Reconfigurable Branch-Line Coupler with Tunable Phase Difference

A branch-line coupler is proposed with tunable phase difference. Variable capacitors are used to control the phase difference between output ports continuously. The expressions of capacitances are derived by using the even-/odd- mode method. To demonstrate the design theory, a phase-tunable prototype is designed at 1 GHz with a swap phase inverter. The full-wave simulated results show that this structure can provide tunable phase difference from 45° to 135° while maintaining the equal power division with relative wide operating band of 23%.