ALBERT

Description: Describes the above-named upcoming special issue or section. May include topics to be covered or calls for papers.

Description: We present a robust space mapping (SM) algorithm exploiting electromagnetic (EM)-based adjoint sensitivities for microwave design optimization. Our approach utilizes low-cost EM-based adjoint sensitivities and trust region methods to improve an SM algorithm at three levels, which are: 1) to build a better overall surrogate while ensuring convergence; 2) to speed up and safeguard the parameter extraction steps; and 3) to speed up and safeguard the surrogate optimization process. We describe the implementation at each level in detail. We review relevant adjoint sensitivity analysis methods. We also review prior SM methods that exploit both sensitivity and adjoint sensitivity. We summarize these methods in four categories. We compare our proposed approach with them. Efficiency, robustness, and versatility of our method are demonstrated by three design examples: an antenna, a planar filter, and a 3-D resonator filter. We compare the results with those obtained by SM without using adjoint sensitivity information and by direct optimization of the high-fidelity EM models.

Description: This paper reports a novel synthesis method for microwave bandpass filters with resonant source–load connection. In effect, a network realizing $N+1$ transmission zeros (where $N$ is the number of reflection zeros) is obtained. The method is based on a prototype transversal coupling matrix $(N+2, N+2)$ with source and load connected by a resonant circuit formed by a capacitor in parallel with a frequency-invariant susceptance. To complement the proposed synthesis technique, a method of reconfiguring the transversal coupling matrix as a more practical cross-coupled circuit is outlined. The technique is based on quickly converging gradient optimization with a cost function involving generalized eigenvalues of the transversal coupling matrix and its principal upper and lower submatrices. To illustrate and validate the proposed synthesis procedure, numerical tests have been carried out. Moreover, some aspects of implementation of the resonant connection between source and load were investigated, and experimental verification was performed. A third-order generalized Chebyshev filter with four transmission zeros was designed, fabricated, and tested. The measured results validate the proposed synthesis method.

Description: A new class of three-dimensional (3-D) bandpass frequency-selective structures (FSSs) with multiple transmission zeros is presented to realize wide out-of-band rejection. The proposed FSSs are based on a two-dimensional (2-D) array of shielded microstrip lines with shorting via to ground, where two different resonators in the substrate are constructed based on the excited substrate mode. Furthermore, metallic plates of rectangular shape and “T-type” are inserted in the air region of shielded microstrip lines, which can introduce additional resonators provided by the air mode. Using this arrangement, a passband with two transmission poles can be obtained. Moreover, multiple transmission zeros outside the passband are produced for improving the out-of-band rejection. The operating principles of these FSSs are explained with the aid of equivalent circuit models. Two examples are designed, fabricated, and measured to verify the proposed structures and circuit models. Measured results demonstrate that the FSSs exhibit high out-of-band rejection and stable filtering response under a large variation of the incidence angle.

Description: This paper presents an accurate synthesis method for inline and cross-coupled generalized Chebyshev bandpass filters with frequency-dependent couplings implemented via open and short stubs. The technique involves the synthesis of a lumped-element prototype in the form of a coupling matrix with a frequency-dependent term and the conversion of this prototype to a distributed-element model composed of sections of TEM lines. This takes into account the impedance (or admittance) of the stubs, thus allowing compensation for the loading effect. The design equations are derived for the stub impedance in terms of a coupling coefficient and for the allowable frequency range in which the model is valid. Additionally, the proposed methodology allows the simultaneous application of frequency-dependent couplings with positive and negative dispersive parts within the same network. The validity of this method is confirmed by numerical tests and through experiments, including filters with dispersive couplings of the opposite signs.

Description: This paper presents a method of creating multi-port couplers by mirroring conventional coupler structures, such as 90 $^{circ}$ hybrids, Saleh power dividers, and Wilkinson couplers. These created structures maintain some very useful features of the original structures, for example, stable phase shifting between ports, equal power dividing, and port isolation. Theoretical analysis method of these structures is discussed for $S$ -parameter derivation. Example structures: a four-way coupler by mirroring 90 $^{circ}$ hybrid couplers, and an eight-way coupler by mirroring Saleh power-dividing couplers were built and tested according to the method discussed. A good match was found between theoretical analysis and measurements.

Description: In this paper, a third-order tunable diplexer and a third-order tunable dual-band bandpass filter with flexible tuning capabilities and high selectivity are proposed. Both the diplexer and dual-band filter consist of two passbands that share a common resonator for size reduction. By adding tuning elements in the middle and ends of the common resonator, the resonant frequencies of the even and odd modes can be independently tuned, thus offering flexible tuning for multi-band operations. Also, by adding extra resonators next to the common resonator, high-order tunable multi-band filters can be obtained with higher stopband suppression. The 1.3–2.4-GHz tunable diplexer shows that the two channels can be either independently tuned or simultaneously tuned as desired. The two channels cover a fractional tuning range of 34% and 18.6%, respectively, while keeping high stopband suppressions, higher isolation, and good input impedance matching. Similarly, the 1.1–2.45-GHz tunable dual-band filter shows independent and simultaneous tuning capability operating with good impedance matching and high stopband suppression.

Description: A microwave three-channel selector, showing twofold symmetry using tri-operational mode synthesized transmission lines, is proposed and investigated in this paper. On one hand, just like a typical triplexer, the three-channel selector provides independent transmission paths at three different frequencies; however, on the other hand, the twofold symmetry makes each of the ports able to serve as the common input. The arrangement of the proposed channel selector is unique and can be applied to synthesize a tri-mode heterogeneous integrated beam-switching/Van Atta/phase-conjugating array. The operational principle is introduced first, followed by the details of the synthesized lines as the core building blocks; design formulas are discussed along with the results. Experimental validation verifies the design concept, and discussions on its potential applications are provided.

Description: Wideband pulsed power amplifiers (PAs) often exhibit undesirable transient oscillations at the trailing edges of the pulsed radiofrequency (RF) output. To combat this problem, this paper introduces an approach for predicting and eliminating such transient oscillations in pulsed PAs. Root causes for the transient oscillations are identified and contrasted with other time-domain pulse-distortion phenomena. Effective analytical techniques are presented for predicting transient instability during the PA design process. These techniques are demonstrated using a series of monolithic GaAs HBT Class-A and Class-C ultra-wideband (UWB) pulsed PA RF integrated circuits (RFICs). RFIC variants designed to exhibit no transient oscillations successfully show no such effects; RFIC variants designed without considering transient stability as a design tradeoff do indeed generate pulsed transients with measured oscillation frequencies and damping ratio parameters in less than 2% error with predictions. These results should greatly facilitate the design of pulsed transmitters for wideband/UWB communications and radar applications.

Description: A $Ka$ -band monolithic high-efficiency frequency quadrupler using a GaAs heterojunction bipolar transistor and pseudomorphic high electron-mobility transistor technology is presented in this paper. The frequency quadrupler is constructed cascading two frequency doublers. The frequency doubler employs a modified common-base/common-source topology to enhance the second harmonic efficiently. The dc bias condition, harmonic output power, conversion gain, and efficiency for variable configurations are investigated. Two phase-shifter networks are used to reduce phase error and improve the fundamental rejection. Between 23–30 GHz, the proposed frequency quadrupler features a conversion gain of higher than $-$ 1 dB with an input power of 4 dBm. The maximum conversion gain is 2.7 dB at 28 GHz with an efficiency of up to 8% and a power-added efficiency of 3.6%. The maximum output 1-dB compression point $(P_{1 {rm {dB}}})$ and the saturation output power $(P_{rm sat})$ are higher than 7 and 8.2 dBm, respectively. The overall chip size is ${hbox {2}}times {hbox {1}} {hbox {mm}}^{2}$ .

Description: This paper presents a highly linear wideband differential low-noise amplifier (LNA) for digital TV applications. The proposed LNA is a modified version of the wideband LNA reported by Bruccoleri in 2004. In order to increase the linearity of Bruccoleri 's LNA, the Volterra series is adopted to identify the nonlinear components and the noise-cancelling circuit is modified to eliminate the whole nonlinear components. Implemented in 0.13- $mu{hbox {m}}$ CMOS technology, the proposed wideband LNA has a gain of 12.4 dB and a noise figure of 1.6 dB, as determined from measurements, while drawing 18.45 mA from a 1.2-V supply. The proposed LNA has an ${rm IIP}_{3}$ of 16.6 dBm with 6-MHz frequency offset at 100 MHz, far exceeding the values of existing wideband LNAs.

Description: A silicon-on-insulator (SOI) CMOS technology on high-resistivity silicon substrates is presented for the design of high-power switches for cellular and wireless local area network handset applications. A design methodology is introduced to design high-order switches for optimal insertion loss and isolation performance. Sources of nonlinearities in SOI switches are discussed. To the best of our knowledge, this work is the first demonstration of high-power switches on a high-resistivity SOI CMOS technology for high-volume cellular handset applications with adequate intermodulation and harmonic distortion performance. The design details and measurement results for a variety of RF switches with general-purpose input/output and mobile industry processor interface control interfaces, flip-chip/wire-bond packaging, and for various standards are discussed.

