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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. Table I 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.

This paper presents a supply modulated $X$ -band 12-W peak power transmitter that maintains an average efficiency greater than 50% for various shapes of amplitude-modulated pulses. The main power amplifier is a two-stage GaN-on-SiC MMIC with a peak efficiency of 65%, while the pulse envelope modulator is a 95% efficient hybrid 3-b power DAC implemented with GaN-on-Si transistor switches. Envelope shaping of a pulsed waveform results in improved spectral confinement of greater than 15 dB for the first sideband compared with constant-envelope pulses, with over 20 points improvement in total efficiency. The combination of supply modulation and digital predistortion is shown to result in high composite (total) efficiency of over 55%, with simultaneous high dynamic range and with flexible digitally programmable pulse shaping.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

This paper proposes a measurement strategy to remove the random phase contributions of the sweeping local oscillator (LO) from modulated radio frequency phase measurements based on downconversion. To obtain a stable phase spectrum for each run of tone-by-tone sweeping measurement, the LO used for downconversion is coupled out to an extra path and modulated to be a wideband multisine signal. By monitoring the phase change of multisine signal at a specific and fixed frequency point, random LO phase offsets during the frequency sweep can be measured and compensated. In this paper, two experimental test benches with the same core measurement strategy but different architectures are established for method validation. According to the experimental results using test bench one, the phase stability is ±(0.2°–0.4°) at 1.8 GHz for fundamental mixing-based downconversion and ±(0.6°–1°) for harmonic mixing at 6 GHz. Based on test bench two, relative phase deviations of ±(0.8°–1.2°) at 22 GHz for fundamental mixing and ±(2°–3°) at 66 GHz for harmonic mixing are reachable.

This paper presents the design of a capacitive wireless power transfer system for operation in fresh water. This paper clarifies two particular points. One is the behavior of $k$ and kQ product for the frequency; $k$ means coupling coefficient in the coupler and kQ product means the product of $k$ and $Q$ -factor in the coupler. The other is the design method of the general capacitive coupler under fresh water. First, $k$ is derived from the equivalent circuit of the coupler, and it is elucidated that $k$ and kQ product are dependent on the frequency. The pivotal elements that improve kQ product are also found. Next, it is then clarified that the design parameters at maximum kQ product have the maximum available efficiency and we clarify the applicable condition for our design method. We achieved an efficiency of 91.3% at a transfer distance of 20 mm via experimentation. Finally, it is demonstrated that power is wirelessly transferred to the Lux sensor module using our coupler implemented on the charging station and that measured data are also wirelessly transferred to it.

This paper presents a comprehensive guide to co-design piezoelectric RF-micro-electromechanical system (MEMS) resonators and CMOS for enabling voltage-controlled MEMS oscillators (VCMOs) that harness the best benefits out of both platforms. The analysis, focusing on understanding different tradeoffs among the tuning range, power consumption, gain, and phase noise, is generic to any kind of piezoelectric resonators and specific for Colpitts VCMOs. As a result of this paper, the first VCMO based on the heterogeneous integration of a high-Q lithium niobate (LiNbO3) micromechanical resonator and CMOS has been demonstrated. A LiNbO3 resonator array with a series resonance at 171.1 MHz, a Q of 410, and an electromechanically coupling factor of 12.7% is adopted, while the TSMC 65-nm RF LP CMOS technology is used to implement the feedback and tuning circuitry with an active area of $220\times 70\,\,\mu \text{m}^{2}$ . The frequency tuning of the VCMO is achieved by programming a binary weighted digital capacitor bank and a varactor that are both connected in series to the resonator. The best measured phase noise performance of the VCMO is −72 and −153 dBc/Hz at 1 kHz and 10-MHz offsets from 178.23- and 175.83-MHz carriers, respectively. The VCMO consumes a dc current of $60~\mu \text{A}$ from a 1.2-V supply while realizing a tuning range of 2.4 MHz (~1.4% fractional tuning range). Such VCMOs can be applied to enable ultralow power, low phase noise, and wideband RF signal synthesis for emerging applications in Internet of Things.

