Re: [amsat-bb] Dish Formulas ?

[Michael Kjorling <michael@xxxxxxxxxxxx>]

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On Aug 28 2003 14:38 -0700, Jim Tudehope (Peoria Arizona) wrote:

>     Does someone out there have a program already written to calculate dish
> antenna parameters with just a few input variables ?

I found the following formula for dish gain and -3 dB beamwidth. I don't know
how accurate it is (it might be valid only for circular and near-circular
parabolic reflectors), but the result matches that in a textbook I have that
deals in part with satellite link budget calculations.

	$gain = (20 * (log10 ($dia / $wave))) + ((10 * (log10 $illum)) + 9.938);
	$theta = 70 / (($dia / 30.48) * $freq);

The variables are as follows:

	$gain is the dish gain in dBi
	$theta is the -3 dB beamwidth in degrees
	$dia is the reflector diameter in cm
	$freq is the frequency in GHz
	$wave is the wave length in cm
	$illum is the illumination factor (typically 0.6?)

'log10 x' is simply the base-10 logarithm of x, such that 10^{log10 x} = x.

Hope this helps. I realize that not everyone is a programmer, but if you just
take out the $ signs (indicating variables) in the equations above and the
semicolons at the end of the lines, it's pretty standard algebra.


Michael Kjörling

- -- 
Michael Kjörling :: michael@kjorling.com :: SMØYBY JO89  ^..^
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