This thesis employ the method of moments, a numerical integral equation method, to model the induced surface currents on metallic antennas located on a semiconductor substrate. The purpose is to gain insight into modelling photoconductive antennas for THz generation. The electric field integral equation and the dyadic Green's tensor for a planar interface between isotropic media is obtained. Using the method of moments, the electric surface currents induced on a perfect electric conductor by an incident field is acquired, which allows for the calculation of scattered fields. A MATLAB script, which calculates the induced current on an arbitrary three-dimensional perfect electric conductor, and the scattered electric field have been produced, as well as the far-field scattered radiation pattern for antenna structures located on a semiconductor substrate. A possible short coming of the method of moments was identified, namely that a variation in the cross sectional surface current was present when the excitation source was an incident plane-wave. A possible solution to this was presented as a voltage feed excitation method. Using this method, the radiation patterns for antenna arrays with different inter antenna distances placed on a substrate was presented, and a possible optimal inter antenna distance was proposed.