Design of a Beam Switching/Steering Butler Matrix for Phased Array System

A compact broadband 8-way Butler matrix integrated with tunable phase shifters is proposed to provide full beam switching/steering capability. The newly designed multilayer stripline Butler matrix exhibits an average insertion loss of 1.1 dB with amplitude variation less than ??2.2 dB and an average phase imbalance of less than 20.7?? from 1.6 GHz to 2.8 GHz. The circuit size is only 160 ?? 100 mm², which corresponds to an 85% size reduction compared with a comparable conventional microstrip 8-way Butler matrix. The stripline tunable phase shifter is designed based on the asymmetric reflection-type configuration, where a Chebyshev matching network is utilized to convert the port impedance from 50 ?? to 25 ?? so that a phase tuning range in excess of 120?? can be obtained from 1.6 GHz to 2.8 GHz. To demonstrate the beam switching/steering functionality, the proposed tunable Butler matrix is applied to a 1 ?? 8 antenna array system. The measured radiation patterns show that the beam can be fully steered within a spatial range of 108??.