Sensitivity and Temperature Analyses of Open-Ended Rectangular Waveguide Sensors

This paper presents the first sensitivity analysis of open-ended rectangular waveguide sensors in extracting the dielectric properties of materials. Our previous analytical modal approach is extended to calculate the sensitivity of the dominant mode reflection coefficient to the material under test (MUT) characteristics. By defining the sensitivity matrix, it is shown that higher sensitivity is achieved at lower operating frequencies and when MUT has a permittivity magnitude approximately half of that of the waveguide dielectric permittivity. Also, a temperature analysis is used to calculate the extracted dielectric permittivity of a temperature-independent material to predict the effect of temperature on measurement accuracy. It is shown that the magnitude errors due to ignoring the temperature effects on the waveguide dimensions and waveguide dielectric are 0.29% and 4.18% at 150°C and 0.58% and 9.97% at 250°C, respectively.