The OE-222 Parabloic antenna, used by the AN/FSC-52 & the AN/FSC-78/39 (in the 39 configuration...the 79 means that you got the big dish which is not quite 100 feet in diameter) are standard DSCS dishes. This is fixed station. Places like Landstuhl, k-16, ECTC, Ft Meade, ROC, LOC, Sunnyvale, Ft. Belvoir & of course the school at Ft. Gordon. You may be referrering/used to the little tactical vans like the 85/93 (army) 86/100 (air force) which use the the quick setup/tear down dishes or heck even MILSTAR.
All of the fixed stations above use non flexible wave guide. They are literally "cut" (actually if you run your hand along the inside it just feels like smooth waves to your fingers) so that they attenuate certain, unwanted fequencies & let the ones that you want ( 7.9Ghz to 8.4Ghz up & 7.2GHz to 7.5GHz down) pass through with the least amount of attenuation.
Yes I'm talking about the approx. 200dB of attenuation for a ground station, bird, ground station trip.
Bob, the gain of a parabolic antenna is not constant over it's entire surface, even at the same frequency. At any certain point, if you could isolate your signal, you will find that as you move away from that point in any direction, your gain will change.