I want to build a TRL cal kit( for use with NWA) for 24 GHz using microstrip lines. I have read a lot about the theory of cal kits and I have already build some samples, but I am not satisfied with calibration results. I am using a coax to microstrip transition from Rosenberger
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which is specified up to 26.5GHz - as you can see in the data sheet (03K421-600S3) the transition "starts" as a CPW (coplanar waveguide)and not as a classical microstrip, so I extended the microstrip line (50 ohms) for about 2 wavelengths (to stabilize the microstrip mode) until reaching the actual calibration plane. Of course the 50 ohm microstrip line is not 50 ohm for CPW design. Do you think it is still a correct way to calibrate ? I am using this kind of transition because I didn't finde any coax to microstrip transitions specified up to 24GHz? Thanks for your help.