Millimeter-wave radar interferometry is superior in detecting small displacement motions owing to its short wavelength. However, it is subject to phase ambiguity as the target displacement may often exceed a quarter wavelength. In this article, a modified differentiate and cross-multiply (MDACM) technique is proposed to tackle the phase ambiguity issue for accurate reconstruction of the phase history in millimeter-wave interferometry. In addition, to resolve the imperfections of the interferometric radar system, an MDACM-based integral phase reconstruction approach is presented, which seamlessly integrates alternating current (ac)-coupling-induced distortion correction, $I/Q$ mismatch correction, and direct current (dc) offsets’ calibration. Without causing any phase ambiguity, the proposed technique acts as a black box to take in the raw $I/Q$ signals and correct all the hardware imperfections, and it outputs the desired displacement motions with micrometer accuracy. The simulation results show that the proposed technique can not only linearly recover the displacement motions across a wide range in different noise conditions without any phase ambiguity but also improve the stability by 11 times under ac-coupling-induced distortion. With a custom-designed 120-GHz interferometric radar sensor, experiments were carried out to validate various scenarios including mechanical vibrations and gesture sensing. The experimental results show that the proposed technique can accurately track not only deep subwavelength motion of only $1~\mu \text{m}$ but also multiwavelength displacement of >40 times of the wavelength at 120 GHz.

Large Displacement Motion Interferometry With Modified Differentiate and Cross-Multiply Technique

Modern microwave radar technologies and systems are taking important roles in healthcare, security, and human–machine interface by remote sensing of human life activities. This paper first reviews the developments in the past decade on the sensing front-end, transponder tag, and leveraging of other wireless infrastructure such as Wi-Fi. Based on the state-of-the-art engineering technologies, several emerging applications will then be studied, including continuous authentication, behavior recognition, human-aware localization, occupancy sensing, blood pressure monitoring, and sleep medicine. As radio frequency spectrum becomes a scarce resource, the allocation and spectrum sharing of life activity sensing bandwidth with other wireless infrastructures will be discussed. Several future research directions will be laid out to solve challenges for ubiquitous deployment of these sensing technologies at the human–microwave frontier.

/pdf/sensing-of-life-activities-at-the-human-microwave-frontier-1pnx5v2i3f.pdf

Sensing of Life Activities at the Human-Microwave Frontier

Abstract Vital sign detection is used across ubiquitous scenarios in medical and health settings, and contact and wearable sensors have been widely deployed. However, they are unsuitable for patients with burn wounds or infants with insufficient areas for attachment. Contactless detection can be achieved using camera imaging, but it is susceptible to ambient light conditions and has privacy concerns. Here we report a photonic radar for non-contact vital sign detection to overcome these challenges. This photonic radar can achieve millimetre-level range resolution based on synthesized radar signals with a bandwidth of up to 30 GHz. The high resolution of the radar system enables accurate respiratory detection from breathing simulators and a cane toad as a human proxy. Moreover, we demonstrate that the optical signals generated from the proposed system can enable vital sign detection based on light detection and ranging (LiDAR). This demonstration reveals the potential of a sensor-fusion architecture that can combine the complementary features of radar and LiDAR to achieve improved sensing accuracy and system resilience. The work provides a technical basis for contactless and high-resolution vital sign detection to meet the increasing demands of future medical and healthcare applications. 

/pdf/photonic-radar-for-contactless-vital-sign-detection-3f3zp1c4.pdf

Photonic radar for contactless vital sign detection

Highly accurate vibrometry and ranging are important topics in the industrialized economy. Wherever optical measurement technology fails due to its high prices and vulnerability within harsh environments, millimeter-wave (mmWave) radar technology is well suited. This article introduces a signal processing chain for ultrawideband frequency-modulated continuous-wave (FMCW) radar. It uses fast-time measurement to evaluate the instantaneous phase, thus allowing for spatially resolved sensing of multiple simultaneously vibrating radar targets, faster than the chirp rate. In order to accomplish this, a sophisticated error model and a calibration scheme were derived. We used three FMCW radar systems covering a broad range of the mmWave spectrum to demonstrate the signal processing approach. In contrast to the commonly used slow-time measurement principle, the highest detectable frequency was improved from 55 Hz to at least 16 kHz, which is the upper limit of the audio range. Up to 10 kHz could be measured with an underlying large-scale motion of 0.4 m/s, while the vibration displacement was at a minimum of 30 nm.

