This Special Issue of the IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES (TMTT) is comprised of expanded articles from the 2020 IEEE International Microwave Symposium (IEEE IMS) held virtually on August 4–6, 2020, in response to the worldwide COVID-19 pandemic. We thank the hard work of the IMS2020 executive and technical committees that helped to rapidly pivot from plans to hold a physical conference

In this article, we propose an adaptively weighted yield-driven EM optimization technique incorporating neurotransfer function (neuro-TF) surrogate. In the proposed technique, an adaptive weighting factor is set up for each frequency point of interest based on the degree to which the EM response may violate the design specification. These weighting factors are first incorporated into the error function

This article presents a novel type of time-modulated magnetless circulators, where modulation is generated locally at each modulated element through a network of local oscillators instead of a central source and a complex distribution network based on phase shifters and filters. The design follows the angular-momentum approach, and the modulation signals are generated from three cross-coupled oscillators

A reduced-order envelope-domain formulation of coupled-oscillator systems based on realistic nonlinear models of the oscillator elements is presented for the first time to our knowledge. The formulation, based on numerical models of the transistor-based oscillators, enables an accurate prediction of the nonlinear dynamics of the coupled system, including the oscillation build-up, the locked and unlocked

Lumped-element superconducting resonators are a promising technology for their use in millimeter-wave observations and quantum computing applications that require large arrays of extremely sensitive detectors. Among them, lumped-element kinetic inductance detectors (LEKIDs) have shown good performance in the submillimeter band in several earth-based telescopes. In this work, LEKIDs for their use as

In this article, a novel miniature dual-band rat-race coupler design is proposed. The proposed dual-band rat-race coupler employs differential bridged-T coils (DBTCs) as building blocks such that a very compact circuit size and a dual-band response can be achieved at the same time. Especially, through the proposed dual-band design of DBTC, arbitrary power division ratios over the two operating bands

This article introduces two-way broadband air-filled substrate integrated waveguide (AFSIW) isolated power dividers/combiners based on surface mounted absorbing materials. The proposed structures take advantage of the AFSIW multilayer feature. The absorber implementation is found highly tolerant of variations in dimensions and positioning. Three different power dividers/combiners topologies are analyzed

This article presents different physical arrangements of filters using conical posts as the basic element of design. The proposed resonator is similar to that of the classical combline filter, however, in this case, a conical post (truncated cone) is exploited. A hollowed enclosure is positioned on top of a rectangular metallic cavity for housing the upper part of the conical resonating post. Considering

In this article, we explore how acoustic wave filters starting with shunt resonator require particular reflection phase conditions to ensure that the synthesized filter is feasible. The position of transmission zeros (TZs) along with the phase of the objective filter function might lead to nonfeasible solutions where the first and last resonators require elements with positive reactance slope in the

This article proposes a novel approach for extracted pole (EP) filter synthesis. The pole producing elements can be extracted without introducing phase shifters. It is made possible by extracting lowpass elements in the prototype without reducing the order of filter functions. Using the proposed elements as added redundancy, the nonideal effect in the physical model is absorbed by adjacent resonators

In this article, a novel design approach for a general configuration of extracted-pole filters is presented. The proposed solution is based on the synthesis of a prototype network, followed by the evaluation of universal coefficients. The prototype is then denormalized into a form suitable for the implementation that is characterized by parameters recoverable from the physical structure that implements

In this article, two types of substrate-integrated defected ground structure (SIDGS) resonant cells with wide upper stopband and low radiation loss are presented for filter implementation. Such SIDGS resonant cells are composed of two dissimilar DGSs surrounded by the bottom ground and metal-vias, which cannot only introduce wide stopband with low radiation loss but also be flexible for integration

This article discusses the synthesis of a new class of cross-coupled blocks incorporating frequency-variant couplings, that is, the frequency-variant blocks (FVBs), and their planar implementations based on an analytical approach. The proposed FVBs require fewer coupling elements with regard to traditional blocks, while can realize a quasi-canonical characteristic (i.e., realizing $k$ -1 transmission

