A Passive Harmonic Tag Using Nested Dual-Band Patch Antennas for Harmonic Doppler Sensing

A new harmonic tag based on a dual-band patch antenna designed for detecting harmonic Doppler signals is presented. The antenna structure is made from a patch antenna and parasitic antenna ring surrounded by a grounded ring. The tag is designed to receive a 2.5 GHz continuous-wave signal and using a nonlinear component retransmit the received signal at the second harmonic frequency (5 GHz), the Doppler shift of which can be detected for moving target measurements in cluttered environments. The patch design is used to achieve higher gain than common dipole-based harmonic tags can earn. We present simulation results of the antenna performance, and show measured reception of the scattered fundamental and generated harmonic signals. The proposed design would be suitable for applications ranging from home health care to internet of things (IoT) among other applications.