Hi everyone:
This is my circuit :
schematic.png(using CPWG component in TLines-Waveguide)
layout_all.png
layout.png
cosimulation.png
I want to see S11 on the smith chart.
But I don't know exactly how to set the mesh frequency and mesh density at the em setup.
Someone tells me the mesh frequency should be 3 times as much as the operating frequency, and the mesh density can be set to be 20 cells/wavelength.
Here is my em setup:
Mesh setup.png
My operating frequency is at 2.4GHz ,single sweep, so I set the mesh frequency=2.4*3=7.2 GHz, and the mesh density=20.
But when I change the mesh density to be 40, the result on the smith chart is different from the result of which the mesh frequency is 20.
Here is the result, where the green point is the result of schematic, the red point is the result of cosimulation at mesh frequency=40, and the blue point is the one at mesh frequency =20.
result.png
I don't know which is the correct result and setting.
Thanks for replying.
This is my circuit :
schematic.png(using CPWG component in TLines-Waveguide)
layout_all.png
layout.png
cosimulation.png
I want to see S11 on the smith chart.
But I don't know exactly how to set the mesh frequency and mesh density at the em setup.
Someone tells me the mesh frequency should be 3 times as much as the operating frequency, and the mesh density can be set to be 20 cells/wavelength.
Here is my em setup:
Mesh setup.png
My operating frequency is at 2.4GHz ,single sweep, so I set the mesh frequency=2.4*3=7.2 GHz, and the mesh density=20.
But when I change the mesh density to be 40, the result on the smith chart is different from the result of which the mesh frequency is 20.
Here is the result, where the green point is the result of schematic, the red point is the result of cosimulation at mesh frequency=40, and the blue point is the one at mesh frequency =20.
result.png
I don't know which is the correct result and setting.
Thanks for replying.
> But I don't know exactly how to set the mesh frequency and mesh density at the em setup.
> Someone tells me the mesh frequency should be 3 times as much as the operating frequency, and the mesh density can be set to be 20 cells/wavelength.
In other solvers that use FEM 3D simulation, the meshing frequency is used to adaptively refine the mesh, based on simulation results at this frequency.
In Method of Moment, it is much simpler than that: the mesh frequency and the dielectric materials are evaluated, to calculate the wavelength in the dielectric. Then, maximum size of a mesh element is limited to (wavelength in dielectric) / (cells per wavelength). So it is really the same if you use 3*fmax at 20 cells/lambda, or use fmax at 60 cells/lambda.
The importance of mesh density depends on the amount of layout details that force the mesh algorithm to use a denser mesh. If you have a simple layout, the resulting mesh might have many large cells that reach the "cells per wavelength" limit. In a complex, electrically small layout the effective mesh size is determined by the amount of layout detail.
In general, results with higher mesh density are more accurate, because currents on the conductors have more degrees of freedom to flow in the physically correct way when the moment matrix is solved. The only exception would be extreme mesh density or exterem mesh shape where numerical issue might come up.
In your case, we would expect a rather fine mesh density near the line, caused by the via fences. The large areas outside shouldn't have much signal anyway. However, the "Mesh reduction" setting in emSetup > Options > Mesh might have an effect as well. Can you show a screenshot of the mesh view for both cases that you compare?