I. Introduction
The quest for compact, high directivity antennas to facilitate the many wireless applications associated with NextG systems and the Internet-of-Things (IoT)/Internet-of-Everything (IoE) continues. Activities have escalated with the anticipated expansion to integrated space and terrestrial networks (ISTNs) [1], [2] and space–air–ground–sea integrated networks (SAGSINs) that hope to integrate satellite communication, aerial, terrestrial, and marine communication networks [3], [4]. Multibeam antenna technologies [5], [6], [7] are expected to play a significant role in achieving the anticipated benefits of these integrated networks.