Low-Profile Transmitarray Antenna With Cassegrain Reflectarray Feed

This paper proposes a novel hybrid antenna configuration, which combines two kinds of high-performance antennas, i.e., reflectarray and transmitarray, creating a low-profile low-cost low-mass design with both amplitude and phase distribution controls. In this hybrid arrangement, a flat Cassegrain reflectarray, with compact ring focus, is implemented as the feed to illuminate the upper transmitarray. In the process of reflectarray design, the particle swarm optimization technique is utilized to synthesize the phase distribution on the reflectarray aperture to generate a desired amplitude distribution on the upper transmitarray aperture. During the transmitarray design process, the dimensions of the double-loop elements of the upper transmitarray are adjusted to compensate for the phase delay of the wave from the lower reflectarray and form a desired phase distribution on the transmitarray aperture. A detailed design procedure for a Cassegrain-reflectarray-fed transmitarray antenna with a small focus-to-diameter ratio of 0.3 is presented. The simulated and measured results demonstrate that the hybrid-configuration antenna can achieve an aperture efficiency of around 40%.