Re: G/T for parabolic dishes


 

On Thu, 16 Jul 2020 at 21:57, Chris Bartram G4DGU <chris@...> wrote:
Hello Dave,

> what physics comes into play here? It's either something I never knew,
> or have forgotten.

It's all to do with diffraction. Optical telescope designers know all
about it, but I'd have to go back to a text to refresh my limited
understanding in order to say more.

73

Chris G4DGU

I’m not convinced that one can arrive at the same levels for a Yagi-Uda though, which I believe was mentioned earlier.  You can compute a capture area, which is itself not circular. 

I have thought about trying to reduce the first sidelobe on a Yagi-Uda type antenna, perhaps with a small bend on the ends of the elements. I personally find that sidelobe annoying as if one knows the general direction of a station one can rotate the beam and think one has the peak but doesn’t.

You can argue sidelobes are advantageous in a contest. 

Anyway, I will not take the argument too far from the dish. Yagis are a quite different beast. 

Dave
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...
https://www.kirkbymicrowave.co.uk/
Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom

Join UKMicrowaves@groups.io to automatically receive all group messages.