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Mobile and wireless communications are playing an irreplaceable role in our daily life. 5G is highly expected and can be considered as the convergence of mobile and wireless communications. This topic becomes one of the hottest research topics recently, and papers on this topic have been paid much attention. lists the top ten papers published in the IEEE Transactions on Microwave Theory and Techniques (TMTT) in 2019 with the highest numbers of Full Text View since published. Seven papers are about millimeter-waves (mm-waves), and because mm-waves multiple-input–multiple-output (MIMO) will be adopted globally, the 24.25–27.5-GHz band and 27–29.5-GHz bands are now approved worldwide as the standard 5G communication bands. The most popular paper is published by Asbeck et al. [item 1) in the Appendix] for mm-wave power amplifiers. [ABSTRACT FROM AUTHOR]

This paper introduces a novel compact ultralightweight multiband RF energy harvester fabricated on a paper substrate. The proposed rectenna is designed to operate in all recently released LTE bands (range 0.79–0.96 GHz; 1.71–2.17 GHz; and 2.5–2.69 GHz). High compactness and ease of integration between antenna and rectifier are achieved by using a topology of nested annular slots. The proposed rectifier features an RF-to-dc conversion efficiency in the range of 5%–16% for an available input power of −20 dBm in all bands of interest, which increases up to 11%–30% at −15 dBm. The rectenna has been finally tested both in laboratory and in realistic scenarios featuring a superior performance to other state-of-the-art RF harvesters on flexible substrates. [ABSTRACT FROM PUBLISHER]

In this paper, the feasibility of inkjet printing of circuit and microwave structures on paper-based substrates is investigated for the first time in the implementation of a complete low-cost wireless platform for sensors. First, the system-level design of the module including the amplifier characterization were carried out to ensure optimum performance of the sensor modules in the UHF bands used in RF identification communication. These results were then used to design two different antenna structures, which are printed on paper along with their respective circuit layouts using inket-printing technology. Different techniques were investigated for the assembly of circuit components on the silver printed layouts. Finally, wireless link measurements on the assembled prototypes verified the good performance on the wireless and sensing sides. [ABSTRACT FROM AUTHOR]

In this paper, inkjet-printed UHF and microwave circuits fabricated on paper substrates are investigated for the first time as an approach that aims for a system-level solution for fast and ultra-low-cost mass production. First, the RF characteristics of the paper substrate are studied by using the microstrip ring resonator in order to characterize the relative permittivity (ϵτ) and loss tangent (tan δ) of the substrate at the UHF band for the first time reported. A UHF RFID tag module is then developed with the inkjet-printing technology, proving this approach could function as an enabling technology for much simpler and faster fabrication on/in paper. Simulation and well-agreed measurement results, which show very good agreement, verify a good performance of the tag module. In addition, the possibility of multilayer RF structures on a paper substrate is explored, and a multilayer patch resonator bandpass filter demonstrates the feasibility of ultra-low-cost 3-D paper-on-paper RF/wireless structures. [ABSTRACT FROM AUTHOR]

This paper demonstrates the design of an 800-MHz solar-powered active wireless beacon composed of an antenna and an integrated oscillator on a low-cost paper substrate. Inkjet printing is used to fabricate the conductive circuit traces and the folded slot antenna, while the oscillator circuit is designed using off-the-shelf components mounted on the paper substrate. Flexible, low-cost, amorphous silicon (a-Si) solar cells are placed on top of the slot ground and provide autonomous operation of the active circuit eliminating the use of a battery. A prototype is built and characterized in terms of phase noise, radiation patterns, and the effect of solar irradiance. Such low-cost flexible circuits can find significant applications as beacon generator circuits for real-time identification and position purposes, wearable biomonitoring as well as solar-to-wireless power transfer topologies. The measured phase noise is -\116 dBc/\Hz at 1-MHz offset, while drain current is 4 mA and supply voltage is 1.8 V. [ABSTRACT FROM AUTHOR]

This paper deals with a low-cost method for the assembly of flexible substrate antennas and UHF RF identification silicon (Si) chips. Such a method exploits a magnetic coupling mechanism, thus not requiring for galvanic contacts between the Si chip and antenna itself. The magnetic coupling is established by a planar transformer, the primary and secondary windings of which are implemented on flexible substrate and Si chip, respectively. As a result, the Si chip can be assembled on the antenna with a mere placing and gluing process. First, the idea has been validated by theory. Electromagnetic simulations of a square heterogeneous transformer (1.0-mm side) show a maximum available power gain (MAG) of -0.4 dB at 868 MHz. In addition, the heterogeneous transformer is also quite tolerant with respect to misalignment between primary and secondary. An offset error of 150 \mu\ m reduces the MAG to -0.5 dB. A sub-optimal matching strategy, exploiting a simple on-chip capacitor, is then developed for antennas with 50-\Omega input impedances. Finally, the idea has been experimentally validated exploiting printed circuit board (PCB) prototypes. A PCB transformer (1.5-mm side) and a transformer rectifier (two-diode Dickson multiplier) have been fabricated and tested. Measurements indicates a MAG of -0.3 dB at 868 MHz for the transformer and the capability of the developed rectifier to supply a 220-\k\Omega load at 1.5 V with a -2-dBm input power. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotubes (MWNTs) are characterized at X-, Ku-, Ka-, and Q-bands by rectangular wave- guide measurements. The scattering parameters (S-parameters) of thin MWNT papers containing a large ensemble of randomly oriented nanotubes are measured by a vector network analyzer from 8 to 50 GHz. A rigorous extraction algorithm has been developed to compute the effective complex permittivity (ϵ = ϵ′ - jϵ″) and permeability (μ = μ′ - jμ″) of the nanotube papers from the measured S-parameters. The extracted effective medium parameters are verified by finite-element simulations using Ansoft's High Frequency Structure Simulator (HFSS). The uncertainties for this characterization method are analyzed. The systematic uncertainties are found larger at lower frequencies than at higher frequencies. The extracted conductivity of the nanotube papers is in the range of 810-1500 S/m and the dielectric constant is from 250 to 700. The extracted complex permittivity can be fitted with the Drude-Lorentz model for the 8-50-GHz frequency range. The effective medium theory is then applied to remove the impact of air in the nanotube paper. [ABSTRACT FROM AUTHOR]

