Photoconductive THz antennas

Terahertz (THz) antennas based upon photoconduction techniques in THz pulsed and continuous-wave (CW) systems are introduced and compared. It is addressed that the differences in the excitation of these antennas lead to different design requirements. In both antenna types, optical-to-electrical conversion efficiency is very low - this means that employing techniques which can enhance the generated THz photocurrent in the antenna gap is necessary. Comparison of impedance matching of these antennas demonstrates that matching efficiency is a much more severe problem in a CW system than in a pulsed system. Regarding the coupling of the THz wave to the air, both antenna types suffer from low radiation efficiency due to the losses in photoconductive substrate. Considering these analyses, a simplified block diagram on how different parameters can improve the radiated THz power and efficiency is presented and finally a new THz photomixer solution with improved performance is demonstrated.