A magnetless filtering circulator with enhanced isolation bandwidth using mixed static and time-modulated resonators

This paper presents a design of magnetless microstrip line circulator with filtering response and extended isolation bandwidth through integration of mixed static and time-modulated resonators. By effectively coupling static resonators with time-modulated resonators, the proposed circulator can achieve a low forward transmission insertion loss with filtering response along with a wide isolation bandwidth. Wideband isolation can be achieved by creating two isolation nulls within the passband. For proof-of-concept, a microstrip line circulator is designed, simulated, and fabricated at center frequency of 1.75 GHz. The measured results are well agreed with simulations. The measurement results show maximum forward transmission insertion loss of 2.70 dB, in-band 20-dB isolation of 80 MHz, and in-band return losses better than 18 dB.