Optical Dish Gain

Hi Syphrum

Shooting from the hip here--most of what I know is from hands-on, not mathematical analysis, but I suspect that the optical guys don't have the problem mainly because of the much shorter wavelength of light. They don't have to use wave guide technology to get the signal to the eye or the camera lense. They use a lense in place of an antenna and they can probably deal with any similar issue by adjusting the refractive behavior of the glass layers in the lens.

My understanding of the purpose of the feed horn rings at the focal point of a dish antenna is to essentially collimate (hope that is the right word) the incoming signal much like the reflector and directors of a yagi antenna, except that they must deal with it as though it were circularly polarized. That way they can get a more nearly coherent signal into the waveguide leading to the little 1/4 wave stub that feeds the first RF stage of the LNB.

I believe this RF issue is reduced in a shallow dish with a long focal length because the reflected portions of the signal from various points on the dish are more nearly parallel.

Interesting topic--I must do some reading. Thank you.