A single-layer hollow-waveguide 8-way Butler matrix

The authors apply a reduction method to hollow waveguides. The post-wall waveguide is a dielectric-filled waveguide and the measured transmission loss is 0.039 dB/cm at 25.6 GHz. A hollow waveguide has very low loss and the calculated transmission loss is 0.004 dB/cm. The loss of the full structure of an 8-way Butler matrix using hollow waveguides is estimated to be only 0.2 dB. In order to realize many divisions in a single layer waveguide, many cross couplers are arranged. The length reduction of the couplers, especially the cross couplers, is important in order to miniaturize the full structure. By the proposed method, the cross coupler is 50% shorter than the conventional design method.