The effects of DC bias lines on terahertz photomixer antennas

Photomixer antenna is an essential part of photomixer design. The development on photomixer antennas has still being received considerable attention. DC bias lines are being used in photomixer design to provide required DC voltage to photomixer antenna in order to collect the electron-hole pairs that is excited by a laser beam focused on semiconductor substrate. This research investigates the effects of the DC bias lines on several types of antennas for terahertz photomixers and proposes a method, namely resistively loaded lines (RLL), to compensate the effects of the DC bias lines. The RLL is formed by placing lumped resistances periodically on the DC bias line in order to cease the leakage current virtually, which cause a significant amount of distortion on the antenna performance. In order to achieve a proper simulations of bias line effects on photomixer antennas, a parametric investigation is carried on electromagnetic simulator HFSS to obtain an optimized simulation technique. The simulation results of the dipole, folded dipole, log-periodic, and spiral antennas show that RLL almost removes the effects of the bias lines and improves the radiation pattern notably compared to that of the commonly used bias line types, such as coplanar stripline and photonic bandgap type bias lines.