Predicted and measured performance of a shaped reflector in a dual-gridded reflector system

The proven means of satisfying the antenna requirements of satellite communications systems is by the use of dual-gridded reflectors with multiple feed blocks. Practical issues and advantages concerning the choice of using a shaped reflector to replace one of the multiple feed antennas (MFAs) within a dual-gridded pair are addressed. The authors use as an example a realistic MFA design devised during the Orion contract procurement stage and its performance is compared with that of an equivalent shaped reflector design optimised at single and multiple frequencies. The susceptibility to predicted in service thermal distortions of the two designs is then assessed. Some results are presented of measured and predicted feed cross-polar radiation collimated by a gridded shaped reflector; the feed being at the focus of an unshaped reflector behind the shaped dish