Design of a Ka-band broadband TE01○ - TE10□ multi-aperture directional coupler

Based on the theory of small aperture coupling, a Ka-band broadband TE₀₁^ο- TE₁₀^□ multi-aperture array directional coupler is designed to measure the output power and monitor the spectrum for Gyro-TWT. The radius of circular waveguide and the distance between adjacent coupling apertures are determined according to the principle of forward superposition and backward offset. Some numerical calculations about the change of coupling degree and directivity with coupler´s size have been done. The analysis shows that increasing the number, reducing the thickness of coupling aperture and enlarging the radius of hole can improve the coupling degree, and that increasing the number also can raise the directivity within a certain working frequency band. At the same time, the optimal parameters of 16-apertures directional coupler are given and simulated by the electromagnetic simulation software CST, the results of simulation agree with numerical calculation approximately. The coupling degree is -35 dB±0.9 dB and the directivity is over 20 dB within 6 GHz bandwidth.