Miniaturized Dual-Band Bandpass Filter Using Triple-Mode Dielectric Waveguide Resonators With Adjustable Capacity in Transmission Zeros

In this letter, a miniaturized dual-band bandpass filter (BPF) using triple-mode dielectric waveguide resonators (DWRs) with two adjustable transmission zeros (TZs) is presented. In the triple-mode DWR, three TM modes are divided into two groups and utilized to generate a dual-band response. Specifically, the fundamental TM110 modes are utilized to construct the lower passband, which contains two poles, while the degenerate TM120 and TM210 modes form a cascaded quadruplet (CQ) unit that generates the upper passband with four poles. Both positive and negative couplings within the upper passband are readily achieved by simply adjusting the positions of two coupling holes. A TZ pair near the upper passband is introduced with significant flexibility and can be arbitrarily positioned. Finally, a dual-band BPF with a symmetric TZ pair using the DWR is designed and fabricated. Good agreement between the simulated and measured responses validates the design idea.