4NEC2 Antenna Program: Patch definition and wire connections

[DougBC]

Having trouble getting consistent results when trying to connect a wire to a patch. 4nec2 manual says end of wire must terminate in "center" of patch. So how do we find the center coordinates of a non-rectangular patch?
The cards to define a patch in the input file must list coordinates of the patch corners. But the manual goes into detail about a different method of patch definition, which uses a vector normal to the center of the patch and another vector parallel to one side and in the same plane as the patch, and the area of the patch. I understand that this definition is needed for the calculations internal to the program. So the program must read the patch corners and calculate the vectors and area.
If the program made available to the user, the internal vectors+area it used for each of the patches, then it would be a simple matter to find the center of the patch, and where one should connect a wire. But I see no way to have the program list these internal patch definitions.
So how does one make sure they are connecting a wire to the "center" of a non-rectangular patch?

 

[khiggler]

This statement "4nec2 manual says end of wire must terminate in "center" of patch." has to mean "in the center line, but definitely not in the center of the patch". Patch antennas suck if the antenna cable or connector is directly in the center.

A patch antenna is simple to make, no computations.
Length is just under 1/2 wavelength electrically (not physically).
Width is shorter than length. Say by 10% to 50% shorter.
Thin circuit cards, the center conductor has to be close to the patch center (but never on the patch center). Thick circuit cards, or very light dielectric, the center conductor moves progressively out, away from the center, almost towards the edge of the patch, if the thickness approaches 0.2 Lambda (using air dielectric). In which case, the patch bandwidth can be more than 10 percent, 20 percent max. per Pozar.

To make and tune a patch, put the center conductor of the cable exactly in the center, and start removing material from one side until you achieve good VSWR. Then remove equal amounts from both sides to set the frequency. The side you trim is the approx. half wave length. Start longer than 1/2 wave electrically, by say 20% then start removing top layer of circuit board, etching or scraping away metal.

Kevin