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This article presents a $W$ -band rectenna unit that incorporates a novel CMOS switching rectifier and a print tapered slot antenna. The operation principle of the switching rectifier is analyzed. The proposed rectifier topology shows improved reliability, and it utilizes the body-diode effect (BDE) to improve power conversion efficiency (PCE). Besides, a high-gain $W$ -band antipodal linearly tapered slot antenna is implemented on PCB to improve the overall efficiency. In order to demonstrate the utility of the proposed rectenna unit for large-scale rectenna array, a $1\times 2$ (parallel) and $2\times 2$ (series-parallel) rectenna arrays in 40-nm bulk CMOS technology and PCB process have been implemented. The switching rectifier achieves a peak PCE of 45.8% at 94GHz with improved reliability. Occupying only 0.0756 mm2, the overall PCEs of the rectenna unit and the $2\times 2$ rectenna array are 25% and 23%, delivering 5.6- and 20-mW output dc power, respectively, at 90-mW/cm2 incident power density. The proposed rectifier and rectenna array achieve the highest PCE among recently reported $W$ -band rectifiers and rectenna arrays with different technologies. [ABSTRACT FROM AUTHOR]

A W‐band wide‐beam horn suitable for prime‐focus feed is described in this paper. It was designed to provide better illuminations for outer panels of larger reflector antennas and to improve performance of radio holography systems. Much effort has been spent on precise characterization of the amplitude and phase patterns of the wide beam horn which has a direct impact on the measurement accuracy of the radio holography. A far‐field measurement setup with the correction of phase errors due to cable flexing has been developed. Good beam pattern agreement has been achieved between simulation and measurement. [ABSTRACT FROM AUTHOR]

The input/output microwave circuit of a W-band gyrotron traveling-wave tube (gyro-TWT) with a predicted output pulse power of more than 300 kW and a bandwidth of about 8% is under investigation. A distinctive feature of this circuit is the transverse (relative to the axial velocity of the electrons in the gyro-TWT) extraction of the output power and its compatibility for feeding and coupling the microwaves out through one oversized barrier window. The whole circuit consists of components inside and outside the tube vacuum volume. The key elements of the inner circuit are a waveguide mode converter forming the ring-like distribution of the radiation from the incoming TE1,1 mode and a 45° inclined mirror with a hole enabling a lossless transport of the gyro-TWT electron beam to the collector. Aluminum prototypes of these components have been fabricated and cold-tested in the frequency range of 90–102 GHz. The measured 2D mode patterns and level of the cross-polarization are found to be in good agreement with the simulations. [ABSTRACT FROM AUTHOR]

In this work, a dual-mode (divide-by-2 and divide-by-3) dynamic frequency divider is presented. A tunable delay gated ring oscillator (TDGRO) topology is proposed for dual-mode operation and bandwidth extension. It uses a 130-nm gate length SiGe BiCMOS technology with the $f_{t}$ and $f_{\mathrm {max}}$ of 250 and 370 GHz, respectively. Verification shows that it works at $W$ -band from 70 to 114 GHz (47.8% bandwidth) for divide-by-2 and works at $D$ -band from 105 to 160 GHz (41.5% bandwidth) for divide-by-3. This divider can be used in integrated phase-locked loops (PLLs) at millimeter-wave frequencies. [ABSTRACT FROM AUTHOR]

The $W$ -band flat-roofed sine waveguide (SWG) slow wave circuit was designed and processed in this article. Considering the limitations on present practical fabrication level, sensitivity analysis was performed on the potential influencing factors for the performance of the flat-roofed SWG slow wave structure (SWS). As indicated by the calculation results, the gap between the SWSs and the side-wall strips could have a significant impact on the dispersion, interaction impedance, and the transmission of the entire slow wave circuit. Based on the theoretical analysis, two types of $W$ -band flat-roofed SWG slow wave circuits were fabricated and tested. The side-wall strips of the two circuits are processed with/without rounded corner. The circuit without rounded corner may cause a large gap and severe reflection. In comparison, the other one with rounded corners can make the parts fit tighter, thus minimizing the potential gap. The test results demonstrate that the $W$ -band flat-roofed SWG traveling-wave tube (TWT) possesses a voltage standing wave ratio less than 1.8, which is basically consistent with the simulation results. [ABSTRACT FROM AUTHOR]

This work presents recent progress in the W-band (94 GHz) power performance of N-polar GaN deep recess HEMTs grown on sapphire substrates. While SiC has been the substrate of choice to achieve the highest level of performance, sapphire substrates are a lower cost alternative. In this work we show that N-polar GaN deep recess HEMTs grown on sapphire match the power performance of a device on SiC up to 14 V with 5.1 W/mm of output power density. At 16 V the device on sapphire starts to suffer from thermal effects but still demonstrated 5.5 W/mm with an associated 20.6% power-added efficiency. This work also examines the impact of encapsulating the device in a low dielectric constant film often used for the implementation of a RF wiring environment. [ABSTRACT FROM AUTHOR]

