Some aspects of beam waveguide design

Results of a numerical analysis study of beam waveguide (BWG) characteristics are presented in the paper. Vector-diffraction integrals have been used to analyse a particular configuration of the BWG which uses parabolas as the curved mirrors in a four-mirror system. In those configurations where the curved mirrors are rotated with respect to one another, it is found that a crosspolarised field is introduced into the plane of offset. This component is directly proportional to the angle of rotation. Except for this consideration, the four-mirror configuration can be reduced to a two-mirror configuration with a small error in performance prediction. Computed results characterising the BWG performance in terms of spillover losses, crosspolarisation generation and beamwidths of the emergent beam are presented. The effect of protective paint on the mirror surfaces is also analysed and it is found to depolarise the guided beam.