Analytical evaluation of the efficiency improvement of shaped over classical offset dual-reflector antennas including sub-reflector diffraction

This paper provides a simple analytical formulation to predict the effect of sub-reflector diffraction on the efficiency performance of shaped offset dual-reflector antenna systems, without the need to design and simulate the shaped surfaces. It is shown, through simple analytical approximations, that for strong edge illumination of the sub-reflector the increased efficiency obtained by shaping can be lost and even degraded due to the diffraction from the sub-reflector edge. Results compare favorably to physical optics simulations of the structures.