Spurious-Free Differential Bandpass Filter Using Hybrid Dielectric and Coaxial Resonators

In this paper, a novel spurious-free differential bandpass filter (BPF) based on the hybrid dielectric resonator (DR) and coaxial resonator (CR) is proposed for the first time. The dominate TE
_01δ
mode of the DR cavity (fed by a pair of face-to-face probes) and the fundamental TEM mode of the CR cavity are used for constructing the passband of the differential BPF, while the spurious modes from the DR cavity that function as differential- or common-mode responses are suppressed to a great extent due to the adoption of the CR cavity. As a result, the differential-mode (DM) stopband can be widened and wideband common-mode (CM) suppression can be obtained. To validate the proposed idea, a third-order differential BPF is designed, fabricated and measured. Good agreement can be obtained between the simulated and measured results, showcasing good performance.