Presents a paper which focuses on the use of the finite-difference time-domain (FDTD) method in conjunction with the generalized pencil of function (GPOF) technique, to evaluate the reflection coefficient from shorted slotlines and coplanar waveguides, on anisotropic substrates. Identification of finite-difference time-domain solutions; Conclusions of the paper.

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

This invited paper reviews the progress of silicon-based integrated analyzers for biomedical applications over the last two decades. Focus is set on various integrated circuit realizations in the millimeter-wave range from 30 GHz and at the terahertz frequencies of above 300 GHz. This article discusses high-frequency architectures and concrete implementations of both narrowband as well as broadband integrated readout circuits, including their use in miniaturized sensor solutions. A variety of circuits ranging from low-power sensing oscillators to highly integrated broadband vector network analyzers (VNAs), and example realizations of millimeter-wave cardiovascular sensors and implants to THz microfluidic labs-on-chip and exhaled human breath analyzers are recapitulated. This article closes with an outlook on emerging fields of research for future advancement of such biomedical sensors toward reliable and specific systems. [ABSTRACT FROM AUTHOR]

A rigorous approach for solving canonical circular open-ended dielectric-lined waveguide diffraction problems is presented. This is continuation of our recent paper (Galyamin et al., 2021) where a simpler case of uniform dielectric filling has been considered. Here we use the same analytical approach based on Wiener–Hopf–Fock technique and deal with more complicated case of a layered dielectric filling which is closer to potential applications. The latter are connected with analytical description of electromagnetic processes involving open-ended waveguide structures prospective due to the modern trends in beam-driven radiation sources (mainly in the terahertz (THz) frequency region) and THz-based bunch manipulation. [ABSTRACT FROM AUTHOR]

This paper presents a phase correction method to improve direction-of-arrival (DOA) estimation in spectrally interleaved orthogonal frequency-division multiplexing (OFDM) multiple-input-multiple-output (MIMO) radar systems. It is new in the way that a phase correction step is introduced between the range-Doppler processing and the DOA estimation. The phase correction results in an improved dynamic range. Both processing steps, range–velocity and DOA, are performed using discrete Fourier transforms (DFTs). This paper starts by introducing the waveform and reviewing range–velocity processing in OFDM radars. After that, the new phase correction method is introduced. Then, the concept is implemented in a quantitative simulation. The last part includes the system description and measurement in an outdoor scenario. Finally, the simulation and measurement results are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the investigation and testing of novel substrate integrated waveguide (SIW) bandpass filters, based on air-filled cavity resonators. Removing the lateral parts of the dielectric substrate in SIW rectangular cavities enables the use of the TM120 and TM210 modes to implement a dual-mode resonator. In addition, the fundamental TM110cavity mode is adopted to implement a transmission zero. This paper demonstrates the complete control of the central operation frequency, the pass bandwidth, the spurious-free bandwidth region, and the location of the transmission zeros. After a comprehensive theoretical investigation, design rules are derived and applied to the implementation of a variety of dual-mode cavities, which have been manufactured and tested. Moreover, these basic structures have been used as building blocks to design higher order filters: simulations and measurements of four-pole filters are reported for validation. [ABSTRACT FROM AUTHOR]

This paper presents the design of a broadband and high-power amplifier with bounded performance technique (BPT). Like the real frequency technique (RFT) or the simplified RFT (SRFT), BPT achieves broadband performance via matching at some in-band discrete real frequencies. It solves some design issues that are not addressed in the RFT and the SRFT. Among them are the inclusion of the design specifications in the device selection and design process and the possible degradation of operation metrics that are not optimized. BPT also avoids complicated analytic mathematics by using circuit prototypes. In this paper, we show the design of an amplifier with BPT. It has a 3-dB compression power of at least 100 W and a drain efficiency of at least 50% over the band 1–2.8 GHz or 94.7% fractional bandwidth. We also show the design of the same amplifier with the traditional SRFT and compare its expected performance with that designed with BPT. [ABSTRACT FROM AUTHOR]

This paper presents a novel method to widely tune high-quality factor evanescent-mode cavity resonators and filters using contactless tuners. The proposed method resolves multiple challenges facing reliable manufacturing and operation of these filters by avoiding the attachment of the flexible tuner to the cavity and replacing it with capacitive contactless tuners. This paper discusses the design consideration and tradeoffs as well as demonstrates the performance of the proposed concept using the substrate-integrated-waveguide technology. The resonators demonstrate more than octave tuning range (TR), quality factor up to 650, and power handling exceeding 100 W. In addition, the second-order bandpass filters are demonstrated, along with the long-term measurements, showing better than 1.17% frequency error after a 15-h stability test, and less than 1.47% frequency error after a 450 cycles repeatability test over an octave TR from 1.8 to 3.6 GHz. [ABSTRACT FROM AUTHOR]

