Co-Design of Full-Duplex Filter-Circulator-Antenna System Based on Mixed Static and Time-Modulated Coupling Topology

This letter presents, for the first time, a full-duplex substrate integrated waveguide (SIW) filter-circulator-antenna system based on mixed static and time-modulated coupling topology. The topology has three branches connected by a central node, and each branch is composed of a static resonator and a time-modulated resonator with specific phase. Furthermore, the time-modulated resonators are realized by the pentagonal SIW cavity loaded with a time-modulated varactor. Two static resonators are realized by rectangular SIW cavities connected by Tx and Rx ports, while the other one is realized by a square cavity integrated with the slot antenna. By tuning the time-modulated varactors, it achieves transmitting and receiving signals at the same frequency with filtering responses. For verification, a SIW filter-circulator-antenna system is designed and fabricated. The measured Tx-to-Rx isolation at center frequency of 2.39 GHz is 18.5 dB. The measured transmitting (receiving) gain is 0.3 dBi (0.5 dBi), and the lower and upper passband selectivities in the Tx mode (Rx mode) are 347 (266) dB/GHz and 433 (393) dB/GHz, respectively.