This letter presents the design, performance, and analysis of four low-noise amplifier (LNA) monolithic microwave integrated circuits (MMICs) operating in ${W}$ -band. Two LNA designs were fabricated in two variations of a 20-nm gate-length metal–oxide–semiconductor high-electron-mobility transistor (MOSHEMT) technology each. While for the first technology version the heterostructure is directly grown on the final gallium arsenide (GaAs) wafer, the second version uses direct wafer bonding to transfer the III–V heterostructure after the epitaxial growth to a silicon (Si) substrate. Based on the measured noise figure (NF) of the four MMICs over a comprehensive set of bias conditions, the impact of short-channel effects on the RF performance and possible improvements are analyzed. The first LNA covers an octave bandwidth with more than 15 dB of gain and an average NF (75–105 GHz) of 3.5 dB on a Si substrate. At 80 GHz, the second amplifier exhibits minimal NFs of 2.3 and 2.5 dB on GaAs and Si substrates, respectively. Compared to previously reported MOS- or Si-based technologies, the presented LNAs demonstrate state-of-the-art noise performance emphasizing the importance of electron confinement for highly scaled transistor technologies. [ABSTRACT FROM AUTHOR]

A 77 GHz quadrature frequency multiplier-by-nine is demonstrated using the 90 nm CMOS process. The implemented multiplier-by-nine is composed of a high conversion gain quadrature frequency tripler with coupled lines as the buffer stage to reduce power consumption and increase power output. This frequency multiplier-by-nine achieves good suppression for the fundamental, second, and other harmonics. The conversion loss is â?'33 dB at 77 GHz. The DC power consumption is only 5.2 mW. The chip area is 0.46 mm². This device can help to improve the performance of high-frequency radar sensors. [ABSTRACT FROM AUTHOR]

Based on the self‐consistent nonlinear theory, a W‐band continuous wave 30 kW fundamental harmonic gyrotron oscillator is designed and simulated. With a 30.0 kV, 3.0 A electron beam, the output power of more than 35 kW is obtained and the maximum electronic efficiency is equal to 40.3%. The effects of electron beam voltage, beam current, magnetic field intensity, guiding center radius, and velocity spread on electron efficiency and output power are analyzed in detail. In addition, the images of correlative electron clustering states in the process of beam‐wave interaction are presented intuitively. [ABSTRACT FROM AUTHOR]

A W-band decoupling structure sandwiched between a pair of high-gain step-profiled horn array antennas using the silicon micromachining technology is proposed. To suppress the surface wave, 18 choke slots with a depth of one quarter wavelength at 94 GHz are arranged in a triangular-grid array and the isolation can be averagely improved by about 7 dB with a range of 2–20 dB. This decoupling structure and two W-band coplanar array antennas are fashioned and fully integrated together by the silicon micromachining technique. Five 400 μm thick and one 650 μm thick silicon wafers are utilized and the total thickness of the antennas is 2.65 mm. Thanks to this technology, light weight, compact size, and high integration of the decoupling structure and array antennas can also be achieved. Additionally, the two array antennas share a common ground plane within a small edge-to-edge spacing of 6.05 mm where TM surface waves exist. Experimental studies validate the performance of the proposed triangular-grid choke slot array. [ABSTRACT FROM AUTHOR]

This brief presents a W-band 6-bit active phase shifter fabricated in 0.13 μm SiGe BiCMOS process. A wideband quadrature signal generator composed of a 90-degree hybrid and a pair of transformers is exploited for low insertion loss and superior balance. Conventional architecture used in gain control unit is replaced by a novel phase inverter-embedded variable gain amplifier to achieve a high gain and low complexity. In addition, a balun-first combiner with symmetrical layout is utilized at the output to keep as low the imbalance of I/Q paths as possible. The proposed phase shifter exhibits a record average gain of 7 dB at 79 GHz with a 3-dB bandwidth from 71.5 to 84.5 GHz. The variation of gain remains below 2.1 dB over 64 phase states. The measured RMS phase error is 1.35° at 78 GHz and remains below 3.5° from 72 to 82 GHz. The RMS gain error is measured to be 0.46 dB at 75 GHz and keeps less than 0.76 dB from 71 to 82 GHz. The measured input 1dB compression point amounts to −10 dBm. To the best of the author’s knowledge, this brief presents the lowest RMS phase error (1.35°) and the highest gain (7 dB) compared with the reported silicon-based W-band active phase shifters. [ABSTRACT FROM AUTHOR]

Two low-noise amplifiers fabricated with 100-nm gate length gallium nitride (GaN)-on-silicon process in $W$ -band are presented in this work. One has a gain of 17.5–20.5 dB in 77.5–84 GHz with 3.8–4.7-dB noise figure (NF), the other has wider bandwidth of 78.5–90 GHz with 14.5–17-dB gain and 4.5–5.2-dB NF. The chip sizes of these two low-noise amplifiers (LNAs) are $3\times 1.6$ mm2 and $3\times 1.4$ mm2 separately. The power dissipation of these two LNAs is about 190 mW. These LNAs can be integrated with high-power GaN power amplifier on the same chip, which avoids the peripheral packaging loss and achieves smaller module size. The universal gate length in commercial process with low-cost silicon substrate brings these LNAs great potential for mass production in future millimeter-wave communications. [ABSTRACT FROM AUTHOR]

