Compact triple-mode bandpass filter using spherical dielectric resonator

This paper presents a compact triple-mode bandpass filter (BPF) using a spherical dielectric resonator which has three degenerate TE_01δ modes. Coupling structures based on metallic plates inside a spherical metallic cavity are also introduced. Therefore, neither additional space nor coupling screws is needed. Moreover, the proposed BPF has three controllable transmission zeros, resulting in extremely sharp skirt characteristic. A three-pole BPF is designed and tested at the center frequency of 863 MHz with the bandwidth of 14MHz. The measured results show the insertion loss of 0.1 dB and the rejection of 31 dB at the frequency of 2 MHz away from the lower passband edge.