In this paper, the power handling capability of microstrip filters is studied in detail. This paper is addressed from two perspectives, depending on the physical phenomenon limiting the maximum power that the microstrip filter can handle. One of these phenomena is air breakdown or corona effect, which is linked to the peak power handling capability (PPHC) of the device, and the other is the self-heating, which limits the device average power handling capability (APHC). The analysis is focused on three kinds of filtering topologies widely used both in academia and industry, such as the coupled-line, stepped impedance resonator and the dual-behavior resonator-based filters. Closed-form expressions are computed to predict both the PPHC and the APHC as a function of the geometrical parameters of the resonators integrating the filter. Guidelines are also given to extrapolate the provided computations to other filtering topologies based on other kinds of resonators. To validate this research study, three bandpass filters centered at 5 GHz have been implemented and fully characterized by means of two measurements campaigns which have been carried out, one for the PPHC and another one for the APHC. The measured results have validated the performed study and corroborated the conclusions obtained throughout this paper. [ABSTRACT FROM AUTHOR]

This paper presents a generalized geometrical equivalent circuit model for a strip-loaded coplanar waveguide (CPW) that carries the even and odd modes simultaneously. The proposed model enables the analysis, sets the design requirements, and defines the constraints of the realization of an air-bridge free all CPW Wilkinson power divider (WPD). To overcome these constraints, this paper proposes two implementations. The first one engineers the dispersion relation of the odd mode to provide a slow-wave factor that compensates the difference in the electrical lengths with the even mode, while the second implementation deploys the floating strips as electrical air-bridges. The proposed power dividers are designed to operate at 2.4 GHz. Measurements, which are in good agreement with the EM simulations, confirm the theoretical predictions. [ABSTRACT FROM AUTHOR]

This paper provides theoretical and experimental evidence that, contrary to what is a widely reported belief, the capture time constant of GaN high-electron-mobility transistor (HEMTs) deep-level traps is not infinitesimally shorter than the modulation envelope time features of usual excitation signals. Instead, it can have a nonnegligible impact on their power amplification. A specifically conceived test bench, capable of measuring capture time constants at guaranteed invariant thermal dissipation conditions, revealed that the capture process can range from less than a microsecond up to a few tens of milliseconds. Furthermore, a theoretical justification based on the Shockley–Read–Hall statistics is provided to explain this widespread time constants’ behavior of deep-level traps. As a practical application example of these findings, the detailed characterization of the capture time constants performed in this paper proved to constitute a valuable tool in understanding the behavior of GaN power amplifiers (PAs) designed for pulsed radar signals. [ABSTRACT FROM AUTHOR]

This paper presents an innovative experimental method for microwave power devices linearity characterization, based on a carefully designed multi-tone signal. Measurements working deeper into the understanding of in-band (IB) signal-to-noise characterization of nonlinear devices are presented. The test signal used in this paper is based on an unequally spaced multi-tone (USMT) signal, which is a tailored stimulus signal with flexible statistics. Its originality stands in its inherent property of allowing signal and intermodulation (IM) distortion separation to facilitate the derivation of the IB signal-to-noise ratio or linearity degradation, without assuming any specific modulation format. For the first time, this paper reports measurements with small $\Delta _{f}$ frequency arrangement using an USMT signal to investigate low frequencies (LFs) parasitic effect on the current and the linearity. Furthermore, this test bench allows to analyze together LF phenomena (“trapping effect”, memory effect, etc.) and high-frequency phenomena under large-signal condition with a telecom like signal. Smith chart load–pull linearity contours under wideband USMT test signals are reported for the first time. This provides a new tool to check system-level design specifications and to optimize radio frequency (RF) power amplifier structures with modulated signals. The measurements were performed using a GaN high-electron-mobility transistors (HEMT) 3-W transistor. [ABSTRACT FROM AUTHOR]

With an incredible increase in the number of wireless devices and an ever-growing demand for high data rates, 5G needs to provide a solution to satisfy the demand for the next decade. Multiple-input multiple-output (MIMO) systems are seen as one of the primary solutions—allowing for spatial multiplexing and the use of millimeter-wave (mmWave) frequencies, which can provide much larger bandwidths and, thus, data rates. MIMO is very closely related to phased arrays, which have been used for radar for the past few decades and requires many antennas and transceivers—on the order of hundreds or thousands for massive MIMO. To make such systems affordable, low-cost, low-power, and low-complexity is required—inherently compromising other system characteristics, such as linearity. The main focus of this paper will be in summarizing the challenges, recent advances, and potential future breakthroughs concerning MIMO/digital array sensitivity to interferers and nonlinear distortion. Specifically, this paper gives an overview of MIMO/digital array architectures and different techniques currently researched for the characterization and mitigation of spatial and spectral interferers and nonlinearities, which can be used to extend the effective dynamic range of low-cost MIMO/digital array systems. [ABSTRACT FROM AUTHOR]

This paper presents a broadband efficient power amplifier (PA) targeting sub-6-GHz 5G base station applications. Due to the demanding requirements in both peak-to-average power ratio (PAPR) and bandwidth in 5G systems, we employ a combination of both load and supply modulation for efficiency enhancement. Active matching, implemented using an RF-input load-modulated balanced amplifier (LMBA) architecture, enables efficient octave-bandwidth operation. Supply modulation, which is carrier frequency agnostic, is then used to further extend the back-off efficiency. This paper focuses on a study of supply modulation strategies for the load-modulated PA using an efficient GaN eight-level discrete supply modulator. To overcome the bandwidth limitations associated with discrete-level switching, a commutation rate reduction (CRR) filter is applied in digital baseband and its effects are analyzed theoretically and experimentally. The supply-modulated LMBA is characterized across 1.8–3.8 GHz with 100-MHz, 10-dB PAPR signals. An output power of 34 dBm with average composite (total) PAE ranging from 22.4% to 43.9% across the band is demonstrated, with an ACLR of about −50 dBc after digital predistortion. [ABSTRACT FROM AUTHOR]

