This paper presents a balanced-to-balanced microstrip power divider with a wide range of continuously tunable power-dividing ratios for either in-phase or out-of-phase outputs. Based on simple design equations, the proposed power divider can theoretically attain ideal mixed-mode responses, including the in-phase and out-of-phase designs, for an arbitrary power ratio by a proper control of the used varactor capacitances. A single-layer power divider was prototyped and measured. Given the differential-mode return loss and output isolation greater than 15 dB, the power-dividing ratio was tuned from 11.1 dB to 24.2 dB and from 1.3 dB to 21.1 dB for the in-phase and out-of-phase outputs, respectively. For all states, the common-mode suppression achieved greater than 63.9 dB at the center frequency.