[Moon-net] Fw: Feed choice

[Rastislav Galuscak]

Gentlemen,

  The Gain of a dish antenna is given by formula

   
                                                    π² D²
                                         G =  ––––––   η        (ratio)                             
                                                      λ²
   
    where D is dish diameter, λ is wavelength, and η 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, η 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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