Crosstalk in uniformly coupled lossy transmission lines

The crosstalk between two identical, uniformly coupled, lossy transmission lines is examined. Equations are derived which can be solved to obtain formulas for the near-end crosstalk (NEXT) and far-end crosstalk (FEXT). An example is worked which illustrates the mutual influence of the two lines in terms of the modal voltages and currents. The mutual influence of the two lines is also studied by comparing the results of this example with the “classical” crosstalk formulas which assume weak coupling and neglect the influence of the disturbed line on the disturbing line. It is shown that the influence of the disturbed line on the disturbing line can be neglected for NEXT for most weak coupling situations. For sufficiently high frequencies and/or long line lengths, however, this influence cannot be neglected for FEXT.