A compact, 60-GHz high-power, wideband balanced power amplifier, implemented in a 90-nm SiGe BiCMOS technology, is demonstrated. A three-conductor transmission-line-based asymmetric coupled-line directional coupler is used to achieve impedance transformation and quadrature power combining simultaneously. A Wilkinson balun based on a three-conductor transmission line structure is implemented to achieve

This article presents a very compact highly efficient solid-state power amplifier (SSPA) module at kilowatt level in a push–pull architecture. This SSPA is intended to be used as a modular RF source for a 20 kW cyclotron that operates in the low VHF band for radioisotopes production. For a compact design, a lumped $LC$ balun is adopted instead of a traditional ferrite transformer for the 180° phase

This article presents a wideband balanced variable-gain low-noise amplifier (VG-LNA) implemented in a 55-nm CMOS process. The proposed LNA has two cascode stages with an interstage matching transformer to constitute a fourth-order magnetically coupled resonator with two resonant peaks. The frequency-selective gain equalization technique is proposed to compensate for the gain variation of interstage

This article presents an automatic system that is able to dynamically restore the output power capability of a power amplifier (PA) under variable loading scenarios. This is accomplished by dynamically adapting the supply voltage, ${V_{\mathrm{ DD}}}$ , of the PA according to the developed theoretical model. To dynamically vary ${V_{\mathrm{ DD}}}$ , a GaN dc–dc converter, based on the commercial EPC

Indium phosphide (InP) heterojunction bipolar transistors (HBTs) with $f_{t}/f_{\max}$ of 350/675 GHz are studied and explored for a linear, high efficiency and broadband power amplifiers (PAs) at mm-wave frequencies. Unlike the conventional transmission-like-based design, this article presents a compact, broadband transformer-based power combining and impedance matching using the waveform engineering

The highly power-efficient backscattering communication scheme holds solid potentials to lead the Internet of Things technologies. However, the asymmetric radio frontend architectures that ensure cheap and pervasive communicating things and tags at one end of the link, overburden the other end of the link (“reader”) with complicated and expensive hardware. This turns out to prevent the integration

A concurrent dual-band self-oscillating mixer (SOM), based on a ring-shaped stepped-impedance resonator, is proposed and analyzed in detail. Taking advantage of the ring even and odd resonances, the circuit can operate in concurrent dual quasi-periodic mode and injection-locked mode. In the second case, it behaves as a dual-band zero-intermediate-frequency (IF) mixer. Initially, an analytical study

Orthogonal frequency-division multiplexing (OFDM) backscatter communication promises to enable ultralow-power wireless devices that are robust to time-varying multipath channels. Traditional OFDM transmitters require the use of power-hungry digital-to-analog converters (DACs) and vector modulators to realize the OFDM signal, adding to the complexity and power consumption of wireless sensor nodes. In

This work presents an in-depth investigation of the nonlinear behavior of two mutually injection-locked oscillators through inductor coupling. An analytical formulation, solved through an innovative procedure, facilitates the understanding of the qualitative transformations in the system solutions when increasing the coupling factor. The analysis demonstrates that, in a manner similar to the unilaterally

This article presents a group delay controller (GDC) circuit based on the delay-sum method. The proposed circuit can potentially be employed in a self-interference cancellation circuit in full-duplex radio systems. The proposed GDC splits the input signal into two signals with different magnitudes and then combines them in-phase at the output port. Variable group delay can be achieved by changing the

Millimeter wave-based material inspection methods are capable of providing 3-D-tomographic images of composite materials with a sufficient resolution to detect, localize, and classify critical defects. The nondestructive and noncontact-based measurement methods’ potential can only be utilized with a complete understanding of the signals propagation behavior. Such that the relevant signal processing

We propose a broadband conductivity measurement method in the millimeter-wave bands using a balanced-type circular disk resonator (BCDR). Because of the unique feature of the BCDR’s mode selective behavior over a wide band, the proposed technique can provide broadband conductivity measurements from less than 20 GHz up to over 100 GHz with a single closed-type resonator utilizing higher order mode resonances

