Nonreciprocal Tunable Low-Loss Bandpass Filters With Ultra-Wideband Isolation Based on Magnetostatic Surface Wave

A new type of nonreciprocal
C
-band magnetic tunable bandpass filter (BPF) with ultra-wideband (UWB) isolation is presented. The BPF was designed with a 45° rotated yttrium iron garnet (YIG) slab loaded on an inverted-L-shaped microstrip transducer pair. With external in-plane magnetic fields from 1.1 to 1.9 kOe, the central frequency of the filter was tuned from 5.2 to 7.5 GHz, with an insertion loss of 1.6-3 dB and an UWB isolation of more than 20 dB, which was attributed to the nonreciprocity characteristics of the magnetostatic surface wave. In addition, the measured result demonstrated power-handling capabilities of over 30 dBm under room temperature. The proposed prototype with dual functionality of a tunable BPF and an UWB isolator will have many applications in RF front-end and other microwave circuits.