Modern Antenna Technologies Stimulated by the Arecibo Radio Telescope Upgrade Project 1984-1997

The world's largest single-reflector radio telescope is located in Arecibo. Its Gregorian dual-reflector feed was inaugurated in 1997, representing an enormous improvement in terms of bandwidth (limited by that of a wide-angle corrugated horn) and aperture efficiency compared to using the previous line feeds of about 1% bandwidth. The inauguration was preceded by an upgrading project of more than 10 years duration, during which author of this paper was stimulated to get ideas of several other technologies that were further developed the decades thereafter. The present paper gives an overview of these technologies, and how they are related to the upgrade project: the Comhat antenna (a hat-fed reflector) originating from an initial theoretical model of the line feeds, semi-analytical reflector synthesis by ray tracing, wideband constant widebeamwidth feed for paraboloids, canonical soft and hard surfaces, and gap waveguides