Measurement consistency and the effect of ground planes on common-mode crosstalk

A comparison between four crosstalk measurement techniques is made to investigate the consistency of the results when the ground plane is highly resistive or missing. The measurement techniques used are: balanced VNA measurements, balanced Spectrum Analyzer measurements, balanced EMI Test Receiver measurements and single-ended measurements converted to mixed-mode. The tests were done on differential pairs of microstrips. It was found that for groundless boards the techniques are still consistent, but the results at high frequencies are greatly dependent on the setup. In case of the carbon fiber ground, the results show matching results for the balanced measurements while the mixed-mode results are consistent in only specific frequency ranges which are dictated by the exact material properties of the CFRP and the directionality of the fibers.