Description: A highly efficient push–push voltage-controlled oscillator (VCO) with a new inductive frequency tuning topology for (sub) terahertz frequencies is presented. The tuning technique is based on a variable inductance seen at the emitter node of a base-degenerated transistor. The variable inductor exhibits high quality factor and high tuning range due to the tunable transistor transconductance via bias current. Fabricated in a 0.13- $muhbox{m}$ SiGe BiCMOS process, the VCO achieves a tuning range of 3.5% and an output power of $-$ 7.2 dBm at 201.5 GHz. The dc power consumption of the VCO is 30 mW, resulting in a high dc to RF power efficiency of 0.6% and a figure of merit $({rm FoM}_{T})$ of $-$ 165, which is the highest FoM for any silicon-based VCO reported to date at this frequency range. To demonstrate the functionality of the tuning technique, three VCO prototypes at different oscillation frequencies, including one operating in the 222.7–229-GHz range, are implemented and measured.

Description: This paper presents a linear multi-harmonic analysis method to evaluate the performance of digitally controlled dual RF-input power amplifiers (PAs). The method enables, due to its low computational cost, optimization of PA efficiency and bandwidth in a complex design space involving two independent inputs. Under the idealized assumption of short-circuited higher harmonics, the analysis is used to prove the existence of a Doherty-outphasing continuum, featuring high average efficiency over 100% fractional bandwidth. With this result as a foundation, a combiner incorporating microwave transistor parasitics is analyzed without assuming short-circuited higher harmonics, showing that high average efficiencies are also achievable under more realistic conditions. A PA is straightforwardly designed from these calculation results using two 15-W GaN HEMTs. The simulated layout-ready (large-signal transistor model) PA average drain efficiency exceeds 50% over 1.1–3.7 GHz for a 6.7-dB peak-to-average power-ratio WCDMA signal. The measured PA has a maximum output power of ${hbox{44}} pm {hbox{0.9}}$ dBm and a 6-dB output power back-off (OPBO) power-added efficiency (PAE) of 45% over 1–3 GHz. After applying digital pre-distortion, excellent linearity is demonstrated when transmitting the WCDMA signal, resulting in an adjacent channel leakage power ratio lower than ${-}{hbox{57}}$ dBc with corresponding average PAE of 50% and 40% at 1.2 and 2.3 GHz, respectively. This is, to the authors' knowledge, the most wideband OPBO efficiency enhanced PA reported to date, proving the effectiveness of employing linear multi-harmonic analysis in dual-input PA design.

Description: A novel application of vertical interconnects (vias) in multilayer structures, such as printed circuit boards (PCBs), is presented. By carefully designing the electromagnetic via environment, it is shown that a pair of signal vias can be used as a building block for microwave couplers. Due to the inductive nature of the coupling, the coupled port is the far end. Coupling of $-$ 0.1 dB and directivities beyond 20 dB in the frequency range from 10 to 20 GHz can be achieved. The coupling mechanisms in PCBs are investigated for different electromagnetic environments and the influence of the geometrical and material parameters on the coupler performance is explored. Results are validated by full-wave simulations and $S$ -parameter measurements.

Description: A novel 3-D finite-element modeling technique without matching meshes for the eigenvalue analysis of arbitrary lossy slow-wave structures (SWSs) of traveling-wave tubes is presented. By simulating two examples, it is shown that the cold parameters of SWSs can be accurately and quickly obtained without matching meshes when using this technique. Moreover, a new second-order transverse electric periodic boundary condition (PBC) is proposed to improve the modeling efficiency of lossy SWSs in the nonmatching meshes case, and this technique is very suitable for application of the rotated PBC. This technique would make the modeling of SWSs more flexible, cheaper, and more efficient.

Description: In this paper, the conventional Baum–Liu–Tesche (BLT) equation is modified to achieve $S$ -parameters as outputs, and full-wave analysis data for partial structures are combined with the modified BLT equation to handle a multi-scale problem. Constructing of a topological network for waveguide structures is demonstrated considering propagating modes of the waveguide, to investigate huge waveguide structures such as missiles. Also, in the process of investigations, a coupling mechanism of printed circuit boards (PCBs) inside a waveguide is established. A missile is simplified into a rectangular waveguide, and inside compartments are assumed to be separated by metal plates having apertures. By investigating the coupling effects to PCBs placed in the waveguide with three cases, it is verified that the coupling mechanism is affected by frequency regions of incident fields, transmission characteristics of apertures, and the parallel-plate waveguide resonance characteristics of a target PCB itself. Each result from the modified BLT equation is compared to a graph by calculating the entire structure using full-wave analysis, showing excellent agreements and its validity. Also, time efficiency is observed from comparing the analysis time of the modified BLT equation and full-wave analysis.

Description: 3-D hybrid finite-element (FE) boundary integral equation (BIE) formulations are widely used because of their ability to simulate large inhomogeneous structures in both open and bounded simulation domains by applying each method where it is the most efficient. However, some formulations suffer from breakdown frequencies at which the solution is not uniquely defined and errors are introduced due to internal resonances. In this paper, we investigate the occurrence of spurious solutions resulting from these resonances by using the concept of the Poincaré–Steklov or Dirichlet-to-Neumann operator, which provides a relation between the tangential electric field and the electric current on the boundary of a domain. By identifying this operator in both the FE and BIE method, several new properties of internal resonances in 3-D hybrid FE-BIE formulations are easily derived. Several conformal and nonconformal formulations are studied and the theory is then applied to a scattering problem.

Description: A design approach for developing microwave bandpass filters (BPFs) with continuous control of the center frequency and bandwidth is presented. The proposed approach exploits a simple loop-shaped dual-mode resonator that is tapped and perturbed with varactor diodes to realize center frequency tunability and passband reconfigurabilty. The even- and odd-mode resonances of the resonator can be predominately controlled via the incorporated varactors, and the passband response reconfiguration is obtained with the proposed tunable external coupling mechanism, which resolves the return losses degradation attributed to conventional fixed external coupling mechanisms. The demonstrated approach leads to a relatively simple synthesis of the microwave BPF with an up to 33% center frequency tuning range, an excellent bandwidth tuning capability, as well as a high filter response reconfigurability, including an all-reject response.

Description: This paper presents a new scheme of a tri-band Gysel power divider. A tri-band transmission line transformer and parallel short-and open-ended stub resonators are applied to a dual-band power divider for tri-band application. Exact equations are derived based on even- and odd-mode analysis. There is a good agreement between simulation and experimental results. In addition to good insertion loss, return loss, and isolation, it also has the advantage of high power-handling capability over the Wilkinson power divider.

Description: Carbon nanotube (CNT) yarns are novel CNT-based materials that extend the advantages of CNT from the nanoscale to macroscale applications. In this study, we have modeled CNT yarns as potential data transmission lines. Test structures have been designed to measure electrical properties of CNT yarns, which are attached to these test structures using gold paste. DC testing and microwave $S$ -parameter measurements have been conducted for characterization. The observed frequency independent resistive behavior of the CNT yarn is a very promising indicator that this material, with its added values of mechanical resilience and thermal conductivity, could be invaluable for a range of applications such as body area networks. A model is developed for the CNT yarn, which fits the measured data collected and agrees in general with similar data for non-yarn CNTs.

Description: This paper presents a $Ka$ - to $F$ -band ultra-broadband subharmonic mixer (SHM) using the standard 90-nm CMOS process. The proposed SHM employs a distributed amplifier and antiparallel diode pair configuration to realize wide operation bandwidth from 33 to 103 GHz, low conversion loss from 0.52 to 3.35 dB, good local oscillation (LO)-to-RF isolation greater than 27.7 dB, and high 2LO-to-RF isolation better than 60 dB with a miniature chip dimension of ${hbox {0.49 mm}}^{2}$ at a 10-dBm LO power level. Using the distributed amplifier technique, the proposed SHM offers significant advantages, such as broad operation bandwidth, good flatness, high port-to-port isolation, and good conversion loss.

Description: We propose a gate-width scalable method for extracting the reliable parasitic elements of the 0.1- $mu{hbox {m}}$ GaAs metamorphic high electron-mobility transistors. This method utilizes the de-embedding scheme for coplanar waveguide (CPW) feeding structure by considering the distributed extrinsic parasitic elements in our small-signal model. The parasitic capacitances are determined based on estimation of the sub-model (the model after de-embedding the contribution of the CPW feeding structure). We perform the parameter extraction at four different gate widths of the devices to examine the scaling effect. The model shows the best $S$ -parameter effective fitting error of 9.85% among four different extraction methods evaluated in this study over the entire gate-width variation and in a frequency range of 0.5–110 GHz.

Description: This paper presents two CMOS common-gate (CG) low-noise amplifiers (LNAs) using different dual-feedback techniques, significantly reducing noise figure (NF) to around 2 dB over a wide frequency range. The proposed first CG LNA uses $g_{m}$ -boosted feedback and shunt-series transformer feedback to relieve the tradeoff between input and noise matching. The proposed second CG LNA further extends the input matching bandwidth by using $g_{m}$ -boosted feedback and shunt–shunt transformer feedback. Moreover, the transformer used for feedback in both CG LNAs causes gain peaking and thus a considerable increase of 3-dB gain bandwidth. After implementation in a 0.18- $mu{hbox {m}}$ CMOS process, the first and second CG LNAs achieve an NF of 1.9–2.6 dB over a 3-dB gain bandwidth of 7 and 10 GHz, respectively. The comparison between simulated and measured results shows a good agreement.

