Simultaneous Amplitude- and Phase-Tunable Coupler With Wide Phase Tuning Range

Abstract

In this article, a coupler with simultaneously tunable power division ratio (PDR) and phase difference is proposed based on a multivector summation method. Two groups of varactor diodes are installed on the cross-shaped quarter-wavelength coupled lines to realize the proposed tunable coupler. The horizontal coupled lines serve as the subcouplers to generate multiple vectors, while the vertical coupled lines serve as the phase-tunable units (PTUs) to control the phase of the vectors. The phases of the PTUs can be therefore tuned by the varactor diodes. With a proper combination of the capacitance of the varactor diodes, the amplitude and phase characteristics of the proposed coupler can be controlled independently. For demonstration, a highly tunable coupler operating at 1.8 GHz is designed, fabricated, and measured. The PDR of the coupler can be tuned from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 7 to 1 dB with a 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> phase difference, while the phase difference of the coupler can be tuned within a wide range from 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> to 165 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> with equal power division. Better than 10-dB return loss and 15-dB isolation can be observed under different states.