SU-8 micro-machined WR-4 H-plane diplexer with dual-mode resonator

This article presents a WR-4 band (170-260 GHz) H-plane diplexer based on the SU-8 micromachining process with a dual-mode resonator structure. The proposed diplexer features two fourth-order bandpass filters, achieving passbands of 215-218 and 221-224 GHz. This proposed design employs dual-mode rectangular waveguide resonators, and a non-resonant junction is formed by three non-resonant node resonators connecting the two passbands. The entire diplexer used for measurement includes the designed diplexer and three bends and requires only two SU-8 chips fabricated via a three-layer process to form the entire circuit. In addition, the preparation process of the SU-8 chips, the existing challenges, and the corresponding approaches are described in detail. Moreover, a fixture with upper and lower clamping blocks is designed to ensure measurement accuracy. The measured return loss values of the entire fabricated device in the two channels are about 12 dB and their center frequency shift values in the high-frequency direction are ∼1.5 and 1 GHz for the lower and higher bands, respectively. The good agreement between measurement and simulation results can be attributed to the high-precision fabrication process and carefully optimized design.