The design and performance of a WR-5 band 135–150-GHz Schottky diode-based frequency tripler which uses waveguide resonator filters for low loss impedance matching is presented in this paper. The filters used in this paper provide filtering, impedance matching, and microstrip (MS) to waveguide transitions in one structure. The matching optimization is achieved by scaling the external quality factors and adjusting the resonance frequency of the filter cavities. This approach transfers most of the tripler’s matching networks from MS circuitry to lower loss rectangular waveguide resonators. This is desirable and useful in particular for submillimeter wave and terahertz frequencies. The device presented is a 47.5 to 142.5 GHz bias-less frequency tripler with a 15-GHz output bandwidth. The tripler was measured to have a conversion loss of 13.1–14 dB across the band, at an input power of 17 dBm. The measured $S_{11}$ at the input port is better than 15 dB and all the reflection zeros from the filter resonances are distinct. The good agreement between measurements and simulations verifies the accuracy of the filter-based design approach.

This paper presents a new asymmetric Class-F−1/F Doherty power amplifier (DPA) consisting of a Class-F−1 carrier amplifier and a Class-F peaking amplifier. The asymmetric current waveform due to different harmonic loading conditions offers an asymmetric fundamental current in load modulation region, ensuring an improvement in the performance at the peak output power. In this paper, improvements in the large signal performances, such as the output power and efficiency, are analyzed using the derived fundamental current models. For verification, a 2.4-GHz GaN Class-F−1/F DPA was designed and fabricated. The designed Class-F−1/F DPA achieves a peak output power of 44 dBm with a peak drain efficiency (DE) of 86.7%. Using a local thermal equilibrium 10-MHz signal with a 6.6-dB peak-to-average power ratio, the Class-F−1/F DPA achieves an average output power of 37.3 dBm with a DE of 68% at a supply voltage of 28 V. The measured adjacent channel leakage power ratio with a digital predistortion is below −50 dBc.

In this paper, a highly integrated frequency-modulated continuous-wave (FMCW) radar system with a single-antenna interface for range sensing is proposed. In this paper, a circulator structure was developed and used in the radar system with the single-antenna interface. This structure capitalizes on frequency orthogonality to separate transmitted and received signals; thus, the isolation can be improved by using integrated filters to further suppress transmitter leakage. Without an additional back-end leakage cancellation mechanism and antenna tuner, the single-antenna FMCW radar system can be devised. The proposed system is composed of a radar transceiver, a frequency synthesizer, an analog signal processor, and an AD converter; the system is fabricated using a 65-nm CMOS technology, occupies a chip area of 1.9 mm2, and consumes 147-mW dc power under a 1.2-V power supply. The implemented front-end circuit can provide an output power of 10.5 dBm with power efficiency of 30%, over 1-GHz impedance matching, an insertion loss of 2 dB, a maximum noise figure of 16.8 dB (including the following IF amplifier), $P_{1\,\text {dB}}$ of 2 dBm, and IIP3 of 7 dBm. A wireless measurement process proved that the system can provide a 37-cm range resolution over a 50-m range for a $20 \times 20$ cm2 copper plate. Finally, an FMCW radar front-end board and a digital signal processing board were implemented for data analysis, thus completing the FMCW radar sensor unit. The proposed system can be utilized for multiple applications including 1-D object tracking, 2-D localization, and 3-D object tracking.

This paper presents a low noise figure (NF) and high gain super-regenerative receiver (SRR) with coupled networks for portable millimeter-wave (mm-wave) imaging systems. Compared with the previous SRR designs, this paper presents a novel SRR structure comprising of two oscillators coupled by a serial resonator, which consists of the inductors and capacitors. Due to the coupled oscillators, the gain of the SRR is significantly improved and the NF of the SRR structure is reduced by 3 dB simultaneously. These benefits lead to a high-sensitivity SRR at mm-wave frequency. The circuit is realized in 65-nm CMOS process with a core area of 0.06 mm2. Measured results show that the receiver can detect −84-dBm minimum input power with 541-MHz integration bandwidth (BW). It has a noise-equivalent-power of 0.615 fW/(Hz), a NF of 7.52 dB, a BW of 3.5 GHz, and a power consumption of 8.1 mW. With frequency calibration procedure, these performances show the proposed chip meets portable imaging system requirement.

