NEC-LIST: Modelling Patch antennae (using Nec-Win-Pro)

I am attempting to model a simple square patch antenna, air
dielectric, above a ground plane. I have built a physical model and
tested it for SWR, radiation pattern, resonance, etc. Now I wish to
build a model in NEC to simulate this antenna in order to correlate
the real with the simulation.

I have structured the patch as a grid of wires with grid 'gaps' less
than 0.1 wavelength. The grid is 'suspended' above the NEC
'groundplane'. The feed is coax feed tapped approx .075 wavelength
from the (square) patch center along one side of the patch.

My problems are:

  1) how do I specify the feed point/mechanism in NEC? (also relative
     to the ground plane)

  2) Can I use the NEC ground plane or should I create another
     (gridded) ground plane of appropriate dimension and feed the
     patch between patch and grid ground plane.

I have tried variations on the above but the model never even
approaches the actual. Feed impedances are always way out (1 to 2
orders of magnitude!). Radiation patterns vary by small amounts only
when varying the patch height above ground plane.

In short, HELP!

Any advice would be greatly appreciated.

Joe Noci
 ZR6SA,

  ' having fun with Meteosats'
Received on Mon Dec 18 2000 - 00:17:08 EST