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

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 1.76dB coupler is designed and located between two 3dB couplers. With this arrangement, the signal from one input port can be divided into three output signal with equal amplitude and specify 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