Design of a Photoconductive Antenna with an Angled DC Bias Connection on an Extended Hemispherical Lens Substrate Truong Khang Nguyen and Ikmo Park Department of Electrical and Computer Engineering, Ajou University 5 Woncheon-dong, Youngtong-gu, Suwon 443-749, Korea ipark@ajou.ac.kr Abstract — The input impedance and radiation characteristics of photoconductive antennas with different DC bias connection angles printed on an extended hemispherical lens made of high- dielectric-constant substrate was presented. Antennas with different bias connection angles exhibited different gain and radiation efficiency spectra for a specific lens geometry. The antennas with larger DC bias connection angles provided stable input impedance and improved antenna gain levels, particularly in the low-frequency region. This indicates that the DC bias connection angle has specific effects on the overall performance of the photoconductive antenna design. Index Terms — Terahertz antenna, coplanar stripline dipole antenna, traveling wave, extended hemispherical lens, high- dielectric-constant substrate. I. INTRODUCTION Terahertz photoconductive antennas (THz-PCAs), which are coherent terahertz laser–driven sources, are among the most promising candidates for developing low-cost spectroscopy and imaging systems for various THz applications [1–3]. Two important reasons for the wide use of THz-PCA in THz experimental setups can be attributed to the advancements of lasers with ultrashort pulses [4] and the development of a low temperature grown gallium arsenide (LT-GaAs) layer [5]. THz-PCAs are typically implemented by a planar dipole lithographically patterned on a high- resistivity silicon substrate lens. However, there have been few studies in the literature that carefully considered the effects of the DC bias line as well as the substrate lens structure on the overall performance of the THz-PCA [6–10]. In this paper, we present the effects of DC bias connection angle on the input impedance and radiation characteristics of THz coplanar stripline dipole antennas printed on a substrate lens. Three representative connection angles of 0 o , 45 o , and 90 o , forming three connection schemes—namely horizontal [11], diagonal, and vertical connections, respectively—were used for the investigation. The results showed that with different DC bias connection angles, the antennas exhibited different gain characteristics for a specific lens geometry. Interestingly, the diagonal and vertical bias connections presented an improved gain level at low frequencies in comparison with the typical horizontal connection; this is an important result for applications at the lower limits of the THz electromagnetic spectrum. II. ANTENNA GEOMETRY Figure 1 shows the geometry of the THz coplanar stripline dipole antenna on an extended hemispherical silicon (Si) lens substrate with a dielectric constant of r = 11.7. The width and the length of the center dipole are denoted as w d = 10 m and L d = 40 m, while those of the DC bias line are denoted as w b = 5 m and L b = 1200 m, respectively. The feeding (a) (b) Fig. 1. Terahertz coplanar stripline dipole antennas with different DC bias connection angles on an extended hemispherical Si lens; (a) top view and (b) front view. 2013 Asia-Pacific Microwave Conference Proceedings 978-1-4799-1472-2/13/$31.00 ©2013 IEEE [P3-52] 1197