Re: NEC-LIST: converting from dBi to RCS

At 06:33 AM 9/26/2005, David Phillips wrote:
>Is it possible to convert from the dBi values produced by 4nec to RCS?
>
>We've been using the equation
> dBi
> ( ---- )
> 10
>sigma=(10 )^2*lambda^2
> ---------------------------
> pi
>
>which comes from Balanis (Antenna Theory, eq 2-143), but it gives us some
>rather large values. Is this equation correct?
>
>Thanks

Are you looking at the actual output file from the NEC engine?
I assume you've looked at examples 7 and 8 in the NEC2 documentation. It
says that the column labelled gain is the scattering cross section in
square wavelengths (i.e. sigma/lambda^2). I assume then, that you should
be doing something like:

sigma = 10^(gain/10)* lambda^2

No need to square the gain, as you've been doing.

If you are using 4nec2, you need to cross check the value in the plot
against the value in the actual output file, to see whether Arie has scaled
it for you already.

Have you run something like the RCS of a conductive sphere? That would
give you a great analytical comparison.

James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875

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