Dielectric Waveguide Bandpass Filters With Multiple Transmission Zeros by Constructing Cascaded-Trisection Coupling Structures

This article presents a new design concept for dielectric waveguide bandpass filters (BPFs) with multiple transmission zeros (TZs) by constructing multiple cascaded-trisection (CT) coupling structures. Theoretically, one trisection can introduce one independently controllable TZ. To control the TZ, both the electric coupling and the magnetic coupling are necessary. A metallized blind hole is set in the middle of the coupling window between two dielectric waveguide resonators (DWRs), forming a hybrid electromagnetic coupling structure. The polarity and magnitude of the coupling can be controlled by the depth of the blind hole, making the proposed coupling structure suitable for constructing the CTs. Besides, in order to achieve a maximum number of TZs, the dual port-excitation (i.e., one port excites two resonators simultaneously) and the source-to-load coupling are utilized to construct more CTs. Four different BPFs, i.e., a third-order one with two CTs, a third-order one with three CTs, a fifth-order one with two CTs, and a fifth-order one with five CTs, are designed, simulated, and measured based on the DWRs to verify the design concept. Good accordance between the simulated and measured results is achieved. The designed DWR BPFs feature low insertion loss, compact size, lightweight, and flexibly controllable TZs, simultaneously.