[Moon-net] Near field far field question 1296 MHz de SM5LE

[Marko Cebokli]

Hello Sven,

the biggest problem with such small dish (feed close to vertex) is usually 
return loss (matching) - in the case of circular pol, this will manifest 
itself not as a bad match of the TX port, but as a bad isolation between TX 
and RX, because circ pol reverses on reflection.

What your software calculates depends on the software :-)
A real 3D EM field simulator will calculate the currents on the surfaces, and 
from these you can calculate the field at any point, near or far.
If you requested "directional patterns" from your SW, it will give you far 
field, because that is where the radiation pattern is defined....

73, Marko S57UUU



On Wednesday 31 October 2007 10:25, SM5LE wrote:
> Hi all clever people
>
> Near field far field question
>
>
>
> Is there a near/far field problem when, on small dish, the feed (septum) is
> only ~3 wavelength away from the dish? Those calculated radiation patterns
> for septum, simulated in software, are far field diagrams aren't they? Of
> course I put the septum in focus and don't care . but I am just curios to
> see if there is some "1/10th of a dB" to squeeze out of my 2.2 m dish by
> doing some modification of septum or dish form.
>
>
>
> 73 and tnx  / Sven "2.2 m disher"
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