NEC-LIST: calculating antenna bandwidth

Is there an easy way of calculating antenna bandwidth in NEC2

Currently I am using my Mathematica interface and the FindMinimum function to
numerically find the point that the antenna port S11 goes to the desired level
(-1, -3, -10 dB). It does this by repeatedly calling NEC to calculate the
port Z for different frequencies. It is not very bad. For my simple loaded
dipoles I can find the upper and lower band edge in 10 to 20 seconds.

It seems to me that it should be possible to calculate the bandwidth from just
the fields at resonance.

One way would be to evaluate (Stored Energy/ Lost Energy) in the field. I can
calculate the near field, but it seems that I need to integrate through the
volume of all space. I suspect that this could be done by repeated calls to
NEC to calculate the Near field at different R, but that seems almost as bad
as my numeric FindRoot algorithm.

Perhaps I need only the antenna currents.... or the currents and the segment
charge.

I am sure I can figure this out, but Has the Wheel already been invented?

What is a good way to get antenna bandwidth out of NEC2 ?

Wayne Shanks

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