In this letter, a self-balanced wideband patch antenna fed with a U-resonator is proposed to realize sidelobe reduction, even-mode suppression and bandwidth enhancement. Initially, a rectangular slot is embedded at the center of patch to interrupt and reshape its out-of-phase current, by which sidelobe radiation is significantly reduced. Then, a U-resonator is introduced at the bottom to improve the radiation performances of the resultant antenna in two ways. First, the half-wavelength U-resonator can differentially feed the patch and suppress the even mode of the radiating patch, so as to realize stable broadside radiation with no need of additional phase shifters or baluns. Second, an additional resonant mode is generated by the U-resonator, contributing to wider bandwidth. The simulated and measured results demonstrate that its impedance bandwidth is dramatically enhanced to 60% under triple resonance. Besides, improved radiation performance with low sidelobe level and more consistent beamwidth are realized, while the gain response is nearly flat in operating band and effectively rejected out of band.