A Novel 3-dB Waveguide Hybrid Coupler for Terahertz Operation

This letter presents our investigation into a 3-dB waveguide hybrid coupler of a novel structure in the submillimeter frequency band. The proposed coupler has only three coupling branches with a circular cutout at the top and the bottom on both sides of the main branch and is of compact size. The simulation shows that the proposed design has eased the machining difficulty by providing more tolerance to fabrication errors. The simulation also shows that the amplitude imbalance of the proposed hybrid branch is 25% less than that of the traditional three-branch hybrid structure. The proposed coupler structure is verified in experiment through measuring a fabricated 90° waveguide coupler at a center frequency of 195 GHz with approximately 13% bandwidth where the amplitude imbalance is less than 0.3 dB. The simulated and measured S-parameters have shown that the amplitude and phase imbalances are within 0.3 dB and 4°, respectively, with an isolation and return loss of 17 dB.