The generation of terahertz radiation using photoconductive antennas is becoming very popular. Several experimental and simulation studies have been performed to study the characteristics of the photoconductive antenna (PCA). Although various methods have been proposed to increase the radiated power from it, the radiated power remains very low. In this paper, we present an analytical study of improving the radiated power from a large aperture PCA using an external magnetic field source. The transit time behavior of the carriers is computed using the basic semiconductor carrier dynamics model, including the transient mobilities with the dependencies on the electric field and carrier's concentration. Analytical studies show that substantial enhancement in the radiated field can be achieved when such external magnetic field is applied. Furthermore, the polarity of the radiated field depends on the orientation of the applied magnetic field. The results obtained from analytical calculations exhibit similar behavior as reported in some experimental results. © 2017 IEEE.