Description: This paper presents a high-power high-efficiency wideband suboptimum Class-E RF power amplifier based on a packaged high-power GaN HEMT. It uses a simple double-reactance compensation and impedance transformation load network that includes device intrinsic capacitance, package parasitics, low-loss microstrip transmission lines, and lumped components. This load network makes the GaN HEMT operate in suboptimum Class-E from 900 to 1500 MHz (50% fractional bandwidth at 1200 MHz). The amplifier can operate both in continuous wave and pulsed modes over its full bandwidth without tuning. It delivers up to 180-W output power with up to 85% drain efficiency and ${rm PAE}=81%$ . To the best of the authors' knowledge, the amplifier proposed in this work outperforms commercial grade amplifiers that operate in the same frequency band with similar output power levels. Direct applications for this amplifier include mobile satellite communications transmitters, envelope elimination and restoration digital audio broadcasting transmitters, and power stages for primary and secondary RADAR transmitters.

Description: This paper describes the design and implementation of a package-integrated Chireix outphasing RF switch-mode power amplifier (PA). The optimum loading conditions, based on class E, and the Chireix compensation elements are provided to the active devices by a dedicated low-loss bondwire-based transformer power combiner that enables a very small form factor and low cost. The realized prototype achieved 70.6-W peak power with 73% peak drain efficiency at 2.3 GHz and 28 V, and up to 81% peak drain efficiency at 2.2 GHz and 20 V. When operated for maximum power at 28 V, it reached 53.5%/43.5% average drain/total efficiency for a 9.6-dB peak-to-average-power-ratio W-CDMA signal at 2.3 GHz with low ACLR1/2 levels ( ${-}{hbox{49}}$ / ${-}{hbox{56}}$ dBc after memoryless digital predistortion). Moreover, from 2.1 to 2.4 GHz, the realized PA demonstrated more than 50% drain efficiency across ${〉}{hbox{260}}$ , ${〉}{hbox{160}}$ , and ${〉}{hbox{80}}$ MHz at 6-, 8-, and 10-dB back-off, respectively.

Description: Design techniques for a load-independent low-power low-phase-noise CMOS LC direct bulk-coupled quadrature voltage-controlled oscillator (DBC-QVCO) is presented in this paper. A capacitor tapping technique is used to lower the phase noise and achieve load-independent frequency of oscillation. Class-C operation is used to further reduce the phase noise and power consumption. Quadrature coupling is achieved using bulk coupling, leading to reduction in both power and area. The DBC-QVCO has been implemented in a standard 0.18- $muhbox{m}$ BiCMOS process and occupies an area of 0.3 $hbox{mm}^{2}$ . The implemented DBC-QVCO achieves a measured phase noise of $-$ 114.2 $~$ dBc/Hz at 1-MHz offset from the 6.26-GHz carrier while consuming only 3.2 mW from a 1-V power supply. The DBC-QVCO achieves a figure of merit (FOM) of $-$ 185.1 dBc/Hz and an FOM with area of $-$ 190.3 dBc/Hz, which are among the best compared with recently published QVCOs operating in a similar frequency range.

Description: This paper presents the design of a receiver (Rx) front-end for automotive radar application operating at 76–77 GHz. The Rx employs a double conversion architecture, which consists of a five-stage low-noise amplifier (LNA), a sub-harmonic mixer (SHM), and a double-balanced passive mixer (PSM). By adopting this architecture, millimeter-wave frequency synthesizer design can be relaxed. In the LNA layout, the output of each stage is positioned close to the input of the follow stage, thus creating a $LC$ resonance load. As a result, complex interstage matching networks is simplified. The SHM driven by a 38-GHz local oscillator (LO) is adopted to avoid push/pull effect and power consumption of the voltage-controlled oscillator. A PSM is utilized for the second conversion since it consumes no dc current and has low flickering noise. To connect the singled-ended LNA and SHM, a 77-GHz balun is designed; and for driving the SHM, two 38-GHz baluns and an in-phase/quadrature coupler to provide quadrature 38-GHz LO are designed. The proposed Rx is implemented in a 65-nm CMOS technology and measurement results show 16-dB voltage gain and 13-dB calculated noise figure while dissipating 23.5 mA from a black 1.2-V supply.

Description: A new method for the sensitivity analysis of $S$ -parameter measurements due to the uncertainty of the calibration standards is presented. It is a fully analytic, straightforward calculation and can be applied to any analytic calibration routine. As a result, simple equations for the sensitivity coefficients are obtained, thus providing an in-depth view into the error propagation mechanisms. In contrast to numerical methods, general findings independent from the particular measurement setup or frequency setting are possible. The method is demonstrated for one-port calibration and for two-port calibration with the common thru-reflect-match and thru-reflect-line calibration procedures, as well as for their nonzero-length thru extensions line-reflect-match and line-reflect-line, respectively.

Description: We present a 220-GHz homodyne transceiver module intended for frequency modulated continuous wave radar applications. The RF transceiver circuits are fabricated on 3- $mu{hbox {m}}$ -thick GaAs membranes, and consist of a Schottky diode based transmitter frequency doubler that simultaneously operates as a sub-harmonic down-converting mixer. Two circuits are used in a balanced configuration to improve the noise performance. The output power is $〉 {hbox{3 dBm}}$ over a 40-GHz bandwidth (BW) centered at 220 GHz, and the receiver function is characterized by a typical mixer conversion loss of 16 dB. We present radar images at 4-m target distance with up to 60-dB dynamic range using a 30- $mu{hbox {s}}$ chirp time, and near-BW-limited range resolution. The module is intended for applications in high-resolution real-time 3-D radar imaging, and the unit is therefore designed so that it can be assembled into 1-D or 2-D arrays.

Description: A fully integrated linear CMOS power amplifier (PA) for the broadband operation is developed for handset applications. This amplifier can handle a wideband signal. To achieve broadband/wideband operation, an analysis of the intermodulation distortion for the asymmetric source in a differential cascode structure is presented. Based on the analysis, the linearization technique using a second harmonic circuit at the gate of the common gate is proposed to reduce the asymmetry. The proposed PA with an on-chip transmission-line transformer, which has a broadband matching characteristic, is fabricated using a 0.18- $mu$ m RF CMOS technology. The measurement results show that the sideband asymmetry is less than 0.6 dB for a signal with up to 50-MHz bandwidth, and the peak average power is improved by 1.2 dB within the linearity spec of a 16-QAM 7.5-dB peak-to-average power ratio long-term evolution signal. The PA delivers a power-added efficiency of 36.5%–31.2% and an average output power of 27.5–27.1 dBm under an ${rm{ACLR}}_{rm E-UTRA}$ of ${-}{hbox{30.5}}$ dBc for a 50-MHz bandwidth signal across 1.4–2.0-GHz carrier frequency.

Description: This paper presents the first built-in self-test system (BIST) for $W$ -band transmit–receive phased-array modules. Low-loss high-isolation switches are attached to the RF input and output ports using $lambda/4$ transmission-line sections, which result in a high shunt impedance when the BIST is disabled and minimal penalty in additional loss. A $W$ -band in-phase/quadrature down-conversion mixer/receiver with $〈$ 0.5-dB amplitude and 4 $^{circ}$ –5 $^{circ}$ phase imbalance at 90–100 GHz is also implemented on-chip and is used as an on-chip vector network analyzer. The BIST allows the measurement of the normalized ${ S}_{21}$ in both transmit and receive modes with high accuracy (4-bit phase response, $〈$ 0.5-dB amplitude variation) at 90–100 GHz without any external calibration. The BIST also results in a normalized frequency response that agrees well with the measured $S$ -parameters at 90–100 GHz.

Description: An envelope-tracking (ET) CMOS power amplifier (PA) is fabricated using a 0.18- $mu$ m CMOS process. The module containing the supply modulator, the PA, and the output transformer is implemented on a printed circuit board (PCB). The CMOS PA employs the second and third harmonic controls at the input and the second harmonic short at the output for improved linearity. The impact on the nonlinearity of the cascode differential structure is studied and optimized. A proposed output transformer on the PCB minimizes the loss and enhances the efficiency of the PA. The ET on the gate of the common gate transistor is proposed to achieve high linearity and efficiency without using a digital pre-distortion technique. For a long-term evolution (LTE) signal at 1.85 GHz with a 10-MHz bandwidth and a 16QAM 7.5-dB peak-to-average power ratio, the ET CMOS PA module achieves a power-added efficiency of 34%, an error vector magnitude of 2.8%, and an adjacent channel leakage ratio of ${-}{hbox{34.2}}$ dBc at an average output power of 26 dBm. The ET operation reduces the total current consumption by 10% to 34%, according to the power level, over that of the standalone PA for the LTE signal.

