This book addresses wideband spectroscopy of dielectric materials based on a Six-Port technology. State-of-the-art laboratory instruments for spectroscopy of dielectric liquids in the micro- and millimeter wave range, suffer from penetrating measurement techniques and considerable costs. A novel contactless measurement concept for dielectric characterization of liquid samples is explained, with a particular focus on industrial and medical applications. Several measurements on animal and human tissue materials are presented and discussed in this book. The demonstration of a contactless, dielectric measurement procedure including its calibration algorithm is subsequently described. The presented wideband measurement system consists of an on-line, non-invasive, dielectric sensor, an alternative vector network analyzer including its sub-components, such as Wilkinson power divider, quadrature coupler and power detectors. The demonstrated frequency range is between 2 GHz and 30 Ghz, thus a frequency bandwidth of multiple octaves i.e. a relative frequency range of more than 170% has been achieved.