In this article, the design, characterization, and manufacture of a circuit for a ${W}$ -band, ultracompact continuous wave sheet beam klystron are described. This klystron, aiming to produce more than 1.5-kW output power, operates at a comparatively low voltage benefiting the device size and extending its application space. However, a lower operation voltage adversely affects the beam-gap interaction efficiency. Two multigap output cavities have been employed to achieve a higher beam interaction efficiency without introducing additional competing modes or shrinking the interval between the operation mode and competing mode. Inspired by the resynchronization technology, the second output cavity can be optimized for the spent beam from the first output cavity. Comprising a single cavity output structure, the circuit efficiency of this double output cavity circuit is increased from 2.37% to 4.96%. In this circuit, electromagnetic modeling and design have been optimized to avoid complicated structures which are constrained by current mechanical design and manufacturing techniques. The MAGIC simulation shows that, driven by a 1-W RF signal, this circuit can extract more than 1.7-kW output power from a 35-kV, 1-A beam. A prototype single output cavity circuit has been designed and manufactured to determine the required machining tolerances for the final double output cavity circuit. [ABSTRACT FROM AUTHOR]

A ${W}$ -band large-scale substrate-integrated waveguide (SIW) cavity-backed slot array for high-gain applications is presented in this communication. The proposed antenna consists of a compact 16-way power divider and a $32\times33$ slot array. The 16-way power divider at the bottom-layer PCB provides equal-amplitude and alternative-phase excitation for 32 SIWs on the top layer PCB, and each of them supports 33 radiation slots. The loss along with the complexity of the feeding network is reduced by the implementation of alternative-phase excitation. To demonstrate the proposed slot array, a $4\times 33$ slot array excited by a two-way power divider is designed first. Then, the $4\times33$ slot array is extended to a $32\times33$ slot array by a 16-way power divider. To verify the proposed slot array, the designed array is fabricated and measured. The measured peak gain, radiation, and aperture efficiencies are 30.88 dBi, 42%, and 22.8% at 93.2 GHz, respectively. The proposed high-gain antenna is an excellent candidate for the high-frequency millimeter-wave (mm-wave) wireless system. [ABSTRACT FROM AUTHOR]

A turnstile junction orthomode transducer (OMT) provides polarization separation/combining on a full waveguide bandwidth; however, it bears a complex connecting structure, which accordingly leads to a bulky volume. We present a compact W-band (75–110 GHz) OMT using a “swan neck” twist for the connection between a turnstile junction and an $E$ -plane Y-junction, for minimizing the overall OMT structure. The core volume for the proposed OMT is $9\times $ less than the previously reported stacked-layer OMT. The compact W-band OMT was built by digital light processing (DLP) 3-D printing technology and was postmetallized by silver electroless plating. The return loss of the vertical-polarized port (V-port) and the horizontal-polarized port (H-port) is characterized, as averagely 17 and 15 dB, respectively. The measured average insertion loss from H- and V-ports to the common port is 0.5 and 0.6 dB. The measured isolation between V- and H-ports is averagely 28 dB. Furthermore, the turnstile junction asymmetry along the central axis was revealed in computed tomography (CT) scanned images. The simulation shows a negative effect of the asymmetric structure on the OMT isolation. In addition, the dual-polarized (dual-pol) antenna combining such OMT and a corrugated horn was realized in a compact size. The cross-polarization level of the OMT, characterized in a far-field test of this dual-pol antenna, is averagely −18 dB at the W-band. [ABSTRACT FROM AUTHOR]

The folded waveguide (FWG) traveling wave tube (TWT) developed in the frame of the Horizon 2020 TWEETHER project for enabling a novel W-band (92–95 GHz) high capacity wireless network for 5G is presented. The FWG TWT was designed by particle-in-cell (PIC) simulations. The technology and the results in terms of measured RF losses and beam transmission from the realized beam tester are presented. Amplification on the first TWT breadboard has been observed but with a poor multireflection pattern resulting from spurious burrs inside the FWG. It indicates, however, that the FWG technology offers great manufacturing simplification compared to conventional helix TWTs, thus enabling a low-cost device with large series production suitable for the wide market of wireless communications. [ABSTRACT FROM AUTHOR]

A W-band multiple-input multiple-output (MIMO) radar imaging system has been proposed. The $4 \times 4$ radar system that forms a 2-D virtual array operates at a center frequency of 94 GHz and bandwidth of 1 GHz with frequency-modulated continuous wave. A hybrid scheme comprising time- and frequency-division multiplexing is introduced for establishing orthogonal waveforms, where the transmit channels perform alternate transmission in pairs. The proposed scheme can efficiently extend the number of MIMO channels utilizing the existing hardware with simultaneous transmission. The design, implementation, measurements, and imaging results of the proposed radar system have been presented. The imaging performance was tested through outdoor experiments. The high-resolution performance was shown with images generated using a synthetic aperture radar. The impulse responses of all channels were measured, and the resolution was confirmed to be 0.15 m in all the channels. In addition, a human and a car at 100-m range were imaged using the proposed radar system. The polarimetric and interferometric capabilities were tested for multimode imaging with the MIMO configuration. Overall, the measurements and experimental results verified the feasibility of the proposed MIMO radar with hybrid scheme as a high-resolution multimode imaging system. [ABSTRACT FROM AUTHOR]

