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Plotting an antenna's far field

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Hello,

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!

6 Replies Last Post 29 lug 2010, 08:45 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 7 giu 2010, 02:01 GMT-4
Hi

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
Hi 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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Posted: 1 decade ago 7 giu 2010, 08:50 GMT-4
Thanks for the answer!

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)
Thanks for the answer! 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)

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 8 giu 2010, 10:53 GMT-4
Hi

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
Hi 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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Posted: 1 decade ago 1 lug 2010, 05:05 GMT-4
Hello,
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?
Hello, 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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Posted: 1 decade ago 29 lug 2010, 05:53 GMT-4
I have similar problem with the far-field plotting in a Pressure Acoustics model. The far-field plot takes less than a minute in 3.5a, but ages in 4.0a (4.0.0.993).
I have similar problem with the far-field plotting in a Pressure Acoustics model. The far-field plot takes less than a minute in 3.5a, but ages in 4.0a (4.0.0.993).

Linus Andersson COMSOL Employee

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Posted: 1 decade ago 29 lug 2010, 08:45 GMT-4
Hi everybody! This seems to be something we should look closer into. If anyone has a simple reproduction of the problem, preferably a 3.5a model giving slower far fields in 4.0(a), please send the model mph-file to support@comsol.com. Thanks!
Hi everybody! This seems to be something we should look closer into. If anyone has a simple reproduction of the problem, preferably a 3.5a model giving slower far fields in 4.0(a), please send the model mph-file to support@comsol.com. Thanks!

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