I. Introduction
The transmitarray (TA) antennas belong to the family of high gain antennas having the advantage of low profile, no source blockage as in reflectarray antennas and the beam switching capabilities. The research work on transmitarray antennas started in in 1968 with the renowned HAPDAR design [1]. Subsequently, it has taken the form of lens antennas [2]–[13] due to its phase convergence and compensation capability. It also enhances the directivity of space-fed transmitarray by generating the pencil beam radiation pattern. Previously, the research work was focused mainly towards the transmitarray antenna designs using receiver-transmitter type configurations in which three layers were mostly used [11, 14–20]. The bottom layer in these configurations works as a receiver layer and the top most layer as the transmitter layer. However, the middle layer provides the isolation as well as phase delay required for phase compensation in each unit cell. Moreover, the complexity of complete transmitarray design can increase due to the involvement of vias and layer alignment issues. The involvement of active devices in the middle layer can also increase the causes of errors manifolds. Frequency selective surface (FSS)-based multilayer transmitarrays are being designed [6, 21–28] to reduce complexity, with high transmittance magnitude and can cover full 360° phase range.