Description: A solution based on series reversion is derived and tested to estimate an ${ N}$ -port device-under-test (DUT) scattering matrix through a multiple-in/multiple-out microwave feed network. The feed network uses power dividers in place of fan-in/fan-out stages of traditional double-pole ${ N}$ -throw (2PNT) switching matrices. A fast recursive algorithm is derived to simultaneously estimate the DUT scattering matrix and solve the multiple scattering problem for weakly interacting networks. In experiment, the method was able to recover the scattering matrix of a passive DUT to within 0.1 dB in magnitude and 2° in phase.

Description: In this paper, an output-controllable digital predistortion (DPD) technique is proposed to partially inverse the nonlinear behavior of RF power amplifiers (PAs). Compared to the existing DPD, the proposed method changes the goal that the PA output must be exactly the same as the original input to a new one that the PA output can be arbitrarily controlled according to user's demand. The proposed approach largely expands the capability of DPD and thus provides more flexibility for system designers to effectively use DPD to manipulate the PA output in order to handle more application scenarios and objectively conduct further system optimization. Various application cases have been tested. The experimental results demonstrate that the proposed approach has great potential in future wireless communication system design.

Description: Any amplifier operated with a varying supply voltage is actually a three-port circuit, having two inputs and one output. When an amplifier is characterized as a three-port for dynamic supply voltage operation, three separate operating modes appear: linear L-mode and the two nonlinear modes C-mode and P-mode. Each of these modes, along with their relationships and differences, are identified, characterized, and discussed. Relations of these modes to the dynamic power supply transmitter techniques of envelope tracking and/or direct polar are presented. Measurements are reported that provide experimental verification for these amplifier operating modes.

Description: In this paper, a Doherty power amplifier for K-band point-to-point microwave radio, developed in TriQuint GaAs ${hbox{0.15-}}{mu{hbox {m}}}$ PWR pHEMT monolithic technology, is presented. Highly efficient driver stages on both the main and auxiliary branches have been designed and optimized to boost gain with minimal impact on power-added efficiency. The selected architecture enables a modular combination to reach higher power levels. Matching network structures have been designed, according to simple equivalent circuit approaches, to obtain the desired 10% fractional bandwidth. The fabricated power amplifier (PA) exhibits, at 24 GHz in continuous-wave conditions, an output power of 30.9 dBm, with a power-added efficiency of 38% at saturation and 20% at 6 dB of output power back-off, together with a gain of 12.5 dB. System-level characterization at 24 GHz, in very demanding conditions, with a 28-MHz channel 7.5-dB peak-to-average ratio modulated signal, showed full compliance with the standard emission mask, adopting a simple predistorter, with average output power of 23.5 dBm, and average efficiency above 14%. The measured performance favorably compare with other academic and commercial K-band PAs for similar applications.

Description: A novel single-source surface–volume–surface integral equation is proposed for accurate broadband resistance and inductance extraction in 3-D interconnects. The new equation originates in the volume integral equation (VIE) traditionally used for magneto-quasi-static modeling of current flow in 3-D wires. The latter is reduced to a surface integral equation by representing the electric field inside each conductor segment as a superposition of cylindrical waves emanating from the conductor's boundary. As no approximation is utilized and all underlying boundary conditions and pertinent equations are satisfied in the reduction, the new integral equation is rigorously equivalent to the solution of the traditional volume electric field integral equation. The rigorous nature of the proposed single-source surface integral equation is corroborated numerically. In this paper, a detailed description of the method of moments discretization for the proposed surface integral equation is also presented. Numerical solution of the proposed surface integral equation for a 12-conductor bond-wire package is used to demonstrate the accuracy of the method and its computational benefits compared to the traditional solution based on the VIE.

Description: This paper presents a method for pruning power amplifier (PA) behavioral models and digital predistorters based on compressed sampling theory. Using this method, the number of coefficients required by behavioral models and predistorters can be significantly reduced while achieving comparable performance in terms of both modeling accuracy and suppressing distortions. Hardware measurements obtained for a Doherty PA driven by a five-carrier 100-MHz wide long-term evolution-advanced signal demonstrate the capability of the proposed method to linearize a highly nonlinear PA prototype using a minimal number of coefficients, revealing the attractive properties of the proposed method and its desirable performance. Using the proposed technique, predistorters achieving similar linearization performance while requiring significantly less coefficients than the traditional models were demonstrated.

Description: This paper presents a new baseband equivalent (BBE) Volterra-series model suitable for the behavioral modeling and linearization of wideband RF power amplifiers (PAs). Starting with passband Volterra series, and following a number of signal transformations, a discrete expression relating the envelopes of the output and input signals to the carrier frequency was derived. The new BBE Volterra series reduces the number of kernels, and hence, avoids resorting to the pruning approaches commonly applied in the literature to the classical low-pass equivalent (LPE) Volterra formulation. The proposed baseband Volterra series has similar modeling and linearization performance to the full classical LPE Volterra series. It also outperforms the pruned LPE Volterra models, which use a dynamic deviation reduction approach, in terms of both linearization performance and complexity. The proposed BBE Volterra series was successfully used to linearize different PAs (200-W LDMOS Doherty and 45-W broadband GaN PA) driven with wideband and intra-band carrier aggregated signals (mixed LTE and WCDMA signals).

Description: A compact self-packaged dual-band filter structure using multilayer liquid crystal polymer technology is presented in this paper. The frequency and bandwidth of each passband can be more conveniently controlled by means of vertically embedded elements, i.e., metal patches, placed above the coupled folded multi-stepped impedance resonators. The packaged solution is connected to the outer environment through a coplanar waveguide that allows flip-chip interconnection to a host board. The proposed design is validated with the fabrication of two prototypes. The measured results show good agreement with the simulations.

Description: In the paper, the nonlinear model of a microwave transistor is extracted from large-signal measurements acquired under “dynamic-bias” operation. Specifically, the transistor is driven by low-frequency large signals while a high-frequency tickle is applied on top of them. The low-frequency large signals, along with the dc bias voltages, set the large-signal operating point which represents a dynamic-bias condition for the device under test. Thanks to this technique, one can get at once and separately the nonlinear currents and charges of the transistor as a result of a very few nonlinear measurements. Additionally, the proposed technique allows one to accurately reconstruct the time-domain waveforms at the device-under-test terminals while the frequency of the tickle can be set as high as the bandwidth of today's vector calibrated nonlinear measurement systems (i.e., 67 GHz). The approach, which is general and independent of device technology, is applied on a 0.15- $mu$ m GaAs pHEMT specifically designed for resistive cold-FET mixer applications.

Description: In this paper, an explicit and unconditionally stable finite-difference time-domain (FDTD) method is developed for electromagnetic analysis. Its time step is not restricted by the space step, and its accuracy is ensured for the time step chosen based on accuracy. The strength of the conventional explicit FDTD is thus preserved in avoiding a system matrix solution, while the shortcoming of the conventional FDTD is eliminated in the time step's dependence on space step. Numerical experiments in both 2-D and 3-D simulations have demonstrated the performance of the proposed method in stability and efficiency without sacrificing accuracy.

Description: A 0.7–1.0-GHz reconfigurable bandpass-to-bandstop filter with selectable 2- and 4-pole responses is presented. The proposed filter can act as a 2- or 4-pole bandpass or bandstop filter by changing the coupling paths using zero-value coupling coefficients. The 4-pole bandpass filter mode also includes bandwidth control. The filter is built on a Duroid substrate with $varepsilon_{ r}=10.2$ and $h=25$ mil. The center frequency tuning, as well as the bandpass-to-bandstop transformation and the selection of the number of poles are achieved using silicon varactor diodes and RF microelectromechanical systems switches. In the 2- and 4-pole bandpass modes, an insertion loss of 4.9–2.9 and 6.1–4.8 dB is measured at 0.71–0.99 and 0.72–1.01 GHz, respectively. The 4-pole bandpass mode also shows a bandwidth tuning of 28–85 MHz at 0.9 GHz. In the 2- and 4-pole bandstop modes, rejection levels of 24–28 and 32–41 dB are measured at 0.64–0.96 and 0.71–0.96 GHz, respectively. The application areas are in reconfigurable filters for wideband radios under high interference environments.

Description: An experimental approach to investigate the forward scattering sum rule for periodic structures is presented. This approach allows an upper bound on the total cross section integrated over a bandwidth from a simple static problem to be found. Based on energy conservation, the optical theorem is used to construct a relation between the total cross section and the forward scattering of periodic structures as well as single scatterers inside a parallel-plate waveguide. Dynamic measurements are performed using a parallel-plate waveguide and a parallel-plate capacitor is utilized to find the static polarizability. Convex optimization is introduced to identify the total cross section in the dynamic measurements and estimate an optimal lower bound on the polarizability for objects. The results show that the interactions between the electromagnetic field and an object over all wavelengths are given by the static polarizability of the object.

Description: In this paper, we present an efficient numerical algorithm to solve the vector wave equation in general cylindrically layered media. The method is based on the fact that appropriate choices of basis and weighting functions make it possible to separate the vector wave equation numerically. To this end, we present a set of curl-conforming vector basis functions in a 2-D doubly connected domain and another set of different vector weighting functions. The former is responsible for the avoidance of spurious solutions while the later provides a numerical separation. The proposed method is applied to calculate the propagation constants of the lower order guided and leaky modes of several cylindrically layered dielectric waveguides and the accuracy and efficiency of the method are investigated.