This work investigates wideband active load–pull (WALP) on microwave electron devices with a standard vector network analyzer (VNA), solely using calibrated frequency-domain relative measurements. Differently from the methods requiring full time-domain waveform acquisition capabilities, this approach removes any instantaneous bandwidth (BW) requirement, allowing to target modulated signals with arbitrarily

This article is a study of dielectric characterization of packaging substrates using a 1.85-mm coaxial airline. To the authors’ knowledge, this is the first time that wideband dielectric properties have been demonstrated up to 67 GHz using a single coaxial airline. The algorithm used to extract the material properties is Chalapat’s reference-plane-invariant (RPI) method. The measurement system and

A battery-less 5.8-GHz transmitter (TX), compact and lightweight enough to enable flight of $\sim 90$ mg honeybees and free roaming of bumblebees within their nest, was developed. The TX was coupled to a compact phased-array antenna receiver to achieve angle of arrival (AOA) estimation and bee localization through a received signal strength indicator approach (RSSI). The receiver was integrated into

This article presents a CMOS-based, code-domain (CD), full-duplex (FD) transceiver operating in a link at 1 GHz. The CD FD link rejects in-band transmitter self-interference (TX SI) by more than 100 dB through a combination of pseudo-noise (PN) code orthogonality, circulator, and digital cancellation algorithms. A nonmagnetic CMOS circulator based on switched transmission lines is used as an antenna

This article presents a $W$ -band rectenna unit that incorporates a novel CMOS switching rectifier and a print tapered slot antenna. The operation principle of the switching rectifier is analyzed. The proposed rectifier topology shows improved reliability, and it utilizes the body-diode effect (BDE) to improve power conversion efficiency (PCE). Besides, a high-gain $W$ -band antipodal linearly tapered

This article presents the 38-GHz phased array 32-element Tx and 16-element Rx with 2-GHz IF and 5-GHz LO for fifth-generation (5G) millimeter-wave (MMW) communications. The Tx and Rx beamformers and upconverters/downconverters are fabricated in 65-nm CMOS. The PAs and LNAs near antenna ends are fabricated in 0.15- $\mu \text{m}$ GaAs pHEMT. The eight-element Tx and four-element Rx phased array printed

This article presents the combination of a self-injection-locked (SIL) radar with frequency-modulated continuous-wave (FMCW) and switched phased-array (SPA) techniques to locate multiple people and detect their vital signs with high resolution and high sensitivity. The proposed system utilizes a subharmonic upconverter/downconverter with a 1.675–2.175-GHz chirp local oscillator (LO) signal to convert

Digital predistortion (DPD) of a phased array requires that multiple transmit paths must be measured by a feedback (FB) receiver (Rx). In this article, we propose an FB concept for DPD in a time-division-duplex (TDD) phased arrays. We use a single FB line to collect the waveform samples from the parallel transmit paths to the FB Rx. The TDD switches are used to enable and disable individual transmit

This article presents a reflectometer-based on-chip dielectric sensor with integrated transducers at 240 GHz. The chip simplifies the measurement of a vector network analyzer (VNA) to sense the incident and reflected waves by using two heterodyne mixer-based receivers with a dielectric sensing element. Radio frequency (RF) and local oscillator (LO) submillimeter waves are generated by two frequency

This article demonstrates the implementation of 80- and 160-GHz four-channel radar sensors employing the modular scalable platform based on a single relaxed 40-GHz local oscillator and cascadable transceiver chips. The first two channels synthesize $2 \times 2$ multiple-input–multiple-output (MIMO) radar at 80 GHz with onboard $8 \times 1$ patch arrays for enhanced angular resolution, whereas the other

In this article, we study digital predistortion (DPD)-based linearization with a specific focus on millimeter-wave (mmW) active antenna arrays. Due to the very large-channel bandwidths and beam-dependence of nonlinear distortion in such systems, we present a closed-loop DPD learning architecture, lookup table (LUT)-based memory DPD models, and low-complexity sign-based estimation algorithms such that