This paper presents a frequency-agile in-band full-duplex (FD) receiver based on a switched-capacitor continuous-mode vector modulator (VM). The passive VM presented in this paper provides simultaneous downmixing, attenuation, and phase shifting and is used to generate a baseband canceler signal for self-interference (SI) cancelation. A prototype FD receiver is implemented in CMOS 130 nm technology. The receiver is tunable from 0.1 to 0.95 GHz. In FD mode at 900 MHz, the receiver has an effective input-referred third-order intercept power (IIP3) of +7 dBm, SI-to-noise-and-distortion-ratio (SINDR) of ≈ +65.3 dB at −27.5 dBm SI in 15 MHz bandwidth, and noise figure (NF) degradation of less than 1 dB. [ABSTRACT FROM AUTHOR]

This paper investigates the source and implication of efficiency minima that is typically observed during the second-harmonic load–pull of transistor amplifiers. The study starts with the theoretical derivation of time-domain voltage and current waveforms as a function of conduction angle ($\alpha$) at the second-harmonic efficiency minima, where the output power and drain efficiency (DE) are at minimum. Thereafter, this paper unfolds a systematic re-engineering approach that is developed to recover the performance degradation and to exploit the region of efficiency minima in favor of design and implementation of high-efficiency inverse class-F power amplifiers (PAs). Interestingly, the inferences drawn from the in-depth analysis are shown to provide a simplified first-pass design approach that guarantees inverse class-F PA operation without an a priori knowledge of device parasitic elements. Theoretical postulations and simulation results are experimentally validated using an on-wafer active harmonic load–pull and a prototype design using 1.95-mm NXP gallium nitride die at a frequency of 2.6 GHz. The designed PA delivers an output power of 40 dBm with DE of 76% and gain of 12 dB at 3-dB gain compression. The measurement results confirm the theoretical framework reported in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a spatially distributed multi-input direct conversion receiver architecture based on interferometric correlations of wave signals for fifth generation systems and beyond. The proposed receiver scheme inherits the advantages of conventional six-port receivers. The spatially distributed multi-input architecture is based on the use of a set of equally spaced four antenna elements instead of using a six-port junction composed of four hybrid couplers or other alternative circuit-based topologies. In this paper, the mathematical modeling of the proposed receiver is derived and presented. Then, an experimental test bench that is fabricated to operate around 5 GHz is introduced in order to validate the proposed scheme and its theoretical results. Various modulations including BPSK, QPSK, QAM-16, and QAM-32 have been successfully studied and demonstrated by this receiver at a relatively low date rate of 1 mega symbol per second with a maximum error vector magnitude of 10.3%. The maximum bit rate is fundamentally limited by the speed of power detectors, which is linked to their high rise time in our experiments. It is anticipated that multiple hundred megabits and gigabits per second can be achieved with the proposed direct conversion receiver if higher speed power detectors are used. [ABSTRACT FROM AUTHOR]

This invited paper reviews the progress of silicon–germanium (SiGe) bipolar-complementary metal–oxide–semiconductor (BiCMOS) technology-based integrated circuits (ICs) during the last two decades. Focus is set on various transceiver (TRX) realizations in the millimeter-wave range from 60 GHz and at terahertz (THz) frequencies above 300 GHz. This article discusses the development of SiGe technologies and ICs with the latter focusing on the commercially most important applications of radar and beyond 5G wireless communications. A variety of examples ranging from 77-GHz automotive radar to THz sensing as well as the beginnings of 60-GHz wireless communication up to THz chipsets for 100-Gb/s data transmission are recapitulated. This article closes with an outlook on emerging fields of research for future advancement of SiGe TRX performance. [ABSTRACT FROM AUTHOR]

In the recent years, Wireless Power Transfer (WPT) related technologies experienced a great growth. With the introduction in 2010 of the Qj standard, many wireless rechargeable devices appeared on the market, calling for solution of several classes of problems ranging from EMC, health compliance, and power efficiency, representing a stimulating field of activity for scientists and researchers. Beside this leading application area, great interest is being received by two other application categories: Electric Vehicles (EV) and long range electromagnetic transmission of energy. The first is about to approach the market as testified by recent demonstration activities carried on by leading car makers (mostly from Japan). The second is mostly driven by the Internet of Things (loT) perspective evolution that requires energizing plenty of contactless devices, often non-precisely referred in space. It is clear, even from this very synthetic description of the WPT scenario, how WPT actually is an inclusive, multidiscipline field of different but dependent researches. This special issue aims at evidencing, within this scientific vastness, those aspects more precisely related to RF and microwave technologies in a wide extent (from MHz up to THz). Authors should see http://www.mtt.org/transactions/34-author-information-transactions.html for submission instructions. [ABSTRACT FROM PUBLISHER]

This paper presents a 77-GHz automotive radar receiver in a 28-nm fully depleted silicon-on-insulator CMOS technology. It exploits a mixer-first direct-conversion architecture to trade-off noise and linearity performance. The receiver is composed of a 77-GHz downconverter, a variable-gain amplifier, and a switched-capacitor low-pass filter. It adopts an effective and robust approach for leakage suppression due to the TX to RX crosstalk, which overcomes both gain and linearity limitations. The receiver draws an overall quiescent current as low as 27 mA from a 1-V supply voltage and provides an overall gain up to 75 dB with a noise figure of 8.2 dB. Despite the low supply voltage, an excellent blocker immunity of −9.5 dBm is achieved along with an output 1-dB compression point as high as −1.5 dBV. [ABSTRACT FROM AUTHOR]

The editor reflects on the special issue of the periodical which is based on the 2012 International Microwave Symposium held on June 17-22, 2012 in Montreal, Quebec. He mentions that due to increased number of submissions to the special issue, it has been divided into two issues the first one was published in December 2012, and the next one in January 2013. He adds that the aim behind including conference papers in the issue is to present results that might help improve engineering designs.

