Waveguide Multiplexer for Sub-Terahertz Direct Detection Receivers

A four-channel waveguide multiplexer operating at 180 GHz is presented and analyzed in this paper. The four channel filters are centered at 178.8 GHz, 180.3 GHz, 181.5 GHz, and 182.3 GHz, with very narrow bandwidths of 1.7 GHz (0.9%), 0.85 GHz (0.47%), 0.85 GHz (0.47%), and 0.425 GHz (0.23%), respectively. The three lower-frequency channels employ 8thorder configurations, each consisting of four dualmode TE301/TE102 rectangular cavity resonators, while the highest-frequency channel adopts four TE201 and one TE101 rectangular cavity resonators. The multiplexer was fabricated in brass using high-precision computer numerical control (CNC) milling, followed by a gold surface coating to minimize losses. The measured insertion losses (ILs) of the four channel filters were 3.0 dB, 5.0 dB, 5.7 dB, and 22.5 dB, respectively, with observed centre frequency upward shifts of 0.80 GHz (0.45%), 0.88 GHz (0.49%), 0.76 GHz (0.42%), and 1.47 GHz (0.81%).