The first measurements of moving humans using a dual-mode millimeter-wave radar sensor are presented. The radar sensor is comprised of a Doppler detection mode for measuring the radial velocity of a moving object, as well as a recently developed interferometric mode for directly measuring the angular velocity. Combining the two detection modes, it is shown that the motion of a walking human can be detected and measured regardless of the direction of trajectory relative to the radar sensor. Such a capability has the potential to significantly improve the effectiveness of security radars, and may apply to a broad range of other motion detection radar applications. The frequency shifts imparted on the signal in both Doppler and interferometric detection modes are measured in the time-frequency domain, and show that as the trajectory moves from a completely radial motion to a completely angular motion, the Doppler frequency shift decreases while the interferometric frequency shift increases. The two detection modes therefore represent complementary measurements, improving the ability to measure the motion of randomly moving objects.
New methods for reducing signal distortion in interferometric angular velocity measurements are introduced. Two waveform approaches are proposed: long-wavelength signals and short-pulse signals. The source of nonlinear distortion is derived and analysed, and the strengths and drawbacks of each method are discussed. Although the focus is on the distortion generated when measuring the angular velocity of walking humans, the results are applicable to interferometric measurements of the angular velocity of non-rigid or multiple objects in general.Introduction: Simultaneous measurement of both the angular and radial velocities of a moving object can provide a multidimensional trajectory measurement. Radial velocity is measured electromagnetically using Doppler radar systems, whereas the angular velocity can be measured using an interferometric radar technique [1]. Such measurements can be beneficial in applications like security sensing where the object trajectory is not always radial relative to the sensor. In measurements of humans with low radial velocity the Doppler frequency shift will decrease, becoming too small for detection and classification near 60°a way from the radial [2]. The interferometric and Doppler measurements are complementary: when the Doppler frequency shift decreases the interferometric frequency shift increases; thus, the motion of a person can be detected regardless of the trajectory relative to the sensor. The first simultaneous measurements of the angular and radial velocity of a moving person using a dual interferometric-Doppler radar were presented in [1]. Time-frequency analysis of the interferometric and Doppler signals showed that the frequency shifts increased and decreased in proportion to the angle of the velocity vector relative to the sensor, demonstrating the complementary nature of the two measurement modes. It was also seen that non-rigid objects like humans generated distortion in the time-frequency response; such distortion will also be present when viewing multiple closely spaced objects. Although the bulk trajectory of a person can be discerned, it is beneficial to reduce the distortion so the frequency shifts corresponding to separate moving parts can be detected and processed, as in micro-Doppler signal analysis [3,4]. In this Letter, the source of signal distortion due to nonlinear processing of the interferometric signals is derived, and two techniques for reducing distortion are proposed and investigated.
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