Applicability of the Transmission-Reflection Method for Broadband Characterization of Seawater Permittivity in a Semi-Open Coaxial Test Cell

We validate applicability of the known transmission-reflection (T/R) method to measuring complex permittivity of seawater in broadband frequency range. We consider a liquid sample that partly fills space of a coaxial test cell operating in vertical position. The cell is plugged with a single dielectric bead at the bottom and thus has a semi-open, versatile design. We develop transfer matrix formulae for de-embedding the sample from effects of the bead and the airline sections so as best fulfill assumptions of the T/R method. The de-embedded scattering parameters of the sample let us analyze effects of an asymmetry in the sample's reflection coefficients due to a meniscus formed at the top of the sample. Experimental results, obtained for seawater in a 7 mm coaxial-line fixture, evidence that the meniscus effects are negligible below 5 GHz. The measured permittivity of the seawater agrees very well with the data published elsewhere.