RF resonant polymer-coated sensors are a proven effective approach to enhance the sensitivity of polymeric sensing materials. However, the level of sensitivity improvement offered by an RF resonant sensor is directly proportional to the quality factor (Q) of the resonator—the larger the Q-factor, the higher the sensitivity enhancement is. This paper first presents a miniature polymer-based dielectric resonant (DR) sensor design operated at its fundamental mode (TEH) at 24 GHz demonstrating a measured Q-factor of 3820. The sensor is coated with a (per)nigraniline-based conductive sensing material for detections of acetone and isopropanol volatile organic compounds and has a small footprint of $4.5\,\,\text {mm} \times 4.5$ mm. The sensor has demonstrated a low-ppm detection capability for acetone and isopropanol gases with a response onset time less than 15 s. This paper further demonstrates a novel airborne carcinogenic agent sensor array implemented with a single dielectric resonator operating in dual mode (HEH) at 27 GHz. It is functionalized by placing two carcinogen sensing materials—polyhydroxyethyl-methacrylate (PHM) and fluoroalcohol polysiloxanes (FAPS)—at the optimal geometrical locations on the DR, such that the polymers would independently affect the resonant frequencies of the two orthogonal HEH degenerate modes. By monitoring $\Delta f_{0}$ and $\Delta S_{11}$ near $f_{0,\mathrm {HEH1}}$ and $f_{0,\mathrm {HEH2}}$ , both the concentrations and the response signatures of the airborne carcinogenic agents can be detected. The measurement results indicate that the HEH-mode two-sensor array carrying PHM and FAPS is successful in identifying and differentiating two carcinogenic agents—dioxane and benzene—and their respective concentrations.

This paper presents a multifunctional reconfigurable frequency-selective surface (FSS) based on liquid-metal-filled microchannels engraved in an elastomeric substrate. The proposed FSS comprises two layers of periodic meandered patterns encased within the opposite sides of a dielectric, where the layers are arranged in orthogonal polarization with independent control of reconfigurability. The novelty of the design lies in its switching characteristic between four different working states (dual-polarized all pass, single-polarized low pass, single-polarized bandpass, and dual-polarized bandpass) with the injection of a liquid metal in the top and bottom microchannels. Moreover, the design exhibits miniaturization performance during one of the states (exhibiting dual-polarized bandpass response at 1.58 GHz) corresponding to the unit cell dimensions of $0.052\lambda _{0} \times 0.052\lambda _{0}$ . The equivalent circuit models and parametric variations are extensively analyzed for understanding the design principles. Because any liquid-metal-based reconfigurable FSS structure has not been reported earlier, a detailed description of the fabrication and measurement procedure are presented in this paper. The experimental validation of the fabricated prototype also confirms the potential use of microfluidic technology-based reconfigurable structures in future.

[EN] The objective of this paper is to advance the state of the art in the characterization of the multipactor effect in dielectric materials. The materials studied are the most commonly used dielectrics in space applications, namely, Alumina, Rexolite, Rogers RT5870, Rohacell, Teflon, and Ultem 1000. In this paper, a new family of coaxial waveguide components, covering the L- and S-bands, with a wideband, low-pass response has been designed, and six different prototypes have been specifically optimized and manufactured. The six prototypes have then been used to simulate and measure the multipactor breakdown susceptibility charts for the six dielectric materials investigated. Finally, the simulation results are compared with the results of the measurement campaign indicating good agreement., This work was supported in part by the European Space Agency through Research Project "Novel Investigation in Multipactor Effect in Ferrite and Other Dielectrics Used in High Power RF Space Hardware" under Grant AO 1-7551/13/NL/GLC and in part by MINECO (Spanish Government) through Research and Development Project under Grant TEC2016-75934-C4-1-R. This paper is an expanded version from the IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes IMWS-AMP 2017, Pavia, Italy, September 20-22, 2017.

This paper presents, for the first time, tunable dual-mode substrate integrated waveguide (SIW) diplexers with various single-ended (SE) or balanced (BAL) ports. Dual-mode diplexing reduces the required volume by half while signal routing is achieved by proper coupling sections. Furthermore, the SIW resonators result in low loss and wide tunability. This paper experimentally demonstrates three designs with SE–SE, SE–BAL, and BAL–BAL port configurations. The SE–SE, SE–BAL, and BAL–BAL diplexers can be tuned starting from 2.07, 2.2, and 2 GHz, respectively, with a tuning range of 45%, 57.2%, and 63.5%, respectively. The average measured insertion loss is 1.32 dB for the SE–SE, 1.95 dB for the SE–BAL, and 2.15 dB for the BAL–BAL. The average size of the diplexer is $55{\times} 55$ mm2. For the proposed SE–BAL and BAL–BAL diplexers, the measured in-band common-mode rejection is better than 40 dB throughout the tuning range.