In this article, a $W$ -band gyrotron traveling wave tube (gyro-TWT) amplifier that uses periodically dielectric-loaded (PDL) waveguide and operates in TE01 mode is designed and studied for its stability against backward wave oscillations and beam wave interaction behavior. The subassemblies including a magnetron injection gun using E-GUN code, RF output window, and electron collector using “MAGIC 3-D” are investigated. The present particle-in-cell (PIC) simulation of millimeter-wave gyro-TWT results in a peak RF power ~195 kW in TE01 mode with an electronic efficiency of ~28% and a saturated gain of ~63 dB. Further, the overall efficiency of the device is enhanced by using a three-stage depressed collector, which is designed and simulated using “MAGIC 3-D. ” The collection efficiency of the present collector is calculated as ~74% and the overall efficiency of the gyro-TWT is improved to ~60%. [ABSTRACT FROM AUTHOR]

Two W-band CMOS elliptical baluns (i.e. balun-1 and balun-2) for 94 GHz image radar, and one miniature Ka-band CMOS square balun (i.e. balun-3) with short-terminal and input capacitor (for elimination of the inductive imaginary part of the input impedance at the input port) for 28 GHz 5G communication system are demonstrated. These baluns are applicable to a down-conversion mixer for conversion of the single RF and LO input signals to differential signals. They are also applicable to a phase shifter for conversion of the single I and Q signals (from the quadrature coupler) to differential I (i.e. I + and I −) and Q (i.e. Q + and Q −) signals. Instead of the traditional balun structure that uses three sections of thin M5 (or M8) interconnection lines (underneath the thick top M6 (or top M9) main structure), the proposed balun structures use only one section of thin M5 (or M8) interconnection line to enhance S21 and S31. Balun-2 (with M9 main structure thickness of 3.4 μm) attains S21 of − 4.98 to − 4.57 dB, S31 of − 4.85 to − 4.59 dB, amplitude imbalance magnitude (AIM) smaller than 0.15 dB and phase difference deviation (PDD) smaller than 4° for 90–100 GHz. Balun-3 (with M6 main structure thickness of 2.34 μm) occupies a small chip area of 0.042 mm2, and achieves S21 of − 4.97 to − 4.44 dB, S31 of − 4.68 to − 4.29 dB, AIM smaller than 0.28 dB and PDD smaller than 2.3° for 27–29 GHz. The prominent results of these baluns indicate that they are suitable for W-band and Ka-band systems. [ABSTRACT FROM AUTHOR]

In this letter, a 75.1–151.4-GHz silicon power amplifier (PA) is devised with the help of sandwiched slab transformer, which is proposed to increase the tuning ranges of coupling coefficient, quality factor, and conductivity. Being compact in size and simple in implementation enables it to be well-applied in multiple-way power combination. Based on this device, the fabricated PA in the 130-nm silicon germanium (SiGe) process demonstrates more than 14.1-dB gain at full $W$ -band and 77% of the $D$ -band. From 75 to 117.7 GHz, its measured $P_{\mathrm {sat}}$ is all above 16.8 dBm, while its peak point is 19.8 dBm at 100 GHz with 8.8% PAE. [ABSTRACT FROM AUTHOR]

A w-band electronic focus-scanning function, which is desired for high-resolution fast-speed millimeterwave imaging systems, is realized by a reconfigurable transmitarray antenna (RTA). As a two-layer structure, each RTA element is integrated with two packaged PIN diodes symmetrically within a limited area (1.6×1.6mm2). When a linearly polarized electromagnetic wave incidents on this reconfigurable element, an orthogonally polarized transmission wave is generated, with the ability of 1-bit phase adjustment (0°/180°). Using this element, a 32×2 reconfigurable transmitarray is designed and fabricated to realize 1-D steerable focal points in a near-distance focal plane. The measured focal points agree well with the design, illustrating the feasibility of the proposed RTA for w-band microwave imaging systems. [ABSTRACT FROM AUTHOR]

This article presents a two-channel 70–110-GHz frequency quadrupler in the GF8HP 0.12- $\mu \text{m}$ SiGe BiCMOS process. The $\times 4$ frequency multiplication is based on cascaded frequency doublers with an interstage bandpass filter to reject undesired harmonics. The measured peak output power is −1.5 to 3 dBm at 70–110 GHz, with a worst case harmonic rejection ratio (HRR) of >30 dBc. The chip size is 1.9 mm2 and consumes 240 mW for the two-channel operation. To the best of our knowledge, this article represents state-of-the-art in terms of bandwidth, output power, and excellent HRR. Application areas include mm-wave multi-channel, mm-wave network analyzers, and wideband sources for radar and imaging systems and reconfigurable E-band radios. [ABSTRACT FROM AUTHOR]

This paper presents a 100‐GHz phase shifter capable of providing full 360° continuous phase tuning range in 55 nm CMOS technology. The phase shifter is based on reflection‐type phase shifter (RTPS), which has more than 180° phase shift and employs a 0°/180° phase inverter (PI). The amplitude difference between 0°/180° modes of the PI is less than 0.5 dB while the phase imbalance is less than 1° at 90‐100 GHz. The measured insertion loss of the proposed phase shifter for all phase states is 6.1‐10.2 dB at 95 GHz. The chip of our proposed phase shifter occupies an area of 710 × 510 μm2, and the DC power consumption is 20 mW. [ABSTRACT FROM AUTHOR]

