[Moon-net] Fw: Feed choice

[vladimir.masek at volny.cz]

Dears,
on behalf of Rosta, OM6AA, who, flying in an airplan can not proceed
at the moment, find below the corrected simple formulae for a dish gain,
which became unreadable in the Roosta's previous e-mail.
The properly readable text looks as follows:

The Gain of a dish antenna is given by formula

Gain= eta *(pi^2)*(D^2)/(lambda^2) (as a ratio, or 10*log... in dB),

where D is dish diameter, lambda is wavelength, and eta is total efficiency.
Efficiency consists of many individual components consequently, total
efficiency is a function of their product.  For circular polarization
(CP) the total efficiency differs from that of efficiency components
for linear polarization.
That is the reason why waveguide which is used as a feed for linear polarization
antennae may have differ size than waveguide for CP.
More om that you can find in my and Mr. Hazdra article in 1/2007 DUBUS
magazine.
Form of electromagnetic field on the septum is very complicated. Some
works about this subject were published in IEEE materials. Using modern
software allows us to optimalize septum dimension. The most suitable
software to do that, appears MICIAN MICROWAVE WIZARD soft. see  www.mician.com
Anyway, septum optimalization is not easy job. You must be prepared
to spend lot of time with calculations.

Sincerely,
Rasto, OM6AA

GL,Vladimir,OK1DAK/OK1KIR


----- PŮVODNÍ ZPRÁVA -----
Od: "Rastislav Galuscak" <om6aa at yahoo.com>
Komu: moon-net at list-serv.davidv.net
Předmět: Re: [Moon-net] Fw:  Feed choice
Datum: 8.2.2007 - 11:53:57

> Gentlemen,
> 
> The Gain of a dish antenna is given by formula
> 
> 
> &#960;² D²
> G =  ––––––   &#951;        (ratio)
> 
> &#955;²
> 
> where D is dish diameter, &#955; is wavelength, and
> &#951; is total efficiency.
> Efficiency consists of many  individual components
> consequently, total efficiency is a function of their
> product.  For circular polarization (CP) the total
> efficiency, &#951; differ from that of efficiency
> components for linear polarization. That is the reason
> why waveguide which is used as a feed for linear polarization
> antennas may have differ size than waveduide for CP.
> More  you can find in my and Mr. Hazdra article in
> 1/2007 DUBUS magazine.
> Form of electromagnetic field on the septum is very
> complicated. Some works about this subject were published
> in IEEE materials. Using modern software allows us
> to optimalize septum dimension. The most suitable
> software to do that, appears MICIAN MICROWAVE WIZARD
> soft. see www.mician.com Anyway, septum optimalization
> is not easy  job. You must be prepared to spend lot
> of time with calculations.
> 
> Sincerely,
> Rasto, OM6AA
> 
> 
> 
> 
> 
> 
> DEHAYS Dominique <dominique.dehays at enac.fr> wrote:
> Hi all ,
> 
> if my informations are acurate ,  there will be a "SUPER
> VE4MA" feed with
> Septum polarizer described in DUBUS for 23 and 13cm
> ( maybe in the next
> issue? ). So you will get good information.
> I had the opportunity to read it in avance ( tnx to
> the author). I just
> wonder one thing : there is some calculations done
> in the article , one of
> them is feed horn diameter. I saw that this diameter
> is different for
> linear and for circular polarisation , I wonder why?
> Anybody knows?
> 
> 73's Dom/F6DRO/JN03TJ 
> 
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