An accurate physical model for GaN high-electron-mobility-transistors (HEMTs) device is imperative and crucial for circuit design and technology optimization. In this paper, a scalable large-signal surface-potential (SP) model of AlGaN/GaN HEMTs is presented. The drain current model is capable of accurately modeling the self-heating effect and trapping effect. The self-heating effect is modeled by embedding temperature increment into free-carrier mobility model, and the trapping effect is modeled by introducing an indirect variable effective gate voltage $V_{\mathrm {gseff}}$ . Moreover, the scaling and multiharmonic characteristics of the SP model are studied for the first time. The geometry-dependent thermal resistance $R_{\mathrm {ths}}$ is identified by the electrothermal finite-element method simulations, which is scalable with the gate width W and power dissipations $P_{\mathrm {diss}}$ of the device. Single-tone on-wafer load–pull measurements at operating frequency 8 GHz is carried out for verification purpose. Accurate predictions of the static (dc) $I\!-\!V$ , pulsed-gate-and-drain $I\!-\!V$ , S-parameters up to 40 GHz and large-signal harmonic performance (the fundamental, second- and third-harmonics output power, and power-added efficiency) for the devices with different gate peripheries have been achieved by the proposed model. The results of this paper can pave the way for the full application of the physical-based model in circuits design.

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

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

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

This paper proposes a new approach for inductive wireless power transfer (IWPT) tag-to-reader communication. A new technique to achieve transmitter/receiver (Tx/Rx) frequency separation is demonstrated. A two-tone Tx is adopted at the reader, and the third-order intermodulation (IM3) frequency generated by the tag rectifier nonlinearity is used as the Rx carrier, which is modulated by a baseband signal sent by the tag. The uplink signal at the IM3 frequency can be picked up by the reader coil. The IWPT impedance matching networks for both the reader and the tag coil can be reused efficiently, since the IM3 frequency at 5.06 GHz is close to the Tx fundamental frequencies at 4.94 and 5 GHz. Due to the Tx/Rx frequency separation, the Tx-to-Rx leakage at the Rx frequency can be suppressed by external filters to improve the Rx signal-to-noise ratio (SNR). The proposed technique is implemented within a 5-GHz IWPT system, and a tiny CMOS tag with a coil size of only 0.01 mm2 is used. This paper also implements conventional direct and intermediate frequency-based backscattering uplinks for comparison, and the proposed IM3 uplink is able to improve the Rx SNR by more than 20 dB. The achieved uplink data rate (100 kb/s) is also higher than the published work (20 kb/s) that adopted the conventional backscattering method.

This paper presents a mechanically assisted microwave drill (MWD) capable of drilling 26-cm-deep 12-mm-diameter holes in concrete. This record significantly extends the inherent $\lambda $ /4-depth capability (~1.5 cm at 2.45 GHz) of the basic MWD scheme. Compared with conventional mechanical drills, this MWD is characterized by a relatively silent and vibration-free operation, but its drilling speed is yet slower than 1 cm/min. This paper reviews the fundamental MWD mechanism (utilizing localized microwave heating and thermal-runaway instability), and extends it for deeper holes by also using the coaxial applicator as a slowly rotating hollow reamer to remove the debris. The MWD prototype is introduced, including its adaptive impedance matching and remote-operation features, and its experimental results are presented. Theoretical and practical MWD aspects are discussed, and potential developments are indicated (e.g., for faster drilling and iron-rebar cutting). The present MWD performance can be useful for specific applications which critically require silent drilling operations in concrete.

This paper presents a rotatable cyclic Vernier digital-to-time converter (DTC) with 1.8 ps timing resolution on an 80 ns time scale. The proposed DTC features high timing resolution, and can be utilized in beam-steering arrays, which is infeasible for ordinary Vernier DTCs. The proposed DTC was implemented within a passive time-equivalent direct-sampling ultra-wideband impulse-radio radar system and was fabricated in 65 nm CMOS technology. This radar system is capable of quantizing direct-sampled impulse waveforms to provide full degrees of freedom for backend digital signal processing. The measured differential nonlinearity/integral nonlinearity of the DTC was +4.6/−3 and 12.4/−9.4 where the LSB was 1.8 ps, and the total power consumption was 133 mW. Also, a new method for localization between wireless sensor nodes of equivalent-time direct-sampling radar is presented in this paper; this method can theoretically achieve resolution as high as that of regular radar.

