In this article, a wideband linear-to-linear and linear-to-circular reflective polarization converter is discussed. The proposed polarization converter can efficiently convert an incoming wave with a linear polarization into a reflected wave with orthogonal polarization in the frequency ranges: 7.63–12.21 GHz and 19.34–21.2 GHz. Moreover, a circularly polarized reflected wave in the frequency band of 13.85–18.50 GHz is also obtained. The proposed polarization converter constitutes a split-ring and a metallic strip cut in the middle designed on an ultrathin single substrate layer (thickness of 0.079λ o, where λ o corresponds to wavelength at center frequency of lowest operational bandwidth). The study related to angular dependence of the proposed polarization converter is also carried out and a stability upto 15° is achieved at the lower and upper-frequency bands of operation, respectively. A prototype of the proposed polarization with 25 × 25 cells of the converter is fabricated and measured. Measurement results are in consensus with their simulated counterparts. Furthermore, a 12 × 12 array of the proposed polarization converter is used to study the radar cross-section (RCS) reduction ability of a microstrip patch antenna operating in X-band. The average RCS reduction of about 11 dBsm is obtained at normal incidence. The proposed polarization converter can be utilized in X/Ku/K frequency band applications.