NEC-LIST: Trouble with dipoles

Hello,

I'm doing some simple dipole impedance calculations using NEC4. I'm
modeling a 23.5cm half-wavelength dipole with a radius of .000425 in
free space. I'm comparing these results to an finite-difference
time-domain calculation of impedance for the same dipole. A frequency
of 638 MHz corresponds to a half-wavelength of 23.5 cm. My NEC dipole
contains 7 segments, and I'm using a frequency step of 22.5MHz in the
NEC simulation to match the step-size in the FDTD simulation. I get a
match frequency of 607 MHz from the NEC code, and a match frequency of
630 MHz from the FDTD simulation. (I have investigated running the
NEC code with a much smaller frequency step of 1 MHz over the region
of interest and again found a match at approximately 600 MHz) It would
seem that the FDTD is giving more accurate results.

I am looking for an explanation for the discrepancy. If anyone can
give me any insight, suggestions, or corrections, it would be greatly
appreciated. A listing of my NEC input file is below.

Thanks,
Tiffany

CM LAMBDA/2 DIPOLE
CE
GW 0 7 0. 0. -.1175 0. 0. .1175 .000425
GE
EX 0 0 4 0 1.
FR 0 255 0 0 22.5 22.5
XQ
EN
Received on Thu Oct 29 1998 - 09:56:12 EST