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different results in Momentum and ADS Schematic

Question asked by LHFT on May 19, 2005
Latest reply on May 20, 2005 by ALEPEREZ

I have the following problem:
Using the Filter Design Guide I have synthesized a lowpass filter, (cuttoff f=40 GHz) transformed it to microstip elements(I used radial stubs) and then optimized the smart components using the Passive Circuit Design Guide. The simulation in ADS met the set specifications. So I generated the Layout and started a simulation in Momentum. The results were completely different from the ADS simulation. The cutoff frequency was about the same, but there was less attenuation and the repetition of the passband appeared much earlier.
What is the reason for this differences? Are maybe the models not specified for that broad frequency range?