Experimental details are discussed and millimeter wave measurements presented of a W-band gyrotron traveling-wave tube (gyro-TWT) that uses a helically corrugated interaction waveguide operating at the second electron cyclotron harmonic. A method for increasing the gain by using an interaction circuit with two sections separated by a long sub-cutoff drift section has been experimentally verified. A 10-mW driving source was sufficient to enable an amplified signal output power of 3 kWs. The continuous-wave (CW) operation with a single-stage depressed collector and deposited beam power of about 20 kW is believed to be the first demonstration of its kind for a W-band gyro-TWT. [ABSTRACT FROM AUTHOR]

A compact ${W}$ -band divide-by-three injection-locked frequency divider (ILFD) is presented in 65-nm CMOS technology. To provide a wide locking range, we propose inductive feedback to boost the injection current. With the proposed approach, the locking range of the ILFD can be wider than 10% without any varactor and additional power dissipation which is more than three times the locking range compared with the reference ILFD without boosting of the current injection. The measured locking range of the proposed ILFD was from 73.9 to 82.5 GHz with the ${W}$ -band input signal power of 0 dBm, and the phase noise at 1 MHz was −117.13 dBc/Hz at the input frequency of 78 GHz. The implemented ILFD with the inductive feedback consumes 7.88 mW under a 1 V supply, and its core size is 0.22 mm2. [ABSTRACT FROM AUTHOR]

We describe the development of a W-band lumped element kinetic inductance detector array for application in large ground-based telescopes, like the Sardinia radio telescope. Based on the previous studies, we use a Ti/Al bi-layer film (10 nm thick Ti + 25 nm thick Al) for the resonators, to cover frequencies greater than 65 GHz. Optical simulations have been performed using ANSYS HFSS software suite, to optimize the absorber geometry, the illumination configuration, and the thickness of the dielectric substrate. Simulations suggest that the best geometry of the absorber is a front-illuminated third-order Hilbert curve, with a Si substrate 235 μ m thick, coupled to a single-mode circular waveguide. Electrical simulations have been performed using SONNET, to complete the design of the detectors by choosing the size of the capacitor, the bias coupling, and the feedline. In addition, the electrical simulations allow us to verify the lumped condition, to tune the feedline impedance and resonant frequencies, to constrain the coupling quality factor, and to minimize the electrical cross-talk between different pixels of the same array. [ABSTRACT FROM AUTHOR]

Second harmonic W-band gyrotron with room-temperature solenoid experimental results is presented. The solenoid consumes a power of ~15 kW with a cooling water flow rate of 15 L/min and an inlet water temperature of 25 °C. The gyrotron interaction mode is TE02, and with the use of Vlasov mode converter, the output mode is Gaussian-like mode. The gyrotron produces 33-kW output power in short pulses with an efficiency of 23%, and in long pulses 10 kW with an efficiency of 14% (power supply limited). The gyrotron was successfully tested for pulse duration over than 10 s. [ABSTRACT FROM AUTHOR]

A conceptual design and the results of concrete simulations of the output microwave system of a W-band gyrotron traveling-wave tube (gyro-TWT) with a predicted output pulse power of more than 300 kW are presented. A distinctive feature of this system is the transverse (relative to the translational velocity of the electrons in the gyro-TWT) extraction of the output power. The designed microwave circuit includes a waveguide mode converter and a set of quasi-optical mirrors. An oversized hole in the first 45° inclined mirror enables a lossless transport of the electron beam to the collector. The ring-like distribution of microwave radiation on the mirror is formed by a profiled waveguide mode converter and provides minimal radiation diffraction loss. For the synthesis of the mode converter, particle swarm optimization (PSO) method was used. The system of external quasi-optical mirrors provides the transformation of the ring-like beam into the HE1,1 mode of a corrugated waveguide with an efficiency of more than 94% in the frequency range 92–98 GHz. The mirror profiles were synthesized using the Katsenelenbaum–Semenov iterative procedure. [ABSTRACT FROM AUTHOR]

A serpentine-folded waveguide traveling-wave tube (FWTWT) in W -band was fabricated using chemical machining to pattern 200-μm-thick copper sheets. These were stacked together inside a jig to form the final device. The challenge in realizing a beam hole for electron beam/wave interaction at millimeter wavelengths was addressed by incorporating a circular beam hole realized using stepped chemical machining. The surface characteristics were improved using chemical polishing. This surface was characterized using a scanning electron microscope images and surface roughness measurements. To improve the conductivity further, gold plating with a thickness of 1–2 μm was applied. The fabricated circuit was tested and the cold-test parameters were found to be satisfactory. [ABSTRACT FROM AUTHOR]

Airborne applications demand exceptional overall radar system performance and eminently high output power for high range target detection. The frequency modulated continuous wave (FMCW) radar system presented in this article is capable of achieving this task due to its high output power at 94-GHz center frequency with over 26-GHz tuning range. Nevertheless, the radar still provides a small form factor and low power consumption of 4.25 W at 5 V single Universal Serial Bus (USB) supply. The key system component is a Silicon Germanium (SiGe) bipolar complementary metal-oxide-semiconductor (BiCMOS) monolithic microwave integrated circuit (MMIC) that contains a 94-GHz voltage-controlled oscillator (VCO), and a 27-GHz VCO for dual-loop phase-locked loop (PLL) stabilization, a power amplifier (PA), and two receive mixers. It generates frequency ramps between 83- and 109-GHz with a maximum output power of 19.7 dBm at its output after the bond wires on the printed circuit board (PCB) and 14.8-dBm output power at the radar’s transmit (TX)-waveguide WR-10-flange. The sensor was also tested in a temperature range from −40 °C to +70 °C with menial deviation. Thus, the system offers high system dynamic range and far distance target detection range. Following a detailed system description, we finally present the FMCW range and Doppler measurements performed with the presented radar sensor as well as the application on unmanned aerial vehicles (UAVs) for flight altitude control and as airborne collision avoidance system (ACAS). [ABSTRACT FROM AUTHOR]

