In this paper, a 20-GHz-band 64 × 64 hollow waveguide Butler matrix is proposed. By using two-plane short slot couplers and a modified diagram, a short-axis two dimensional Butler matrix is realized. The design method of the diagram and components is presented. The Butler matrix is composed of two plane hybrids, cross couplers and phase shifters. The designed Butler matrix is fabricated by milling and screwing together nine aluminum plates. The dimensions and weight are 86.40 mm × 74.19 mm × 396.34 mm and 7.0 kg, respectively. Transmission characteristics as a beam switching circuit are characterized by measurements, with a low insertion loss of less than 1.8 dB and an excitation error of 4-dB and 40-deg. standard deviation. Radiation characteristics as a 64-beam antenna are measured, and a wide coverage area of 40% of the hemisphere and high directivity of more than 18.7 dBi were determined by measurements. INDEX TERMS Butler matrix, hollow waveguide, two dimensional beam switching, two-plane short slot coupler.
This paper presents the mode matching (MM)/finite element method (FEM) hybrid analysis for a short-slot 2-plane coupler, and an optimization process for a wideband design based on a genetic algorithm (GA). The method of the analysis combines a fast modal analysis of the MM which reduces the computation time, with the flexibility of an FEM which can be used with an arbitrary cross-section. In the analysis, the model is reduced into the one-eighth model by using the three-dimensional structural symmetry. The computed results agree well with those by the simulation and the computation time is reduced. The bandwidth is improved by the optimization based on the GA from 2.4% to 6.9% for the 2-plane hybrid coupler and from 5.4% to 7.5% for the 2-plane cross coupler. The measured results confirm the wideband design.
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