# Magnetic field distribution on CPW

Member

Hello,

I simulated a coplanar waveguide to see the field distribution on the signal line. In this design (attached), although everything is symmetric, e.g. the geometry, the wave ports, etc., H field's plotted magnitude using ComplexMag_H does not seem to be homogeneous over the surface of the signal line. There is inhomogeneity in other regions, but the important region for me is the signal line's top surface. I expected the field to be symmetric because, at least in the simulation, there are no geometry imperfections. Please see the attached field plots. Note that I have scaled the field in some of the plots for better clarification.

My question is that, first, is there something wrong with my simulations? Or is it something just natural (if it is, it would be great if you can explain)? Secondly, the field strength range in the signal is ~ 875 to 11900 A/m, but the field's average on the signal surface is about 1700 A/m. Is there a way to increase this average value?

Here is the way I simulated:

1. There are two wave ports at the endpoints of CPW. The integration line has been defined for both, and the port normalization is set to renormalize all modes to 50 ohms. The L and W of the ports are designed to be ten times bigger than the signal's width and thickness.
2. The radiation box has been defined.
3. The analysis is set up to a single frequency solution (10 GHz), and I defined the frequency sweep. The maximum number of passes is set to 12, with max delta s set to 0.02.
4. The width of the signal is 20 um, and its thickness is 150 nm made of gold.

Thanks,

Mojtaba

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• Member

In order to get an Idea on what's happening, examine the cross-section, and port configuration.

it may be a wrong mode, or just a meshing problem. Coplanars work better when side planes are connected with shorter path. Either make it with vias, or airbridges.

• Pune, IndiaForum Coordinator

Hello @Mojtaba,

FYI : Please embed the images into the post rather than using attachments.

The way you simulated the CPW seems fine.

The appearance of the field distribution depends on the meshing quality of the model. You can just try plotting the mesh and see how it is distributed along the trace. If the simulation is converged on a particular delta S then that much of mesh might be necessary to pull the required model information.

But if you are more concerned on the symmetry of the Fields and its appearance, I would suggest to give smaller delta S and see the distribution at a particular plane.

For example, in your case plot the 'ComplexMag_H' at a certain plane, after opting for a smaller delta S.

And about the field strength, you can't increase the value of the signal strength unless the model is giving that!

If you need to adjust the scale of the field strength, that is possible (You might be aware of that as well)