/pdf/spatially-resolved-fast-time-vibrometry-using-ultrawideband-2ict5fupkl.pdf

Spatially Resolved Fast-Time Vibrometry Using Ultrawideband FMCW Radar Systems

With the rapid development of semiconductor technologies, the wideband transceiver is in the trend to be integrated on-chip with compact size and low power consumption. This survey investigates the integrated wideband chip-scale RF transceivers for radar applications including imaging, multimodal sensing, and recognition on gaits, where frequency modulated continuous wave (FMCW) radar sensors are investigated in detail. Besides radar sensing, integrated wideband RF transceivers for accurate localization and efficient communications with spectrum sharing are discussed, in which the integrated wideband transceiver techniques for ultra-wideband (UWB) communications are highlighted. The compact and efficient antenna designs for integrated wideband RF transceivers are discussed. Furthermore, leveraging the artificial intelligence (AI)-enhanced signal processing techniques, edge devices with energy-efficient integrated RF transceivers can ensure precise localization and realize versatile sensing to empower accurate health status monitoring, intelligent robots, gesture recognition, and enhanced communications. We envisioned the future integrated wideband RF transceiver development trends, where the promising tera-Hertz (THz) integrated transceiver techniques are discussed. Notably, the wideband integrated RF transceiver technique is promising to enable efficient, flexible, and seamless communications and sensing for the future-generation intelligent Internet of Everything (IoE) applications.

Integrated Wideband Chip-Scale RF Transceivers for Radar Sensing and UWB Communications: A Survey

This article presents a fully integrated 100-GHz continuous-wave Doppler radar transceiver with the double-sideband low-intermediate-frequency (IF) architecture for mechanical vibration and vital sign detection. Fabricated in a 65-nm CMOS process, the whole radar chip transceiver consumes 262 mW with a size of 0.9 mm $\times2.0$ mm. Instead of utilizing a fundamental 100-GHz voltage controlled oscillator (VCO) in the chip, a push–push frequency doubler with the 50-GHz external source is adopted to drive the transceiver. Under a dedicated design on the system architecture and circuit blocks, the chip could transmit 4-dBm saturated power ( $P_{\mathrm {sat}}$ ) over 93–105 GHz with a 40-mV 1-kHz IF carrier and achieve good I/Q performance of phase mismatch $\mu \text{m}$ displacement from 1.5 m, the human vital-sign signal from 2 m, and even a small bullfrog’s hybrid respiratory motion from 0.6 m. To the best of our knowledge, this is the first 100-GHz CMOS Doppler radar transceiver chip with the low-IF architecture for the biological vital sign detection.

Design of a 100-GHz Double-Sideband Low-IF CW Doppler Radar Transceiver for Micrometer Mechanical Vibration and Vital Sign Detection

This letter presents a 39-GHz phase-inverting variable gain power amplifier (VGPA) for 5G communication. Adopting a Gilbert structure-based variable gain amplifier (VGA) stage, the VGPA realized the dB-linear gain control characteristic as well as 180° phase inversion. At 0°/180° phase states, the 39-GHz VGPA achieves the maximum gain of 38.7/38.9 dB with gain tuning range of 5.6/5.2 dB, respectively. Over 38–43 GHz, the phase inversion error is limited within 5.9°, and the rms phase error is less than 3.6°/2.2°. Meanwhile, with the metal interleaving coplanar transformer matching network, this VGPA achieves 17.7/17.6-dBm Psat and 13.2/13.36-dBm OP1 dB, with the power added efficiency (PAE) of 35%/34.5% and 13.6%/14.4% at the saturation and 1-dB compression points, respectively. Over the gain control states, the OP1 dB fluctuation is less than 0.3 dB. Implemented in a 65-nm CMOS process, the proposed VGPA consumes 150 mW with a chip area of 0.3 mm2.

