A wideband design of the waveguide short-slot 2-plane coupler with 2×2 input/output ports is designed, fabricated, and evaluated. Using coupling coefficients of complementary propagating modes which are TE11, TE21, and TE30 modes, the flatness of the output amplitudes of 2-plane coupler is improved. The coupler operates from 4.96GHz to 5.27GHz (bandwidth 6.1%) which is wider than the former coupler without considering the complementary propagating mode from 5.04GHz to 5.17GHz (bandwidth 2.5%).

A 42×42-way one-body 2-D beam-switching Butler matrix with waveguide short-slot 2-plane couplers is designed and fabricated in the 22GHz band. The one-body configuration using the commutativity and the overlapping of units allows reducing the size and loss in comparison with a cascade of matrices beam-switching for the horizontal and the vertical planes. It is achieved by replacing 2×2-way 1-plane couplers in the conventional block configuration for a Butler matrix with 22×22-way 2-plane couplers. The measured bandwidth is approximately 2% restricted by the frequency characteristics of the 2-plane couplers. In the radiation from the aperture array antenna of the 42 output ports, the 3.9dB-down coverage of 3-D solid angle by the sixteen beams is around 1.72 steradian which is same as 27.4% of hemisphere at the design frequency for the aperture spacing of 0.73×0.73 wavelength.

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 17.1λg6.0λg. 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.

The authors realize a 50% length reduction of short-slot couplers in a post-wall dielectric substrate by two techniques. One is to introduce hollow rectangular holes near the side walls of the coupled region. The difference of phase constant between the TE10 and TE20 propagating modes increases and the required length to realize a desired dividing ratio is reduced. Another is to remove two reflection-suppressing posts in the coupled region. The length of the coupled region is determined to cancel the reflections at both ends of the coupled region. The total length of a 4-way Butler matrix can be reduced to 48% in comparison with the conventional one and the couplers still maintain good dividing characteristics; the dividing ratio of the hybrid is less than 0.1 dB and the isolations of the couplers are more than 20 dB.