Photoconductive antenna for THz-imaging system

Abstract

In recent years, there has been an expansive growth of interest in THz band using ultrafast short pulse laser. In this thesis, free-space propagating THz electromagnetic pulse radiated from photoconductive dipole antenna was measured by photoconductive sampling and radiation from photoconductive dipole antenna was numerically analyzed using FDTD(Finite-Difference Time-Domain method). In terms of simplicity, high SNR, fabrication, and availability in room temperature, photoconductive dipole antenna pair for THz generation and detection is selected. And FDTD is computational electromagnetic method that is popular, efficient and easy to implement and understand algorithm. Because the majority of THz research group has been in the optical society, the role and characteristics of the antenna have been disregarded. It is important to understand the radiation mechanism and radiation pattern of antenna, which FDTD helps. For FDTD simulation, three antennas were designed, which are dipole antenna with coplanar strip line, bow-tie antenna, and log-spiral antenna. For each antenna, near- and far-field pattern are obtained by near- and far-field FDTD. For photoconductive sampling measurement, a bow-tie antenna was used. For short-time duration of the radiated electromagnetic field, the current flowing through the antenna must be minimized or attenuated. The lens and reflector antenna can collimate the radiated power of photoconductive antenna, which enhances SNR of the coherent THz-imaging system.