Pulsed Harmonic Doppler Radar and Passive RF Tags for Tracking the Dynamic Motion of Held Objects

A new method for detecting microwave harmonic Doppler signatures of held objects in cluttered environments is presented. Based on a passive harmonic tag combined with a pulsed microwave radar, the motion of tagged objects held by a person can be detected in high-clutter environments. In this letter, we present a new derivation of the dynamic harmonic signal response of a harmonic tag in motion. Based on a truncated Bessel function expansion, the model predicts the time-frequency signatures of sinusoidally moving objects with high accuracy. We present a pulsed harmonic radar transmitting at 2.51 GHz and receiving at 5.02 GHz, which is capable of measuring the harmonic micro-Doppler response of the tag with better signal-to-noise since the clutter response only exists at 2.51 GHz. The pulse waveform provides detection of the harmonic tag at larger distances than continuous-wave systems by increasing the peak power of the signal incident on the tag, while the average power is fixed with a low level. Measurements of a held tag at a distance of 1 m in a highly cluttered environment are presented, showing a strong match to the simulated results.