Microstrip Bandpass Filter Based on Dual-mode Folded SIR Resonator

A compact microstrip bandpass filter (BPF) based on shorted dual-mode folded SIR resonators is proposed in this paper. The filter is analyzed and designed at a center frequency of 9 GHz with an FBW of around 24%. There are four modes or poles for the filter because each dual-mode resonator has two resonant modes (even-mode and odd-mode). The coupling between resonators can generate four transmission poles in the passband. And there are also two transmission zeros in the stopband which improves the performance of the filter. The measured result of the fabricated filter matches the simulation.