HELP on Near-Field to FAR-FIELD Transform

[Mortin]

Hi everyone!
I'm trying to get some information on NF to FF transform an maybe any of you can help me. My problem is that I made some antenna measurements but my range is not long enough to fulfill the far-field condition (2*D^2/lambda) I thought that there might be some piece of software with wich I could process those measurements and get the real far-field pattern I was expecting. I don't know if FDTD is the right way to go or maybe there are ohter algorithms for that porpouse. My search through internet was not very succesfull, so if someone knows how could I start my investigation (considering I'm not too kneen on this "computation stuff"), I would be really appreciate.
Thanx a lot!

Mortin

 

[Mortin]

Hi! It's me again...
Related to what I posted before: Could GRASP8W do that transformation form NF to FF? I've heard it's possible to go from Far-Field to Near-field with that software, but is it to get FF values from a NF measurement?
Thanx again!

Mortin

 

[loucy]

Using existing FDTD code is not a good way to go. You would need to assign a distributed excitation, and the phase difference in your measurement would need to be changed to time delay. Depending on your measurement grid, this might not be easy to assign accurately.

Suppose you have done a "near field" measurement, if you don't need to do the probe correction (i.e. account for the fact that your measurement antenna is not ideal), then you can simply apply a 2-D FFT to get the far field pattern. I suppose this takes the same level of time as "formating" your data to put into a fdtd code.

Search for "near-field" "antenna measurement" on IEEE, you will find a lot of papers.

 

[springf2000]

use the moment method to relate the NF and FE,but you shall compensate the probe,it is a very difficult job to do this kind job,but you can buy the measurement device ,then it is simple

 

[Mortin]

what measurement device?
What's the point in probe compensation?

 

[plasma]

Hi Mortin

what measurement device?
What's the point in probe compensation?

First the probe don’t have planar wave and planar phase it’s not
Receiving with the same amplitude in all direction.
So you have to Take care, and compensate the Receiving field of the probe and calculate it to get accurate results

Now if you have some money or friend you can buy scanner
And code form “NSI” or “ORBIT-FR” they do it and sell it.
also "TICRA" sells probes with compensating data.
Here two links
**broken link removed**
**broken link removed**

RGZ PL

 

[mohamed kholy]

hiii,
i want matlab code for this problem ( NF to FF transdormation )

 

[Andryuha]

Can anybody tell me simple exact math for converting in-plane complex S21(x,y) probe data for measured near-field to far-field pattern F(θ,φ) ?

It is very easy to throw, "just use 2D FT", everybody says that, I know it myself. But no one can tell how exactly can it be calculated. Matrices composition, parameters, dimensions, normalization, units(absolute or relative to λ/2). Should the elevated data be transformed to surface current first, etc... it doesn't seem that trivial when I read available paper abstracts on this matter.

I tried to search a couple of books on array filter synthesis... I am not good in math, and nobody explains the inverse problem of pattern finding. only response problems are explained. :sad: