A Compact Narrow-Band Harmonic Tag for Harmonic Radar Applications

In this work, we present a compact, narrow-band harmonic tag based on a circular patch antenna embedded within a micro-strip ring resonator antenna. The 2.8 GHz ring resonator filters incident harmonic radar signals over a narrow fractional bandwidth, passing the received signal to a diode that generates a frequency at the second harmonic of the incident signal, which is retransmitted by the 5.6 GHz circular patch antenna. The ring antenna is capacitively coupled to the diode to further reduce the bandwidth. The tag obtains a fractional bandwidth of 0.43% at 2.6 GHz (0.22% at 5.8 GHz) with antenna gains of 3.6 dBi and 3.0 dBi at 2.6 GHz and 5.8 GHz, respectively.