THz photoconductive antennas are among the most popular devices for THz wave generation and detection. A novel and accurate circuit is proposed to model the performance of such antennas, especially those which are frequency dependant. The suggested equivalent circuit consists of an external source voltage, a source input admittance, a loss resistance related to the electrode loss resistance, a frequency-dependant capacitance associated with capacitive behaviour of the gap between the electrodes, and a controlled voltagedependant source representing the screening of photo-carriers. Based on this model, the radiation from a simple frequency dependent antenna, i.e. a dipole antenna, is investigated. Excellent agreement is observed between the obtained results by the proposed equivalent circuit model and those by measurement.