miso@sushi.com hath wroth:

>I'm trying to visualize how the pcb material interacts with the copper
>track. It's not like you are doing stripline, i.e. metal traces with
>the fr4 between the traces. The signal hits the copper from free air.
>But a reflector would have the dielectric of the pcb in the path.

Oh, that's easy. A non-radiating transmission line has at least one
ground plane below the trace and is terminated at both ends.
Sometimes, it's sandwitched between two ground planes but must always
be terminated. A radiating trace antenna has no ground planes and is
matched only at only one end by the output impedance of the
transmitter or the input impedance of the receiver. The other end is
matched to the impedance of free space or 377 ohms. Think of an
antenna as an impedance transformer between 50 ohms (or whatever) and
377 ohms.

The easiest way to visualize this by having the dielectric between
between the antenna elements and the reflector be composed of two
different materials, air with e=1.0 and G10 with e=5.0 (approx) with
corresponding variations in thickness. I don't know exactly how to
model such an antenna. I'm also lazy and think it's time you dig out
4NEC2 or other modeling program and try it thyself first.
http://home.ict.nl/~arivoors/
Send me you model and I'll try to untangle it. Use this model:
http://802.11junk.com/jeffl/antennas/Biquad/biquad.nec
as a starting point. You might also find it interesting to look at
the web site where I stole the model:
http://www.pow.za.net
http://www.pow.za.net/panel_2x2commercial.jpg

If you're going to dive into surface radiating patch or panel
antennas, most of the NEC2 surface models are marginal approximations.
Instead, use MSTRIP40:
http://www.e-technik.fh-kiel.de/~splitt/html/mstrip.htm
for something more accurate. Incidentally, there's quite a bit on
strip line and surface radiating calcs in the "lab manual" at:
http://www.e-technik.fh-kiel.de/~spl...0LabManual.pdf
which might explain how to visualize the antenna.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558