Advances in Transmitarray Antennas

Abstract

Recent advances in the art of transmitarray antenna (TAA) designs are summarized in this article, mainly focusing on the TAA element designs, improved feeding mechanisms, methods of designing wideband and ultra‐wideband TAAs, and TAAs for beam‐steering applications. Firstly, according to the diverse‐phase shifting mechanisms, representative TAA elements in the available literatures are categorized into four groups, including the receiving–transmitting elements, multilayer frequency‐selective surface‐type elements, polarization‐conversion elements, and phase‐rotation elements. Based on their own specific properties, designers can flexibly select the proper elements for different application scenarios. Moreover, primarily aiming at reducing the overall profile, some improved feeding mechanisms are discussed, for example, the folded TAA, TAA with the feeds of the multihorn configuration, the auxiliary small TAA, the integrated leaky‐wave antenna, the Cassegrain reflectarray, or a small‐scale array antenna. Subsequently, numerous typical solutions to improve the inherently narrow bandwidths of the TAAs are also presented. It can be concluded that the wideband performances of the non‐true‐time‐delay TAA are realized by optimizing the element‐phase errors and transmission losses at all designing frequencies. If the true‐time‐delay elements are employed, the key point is utilizing their group delays to appropriately compensate the spatial phase delays. Finally, for highly demanded beam‐steering applications, the TAAs incorporated with the techniques of reconfigurable, mechanical scan, switched beam, or phased array antenna (PAA) feed are introduced. Specifically, representative designs of the PAA‐fed TAAs are presented in detail, which will be a promising technical candidate of high‐gain beam scanning antennas.