Harmonic Micro-Doppler Detection Using Passive RF Tags and Pulsed
Microwave Harmonic Radar
A pulsed radar system and harmonic tag design for the detection of harmonic micro-Doppler signatures in cluttered environments is presented. While radio-frequency identification research has focused heavily on detection, this work uniquely focuses on measuring the tag motion based on harmonic frequency shifts. The tag retransmits the incident signal at a harmonic frequency, enabling the harmonic radar receiver to detect the frequency shift without the presence of clutter, which is confined to the fundamental frequency band. A new harmonic tag based on a wire dipole, diode, and wire-based reactive components is presented, which operates at 2.51 and 5.02 GHz frequencies. A pulsed harmonic radar is offered that is able to achieve measurements at greater distance than continuous-wave systems. We present time-frequency responses of the tag movement at a distance of 1 m to demonstrate the ability to detect object motion based on the frequency shift of the harmonic micro-Doppler response.