In this work, we report a THz generalized Ellipsometer which is able to independently genereate and detect s- and p- polarization by tailoring the metal pattern of photoconductive antennas used as both the emitter and detecotr. Coupled with a rapid-scanning delay line (10Hz), we are therefore able to retrieve the optical constants of birefringent samples with randomly orientated optical axis without cumbersome extra components or time-consuming mechanical operations.