Advances on Huygens Metasurface Based Transmitarrays at University of Technology Sydney

Transmitarray antennas have attracted significant attention due to their advantages of high gain, compact profile, and adaptable radiation characteristics. Typically, they comprise multiple layers of flat antenna elements and a feed source for illumination. The phases of these elements are individually tailored to ensure suitable phase responses, thereby enabling the realization of a highly directional radiation beam with considerable gain. Transmitarrays can electronically manipulate their beams by adjusting the transmission phases of the array unit cells using PIN diodes, micro-electro-mechanical system (MEMS) switches or varactor diodes. In various wireless communication applications such as satellites, aircraft, and unmanned aerial vehicles (UAVs), there is a demand for conformal high-gain antennas to meet aerodynamic requirements. To address this need, conformal transmitarray antennas are highly sought after, as they can be designed to conform to the shapes of different mounting platforms. This allows for integration onto the platform surface with the feed positioned inside the platform. Given current manufacturing capabilities, one of the most practical approaches to implementing conformal transmitarrays is to utilize very thin array elements with thicknesses ranging from approximately 0.5 mm to 1 mm, facilitating ease of bending. Nevertheless, the majority of the planar transmitarrays documented in literature utilize multi-layer array elements, typically involving three or more metal layers printed onto two or more dielectric substrates. Many of these elements consists of a number of metallic vias. Consequently, these configurations are not suited for conformal transmitarray applications. Additionally, it is important to highlight that multi-layer structures incorporating metal vias for beam steering in transmitarray designs require complex packaging and fabrication procedures, potentially impacting antenna performance, particularly within millimeter-wave frequency bands. Hence, there is a pressing need for the development of dual-layer unit cells without metal vias to facilitate conformal transmitarrays and beam-steering transmitarrays.