The evolution of wireless communication points to increasing demands on throughput for data-intensive applications in modern society. Integrated millimeter-wave systems with electrical beam-steering capabilities are promising candidates for wireless technologies of the future and are currently the subject of widespread academic and commercial research. The $D$ -band, ranging from 110–170 GHz, offers high aggregate bandwidths (BWs), low atmospheric absorption, and multi-GHz operation at amenable fractional BWs. It, therefore, has the potential to foster efficient, highly integrated wireless-communication systems with data rates approaching 100 Gb/s. This article reviews all aspects of hardware integration against the backdrop of an extensive literature review and outlines the challenges and possible solutions for practical 6G wireless systems in the $D$ -band. To this end, this article covers a number of related topics in depth, which includes system definition, possible radio architectures and array configurations, the scope and potential of integrated circuit (IC) technologies, the design and characterization of key circuit blocks, advances in antenna and packaging technologies for high-frequency systems, and an overview of measurement techniques currently employed at $D$ -band frequencies. A system-level study based on radio-link simulations of different single-carrier quadrature amplitude modulation (QAM) schemes is presented, which quantifies that the impact physical nonidealities, such as signal-to-noise ratio, phase noise, intermodulation distortion, and amplitude and phase imbalances in quadrature signal paths, have on bit-error rates in broadband $D$ -band communication systems. This is followed by a comparative assessment of different arrayed-system configurations that include traditional phased arrays, the use of polarization diversity for the transmission of different or identical data streams, and multiple input multiple output (MIMO) operation. The article also presents an overview of possible transceiver architectures for implementing beam-steering arrays and an outline of the associated tradeoffs. The beam-squinting effect seen in large arrays is also investigated in detail. On the implementation front, we present a comparison between different integrated-circuit technologies for high-frequency applications. These include CMOS and SiGe bipolar complementary metal oxide semiconductor (BiCMOS) heterojunction bipolar transistors (HBTs) in silicon technologies, and MOSFETs, HBTs, and HEMTs in III–V technologies, such as InP and GaAs. Implementation challenges are then addressed, and these include the design of high-frequency circuits in the latest IC technologies, current advances in antenna and packaging technologies, and emerging solutions for hybrid integration. The article also details the design and characterization of critical $D$ -band transceiver circuit blocks, namely, power and low-noise amplifiers, mixers, phase shifters, passive components for quadrature-phase generation, and radiators exploring hybrid antennas, which we have developed over the course of the past five years. These results compliment the literature survey with comparisons with state-of-the-art designs and are applied to radio-link simulations to predict the performance of practicable wireless links.

This invited paper reviews the progress of silicon-germanium (SiGe) bipolar-complementary metal-oxide-semiconductor (BiCMOS) technology-based integrated circuits (ICs) during the last two decades. Focus is set on various transceiver (TRX) realizations in the millimeter-wave range from 60 GHz and at terahertz (THz) frequencies above 300 GHz. This article discusses the development of SiGe technologies and ICs with the latter focusing on the commercially most important applications of radar and beyond 5G wireless communications. A variety of examples ranging from 77-GHz automotive radar to THz sensing as well as the beginnings of 60-GHz wireless communication up to THz chipsets for 100-Gb/s data transmission are recapitulated. This article closes with an outlook on emerging fields of research for future advancement of SiGe TRX performance.

Wireless surface acoustic wave (SAW) sensors have some unique features that make them promising for industrial metrology. Their decisive advantage lies in their purely passive operation and the wireless readout capability allowing the installation also at particularly inaccessible locations. Furthermore, they are small, low-cost and rugged components on highly stable substrate materials and thus particularly suited for harsh environments. Nevertheless, a sensor itself does not carry out any measurement but always requires a suitable excitation and interrogation circuit: a reader. A variety of different architectures have been presented and investigated up to now. This review paper gives a comprehensive survey of the present state of reader architectures such as time domain sampling (TDS), frequency domain sampling (FDS) and hybrid concepts for both SAW resonators and reflective SAW delay line sensors. Furthermore, critical performance parameters such as measurement accuracy, dynamic range, update rate, and hardware costs of the state of the art in science and industry are presented, compared and discussed.

This paper describes the design and characterization of a linear polarized 6 × 6 element transmitarray providing a beam steering range of 100° at 24.6 GHz. The transmitarray is formed of unit-cells providing a continuous electronically reconfigurable phase range of 360° by using varactor diodes as tunable elements. The unit-cell consists of four single RO4350B laminate layers. Unit-cell and transmitarray have been characterized by measurements showing good agreement with the numerical results.

Although a lot of research has been done into radar based heartbeat detection for the last years, it is still unknown which physiological effects truly underlie these measurement signals. This paper investigates the cardiovascular system as well as the effects due to the antenna characteristics and establishes a connection to the variety of heartbeat signals that can be found in comparable publications. For the first time, the cause of the diverging signal shapes is researched revealing the locally specific pulse wave curves named sphygmograms. Three different types are investigated: the carotid, the venous and the ventricle sphygmogram. Verification of the measured signal shapes is ensured by a laser sensor. Afterward, the influence of the filtering on the sphygmograms is researched as well as the influence of the antenna propagation on the radar signal. Finally, all novel insights are combined to substantiate the variety of published heartbeat signal curves.

Vital parameters are key indicators for the assessment of health. Conventional methods rely on direct contact with the patients’ skin and can hence cause discomfort and reduce autonomy. This article presents a bistatic 24 GHz radar system based on an interferometric six-port architecture and features a precision of 1 µm in distance measurements. Placed at a distance of 40 cm in front of the human chest, it detects vibrations containing respiratory movements, pulse waves and heart sounds. For the extraction of the respiration rate, time-domain approaches like autocorrelation, peaksearch and zero crossing rate are compared to the Fourier transform, while template matching and a hidden semi-Markov model are utilized for the detection of the heart rate from sphygmograms and heart sounds. A medical study with 30 healthy volunteers was conducted to collect 5.5 h of data, where impedance cardiogram and electrocardiogram were used as gold standard for synchronously recording respiration and heart rate, respectively. A low root mean square error for the breathing rate (0.828 BrPM) and a high overall F1 score for heartbeat detection (93.14%) could be achieved using the proposed radar system and signal processing.