the distortion of the transmitted waveform. We conclude that a distortion-limited superluminal output pulse cannot emerge more than the original pulse duration ahead of the same pulse transmitted in vacuum, in agreement with causality. This investigation provides an alternative solution to the gain/absorption approaches, and is directed toward a more comprehensive understanding of superluminal propagation.

Description: An extrapolation method was proposed to increase the calculation efficiency and the accuracy of the incident power and specific absorption rate (SAR) in resonant exposure setups. The stable incident power and SAR were derived by observing the oscillating ${E}$ -field envelope recorded during the finite-difference time-domain calculation. The extrapolation method was validated when applied to a waveguide loaded with two or four 35-mm-diameter Petri dishes at the ${H}$ -field maximum for the resonant exposure at 1800 MHz. With the extrapolation, the computational time was reduced by 80% to derive the incident power with the error reduction of 93%, as compared to the calculation with the current mechanism until the accepted wave stability. For the SAR, the computational time was reduced by 77%. With the proper position and weighting of the ${E}$ -field samples, the error of the averaged SAR in the cell monolayer was reduced from 4.62% to 1.31%. The proposed method applies to the scenario where the resonant frequency of the loaded setup drifts away from the driven frequency so that an oscillating ${E}$ -field envelope is available.

Description: A new through-substrate via (TSV) for millimeter-wave frequencies is proposed. The via is formed by copper nanowires connecting the bottom and top surfaces of a porous alumina membrane. It is shown here that the nanowire via is simple to fabricate using a low-cost technology. The nanowire vias were tested as coplanar waveguide transitions and characterized up to 110 GHz. The results show insertion loss better than 0.37 dB and return loss better than 14 dB per transition at 110 GHz. An electrical model for the vias was derived to give a design tool for circuit designers. These TSVs, along with the high-performance transmission lines already developed on the porous alumina membranes, contribute to a powerful platform for the design of high-performance circuits on this innovative interposer.

Description: The objective of this paper is to use electromagnetic-based computer-aided design (CAD) tools to investigate the maximum tuning range of channel filters, typically used in satellite payloads. Both circular and rectangular waveguide technologies are investigated. The results of the investigation show that single-mode rectangular waveguide implementations offer substantially wider tuning range, as opposed to classical dual-mode circular waveguide implementations. In addition to simulations, measurements are also presented indicating very good agreement with theory, thereby fully validating the CAD procedure.

Description: Products of passive intermodulation (PIM) generated by weak nonlinearities of passive circuits subjected to relatively high transmit power of multicarrier signals may cause strong interference in emerging broadband and multiradio communication systems. This paper presents a new approach to a characterization of distributed nonlinearities in printed circuits fabricated on commercial grade microwave laminate materials. An efficient procedure for PIM characterization has been devised using the commercial RF-CAD software. The phenomenological model has been developed to take into account concurrent distributed nonlinearities of printed transmission lines and to evaluate PIM products of arbitrary order. It has been observed for the first time that the sources of nonlinearity in typical microstrip circuits may have highly uneven distributions which require a different means for PIM characterization and modeling. The proposed methodology has been validated by accurate predictions of the PIM response of complex circuit layouts. The results of this paper pave the way to a holistic approach to the design of planar microwave circuits and devices under given linearity constraints.