This paper describes the modeling, analysis, and design of a complete (dc-to-dc) inductive wireless power transfer (WPT) system for industrial moving applications. The system operates at 6.78 MHz and delivers up to 150 W to a load moving along a linear path, providing a quasi-constant dc output voltage and maintaining a zero voltage switching operation, regardless of position and load, without any retuning or feedback. The inductive link consists of an array of stationary transmitting coils and a moving receiving coil whose length is optimized to achieve a constant coupling coefficient along the path. Each Tx coil is individually driven by a constant amplitude and phase sinusoidal current that is generated from a GaN-based coupled load-independent Class EF inverter. Two adjacent transmitters are activated at a given time depending on the receiver’s position; this effectively creates a virtual series connection between the two transmitting coils. The Rx coil is connected to a passive Class E rectifier that is designed to maintain a constant dc output voltage independent of its load and position. Extensive experimental results are presented to show the performance over different loading conditions and positions. A peak dc-to-dc efficiency of 80% is achieved at 100 W of dc output power and a dc output voltage variation of less than 5% is measured over a load range from 30 to $500~\Omega $ . The work in this paper is foreseen as a design solution for a high-efficient, maintenance-free, and reliable WPT system for powering sliders and mass movers in industrial automation plants.

This paper proposes a novel design approach for a filtering antenna, which contains an array of 4 by 2 waveguide aperture radiation elements. Coupling matrix theory is introduced in this paper to synthesize the multiple coupled-resonators circuit. Unequal amplitude excitation is applied to the $4 \times 2$ elements so as to obtain a low sidelobe level. To demonstrate the concept, an X-band antenna array is designed and fabricated using a three-layer waveguide structure. Measured results show that the filtering antenna array can achieve a gain of more than 15.58 dBi and a radiation efficiency of higher than 90% over the passband (9.91–10.1 GHz). The sidelobe level is −18.3 dB in the ${H}$ -plane and −21.1 dB in the ${E}$ -plane.

Novel 2-D gray-scale inkjet printed microstrip line (MSL) terminations are presented in this paper. The proposed open-end type MSL termination is constructed of a lossy trace printed on paper and placed on a typical dielectric substrate with background. Optimal design guidelines are also discussed for attaining best absorption band given ink resistivity and termination size. Both fixed width and tapered width lines are presented, experimentally showing high absorption levels over a wide bandwidth. These simple to fabricate structures may find applications in scenarios where low-cost wideband planar terminations are needed.

The demand on mobile electronics to continue to shrink in size while increasing in efficiency drives the demand on the internal passive components to do the same. Power amplifiers require inductors with small form factors, high quality factors ( $Q\text{s}$ ), and high operating frequency in the single-digit gigahertz range. This paper explores the use of magnetic materials to satisfy the demands of power amplifier inductor applications. This paper then discusses the optimization choices regarding material selection, device design, and fabrication methodology. The inductors achieved here present the best performance to date for an integrated magnetic core inductor at high frequencies with a 1-nH inductance and peak $Q$ value of four at about 3 GHz. Such compact inductors show potential for efficiently meeting the need of mobile electronics in the future.

This paper aims to effectively integrate a GaN amplifier into a high-efficiency active-antenna design. In this paper, the antenna is designed for a GaN high-electron-mobility-transistor (HEMT) impedances calculated by a load–pull simulation with a GaN nonlinear model, which contributes to a lossless design and prevents power-added-efficiency (PAE) reduction by active-antenna integration. The antenna impedance is selected to reduce the impedance-transform ratio with the GaN HEMT. In addition, the active antenna includes a second-harmonic-tuning circuit for high efficiency. The active antenna comprises antenna- and amplifier-circuit layers piled onto a Peltier unit, which has a high affinity with this cooling systems. The antenna and amplifier circuits are designed on low- and high-dielectric substrates, respectively, enabling the amplifier to be downsized and the antenna gain to be increased. Each layer is connected by a through-hole. First, the single-stage amplifier is fabricated with a maximum output power of 37.95 dBm and a maximum PAE of 62.94%. Next, the GaN active antenna is fabricated with a maximum effective isotropically radiated power of 44.61 dBm and a maximum antenna gain of 23.99 dBi. The assumed amplifier large-signal characteristics of the active antenna agree with those of the single-stage amplifier. Therefore, the amplifier and the antenna are integrated without loss.

