A Compact Broadband 4×4 Butler Matrix With 360° Continuous Progressive Phase Shift

This article presents a novel compact broadband
$4\times 4$
Butler matrix with 360° continuous progressive phase shift. The tunable Butler matrix is composed of a typical
$4\times 4$
Butler matrix and four wideband continuously tunable phase shifters (PSs). To realize the size miniaturization, the right-handed transmission line (RHTL) is employed to construct the compact branch-line couplers and crossovers, which performs well over the operating bandwidth. The size of the proposed Butler matrix utilizing the compact coupler and crossover is reduced about 50% compared with the traditional design. A novel coupled-resonant PS is proposed to realize
$135^{\circ }\pm 10^{\circ }$
continuous phase shift over a wide fractional bandwidth (FBW) of 33.3% (2.0–2.8 GHz). By cascading the miniaturized
$4\times 4$
Butler matrix and the 135° continuously tunable PSs, 360° continuous progressive phase shift between four outputs can be obtained. The measured results verify the feasibility of the design.