Effects of substrate on the performance of photoconductive THz antennas

Photoconductive antennas have been widely used to generate and detect THz waves in recent years. Because the thickness of the substrate is usually larger than the wavelength of THz waves, surface/substrate modes may be generated and the effect of the substrate cannot be ignored - this has not been properly investigated. This paper is therefore to investigate this problem using a numerical simulation tool. The radiation pattern and power of photoconductive antennas with different sizes of substrates are obtained. The results show that the radiated power is sensitive to the dimensions of the substrate: most of the radiated power is radiated towards the substrate side rather than the free space, and a thin substrate is preferred to maximise the radiated power and control the radiation direction.