Most reconfigurable couplers proposed before can only tune single characteristic, thus restricting its application. To address this deficiency, a coupler with simultaneously tunable frequency, phase difference and coupling coefficient is proposed based on a single circular patch. According to the analysis of the circular patch, a cross-shaped slot with different lengths is introduced at the center of the patch to control the coupling coefficient. To realize the reconfigurability, two pairs of varactor diodes are placed at the four feeding lines for frequency and phase difference tunabilities. While another two pairs of varactors are loaded at the four ends of the slot to tune the coupling coefficient. For demonstration, the coupler is designed, fabricated and measured. Good agreement between measured and simulated results verify that the proposed coupler can realize tunable frequency from 1.3 to 1.9 GHz, tunable phase difference from 50° to 130°, and tunable coupling coefficient from 3 to 10 dB at 1.3, 1.5 and 1.7 GHz.