Are you sure that is accurate? MTI makes several size antenna. You might be
confusng dissimilar models?
I've seen 1-2 db difference between polarity on occassion, but never 4 db.
Horizontal itself, is NOT plaqued by having less DB. It is most likely a
circumstance related to the design of the specific MTI antenna in question.
However, Horizontal and Verticle POL do bounce differently. One way to
receive lesser gain is if the polarity of the received signal is out of
polarity.
For example, in an Urban environment will tall brick tenant buildings... a /
polarity might bounce back as a \ polarity. Where as a --- polarity might
just interfere with itself. One idea is that the Verticle pol wave is more
likely to slide between building walls or Tree trunks, with the wave being
unobstructed, compared to a horizontal. This principle also could be
effected differently based on the size of the obstructions and the
wavelength of the wave. In practical purposes, in most cases there should
be little or no difference between the received signal of a Horizontal or
Verticle Pol wave, based on the small wave length. I'm not sure what the
wavelength of a 5.8Ghz wave, but its less than 3 inches, considering 900Mhz
is around 1 ft or so.
But I often wonder... Why companies like Alvarion, Proxim, and Motorola
started our making Verticle POL antennas as standard. The most obvious
reason was they are less expensive to make, and they tend to have less
windload due to their thin design. So its logical to assume... Save dollars
on the high volume components, and then use more expesnive and unsightly
Horizontal on Lower volume backhauls. But in Urban NLOS environments I have
seen slightly better performance with Verticle.
So, I guess I';m saying... Waves got a mind of their own, and hard to know
for sure, whether its fiction or fact (Verticle vs Horizontal).
Tom DeReggi
RapidDSL Wireless, Inc
IntAirNet- Fixed Wireless Broadband
- Original Message -
From: Mike Hammett [EMAIL PROTECTED]
To: WISPA General List wireless@wispa.org
Sent: Wednesday, November 14, 2007 10:24 AM
Subject: [WISPA] Horizontal vs. Vertical
Why are horizontal antenna some times fewer db gain than vertical?
I'm planning for a new tower and the MTI antennas have a 4 db difference
between polarizations. I always thought horizontal had better propagation
characteristics, but is it enough to make up for the 4 db lower antenna
gain?
-
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com
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