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Plotting an antenna's far field
Posted Jun 6, 2010, 11:47 a.m. EDT RF & Microwave Engineering Version 4.0 6 Replies
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Using COMSOL4.0 I modeled an antenna using the emw-Interface and the "Far Field Calculation"-node.
My far-field variable is called "Efar", as in the documentation, the equation view shows emw.Efar{x,y,z} and emw.normEfar{dB}.
From the solution I do a selection of the outer sphere boundary, the auto-generated surface plot shows the near field, the default expression is: "emw.normE". When changing that to "emw.normEfar" I get the error: "cannot evaluate expression: `mod1.emw.normEfar`: Failed to eaulate variable normEfar". Changing the expression to "emw.normEfar(x,y,z)" gives me "Unknown function normEfar". -- But "emw.Efarx(x,y,z)" works, just not the norm/normdB-variants.
The other problem I run into: the plot takes literally hours to compute. It seems to me, as if the far field was not part of the solution, and is being re-calculated every time. (And not just for refinement: plotting the far field not in 3D but on a plane on a rough circle of ~36 points takes 5min)
Is there a way to have the far field calculated at a set of angles (for example using the vertices of the outer sphere's mesh for directions), cache that result and plot in in a few seconds?
This wouldn't be a huge problem, if COMSOL wouldn't re-plot at the drop of a hat: adding a new element to a plot, for example an arrow surface to the existing surface, yields an automatic re-plot of the surface!)
I guess there is a node I can add to force evaluation and storage of the far-field?
Sadly, the "Far Field Postprocessing" chapter doesn't mention it, and neither do the tutorial examples, because they are simple enough to not depend on this…
Thanks for any pointers!
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I agree that "ages" to calculate is not nice, but I do not understand why either, apart that I believe far field is not part of the solution by default and is recalculated on demand. For me this seems that you are hitting a particular issue that is not fully debugged yet in V4, ideally remake it in 3.5 and check. In anycase such problems I typically send to support, documented with the model so they can check. They have always provided me with very good support :)
I havent had time yet to test ACDC and far field calculations in V4, so I cannot tell more
Good luck
Ivar
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The problem is, I don't have access to 3.5, only 4.0.
Is there a way to force storage?
For example, evaluate all far fields at a sphere's vertices into a table and plot that table?
(or even: export it, to plot in another software. I haven't figured out how to automatically evaluate arbitrary points [like: far field in 5° steps] and store them in a file)
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i really do not know, for me typically a issue for support, on the oter hand perhaps its usefull to work with 3.5a, still some weeks ?
Good luck
Ivar
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I have the same problem about the far field plot in Comsol 4: it takes a lot of time.
Any progress in the solution of this problem?
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