Although the beginning of research on automotive radar sensors goes back to the 1960s, automotive radar has remained one of the main drivers of innovation in millimeter wave technology over the past two decades. Today, millions of sensors are produced each year, which was made possible by inexpensive and mature millimeter wave technology. The technology maturity, in turn, enables research to be carried out on systems that are considerably more complex and powerful than was possible just a few years ago. The focus of research has thus shifted from purely hardware-oriented and device-level topics to sophisticated millimeter wave systems and RF signal processing topics. This opens up new research topics such as digital modulation schemes, radar networks, radar imaging, and machine learning. In this review paper, we sketch the path from the very beginning through the state of the art with sophisticated multiple-input multiple-output (MIMO) antenna arrays and mature assembly and interconnect concepts to today's key research topics of automotive radar.

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Automotive Radar — From First Efforts to Future Systems

A clear trend in wireless applications during the last decade has been the push towards higher integration, and multi-mode and multi-band operation, in order to enable low-cost high-functionality consumer devices. As the deployment of silicon-based MMW technology becomes widespread, similar trends may be expected in the MMW space

A Single-Chip Dual-Band 22–29-GHz/77–81-GHz BiCMOS Transceiver

In this paper, an incoherent radar network based on integrated radar sensors is presented. It consists of radar sensor nodes with independently generated frequency-modulated continuous wave-modulated transmit signals, performing both monostatic and bistatic distance measurements. An architecture to operate such a cooperative bistatic network is introduced and an optimal parameterization of the system is presented. Several nonidealities of frequency synthesizers, that are important for such cooperative radar networks, are discussed and their influence on system performance is evaluated. A prototype of the cooperative bistatic network has been realized using highly integrated radar sensors at 122 GHz. Radar measurements using the prototype prove the feasibility and potential of the network approach. The complete signal processing chain is presented, including an adapted multilateration algorithm for target position estimation using all measured distances.

A Cooperative MIMO Radar Network Using Highly Integrated FMCW Radar Sensors

This paper presents the design of the first CMOS distributed active power combiners and splitters with wideband variable delay and gain. These circuits are the key components for use in multi-antenna (MA) ultra-wideband (UWB) point-to-point beamforming communication systems with multiple transmit and receive antennas. Two broadband circuit topologies for each active power combiner and splitter are proposed, one of which being fabricated in a 0.13-μm CMOS process. The proposed fabricated distributed active power combiner and splitter operate across wide range of frequencies that cover the UWB frequency range from 3.1 to 10.6 GHz. The gain of each RF path of the power combiner and splitter is independently controllable from -15 to 6 dB and from -16 to 9.5 dB, respectively. The wideband variable delay of each RF path varies from 32 to 42 ps for the two-stage power combiner, and from 43 to 53 ps for the three-stage power splitter across the UWB frequency rang. Supplied from 1.8-V DC voltage, the power combiner and splitter consume 8.5 mA and 11.4 mA, respectively.

CMOS distributed active power combiners and splitters for multi-antenna UWB beamforming transceivers

In this article, we present a distributed and decentralized synchronization algorithm for wireless sensor networks (WSNs). The proposed method achieves subnanosecond synchronization using low-cost commercial-off-the-shelf (COTS) Universal Software Radio Peripheral (USRP) software-defined radios (SDRs) and is implemented entirely in software without the need for custom hardware or atomic clocks. In an $N$ sensor network, the proposed protocol results in each sensor having full knowledge of baseband clock offsets, RF carrier phase offsets, and pairwise RF time of flight to subnanosecond precision for the entire network after $2N$ total transmissions, making this method efficiently extendible to larger sensor networks. The method is decentralized and does not rely on a hierarchical master–slave structure, making it robust to sensor dropout in contested or harsh environments. The proposed methodology is validated in simulation and tested in field experiments using a three-sensor network. This work has a wide range of applications, including transmit (TX) beamforming, distributed sensor localization, and coherent multistatic/multiple-input–multiple-output (MIMO) radar imaging for autonomous sensor swarms.

