Novel application of Substrate Integrated Cavity (SIC) for suppressing cross-polarized (XP) radiation in hexagonal microstrip antenna has been proposed. The proposed design consists of a pair of tiny circular SICs consisting of metallic vias located symmetrically on the H-plane of the hexagonal patch. The design has been simulated in Ansys HFSSTM to establish the proposition that the incorporation of SIC does not affect the fundamental mode of resonance and the co-polarized radiation levels of the conventional antenna considerably but effectively reduces the cross-polarization radiation levels. An isolation of −81 dB of cross-polarization level from its peak has been obtained at the boresight of the patch. Compared to the conventional hexagonal patch, a relative suppression in cross-polarization of 49 dB at the boresight and 15 dB throughout in both the principal planes has been achieved.