If possible, then an offset dish would always be better. Because, with prime focus dishes (including Cassegrain, etc), various bits "block" part of the radio "beam" falling on the reflective surface.
This effect varies, with dish type, so no "general formula" is possible.
As dishes get bigger, the offset type doesn't have enough mechanical stability, ie, the long lnb pole and dish surface would flex too much, putting the lnb "off focus". |