Description: Compact multi-port power combiners and dividers with filter characteristics are introduced. These components advantageously combine the functions of power distribution and filtering in a single component, thus reducing the number of components in a system and improving overall system performance. The design principle, which is entirely based on filter theory, is first presented for a symmetric filtering four-port combiner/divider and is then extended to an eight-port network. Measurements on a symmetric all-metal waveguide four-port prototype show excellent agreement with simulations and validate the general design approach. The experimental response of an asymmetric substrate integrated waveguide eight-port network agrees reasonably well with simulations and demonstrates that the basic four-port element can be extended to very compact multi-port combiner/dividers to cope with a variety of systems requirements.

Description: This paper presents a novel coupled line 180 $^{circ}$ hybrid with non-interspersed input/output ports. With the combination of a weak coupling parallel coupled line and strong coupling trans-directional coupler, a non-interspersed input/output ports coupled line 180 $^{circ}$ hybrid is obtained by using printed circuit board fabrication process, and reduced substrate area is achieved. The proposed hybrid owns the features of reducing the complexity of dc biasing for the next-stage active circuits. Moreover, it requires no bond wires, via-holes, or multilayer structures. The formula of the proposed hybrid is derived, and the characteristics of the hybrid are analyzed. Two prototypes are designed to verify the concept. One is arranged with the two couplers perpendicular to each other, and the other is constructed with the two couplers arranged in a line. The measured results are in good agreement with the simulated ones

Description: In this paper, an $E$ -plane waveguide power divider and a waveguide-to-microstrip transition are used to form a waveguide magic-T with four arms in the same $E$ -plane. The input port of the original $E$ -plane waveguide power divider acts as the difference port of the magic-T, and a waveguide-to-microstrip transition is utilized to realize the sum port. The four arms are in the same plane, and traditional matching elements, such as cones, wedges, pins, and irises are not needed. The proposed magic-T features easy connection, fabrication, and assembly. The principle and design procedure are described in detail. A $Ka$ -band $E$ -plane waveguide magic-T is designed, fabricated, and measured. A fractional bandwidth of 21% is achieved. The measured and simulated results show good amplitude, phase, and isolation characteristics validating the proposed magic-T.

Description: This paper presents a 90-nm fully integrated CMOS linear power amplifier (PA) using a coupled L-shape concentric vortical transformer (CL-CVT) for the fourth-generation long-term evolution (LTE) communication standard. Using the proposed output combining CL-CVT architecture, the outer diameter required by the power combiner is reduced by 66% compared to the distributed active transformer with similar performance. Moreover, the PA is able to efficiently combine four push–pull output stages and achieve nearly constant power over several LTE bands with a total chip area less than 1 ${hbox {mm}}^{2}$ . With a 1.2-V supply voltage, the PA delivers 27.3-dBm maximum output power with a peak drain efficiency of 47% at 2.4 GHz. Using a 20-MHz LTE 16-QAM test signal, the PA achieves 24.6% power-added efficiency at an output power level of 22 dBm and passes the spectral requirements defined by the LTE standard without using any pre-distortion or calibration techniques.

Description: This paper addresses, for the first time, the digital representation of spectrally periodic signal-interference microwave passive filters. Starting from the theoretical rational transfer function of a synthesized transmission-line signal-interference analog filter, the real-valued coefficients of its digital-domain filter counterpart are derived. This discrete-time formulation for this type of microwave filters allows to clarify some confusing concepts into them, such as filter order. Moreover, some particular phenomena observed in associated experimental proof-of-concept planar prototypes, such as the appearance of out-of-band/spurious resonance peaks, are also explained by this study as zero-pole quasi-cancellations. In addition, it is demonstrated here that the use of the adjective “transversal” for this class of microwave passive filters could be no rigorous as it is understood in a digital sense since its discrete-time modeling commonly obeys an infinite-impulse-response structure. For validation, the expounded theoretical framework is applied to three examples of signal-interference passive filters exhibiting quasi-elliptic-type single-passband, six-passband, and low-pass responses.

Description: In this study, we propose an auxiliary power regulator (APR) for the current-shared cascade (CSC) structure of the driver stages of RF CMOS power. Although the CSC structure provides a method to reduce the power consumption at the driver stages of a differential power amplifier (PA), it is difficult to obtain optimum levels of effective supply voltage for the first and second driver stages. Additionally, the transistor sizes of the first and second driver stages of the CSC structure must be identical to ensure the proper operation of the PA. Thus, in this work, we propose an APR structure that ensures the proper operation of a PA with different transistor sizes in its first and second driver stages. To prove the feasibility of the proposed technique, we designed the PA with a CSC structure using an APR. From the measured results, we successfully verify the feasibility of the proposed structure. Additionally, we provide experimental results for a typical CMOS PA to determine the optimum supply voltage for the second driver stage.

Description: The pin-to-pin electrostatic discharge (ESD) issue for a differential low-noise amplifier (LNA) was studied in this work. A new design of ESD protection diodes with an embedded silicon-controlled rectifier (SCR) was proposed to protect the gigahertz differential LNA. The proposed ESD protection design was modified from the conventional ESD protection design without adding any extra device. The SCR path was established directly from one differential input pad to the other differential input pad so the pin-to-pin ESD robustness can be improved. This design had been verified in a 65-nm CMOS process. Besides, this design had been further applied to a 24-GHz LNA in the same 65-nm CMOS process. Experimental results had shown that the proposed ESD protection design for the differential LNA can achieve excellent ESD robustness and good RF performances.

Description: This paper provides a formulation of the dual-tapped microstrip resonator. The formulation derives the $Q$ -factor of the resonator, and the maximum value of the $Q$ -factor while still satisfying oscillation conditions. It is shown that the optimized $Q$ -factor can be determined without changing the resonant frequency bandwidth. The phase-noise performance of a voltage-controlled oscillator (VCO) using a dual-tapped microstrip resonator can therefore be designed independent of the design of the oscillation bandwidth. This feature results in simple design of low phase-noise VCOs while maintaining the desired oscillation bandwidth. Experimental results of an X-band VCO employing the dual-tapped microstrip resonator verify the theoretical findings. The fabricated X-band VCO achieves an oscillation bandwidth of 11.86–12.09 GHz and phase noise lower than ${-}{hbox{114.4}}$ dBc/Hz at 100-kHz offset from the carrier. This VCO is one of the most low phase-noise planar X-band VCOs published to date.

Description: Co-design of 60-GHz wideband front-end integrated circuit (IC) with on-chip transmit/receive (T/R) switch in 65-nm CMOS is presented. Passive macro-modeling (pmm) is utilized to convert $S$ -parameter files from passive component electromagnetic simulations to state-space models in circuit netlist format that could be used in a commercial SPICE simulator for various analyses without convergence issues. The co-design of the on-chip switch and the low-noise amplifier (LNA)/power amplifier could achieve wideband matching and reduce the effects of insertion loss of the on-chip T/R switch. Combining with the gain-boosting technique in the LNA design and lumped-component-based design methodology, the implemented 60-GHz front-end IC with an on-chip T/R switch achieves 3-dB gain bandwidth (BW) of 12 GHz with a maximum gain of 17.8 dB and minimum noise figure of 5.6 dB in the receiver mode and 3-dB gain BW of 10 GHz with saturated output power of 5.6 dBm in the transmitter mode, and only consumes 1.0 mm $times$ 1.2 mm die area (including pads).

Description: This paper describes the analysis and design of saturated silicon–germanium (SiGe) heterojunction bipolar transistor (HBT) switches for millimeter-wave applications. A switch optimization procedure is developed based on detailed theoretical analysis and is then used to design multiple switch variants. The switches utilize IBM's 90-nm 9HP technology, which features SiGe HBTs with peak ${ f}_{ T}/{ f}_{max}$ of 300/350 GHz. Using a reverse-saturated configuration, a single-pole double-throw switch with a measured insertion loss of 1.05 dB and isolation of 22 dB is achieved at 94 GHz after de-embedding pad losses. The switch draws 5.2 mA from a 1.1-V supply, limiting power consumption to less than 6 mW. The switching speed is analyzed and the simulated turn-on and turn-off times are found to be less than 200 ps. A technique is also introduced to significantly increase the power-handling capabilities of saturated SiGe switches up to an input-referred 1-dB compression point of 22 dBm. Finally, the impact of RF stress on this novel configuration is investigated and initial measurements over a 48-h period show little performance degradation. These results demonstrate that SiGe-based switches may provide significant benefits to millimeter-wave systems.

Description: This paper presents a novel microstrip transmission line method for broadband relative permittivity measurement of planar dielectric substrate materials. The method requires three sets of $S$ -parameter measurements of the microstrip line together with an obstacle in three equidistant positions over the line. The measurement and simulation results for the broadband relative permittivity of high-frequency substrates, TLX-8, RF60A, CER10, and the widely used FR4 are presented. The errors are calculated based on the manufacturers' data sheet value. Both the simulation and measurement results are found to be within 16% of the data sheet values for CER10 and 10% for all other substrates. The proposed method can minimize errors due to the nonreproducibility of connectors and impedance mismatch problems, prevalent in transmission line methods. However, the method is highly sensitive to the positioning of the obstacle, which can be overcome through the use of high accuracy obstacle positioning methods.

