EM网格频率和网格密度问题

> {quote：title = jeff0283写道：} {quote}>但我不确切知道如何在em设置中设置网格频率和网格密度。
>有人告诉我，网格频率应该是工作频率的3倍，网格密度可以设置为20个单元/波长。
在使用FEM 3D模拟的其他求解器中，基于此频率下的模拟结果，网格化频率用于自适应地细化网格。
在矩量法中，它比这简单得多：评估网格频率和介电材料，以计算电介质中的波长。
然后，网格元素的最大尺寸限于（电介质中的波长）/（每个波长的单元）。
因此，如果您使用20 * cell / lambda的3 * fmax，或使用60 cells / lambda的fmax，则实际上是相同的。
网格密度的重要性取决于强制网格算法使用更密集网格的布局细节数量。
如果您具有简单的布局，则生成的网格可能具有许多达到“每个波长的单元格”限制的大单元格。
在复杂的电气小布局中，有效网格尺寸由布局细节的数量决定。
通常，具有较高网格密度的结果更准确，因为当解决矩矩阵时，导体上的电流以物理上正确的方式具有更大的自由度。
唯一的例外是极端网格密度或极端网格形状，可能会出现数值问题。
在你的情况下，我们会期望在线附近有一个相当细的网格密度，由通道围栏引起。
无论如何，外面的大区域应该没有太多信号。
但是，emSetup> Options> Mesh中的“网格缩小”设置也可能具有效果。
您可以为比较的两种情况显示网格视图的屏幕截图吗？



     以下为原文

  > {quote:title=jeff0283 wrote:}{quote}
> 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?

从图中可以看出，网格单元在信号导体和下面的地面之间排列不良。
这会影响电容。
我会在网格设置中将“薄层重叠提取”设置为“Aggressive”来修复它。



     以下为原文

  As far as I can see from the pictures, mesh cells are poorly aligned between the signal conductor and the ground below. That affects capacitance. I would set "Thin layer overlap extraction" in the mesh settings to "Aggressive" to fix that.

> {quote：title = volker_muehlhaus写道：}然后，网格元素的最大大小限于（电介质中的波长）/（每个波长的单元格）。
因此，如果您使用20 * cell / lambda的3 * fmax，或使用60 cells / lambda的fmax，则实际上是相同的。
>>网格密度的重要性取决于强制网格算法使用更密集网格的布局细节数量。
如果您具有简单的布局，则生成的网格可能具有许多达到“每个波长的单元格”限制的大单元格。
在复杂的电气小布局中，有效网格尺寸由布局细节的数量决定。
>>通常，具有更高网格密度的结果更准确，因为当解决矩矩阵时，导体上的电流以物理上正确的方式具有更大的自由度。
唯一的例外是极端网格密度或极端网格形状，可能会出现数值问题。
{quote}在我的情况下，我在20和40个单元格/ lambda上使用3 * fmax，但是史密斯图表上的结果是不同的。
所以我假设40个细胞/λ的情况比20个细胞/λ更准确。
但我可以在60个单元格，80个单元格... / lambda和更高的网格密度下使用3 * fmax，我怎么知道网格密度对于我的布局有多大？



     以下为原文

  > {quote:title=volker_muehlhaus wrote:}
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. {quote}


In my case, I use 3*fmax at both 20 and 40 cells/lambda, but the results on the smith chart are different.

So I assume the 40 cells/lambda case is more accurate than 20 cells/lambda.

But I can use 3*fmax at 60 cells,80 cells.../lambda and higher mesh density, how can I know how much mesh density is enough for my layout??

> {quote：title = jeff0283写道：} {quote}>在我的情况下，我在20和40个单元格/ lambda上使用3 * fmax，但是史密斯图表上的结果是不同的。
>因此我假设40个细胞/λ的情况比20个细胞/λ更准确。
是的，这就是我们通常看到的：更密集的网格更好。
>但是我可以在60个单元格，80个单元格... / lambda和更高的网格密度下使用3 * fmax，我怎么能知道网格密度对于我的布局有多大？
正如我试图解释的那样，并非那么简单。
具有足够精确结果的“良好”网格取决于多种影响，并且细胞/波长仅是其中之一。
还有一些其他网格细节（图层之间的网格对齐）似乎会改变您的结果。
网格对齐由较高的单元格/波次数间接改变，但最好的方法是使用适当的设置固定网格对齐。



     以下为原文

  > {quote:title=jeff0283 wrote:}{quote}
> In my case, I use 3*fmax at both 20 and 40 cells/lambda, but the results on the smith chart are different.
> So I assume the 40 cells/lambda case is more accurate than 20 cells/lambda.

Yes, that's what we usually see: denser mesh is better.

> But I can use 3*fmax at 60 cells,80 cells.../lambda and higher mesh density, how can I know how much mesh density is enough for my layout??

As I tried to explain, it is not that simple. Having a "good" mesh with accurate enough results depends on multiple influences, and  cells/wavelength is only one of them.

There is some other meshing detail (mesh aligment between layers) that seems to change your results. That mesh alignment is indirectly changed by higher cells/wave count, but the best method is to fix the mesh alignment with the appropriate setting.

> {quote：title = jeff0283写道：} {quote}>所以我猜这是有限基质导致不同网格密度（20和40个细胞/波长）的不同结果。
是的，这证实了我上面写的内容：不同之处在于顶部和底部导体之间的网格单元的对齐不足。
如上所述，有一个Moment网格设置来修复它。
但是对于你的情况，没有相关的漏洞，你可以使用简单的使用无限的地面。



     以下为原文

  > {quote:title=jeff0283 wrote:}{quote}
> So I guess it is the finite substrate that causes the different results for different mesh density(20 and 40 cells/wavelength).

Yes, this confirms what I wrote above: the difference are from insufficient aligment of the mesh cells between top and bottom conductor. There is a Moment mesh setting to fix that, as described above.

But for your case, with no relevant holes, you can use simply use infinite ground.

> {quote：title = volker_muehlhaus写道：}>但是对于你的情况，没有相关的漏洞，你可以使用简单地使用无限的地面。
{quote}你是说我的布局有几个洞？
为什么？



     以下为原文

  > {quote:title=volker_muehlhaus wrote:}

> But for your case, with no relevant holes, you can use simply use infinite ground. {quote}

Do you mean my layout has few holes?  Why?

> {quote：title = jeff0283写道：} {quote}>你是说我的布局有几个洞？
为什么？
不用担心，您的布局非常适合无限地面模拟。



     以下为原文

  > {quote:title=jeff0283 wrote:}{quote}
> Do you mean my layout has few holes?  Why?

Don't worry, your layout is perfectly suited for infinite ground simulation.

> {quote：title = jeff0283写道：} {quote}>您认为这种布局是否适合无限地面模拟？
是的，一点没错！



     以下为原文

  > {quote:title=jeff0283 wrote:}{quote}
> Do you think if this layout  is suited for infinite ground simulation?

Yes, absolutely!