A new equivalent dipole model hybrid with artificial neural network (ANN) is proposed in this paper for electromagnetic interference (EMI) estimation. Equivalent dipole method, based on the free-space Green’s function, is usually used to model unknown EMI sources on printed circuit boards. For high-speed and dense circuits, there may be multi-reflection and/or diffraction between the EMI source and its nearby components. Traditional dipole model usually omits such effects and leads to an inaccurate result in some cases. In our proposed method, the Green’s function of dipole is taken as input and the radiated EMI field is taken as the output of ANN. We use the powerful mapping ability of ANN to modify the matrix–vector multiplication between free-space Green’s function and dipole moments in the traditional dipole model, so that a new mapping between equivalent dipoles and their radiated fields is established. The near field of the EMI source is obtained by planar scanning, and is used for ANN training. After training, the ANN is used to predict the EMI field at the region of interest. Both numerical example and measurement example are given to show the effectiveness of the proposed ANN method. This paper provides a novel source reconstruction solution for the EMI problems. [ABSTRACT FROM AUTHOR]

In this paper, a bidirectional absorptive common-mode filter (A-CMF) is proposed to suppress the common-mode (CM) noise which would induce unwanted electromagnetic interference (EMI) and radio-frequency interference (RFI) problems. Different from the conventional CM filters (CMFs) which reflect the CM noise, the proposed A-CMF will absorb the CM wave, and thus suppress the radiation caused by reflected wave. An analysis and design method by using Smith chart with more physical insight is also proposed in this paper. To validate the proposed concept, the A-CMFs are implemented in the two-layer printed circuit boards. The absorbing frequency is selected at 2.4 GHz band where CM insertion loss is larger than 30 dB and the CM reflection loss is larger than 20 dB. With the proposed A-CMFs, more than 98% of the CM power can be eliminated. The proposed A-CMFs also provide a broadband CM suppression with fractional bandwidth lager than 126%, and a high bandwidth of differential-mode (DM) signal from dc to 7.4 GHz, which is about three times of the CM absorbing frequency. Eye diagrams are also measured to check the signal integrity, and the results show that the proposed A-CMF can still keep a good eye even under a high throughput of 7.5 Gb/s. [ABSTRACT FROM AUTHOR]

Time reversal (TR) relies on the reciprocity nature of the wave equation. Waves diverging away from a source can be time reversed and back-propagated to focus back at the source. The transmitting and receiving antenna arrays utilized for TR are collectively termed as the TR mirror (TRM). TR imaging in the microwave regime has shown its promise in nondestructive inspection and target localization. This paper deals with the design of a microwave TRM for the detection of breast tumors. The first part of this paper discusses TR simulations based on a signal processing algorithm, to obtain the tumor location from the total fields. The processed time-reversed fields can be back-propagated in a numerical model to focus the wave at the tumor locations. Simulation results aid in investigating the feasibility and the robustness of the method. The second part of this paper deals with experimental studies for the breast tumor detection, using a pulsed time-domain system and the back-propagation model. The successful detection of single and multiple tumors embedded in a liquid breast tissue-based phantom is shown using the microwave system. [ABSTRACT FROM AUTHOR]

This paper presents the design and the experimental demonstration of transmission of spectrally efficient frequency division multiplexing (SEFDM) signals, using a single 5-GHz channel, from 81 to 86 GHz in the E-band frequency allocation. A purpose-built E-band SEFDM experimental demonstrator, consisting of transmitter and receiver GaAs microwave integrated circuits, along with a complete chain of digital signal processing is explained. Solutions are proposed to solve the channel and phase offset estimation and equalization issues, which arise from the well-known intercarrier interference between the SEFDM signal subcarriers. This paper shows the highest transmission rate of 12 Gb/s over a bandwidth varying between 2.67 to 4 GHz depending on the compression level of the SEFDM signals, which results in a spectral efficiency improvement by up to 50%, compared to the conventional orthogonal frequency division multiplexing modulation format. [ABSTRACT FROM AUTHOR]

This paper presents a seven-port modulator capable of switching the polarization state of the transmitting signal. Similar to the six-port modulator, the proposed device modulates the carrier signal through the reflection coefficients generated by four variable loads. The additional seventh port allows feeding two antennas or a dual-port antenna. The loads control both the complex envelope and the polarization of the transmitted carrier signal. The mathematical model of the device, developed in this paper, is applied to analyze its performance and different modes of operation. For validation, a prototype is manufactured for a center frequency of 1575.42 MHz. It is used to generate M-quadratic-amplitude modulation at different polarizations. The signals recorded at the output of the prototype show good agreement with the values predicted by the model. [ABSTRACT FROM AUTHOR]

