Dual-band/wide-illumination-angle feed horns with low off-axis cross polarization

A design for a wide-angle illumination feed horn appropriate for front-fed, symmetric, and offset-fed reflectors is discussed. Low cross polarization and control of the copolarized beamwidths in two separated frequency bands are achieved. The design combines a Potter (1963) dual-mode (TE/sub 11/+TM/sub 11/) step and scalar rings to achieve this performance. The approach is feasible for frequency band separations of between 1.3 and 1.7 and has been used for the 4/6-, 11/14-, 12/17-, and 20/30-GHz satellite communications bands. The cross-polarization performance is more a function of the individual bandwidths than the separation of the two bandwidths. Data are presented on a feed horn design operating over the frequency bands of 4.0 to 4.2 GHz and 6.2 to 6.4 GHz. Pattern and cross-polarization data on a broader-band feed horn operating from 3.7 to 4.2 GHz and 5.925 to 6.425 GHz are also presented. A swept frequency tuning procedure for minimizing the cross polarization over the frequency bands of interest is also discussed.<>