cisco wireless antenna polarization

[admin_2]

dear all

who can tell me the polarization of cisco antenna ,when I see the training book gived by cisco,it is vertical,but in fact it is vertical and horizontal,who can tell me the right answer?

thanks a lot

[scottmac]

If you follow the general guidelines for antenna installation, it is vertical polorization.

If you install a normally vertical antenna sideways, it would be horizontally polarized.

The test question would be "Why might you want to install an antenna horizontally?" the answer being "Most laptop antennas are horizontally polorized" - if you are in a predominantly laptop-wireless environment, you probably will get a better signal quality using horizontal polarization.

Even a "dish" style antenna will have vertical polarity (imagine a bowtie tied around the radiating element ... that's the basic pattern of the radio signal).

There are methods to cause a "circular" polarity: a good method for reducing terrestrial noise on the signal .... but it's very lossy (typical 3-6db with a bunch of variables) ... and it doesn't survive the bouncing very well. Circular is usually used in Satellite comms (ala DirecTV, DISH, etc).

For all intents and purposes, Cisco antennas are vertically polarized.

FWIW

Scott

[#3]

thanks very much

[wififofum]

What about the signal pattern with horizontal polarity aren't you risking the signal propagating vertically (the doughnut pattern on its side rather than flat) causing leakage through floors and ceilings?

Is it the fact that the signal is "bouncing" (up and down) cleaner with horizontal polarity vs. vertical (which creates more nulls going side-side?) that makes the quality better for laptops on a given plane (floor)?

I'm thinking of a superball analogy here. The idea that if it bounces vertically it has a chance to go horizontally farther...thanks

[scottmac]

Horizontal is better for laptops because laptop antennas are horizontally polorized.

Signals at that frequency have virtually no penetration capability, certainly not through reinforced concrete (like a building's floor / ceiling).

It'll bounce like crazy regardless of the polorization ... it's the nature of the beast. Too many bounces are a bad thing, it degrades the signal and increases the chance of multipath (multipath is bad).

With a wavelength of ~18cm (@2.4G), nulls should be very small and correctable by moving the (client's)antenna a few CM to one side or the other.

FWIW

Scott