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This article presents a 0.68-THz receiver with the third-order subharmonic mixing in a 65-nm CMOS technology. In this work, a third-order subharmonic mixer based on a double-balanced topology is proposed. The spurious mixing product of the mixer is utilized to increase the IF output of the mixer, thus improving the conversion gain and noise figure of the mixer. Besides, compensating capacitors are incorporated in the double-balanced topology to alleviate the severe signal imbalance in this topology at very high frequencies caused by its layout asymmetry. With enhanced signal balance, the conversion gain, noise figure, and isolation of the third-order subharmonic mixer are improved. The receiver achieves a measured noise figure of 28.4 dB at 682 GHz, including the loss of the antenna. Among all the silicon receivers above 430 GHz, this work has the lowest noise figure. Because of the inherent wide bandwidth of the double-balanced topology, the high order of the subharmonic mixer, and the high multiplying factor of the local oscillator (LO) generation circuits, the proposed receiver with an integrated voltage-controlled oscillator obtains a measured input frequency range of 138 GHz, which is the highest among all the silicon receivers above 400 GHz.

Folded transmitarrays (FTAs)/reflectarrays (FRAs) are effective solutions to reduce antenna profiles while maintaining high-gain performance. Typical folded FTAs radiating to the front with two-thirds profile reduction only achieve single polarization due to the polarization-selective property of the employed grid polarizer. This polarizer reflects one polarization and transmits the orthogonal polarization of the incident wave. In this article, we report a novel dual-linearly polarized (DP) FTA by replacing the grid polarizer with a dual-polarization transmissive metasurface. A DP-FTA that radiates to the backside with half profile reduction (DP-FTA_I) is first proposed. A DP, wide beamwidth, short backfire antenna is designed as the source to eliminate the interference between the backside radiation and the measurement accessories such as the transceiver, feeding cable, and connector. The upper reflective perfect electric conductor (PEC) of the DP-FTA_I is replaced with a DP reflective metasurface for phase compensation, leading to a two-thirds profile reduction (DP-FTA_II). A $16\times16$ -element DP-FTA_II prototype is fabricated and experimentally validated, with an aperture efficiency of around 25% and 24.6% at 10 GHz for ${x}$ - and ${y}$ -polarizations, respectively. Beam tilting capabilities are also demonstrated using the proposed dual-polarized FTA.

This article presents a large-scale coherent terahertz (THz) source array with 144 coupled oscillator elements. A novel 2-D scalable coupling topology suitable for large array formation is proposed to enable the desired coherent oscillation mode, in which a differential patch antenna can be incorporated, radiating the third harmonic for high output frequency beyond 600 GHz without a lens. High-efficiency harmonic oscillator design and optimization method are proposed for the third harmonic generation and extraction. This design is also capable of beam steering by changing the bias voltage to establish different phase gradients across the array. Finally, the fabricated chip can radiate 9.1-dBm power and 30.8-dBm lensless effective isotropic-radiated power (EIRP) at 675 GHz. The beam is steerable from −45° to 45° in the $H$ -plane, making it the highest power silicon-based THz source and highest frequency beam-steerable chip. This chip was fabricated in a 65-nm CMOS process, occupying a $2\times1.7$ mm area. The output frequency is tunable from 643 to 689 GHz. At 675 GHz, the measured phase noise at 1-MHz offset is −90.9 dBc/Hz, and the dc-to-THz efficiency is 0.245%.

Conventional horns inevitably suffer from the phase error issue and associated design constraint of contour (e.g., the optimum criteria are typically employed) because of the embedded plane-to-cylindrical (or spherical) wavefront conversion process. These design dilemmas can be well addressed by using the leaky-wave-enabled horn (i.e., the leaky horn), which mainly exploits the intrinsic plane-wavefront characteristics of leaky-waveguides’ wedge-shaped regions. While noticing that previously reported leaky horns are subject to a narrowband nature and somewhat limited contour designability, a leaky horn class exhibiting wideband and customizable contour characteristics, which are based on a leaky grounded coplanar waveguide (GCPW), are developed in this communication. After establishing the theoretical relationship between the aperture length, flaring angle, and leakage constant of a general leaky horn and revealing several relevant design considerations, design technicalities and procedures for simultaneously realizing customizable contour and wideband radiation are systematically described for the GCPW leaky horn. For demonstration, a GCPW leaky horn example using the slow wave technique is constructed, simulated, and measured. It is verified that the proposed GCPW leaky horn has several merits like customizable contour, wide bandwidth, suppressed phase error, compact size, etc., which enable it to be a potential candidate for millimeter-wave applications.

