Compact triple-mode bandpass filter using short- and open-stub loaded spiral resonator

A novel high-selectivity triple-mode microstrip bandpass filter (BPF) using short- and open-stub loaded spiral resonator is presented. Because of the spiral structure, the size of designed BPF is reduced greatly. Then the odd- and even-mode method is used to analyze resonant frequencies of the resonator. Based on the analysis, a prototype of the proposed BPF with good selectivity is designed whose center frequency is at 4.3 GHz. Finally, the measured results are shown, which are in good agreement with simulations.