A Compact Rat-Race Coupler With Widely Tunable Frequency- and Power-Dividing Ratio
Xiangguan Tan, Yuxia Zhang
Abstract
This letter presents a novel compact rat-race coupler that allows for simultaneous tuning of its operating frequency and power-dividing ratio. By substituting the tunable transmission-line Section of the varactor-based rat-race coupler with two novel types of tunable units, it enables a wide tuning range for both frequency and power division ratio. To demonstrate the effectiveness of the design, a compact rat-race coupler was designed, processed, and measured. In the frequency-tunable mode, the measured 3-dB operating frequency can be adjusted from 1.2 to 3.1 GHz, while maintaining return loss and isolation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${>}15$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${>}35$ </tex-math></inline-formula> dB, respectively. Under the power-dividing ratio-tunable mode, the measured power-dividing ratio of the coupler can be adjusted within ranges from −5 to 17 dB, −11.4 to 8 dB, and −12.1 to 4 dB at 1.2, 2.2, and 3.0 GHz, respectively. Compared to the existing couplers of the same type, the proposed coupler has the widest frequency tuning range.