Friend, I believe that you are honestly mistaken on the relationship between dish size and spectrum. I have a 1m prime focus dish for S-band that works quite well.
What this question calls for is a link budget for the satellite, gain of the LNB, and knowledge of the characteristics of the dish the user wants to use. There are small prime focus dishes available out there, and offset dishes (1.2m +) can handle a
C-band LNBF.
Is there someone out there with a solid RF engineering background that can help this user with the math?
A. Yelvington