Design of a variable directional coupler in rectangular waveguide

A design theory for a three-aperture rectangular waveguide coupler with adjustable directivity and coupling factor achieved by introducing a very thin slice of an anisotropically conducting material like pyrolytic graphite in the central aperture is discussed. By suitable adjustment of the orientation angle of the anisotropically conducting aperture, the directivity can be maintained at very high value over a bandwidth given by 0.5 not greater than lambda sub g0/lambda sub g and not less than 1.5. The corresponding variation of coupling factor with lambda sub g0/lambda sub g has been presented and variation of coupling factor and directivity with orientation angle at the design frequency has been studied.