On Mon, 27 Nov 2006, Ashifi wrote:
I have a question about free space propagation of a Gaussian in MEEP. My
source has frequency 5 GHz <= f <= 16 GHz and I'm using the Ex component. I
place the source at the top, place a flux plane right beside it and another
flux plane down at the bottom of the cell. I then compute the flux by
dividing the bottom flux by the top. I thought I would get a transmission
spectrum approximately equal to 1, but the spectrum looks like an M, with the
central part close to 1, but the highest and lowest frequencies dipping to
0.4.
Any idea why this is the case? Extending the length of the computational
cell to a couple of wavelengths doesn't fix it.
The problem is that you are using (run-sources). That is, you are only
running long enough for the source to turn off, not long enough for the
all of the energy of the pulse to propagate accross the cell, which is why
you get different powers at the two flux planes.
Try changing (run-sources) to (run-sources+ 1) to add a some time. Or
better yet, use (stop-when-fields-decayed ....) as described in the
Meep tutorial to run until the fields have decayed sufficiently.
Steven
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