Re: NEC-LIST:Using Current Sources

At 4:26 PM +0100 7/29/02, Tim Brown wrote:
>I was wondering if any of you out there would expect differences from
>using current sources in NEC instead of the conventional voltage
>sources.

Yes, if there is more than one source in the model. No, if just one source.

>Theoretically there should be no difference since the voltage
>source with zero impedance in series with an element is exactly the same
>as a current source in parallel with an element with infinite impedance.

Not if there's another source exciting that "element." If there's a
second source, then the total current through (or voltage across) the
first source depends in part on the second source. [This assumes
that the model is such that there is nonzero coupling (mutual Z)
between the two source-driven segments.]

>I've been simulating an 8 element dipole array with two rows of 4 elements
>like the plan view below (so the dipoles are coming out of the
>email!). The bottom row of elements are in quadrature with the top row.
>
>X X X X (This row in zero phase)
>X X X X (This row 90 degree phase)
>
>Now, if this simulation is carried out with current sources, we get a
>contradiction with the voltage sources and there is no real valid reason
>why we should. The measurements support the voltage source simulations as
>I'd expect them to. Does anyone else have any light on this? Or are the
>current sources actually feeding the elements as they should be? Thanks,

See above. I gather you're using eight sources.

If it's any comfort to you: eight voltage sources each in series with
a "load" representing the source impedance would yield the same
results as eight current sources each in parallel with a "load"
representing the source impedance.

-Chuck, W1HIS

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