Leon
Jamming a parabolic dish outside of the main lobe is, as you say, difficult. The jammer would need to position between the satellite and the RPA to be effecfive (ie. Flying above it). A good example is to look at the jamming of fighter RADAR using a dish - the highest gain is along about a 2 degree beamwidth. So a jammer is only effective along the bearing of the jammer that may be mounted on the target aircraft or a jamming aircraft protecting a COMAO package on the same relative bearing. The fighter RADAR will probably be unaffected outside 4-5 degrees of its sweep unless the jammer is pumping out gigawatts of power and then maybe another 5 degrees might be affected. Against an RPAS, a SAM would be cheaper, easier and likely to be more successful - or if it's single engined then wait for the engine to quit!
I also doubt whether they will be able to produce anything better than that can be purchased off the shelf more cheaper and with better chance of delivering on time.
iRaven