  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
behavior of the gap between the electrodes, and a controlled voltage dependant
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.
