Waveguide loop-type directional coupler using a coupling conductor with protuberances

The waveguide loop-type directional coupler is mainly used as a power monitor of the waveguide circuits. It consists of a rectangular waveguide as a main line and a coaxial line as a coupled line. The coaxial line is coupled with the rectangular waveguide through a coupling hole which is smaller than quarter-wavelength. Therefore the waveguide loop-type directional coupler degrades the coupling deviation. The authors propose the waveguide loop-type directional coupler using a coupling conductor with protuberances in order to improve the coupling deviation. In this report, the proposed waveguide loop-type directional coupler was fabricated in the Ku-band, and compared with the conventional coupler. The coupling deviation in the 10% bandwidth of the proposed waveguide loop-type directional coupler is 0.8 dBp-p lower than the conventional one.