In this paper, a novel decoupling scheme is proposed to suppress the mutual coupling between the two ports of a single patch antenna (SPA), while maintaining the radiation properties of each port with co-linear polarization, co-radiating aperture, and broadside radiation patterns without deterioration in gain. For this purpose, a pair of λ/4 nonradiative stubs are introduced and loaded symmetrically in the SPA. Thanks to the good feature that the nulls of the composite fields of TM and TM modes are present only near the coupled port, both radiating apertures of the SPA can operate simultaneously. Moreover, the decoupling principle, equivalent transmission-line models, and design guidelines are extensively illustrated. The measured results show that each port of the SPA has a broadside radiation pattern with co-linear polarization and about 7-dBi gain under isolation improvement. As such, this two-port SPA, with the size of 0.41*0.37*0.04*λ, can be equivalent to a two-patch antenna array with 0 edge-to-edge distance. Most importantly, the proposed decoupling method is achieved without compromise in the three degrees of freedom (i.e., co-polarization, similar radiation pattern, and co-radiating aperture), which is a tough challenge nowadays. This decoupling approach allows the two-port SPA could be an alternative solution in MIMO systems or in-band full-duplex systems.