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# Re: Dish Formulas ?

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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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