Wireless power transfer (WPT) systems working at several megahertz (MHz) are widely considered as a promising solution for a mid-range transfer of a medium amount of power. The soft-switching-based Class E power amplifier (PA) and rectifier are known to be suitable for high-frequency applications, which may potentially improve the performance of the MHz WPT systems. Meanwhile, the efficiency and output power of the Class E PA are sensitive to its loading condition, particularly when there is variation in the relative position of the coupling coils, namely a changed mutual inductance between the coils. Thus the purpose of this paper is to propose and discuss circuit and design improvements that maintain a high efficiency and output power of the MHz WPT systems over a wide range of mutual inductance, when the Class E PA and the Class E rectifier are employed. Besides, the suppression of the harmonic contents, i.e., the electromagnetic interference problem, is also considered in the circuit design. Both the simulation and experimental results show that the newly added and optimally designed $\pi $ matching network obviously improves the drops of the efficiency and output power of the Class E PA and the overall WPT system when the mutual inductance varies. The reduction of the total harmonic distortion in the input voltage of the coupling coils is also significant, from the original 52.9% to 9.6%. The circuit and design improvements discussed in this paper could serve as a general and practical solution for building high-performance MHz WPT systems.

Free-electron lasers are used to generate laser radiation using an accelerated electron beam. In this paper, an electrostatic accelerator was used with a thermionic cathode. Lasing pulses of the order of tens of microseconds were generated by passing the current pulses through a wiggler and resonator combination. The change in lasing power as a result of postsaturation variation of the energy of the electron beam during the lasing period is presented in this paper in the form of experimental measurements and simulations. In the experiments, the initial electron beam energy was ~1.4 MeV and the current was 1.13 A, whilst the lasing frequency was always close to 102 GHz. It is shown that postsaturation, positively ramping the beam energy increases the radiation extraction efficiency by around 50%. Whilst a falling beam energy results in a reduction in extraction efficiency.

This paper presents the first wirelessly synchronized multichip array (WSMA) in 65-nm CMOS. The proposed architecture makes use of a central wireless signal to synchronize an mm-wave array, eliminating the need for connecting wires between the array elements. Wireless injection locking of a single chip is successfully demonstrated, and a 3-dB linewidth of 400 Hz at a carrier frequency of 50 GHz is achieved (stability ratio of 8 ppb). In addition, a two-element WSMA with an array aperture greater than 20 wavelengths is demonstrated using the proposed transceiver architecture. The reported transceiver includes a receiving on-chip antenna, a low-noise amplifier, an injection-locked voltage-controlled oscillator, a buffer amplifier, an in-phase/quadrature generator, a phase shifter, a power amplifier, and a transmitting on-chip antenna. The chip is fabricated in a 65-nm CMOS process and occupies an area of 1.7 mm $\times 3.8$ mm. This paper sets the foundation for increasing the array aperture through wireless injection locking, extending traditional array systems into the high-resolution, narrow-beamwidth regime.

This paper proposes the use of the coplanar waveguide (CPW) odd mode, also known as the parasitic slotline mode, as a design parameter. It presents a novel equivalent circuit model for the CPW cross-junction, where each CPW has two modes: the even mode, which is the conventional CPW mode also known as the coplanar mode, and the odd mode. The model is simple, intuitive, and physical-based. It can be used in different combinations including the case of slotline cross-junction. The model paves the way to design novel air-bridge free CPW applications. Among them, two are presented in this paper: CPW-to-slotline transition (balun) and Wilkinson power divider. For both applications, closed form expressions for the operating point are derived. Results are verified by EM simulations. An air-bridge free CPW power divider that combines both applications is fabricated and characterized. Simulations and measurements are in a very good agreement.

This paper reports on the analysis of a radio frequency microelectromechanical systems (RF-MEMS) tuned cavity oscillator on $X$ -band based on a GaN-HEMT monolithic microwave integrated circuit reflection amplifier. The RF-MEMS-switches are mounted on a low-loss printed circuit board (PCB) intruded in an aluminum cavity that is coupled to a microstrip line connected to the reflection amplifier. This paper investigates the influence of the number of switches as well as their positions with respect to phase noise and tuning range. Vertical and horizontal positions of the switches are varied with target on optimum trade-off between phase noise and total tuning range. For a three-row MEMS-configuration at 1-mm depth from the end cavity wall, a tuning range of 4.9% is measured. The center frequencies are ranging from 9.84 to 10.33 GHz with measured phase noise of −140 to −129 dBc/Hz at 100-kHz offset. A similar three-row MEMS setup at 2.5-mm depth provides a tuning range of 12.3% with measured phase noise of −133 to −123 dBc/Hz at 100-kHz offset.

