method of measuring antenna array in anechoic chamber using one element

Thread Starter

yef smith

Joined Aug 2, 2020
293
Hello, there is a thing I heard that in anechoic chamber we cant do an accurate measurement of an array radiation patten because we are limited to a certain sample rate in an angle.
Why is that? what is the difference in measuring a regular antenna to a antenna array i anechoic chamber?
Why we would get an innacurate pattern due to the sample rate of the rotating test antenna?

The solution to this problem is testing only one element and make radiation pattern of the array using a radiation pattern of a singl element.
How can we build radiotion pattern of an array using radiation pattern from a single pattern?
Thanks.
 

nsaspook

Joined Aug 27, 2009
8,898
Because when the antenna array radiation pattern is a far-field effect for a simple receiving antenna it gets messy. If the array is electrically large IRT the chamber you will measure the near-field interaction (far too complex for a simple phase/amplitude measurement of X points in space) of elements instead of the peaks and nulls of the far-field moving wavefront as the measurement antenna is moved.

https://www.nsi-mi.com/images/Techn...-Rules-for-Indoor-Anechoic-Chamber-Design.pdf
NEAR-FIELD RANGES There are different approaches for performing near-field measurements. The different techniques are related to the type of antenna being measured. In all approaches, the field (amplitude and phase), radiated from the AUT is measured on a surface. After this near-field measurement, the far-field behavior is mathematically obtained.
 

Thread Starter

yef smith

Joined Aug 2, 2020
293
Hello HNSA spook,I anderstand.so its because the array is too large so we dont go to the frauhofer region (far field)
So what is the solution method?
If you could please descibe how we overcome this problem in detail as possible.
Thanks.
 

nsaspook

Joined Aug 27, 2009
8,898
You understand the basic problem but need to read the literature yourself to understand the problem in detail. Measure the antenna outdoors or in a chamber that meets the far-field measurement requirements.
http://www.ets-lindgren.com/sites/etsauthor/WhitePapers/APM.pdf
Therefore, the bigger the object or the shorter the wavelength, the farther away the receive antenna has to be for that object to appear as a single source. The region inside the 2D^2 /λ distance, but outside the reactive near-field region, is referred to as the radiating near-field or Fresnel region, whereas the region outside this distance is the far-field or Fraunhofer region. 2 In terms of antenna-pattern measurements, normally there is little useful information to be gained within the reactive region of an antenna. The one possible exception would be when the antenna is to be used in the reactive region as well.
 

Deleted member 115935

Joined Dec 31, 1969
0
It can , and is done

The technique is to measure each element on its own,
then in computer simulation, you use superposition and maxwells ,
to derive the new radiated pattern for multiple elements,,

BUT

its not easy, needs some real expensive software, hardware to run it on, and a fair amount of knowledge to not come up with the wrong answer.

I would say, not something to get into if your having to ask,
good luck,
 

Janis59

Joined Aug 21, 2017
1,356
I would reccoment to substitute the damn expensive anechoic chamber with just the normal environment where antenna will work - roof or pole-top etc. Then, mount the antenna on turntable platform, let You may turn it distantially and read the angle. Fix the measurer in one heighth and write down the table of readings by angle. Then change the heigth a bit and make a readings again. Do so until full heigth range is filled with data.
 
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