Issue in Siwave simulation after importing the SNP file

[sunjianwudi19870311]

Hello everyone,
I’m having an issue while simulating with Siwave.
Let me first provide some background:
This is what our OBD++ looks like when opened in Siwave; the component in the red box is a TDK low-pass filter.

I have the S2P file for this LPF, and I simulated it in ADS. This LPF has excellent insertion loss.

I now want to import this S2P file into Siwave and disable all the capacitors and inductors connected to this device, adding a port at each end.

Here are the steps I follow to import S2P file.

Next, I set the frequency range for the simulation.

After simulation, an S2P file was generated, which was opened in ADS.

The insertion loss is surprisingly high.

Next, I wondered if there might be a problem with the traces at either end, so I simulated each trace separately and checked the results in ADS.

Trace 01

Trace 02

Based on the simulation results, there are no issues with these two traces.

So I connected the S2P files for these two traces and the LPF’s S2P file in ADS to view the overall S-parameters.

The results are significantly better than the S-parameters obtained from direct simulation in Siwave.

Right now, I'm really eager to figure out exactly where the problem lies. I've been checking it for several days now, but I still can't find the cause.

Could anyone help me?