In this paper, a novel compact second-order quad-band bandpass filter (BPF) is applied based on a novel quintuple-mode stub-loaded trigonal ring resonator. Resonant characteristics are extracted by even- and odd-mode method. Designing procedure of resonant frequencies has also been presented. The last two resonant modes are utilized to cover a wide bandwidth for 5G WiFi application. The rest of other three resonant modes are used to form three passbands for GPS, WLAN and WiMAX applications. According to pseudo-interdigital structure four transmission zeros are generated among passbands to improve the band to band rejection and enhance the frequency selectivity. The measurement results agree well with the EM simulation ones.
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