Wireless Subnanosecond RF Synchronization for Distributed Ultrawideband Software-Defined Radar Networks

We present a synchronization method and coherent ultra-wideband transceivers for a widely separated multiple-input multiple-output (MIMO) radar. Synchronization is essential for MIMO operation, but a spatially spread radar array is not a good structure for it. A wireless cooperative synchronization method is based on coherency of pulse signals and highly accurate delay estimation and they are implemented through a coherent pulse generator and a fine delay-based receiver. Distance measurements of a radar transceiver (TRX) show that the maximum mean error is 4 mm for the target in a range of 0.2 m-8.0 m. Synchronization measurements of two radar TRXs show that the maximum mean error of the asynchronous time difference is 11 ps for the target in a range of 0.25-8.0 m. 2-D images for multiple targets and fluctuational radar cross sections are achieved with the proposed synchronization method under MIMO operation.

Wireless Cooperative Synchronization of Coherent UWB MIMO Radar

This paper presents a low power UWB radar transceiver IC, which is used to make a radar system with precise range accuracy. The range accuracy is allowed by a variable delay circuit which can control the delay by 5 ps resolution. The detecting range of the transceiver is from 0.15 m to 8.4 m. The measurement results show that the maximum error is 3.75 mm. The circuit is implemented in a 0.13 µm CMOS process with the die area of 1.28 × 1.07 mm2. The total power consumption of the core circuit is 6.89 mA with the supply voltage of 1.5 V.

A low-power K-band CMOS UWB radar transceiver IC for short range detection

A low-noise ultrawideband CMOS mixer circuit for the down conversion of a K-band signal is presented. A bleeding path gm-boosting technique is proposed, which reduces the effect of noise sources of the proposed mixer. The measurement results show that the minimum noise figure is 3.61 dB at 24 GHz when consuming 2.6 mW at a 1.5-V supply voltage. The results also show a conversion gain of 9.15 dB, a of P1dB of -13 dBm, and an isolation of a local oscillator port to a radio frequency port of -40 dB. The circuit was fabricated using 0.13-μm CMOS technology with a chip area of 0.68 x 1.07 mm2.

A K-Band UWB Low-Noise CMOS Mixer With Bleeding Path $G_{m}$ -Boosting Technique

A K-band CMOS ultra-wideband (UWB) four-channel radar front-end based on timed-array coherent pulsed oscillators is presented. The trigger-signal delay method of the oscillator array with an additional 1-bit RF phase shifter is proposed to achieve beam-forming with wide angular coverage and high angular resolution. The phase coherency of the K-band UWB signal is achieved by using an asymmetric control of the pulsed oscillator. This allows it to detect the direction of a target as well as the accurate distance using a single antenna per channel. The chip is fabricated with ${\hbox{0.13-}}\mu{\hbox{m}}$ CMOS technology and the chip size is 3.9 mm by 1.7 mm. The output spectrum is centered on 26.0 GHz and satisfies the Federal Communications Commission spectral mask. The system attains the angular resolution of 9 $^{\circ}$ in the range from $-{\hbox{45}}^{\circ}$ to $+{\hbox{45}}^{\circ}$ . Total power consumption is only $\sim {\hbox{68 mW}}$ , mainly used in the receiver and digital blocks.

A K-Band CMOS UWB Four-Channel Radar Front-End With Coherent Pulsed Oscillator Array

Low-power operation and ease of system integration are increasingly important in a system using multiple amplifiers in parallel, such as a phased array. In this paper, a Kuband pseudomorphic high electron mobility transister (pHEMT) low-noise amplifier (LNA) that can be applied to such a system was designed and measured. The chip was fabricated using InGaAs Enhanced-mode (E-mode) 0.15-um pHEMT process. And by applying a cascode configuration that reuses current to the circuit, it consumes low power and has high gain. The current consumption is 5mA at 4V supply voltage, and the gain is 21.3 dB at 16 GHz. The 3-dB bandwidth of the LNA is 2.59 GHz and noise Figure (NF) is 1.46 dB at 16 GHz. OP1dB is 8.05 dBm and IP1dB is -10.8 dBm. The size of the entire chip including the electrostatic discharge (ESD) protection pad is 1.5x0.95 mm2.

Sunwoo Kong

Papers

Wireless Cooperative Synchronization of Coherent UWB MIMO Radar

A low-power K-band CMOS UWB radar transceiver IC for short range detection

A K-Band UWB Low-Noise CMOS Mixer With Bleeding Path $G_{m}$ -Boosting Technique

A K-Band CMOS UWB Four-Channel Radar Front-End With Coherent Pulsed Oscillator Array

A Ku-band Cascode Low Noise Amplifier using InGaAs E-mode 0.15-um pHEMT Technology