A Compact 3 dB ${\rm E}$-Plane Waveguide Directional Coupler With Full Bandwidth

A compact 3 dB E-Plane waveguide directional coupler (patent pending) with full bandwidth is proposed in this letter. It consists of a pair of rectangular waveguides placed parallel to each other along their broad side. The tight coupling and wide bandwidth are achieved by using reduced height waveguide and large aperture in the common broad wall of the two parallel waveguides. For verification purpose, a prototype has been manufactured and measured. The measured results show that return loss and isolation of the coupler better than 25 and 26 dB, respectively, and the power-split unbalance within 0.6 dB are achieved over the full waveguide bandwidth.