Description: This paper introduces a new class of RF-to-dc rectifiers called the in-phase gate-boosting rectifier (IGR). An IGR utilizes an in-phase passive voltage multiplier (IPVM) to boost in-phase $V_{rm GS}$ swing from the driving $V_{rm DS}$ swing. This design simultaneously reduces the effective threshold voltage, forward resistance, and the reverse leakage current of the rectifying transistor. As a consequence, the sensitivity and the efficiency of a high-frequency rectifier can be improved. Furthermore, a $C_{G}$ -loaded IPVM presents low input conductance and is shunted with the drains/sources of the rectifying transistors. This makes the realization of the input matching network between the IGR core and the antenna easier, and achieves a higher voltage swing at the input terminals of the IGR core. The criteria, properties, and relating proofs of the IPVM are also discussed. A differential seven-stage millimeter-wave IGR is implemented in a 65-nm RF CMOS process. In this design, an interleaving internal threshold cancellation bias scheme is also introduced to further suppress the power consumption due to biasing circuitry without increasing the layout area. The implemented integrated circuit achieves a state-of-the-art $-$ 7-dBm sensitivity with 20% peak efficiency at 53 GHz and a bandwidth of 10 GHz from 46 to 56 GHz.

Description: We present a novel non-contact metrology approach for on-wafer characterization of sub-millimeter-wave devices, components, and integrated circuits. Unlike existing contact probes that rely on small metallic tips that make physical contact with the device on the chip, the new non-contact probes are based on electromagnetic coupling of vector network analyzer (VNA) test ports into the coplanar waveguide environment of integrated devices and circuits. Efficient signal coupling is achieved via a quasi-optical link between the VNA ports and planar antennas that are monolithically integrated with the test device. Experimental validation of the non-contact device metrology system is presented for the first time to demonstrate the accuracy and repeatability of proposed approach for the 325–500-GHz (WR2.2) and 500–750-GHz (WR1.5) bands.

Description: Most conventional wideband digital predistortion (DPD) techniques require the use of a very high-speed analog-to- digital converter (ADC) in the feedback path. This paper proposes a novel technique, termed under-sampling restoration digital predistortion (USR-DPD), to linearize wideband power amplifiers (PAs) with ADCs that operate at sampling rates much lower than required by Nyquist limits for the predistorted band (under-sampling ADCs). The USR processing is implemented in an iterative way to restore full-band PA output information from the under-sampled output signal, allowing memory DPD models to be successfully extracted. The USR-DPD can operate in two modes: without and with a band-limiting filter in the feedback path. In comparison with conventional DPD techniques, the requirement for ADC sampling frequency can be significantly reduced using the USR-DPD approach. Experimental tests were realized for two PAs with numerous signals (10-, 20-, 40-, and 60-MHz long-term evolution signals) using different ADC sampling frequencies. The DPD with the under-sampling ADC could achieve comparable performances to its counterpart with a full-rate ADC, while using 3–5 times lower sampling frequency, and around $-{hbox{50-dBc}}$ adjacent channel power ratios were achieved.

Description: A 16-element phased-array receiver has been developed for advanced W-band automotive radars. The phased-array receiver is based on a single SiGe chip with RF beamforming capabilities, which is packaged using low-cost bond-wire techniques and attached to a 16-element linear microstrip array. The antenna results in a directivity of 29.3 dB and a gain of 28.0 dB at 77–81 GHz, and can be scanned to $pm {hbox{50}}^{circ}$ in the azimuth plane in $sim {hbox {1}}^{circ}$ steps. The packaging details are presented together with the steps taken to ensure a wideband impedance match and low coupling between the phased-array channels. Gain measurements done at 79 GHz agree well with simulations. The 16-element phased array receiver was used with a 2-element frequency-modulated continuous-wave transmitter at 76.5–77 GHz and high-resolution millimeter-wave images were obtained. The work shows that complex millimeter-wave phased arrays can be packaged using traditional bond-wire techniques, and can be a powerful solution for advanced automotive radars.

Description: This paper presents a hybrid radar system that incorporates a linear frequency-modulated continuous-wave (FMCW) mode and an interferometry mode for indoor human localization and life activity monitoring applications. The unique operating principle and signal processing method allow the radar to work at two different modes for different purposes. The FMCW mode is responsible for range detection while the interferometry mode is responsible for life activities (respiration, heart beat, body motion, and gesture) monitoring. Such cooperation is built on each mode's own strength. Beam scanning is employed to determine azimuth information, which enables the system to plot 360 $^{circ}$ 2-D maps on which the room layout and objects' location can be clearly identified. Additionally, the transmitted chirp signal is coherent in phase, which is very sensitive to physiological motion and allows the proposed technique to distinguish human from nearby stationary clutters even when the human subjects are sitting still. Hence, the proposed radar is able to continuously track the location of individuals and monitor their life activities regardless of the complex indoor environment. A series of experiments have been carried out to demonstrate the proposed versatile life activity monitoring system.

Description: A compact 680-GHz waveguide orthomode transducer (OMT) and circular horn combination has been designed, tested, and characterized in a radar transceiver's duplexer. The duplexing capability is implemented by a hybrid waveguide quasi optical solution, combining a linear polarization OMT and an external grating polarizer. Isolation between the OMT's orthogonal ports' flanges was measured with a vector network analyzer to exceed 33 dB over a $〉$ 10% bandwidth between 630 and 710 GHz. Calibrated Y-factor measurements using a mixer attached to the OMT ports reveal losses through the transmit and receive paths that sum to an average of 4.7 dB of two-way loss over 660–690 GHz. This is consistent with radar sensitivity measurements comparing the new OMT/horn with a quasi-optical wire grid beam splitter. Moreover, the radar performance assessment validates the OMT as a suitable compact substitute of the wire grid for the JPL's short-range 680-GHz imaging radar.

Description: This paper presents the design of two combined linear power amplifiers for 7-GHz microwave backhaul, realized in 0.25- $mu$ m GaN on SiC monolithic technology. Both modules are based on a combined class-AB structure conceived for maximum back-off efficiency and reduced phase distortion, which are important requirements in backhaul systems. Different second harmonic loads are exploited in the two power amplifiers, leading to different performance in terms of output power, bandwidth and efficiency. The two stages exhibit a saturated output power in excess of 35 and 36 dBm on 16% and 26% of fractional bandwidth, respectively; moreover, the measured average efficiency in the presence of modulated signals with 7.4-dB peak-to-average power ratio is 18% and 25%. Simulations and experimental results demonstrate that the second-harmonic load has little influence on the linearity of the proposed amplifiers. Compliance with the spectrum emission mask defined for the targeted application has been achieved through low-order polynomial digital predistortion, thus demonstrating the high linearity of the stages. A comparison with a Doherty amplifier realized in the same technology and for the same application shows that the two proposed stages need a simpler predistorter to achieve the linearity required by standard specifications.

Description: A simple equivalent circuit model with empirical equations describing the peripheral feeding ports of conical-line power combiners is presented. The model allows the entire structure to be designed using transverse electromagnetic circuit theory without the need for any full-wave simulations. A summary of the model extraction process is given and the accuracy of the proposed model is confirmed by favorable comparisons with full-wave simulations. The circuit based design method is used to design a compact conical-line combiner showing measured performance similar to the current state of the art combiners in this technology, while being significantly smaller.

Description: A new microwave device called the cascaded type of coupled resonator decoupling network (C-CRDN) is proposed in this paper. The four-port device can be used to reduce the interference between two radio systems that work in adjacent or even contiguous frequency bands. A C-CRDN is cascaded between the two antennas to be decoupled and the I/O ports of their radio systems, respectively. The coupling matrix of a C-CRDN can be designed to meet the required isolation and return-loss specifications. To prove the concept, a fourth- and sixth-order C-CRDN using coaxial combline cavities are designed, fabricated, and measured according to the characteristics of a testing array that consists of two high-gain sleeve dipoles working in the adjacent time-division long-term evolution and wireless fidelity bands. The measured results have demonstrated that the proposed C-CRDN can effectively mitigate the coexistence interference between the two collocated systems by providing at least 20-dB isolation improvement and enhanced matching performance. The proposed technique is general and can find many applications in heterogeneous wireless systems.

Description: Wireless body area network (WBAN) applications benefit extensively from the advantages offered by unique features of ultra-wideband (UWB) wireless communication, such as high data rate, low power consumption, and simple transmitter design. A major disadvantage in using UWB for WBAN applications is the complexities introduced by UWB receivers, such as high power consumption, poor receiver performance due to low sensitivity, and complex hardware implementation. This paper presents hardware implementation of a new communication system, where UWB is used for high data-rate transmission from sensor nodes and a 433-MHz industrial, scientific, and medical (ISM) band receiver is used for receiving low data-rate control messages at the sensor nodes. A full network system for WBAN applications has been implemented including a unique medium access control protocol. The proposed WBAN system is designed to dynamically control the pulses per bit value used for the UWB data communication using control messages received via the narrowband feedback link (i.e., the 433-MHz ISM link). This leads to dynamic bit error rate (BER) and power control at the sensor nodes, which improves the reliability of communication and power efficiency of sensor nodes under dynamic channel conditions. The performance of the system is evaluated in terms of BER, sensor initialization delay, and power consumption. This novel dual-band architecture utilizes the unique advantages offered by UWB communication and narrowband technology to enable high data rate, low-complexity hardware design, low power consumption, and small form factor for WBAN sensor systems.

