2.4 GHz and 5 GHz antennas

Roy_M · 04-18-2007

Hi,

I am just wondering if anyone has any experience mixing 2.4 GHz antennas with 5 GHz radios? The reason why I ask is because I have a research project in wireless mesh networks and I would like to use cheaper 2.4 GHz dipoles for 5 GHz backhaul links. In Australia, I have been unable to source any cheap 5 GHz dipoles.

I have also noticed that in laptops with a/b/g wireless cards, the same antenna is used for 2.4 and 5 GHz transmission: usually a wire that runs behind the screen. Also, I have seen antennas that people claim are dual band. Is this even possible? So, does anyone have any experience with using 2.4 GHz antennas with 802.11a equipment?

Cheers

PS: Although I usually agree with the motto: "buy the proper equipment, do it once and do it right", this project is entirely funded by myself and will involve quite number of radios and antennas. Hence, if I am buying 6 antennas, it makes a big difference if the antennas are $15 each like a 2.4 GHz dipole or $120 each for a 5 GHz omni.

Dutch · 04-18-2007

Quote:

Originally Posted by Roy_M

Hi,

I am just wondering if anyone has any experience mixing 2.4 GHz antennas with 5 GHz radios? The reason why I ask is because I have a research project in wireless mesh networks and I would like to use cheaper 2.4 GHz dipoles for 5 GHz backhaul links. In Australia, I have been unable to source any cheap 5 GHz dipoles.

I have also noticed that in laptops with a/b/g wireless cards, the same antenna is used for 2.4 and 5 GHz transmission: usually a wire that runs behind the screen. Also, I have seen antennas that people claim are dual band. Is this even possible? So, does anyone have any experience with using 2.4 GHz antennas with 802.11a equipment?

Cheers

PS: Although I usually agree with the motto: "buy the proper equipment, do it once and do it right", this project is entirely funded by myself and will involve quite number of radios and antennas. Hence, if I am buying 6 antennas, it makes a big difference if the antennas are $15 each like a 2.4 GHz dipole or $120 each for a 5 GHz omni.

A 2.4 Ghz 1/4 wavelength antenna should be able to function as a 5 Ghz 1/8 wavelength antenna, which is why laptops with multimode WiFi cards only use the same antenna. SWR will be worse, since the antennas are tuned for 2.4 Ghz, so performance will suffer compared to a properly tuned 5 Ghz antenna. Using a balun might help in your case.

At least that's how I understand it, from what I've read about antenna and RF theory. You might better wait untill Thorn or one of the other licensed HAM-operators here get around to answer, they deal with stuff like that for fun.

Dutch

Thorn · 04-18-2007

Quote:

Originally Posted by Dutch

A 2.4 Ghz 1/4 wavelength antenna should be able to function as a 5 Ghz 1/8 wavelength antenna, which is why laptops with multimode WiFi cards only use the same antenna. SWR will be worse, since the antennas are tuned for 2.4 Ghz, so performance will suffer compared to a properly tuned 5 Ghz antenna. Using a balun might help in your case.

Dutch has summed it up very well, although his math is backwards. A 1/4 wavelength antenna for 2.4Ghz is equal to a 1/2 wavelength antenna for 5GHz. A full wavelength for 2.4Ghz is about 12cm., while it is about 6cm for 5GHz.

My suggestion would be to get a couple of the cheap 2.4GHz antennae, find a local Ham*who has an SWR meter that would cover 5GHz and ask him to see how bad the attenuation is with those antennae. I'm guessing that it will be within acceptable limits.

*Buy him a beer or two.

Dutch · 04-18-2007

Quote:

Originally Posted by Thorn

Dutch has summed it up very well, although his math is backwards. A 1/4 wavelength antenna for 2.4Ghz is equal to a 1/2 wavelength antenna for 5GHz. A full wavelength for 2.4Ghz is about 12cm., while it is about 6cm for 5GHz.

My suggestion would be to get a couple of the cheap 2.4GHz antennae, find a local Ham*who has an SWR meter that would cover 5GHz and ask him to see how bad the attenuation is with those antennae. I'm guessing that it will be within acceptable limits.

*Buy him a beer or two.

No no no.. That was on purpose.. Afterall Roy is in Australia, so it should be upside down, right ?
Thats my story, and I'm sticking to it..

Dutch

Roy_M · 04-18-2007

Thanks for the replies,

My interpretation of what you said: because the wavelengths are proportional the 2.4 GHz antenna should work, however, because the antennae are not correctly tuned the SWR (Standing wave ratio) may suffer. The means that the maximum amplitude and minimum amplitude may be 'cut off'.

