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Modelling finite ground

Question asked by FELIXGOH on May 19, 2004
Latest reply on May 20, 2004 by ALEPEREZ
Hi,

I am trying to simulate a bandpass filter using momentum. In a practical circuit, the printed circuit board area is finite.
I am using one substrate layer with thickness 1.2mm and the total area occupied by the bandpass filter is 8 X 9 mm.
There are two layers for the board. On the top layer lies the filter which is surrounded by finite ground and the bottom layer is perfect ground
connected through vias to the top layer finite ground
If I define the substrate as

FreeSpace
-----strip cond
Substrate via
/////Gnd/////

Is the bottom layer ground modelled with a finite area?

I have tried to use the following substrate to simulate the same design

FreeSpace
-----strip cond
Substrate via
------strip cond2
FreeSpace

In such a case, my bottom layer ground has a finite area.
Both have different simulation results.
How do I define the metallization and substrate layers so as to model a finite area, i.e a real practical circuit?  

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