On the Problem With Intermodal Dispersion When Using Multiconductor Transmission Lines as Distributed Sensors

The inverse problem of using an unshielded multiconductor transmission line (MTL) as an distributed sensor is considered. The MTL is analyzed by means of the quasi-TEM mode theory and a propagator formalism. In the inverse problem, the focus is on the problem with intermodal dispersion, due to the possibility of more than one propagating mode. Reconstruction results, from both measured and simulated reflection data, are presented for a three conductor MTL that has been used for diagnosing soil and snow. Both the case when one mode propagates, and the case when two modes propagate are considered. For the latter case it is demonstrated that intermodal dispersion deteriorates the resolution in the reconstruction, due to corruption of the high frequency part of the spectrum.