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Anechoic chamber time!

August 1, 2013

Ok, a really exciting post this time! Over the last few days I’ve been working in the anechoic chamber – soo… time for some cool pictures, and then I’ll explain what it is that I’ve been up to so far in there, and what it all means…

This is inside the chamber. The cones you can see stop the radiation from the antenna being reflected and scattered.

This is inside the chamber. The cones you can see stop the radiation from the antenna being reflected and scattered.

This is the antenna that is used to measure the antennas under test. It measures the amount of radiation produced by the antenna being tested while it is moved through various orientations.

This is the antenna that is used to measure the antennas under test. It measures the amount of radiation produced by the antenna being tested while it is moved through various orientations.

This is where antennas being tested are placed. This motorised platform allows us to rotate the antenna around so we can observe which direction radiation is being emitted in.

This is where antennas being tested are placed. This motorised platform allows us to rotate the antenna around so we can observe which direction radiation is being emitted in.

So, to explain. The anechoic chamber is used to measure the performance of antennas. The reason that this has to be done in a special chamber is that in a normal room the radiation produced by an antenna would simply bounce around the room, reflecting and scattering and generally making it very hard to determine what radiation is being emitted directly from the antenna, and what is simply reflections coming in from other angles.

In order to obtain the measurement of the antenna the antenna is mounted on a motorised platform and spun around. In this way we can measure the pattern. The test is carried out by a piece of equipment called a network vector analyser (which looks something like a large oscilloscope). This provides the test signal for the antenna under test, and then takes in the signal from the reference antenna and then sends the resulting data back to the computer. This process is repeated over and over for different orientations, and the end result looks something like this:

This plot is the radiation patter produced by a simple patch antenna when placed in the chamber.

This plot is the radiation patter produced by a simple patch antenna when placed in the chamber.

This diagram simply shows the radiation pattern. The further away from the origin of the graph a particular point is the more the antenna radiates in that direction. From this graph we can see that this antenna radiates primarily in the z direction, but very little round the back (-z) of the antenna. Other antennas radiate more uniformly. We call this property the directivity of the antenna.

And that’s it really! Using MATLAB I am able to determine other metrics based on the data collected (for example antenna efficiency and polarisation), and using this information I will be able to look for antennas which may be better suited for use either with the gloves, or on the access points we’re going to use.

The requirements for the two antennas are really quite different. The glove antennas must be as omni-directional as possible, and small and easy to incorporate into the gloves. The router antennas, however, must be reasonably directional to try and block out interference from the audience, but can be moderately bulky if required.

Anyway, that’s it for now, back to looking for the right antenna for the job!

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