What I might do: get a 2.4 Ghz and 5 GHz dipole and compare them to see how much performance suffers. I'm sure there must be a ham at my university, I badger him for a SWR meter

. I will try and report back with my findings.

Cheers

Barry · 04-18-2007

Quote:

Originally Posted by Roy_M

Thanks for the replies,

My interpretation of what you said: because the wavelengths are proportional the 2.4 GHz antenna should work, however, because the antennae are not correctly tuned the SWR (Standing wave ratio) may suffer. The means that the maximum amplitude and minimum amplitude may be 'cut off'.

What I might do: get a 2.4 Ghz and 5 GHz dipole and compare them to see how much performance suffers. I'm sure there must be a ham at my university, I badger him for a SWR meter

. I will try and report back with my findings.

Cheers

He don't need no stinking badgers, just give him some beer!

Dutch · 04-19-2007

Quote:

Originally Posted by Roy_M

Thanks for the replies,

My interpretation of what you said: because the wavelengths are proportional the 2.4 GHz antenna should work, however, because the antennae are not correctly tuned the SWR (Standing wave ratio) may suffer. The means that the maximum amplitude and minimum amplitude may be 'cut off'.

What I might do: get a 2.4 Ghz and 5 GHz dipole and compare them to see how much performance suffers. I'm sure there must be a ham at my university, I badger him for a SWR meter

. I will try and report back with my findings.

Cheers

It sounds like an interesting project. Have you gotten anything about it up on the web yet ?
I recall reading about a meshproject involving public transportation some years ago, where WiFi was used to display the position of city busses on a map. Quite interesting to see the diverse ways that this technology has been/is being utilized in.

Dutch

Roy_M · 04-19-2007

Quote:

Originally Posted by Dutch

It sounds like an interesting project. Have you gotten anything about it up on the web yet ?Dutch

No net yet, I am just starting out doing my PhD but I will start up a little website soon to keep track of my work (and hopefully my publications

).

Quote:

Originally Posted by Dutch

I recall reading about a meshproject involving public transportation some years ago, where WiFi was used to display the position of city busses on a map. Quite interesting to see the diverse ways that this technology has been/is being utilized in.

I think there are a bunch of researchers at Johns Hopkins University that were putting WiFi into buses for tracking purposes. Their publications are here: http://wireless.cs.jhu.edu/

For my research, I want to setup an experimental wireless mesh network using the WRAP platform to evaluate the efficiency of mesh routing design. So the idea is to create a multiradio mesh network and try out a few routing protocols, and metrics.

There are also lots of other interesting angles to take and things to investigate. For example, currently, mesh networks are built by putting a wireless interface in ad-hoc mode, giving it an IP address and running a routing protocol on the interface. Some people may have heard that the IEEE are standardizing mesh networking with the 802.11s protocol. Their approach is very different using wireless interfaces in WDS mode and routing at layer 2 with MAC addresses.

So.... Some fun times ahead

Roy

Edit: poor English

Roy_M · 05-01-2007

So after a lot of searching, I have eventually found some cheapish 5 GHz dipoles. However, I am still intrigued as to how the performance differs from using 2.4 GHz dipoles with 5 GHz radios so I am going to test it out. I am going to compare:

Cisco Aironet 5 GHz Articulated Dipole Antenna (AIR-ANT5135D-R) and, Cisco Aironet 2.4 GHz Articulated Dipole Antenna (AIR-ANT4941)

Although I have ordered these antenna, I have a question about connectors. My wireless cards are Wistron CM9 mini-PCI wireless cards. These have a U.FL connector but sit in a PCI cradle which has a pigtail to convert the UFL to a RP-SMA. However, because my antenna are both RPTNC I will have to use a connector / second pigtail.

UFL - RPSMA - RPTNC

Will I lose a lot of power using two connectors?

Cheers

Roy

streaker69 · 05-01-2007

Quote:

Originally Posted by Roy_M

So after a lot of searching, I have eventually found some cheapish 5 GHz dipoles. However, I am still intrigued as to how the performance differs from using 2.4 GHz dipoles with 5 GHz radios so I am going to test it out.

I am going to compare:
Cisco Aironet 5 GHz Articulated Dipole Antenna (AIR-ANT5135D-R)
and
Cisco Aironet 2.4 GHz Articulated Dipole Antenna (AIR-ANT4941)

Although I have ordered these antenna, I have a couple of questions about connectors.

Firstly, my wireless cards are Wistron CM9 mini-PCI wireless cards. These have a U.FL connector but sit in a PCI cradle which has a pigtail to convert the UFL to a RP-SMA. However, because my antenna are both RPTNC I will have to use a connector / second pigtail.

