3 sector ants interfere with each other?

[BobY777]

Some WISPs use an omni antenna at the head end to cover 360 degrees to transmit to the CPEs.

But if more capacity is needed they might use three 120 degree sector antennas to cover 360 degrees.

Those 3 sector antennas are inherently very close to each other on the tower. Channels 1, 6, & 11 would be used...one for each sector.

Since they are just inches away from each other, don't they interfere with each other in some fashion? Maybe overload or desensing? With the sector antennas being inches from each other, I would almost think that the antenna line would need bandpass filters in each line, so there is no overload caused to each adjacent AP.

What have you gurus out there noticed as far as self interference with three 120 degree sector antennas next to each other on a tower?

I imagine any interference would show up in the signal to noise ratio, as is done on a site survey.

I have never tried it. I'm sure someone out there has.

Thanks.

[wirelessoceans]

Hey Bob,

I prefer to use as much vertical and horizontal seperation as is possible even if channel seperation is sufficient. However Maxrad and other mfgrs make antenna arrays that consist on 3 120 deg sectors mounted together to make a "virtual omni" base station. I also have location that require three antennas to be mounted closely together (1,6,11 of course) and internet access is not affected. There is a slight increase in noise from the sidebands being so close but SNR is still very high and does not affect the system a whole lot. So in my experience it has been a non issue.

[BobY777]

Hi wirelessoceans:

Thanks for your reply.

Thats interesting. You actually checked the SNR. Only slightly elevated, but not a problem.

I'm glad to hear that.

Yep. I know some of the ant. manufacturers have the 3 sector antennas mounted close to each oither. I kind of wondered about that causing SNR problems. Evidentally it's not a problem. But I imagine that is a function of the quality of the rf section the manufacturer makes. Maybe some manufacturers do better on the SNR then others, with 3 antennas mounted that close together. Aren't you using Engenius (Senao) APs?

Thanks

Bob

[wirelessoceans]

Sometimes, it depends on the situation. And yes the antenna mfgr is important because of things like backplane noise and front to back ratio