This article reports on the theory and application of a high-speed Marx generator (HSMG) circuit to realize supply modulation (SM). In order to achieve high-modulation bandwidth, the supply modulator complexity is kept low, enabling multilevel SM with four discrete voltage levels. A prototype is designed and fabricated on a four-layer FR4 board. The efficiency of the proposed modulator is measured

In this work, we introduce a multimode and wideband quadrature balanced CMOS RF front end (RFFE) supporting full-duplex (FD), half-duplex (HD), and frequency-division duplex (FDD) operation at the 5–6 GHz band. The proposed RFFE is enhanced by nonlinear digital algorithms that maintain optimal performance at high transmit (Tx) power levels. A theoretical model of the transmit–receive (TR) cross-modulation

Highly accurate vibrometry and ranging are important topics in the industrialized economy. Wherever optical measurement technology fails due to its high prices and vulnerability within harsh environments, millimeter-wave (mmWave) radar technology is well suited. This article introduces a signal processing chain for ultrawideband frequency-modulated continuous-wave (FMCW) radar. It uses fast-time measurement

In this article, we demonstrate the use of interferometric radar for high-accuracy measurement of the ground speed of a moving vehicle. Recent work has shown the capability of radar systems using interferometric antenna apertures to directly measure the angular velocity of objects. In this work, we apply this new measurement to the automotive application of velocity estimation. We start by formulating

This article presents a four-element 7.5–9-GHz phased-array receiver with 1–8 concurrent beams in a 65-nm CMOS technology. Each output beam utilizes all the input elements to maximize the beamforming gain. To realize a low-power and compact design, the multielement multibeam phased-array architecture features the gm-based variable-gain phase shifter (VG-PS) and the current-sharing active combiner.

This article proposes a 28-GHz full-duplex (FD) phased arrays, which consists of 64-element transmitting and receiving arrays, and a 28-GHz radio frequency (RF) canceller. The phased arrays are designed with $2\times 2$ beamformer chips, and the transmitter (TX) and receiver (RX) arrays are oriented to have cross polarized configurations for high isolation. The 28-GHz RF canceller is based on an identical

Frequency-division multiple-access (FDMA) in frequency-modulated continuous-wave (FMCW) radar comprises range-division multiple-access (RDMA) and Doppler-division multiple-access (DDMA). In this article, we present a method using RDMA and DDMA to realize multiple-input multiple-output (MIMO) functionality for FMCW radars. We use single-sideband modulation and quadrature phase shift keying (QPSK) modulation

The proposed frequency-offset self-injection-locked (FOSIL) radar combines two independent SIL radar front-ends with up/down-mixers. The transmit frequency can be held constant by properly adjusting the injection phases and amplitudes of two oscillators. Therefore, electromagnetic interference (EMI) in the monitoring of a moving subject using conventional SIL radars is eliminated, and multiple FOSIL

Realizing capacitive coupling under seawater is difficult, although the capacitive coupler attracts attention as a promising solution for wireless power and data transfer. The coupler consisting of parallel-plate electrodes (e.g., capacitive coupler) has strong conductive coupling because of the high conductivity of seawater. This study introduces the design of a highly efficient coupler utilizing

For supporting communication links with increased date-rate between the base-station and the user, more higher operating frequencies with much broader bandwidth have to be used. Terahertz (THz) bands are very promising to meet such demands and International Telecommunication Union (ITU) has approved a THz-band for the fifth-generation (5G) mobile communication and beyond in 2019, which is driving the

In this article, we propose a double-sided electromagnetic bandgap (DS-EBG) structure for glass interposers (GIs) with low substrate loss to suppress power/ground noise. For the first time, we validated wideband power/ground noise suppression in the GI using the proposed DS-EBG structure based on dispersion analysis and experimental verification. We experimentally verified that the proposed DS-EBG

A half-air-filled substrate-integrated groove-gap waveguide is proposed for millimeter-wave and terahertz applications. The waveguide is constructed by a ball grid array using a flip-chip technique without metallic vias with lightweight and low profile. The possible leakage perpendicular to the groove is prevented by solder balls as modeled by an equivalent circuit. Besides, an inline transition between