Will I lose a lot of power using two connectors?

Cheers

Roy

Why not just go here: http://www.fab-corp.com/product.php?productid=2680 and order the correct pigtail and cut down your convertolutions?

Roy_M · 05-01-2007

Hmm that is kinda nice that they have every connector under the sun. The problem is mainly that I don't want to ship from the US to Australia. Its rather annoying how these things are so readily avaliable in the US and so complicated in Australia.

I will email them about shipping costs but their default quote for shipping was going to cost about 45 USD for 4 pigtails and about 45 USD shipping.

But thanks for the suggestion Streaker

brwrdrvr · 05-01-2007

Quote:

Originally Posted by Roy_M

Hmm that is kinda nice that they have every connector under the sun. The problem is mainly that I don't want to ship from the US to Australia. Its rather annoying how these things are so readily avaliable in the US and so complicated in Australia.

I will email them about shipping costs but their default quote for shipping was going to cost about 45 USD for 4 pigtails and about 45 USD shipping.

But thanks for the suggestion Streaker

Hah. You think that's bad? Have a conversation with Barry. He can't get hardly anything up there where he lives. Except Santa letters.

Barry · 05-01-2007

Quote:

Originally Posted by brwrdrvr

Hah. You think that's bad? Have a conversation with Barry. He can't get hardly anything up there where he lives. Except Santa letters.

YYea, I got santa letters out the ass. It sucks paying more for shipping than you
payed for something.

The guys at fab are cool though. They've actually sent parts to me over night.

04-18-2007	#1 (permalink)
Roy_M Registered Member Join Date: Jun 2005 Posts: 72	2.4 GHz and 5 GHz antennas Hi, I am just wondering if anyone has any experience mixing 2.4 GHz antennas with 5 GHz radios? The reason why I ask is because I have a research project in wireless mesh networks and I would like to use cheaper 2.4 GHz dipoles for 5 GHz backhaul links. In Australia, I have been unable to source any cheap 5 GHz dipoles. I have also noticed that in laptops with a/b/g wireless cards, the same antenna is used for 2.4 and 5 GHz transmission: usually a wire that runs behind the screen. Also, I have seen antennas that people claim are dual band. Is this even possible? So, does anyone have any experience with using 2.4 GHz antennas with 802.11a equipment? Cheers PS: Although I usually agree with the motto: "buy the proper equipment, do it once and do it right", this project is entirely funded by myself and will involve quite number of radios and antennas. Hence, if I am buying 6 antennas, it makes a big difference if the antennas are $15 each like a 2.4 GHz dipole or $120 each for a 5 GHz omni.

05-01-2007	#9 (permalink)
Roy_M Registered Member Join Date: Jun 2005 Posts: 72	So after a lot of searching, I have eventually found some cheapish 5 GHz dipoles. However, I am still intrigued as to how the performance differs from using 2.4 GHz dipoles with 5 GHz radios so I am going to test it out. I am going to compare: Cisco Aironet 5 GHz Articulated Dipole Antenna (AIR-ANT5135D-R) and, Cisco Aironet 2.4 GHz Articulated Dipole Antenna (AIR-ANT4941) Although I have ordered these antenna, I have a question about connectors. My wireless cards are Wistron CM9 mini-PCI wireless cards. These have a U.FL connector but sit in a PCI cradle which has a pigtail to convert the UFL to a RP-SMA. However, because my antenna are both RPTNC I will have to use a connector / second pigtail. UFL - RPSMA - RPTNC Will I lose a lot of power using two connectors? Cheers Roy Last edited by Roy_M : 05-01-2007 at 08:45 PM.

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04-18-2007	#5 (permalink)
Roy_M Registered Member Join Date: Jun 2005 Posts: 72	Thanks for the replies, My interpretation of what you said: because the wavelengths are proportional the 2.4 GHz antenna should work, however, because the antennae are not correctly tuned the SWR (Standing wave ratio) may suffer. The means that the maximum amplitude and minimum amplitude may be 'cut off'. What I might do: get a 2.4 Ghz and 5 GHz dipole and compare them to see how much performance suffers. I'm sure there must be a ham at my university, I badger him for a SWR meter . I will try and report back with my findings. Cheers

05-01-2007	#11 (permalink)
Roy_M Registered Member Join Date: Jun 2005 Posts: 72	Hmm that is kinda nice that they have every connector under the sun. The problem is mainly that I don't want to ship from the US to Australia. Its rather annoying how these things are so readily avaliable in the US and so complicated in Australia. I will email them about shipping costs but their default quote for shipping was going to cost about 45 USD for 4 pigtails and about 45 USD shipping. But thanks for the suggestion Streaker