A 5 × 8 Butler Matrix Based on Substrate Integrated Waveguide Technology for Millimeter-Wave Multibeam Application

A 5 × 8 Butler matrix (BM) operating in the millimeter-wave band is presented in this letter. The matrix is extended from two 3 × 4 Butler matrices by adding two couplers and one power divider, providing an equal amplitude signal distribution with five phase differences between the adjacent output port (0°, ±45°, ±135°). In order to reduce the number of crossover and complexity of the matrix structure, a dual-layer and symmetrical substrate integrated waveguide (SIW) structure is used to design the proposed BM. To verify the concept, an experimental BM is designed and fabricated as the feeding network of a slot antenna array, achieving five beams in the frequency range of 27.8-30.8 GHz.