Microdispensing of thick-film conductive paste has been demonstrated as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper frequency range of these lines is limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around $100~\mu \text{m}$ . In this paper, a picosecond Nd:YAG laser is used to machine slots in a 20–25- $\mu \text{m}$ -thick layer of silver paste (Dupont CB028) that is microdispensed on a Rogers RT5870 substrate, producing coplanar waveguide (CPW) transmission lines with 16– $20~\mu \text{m}$ -wide slots. It is shown that the laser solidifies an about 2- $\mu \text{m}$ -wide region of the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 to 30 MS/m, which represents a $100\times $ improvement when compared to the values obtained with the exclusive use of microdispensing. This paper demonstrates that a hybrid approach of additive manufacturing and laser machining enables the fabrication of higher frequency circuits (up to at least 40 GHz) with improved performance.

This paper proposes a linear and efficient transmitter prototype based on pulsed load modulation (PLM) power amplifier (PA). The proposed transmitter setup utilizes the complex delta–sigma (DS) modulation as a signal processing technique instead of the envelope DS modulation for higher linearity performance. Using the complex DS modulation technique reduces the in-band quantization noise significantly at the output of the modulator and consequently, enhances the linearity of the transmitter. To validate the proposed technique, the linearity and efficiency performance of the complex DS modulator (CDSM)-based transmitter are compared with the performance of its envelope DS modulator (EDSM) counterpart in measurement. For this paper, an efficient and linear PLM PA is designed and fabricated using GaAs E-pHEMT transistors. For a Long-Term Evolution (LTE) uplink standard signal with 3-MHz bandwidth and 7-dB peak-to-average power ratio, the CDSM-based transmitter achieves the drain efficiency and power added efficiency of 46% and 42%, respectively, at an average output power of 25.1 dBm. The comparison measurement study of EDSM-based transmitter and the CDSM-based transmitter with the LTE uplink signal shows about 11-dB improvement in the signal-to-noise and distortion ratio of the output signal. The measurement results for LTE signals were able to pass the spectral requirements defined by the standard without applying predistortion techniques.

A miniaturized millimeter-wave substrate integrated waveguide (SIW) in IBM 130-nm digital CMOS process is presented in this paper. The footprint of the interconnect is reduced compared with previous works using the folding technique. A current-loop transition structure is proposed in this paper that is built inside the SIW interconnect and excites its TE10 mode with minimal area overhead. A simulation-based comparison of T-FSIW and other planar transmission line structures reveals that the T-FSIW interconnect shows a much higher resonant quality factor. A prototype waveguide is designed and fabricated to operate with a cutoff frequency of 175 GHz. Furthermore, the current-loop excitation is optimized for the frequency range of 180–220 GHz. Simulation and experimental data are used to confirm the proposed interconnect approach.

In this paper, we present the performance and imaging results of an integrated single-chip CMOS-microelectromechanical systems (MEMS) scanning microwave microscope (SMM). A systematic analysis for sensitivity improvement is described in detail. We first explain why it is important to have high sensitivity for this type of microscope and then propose a systematic method to analyze and design the entire structure for better sensitivity. For this, accurate lumped models are derived for each section of the system and comparisons are made between different designs. Furthermore, a new concept based on the quality factor of the individual sections is described to give the designer a tool to improve the sensitivity of individual sections without the need to simulate or model the entire system. A high-sensitivity measurement system is also explained. Finally some measurement results are presented. While the analysis presented in this paper is for CMOS-MEMS SMM, it is applicable to any type of SMM.