Description: For predictive simulation of high-speed electronic components, an accurate and numerically efficient hot electron transport model is solved simultaneously with Maxwell's full-wave vector field equations. The transport model is based on ideal Fermi gas kinetics and incorporates electronic band structure as well as the essential electron scattering mechanisms. It couples self-consistently to full-wave electromagnetics through a field discretization scheme based on the relationship between Delaunay and Voronoi meshes. Three-dimensional simulations of different GaAs transistor designs produce dc and high-frequency results that compare well with measured data.

Description: Accurate admittance-transformer (Y-TF) feeds along with short-circuited stub-embedded resonators (SCSERs) are proposed in this study to design the improved parallel coupled-line (PCL) filters with structure-inherent transmission zeros (TZs). The proposed Y-TF feeds for flexible terminations are thoroughly analyzed and found more accurate than conventional approximate tapped-line feedings. Specifically, two basic parallel-coupled bandpass filters with conventional $lambda/2$ stepped-impedance resonators are first successfully implemented to validate the proposed Y-TF feedings. The ideal frequency responses of the two filters by a circuit simulator are compared with those transformed from the coupling matrix. Furthermore, an SCSER-based filter with multiple TZs is designed to verify the feasibility of the described design procedure. The adopted resonating components are composed of two short-circuited stepped-impedance stubs and multiple open-circuited ones all extended from a common joining point. The interstage couplings of the filter are achieved by the short-ended PCLs, while the input/output couplings are realized by the proposed Y-TF feedings. Through the fabrication of the proposed filters, the measured results along with the simulated ones validate the theoretical derivations.

Description: Analysis and applications of coupled cross-shaped resonator (CCSR) for fixed and fully reconfigurable differential bandpass filters (BPFs) design are focused in this paper. CCSRs with open and capacitive terminations are presented and discussed. One differential BPF named Filter I centered at 4.5 GHz with fixed differential-mode (DM) and common-mode (CM) responses using CCSR with open termination; and another one named Filter II using capacitive termination and loaded lumped capacitors offers fully reconfigurable DM center frequency, bandwidth and intuitive CM suppression control are proposed with very compact size $(0.01lambda_{0}^{2})$ . Such that ultra-wide DM center frequency tuning range of 82% fractional tuning range with both constant absolute bandwidth (ABW) and constant fractional bandwidth (FBW), easy control of CM suppression level and rejected range are achieved, respectively. Their experimental characterizations are in good agreement with theoretical analysis validating a simple approach of fixed and fully reconfigurable differential BPFs design.

Description: Compact planar crossovers with a wide passband are proposed. By cascoding two quarter-wavelength branch-line couplers, a wide passband can be obtained. Moreover, the even-odd mode and the fourfold symmetry are adopted to derive the analytical equations. According to the derived formulas, the transmission lines' impedances $Z_{1}$ , $Z_{2}$ , and $Z_{A}$ , which may influence the performance of the operating fractional bandwidth (FBW), should be properly selected. In terms of experimental verification, the circuit size of the fabricated crossover is $0.23lambda_{g}times 0.23lambda_{g}$ . Moreover, the FBW of the developed crossover is the 59% 1-dB insertion-loss relative bandwidth corresponds to the $S_{31}$ parameter, whereas the 55% 15-dB one refers to the $S_{21}$ parameter. In addition, four bandstop filters can be added at four ports of the proposed crossover to achieve a wide stopband performance.

Description: This paper presents a fully integrated eight-way power-combining amplifier for 110–134-GHz applications in an advanced 90-nm silicon–germanium HBT technology. The eight-way amplifier is implemented using four-stage common-emitter single-ended power amplifiers (PAs) as building blocks, and reactive $lambda /4$ impedance transformation networks are used for power combining. The single-ended PA breakout has a small-signal gain of 20 dB at 116 GHz, and saturation output power ( $ { P}_{rm sat}$ ) of 12.5–13.8 dBm at 114–130 GHz. The eight-way power-combining PA achieves a small-signal gain of 15 dB at 116 GHz, and $ { P}_{rm sat}$ of 20–20.8 dBm at 114–126 GHz with a power-added efficiency of 7.6%–6.3%. The eight-way amplifier occupies 4.95 $ {hbox {mm}}^{2}$ (including pads) and consumes a maximum current of 980 mA from a 1.6-V supply. To our knowledge, this is the highest power silicon-based D-band amplifier to date.

Description: This paper reports on two power amplifier (PA) monolithic microwave integrated circuits (MMICs) operating at frequencies around 220 GHz. The PAs use 250-nm InP HBTs and thin-film microstrip technology formed with a benzocyclobutene dielectric. Both PAs utilize a two-emitter-finger HBT unit-cell with each finger having an emitter area of ${hbox{0.25}}times {hbox{6}}~mu{hbox {m}}^{2}$ . The single-stage amplifier MMIC has six two-emitter HBTs in parallel for a total emitter area of ${hbox{18}}~mu{hbox {m}}^{2}$ . This amplifier has $sim {hbox {5 dB}}$ of small-signal gain from 210 to 230 GHz. It has demonstrated saturated output power of 90 mW at 210 and power-added efficiency (PAE) of 10%. This is the highest PAE number demonstrated at these frequencies. The two-stage PA uses three single-stage PAs, one as a driver and two in a balanced configuration in the second stage. The total output emitter area is ${hbox{18}}~mu{hbox {m}}^{2}$ . This PA demonstrated saturated output $〉{hbox {100 mW}}$ and PAE $geq {hbox{4}}{%}$ from 210 to 225 GHz.

Description: Accurately modeling the memory effects is critical in modeling and nonlinearity pre-compensation for wideband radio frequency (RF) power amplifiers (PAs) with strong memory effects. In this paper, the memory effects are divided into two categories: lagging memory effect and leading memory effect, which are defined based on the input samples located after and before the current output samples, separately. Considering the above two types of memory effects, a generalized two-box cascaded (GTBC) nonlinear behavioral model for RF PAs with strong memory effects is proposed: one box for a static nonlinearity block that is used to include the strong static nonlinearities and the other box for a dynamic nonlinearity block which is used to predict the mild dynamic nonlinearities. The modeling accuracy of the proposed model, in terms of the normalized mean square error (NMSE) and the memory effect intensity (MEI), is compared to the generalized memory polynomial (GMP), the augmented Hammerstein (AH) and the enhanced Hammerstein (EH) models for a 450–470 MHz Doherty PA with a three-carrier WCMDA input signal and a 895–935 MHz inverse Class-F Doherty PA with a single-carrier FDD-LTE OFDM input signal. The validation demonstrates that the proposed model leads to high-accuracy with fewer modeling coefficients and floating point operations (FLOPs).

Description: Two novel adaptive steady-state criteria are proposed to adaptively determine whether the steady state has been achieved in finite-difference time-domain (FDTD) method. The proposed criteria are established by the total electromagnetic energy in the computational region. To reduce the computational burden of electromagnetic energy calculation, a new approach is presented to replace the volume integral of energy with a surface integral. In addition, after newly defined attenuation coefficient and stability coefficient, novel adaptive steady-state criteria are proposed to overcome the premature convergence, nonmonotonicity, and nonconvergence challenges, which are serious in traditional adaptive steady-state criteria. At the end of this paper, numerical examples are given to demonstrate the effectiveness and superiority of our proposed criteria.

Description: This paper presents a divide-by-4 (D4) and divide-by-8 (D8) regenerative frequency dividers (RFDs) with the quadrature and the octet outputs. The topologies of the D4 and D8 RFDs use the even-harmonic mixers and the current-mode-logic (CML) loop dividers to achieve high division ratio and wide locking ranges. The modified Gilbert cells with quadrature- and octet-phases local-oscillator switching transistors are adopted to perform 2 $times$ and 4 $times$ subharmonic mixing with good conversion efficiency. The divide-by-2 and D4 CML loop dividers are used to obtain wide frequency range and the quadrature and the octet outputs. The D4 and D8 RFDs were fabricated by using a 90-nm CMOS process. With consuming 10.8 and 17.8 mW of dc power, the measured locking ranges of the D4 and D8 dividers are 13.2–18.4 and 16.8–26 GHz, respectively. Over the whole locking range, the two dividers with the phase deviation between the quadrature and the octet signals to be less than 2.2 $^{circ}$ and 4.4 $^{circ}$ , respectively. The proposed circuits achieve wide locking ranges and accurate output phases, making them very attractive for application into a multi-phase generator.

