# S12 greater than 0 dB for a transmission line !!

1. ## S12 greater than 0 dB for a transmission line !!

Hi everyone,

I tried to simulate a transmission line above a rectangular metallic sheet using the "integral equation solver", and finally i got an S12 parameter which is greater than 0 dB at the resonnant frenquencies of the line.

When i use the "time domain solver" i obtain good results.

Does anyone have any idea how to solve this problem ?

By the way, i used the discret ports.

Thank you for your support !

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2. ## Re: S12 greater than 0 dB for a transmission line !!

There are so many different EM solvers ... it might help if you mention the simulation tool that you used.

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3. ## Re: S12 greater than 0 dB for a transmission line !!

I used CST MWS.

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4. ## Re: S12 greater than 0 dB for a transmission line !!

Don't sure if I can help, but maybe the positive S12 is due to an upper resonance? Be careful to not create a metal (PEC) cavity with the boundaries near the model, or it could lead to unwanted resonances.

Anyway, why are you trying to simulate with the Integral Equation solver? The TDS with the adaptive meshing should be more than enougth (and fast). Also, for TL and planar structures, I suggest using Waveguide ports.

Cheers,

AMD

5. ## Re: S12 greater than 0 dB for a transmission line !!

@anddab thank you for your answer. Indeed the TDS with adaptive meshing is faster than the integral equation solver, but the point is that i want to compare the MoM method (solved in the frequency domain) with a frequency model i developped for transmission lines.

Now i am using the integral equation solver, it's difficult to get good results. We have to pay attention to the meshing features :

- With 5 cells per wavelength, i could get good results in reasonable calculation time.

- With 10 cells per wavelength, i couldn't get good results, sometimes the solver stop the calculation displaying this message (could not solve equation system).

By the way, all the boundaries are open space.

Kindly,

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