5GHz 11N Yagi

[s.vosper]

Hi All

Is there a yagi that I can use to provide 11N coverage within some racking in a large warehouse under the 5GHz band. I understand there is one for the 2.4GHz.

Thanks

Simon                  

[George Stefanick]

Typically yagis aren't used indoors for client connection. They are for ptp outdoor deployments. This is why you probably won't find many options for a 802.11 n option.

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[s.vosper]

Thanks George

This is written in the Atenna Portfolio document:

Patch and Yagi Antennas

These antennas are typically mounted to a wall or a mast and provide coverage in a limited-angle pattern. Application cases for a directional antenna include RF coverage down a hallway in a hospital or office corridor. In a warehouse or manufacturing facility, which typically has high steel-shelving units, aiming a directional antenna down open areas provides coverage for people moving among the shelves with their wireless devices. The mining industry also benefits from the use of directional antennas when wireless is used in the shafts and drifts.

In the Cisco Site Survey and Installation book, it recommends Yagi antennas for large racking in warehouses. I see the logic in this as if I used say a patch antenna I would get a lot of overlap at the ends of racking where the signal is not restricted in its movement. Also the radiation pattern of the patch antenna goes left to right  as much as it does forward (into the gap in the racking).

[George Stefanick]

If youre speaking about the book by Bruce, who I also know and now works for juniper he would even tell you this is the old way of thinking. That book was from 2003 or so as I recall.

I'm not saying you can't use a yagi indoors, but it's not done regularly. Lets do some math..

What dBi antenna were you thinking about deploying? At what transmission power do you plan to use on the ap attached to the yagi.

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[s.vosper]

The antenna is 6 dBi and I was planning to deploy the AP at 14dBm.

[s.vosper]

THats for the 5GHz. 2.4GHz I plan to deploy at 11dBm.

[George Stefanick]

Ok let's peek at the math .. Db is a ratio so we add both dbm and dBI together and come up with 20 dbm which is 100mw. If your client is 100 mw your link should be fine between client and access point.

But what yagi only does 6 dBi ? Most are 9 or above

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[s.vosper]

Sorry 6dBi is the patch I am using. The yagi would be 10, so I would deploy the AP at 8dBi

[Scott Fella]

I agree with my buddy George! If you really want to give it a try... Well you will need to have 3 antenna all aligned perfectly to have diversity and allow for beam forming. Now is this the bet answer... No. Your better off finding an indoor mimo patch antenna

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[s.vosper]

I have the 6dBi patch antenna Scott. My problem is, all of the APs will be on the side wall of the warehouse pointing in to the racks. All the atenna will be visible to each other at high signal strengths and will overlap channels because of the way the signal radiates from the patch. I wanted something a little more narrow, so that they could all sit at the end of the racking happliy. Unfortunately the racking is too long to alternate the antennas at different ends. It will need 2 APs per aisle, one at each end

[George Stefanick]

I feel your pain. Most warehouse don't require n rates. Perhaps going to a 1242 with a yagi may help ?

Also if your looking for a newer design guide check out the CWDP book. Not only do I promote it because I'm mentioned in I it :) , but it's a great book !

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[s.vosper]

Thanks George I will check it out. Unfortunately the customer wants N in the warehouse so my hands are a little tied.

I take it I should do the same math with my client devices (gain and power output) to get it right?

Am I right in my understanding that gain on an antenna not only amplifies tx signal but also rx? Will this help if there is a slight mismatch between client abd AP?

[George Stefanick]

You are correct gain does help rx. Its best practice to always have a common link budget. In most deigns, especially in a warehouse I try and never go over 50mW. I cant mention any names but I recently fixed a very popular "hot sauce" manufacture in Louisiana who is located on an island and from this description I bet you can guess who.

High gain antennas, high power TX, improper antennas and a poor channel plan cause so much RF they couldnt pass traffic.

You may need to educate the customer on 802.11n ...

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