A Single-Layer Hollow-Waveguide 8-Way Butler Matrix

The authors propose a single-layer hollow-waveguide 8-way Butler matrix. All components of the Butler matrix are in a single layer which contributes to low-cost fabrication. To reduce the length of the couplers, a step structure is installed in the coupled region. 50% length reduction is obtained in comparison with the conventional design using reflection-suppressing posts in the coupled region. The total size of the matrix is 17.1λg × 6.0λ g . The full structure of the matrix is fabricated by hollow waveguides at 22 GHz band and the total measured loss is only 0.25 dB.