In this paper, a resonator-fed wideband and high-gain patch antenna with enhanced selectivity and reduced cross-polarization are proposed. First, a slot-loaded square patch antenna is chosen to operate in TM mode, and so high gain can be realized. Second, the antenna consists of two resonators below patch and can be equivalent as a third-order cascaded trisection (CT) filter. Three transmission poles are produced to widen the bandwidth, and additional attenuation pole caused by cross coupling is introduced at the low side of passband to improve the selectivity of antenna response. Third, a new extraction method based on the properties of second-order filter network is proposed to derive the coupling coefficient between each resonator and patch under complex coupling condition. At last, the feeding structure helps to suppress the adjacent even modes, which significantly reduces the cross-polarization of the antenna. The simulated and measured results demonstrate that the antenna has achieved 6.2% bandwidth, up to 14.4-dBi high gain, and more than 30-dB cross-polarization suppression.