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?

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?

What you should find for the filter you are talking about is that the ground ring surrounding the filter is the critical circuit element and the bottom ground being finite or not is negligible. The vias tying the two grounds together effectively shield what's going on outside.