dual antenna pattern

in reading the thread on bi-quad design,
I was wondering what the overall radiation pattern would be
for the standard dual antenna access point.

I mean - with the dual "donuts" around each antenna,
the resulting pattern/coverage would have donut lobes around each vertical,
with extended lopes at right angles to the bisected line between them ?

--
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"If everything seems to be going well,
you have obviously overlooked something." - Steven Wright

"P.Schuman" <pschuman_no_spam_me@interserv.com> hath wroth:

>in reading the thread on bi-quad design,
>I was wondering what the overall radiation pattern would be
>for the standard dual antenna access point.
>
>I mean - with the dual "donuts" around each antenna,

There's only one pattern as only one antenna is active at a time. The
pattern may change slightly as the diversity antenna switch, but with
such low gain antennas, and such close spacing, there's not much
change.

>the resulting pattern/coverage would have donut lobes around each vertical,
>with extended lopes at right angles to the bisected line between them ?

Nope. That would be true if both antennas were simultanously driven
by a proper phasing harness or setup as a simple 2 element Yagi
antenna. However, they're not. It's a switch.

See:
<http://www.freeantennas.com/2400/>
The WAP11 packages and antennas are identical to the typical WRT54G
and is similar to all dual antenna access points.
<http://www.freeantennas.com/2400/WAP-11/WAP-11.jpg>
The problem with modeling low gain (+2dBi) access point antennas is
that the nearby environment has a HUGE effect on the pattern. The
pattern sitting to top of a metal PC box is very different from that
of one sitting on a wooden table. Nearby pieces of metal (i.e.
monitor) can act as an unwanted reflector. For example, the WAP11
with a reflector on top of a ground plane.
<http://www.freeantennas.com/2400/WAP-11-on-a-Plane/wap-11-3d.JPG>
With a low gain vertical colinear antenna (such as typical with the
stock antennas), there's not much directionality. No matter how its
positioned, it still looks like a very fat donut. For more extreme
patterns (i.e. flattened donut) a higher gain antenna is required.

Also, A simple Biquad:
<http://802.11junk.com/jeffl/antennas/Biquad/>

A badly built Biquad:
<http://802.11junk.com/jeffl/antennas/biquad-junk/>
This is an all too common method of building a biquad, where the
coaxial cable does NOT extend all the way to the beginning of the quad
elements. I previous scribbled a rant about this at:
<http://groups.google.com/group/alt.internet.wireless/msg/63d3438fe861bbaa>
Amazingly, even built wrong, the badly built biquad antenna still has
substantial gain.

If you're interested in antenna modeling, see 4NEC2 at:
<http://home.ict.nl/~arivoors/>
It's free, and comes with quite a few examples.

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