Design of Nonreciprocal Filtering Antenna Using Spatio-Temporal Modulated SIW Resonators

This article reports on, for the first time, the design of nonreciprocal filtering antennas using spatio-temporal modulated substrate integrated waveguide (SIW) resonators. It consists of two SIW cavities and a half-mode SIW (HMSIW) cavity, which is designed as the last-stage resonator and the radiator. By integrating time-modulated capacitors on the surface gaps of the three cavities, the nonreciprocal radiation patterns in transmission and reception modes are achieved at the same operating frequency. Three radiation nulls are generated due to the cross-coupling in the time-modulated network and source-load coupling. The theoretical analysis of the co-designed nonreciprocal SIW filtering antenna is detailed, along with methods for its co-simulations and measurements. For the proof-of-concept demonstration, a nonreciprocal SIW filtering antenna operating at 2.4 GHz is designed and fabricated. The measured 10-dB bandwidth and peak gain are 1.7% and 2.6 dBi, respectively. The measured realized gains at transmission and reception show that the reverse isolation is greater than 11 dB within a bandwidth of 30 MHz. The frequency selectivity values are 756 and 368 dB/GHz at the left and right sides of the passband, respectively.