Spurious Stopband Improvement of Dual-Mode Dielectric Resonator Filters Using T-shaped Coupling Probe

This paper presents a new design technique for dual-mode dielectric loaded resonator filter operating at 2.18GHz by using T-shape coupling probe. A cylindrical dielectric puck is suspended in the middle of metallic cavity and short-circuited on the side walls. Four vertically etched-slots through the dielectric puck from the top to the base of the ceramic puck offer a high unloaded quality factor of 4300 at the fundamental T E11δ mode and allows the T-shape coupling to be located close to the centre of the dielectric puck. The size reduction ratio in this resonator was 11% compared with air filled coaxial resonator. Fourth-poles Chebyshev bandpass filter (BPF) with planar configuration was designed and implemented by employing two dielectric-loaded cavities. The experimental results show that the spurious-free window of approximately 820 MHz from the fundamental frequency of 2.18GHz and the operational bandwidth of 77 MHz were achieved.