Fully-Reconfigurable Non-Reciprocal Bandpass Filters

This paper reports on the RF design of quasi-elliptic non-reciprocal bandpass filters (BPFs) with fully-reconfigurable transfer function. It is demonstrated that by modulating the resonant frequency of its constituent resonators, the RF signal propagation is only enabled in one direction―e.g., from port 1-to-2―whereas it is sufficiently suppressed in the reverse one. Furthermore, by varying the resonant frequency of the BPF’s resonators, the transfer function in the forward direction can be tuned in terms of frequency and bandwidth (BW) and can be intrinsically switched-off. For practical demonstration purposes, a lumped-element prototype centered at 300 MHz was designed manufactured and measured. It demonstrated a 1.15:1 center frequency tuning and a 2.77:1 BW tuning range while maintaining a non-reciprocal behavior. For all tuning states, the minimum in-band insertion loss in the forward direction was measured between 1.7 and 4.3 dB, whereas the isolation in the reverse direction was measured up to 30.9 dB.