Hi All. I'm new on this forum and tried but failed looking for more information on TRL calibration in mm-wave frequency - in 140-220 GHz range i my case. I have a waveguide cal kit containing a flush short and two ¾ lambda offset sections for thru calibration to cover 140 to 168 GHz and 168 GHz to 220 GHz, respectively. The calibration does not return the expected results as the S21 and S12 plots are not flat at 0 dB on LogM type of plot when one of the shims is left in between two port flanges. When the two ports are connected back to back with zero length thru the S21, S12 are flat as expected. My suspicion is that the software does not calculate/normalize the data properly or else the results from measurements of the two lines L1 and L2 are not spliced as they should. What should be the Calibration Reference Z0 and Testport Reference Plane set to for the TRL class assignment? Maybe I'm not getting that set up properly. I'm using N5242A on version 09.33 firmware. Thanks.