Originally Posted by Prophessor Do those gregorian dishes get a better reception than a same size offset or prime focus dish?  |
Actually a Gregorian reflector is performing like a 15% larger offset dish.
That means, a 90cm Gregorian performs like 1,15x90 cm = 103,5 cm Offset dish.
This explains why the Fibo 90cm Gregorian performs almost the same as the Triax TDA110, take note that the Triax is actually 105cm, not 110 cm as some people believe.
Here is a short analysis white paper from SWE-DISH about gregorian dual reflectors:
Gain-wise, the dual-optics antenna has a gain corresponding
to a offset antenna with 32% larger area/departure or a 15%
larger diameter.
Analysis of the dual optics geometry used for the SWE-DISH
antennas show that close to 80% efficieny is achieved.
Dual optics have higher aperture efficiency due to the shaping
of the subreflectors and main reflector.
Source: http://www.swe-dish.se/upload/_PDF/W...me%20Focus.pdf