Due to technological advances in various fields and the rising demand for automation, the popularity of service robots is expected to grow rapidly in the upcoming years. One of the core functions of such robots is their interaction with people. One type of interaction, which is studied in this paper, is when the robot leads or follows a person. This presupposes that the position of the person is known relative to the mobile robot. In this paper, we present a 24-GHz wireless locating system to enable this kind of human–robot interaction. The system consists of a radar node attached to the robot and an active portable wireless beacon that is carried by the person. Using a secondary radar approach to measure the distance and angle to the beacon, the 2-D position of the person relative to the mobile robot can be accurately determined by a single radar node on the robot. This is unfeasible with standard multilateration localization approaches. An extended Kalman filter is used to increase the accuracy and reliability of the positioning system. The measurements presented in this paper, performed in a scenario that is both challenging and realistic, demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A novel diplexer-based fully passive transponder is presented in this paper, which targets sub-6-GHz 5G-compatible internet-of-things applications. To alleviate the antenna design restrictions of traditional transponder with two separate antennas, a new architecture has been proposed with the introduction of a diplexer, which allows transponder to simply employ a dual-band antenna. In this paper, a dual-band circularly polarized omnidirectional spiral slot antenna, with enhanced bandwidth and gain performance, is designed as the transponder Tx/Rx antenna. Besides the new architecture, a diode selection criterion is proposed as well. Analytical models are derived, showing relationships between the diode’s SPICE parameters and the conversion efficiency or conversion loss (CL) of such diode-based transponders. With help of the analysis, transponder designers can easily identify diodes to implement transponders with better performance. Under the guidance of the criterion, low-barrier diode SMS7630 is chosen for verification. Measured CL results of the transponder circuitry part show a noticeable improvement over the state-of-the-art works. The complete prototype was tested with radar’s transmitting power of 25 dBm, and it presents a maximum read-out distance up to 7 m when the operating fundamental frequency is 3.5 GHz. [ABSTRACT FROM AUTHOR]

A class of self-isolated harmonic oscillator (SIHO) with a feedback-loop structure is able to significantly reduce the pulling effect without involving extra circuit complexity such as a buffer amplifier. In the first part of this paper, the operation principle of the SIHO is theoretically studied through equivalent circuit models and X-parameter techniques. Closed-form expressions are derived to represent the respective linear and nonlinear equivalent impedances of SIHO subnetworks perturbed by varied load and injected signals. A conventional feedback-loop oscillator structure delivering the fundamental tone is used for comparative study. Such a modeling technique reveals the physical principle and behavior parameters that have an impact on the pulling effect. The experimental verification of the SIHO operation principle and modeling is presented as the second part of this paper. To this end, a harmonic measurement and design system is proposed and implemented for the design of an exemplary SIHO, which delivers a 4-GHz signal with 16.6-dBm power, 28% dc-RF efficiency, and −136.5-dBc/Hz phase noise at 1-MHz offset. The design process does not rely on circuit simulation software packages or a prior knowledge of the large-signal model of transistors, thus demonstrating the concept of a model-free nonlinear circuit design automation based on the experimental optimization. The SIHO circuit model is validated with the measured X-parameters of its nonlinear subnetwork. [ABSTRACT FROM AUTHOR]

This paper presents a new bandwidth tuning theory for Butterworth-response resonator filters. The presented theory shows that the bandwidth of odd-order Butterworth filters can be varied by adjusting only two interresonator coupling structures while maintaining a perfect impedance matching at the center frequency. In other words, this paper presents an analytic approach to reduce the number of tunable coupling structures when designing a bandwidth-tunable resonator filter. Theories for third- and fifth-order direct-coupled filters are discussed in detail, and it is shown that only two interresonator coupling structures are required to be tunable. In addition, for verifying the new bandwidth tuning method, a fifth-order cylindrical cavity filter has been designed, fabricated, and measured. The fabricated filter has an 11:1 bandwidth tuning range. [ABSTRACT FROM AUTHOR]

This paper proposed a method of synthesizing absorptive common-mode filters (A-CMFs) analytically with high absorption efficiency and two designable absorption bands. The proposed method is carried out by a novel circuit architecture and its analysis procedure. In differential mode, the integrity of the differential signals is maintained, and in common mode (CM), two absorption frequency bands can be obtained theoretically. These bands are designable with the analytical equations derived in this paper, so a dual-band or broadband A-CMF design can be easily synthesized by our proposed method. The authors also show that this method can make any one of R-CMFs “upgrade” to an A-CMF by simply adding an additional circuit, and this might be a revolutionary progress for the currently used CM-suppression techniques. To make the proposed concept more understandable, an example is used to demonstrate how the synthesizing methodology works, where a broadband A-CMF with its absorption bands located at 2.4 and 3.6 GHz is designed and implemented. Furthermore, a test sample of this A-CMF is fabricated on a four-layer printed circuit board. It is measured on a probing station, and the measured results are very similar to the simulated results. Finally, a comparison table of all the related works is given, showing that this proposed method really makes a significant improvement for A-CMF techniques. It is worth noting that this circuit design can provide a broadest 95%-absorption band to our best knowledge. [ABSTRACT FROM AUTHOR]

Frequency-dependent coupling (FDC) emerges as a new method to introduce the finite-position transmission zeros (TZs) in the synthesis and design of filtering networks. In this paper, several fundamental building blocks with FDCs are introduced and studied. The higher order filters with many TZs can be constructed by cascading these fundamental building blocks. As compared with the conventional coupled-resonator filters with only constant couplings, the inclusion of FDCs can potentially create more TZs with the same coupling topology. It is also shown that to realize the same TZs, a filter can be realized in a simplified structure with less cross-couplings by using FDCs. In this paper, one complete filter design procedure is illustrated, including the steps of the circuit model synthesis by the method introduced in this paper, physical dimensioning of the filter by the electromagnetic simulation and measurement of the fabricated filter. The measurement results are in very good agreement with the theoretical predictions, which validates the modular design strategy for filters with FDCs. [ABSTRACT FROM AUTHOR]

