Tune-All Substrate-Integrated-Waveguide (SIW) Bandpass Filters

This paper reports on a new type of substrate- integrated-waveguide (SIW) bandpass filters (BPFs) with multiple levels of transfer function adaptivity. They are based on series- cascaded in-line coaxial resonators and a coaxial-resonator-based transmission-zero (TZ) generation section. The proposed architecture allows the realization of the following reconfigurable characteristics: i) tunable center frequency with either constant absolute bandwidth (BW) or constant fractional bandwidth (FBW), ii) tunable BW, and iii) an intrinsically switched-off response. Alternative realization schemes using parallel and series resonators are discussed with the purpose of improving the stopband performance. For proof-of-concept demonstration purposes an L-band SIW-based BPF prototype was designed, manufactured and measured. It exhibited the following RF performance characteristics. Center frequency tuning between 1.24 and 1.8 GHz (1.5: tuning ratio), BW tuning between 190 and 78 MHz (2.44:1 tuning ratio) and intrinsic switching-off with > 30 dB of isolation in the range between 0.75 and 2.25 GHz.