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debugging sim anomaly

Question asked by mantow on Nov 3, 2005
Latest reply on Nov 3, 2005 by ALEPEREZ

I am simulating a CPW-to-ustrip transition design using momentum. In my layout, I have a back-to-back transition. Port 1 (single) is on the LHS with Ports 3 & 4 ground reference associated with Port 1. On the RHS is Port 2 (single) with associated ground reference ports 5 & 6. For meshing I used:

Mesh frequency=10GHz
Cells per wavelength=20

The simulated s-parameters show good agreement with actual measurements up to ~8GHz. However, the momentum simulation shows up a null (< -20dB) in S21 at 3GHz. I have tried increasing mesh frequency and cells/ wavelength but the simulation consistently shows up this null at 3GHz.

Could someone kindly offer any suggestions what can be altered in the simulation setup to help find out the cause of this null and if it's genuine?

Many thanks,