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 mm
²
, 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°.