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" Some words and pictures about our WLAN antenna testing day held on the 9th of June 2002. As usual the British wx was normal - Very wet!"
FRARS held the Wireless LAN antenna testing day, today the 9th of June, 2002. Despite the very poor wx, we managed to have a good day of technical chat and activity.
A number of antennas were tested using the polar plotter designed and written by Carl - G6NLC, pictures of which appear below. We also tested the return loss of antennas using a swept source, directional coupler and a spectrum analyser.
For the polar plotting, the system comprised of a 2.45Ghz source which was stable in terms of frequency control. This was connected to a dipole polarised vertically, and placed about 30 feet away from the receive antenna test rig.
On the receive side, the computer controlled antenna rotator held the antenna under test, this was connected to about 10 M of LDF450 heliax to the spectrum analyser. The analyser was tuned to the frequency of the 2.45Ghz source, and the sweep set to Zero. The IF output from the analyser was then fed to the RF detector unit - based on a G3YGF design. Once the RF has been detected and converted into a DC representation, its fed into a 10 bit A-D converter. Carls software then monitors the input from the A-D and sends a command to the rotator such that it increments round in 1 degree steps. At each step, the signal strength is measured and plotted. The screen shots of the polar plotter can be seen below.
One of the most interesting antennas we tested was the pringles can-tenna - It does actually work and provides a reasonable amount of gain and front to back ratio. The pringles tube was tested with and without the insert, and showed a substancial difference. See the pringles pictures below for more information.
Several commercial antennas were also tested, and had fairly clean polar plots. The MVDS antennas from Southern Ireland of the 13dBi and 17dBi variety provided a nice plot with the expected front to back ratio.
A sandpiper 2.3Ghz helical was tested and this exhibited a very poor polar diagram - quite possibly due to the small reflector diameter at the rear of the helical element.
The short backfire antenna constructed by Carl - G6NLC exhibited an excellant polar diagram, and certainly impressed those people that saw it. The main lobe is fairly narrow in terms of beamwidth and there were very few side lobes.
The sky-mini-dish and feed built by Paul - G7EYT proved to be another good antenna for beamwidth and side lobe performance.
The G1MFG 13cm Yagi antenna was tested and displayed fairly good front to back ratios and a forward lobe thats characteristic of a small yagi.
A halo type antenna consisting of a full wave circular element with a back reflector made from a CD was tested, and showed suprisingly good amounts of gain, and a brilliant front to back ratio. Such an antenna would be very good for locating AP's as its ideal for direction finding.
to be continued.....
| G1MFG 13cm Yagi | http://www.g1mfg.com/website/13yagi.html |
| To view the polar plots of the antennas tested... | 1135 |
| More FRARS Wireless LAN articles | 999999 |
| 13dB mesh antenna source | http://www.wlansource.co.uk/catalog/catalog |
