A Novel Tri-Beam Antenna System Based on U-Shaped Dipole

Abstract

Consisting of 6 radiating elements and a 3 × 3 Butler matrix, a novel tri-beam antenna system is proposed in this paper. The radiating element consists of two U-shaped arms and coupled strips, which shows a wide impedance characteristic. Three branch line couplers and four -90° phase shifters are combined into 3 × 3 Butler matrix as a beam-forming network (BFN). In order to avoid the crossover of transmission lines, one main line of a 1.76 dB coupler is designed and located between two 3 dB couplers. With this arrangement, the signal from one input port can be divided into three output signals with equal amplitude and specified phase differences of 0°, +120° and -120°. Furthermore, a 2 × 3 antenna array is connected with this BFN for three orthogonal beams. Measured results show that three beams at θ = 0°, 40° and -40° are produced when different input ports are excited.