Wideband arbitrary phase-difference coupled-line coupler with tight coupling coefficient and small phase variation

摘要

In this study, a planar arbitrary phase-difference coupled-line coupler having wide bandwidth, tight coupling coefficient, and small phase variation are proposed. The proposed coupler consists of two quarter-wavelength coupled-line sections connected with two different transmission lines. Moreover, the interconnection transmission line can be designed as a small phase variation phase shifter with the introduction of a shorted stub. The detailed theoretical analysis is provided to illustrate the design concept. The circuit parameters of this novel arbitrary phase-difference coupler can be easily determined by the derived closed-form equations. For verification, two 3 dB couplers with 45°/135° and 60°/120° phase differences are fabricated and measured. The 45°/135° coupler achieves 34.2% fractional bandwidth for 45° phase difference with 2° phase variation and 36.3% fractional bandwidth for 135° phase difference with 3.4° phase variation. Moreover, the 60°/120° coupler achieves 30% fractional bandwidth for 60° phase difference with 0.9° phase variation and 32.9% fractional bandwidth for 120° phase difference with 1.5° phase variation.