Description: A theoretical comparison of fundamental limitations on the output power of balanced diode mixers and even harmonic mixers is presented in this paper. The modulator operation is employed for the formulation. Additionally, the maximum output power, the output power at the 1-dB gain compression point, and the conversion loss of both mixers are formulated. It is theoretically confirmed that even harmonic mixers exhibit output power saturation when there is a high local oscillator power, although balanced diode mixers exhibit no saturation. This saturation is caused by restrictions in the built-in voltage of diodes, and even harmonic mixers therefore have lower output power capability when compared to balanced diode mixers. Derived formulas are confirmed by performing experimental investigations at 100 MHz.

Description: Dielectric spectroscopy (DS) is an important technique for scientific and technological investigations in various areas. DS sensitivity and operating frequency ranges are critical for many applications, including lab-on-chip development where sample volumes are small with a wide range of dynamic processes to probe. In this work, we present the design and operation considerations of radio-frequency (RF) interferometers that are based on power-dividers (PDs) and quadrature-hybrids (QHs). Such interferometers are proposed to address the sensitivity and frequency tuning challenges of current DS techniques. Verified algorithms together with mathematical models are presented to quantify material properties from scattering parameters for three common transmission line sensing structures, i.e., coplanar waveguides (CPWs), conductor-backed CPWs, and microstrip lines. A high-sensitivity and stable QH-based interferometer is demonstrated by measuring glucose–water solution at a concentration level that is ten times lower than some recent RF sensors while our sample volume is $sim$ 1 nL. Composition analysis of ternary mixture solutions are also demonstrated with a PD-based interferometer. Further work is needed to address issues like system automation, model improvement at high frequencies, and interferometer scaling.

Description: An analytical formulation for relative dielectric constant retrieval is reconstructed to establish a relationship between the response of a spiral microstrip resonator and effective relative dielectric constant of a lossy superstrate, such as biological tissue. To do so, an analytical equation is modified by constructing functions for the two unknowns, the filling factor $A$ and effective length $l_{rm eff}$ of the resonator. This is done by simulating the resonator with digital phantoms of varying permittivity. The values of $A$ and $l_{{rm eff}}$ are determined for each phantom from the resulting S-parameter response, using particle swarm optimization. Multiple nonlinear regression is applied to produce equations for $A$ and $l_{{rm eff}}$ , expressed as a function of frequency and the phantom's relative dielectric constant. These equations are combined to form a new nonlinear analytical equation, which is then solved using the Newton–Raphson iterative method, for both simulations and measurements of physical phantoms. To verify the reconstructed dielectric constant, the dielectric properties of the physical phantoms are determined with commercial high temperature open-ended coaxial probe. The dielectric properties are reconstructed by the described method, with less than 3.67% error with respect to the measurements.

Description: This paper reports a full-rate direct decision-feedback-equalization (DFE) receiver with circuit techniques to widen the data eye opening with competitive power and area efficiencies. Specifically, a current-reuse active-inductor (AI) linear equalizer is merged into a clocked-one-tap DFE core for joint-elimination of pre-cursor and long-tail post-cursors. Unlike the passive-inductor designs that are bulky and untunable, the AI linear equalizer offers orthogonally tunable low- and high-frequency de-emphasis. The clocked-one-tap DFE resolves the first post-cursor via return-to-zero feedback data patterns for sharper data transition (i.e., horizontal eye opening), and is followed by a D-flip-flop slicer to maximize the data height (i.e., vertical eye opening). A 10-Gb/s DFE receiver was fabricated in 65-nm CMOS. Measured over an 84-cm printed circuit board differential trace with 23.3-dB channel loss at Nyquist frequency (5 GHz), the achieved figure-of-merit is 0.027 pJ/bit/dB (power consumption/date rate/channel loss). At 10 $^{-12}$ bit error rate under ${hbox{2}}^{7}-{hbox{1}}$ pseudorandom binary sequence, the horizontal and vertical eye opening are 59.6% and 189.3 mV, respectively. The die size is 0.002 mm $^{2}$ .

Description: This paper presents an unilateralization technique for distributed amplifiers (DAs) based on the transformer coupling between the gate and drain lines. Theoretical analysis of the DA indicates that the voltage waves in the gate and drain lines can be described by a system of linear partial differential equations. The transformer coupling between the lines allows for cancellation of the reverse transmission coefficient of the system. There is an optimal value for the coupling coefficient between the lines that unilateralizes the DA. This optimal coupling coefficient is derived in terms of the gate–drain capacitance and capacitances of the gate and drain lines. Using the proposed technique, two monolithic microwave integrated circuit DAs are designed and implemented in a 0.1- $mu{hbox {m}}$ GaAs pHEMT process. The first DA provides average gain of 10 dB and 3-dB bandwidth (BW) of 39 GHz. The amplifier exhibits the minimum noise figure (NF) of 2.3 dB and the maximum output 1-dB compression point $({ P}_{1 {rm {dB}}})$ of 14.0 dBm, while consuming 80 mW from a 2-V supply. The second amplifier, composed of two cascaded coupled-line DAs, provides average gain of 19.2 dB, 3-dB BW of 37.5 GHz, the minimum NF of 2.3 dB, and the maximum ${ P}_{1 {rm {dB}}}$ of 12.6 dBm. It consumes 131 mW from a 2-V supply. The designed amplifiers can operate with supply voltages as low as 0.5 V to reduce power consumption, while their gain, BW, and NF are preserved. The maximum ratio of gain-bandwidth product to power consumption ${rm GBW/P}_{rm dc}$ of 11.9 GHz/mW is provided by the cascaded DA.

Description: This paper presents a fully integrated 5.8-GHz dedicated short-range communication transceiver with a 10- $mu{hbox {A}}$ interference-aware wake-up receiver (WuRx) for Chinese electronic toll collection system terminals that can operate with a low standby and operating current consumption. To reduce the current consumption, a high-gain RF envelope detector using a voltage-boosting method is proposed for both the WuRx and receiver (Rx) while the proposed high-power ASK modulator extends output dynamic range in low power consumption. Additionally, a delay-based bandpass filter is adopted in the WuRx to filter out interference from automotive applications, thus increasing the battery lifetime by reducing the probability of a false wake-up. The proposed transceiver is fabricated using 0.13- $mu{hbox {m}}$ CMOS technology with a chip size of 2.8 ${hbox {mm}}^{2}$ for the target frequency range of 5.8 GHz. The measured results demonstrate sensitivities of $-$ 44 and $-$ 61 dBm for the WuRx and Rx, dissipating currents of 10 $mu{hbox {A}}$ and 19 mA from 3.3-V supply voltage, respectively. The transmitter exhibits a normal output power of $+$ 5 dBm at an operating current of 46 mA.

Description: Precise formulas to express the formal relationship between the time average stored energy in the resonators of a low-pass filter network and the sensitivity of the reflection S -parameter with respect to the coupling matrix terms are demonstrated in this paper, considering the normalized frequency axis. These relationships are found in the modern context of the N +2 coupling matrix, and for both diagonal and general nondiagonal coupling elements of the matrix. The results are valid for any type of coupling topology represented by the N +2 coupling matrix. Different examples are included as validation. Furthermore, important implications and applications derived from the new relationships are highlighted.

Description: This paper proposes a new microstrip slow-wave structure. The unit cell comprises a Schiffman section of meander line and a shunt open-circuited stub. No via-holes and ground-plane patterns are required. Simple design formulas can be used to obtain line parameters, such as the characteristic impedance and phase velocity. According to the analysis, the characteristic impedance and slow-wave factor of the proposed slow-wave line can be independently controlled by merely two layout parameters. The proposed uniplanar structure only requires a single-layer substrate and is simply constructed using the conventional printed circuit board manufacturing process. A branch-line and a rat-race coupler were designed and fabricated using the proposed structure to demonstrate its feasibility. Their sizes are only 8.49% and 4.87% of the conventional ones, respectively. This novel slow-wave structure should find wide applications in compact microwave circuits.

Description: In this paper, we propose and demonstrate a new technique for the design of arbitrary-order differentiators, intended for ultra-wideband (UWB) applications in microwave coupled-line technology. The technique employs an exact analytical series solution for the synthesis problem derived by the authors from the coupled-mode theory. This solution allows for the synthesis of microwave devices with arbitrary frequency responses, only limited by the principles of causality, passivity, and stability. The method has been successfully applied in the past to the design of two-port waveguide and transmission-line components operating in a reflection-type configuration. Here, the synthesis technique is extended to coupled-line structures, where the input port is matched at all frequencies and the reflected signal is redirected to the coupled port, enabling an effective transmission-type operation for the device. First-, second-, third-, and fourth-order UWB differentiators have been successfully designed, fabricated, and measured, validating the general design technique proposed.

Description: A systematic method for the integration of correlated shot-noise sources into compact models (CMs) is presented, which significantly improves the accuracy of predicted high-frequency noise in transistors. The developed method relies on a system theory approach, and hence, is not limited to specific CM or device type. In this paper, the method is applied to the CM HICUM, which serves a vehicle for verification purposes. The method and its implementation were verified for SiGe heterojunction bipolar transistors based on measured data for frequencies up to 50 GHz, as well as on device simulation data up to 500 GHz, obtained from simulations of both hydrodynamic and a Boltzmann transport model.