Phase Reconfigurable Hybrid Coupler Implemented Using Capacitor-Loaded Transmission Lines

Abstract

This paper presents a reconfigurable phase difference of hybrid coupler design. The proposed design is developed based on a branch-line coupler structure where a pair of conventional lines directly connecting the input and output ports are replaced by variable electrical length lines. To realize variable-length lines, a loaded-line structure composed of three microstrip line segments with four loading capacitors is adopted. A circuit prototype working at 2.4 GHz frequency is realized and measured for verification. Measurement results demonstrate that the proposed coupler can exhibit a reconfigurable phase difference characteristic. By varying capacitances of 0.5 pF to 2.5 pF, a phase difference range of 45° from -67.5° to -112.5° can be achieved. The prototype has the size of 18.2 mm by 41.2 mm, which is smaller than the conventional one.