W-Band Waveguide Filters and Diplexer Using Metal Stripline Resonators

A method to design E-plane W-band waveguide bandpass filters (BPFs) and diplexer using metal stripline resonators (MSRs) is presented in this article. The center frequency and bandwidth of the BPF can be flexibly tuned by controlling the locations of the transmission zeros (TZs), which are generated by MSRs. To understand the working mechanism behind the BPF, an LC equivalent circuit model is constructed and extracted. For demonstration, two BPF examples with different operating frequencies are fabricated and tested. Both of the low-frequency BPF and high-frequency BPF have four TZs and two transmission poles (TPs), with center frequencies at 85.6 and 94.5 GHz, respectively. Furthermore, a diplexer is constructed through the combination of two above BPFs and a waveguide T-junction, whose experimental results validate the proposed idea. The measured minimum insertion losses (ILs) are 1 and 0.8 dB in the low-frequency and high-frequency passbands, respectively. The designed filters and diplexer have the properties of easy fabrication, small sizes, and low losses with multiple TZs.