Receiving Sensitivity Ripple in Electrically Small Offset Gregorian Reflector Antennas

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Abstract
Reflector antenna systems used in applications such as radio astronomy and radiometry are required to have a stable and predictable receiving sensitivity response as a function of frequency, among other characteristics. It is well known that a chromatic aberration, or ripple, occurs in the frequency response of the these systems due to the multiple reflections between the feed antenna and reflector surface. In clear aperture optics, such as an offset Gregorian system, this effect is drastically reduced by removing the feed out of the optical path. However, this paper shows how diffraction mechanisms may cause further ripples in the response, whose structure is a strong function of reflector pointing angle. For the analysis herein the reflector/feed interaction is completely removed from the simulation to highlight the diffraction interference effects, which are illuminated by a graphical illustration of the mechanisms at play.
Funding Information
  • South African Radio Astronomy Observatory
  • Department of Science and Technology (75322)