This communication proposes a near-field millimeter-wave (mmWave) frequency-diverse sensing system based on a spoof surface plasmon polariton (SSPP) transmission line. SSPP structure features high-dispersion field distribution along the line, greatly enhancing the sensing capacity within the specified frequency band. A probe-free retrieval approach is proposed to build the measurement matrix based on a small number of designed tests instead of probing the field distribution. Such a probe-free approach does not require experimentally probing field distribution which may bring errors to the measured field due to the perturbation of probes, and hence greatly improves the accuracy of the measurement matrix and, therefore, the sensing resolution. This is especially useful at mmWave frequencies where probe perturbation is relatively strong in field measurement. As an illustrative example, we recovered a measurement matrix of 1001 spatial pixels by making only 20 tests using a known object at different known positions. The pixel resolution has reached $\lambda /100$ . And using this measurement matrix, we are able to accurately sense the position of a copper strip with a sensing error of 0.1 mm (about $\lambda /50$ ).

This communication introduces a low-profile circular-polarized (CP) filtering transmitarray antenna operating in V-band frequencies. The proposed antenna is composed of three well-designed components: the metamaterial filtering surface, reflective polarization rotator, and planar filtering illumination source. The filtering surface inherently possesses threefold functionalities: the ${y}$ -polarization to circular polarization converter with filtering capability, full-span $2\pi $ phase compensator, and reflector for ${x}$ -polarization. Different from the conventional illumination source with a 3-D horn structure, the proposed one has a planar configuration and presents excellent filtering characteristics. It is integrated with the reflective polarization rotator, which can reflect a linear-polarization incident wave with 90° polarization rotation. Thanks to the double filtering contribution made by the filtering source and filtering surface, the proposed transmitarray antenna shows excellent filtering performance. Its low profile is achieved by applying the folded propagation concept and adopting the planar feeding strategy. Featuring the merits of outstanding filtering response, stable CP radiation, easy integration, and low profile, the proposed antenna is promising for applications in high-speed millimeter-wave communications.

A differentially-fed shared aperture patch antenna with on-chip power combining and radiation function is proposed for a compact terahertz (THz) source design. The input impedance of the antenna can well match with the transistor over an extended bandwidth for high-efficiency third harmonic extraction by the proposed feeding method. A high-density parallel coupled oscillator topology is proposed to feed the antenna for realizing high area efficiency. The single patch-antenna-based source can easily feed a low-cost Teflon lens for high-EIRP radiation. A prototype is designed and fabricated in 65-nm CMOS technology with a 0.216 mm2 core area. A peak-radiated power of −3.7 dBm is measured at 600.5 GHz under 304-mW power consumption, realizing a 0.139% dc-to-THz conversion efficiency and a 1.95 mW/mm2core $^{}$ area efficiency. By adding the lens, a peak EIRP of 29.6 dBm is measured. The frequency tuning range of the source is 4.9%, from 584.8 to 614.3 GHz. At 602.2 GHz, the measured phase noise at 1-MHz offset is −75.3 dBc/Hz.

This communication presents a novel independent phase and amplitude control metasurface to achieve broadband sidelobe suppression. The metasurface is a receiver and transmitter (R/T) structure with the ability to transform incoming linearly polarized (LP) waves to circularly polarized (CP) waves. At the bottom of the R/T-based element, a modified E-shaped patch is employed to receive the co-polarized LP waves, while the top layer has a similar configuration with connected arms for generating CP waves. A metallic via connects the top and bottom patches for power transmission. The transmission phase and amplitude can be independently controlled by tuning the orientations of patches on the top and bottom layers, respectively. As proof of concept, a transmitarray antenna based on the proposed metasurface is designed and fabricated to obtain high gain and low sidelobe performance. The measured results demonstrate that the designed antenna achieves a gain of 28.1 dBic at 60 GHz with a wide 3-dB gain bandwidth of 32.2%. The proposed transmissive metasurface holds great potential in radar and future wireless communication systems.