This paper presents a set of wideband, fully integrated E-band power amplifiers (PAs) designed in 0.12- $\mu \text{m}$ silicon-germanium (SiGe) BiCMOS and working in the range of 60–75 GHz. The single PA is based on common-emitter (CE) driver stages followed by a CE output stage. A three-stage and four-stage versions of the single-PA as well as four- and eight-way combined variants of the four-stage PA are measured and compared. The single, four-way, and eight-way combined PAs achieve saturated output powers of 16, 19.5, and 24 dBm with peak power-added efficiencies (PAEs) of 18%, 11%, and 12%, respectively. Modulated waveforms are passed through each amplifier and data rates as high as 32 Gb/s are demonstrated for all amplifiers when driven in the linear mode. Measurements of how error-vector magnitude (EVM) and PAE degrade versus output power are presented and it is demonstrated that the eight-way combined PA can deliver 17–20 dBm of average power in a 64-quadratic-amplitude modulation, 1-Gbaud waveform (6 Gb/s), with an EVM of −32 to −24 dB and a PAE of 3%–5% without predistortion. To the author’s knowledge, this is the first paper reporting detailed measurements of PA EVM and PAE versus output power at these frequencies. [ABSTRACT FROM AUTHOR]

This paper presents a new miniaturized ultra-wideband (UWB) multilayer balanced bandpass filter (BPF) using the liquid-crystal polymer technology. The design is based on the use of two baluns and uses the transversal signal-interference concept for the realization of differential-mode (DM) passband and common-mode (CM) stopband. The broadside coupled stripline structure is adopted in this paper to realize UWB performances and pure TEM mode. The fabricated prototype is self-packaged, light in weight, and cost effective with a small footprint. The demonstrated balanced BPF achieves the excellent DM and CM responses within the entire bandwidth, centered at 6.85 GHz. The simulation and measurement results show good agreement. [ABSTRACT FROM AUTHOR]

This paper describes a simple analysis of the guided waves in an eccentric circular waveguide based on the bipolar coordinate system (BCS). The separation of the variable technique is used for the solution. The structure under study is an infinite perfect electric conductor (PEC) cylinder in the z-direction, which encloses eccentrically another infinite PEC cylinder. The modal analysis has been conducted using an analytical method, solving the TE and TM modes by the aid of electromagnetic formulation. Despite previous studies which mostly rely on numerical techniques or otherwise considering the dominant TEM mode, in this paper, the analytical solution is proposed for the electromagnetic fields which consequently lead to the characterization of the cutoff wavenumbers of higher order modes and explicit solution to electric and magnetic fields in BCS. The solution of the Helmholtz equation in BCS using the technique of separation of variables exhibits as a one of the contributions of this paper, and the validity range of the answer is discussed. The values of the cutoff wavenumbers for the first few modes are calculated and compared with the benchmark results. The precise correspondence of the obtained values with the proposed method with those of the previous studies and computer simulations, along with the high speed and simplicity in implementation, introduces the present method as an appropriate option for analyzing eccentric circular cylindrical structures. [ABSTRACT FROM AUTHOR]

This paper presents the first experimental assessment of a highly integrated dual-band dual-polarized antenna tile designed for synthetic aperture radar (SAR) digital beamforming (DBF) satellite applications. The demonstrator described in this paper is the first comprehensive experimental validation of an RF module providing the X-band and Ka-band (9.6- and 35.75-GHz) operation with custom downconversion stages. All the antennas, transitions, and downconversion chips are integrated in the same antenna tile fabricated using a customized 15-layer high density interconnect process. The designed tile goes to the limits of the proposed technology and for the high trace density and for the size of the vertical transitions. The proposed results represent the state of the art in terms of compactness for a DBF SAR RF module even though the demonstrator was manufactured with a standard low-cost technology. The experimental assessment proves the validity of the proposed manufacturing and integration approaches showing a substantial agreement between the performance of the individual blocks and of the integrated system. [ABSTRACT FROM AUTHOR]

This paper presents geometrical-based wideband circuit models for different configurations of loaded slotline and loaded coplanar waveguide (CPW). It investigates, first, the strip-loaded slotline and then extends the developed model to strip and split-ring resonator (SRR)-loaded CPW. The proposed models successfully describe the behavior of several structures of interest in the literature and provide new insights on the design procedure. They operate over the entire frequency range if higher order modes are not generated without the need for fitting parameters. This paper also presents three applications, of which the design relies on the proposed modeling methodology. They are a third order maximally flat low-pass filter with 1.4-GHz cutoff frequency, a 3-GHz slow wave structure with a slow wave factor larger than 2 in the linear range of the dispersion relation, and a balanced composite right-/left-handed SRR-loaded CPW with 100% (2.31–7.1 GHz) fractional bandwidth. Experimental results, which are in a very good agreement with the electromagnetic simulations, confirm the proposed theory. [ABSTRACT FROM AUTHOR]

