Radiation from a Terahertz Photomixing Antenna (PMA) involves multi-physical phenomena. We introduce a simple analytical model that combines the multi-physical phenomena in the PMA using a conventional 2-ray model. We observe reasonably close agreement between the antenna output obtained from the proposed model and the available measured results. We extend our analytical framework to incorporate the presence of an additional signal source on one of the laser beams, intended towards producing modulation in the PMA output signal. We analytically investigate the active region current density and radiated fields of the PMA. We also present a brief discussion on the efficiency of the PMA and the different factors that impact the efficiency. The output power depends on some key parameters which can be utilized to make PMAs suitable for sensing as well as wireless communication applications. © 2019, © 2019 IETE.