This article presents the design and fabrication of low-loss, -weight, and -cost, modified Butler matrix in groove gap waveguide technology at W-band, implemented by additive manufacturing. The design, simulations, and measurements of each of the elements that conform to the modified Butler matrix are presented. The proposed modified Butler matrix is asymmetric and oriented to an easy assembly with a radial antenna in order to obtain simultaneous sum and difference patterns for a narrowband radar application. The measured individual components of the modified Butler matrix fit very well with the simulations. As for the full modified Butler matrix, measurements provide a 0.7% bandwidth below −20 dB for sum and difference ports centered at 94 GHz. The amplitude and phase imbalance are below 1.5 dB and 20°, respectively. This narrow bandwidth is due to the difference in length between input and output ports due to the asymmetry of the design. The total losses of the modified Butler matrix are below 1 dB. [ABSTRACT FROM AUTHOR]

This letter reports on the improvement of the large-signal W-band power performance of nitrogen-polar gallium nitride deep recess high electron mobility transistors with the addition of a 40-nm-thick ex-situ silicon nitride passivation layer deposited by plasma enhanced chemical vapor deposition. The additional passivation improves the dispersion control allowing the device to be operated at higher voltages. Continuous-wave load pull measurements performed at 94 GHz on a $2\times 37.5\,\,\mu \text{m}$ transistor demonstrated an improvement in the peak power-added efficiency (PAE) to 30.2% with an associated output power density of 7.2 W/mm at 20 V drain bias. Furthermore, at 23 V, a new record-high W-band power density of 8.84 W/mm (663 mW) was achieved with an associated PAE of 27.0%. [ABSTRACT FROM AUTHOR]

A design of a modular antenna/detector array for the electron cyclotron emission (ECE) imaging system at the Korea Superconducting Tokamak Advanced Research (KSTAR) is proposed. The modular antenna/detector array is based on a unit antenna/detector module, which consists of an elliptical mini-lens, a dual-dipole antenna, an antenna balun, a low-noise amplifier, and a metal frame. The proposed modular antenna/detector array resolves the problem in the conventional antenna/detector array where one faulty channel requires the entire array to be removed for the service. With the proposed modular array, each channel module can be easily and independently removed and replaced without interference to the rest of the array, thus minimizing the interrupted service time for maintenance. Moreover, the unit channel modules can be efficiently updated under a variety of the tokamak operation conditions. The antenna/detector modules are optimized to have improved performance, and are tested in a W-band test setup, and consistently provide the gain increase by 10~20 dB as compared with the conventional antenna/detector array. A set of the proposed modular antenna/detector array is currently installed and tested in the KSTAR ECE imaging system, and will consistently produce the improved ECE imaging to monitor MHD instability activities under various plasma operation conditions.

We experimentally demonstrate a frequency-diverse, computational imaging system at W-band frequencies utilizing an array of cavity-fed metasurface antennas. Each metasurface antenna consists of a cavity milled from aluminum stock, with an upper plate patterned with a set of radiating slots. As a function of frequency, the metasurface cavities produce a set of spatially diverse radiation patterns that probe the reflectivity distribution of a scene. The antennas are designed to maximize the measurement diversity and hence imaging capacity of the system. The number and distribution of the radiating slots is optimized by balancing the cavity quality factor (Q) and Fourier space coverage. In the experimental realizations, the radiation patterns from each cavity-fed metasurface antenna is first measured using near-field scanning techniques, propagated over the imaging domain, and then stored for use in the image reconstruction step. Comprehensive alignment procedure is implemented to align the measured radiation patterns with regard to the physical position of the cavities. Using a modeling platform, we find excellent agreement between the simulation and experiment, indicating the validity of the calibration and alignment procedures. The scaling of the cavity-fed metasurface antenna represents a key step in the development of alternative high-frequency apertures for imaging and beam-forming applications.

The development of novel high-gradient accelerating structures operating at THz frequencies is critical for future free-electron lasers and TeV scale linear colliders. To reach high energies with reasonable length requires high accelerating gradients of ~100 MV/m. The main limitation to reaching these high-energy gradients is the vacuum RF breakdown phenomenon, which disrupts normal accelerator operations. For stable operations and to understand the breakdown microscopic dynamics, a new device capable of detecting the breakdown occurrences is required. In this paper, we provide the design of a pulse length monitor based on an analog to digital converter for fast signal digitization without the need to use high-speed digitizers to be used in a commercial mm-wave heterodyne spectrometer.

