Design of Blass-like Matrix Based Wideband Beamforming Network with Arbitrary Power Distributions

In the paper, a wideband 4 × 4 beamforming network with arbitrary power distributions is proposed which is based on the topology of Blass-like matrix. The structure consists of several directional couplers and phase shifters. The directional couplers contribute to the output amplitude distributions. While the phase shifters maintain the consistent of the output phase differences and provide phase compensation for realize wide phase bandwidth. Theoretical analysis is performed for this beamforming network, and the exact relations between the circuit parameters and the output distributions are derived. For the purpose of bandwidth enhancement, different directional couplers are utilized, which includes four three-branch directional couplers and twelve four-branch directional couplers. In addition, phase shifters are inserted to the output ports and between the couplers for balancing the phase slope of this serial network, leading to wide phase bandwidth. For demonstration, a 4 × 4 prototype with the power division ratio of 0.143 : 0.341 : 0.710 : 1 and the output ports phase differences of −45°, 135°, 45° and −135° is designed at the center frequency of 5.8 GHz. Measurement results show that the designed prototype exhibits an overlapped fractional bandwidth (FBW) of 15% under the criterion of |S
11
| < −10 dB. And in this bandwidth, the isolations between the adjacent input ports are all larger than 20 dB. Moreover, in the FBW of 10% (5.51–6.09 GHz), the maximum amplitude and phase difference errors are 1.5 dB and 16°, respectively. Due to the advantages of wideband, arbitrary output power distributions, and balanced phase performance, the proposed beamforming network has potential applications in low side lobe multibeam antennas.