Design of waveguide narrow-wall 3dB coupler for 3mm-wave frequency band

A wideband waveguide narrow-wall short-slot 3dB directional coupler is proposed for 3mm-wave frequency band. It is based on the optimized oversized coupling region length and impedance matching block size with as few as possible parameters and without using waveguide transformers, so the coupler has a low fabrication cost and compact size. Design result has achieved an over 15% bandwidth at center 92GHz with a coupling variation of less than 0.25dB, -30 dB isolation and return loss, and result of the tolerance analysis is shown that the proposed coupler is applicable to engineering applications.