In this paper, to ensure a broadband and accurate 180° phase, the element mirroring design is adopted, achieve cross-polarization conversion for incident polarizations. The proposed unit exhibits a relative bandwidth of 20.9% and demonstrates excellent angular stability, maintaining a maximum oblique incidence angle of up to 30°, under which the polarization conversion rate remains above 90%. Simulation results indicate that the unit exhibits exceptional amplitude and phase performance within the frequency range of 25.3–31.2 GHz, with the cross-polarized reflection coefficient consistently exceeding −2 dB. Then, an electronically reconfigurable reflectarray comprising 196 units has been developed, achieving low-loss beam scanning functionality in full space at 30 GHz, with a maximum gain of 21 dB. Furthermore, the proposed technique can be applied to terahertz reconfigurable reflectarray metasurfaces, enhancing multi-polarization detection and the wide beam-steering capability of terahertz radar systems. This advancement enables flexible transmission and reception of terahertz waves and phased radiation, demonstrating significant potential for low-loss terahertz radar systems.