A novel tri-beam slot antenna array based on substrate integrated waveguide (SIW) technology is proposed in this paper. The beam forming network is a 3 × 3 Butler matrix consisted of three couplers and four phase shifters. A 1.76 dB coupler is located between two 3 dB couplers, with this arrangement; the input signal can be divided into three parts with the same amplitude and certain phase differences. Two parallel slots are cut off broadside of SIW transmission line, which constitutes the basic unit of the antenna array. A 3 × 2 slot antenna array is connected with this circuit. Three beams with the directions of −30, 0 and 30° are produced when different ports are excited, respectively. The S parameters, radiation patterns, and gains are simulated and measured, which show that it can be a candidate for multi-beam wireless communication systems.
