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Xfdtd Microstrip line..Please Help!!

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Newbie level 5
Jun 8, 2011
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Hello Everyone,

I am trying to simulate a microstrip Rf coil at 123.48 Mhz in Xfdtd. But, the S11 is very bad. I got good result with Ansoft HFSS ( FEM based) and Semcad (FDTD based) with the same structure. I do not know why s11 is different in xfdtd.

I tried gaussian pulse for the excitation and so that I can see the S11 curve. I just wonder whether there is any problem with meshing /excitation/geometry. Can anyone please help me in this? I attached the xfdtd file for the convenience.

Thanks in advance.


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Thanks for the link.

Actually I have done all of those simulations which are given in Xfdtd user guide.

I would like to explain my problem more elaborately. I am trying to design a Microstrip (TEM) RF coil for MRI. The dimension of the Microstrip structure is much smaller than the wavelength of the Resonance frequency (123.4 MHz). So, I inserted capacitance to maintain the smaller size and to find the resonance (S11). I tried different grid size to generate the mesh. In every cases, I made sure that the rule of of the meshing (i.e.; 10 cells/wavelength) satisfied. I used Gaussian wave for the excitation and my frequency range of interest 100 MHz ~150 MHz (resonance frequency 123.4 MHz). Unfortunately, I am not getting any convergence and as a result, very bad S11.

It is worth to mention here that, I found very good s11 with ansoft HFSS (FEM) Semcad (FDTD) with the same structure. I really don't understand what is wrong with my design in XFDTD. I want to draw the attention of those who are experienced in Remocom Xfdtd and microstrip line. Please help me to solve this problem. Thanks!!

I think 10 mesh/wavelength is very low for FDTD based solvers, please increase the number of cell in wavelength to 20/40 and execute your files again.

I tried, but the result remain the same. Does anybody know what is cell impedance (fdtd cell) and how it is related to the lumped elements? There's some explanation in remcom manual but it's not clear enough for me. I tried to design another microstrip line by using quarter wave transformer matching technique at 128 Mhz. At first, I designed this microstrip line in AWR microwave office (128 Mhz), but when I implemented the same design in XFDTD the resonance frequency decreased to ~103 Mhz!! Is there any explanation for this?

If anyone successfully done the simulation of microstrip line in xfdtd, please help me. Thanks!

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