Design of Dual-Reflector Offset Antennas and Beam-Waveguides with a Pattern Symmetry and Zero Cross-polarization

摘要

Quasi-optical transmission lines - beam-waveguides (BWG) consisting of several offset reflectors are often used in feed systems of large reflector antennas. The main requirement to the beam-waveguides is minimizing losses and distortions of the initial field distribution, that is, maintenance the input pattern symmetry and zero cross-polarization. Traditionally, Mizusawa’s criteria are used for the beam-waveguide design in order to meet these requirements. The fulfillment of these criteria results in the equality of the input and output beamwidths, which imposes restrictions on the feed system configuration. In this paper, the general criteria for the beam-waveguide design are presented. The beam-waveguide designed according to the general criteria maintains the pattern symmetry and zero cross-polarization in the propagating wave, while also allowing to transform the beamwidth. The criteria are developed within the geometrical optics approximation. Theoretical foundations of the developed approach are given and a method of BWG synthesis with a given beamwidth transformation coefficient is presented in the paper. A dual-reflector beam-waveguide is designed and simulated in order to demonstrate the method and verify the results. The developed criteria are also applicable to offset antennas.