Magnetless Nonreciprocal Microstrip Filter With Low Insertion Loss and Reconfigurable Frequency

ABSTRACT This paper presents a low insertion loss frequency reconfigurable magnetless nonreciprocal filter based on time‐modulated microstrip resonators. To achieve nonreciprocity, modulation signals are applied to the varactors through the microstrip circuits connected to each resonator. The center frequency of the proposed filter can be continuously tuned by changing the DC bias voltage applied to the varactors. We designed, simulated, and experimentally validated a fourth‐order microstrip nonreciprocal bandpass filter at L‐band. The results confirm that the center frequency of the proposed nonreciprocal filter can be tuned from 1.37 to 1.78 GHz (1.3:1 tuning) with a forward insertion loss from 2.1 to 2.6 dB and a backward isolation from 25 to 32 dB.