S11 Calibration Method for a Coaxial Line with Three Reference Materials and no Short Termination Condition for Dielectric Measurement in Liquids

This paper proposes an S11 calibration method for a coaxial-feed-type open-ended cut-off waveguide with a vector network analyzer (VNA) from three reference materials with no short termination condition. The equation for S11 calibration from three arbitrary impedance standards was first derived, and the electrostatic capacitance unique to the jig was then quantified. The theoretical values for input impedance at the front surface of the sample material were then determined by substituting the capacitance value into the equivalent circuit at frequencies of 0.50, 0.75 and 1.0 GHz. The calibrated S11 value for the front surface of the sample material was then determined. The validity and measurement accuracy of the proposed method were verified via comparison of this S11 calibration value with that calculated using EM analysis. The results numerically indicated the validity of S11 calibration for the coaxial-feed type open-ended cut-off waveguide using VNA from the three reference materials with no short termination condition based on the proposed procedure. The effectiveness of the method was also verified from actual measurement of S11 in the frequency range from 0.5 to 3.0 GHz, thereby confirming its effectiveness.