Bandwidth Enhancement of 4 $,\times,$ 4 Butler Matrix Using Broadband Forward-Wave Directional Coupler and Phase Difference Compensation

A broadband Butler matrix by combining the proposed broadband forward-wave directional coupler and a broadband middle network is proposed. Test samples of both the proposed coupler and Butler matrix are fabricated on Ro4003 and the sizes are 0.4 λ_g × 0.14 λ_g and 1.02 λ_g × 1.17 λ_g, respectively. For the Butler matrix, the amplitudes of the output signals and the phase imbalances between output ports can be kept at an approximately constant level. The errors of phase imbalances can be kept within ±6^° from 1.96 GHz to 3.15 GHz and the corresponding fractional bandwidth is 47%.