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Near field plot in CST MW Studio

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fparveen

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Hello,

I am trying to plot the near field pattern of an antenna in CST MW studio. I have the following confusions:

1.
I plotted the far field. Then in the properties window, I unchecked the 'use farfield approximation'. In the origin tab, I set the origin of farfield as 'Origin of coordinate system'.
Can anyone suggest how should I set the reference distance in the 'plot mode' tab? Is it the distance from the origin where I want to see the near field?
For example if my antenna is up to 2.4 cm, and I want to see near field at 5 cm away from my antenna, will I set the reference distance = (2.4 + 5) cm?

2.
If I set a small reference distance, I get a warning like the following screenshot - 'The reference distance is smaller than the required minimum distance (0.31852 m) regarding the selected origin. Thus, the farfield calculation results may be of poor quality.'
This minimum distance in the warning changes with frequency. It also changes for the same frequency if the antenna is changed.
Can anyone suggest what is this minimum distance? Is it the far field starting distance from the origin? How is this minimum distance calculated? I calculated the farfield distance from the antenna using the 2D^2/lambda formula, where D is the largest dimension of the antenna. But it doesn't match with this minimum distance shown in the warning.



3.
Can anyone suggest how to calculate the far field distance from an antenna? I usually use the 2D^2/lambda formula, where D is the largest dimension of the antenna.
But when I plotted the near field at distances greater than the distance calculated form this formula, I still do not get the plot like the far-field pattern. I get farfield pattern after a much longer distance than that obtained form this formula.


Thanks.
 

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