This article presents a novel 200-GHz four-element phased-array receiver system-in-package (SiP) using high-temperature co-fired ceramic (HTCC) technology for wireless communications. The receiver employs a local oscillator (LO) phase-shifting architecture to realize sub-terahertz (THz) beamforming. All components of the front-end array are heterogeneously integrated within the HTCC. To achieve low-loss interconnection and 3-D integration, quartz substrates and vertical air-filled waveguides are incorporated within the HTCC. Meanwhile, an electromagnetic bandgap (EBG) structure is introduced in the vertical transitions to mitigate energy leakage caused by assembly gaps, thus reducing the sensitivity to assembly errors. Besides, a highly efficient parabolic reflector antenna array with a multilayered structure is designed for beam scanning. The overall size of the front-end package is 40.7 $\times$ 43 $\times$ 7.3 mm $^{3}$ . The measured channel gain is 8.2–23 dB from 194.5 to 234.5 GHz (18.6% bandwidth), and the measured lower-sideband noise figure is 7.5–9.4 dB, covering from 196 to 215 GHz. The phased-array receiver can achieve a scanning range of $\pm$ 30 $^{\circ}$ in the E -plane. To evaluate its over-the-air (OTA) performance, a wireless link is demonstrated with 16-quadrature amplitude modulation (QAM) and 64-QAM waveforms, achieving a maximum data rate of 32 Gbps.

In terahertz communication systems, amplifiers and other components can induce non-linear distortion in terms of amplitude and phase, resulting in system performance degradation. This paper presents a terahertz metamaterial waveguide to mitigate amplitude and phase distortions in some terahertz systems. A simple method based on free-space analysis is proposed for designing metamaterial waveguides in an enclosed space. The quasi-periodic metamaterial structures, which feature I-shaped resonant patterns, are integrated onto the inner walls of rectangular waveguides. The phase and amplitude of electromagnetic waves within the waveguide can be modulated by varying the dimensions and number of these resonators. Utilizing the effective medium theory and the equivalent circuits, the metamaterial waveguide’s phase and absorption modulation mechanisms are analyzed. Based on the proposed structure, a metamaterial waveguide with I-shaped resonators is designed and fabricated, and its abilities to modulate the phase and absorption of terahertz waves around 0.2 THz are demonstrated.

A wideband front-end module with antenna-in-package (AiP) for X -band phased-array radar applications is newly presented using low-temperature con-fired ceramic (LTCC) technology. This work integrates multiple chips into the AiP, resulting in a multi-functional front-end prototype. For improving antenna bandwidth and radiation efficiency, four air cavities are embedded inside the package to lower the effective dielectric constant. Additionally, bowtie-shaped patches and improved apertures are introduced to increase the antenna bandwidth further. The overall size of the LTCC package is 14.3 × 24.5 × 3.55 mm ³ . The antenna's voltage standing wave ratio is better than 2.5 at the full X band (40% bandwidth), and the maximum gain is 8 dBi. Besides, the receive gain of the active prototype is better than 30 dB at the full X band, and the transmit equivalent isotropic radiated power is 32–38.5 dBm, showing a good performance.

This article presents a 200-GHz phased-array wireless communication system featuring local oscillator (LO) beamforming using high-temperature co-fired ceramic (HTCC) technology. The system is constructed using HTCC transmit (Tx) and receive (Rx) system-in-packages (SiPs), which are mounted on printed circuit boards (PCBs) and connected to parabolic antennas through waveguide feeders. These SiPs heterogeneously integrate all components of the front-end channels, achieving low-loss interconnection and 3-D integration through vertical hollow waveguides within the HTCC. The Tx SiPs incorporate integrated Schottky diode mixers with MoCu waveguide filters, performing single-sideband upconversion with high image rejection. Measured Tx channel gain ranges from 17 to 40 dB over 192.5 to 212.5 GHz, with channel saturated output power from 5.2 to 9.6 dBm over 193.5 to 211.5 GHz. Furthermore, the eight-element Tx array achieves an effective isotropic radiated power (EIRP) of 35.9 to 43.3 dBm across 196 to 213 GHz and supports a scanning capability of ±30° in the E-plane. The phased-array Tx-Rx wireless link is demonstrated over a 30-m distance using 16-quadrature amplitude modulation (QAM) and 64-QAM waveforms, supporting maximum data rates of 32 and 24 Gbps, respectively.

This article presents a 220-GHz wideband converter for terahertz (THz) applications, which facilitates the transition from the TE $_{10}$ mode of the rectangular waveguide (RWG) to the TE $_{20}$ mode of the substrate-integrated waveguide (SIW). This converter consists of waveguides, a dipole antenna, a grounded slotline, and a SIW. The dipole antenna effectively couples the TE $_{10}$ -mode guided wave from the RWG into the slotline. Due to the quasi-slotline mode and SIW TE $_{20}$ mode being odd modes with similar electric field distributions, the longitudinal slotline effectively excites the TE $_{20}$ mode within the SIW. This study elucidates the converter’s principles and propagation properties through electric field analysis and electromagnetic (EM) simulations. Besides, a back-to-back converter prototype was fabricated and measured, exhibiting an insertion loss of 2.1–5.0 dB from 198 to 238 GHz (18.3% bandwidth) and a return loss better than 6.1 dB. The estimated loss for a single converter is 1.1–2.5 dB, including the loss of a 1.4-mm-long SIW. Furthermore, based on the proposed mode converter, an SIW bandpass filter and a balun were designed and demonstrated, providing further evidence of the existence of the TE $_{20}$ mode in SIW. To the best of our knowledge, this article presents the first 220-GHz converter from the RWG TE $_{10}$ mode to the SIW TE $_{20}$ mode, demonstrating its potential applications in THz planar integration.

A 194–214-GHz single-sideband (SSB) Schottky diode-based subharmonic mixer is newly presented for linear array applications. To realize 3-D integration, a vertical transition is adopted, which also acts as an IF-LO duplexer and an impedance transformer. A waveguide filter is integrated into the mixer for high image rejection, and an inline transition performs efficient mode conversion and impedance matching between the waveguide filter and the diode. The proposed mixer is more suitable for repeated arrangement in a linear array than conventional mixers with orthogonal configuration. A four-element mixer array is fabricated and measured. The array’s minimum SSB conversion loss (CL) is 8.1–10.4 dB from 194 to 214 GHz, the CL difference between elements is less than 1.3 dB, and the sideband rejection ratio is better than 30 dBc.