In this article, to reduce the operating frequency and the size of the spoof surface plasmon polariton (SSPP) attenuator and introduce the filtering function into the graphene attenuator, we propose a tunable graphene filtering attenuator, namely the graphene-based effective SSPP (ESSPP) attenuator. It consists of an ESSPP waveguide and a graphene sandwich structure (GSS). The effect of GSS on the

This article proposes a novel substrate integrated suspended slot line (SISSL) platform, which embeds the slot line inside a metallic shielding enclosure to minimize the radiation loss and solve packaging problems. The propagation characteristics of SISSL including characteristic impedance and guided wavelength are investigated. By using the transition from SISSL to shielded microstrip, a type of differential

Compact re-entrant cavities, widely used as microwave resonators, can be employed as high-performance sensors. A new approach is proposed here to calculate the resonance frequency, its sensitivity, and quality factor ( $Q$ -factor) of these cavities, having diverse taper shapes of the re-entrant post. The proposed closed-form expressions are based on the chain matrix approach for tapered coaxial transmission

Rectifier design nowadays relies heavily on iterative optimization, which is prone to fall into local minima or end up with no solution. Such a procedure is time-consuming and requires lots of experience from designers. Guided rectifier synthesis with the least engagement of optimization is thus desired. In this article, a lookup-table-based automated rectifier synthesis method is presented. The lookup

This work presents a new class of microelectromechanical system (MEMS) resonator toward 60 GHz for the fifth-generation (5G) wireless communications. The wide range of the operating frequencies is achieved by resorting to different orders of the antisymmetric Lamb wave modes in a 400-nm-thick Z-cut lithium niobate thin film. The resonance of 55 GHz demonstrated in this work marks the highest operating

In this article, a new class of wideband phase shifters with very compact size, large phase shift value, low insertion loss (IL), and low cost are presented and developed. The proposed phase shifter consists of $N$ series and shunt resonators, which can achieve the magnitude and phase shift bandwidth of more than 120% thanks to $N$ transmission poles. Besides the wideband property, the proposed phase

In a conventional power divider, power dividing network and isolation network are usually independent of each other. To reduce the size of out-of-phase power divider with arbitrary power ratio, coupled microstrip lines are proposed to facilitate power dividing and isolation of a power divider simultaneously in this article. Formulations have been derived for the proposed out-of-phase power divider

A generalized mesh-network equivalent model for a microstrip rectangular patch antenna (RPA), which is simple yet efficient is proposed, studied, and demonstrated in this article. The mesh-network equivalent model is established through the segmentation of RPA width and radiation parameters into $M$ sections, as well as the segmentation of RPA length into $N$ sections. A general design procedure to

The gradual transition from a reactive to a radiative regime is studied for leaky modes supported by multilayered planar open waveguides. The so-called leaky cutoff condition, i.e., the frequency for which the leaky phase constant $\beta $ equals the leaky attenuation constant $\alpha $ , originally introduced for microstrip lines and other printed structures, is investigated here with the aim of providing

This article proposes a novel decomposition technique to address the challenges of electromagnetic (EM) parametric modeling, where the values of geometrical parameters change in a large range. In this method, a systematic and automated algorithm based on second-order derivative information is proposed to decompose the overall geometrical range into a set of subranges. Using the proposed technique,

The nonreciprocal bandpass filter has been achieved by utilizing the nonreciprocity characteristics of the magnetostatic surface wave (MSSW) in planar ferrite slabs. In this article, the dispersion relation, impedance, and attenuation of MSSW between the pure and metallized ferrite slabs have been analyzed and compared. Theoretical analysis indicates that the ferrite slab metallized by a thin conductive

An innovative mixing unit of the proposed mixer named joint-injection-mixer (JIM) features both wide IF and RF bandwidths (BWs) for next-generation advanced heterodyne receivers of millimeter-wave astronomy. This proposed mixer demonstrates an RF frequency range from 60 to 148 GHz and an IF frequency range from dc to 36 GHz. The dc power consumption of the JIM mixer is 2 mW with LO driving power of