What Feed antenna for Dish?

If you have a dish of (d) diameter, does it matter what type of feed
antenna you use?
Monopole, dipole, biquad, patch, will the gain change with a different feed
antenna?
Mike

"amdx" <(E-Mail Removed)> wrote in message
news:3cfcb$4862bf38$18d6b40c$(E-Mail Removed)...
> If you have a dish of (d) diameter, does it matter what type of feed
> antenna you use?
> Monopole, dipole, biquad, patch, will the gain change with a different
> feed antenna?
> Mike
>
>
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

On Wed, 25 Jun 2008 16:57:11 -0500, "amdx" <(E-Mail Removed)> wrote:

> If you have a dish of (d) diameter, does it matter what type of feed
>antenna you use?
> Monopole, dipole, biquad, patch, will the gain change with a different feed
>antenna?

See article on the subject at:
<http://www.qsl.net/n1bwt/contents.htm>

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:
<http://www.qsl.net/n1bwt/chap4.pdf>
for details.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558