Miniaturized Triple-Mode Dielectric Waveguide Filters With Controllable Transmission Zeros

This letter proposes a novel miniaturized triple-mode (TM) dielectric waveguide resonator (DWR) for the design of bandpass filters (BPFs) with controllable transmission zeros (TZs). The TM DWR consists of two quarter-wavelength metallized non-through holes and one T-shaped half-wavelength metallized through hole on a dielectric block with silver-plated surface. The three modes employed are the quasi-TEM modes generated by the two metallized non-through holes and the TEM mode generated by the metallized through hole. The resonant frequency of each mode and the coupling between different modes can be controlled independently. The position of the TZs can be controlled by adjusting the relative location of the metallized non-through holes. Based on the TM DWR, two BPFs were designed with TZs located above and below the passband.