The effect of the output impedance of peaking power amplifier (PA) on Doherty PAs (DPAs) is analyzed in this paper. In the design procedure of DPAs, the ideal case is that the output impedance of auxiliary PA is infinite at output power back-off (OPBO) level. However, it is almost impossible to realize this perfect condition in broadband DPAs. Therefore, when the output impedance of peaking path deviates from infinity, some potential effects on DPAs must be produced. In this paper, these effects are explained at the internal plane of transistors. The conclusion is that, at different normalized frequencies, there are different optimal impedance regions for the output impedance of peaking stage. This means that the noninfinite output impedances of peaking stage can enhance the performances of broadband DPAs so long as they are elaborately processed. A 1.65–2.7-GHz (48% bandwidth) broadband DPA is designed considering the effects of peaking PA. The experimental results show that this DPA obtains a drain efficiency of 41%–59.6% at 6-dB OPBO levels and a drain efficiency of 55.8%–72.2% at saturation power levels. The maximum output power across the entire operating band is 43.1–45.2 dBm with a gain of 9.0–10.2 dB. Furthermore, the designed DPA achieves an adjacent channel leakage ratio of −45.8 dBc with an output power of 36.1 dBm at 2.0 GHz after digital predistortion when it is excited by 5-MHz WCDMA signal with a peaking-to-average power ratio of 8.6 dB.

This paper presents a new spiral inductor based on substrate integrated suspended line (SISL) technology. SISL is a new type of transmission line, which has many merits, such as low loss, low dispersion, and self-packaging. New series of spiral inductors based on this advanced SISL platform is proposed and modeled in this paper. SISL to microstrip transition is designed for the measurement of the SISL inductor, and an open-short deembedding method is introduced for the accurate extraction of inductor network parameters. A $\pi$ equivalent circuit model is applied for modeling of the SISL inductor and new double-sided SISL (DSISL) inductor, and the accurate empirical expression of inductance $L$ , peak quality factor $Q_{\mathrm {max}}$ , and self-resonance frequency are given. The typical relative error of each expression is less than 8%. Finally, a new DSISL inductor with patterned substrate is proposed, which can significantly improve the quality factor up to 40%. Simulation and measurement results show good agreement.

This paper presents a rigorous scattering model of an infinite slit on a dielectric-loaded parallel-plate waveguide with an oblique incident TEM wave. The dyadic Green’s functions of an equivalent line source are derived first and then applied to solve the scattered fields in terms of reflection, transmission, and radiation. Special treatment with PEC/PMC symmetry is employed for fast and accurate calculation. The proposed model was carefully validated by the full-wave simulator with excellent agreement. Some interesting scattering phenomena are found and emphasized, as they are crucial in explaining the special features of slit-based planar structures. In this paper, we demonstrate the presented model for the analysis and physical explanation of unique features found in a slitted substrate integrated waveguide, grounded coplanar waveguide, and grounded coplanar stripline. The proposed model provides a simple and effective approach for the design of potential slit-based planar circuits and antennas based on the presented structures in this paper.

This paper presents a new class of dual-band filters and diplexers, realized based on dual-band resonators. The proposed dual-band filter and diplexer do not require junctions and can achieve equivalent performance with fewer cavities, thus offering a significant reduction in size compared with traditional approaches. The concept is potentially applicable to most dual-band cavities and is demonstrated in this paper using elliptical and rectangular waveguide cavities. The first design is an inline structure employing elliptical cavities, whereas the second design is implemented through a unique layout that combines the use of dual-band and single-band rectangular cavities. The result is a group of highly compact dual-band filters and diplexers that offer increased Q and an improved spurious-free window. To verify the concept, an eighth-order Ku-band elliptical dual-band filter and a fourth-order Ku-band rectangular diplexer are designed, manufactured, and tested to allow comparisons with traditional designs.

The unique fingerprint spectra of volatile organic compounds for breath analysis and toxic industrial chemicals make an mm-wave (mmW)/THz gas sensor very specific and sensitive. This paper reviews and updates results of our recent work on sensor systems for gas spectroscopy based on integrated transmitter (TX) and receiver (RX), which are developed and fabricated in IHP’s $0.13~\mu \text{m}$ SiGe BiCMOS technology. In this paper, we present an mmW/THz spectroscopic system including a folded gas absorption cell of 1.9 m length between the TX and RX modules. We discuss the results and specifications of our sensor system based on integrated TX and RX. We demonstrate TXs and RXs with integrated antennas for spectroscopy at 238–252 GHz and 494–500 GHz using integer- $N$ phase-locked loops (PLLs). We present a compact system by using fractional- ${N}$ PLLs allowing frequency ramps for the TX and RX, and for TX with superimposed frequency shift keying or reference frequency modulation. In another configuration, the voltage controlled oscillators of the TX and RX local oscillator are tuned directly without PLLs by applying external voltages. Further developments of our system are aimed at realizing an even wider frequency span by switching between frequency bands, and to use a more compact gas absorption cell.