To overcome the disadvantage of low radiation power for photoconductive antenna,three types of antennas,including dipole,bow-tie and spiral antennas,are studied,where finite integration technology are used to compute their radiation impedances.The simulation results show that the impedance of dipole antenna is dependent on the dipole length,width,photoconductive gap and the width of transmission line,and has a peak value in resonant frequency,so the dipole antenna is suitable for applications working at specific terahertz frequency.The bow-tie and spiral antennas,known as broadband antennas,have approximately stable impedance over the terahertz frequency range under study.The simulation results also show that,the interdigitated fingers,which can be modelled as an additional capacitance,cause the antenna impedance to fall dramatically at high frequency.