Scanning characteristics of two-reflector antenna systems

Abstract

The off-axis properties of two-reflector systems of the Cassegrain and Schwarzschild type have been investigated on a theoretical basis to determine the allowable scan angle. Design parameters for systems of this type as a function of beamwidth, scan angle, magnification, and aperture block have been obtained and are presented in graphical form. In addition, a modification of the Schwarzschild system that involves overcompensating the reflecting surfaces has resulted in a larger allowable scan angle. The effects of astigmatism, location of the best focus for off-axis performance, and the effects upon the radiation patterns are presented in graphical form. A method of reducing the effects of aperture block by using the secondary reflector as a secondary source of radiation are also described.