On Mon, 8 Dec 2008 08:24:55 -0800, SparkyGuy
wrote:

Q: how do I take into account the "pigtails" of the driven
element? A nice square loop is nice, but I've got to connect it to the
(relatively) big diode,

You don't need to include diode lead length in the quad antenna
calculations. The "loop" in the quad driven element is just an LC
tuned circuit. It's as bit less than one wavelength around the loop
and resonated to 2.4GHz by the tuning cap. The diode and other
components do add some capacitance, which will lower the frequency
somewhat, but the adjustment cap is substantially larger than these
capacitances. For example, the off capacitance of a Schottky diode is
about 0.5pf. You do need to keep lead length short as the added
inductance will act as an RF choke.

However, instead of the giant diode, I suggest something smaller and
better, such as a Schottky diode:
http://www.adsemi.com/diodes/schottky_barrier_mixer_detector.shtml
http://www.macom.com/psc/jsp/ListParts.jsp?dataFile=mixing_detector_diodes.txt

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558