We describe a variable path length waveguide setup developed to accurately measure the complex dielectric permittivity of liquids. This is achieved by measuring the complex scattering parameter of the liquid in a waveguide section with a vector network analyzer in combination with an E-band frequency converter. The automated measurement procedure allows fast acquisition at closely spaced intervals over the entire measurement bandwidth: 60-90 GHz. The presented technique is an absolute method and as such is not prone to calibration errors. The technique is suited to investigate low-loss as well as high-loss liquids in contrast to similar setups described previously. We present measurements for a high-loss liquid (water), an intermediate-loss sample (ethanol), and for nearly loss-less n-octane. Due to the available phase information, the present data have an improved accuracy in comparison with literature data.

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Persistent URL dx.doi.org/10.1063/1.3647982
Journal Rev. Sci. Instrum.
Hunger, J, Cerjak, J, Schoenmaker, H, Bonn, M, & Bakker, H.J. (2011). Precision waveguide system for measurement of complex permittivity of liquids at frequencies from 60 to 90 GHz. Rev. Sci. Instrum., 82(10). doi:10.1063/1.3647982