Design of a reconfigurable trapezoidal log-periodic photoconductive antenna enabled by laser-driven dynamic impedance matching for wideband terahertz emission

Abstract Photoconductive antennas (PCAs) operating in the terahertz (THz) regime are limited by the low optical-to-THz conversion efficiency, owing to several factors, one of which is impedance mismatch across their broad operating bandwidths. To address this challenge, we propose in this work, a frequency reconfigurable trapezoidal log-periodic (RTLP) PCA, that employs dynamic laser-driven impedance matching to enhance conversion efficiency, and enable an adaptive frequency control. The trapezoidal log-periodic geometry inherently supports multiband resonances, and together with a dynamic impedance matching strategy, that leverages the dependence of the source impedance on the optical excitation power, enables an adaptive frequency control. By precisely correlating the laser power with the antenna impedance, mapped via full-wave simulations, we have achieved a selective impedance matching across individual sub-bands. In addition, the suggested approach enables a bandwidth tunability via the structural optimization.The proposed design incorporates four predefined laser excitation modes, ranging from 35 mW to 140 mW, resulting in an operational coverage from 0.5 to 6 THz. The antenna exhibits twelve distinct resonance dips bellow -10 dB between 0.5 and 3 THz, which can be practically grouped into six broader sub-bands, namely [0.50–1.27 THz], [1.33–1.52 THz], [1.61–1.78 THz], [1.95–2.11 THz], [2.30–2.54 THz], and [2.84–3.00 THz], as well as an ultra-wideband (UWB) regime spanning 3 to 6 THz. The antenna performance evaluation based on the analytical modeling, reveals a nearly stable optical-to-THz conversion efficiency of approximately 0.1% across the entire band, with a maximum average THz output power of 1.2 mW. Moreover, the radiation performances analysis through full-wave (FW) simulations demonstrates a peak gain of 13.15 dBi at 5.54 THz, a maximum fractional bandwidth of 66.7%, and a maximum bandwidth ratio of 2:1. The designed PCA, with its reconfigurable impedance matching and scalable architecture, offers a versatile platform for broadband THz applications, particularly in spectroscopy and high-resolution imaging, where precise frequency control across a wide band is essential.