AnsweredAssumed Answered

Unphysical behaviour in momentum

Question asked by shadi.michael on Sep 11, 2007
Latest reply on Sep 18, 2007 by shadi.michael

I am trying to use momentum to simulate a simple case of two quarter wavelnegth (fo = 1.9 GHz) microstrip lines running parallel to each other on top of a PCB substrate, with a separation distance of 9 mil between the two lines.

Main simulation parameters are as follows:
Mode: MW mode.
Frequency: 1 Hz - 10 GHz
Ports: 4 single ended edge ports

However, during simulation, momentum gives the following warning:

WARNING : S-parameter results show unphysical behavior for certain frequencies.
Cause        : - inaccurate (high frequency) calibration ;
              - higher order modes at the ports ;
              - slot mode at coplanar ports ;
              - grouped strip-slot ports ;
              - too coarse of a mesh.

When I check the resulting s-parameters, I find S11 greater than unity at around 6 GHz. If I try to simulate the same case with RF mode, the warning message disappears and all reflection parameters are less than unity.

Any hints?

/Shadi Yousef