An X-band waveguide bandpass filter with enhanced stopband using offset resonators

This letter presents a narrowband third-order waveguide bandpass filter (BPF) with extended out-of-band response. The is composed of three offset resonators, and each resonator constructed by shifting half rectangular resonator, featuring very large distance between the first second resonant frequencies. BPF was designed center frequency (f0) 9.5 GHz passband bandwidth 100 MHz fabricated using Computer Numerical Control (CNC) milling process. experiment results show that has an average insertion loss 0.45 dB, return >16 30-dB stopband suppression up to 1.75 f0. measured agree well electromagnetic (EM) simulations.