wrote in message
ps.com...
Hi all,

I am looking for a vendor that supplies dipole antennas @2.4Ghz such
that the feed extends from the phase center of the antenna.

The reason for this criteria is that I am hoping to measure the
wireless link with the antenna element at the receiver at both
horizontal and vertical polarizations. It is important for my
measurement that I am able to keep the phase center constant for both
polarization configurations.

The easiest way I can think to do this is to have a centerfed dipole,
fix the feed in position, and then rotate the element around the feed
for the orthogonal element. All the dipoles at hypertech where I
usually purchase from are end fed.

Any suggestions on a vendor or perhaps an alternative approach for
taking such a measurement would be greatly appreciated. Thanks,

Kev


I believe the standard "elbow" (right-angle) antenna that you find screwed
into the RPSMA connector on most routers and access points is a center-fed
dipole. The reason I believe this is I recently bought an old DWL-900AP+
Access Point at the flea market for $1.00 and when I found it didn't work
(who would have guessed that?) I had the pleasure of removing the covers and
feasting my eyes on its innards. Inside the case I found the second antenna
(of the diversity pair) consisting of two elements: a) the center conductor
of the RG-316 cable extended 1.160" from the shield end, and b) a silver
plated cylinder 1.0315" long and 0.185" o.d. connected at the shield end,
and "folded back down" around the coax feed. Of course the coax feed line
runs up its center, and there is a plastic sleeve to keep the feed line
centered and spaced away from it.. I believe these two elements make up a
half wave dipole, and since the feed line goes up the center of the lower
element, it is ideally suited to the simple configuration of the
straight-stick antenna. It might look end fed, but I believe it is center
fed.

You may be more interested in something that is physically symmetrical about
its center, and for that I can only suggest fabricating a dipole from a
strip of copperclad PCB stock 2.31" long with a gap cut in the center and
the coax feed soldered across the gap. Its width can be anything around
0.10" or so.

Chuck W6PKP