Design of a compact 3dB Ka-band directional coupler

Based on the theory of Bethe hole coupling, a broadband directional coupler is designed by combining the attenuation factor of coupled waves and the field averaging correction factor. A 3dB directional coupler at Ka-band is designed in this paper. First, according to the required specification, the relevant parameters of equally spaced waveguide directional coupler are preliminarily designed based on the modified Bethe aperture coupling theory. Then in order to get the required specification directional coupler, the distance between two coupling holes and the diameter of the holes are simulated and optimized using the electromagnetic simulation software CST. Finally by folding the coupling waveguide, the length of the directional coupler is reduced by 30% to achieve miniaturization.