AnsweredAssumed Answered

Switch term correction

Question asked by zhenzhou on May 23, 2008
Dear All,
I tried to calculate the complex propagation constant of a microstrip line with CPW-to-microstrip transition using uncalibrated S-parameter measurements on two identical lines with different lengths. I used T matrices and calculated the eigenvalues in order to get the propagation constant for the microstrip line.

I found that the phase constant calculation is in very good agreement with my HFSS simulation. However, the attenuation constant from the measurement is much larger than the HFSS simulation. My HFSS simulation took the surface roughness, the dielectric complex permittivity frequency dependency into consideration. I suspected that the difference between the simulated and measured ones on the attenuation constant is caused by the uncalibrated S-parameter measurements that were not corrected with switch term correction. 

I also tried to calculate the complex propagation constant of  CPW lines using the same approach as I used for microstrip lines. I ended up having the same problems. For CPW, the calculated phase constant from uncalibrated S-parameter is larger than the ones measured with Multiline TRL and the attenuation measured is also larger than Multiline TRL measurement.  

If my guess on the error source is right, how can I correct the uncalibrated data with the switch-term correction without adding any measurement complexity? 

Thank you