The photoconductive antenna is the most widely used device to generate the Terahertz (THz) wave but it has a limitation that the generated power is very low, and usually has poor directivity. In order to improve output power and directivity of photoconductive terahertz antenna, this paper investigate effects of substrate thickness on the performance of photoconductive terahertz antennas. The radiation pattern and power of photoconductive antennas with different sizes of substrates are obtained. The results show that most of the radiated power is radiated towards the substrate side rather than the free space, and a thin substrate is preferred to maximize the radiated power. In order to improve the power of the photoconductive terahertz antenna at a desired direction, this paper introduces a structure integrates a conical horn to a photoconductive antenna. After optimization, simulated results show that a directivity of 20. 7 dBi can be achieved. So the antenna can generate THz wave efficiently and radiate to a desired direction.%光电导天线被广泛用于太赫兹波的产生,但是产生的太赫兹功率较低,方向性差.为了改进光电导太赫兹天线输出功率与方向,研究了不同基底厚度对光电导天线辐射功率的影响,其仿真结果表明:辐射功率受基底厚度影响明显,大部分辐射功率进入基底的一侧而不是自由空间,厚度薄的基底更能辐射出较大的功率.为了提高光电导天线的方向性,设计出一个加载在光电导天线输出端的锥形喇叭天线结构,仿真得到该喇叭天线的方向性为20.7 dBi,这表明可以通过加载锥形喇叭,在期望的方向上获得较高的太赫兹波功率.
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