Below is a summary of my experiences in building the patch
antenna posted by outcast_one and otaku42 at
http://devices.planet-wireless.de/comtelco/index.html
Construction
I won't go into details about dimensions since they are
well documented at the above link. I used the lid from a fisherman's friend tin
(nasty menthol mints) for the patch and a piece of scrap galvanized steel for
the ground plane. I cut all the parts with a pair of tin snips (actually it took
me longer to hunt down a screw in my garage to fix my broken snips than it took
to make everything!). I'm not sure how good the dielectric constant of cheap
plastic pens is, but it's the only thing I had handy last night; that's what I
used as a spacer for patch and ground plane. Hot melt glue holds everything
together except for the N jack, which is soldered on. The whole assembly is
contained inside a compact (4x4") plastic food container. It's a pretty messy
job I did, partly because I didn't have much time and built the thing in a rush,
and partly because I wanted to demonstrate what a rip-off commercial antennas
are; that even with crude and imprecise contruction techniques and unglamorous
materials, you can get decent performance.
Here is a handy tool for
making odd-sized round holes. First, you drill a hole with the best matched bit
you have, and then ream it out to the exact size you want with this:
I bought mine at Rat Shack when I was a kid. Hopefully, they still have them;
if not, any decent electronic supply store should carry them.
In retrospect, hot melt glue
is probably not a good idea; a hot car baking in the sun easily gets it gooey
enough for everything to just fall apart. Next time I'll use epoxy putty or
PC7.
Qualitative Testing
Lacking any decent test equipment, I've only done
some qualitative tests with this antenna, and it seems to have decent gain.
First I tried to use ministumbler as a signal strength meter, but the numbers
were fluctuating too much to get stable results. The signal strength and SNR w/
the patch antenna were anywhere from 1-3dB better than w/ my Hunts beans
waveguide "cantenna" after adjusting pointing each one optimally.
Next, I did a ministumbler AP detection test. First walked far enough from my
house that none of the antennas could pick up my AP. Then I started walking towards
my AP with each antenna until ministumbler detected it. The patch antenna wins
by a narrow margin in terms of range. There is a tree with thick foliage blocking
the view of my AP from the street, so the range is greatly reduced, but anyway
ministumbler found my AP 6 houses away the patch, about 15 feet closer with the
cantenna, and with my Orinoco Gold's built-in patch antenna about 3.5 houses away.
What's nice about the patch antenna over the "cantenna" is its broad beamwidth.
The cantenna has to be pointed very precisely at the AP to get anything at that
range, but the patch can be tilted several degrees and still get a signal. All
in all I was pretty impressed at the performance I got. This antenna is so tiny
and portable and discreet compared to the cantenna. I'm going to use it as my
main stumbling antenna from now on.
Closing thoughts/questions
I think I could probably eke out better
performance with more careful construction techniques; when I have more time
I'll probably redo all the metal parts with more accurate measurements/cutting
and support the patch on all 4 corners to get more accurate spacing.
Does anyone know where I can get more info on designing patch antennas?
I'm interested in finding out the effects of the dimensions, shape, distance
between patch and ground plane, and accuracy in the dimensions. Please e-mail me
at lincomatic@hotmail.com if you
have any good info.
Thanks again to outcast_one and otaku42
providing the design.