Terrestrial Radar Interferometry (TRI) is a measurement technique capable of measuring displacements with high temporal resolution at high accuracy. Current implementations of TRI use large and/or movable antennas for generating two-dimensional displacement maps. Multiple Input Multiple Output Synthetic Aperture Radar (MIMO-SAR) systems are an emerging alternative. As they have no moving parts, they are more easily deployable and cost-effective. These features suggest the potential usage of MIMO-SAR interferometry for structural health monitoring (SHM) supplementing classical geodetic and mechanical measurement systems. The effects impacting the performance of MIMO-SAR systems are, however, not yet sufficiently well understood for practical applications. In this paper, we present an experimental investigation of a MIMO-SAR system originally devised for automotive sensing, and assess its capabilities for deformation monitoring. The acquisitions generated for these investigations feature a 180∘ Field-of-View (FOV), distances of up to 60 m and a temporal sampling rate of up to 400 Hz. Experiments include static and dynamic setups carried out in a lab-environment and under more challenging meteorological conditions featuring sunshine, fog, and cloud-cover. The experiments highlight the capabilities and limitations of the radar, while allowing quantification of the measurement uncertainties, whose sources and impacts we discuss. We demonstrate that, under sufficiently stable meteorological conditions with humidity variations smaller than 1%, displacements as low as 25 μm can be detected reliably. Detecting displacements occurring over longer time frames is limited by the uncertainty induced by changes in the refractive index.

In this paper, a high-power amplifier integrated circuit (IC) in gallium-nitride (GaN) on silicon (Si) technology is presented at a W-band (75–110 GHz). In order to mitigate the losses caused by relatively high loss tangent of Si substrate compared to silicon carbide (SiC), low-impedance microstrip lines (20–30 Ω) are adopted in the impedance matching networks. They allow for the impedance transformation between 50 Ω and very low impedances of the wide-gate transistors used for high power generation. Each stage is matched to produce enough power to drive the next stage. A Lange coupler is employed to combine two three-stage common source amplifiers, providing high output power and good input/output return loss. The designed power amplifier IC was fabricated in the commercially available 60 nm GaN-on-Si high electron mobility transistor (HEMT) foundry. From on-wafer probe measurements, it exhibits the output power higher than 26.5 dBm and power added efficiency (PAE) higher than 8.5% from 88 to 93 GHz with a large-signal gain > 10.5 dB. Peak output power is measured to be 28.9 dBm with a PAE of 13.3% and a gain of 9.9 dB at 90 GHz, which corresponds to the power density of 1.94 W/mm. To the best of the authors’ knowledge, this result belongs to the highest output power and power density among the reported power amplifier ICs in GaN-on-Si HEMT technologies operating at the W-band.

A wideband multi-polarized square-horn antenna based on an orthogonal mode transducer (OMT) is developed for working in the whole W-band in this paper. The designed antenna is capable of radiating multiple polarization modes as horizontal polarization (HP) and vertical polarization (VP) when as single-port excitation and left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) when as dual-port excitation, owing to the characteristic of the OMT with the transmitting of orthogonally polarized waves. A CNC-layered fabrication approach is proposed, which means that the antenna prototype integrating with a Boifot-type OMT, turning waveguide, twisting waveguide and phase shifter is divided into three layers along the vertical direction to be fabricated based on computerized numerical control (CNC) technology. In the design, the turning waveguide and twisting waveguide are employed to achieve plane consistency of the antenna branch ports. Furthermore, a phase shifter is designed to compensate the orthogonally polarized waves, which can keep the phase of the orthogonally polarized waves consistent in a wideband frequency range from 75 GHz to 110 GHz. A prototype is fabricated and measured to verify the performance of the proposed multi-polarization antenna, and the measured results agree well with the simulation ones. In the whole W-band, the value of return loss is better than 10 dB of all polarization modes, and the value of AR of the LHCP and RHCP is below 3.5 dB. The maximum gain of the antenna reaches up to 18.8 dBi at 110 GHz. In addition, regarding the layered structure, the possible layered assembly error analysis is discussed, which verifies the feasibility of the layered machining for this antenna.

A 94-GHz highly efficient frequency octupler ($\times 8$) is presented, which consists of a 47-GHz frequency quadrupler followed by a 94-GHz push–push frequency doubler. To achieve high efficiency, the former adopts the current reusing technique of which transistors are biased to be in the class-C region. In addition, the core transistors and the input-matching network of the latter are optimized simultaneously by using a premade input matching network library, which yields a maximum conversion gain under a given dc power budget. It is implemented with a commercial 65-nm CMOS process, which generates −7.12-dBm output power with 0-dBm input signal, consuming only 1 mW of dc power. It operates in the frequency range from 84 to 98.4 GHz (15.3%) within 3-dB gain variation. The total efficiency ($P_{\text {OUT}}/(P_{\text {dc}} + P_{\text {IN}})$) is 9.69%, which is the highest among those of reported frequency octuplers. [ABSTRACT FROM AUTHOR]

We present a $W$ -band four-stage power amplifier (PA) in a 65-nm CMOS using a push–pull configuration with inductive feedback neutralization which achieves the highest figure of merit (FOM) compared to the recently reported CMOS PAs. The device was gradually tapered from the output to the input stage to optimize the power-added efficiency (PAE) while achieving high power gain with compact impedance matching with a transformer (TF). Interstage conjugate matching was also carried out with a TF to design a compact high-gain PA. Working under a supply voltage of 1.2 V, the proposed PA achieves a power gain of 28.2 dB with the 3-dB gain bandwidth of 7 GHz (76.8–83.8 GHz), a saturated output power of 16.3 dBm, and a peak PAE of 14.1% at 81.6 GHz with power dissipation of 234 mW. The total chip size is 0.714 mm2, and the core size excluding pads is only 0.121 mm2. [ABSTRACT FROM AUTHOR]