In this paper, a novel complementary split-ring resonator (CSRR)-based sensor for full characterization of magneto-dielectric materials is proposed. In general, the operation of microwave resonance-based sensor hinges on the shift in the resonance frequency and the change in the quality factor of the loaded structure. However, both the electric permittivity and the magnetic permeability of the material under test (MUT) have similar effect on the response of the sensor that makes the simultaneous determination of the permittivity and permeability challenging. To remove this difficulty, the main idea behind this paper is to localize the highest intensity of the electric and magnetic fields in two separate zones. By the analysis of the measured resonance frequency and quality factor, the real and imaginary parts of the electric permittivity and the magnetic permeability of the MUT can be determined. Although the characterization of the permittivity and permeability of materials using split-ring resonator and CSRR-based sensors has been widely used, to the best of our knowledge, the full characterization of magneto-dielectric materials using a single sensor has not yet been reported in this paper. As a proof of concept, the sensor was fabricated and used to measure the permittivity and permeability of several materials. Strong agreement between the extracted values and the reference data was achieved. [ABSTRACT FROM AUTHOR]

In this paper, we propose a compact, lightweight, and easy-to-fabricate Hilbert curve-based metasurface resonator that can effectively increase the sensitivity (radio frequency (RF) field intensity) and penetration depth of an RF coil for 7-T magnetic resonance imaging scanner. A circuit model is proposed to accurately calculate the resonance frequency of Hilbert curve resonators of different orders. A single element of a transverse electromagnetic (EM) coil was used for this paper. The increase in the field sensitivity introduced by the proposed metasurface to an RF coil was successfully demonstrated through simulations and experiments. The EM field produced by the RF coil is redistributed due to the presence of the proposed metasurface. The key feature of the proposed structure is its significant increase in the penetration depth of magnetic fields into the imaging volume. An enhancement of the magnetic field by more than four times was observed at 13.5 cm away from the coil experimentally. Flexibility for matching the coil integrated with the proposed surface is shown. [ABSTRACT FROM AUTHOR]

Fully coupled transient analysis of electromagnetic (EM)-circuit systems is highly desirable for a number of applications. Over the last decade or so, there have been several papers that present effective solutions to this problem within the context of full-wave differential or integral equation solvers. The method typically espoused is as follows: discretize the underlying EM system, couple with the circuit subsystem self-consistently, and then solve the coupled system. Within this framework, nonlinearities are easily accounted for in the solution process. This is in direct contrast to frequency domain analysis, wherein one defines ports that couple the EM and circuit subsystems, i.e., the representation of the EM system using an effective impedance/admittance as seen at the circuit terminals. This approach permits: 1) solution only at the circuit level and 2) one can readily incorporate different circuits without having to solve the coupled system repeatedly. Achieving the same functionality in the time domain is a challenge. In this paper, we present a solution to this problem. We will prescribe the means to effectively represent the EM subsystem in terms of a transient admittance, thus facilitating a solution to the coupled system via a circuit-level solve. Several results are presented that serve to validate the proposed approach and demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

It is very difficult to analyze electromagnetic (EM) responses of electrically large and complex objects because this requires a large amount of computing resources or extremely long calculation times. The EM topology (EMT) technique has been developed as a potential solution to overcome this resource-consuming limitation. The EMT technique can reduce computing resource by recombining EM analysis results of physically or electrically divided subblock models, instead of an entire model. However, the EMT technique still has some shortcomings to be overcome when applied to complex electrical systems subject to arbitrarily directional incoming sources. In this paper, we propose a wideband coupling analysis method by arbitrarily incoming sources based on the EMT technique for complex waveguide structures including a printed circuit board. A topological network is proposed that takes into account the effect on arbitrarily directional incoming sources with their polarization (vertical, horizontal, and circular). Explanations and definitions of several parameters for the proposed topological network are discussed. S-parameters are obtained using the CST-MWS tool. The analysis results of the proposed method, the entire model by the CST-MWS, and measurement results from a reference paper are compared, and the validity of the approach is verified. [ABSTRACT FROM AUTHOR]

This paper presents a novel rectifier array for a wide dynamic range of RF-dc conversion. The rectifier array consists of multiple rectifier cells optimized for operation at different power levels and uses an adaptive power distribution method to divide the RF input power among these rectifier cells according to the RF power levels. The adaptive power distribution takes advantage of the power-dependent input impedances of the rectifier cells and is implemented with passive devices. This method both improves the rectification efficiency and minimizes the impedance mismatch as the input power level varies, and therefore, significantly enhances the dynamic range. The rectifier array can be designed using either the same type or different types of rectifying devices and can be expanded by including more cells in the network to further increase the dynamic range. In this paper, three different implementations of such rectifier array circuits are described, including a two-diode rectifier array designed with the same type of diodes, a two-diode rectifier array designed with different types of diodes, and a three-diode rectifier array with different types of diodes. The performances of these circuits are validated with measurement and compared with each other. Significant enhancement of dynamic range over conventional rectifiers is demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, a novel Eulerian nonlinear beam-wave interaction (BWI) theory considering harmonic interaction of a helix traveling-wave tube (TWT) is developed. Derived from this Eulerian model, the novel Eulerian nonlinear analytic solutions (the fourth-order analytic solution of fundamental and the second-order analytic solution of harmonic) are first obtained by the method of successive approximation. The analytic relationships between electric fields of fundamental/harmonic frequencies and electron phases are also found. Then, the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory are compared to a Lagrangian theory. C-band and Ku-band helix TWTs based on a single pitch section are included in the simulation. It is found that the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory agree well with the Lagrangian theory at 1-dB gain compression point. Interestingly, the saturation effects caused by electron overtaking cannot be found by the traditional Eulerian analysis but can be described by the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory. Moreover, Eulerian nonlinear analytic solutions are simpler and more accurately than existing approaches and, thus, allow analytical progress. This paper confirms that the Eulerian nonlinear analytic solutions can outperform the previous proposals. [ABSTRACT FROM AUTHOR]