Reflector Antennas

Abstract

Reflector antennas are in widespread use in communications and radar applications in the twenty-first century. They are seen on towers for point-to-point telecommunication links, on houses for pay tv and in news items of spacecraft travelling to distant galaxies. This chapter provides an introduction to reflector antenna fundamentals for design and analysis. The history of the focusing properties of reflectors extends back to ancient times, but some of the more intricate properties such as defocusing have not been realised until recent times. Some basic reflector geometries are considered initially through a review of geometric optics. The basic design principles of a reflector are established from a rigorous point of view through a study of the paraboloid geometry, its radiation pattern and focal region fields. Practical reflectors have imperfections due to surface errors or misalignments, and how these impact the reflector radiation pattern is outlined. The means of feeding a parabolic reflector is outlined through a description of the dipole, waveguide and horn feeds. Some other reflector configurations are discussed including the offset parabolic reflector, the symmetrical and offset Cassegrain geometries and the spheroid. An introduction to reflector shaping is given through a description of two techniques. The chapter concludes with a description of three typical reflector applications in satellite communications, weather radar and radio astronomy.