Re: Problem with nec2


"Detlef Conradin" <skyline@xxxxxxxxxxxxx> wrote in message
news:436125c1$0$1163$5402220f@xxxxxxxxxxxxxxxxxx
> Hi
>
> To get started with nec2 I tried to simulate a simple dipole.
> The graphical view of the pattern looks okay, however the gain seems
> to be to high. To what are the DBs refered in the output file?
> Or what do I have to change to get the gain in dBi ?
>
> Here is my input file:
> -----------------------------------------
> CM Test
> CE
> GW 1 20 0 0.005 0 0 7.5 0 0.01
> GW 2 20 0 -0.005 0 0 -7.5 0 0.01
> GW 3 1 0 -0.005 0 0 0.005 0 0.01
> GE 0
> EX 0 3 1 1 10. 0 0 0 0 0
> FR 0 30 0 0 6. 1. 0 0 0 0
> RP 0 37 72 1001 0. 0. 5. 5. 1000 1.
> EN
> -----------------------------------------
>
> Detlef
>
> PS:
> If I calculate the gain with the formula:
>
> 4 * Pi * r^2 * |E|^2
> Gain = -----------------------
> P_in * 2 * 120 * Pi
>
> by using the E-Field magnitude values from nec2's output I get also
> those very high values. (?)
>

PS, also confused by your formula. Which Value of E are you using? Are you
trying to calculate the "Total radiated power" (TRP)? If so you need to
integrate the power density over a spherical region. The calculation is
greatly simplified if you take advantage of any natural symetry in the
radiation pattern -- i.e. integrate from axis end to axis end, then multiply
by 2*PI -- as in elementary calculus, you are using a single integral for a
"Solids of revolution" method, instead of a double (Surface integral).

If you are trying to caluculate the gain in a given direction you need to
take 20*log(E/Ei). Where E is the NEC calculated E field in the desired
direction, and Ei is the computed E field from an ideal isotropic source
with the same input power as the test antenna.

As for your RP card, I notice that you are attempting to vary both "Theta"
and "Phi". I usually keep one fixed and vary the other, but to be honest I
am not sure if what you are doing is incorrect, although I notice that the
"Phi" pattern is only computed for one frequency. The only other difference
is that I normally do not use gain averaging. Also using 1 degree
increments does not seem to slow things down very much. With your RP card I
was also getting some weird pattern discontinuities.

Regards,

Frank


.

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