This letter presents the design and performance of two single-pole double-throw (SPDT) switches operating in $V$ -band (50–75 GHz) and $W$ -band (75–110 GHz). The millimeter-wave (mmW) integrated circuits (MMICs) are fabricated in a 50-nm gate-length metamorphic high-electron-mobility transistor technology. Special attention was paid to the reduction of the insertion loss (IL). Thus, both switch MMICs achieve an IL of 1–1.6 dB (average 1.2 dB), covering the entire $V$ -band and $W$ -band, respectively. The isolation (ISO) of the switches is better than 31.6 and 28.5 dB, respectively. The input power for 1 dB of IL compression is at least 22 and 19 dBm, respectively. A wafer mapping of both circuits exhibits a high yield and low spread of IL and ISO. Based on the given results, the presented SPDT switch MMICs demonstrates state-of-the-art performance. [ABSTRACT FROM AUTHOR]

This article proposes the concept of millimeter-wave (mm-wave) switching rectifiers originated from drain-pumped mixers. The topology and circuit design methodology are distinctly different from other CMOS mm-wave rectifiers which adopt voltage multiplier techniques. Operation principle and RF-to-dc power conversion efficiency (PCE) of the proposed switching rectifiers are analyzed to overcome the fundamental limits on achievable performance of switching rectifiers at mm wave. In order to demonstrate the utility of the proposed concept, two prototypes in 65-nm bulk CMOS technology have been implemented: two fully integrated switching rectifiers operating at Ka-band and W-band. A peak PCE of 36.5% at 35 GHz with a load resistance of $50~\Omega $ at about 15-dBm input power is measured for the Ka-band rectifier. Measurement results for the W-band rectifier also indicate that the PCE peaks at 27% at 91 GHz for a load resistance of $43~\Omega $ at about 16-dBm input power. To the best of our knowledge, the two fully integrated rectifiers which occupy the smallest chip area exhibit a competitive PCE reported among Ka-band and W-band CMOS rectifiers, competing well with GaAs counterparts where the Schottky diode is available. [ABSTRACT FROM AUTHOR]

We demonstrate a W-band down-conversion micromixer for imaging and gesture recognition transceiver. Micromixer-based gain-boosted technique, i.e. inductive-peaking gain-boosted single-to- differential transconductance (gm) stage, is adopted to increase the output impedance and restrain the feedback capacitance Cgd of the gm stage. This leads to the conversion gain (CG), noise figure (NF) and LO-to-RF leakage of the micromixer being significantly improved. The micromixer dissipates 7.2 mW and attains marvellous RF-port return loss of −12.7~ −14.7 dB for 85 ~ 110 GHz. That is, the −10 dB matching bandwidth is wider than 25 GHz. Moreover, for 90 ~ 96 GHz, the micromixer attains CG of 10.5 ~ 12 dB and LO-to-RF isolation of 40.2 ~ 46.2 dB, one of the highest values ever demonstrated for a W-band mixer/micromixer. The 3 dB CG bandwidth is 22 GHz (83 ~ 105 GHz), and the input third-order intercept point (IIP3) is 1 dBm. These results indicate the micromixer is appropriate for W-band imaging and gesture recognition transceivers. [ABSTRACT FROM AUTHOR]

A $4\times4$ high-gain substrate integrated cavity (SIC) antenna array using multilayered low-temperature cofired ceramic (LTCC) technology is proposed and designed for $W$ -band applications. The TM211 mode of the SIC is utilized. Two parasitic patches are introduced on the top surface of the SIC to adjust the aperture electromagnetic field distribution of the TM211 mode in the cavity for obtaining a high-gain broadside radiation pattern. A bow tie shape is adopted for the parasitic patches to improve the matching characteristic of the SIC. The SIC is modified to a stepped flared shape to improve the gain characteristic of the antenna element. Subsequently, a two-layer low-loss substrate integrated waveguide (SIW) feeding network is designed for the $4\times4$ antenna array on the basis of the proposed high-gain SIC radiating element. The proposed antenna array shows a wide measured bandwidth of 17.48% from 81.45 to 97.05 GHz at $\vert \textrm {S}_{11} \vert < -10$ dB and a measured gain of up to 20.3 dBi. [ABSTRACT FROM AUTHOR]

A 94-GHz dual-polarization low-sidelobelevel slot array antenna is proposed. A 2x2-slot cavitybacked subarray is adopted as the basic unit of the array. A high-isolation orthogonal-mode transducer (OMT) with a simple structure is used to excite the dualpolarization subarray. The realization of a low sidelobe level depends on the amplitude-weighted waveguide feed network. A novel unequal power dividing ratio but equal phase (UPEP) single-ridged waveguide divider is presented for the construction of the vertical polarization (VP) array feed network. A 16x16-slot low-sidelobelevel dual-polarization array antenna is fabricated. The machining difficulties of the W-band array are reduced by using simpler structures. The measured results show that the impedance bandwidth is greater than 7.3 GHz, while the first sidelobe levels are lower than -20.1 dB for both polarization arrays within the operating bandwidth. The measured gain is higher than 30.9 dBi for the two polarization arrays with an antenna efficiency better than 64%. [ABSTRACT FROM AUTHOR]