Sub-THz Conformal Lens Integrated WR3.4 Antenna for High-Gain Beam-Steering

Abstract

This paper demonstrates the first conformal lens-integrated rectangular waveguide antenna that achieves high-gain beam-steering in the sub-THz range of 230 GHz to 330 GHz, to the best of the authors’ knowledge. The antenna consists of a $2 \times 32$ array of elliptical slots (E-slots) fed by a standard WR3.4 rectangular waveguide, ensuring that the antenna operates in its dominant TE10 mode. The E-slots are spaced by less than half of the guided wavelength, which causes them to be fed with a constant phase difference, thus leading to a progressive phase shift along the antenna aperture. Consequently, the antenna main lobe steers from -71° to -16° as the operating frequency varies from 230 GHz to 330 GHz, respectively. The WR3.4 antenna gain is enhanced by integrating it with a conformal plano-convex parabolic lens. The conformal lens is designed taking into consideration the phase center of multiple steered beams, which leads to a significant gain enhancement of up to 10 dB over the complete beam-steering range. The conformal lens integrated WR3.4 antenna achieves a peak antenna gain of up to 30 dBi. An antenna prototype is manufactured using a mechanical assembly concept based on standard computerized numerical control (CNC) milling and a laser ablation process. For the prototype, a WR3.4 waveguide with an H-plane bend and a short termination is fabricated in a brass split-block module using CNC milling. The E-slots are ablated on a $\mathrm {125~\mu \text { m} }$ thick aluminum (Al) sheet using a picosecond laser. Furthermore, a laser-structured die attach foil is interposed between the Al sheet and the brass split-block module to minimize the contact resistance between the E-slots and the WR3.4 waveguide. Additionally, a standard WR3.4 flange is manufactured to facilitate the antenna measurement.The conformal lens-integrated WR3.4 antenna has a compact size of $ {\mathrm {65~\text {m}\text {m} }} \times {\mathrm {30~\text {m}\text {m} }} \times {\mathrm {32.35~\text {m}\text {m} }}$ . It achieves the largest beam-steering range combined with the highest peak antenna gain in the broadband sub-THz range of 230 GHz to 330 GHz published to date.