Compact Dielectric Waveguide Filters With Controllable Transmission Zeros Using Dual External Coupling and Hybrid Ridge and Post

This article proposes a compact dielectric waveguide filter (DWF) using dual external coupling (DEC) and hybrid ridge and post resonators. The basic configuration comprises an evanescent-mode cavity loaded with a feeding probe, a post, and a ridge. The feeding probe is simultaneously coupled to the posts and ridge, thereby forming a trisection. By strategically adjusting the geometric parameters of the probe, the external quality factors of the post and ridge can be controlled separately. Meanwhile, changing the orientation of the post can alter the sign of the external coupling coefficient, providing flexibility in arranging the transmission zeros (TZs). Furthermore, cascaded trisections (CTs) using the proposed trisections can be used to implement higher-order bandpass filters (BPFs) with multiple TZs while reducing dependence on cross-coupling. To demonstrate the effectiveness of the proposed design, five BPFs are designed and simulated. For validation, two BPFs are fabricated and measured. Good agreement between the simulated and measured results is achieved. The designed DWFs feature low insertion loss, compact size, and flexibly controllable TZs.