Magnet-less Non-Reciprocal Bandpass Filters with Tunable Center Frequency

This paper reports on the RF design of non-reciprocal magnet-less bandpass filters (BPFs) with continuously tunable center frequency. It is shown that by modulating the resonant frequencies of the BPF resonators with progressively shifted AC signals, the RF signal propagation in the overall BPF is enabled in one direction - e.g., from port 1-to - 2-whereas it is sufficiently suppressed in the reverse one. The operating principles of the magnet-less non-reciprocal BPF concept are demonstrated through circuit-based analysis of a three-resonator BPF. For practical validation purposes, a lumped-element proof-of-concept prototype was designed, manufactured, and tested at 140 MHz. It demonstrated minimum in-band insertion loss in the forward direction of 3.7 dB, maximum isolation of up to 52.8 dB in the reverse direction, and center frequency tuning from 136 MHz to 163 MHz (1.2:1 tuning).