A study on broadband multi-hole directional coupler

The conventional theories of waveguide directional couplers, including Bethe's theory, correction theory, and multi-hole array theory, can be a good start for designing very tight multi-hole couplers with square coupling apertures. Comparing with the conventional theory and HFSS, a modified Cohn's empirical factor of thickness attenuation was obtained. A 0 dB-waveguide multi-hole coupler (X-band) is fabricated, and the calculated coupling and directivity are compared with HFSS simulation and measured values, showing a good agreement.