Design and Characterization of 4×4 Butler Matrix for Switched-Beam Antenna Array

As is already known, Butler matrix is one of essential beamforming networks frequently applied for multiple beams. This is due to its characteristics which has high beam crossover level and lossless property. In this paper, a 4×4 Butler matrix is designed and fabricated to be implemented for switched-beam antenna array. It is deployed on an FR4 epoxy dielectric substrate with the thickness of 0.8 mm and the dielectric constant of 4.3. The conductor patch and groundplane use metallic copper with the thickness of 0.035 mm. Some key parameters of Butler matrix such as the amplitude and phase responses are characterized and investigated through simulation and measurement. The characterization results demonstrate that the proposed 4×4 Butler matrix takes the overall size of 136.4 mm × 87.5 mm (2.26λg × 1.45λg) and shows good amplitude and phase performances. The progressive phase difference of −40.52° ± 6.99° and the amplitude of −8.32 ± 1.08 dB were achieved at the operating frequency of 2.4 GHz. Meanwhile, the measured return loss fractional bandwidth of 16.25% could be attained at the frequency range of 2.15 GHz to 2.54 GHz.