Terahertz couplers based on branch lines and waveguide resonators

This paper presents two waveguide quadrature hybrids in the WR-3 band, which are designed to be fabricated by computer numerical control milling process with relaxed branch width requirements. An E-plane four-branch directional coupler gives an amplitude imbalance less than 0.8 dB and a phase difference between 88° and 94° from 240 to 324 GHz. Another design is an H-plane bandpass coupler composed of cavity resonators, showing a bandwidth of 2% near 300 GHz.