An $E$ -band air-filled rectangular waveguide (RWG) to single thin-layer (0.127 mm) substrate integrated waveguide (SIW) transition is proposed for automotive radar applications. The compact transition structure is realized using a symmetric narrow aperture coupled comb patches. With the mutual coupling effect between patches, a bandwidth greater than 22% for $|S_{11}| < -15$ dB is achieved. A back-to-back prototype is fabricated and measured. The results show that the insertion loss of a single transition is less than 0.5 dB within 71–86 GHz, which covers the whole attractive frequency range for automotive radar. With broadband and compact size, the proposed transition presents potential for automotive radar.

In this article, we report an antenna-coupled AlGaN/GaN high-electron-mobility transistor integrated on a hyper-hemispheric silicon lens for heterodyne detection in a 340 GHz band at room temperature. The responsivity, elevated shot noise, flicker noise, and dynamic source-drain resistance for homodyne and heterodyne detection are characterized and analyzed at different local terahertz (LO) power levels. With a LO power of only −3.9 dBm, the detector offers a conversion loss less than 28 dB and a noise-equivalent power (NEP) about −132 dBm/Hz. A threshold LO power about −5 dBm is identified above which the shot noise becomes the dominant noise source, and the intermediate-frequency response is strongly suppressed. The elevated noise and the saturation in responsivity are found to be closely related to the strong direct-current homodyne current and the charge modulation/accumulation by the LO signal. Possible solutions are discussed to further reduce the NEP and the conversion loss.

A wide-band and high-efficiency planar antenna array with a novel hybrid-feed structure is proposed in this article. By combing the coaxial-line feed magneto-electric (ME) dipoles with the aperture coupled dielectric cavity, a hybrid-feed 2 × 2-unit ME-dipole sub-array is invented. The low-loss ridge gap waveguide (RGWG) corporate-feed network is used to replace the high-loss substrate-based feed networks and high-cost RWG feed networks. New forms of RGWG H-plane divider are designed to build the RGWG feed network. An 8 × 8-unit ME-dipole antenna array is designed and fabricated to verify the validity of the array. The radiation part consists of two layers of a low-cost printed circuit board (PCB), and the feeding part consists of two copper plates manufactured by computer numerical control (CNC) milling. Measured results show that a relative bandwidth of 16.4% with |S₁₁| < −10 dB is achieved, with a maximum radiation efficiency of 85%. The stable symmetric radiation patterns are observed in both the E-plane and H-plane, covering the operation band. Based on the measured results, a 16 × 16-unit ME-dipole antenna array is simulated. Results indicate that the proposed array has wide-band and high-efficiency features, which is suitable for large-scale array design in mm-wave wireless systems.

This letter presents a vertically polarized omnidirectional antenna designed for operation within the 50-75 GHz (V-band) frequency range. The compact antenna structure and wide working bandwidth are achieved through the use of a radial waveguide radiator and an axial intermediate converter. The measured results from the manufactured prototype agree well with the simulated data in terms of radiation pattern and return loss. The antenna exhibits a 3 dB beamwidth in the elevation direction exceeding 30 $^\circ$ and a return loss greater than 10 dB across the working band. Owing to its wide bandwidth and omnidirectional radiation performance, the proposed antenna emerges as a promising candidate for indoor wireless communication system.

We report a room-temperature, low output impedance, broad intermediate-frequency (IF) bandwidth field-effect terahertz detector based on an AlGaN/GaN high-electron-mobility transistor (HEMT) integrated in a metal waveguide. The waveguide detector equips a pair of quasi-Yagi antenna probes that are used to couple the terahertz energy to the HEMT channel. The gate is configured as an asymmetric edge-coupled coplanar waveguide transmission line. This terahertz electric field is asymmetrically distributed in the channel along the edges of the transmission lines. The responsivity and noise for direct and heterodyne detections are characterized and analyzed at different local oscillator (LO) powers. The noise-equivalent power in direct detection is below 189 pW/${\text{Hz}}^{1/2}$ . Operated in a heterodyne mode with a LO power of −3 dBm, the detector offers a conversion loss less than 55 dB in a frequency band of 320–340 GHz. The channel in a form of transmission line performs the broad IF bandwidth, which is increased to gigahertz range (3 GHz), and reduces the output impedance to 377 Ω which is about 20 times lower than previously reported. The transmission-line impedance could be optimized together with the distribution of the terahertz electric field in the gated channel to reduce the conversion loss.

A 16-pixel terahertz (THz) receiver front-end working at room temperature was designed, built, and measured in this paper. The designed receiver front-end is based on the antenna-coupled AlGaN/GaN high-electron-mobility transistor (HEMT) THz linear detector array (TeraLDA) and a 16-way THz power divider. The local oscillator (LO) signal is divided by the power divider into 16 ways and transmits to the TeraLDA. Each detector contains a planar unified antenna printed on a 150 $\mathsf{\mu }\mathrm{m}$-thick sapphire substrate and a transistor fabricated on AlGaN/GaN heterostructure. There are 16 silicon hemispheric lenses located on the TeraLDA to increase the responsivity of the TeraLDA. The focus of each lens is aligned in the center of the TeraLDA pixels. Depending on different read out circuits, the receiver front-end could work in homodyne and heterodyne modes. The 16-way power divider is a four-stage power divider that consists of fifteen same 2-way dividers, and was fabricated by bulk silicon microelectromechanical systems (MEMS) technology to achieve low insertion loss (IL). This designed receiver front-end could be a key component of a THz coherent focal plane imaging radar system, that may play a crucial role in nondestructive 3D imaging application.