A 39-GHz Phase-Inverting Variable Gain Power Amplifier in 65-nm CMOS for 5G Communication

This paper presents a differential two-stage 39-GHz bi-directional variable gain amplifier (Bi-VGA) for 5G mm-Wave applications. Based on a phase compensated bi-directional structure with tail current tuning technique, a variable gain cell with small phase variation and compact area is realized. To boost the gain and ease the impedance matching, the cross-coupled transistor pairs are adopted. Analysis and simulations are undertaken to illustrate the working mechanism of accurate gain control and low phase variation. The measured Bi-VGA achieves peak gain of 15.6 dB with 3-dB bandwidth over 35–45 GHz, covering the 5G 39-GHz band (37–43.5 GHz), and a maximum OP1dB of 3.5 dBm. Fabricated in 65-nm CMOS process, the Bi-VGA consumes 67 mW from a 1.2 V power supply with a small core area of 0.46 × 0.14 mm2, and its minimum noise figure is about 6.4 dB at the maximum gain state. Across a gain tuning range of 12 dB, the phase variation is less than 6.1° over the operating frequency range. 

Design of a 39-GHz compact bi-directional variable gain amplifier in 65-nm CMOS

This letter presents a fully integrated 16-element phased-array transceiver (TRX) supporting dual-polarization multi-input multi-output (DP-MIMO). transmitting/receiving (T/R) switches are embedded for time division duplexing (TDD) operation. High-linearity bidirectional variable gain amplifiers (Bi-VGAs) and passive phase shifters (PSs) are designed for compact area and low power consumption, respectively. Fabricated in a 65-nm CMOS process, this TRX occupies an area of 25.76 mm2. With integrated frequency synthesizer, the TRX can work from 37 to 43.5 GHz, which can fully cover 5G new radio (NR) frequency range 2 (FR2) n259 and n260 bands. In the receiver (RX) mode, a noise figure (NF) of 5.4–6.3 dB and a peak conversion gain (CG) of 27.3 dB are achieved. The transmitter (TX) mode achieves a peak CG of 48.7 dB, a 13.1-dBm OP1 dB, and a 15.8-dBm $P_{\mathrm {sat}}$ . By using 64-QAM modulation, measurement results show that the TRX achieves a data rate up to 7.2 Gb/s per independent data stream with 7.65 dBm output power per channel.

A 37–43.5-GHz Fully Integrated 16-Element Phased-Array Transceiver With 64-QAM 7.2-Gb/s Data Rates Supporting Dual-Polarized MIMO

Caused by inappropriate allocation of the interstage power mismatches during broadband matching, the boosted dynamic dc current of the frequency doubler (FD) would deteriorate the broadband efficiency. To tackle this issue, an efficiency-optimized broadband matching strategy is proposed by allocating all of the desired low-frequency mismatches ahead of the push-push (PP) pair, which not only keeps a broadband output but also reduces the dynamic dc current and improves the efficiency over the entire operating bandwidth simultaneously. To further enhance the 2nd harmonic (HR2) output power, a fourth-order notch filter is also designed at the PP pair input. Fabricated in a 65-nm CMOS process, the proposed Ka-band FD exhibits >15% efficiency from 24.6 to 36 GHz, and a 23.5% peak efficiency is achieved. A 42.6% fractional bandwidth (FBW) is also realized with a fundamental rejection ratio (FRR) over 45 dBc.

A Ka-Band Frequency Doubler With a Broadband Matching Scheme for Efficiency Optimization

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