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BillDumke1-Visitor
1-Visitor
November 3, 2011
Question

How to get Near Field From Far Field Antenna Pattern?

  • November 3, 2011
  • 2 replies
  • 3966 views

I want to find the horizontal near field pattern of an antenna at a given distance in wavelengths from the horizontal far field antenna pattern.

I had to post this in Mathcad 15 since Mathcad 11 does not show negative radii in polar plots. But the txt file has the degrees in the first column and dB in the second column. (All the Matchad 15 doc does is display the antenna pattern on a polar plot.)

Anybody have a solution for doing this? I am trying to get an estimate of the isolation between two identical antennas spaced a given distance apart in wavelengths horizontally within the radiating near field.

Bill

2 replies

J
JamesRedding1-Visitor
1-Visitor
January 16, 2012

The text file provided is a 2-D field plot that does not show polarization, phase, or magnitude (wrt to iso/dipole) of the components. The question is also, DB to what power reference? However, the 2-D cardoid pattern given looks very similar to a two half wave element inline array, a bit under a halfwave spacing, fed in phase. Without more data, like limiting the antennas to linear conductors, there are infinite sets of solutions. As for the isolation between co-located antennas, it well investigated and is already in the literature. The original theoretical calculations for antenna coupling were published by GH Brown (RCA) in the Transactions of the IRE 1937, Volume 25, Number 1, Part 1. However, the calculations seem at best estimates and never exactly match field measurements.

B
BillDumke1-VisitorAuthor
1-Visitor
January 16, 2012

Thanks for the reply, James. When I asked that question I had no idea it would was that complex a problem. Later doing some searching on the Internet I found there is a MATLAB program available to convert measured Near Field Patterns to Far Field Patterns, but nothng the other way around. Also I found that different methods of doing this work well in the direction of the main beam but crap out at 90 degrees from the main beam, and I needed to know that accurately as well.

The text file was just some published panel antenna data from a vendor. And you are correct it would have to include phase as well as magnitude. Also the vertical and horizontal patterns are just in orthogonal planes, and so are not really 3 dimensional either.

Thank you very much for the reference. And thank you for the reply as well.

I eventually was able to come up with a estimate for the isolation, but I had to use the far field data, since that was all I had available.

Bill

J
JamesRedding1-Visitor
1-Visitor
January 16, 2012

It was remiss for me not to include the link to a public resource for the 1937 IRE document:

http://materias.fi.uba.ar/6654/download/01686257.pdf

JVR

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