A metal-only reflect-transmit-array unit cell whose operation is dependent on the incident polarization is presented. The proposed unit cell is based on 3D geometry which allows a high level of independent phase tuning for orthogonal and linear incident polarizations. In our unit cell, the horizontal polarization is reflected while the vertical polarization is transmitted. The modification of the reflected phase is done by the length of a metal block located at the end of the slits where the horizontal polarization propagates. The modification of the transmitted phase is changed by the depth of the corrugations implemented in the slit that supports the propagation of the vertical polarization. The results obtained in transmission mode show an impedance matching below -15 dB with a linear phase response from 30 GHz to 50 GHz. For the reflected polarization, there is almost total reflection with phase performance that is also linear along the frequency.