A measurement of balanced transmission lines using S-parameters

A new method for measuring both balanced and unbalanced parameters of a twisted pair cable up to 500 MHz is presented. The parameters are derived from the unbalanced data measured by a conventional network analyzer with an S-parameter test set without using balanced-to-unbalanced conversion transformers (baluns). The common mode rejection ratio (CMRR) of the measurement system is -70 dB constant over the frequency range from 10 kHz to 500 MHz. The resultant data matched within 0.5 dB for insertion loss and 3% for the characteristic impedance with those measured by a conventional method using balun. The data of the near end crosstalk also matched well at the frequency range higher than 1 MHz