This paper presents millimeter wave (MMW) pulse-Doppler radar for the remote sensing of acoustic vibration for targets in motion. A key advance in this work is the development of precision motion compensation for MMW vibrometry, making it possible for a monostatic radar to extract and reproduce small-scale vibrations on platforms undergoing large-scale motion. The motion compensation methodology uses a hierarchical approach combining direct and indirect estimation for the time dependent variation of target motion parameters across coherent samples in radar fast time and slow time. Additionally, the wide bandwidth commonly available at MMW allows vibrations to be selectively detected and disambiguated in range across the length of moving targets. Stretch processing compresses the received radar bandwidth by more than 10x, so that Hilbert sampling can be used to acquire quadrature samples using a single analogto-digital converter. The resulting complex baseband response directly reproduces the target's acoustic signature. To demonstrate the technique, a 94 GHz pulsed linear frequency modulated (LFM) radar accurately reproduces the pitch of audio waveforms generated by a speaker in the rear of an accelerating automobile at an outdoor test range. These results should have major consequences for the development of MMW vibrometry as a remote sensing technique.

Digitizing RF signals using few bit ADCs can provide system advantages in terms of reduced power dissipation, wider sampling bandwidth, and decreased demand for digital throughput. The diversity of established applications based on few bit ADCs, together with the recent surge of interest in the topic for 5G wireless communications and millimeter-wave radar, has created a need for practical design guidance governing their use in general RF systems. This paper, therefore, summarizes the state-of-the-art in few bit ADCs, comparing the dynamic range considerations involved with those of conventional RF receiver design. A simple analytic model for the monobit ADC is extended to multiple bits. Parametric analysis, independent of sampling considerations and system-specific signal processing, is used to illustrate the variation in the ADC output signal-to-noise-and-distortion ratio (SNDR) versus both the number of quantization bits and the input signal-to-noise ratio (SNR). At low and negative input SNR, increasing ADC resolution beyond 3-4 bits yields little advantage in output SNDR. Experiment confirms analytic predictions for the specific conditions under which the loss of signal fidelity due to quantization can be made negligible. In addition, parametric analysis of two-tone intermodulation distortion shows clear disadvantages to quantizing with <4 bits in the presence of strong blockers. The results reported in this paper, which are general and independent of system application, can be used to customize the number of ADC bits in an RF system based on system-specific performance requirements for receiver dynamic range. INDEX TERMS Analog-to-digital converters (ADCs), 5G, low resolution ADCs, quantization, coherent receivers, radiofrequency integrated circuits, wireless communications, radar.

This Letter demonstrates the technical capability of millimetre wave pulse‐Doppler radar to identify safety‐critical operating status information for parked cars. A simple 94‐GHz pulsed linear frequency modulated radar with stretch processing on receive provides range‐selective detection of small‐scale vibration along the length of a parked car. The resulting range‐Doppler signature clearly differentiates whether the car's engine is running or not as well as whether the car's transmission is shifting between ‘park’ and ‘drive’. The rotational motion of an opening car door also produces a distinct signature in range‐Doppler space. Incorporating this knowledge into future automotive sensors can alert oncoming vehicles to unanticipated actions of parked cars to avert potential damage or injury.

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