This paper presents design and characterization of single-chip 110-170-GHz ( D-band) direct conversion in-phase/quadrature-phase (I/Q) transmitter (TX) and receiver (RX) monolithic microwave integrated circuits (MMICs), realized in a 250-nm indium phosphide (InP) double heterojunction bipolar transistor (DHBT) technology. The chipset is suitable for low-power ultrahigh-speed wireless communication and can be used in both homodyne and heterodyne architectures. The TX consists of an I/Q modulator, a frequency tripler, and a broadband three-stage power amplifier. It has single sideband (SSB) conversion gain of 25 dB and saturated output power of 9 dBm. The RX includes an I/Q demodulator with D-band amplifier and ×3 multiplier chain at the LO port. The RX provides a conversion gain of 26 dB and has noise figure of 9 dB. A 48-Gbit/s direct quadrature phase-shift keying (QPSK) data transmission using a 144-GHz millimeter-wave carrier signal is demonstrated with a bit error rate (BER) of 2.3 × 10 ^-3 and energy efficiency of 7.44 pJ/bit. An 18-Gbit/s 64-quadrature amplitude modulation (QAM) signal was transmitted in heterodyne mode with measured TX-to-RX error vector magnitude (EVM) of less than 6.8% and spectrum efficiency of 3.6 bit/s/Hz. The TX and RX have dc power consumption of 165 and 192 mW, respectively. The chip area of each TX and RX circuit is 1.3 × 0.9 mm ² .

Reconfigurable intelligent surfaces (RISs) have tremendous potential for both communication and localization. While communication benefits are now well understood, the breakthrough nature of the technology may well lie in its capability to provide and support localization capabilities. We present an overview of RIS-enabled localization scenarios, considering various numbers of RISs, single- or multi-antenna base stations, narrowband or wideband transmissions, and near- and far-field operations. Based on this overview, we also highlight key research directions and open challenges specific to RIS-enabled localization and sensing.

This paper presents a novel way of constructing wave guiding structures by stacking several thin metal plates for millimeter-wave and terahertz applications. The metallic layers do not require any electrical contacts among them. An air-filled multi-layer waveguide (MLW) transmission line is successfully designed and manufactured at D-band. Five vertically stacked thin metal layers are used to form an air-filled rectangular waveguide line. The layers are simply assembled by allowing a small air gap among them, without the need of using advanced manufacturing methods such as adhesive bonding techniques. The possible field leakage due to the air gaps is prevented by using an electromagnetic band gap (EBG) structure, consisting of glide-symmetric holes. A straight MLW line and a line with a double 90° bends are fabricated by using chemical metal etching, as a proof of concept. The measurement results of the straight line show that the reflection coefficient is better than -18 dB with average insertion loss of 0.02 dB/mm over the frequency band 110-170 GHz. For the double 90° bends line, the reflection coefficient is better than -18 dB with a similar average insertion loss of 0.02 dB/mm over the frequency band 110-150 GHz. The proposed concept could be an excellent candidate for designing compact and thin passive waveguide components and active components packaging, with a great potential for low-cost, light weight and mass-producible at millimeter-wave frequencies.

A novel theory is proposed in this article to design a bandpass frequency-selective surface (FSS) with a stable angular response. Based on this theory, the performance of the structure is closely related to its tangential and normal components of permittivity and permeability. Theoretical formulas are derived to realize a high-efficiency transmission response with angular independence. To validate our design concept, an ultrawide-angle bandpass FSS with metallic strips and square patch printed on the dielectric substrate is designed, and it exhibits a characteristic impedance matching for nearly all incident angles from 0° to 80 °. Moreover, varactor diodes are mounted at the center of the square patch, and the transmission window can be tuned by changing the capacitance of the varactors from 6.07 to 6.61 GHz without affecting its ultrawide-angle characteristic. Finally, a prototype of the tunable ultrawide-angle bandpass FSS is fabricated and measured, and the experimental results are in satisfying agreement with the predicted ones.

This paper presents the design and realization of a high data rate radio front-end module for point-to-point backhaul links at E-band. The design module consists of four vertically stacked unconnected metal layers without any galvanic and electrical contact requirements among the building blocks, by using gap waveguide technology. The module components are a high-gain array antenna, diplexer, and circuitry consisting of a transmitter (Tx) and a receiver (Rx) monolithic microwave integrated circuits (MMICs) on a carrier board, which is successfully integrated into one package with a novel architecture and a compact form. The diplexer consists of two direct-coupled cavity bandpass filters with channels at 71-76 GHz and 81-86 GHz with a measured return loss of 15 dB and an isolation greater than 50 dB. A wideband $16x16$ slot array antenna with a measured gain of more than 31 dBi is used to provide high directivity. The measured results show that the packaged transmitter provides a conversion gain of 22 and 20 dB at 76 and 86 GHz, respectively, with an output power of 14 and 16 dBm at 1-dB gain compression point, at the same frequencies. The packaged receiver shows an average conversion gain of 20 dB at 71-76-GHz and 24 dB at 81-86-GHz bands. A real-time wireless data transmission is successfully demonstrated with a data rate of 8 Gbit/s using 32-quadrature amplitude modulated signal over 1.8-GHz channel bandwidth with spectral efficiency of 4.44 bit/s/Hz. The proposed radio front end provides the advantages of low loss, high efficiency, compact integration, and a simple mechanical assembly, which makes it a suitable solution for small-cell backhaul links.

A new integration concept for THz systems is presented, wherein patterned silicon-on-insulator wafers form all DC, IF and RF networks in a homogeneous medium, in contrast to existing solutions. Using this concept, silicon-micromachined waveguides are combined with silicon germanium (SiGe) microwave monolithic integrated circuits (MMICs) for the first time. All features of the integration platform lie in the waveguide's H-plane. Heterogeneous integration of SiGe chips is achieved using a novel in-line H-plane transition. As an initial step towards complete systems, we outline the design, fabrication and assembly of back-to-back transition structures, for use at D-band frequencies (110 – 170 GHz). Special focus is given to the industrial compatibility of all components, fabrication and assembly processes, with an eye on the future commercialisation of THz systems. Prototype devices are assembled via two distinct processes, one of which utilises semi-automated die-bonding tools. Positional and orientation tolerances for each process are quantified. An accuracy of ±3.5 μm, ±1.5 ° is achieved. Measured S-parameters for each device are presented. The insertion loss of a single-ended transition, largely due to MMIC substrate losses, is 4.2 – 5.5 dB, with a bandwidth of 25 GHz (135 – 160 GHz). Return loss is in excess of 5 dB. Measurements confirm the excellent repeatability of the fabrication and assembly processes and thus their suitability for use in high-volume applications. The proposed integration concept is highly scalable, permitting its usage far into the THz frequency spectrum. This work represents the first stage in the shift to highly-compact, low-cost, volume-manufacturable THz waveguide systems.