A Magnetless Microstrip Filtering Circulator based on Coupled Static and Time-Modulated Resonators

This paper reports for the first time a magnetless microstrip circulator with a filtering response. By coupling static resonators to spatio-temporally modulated resonators, two isolation poles and two reflection poles can be obtained within the passband, showing wideband nonreciprocal transmission and impedance matching characteristics. As a proof-of-concept, a microstrip circulator at 825 MHz is designed, simulated, and measured. The measurement shows excellent circulator responses with minimum in-band insertion loss of 1.75 dB, in-band isolation better than 20 dB, and in-band return loss better than 20 dB. The measurement agrees very well with simulation.