What Feed antenna for Dish?

Never mind, it looks like it is just the efficiency of the feed that maters. The dish diameter, proper geometry and alignment that matter most. Mike

See article on the subject at:

The type doesn't matter. What's important is the illumination angle. If the feed sprays RF in directions other than at the dish, you lose some transmit gain. If the feed is too narrow, and only illuminates part of the dish, then you lose both transmit and receive gain.

The bad news is that it's almost impossible to get all of the RF to hit the dish. The feed pattern is not going to have an abrupt transition at the edges (edge taper). Instead, it just tapers off, like any other antenna pattern. The result is that a dish will never have 100.0% efficiency. At best, you'll see about 50% efficiency. See:

for details.