Broadband isotropic and anisotropic permittivity determination using partially filled coaxial airlines

A method for determining the complex permittivity for material specimens with isotropic or biaxially anisotropic dielectric properties is described and representative measured results are presented. The method extracts the material permittivity through the utilization of computational electromagnetic simulations of specimen transmission measurements made with a broadband (50 MHz to over 500 MHz) coaxial airline with a material specimen which partially fills the waveguide cross-section. A number of independent transmission measurements equal to the number of unknown permittivity terms is required for unique material permittivity determination. For isotropic specimens, a single specimen orientation is required, whereas for anisotropic specimens, different specimen orientations in the airline are required to probe the unknown permittivity axes and thus ensure unique material permittivity determination. Measurements using a 3.5-inch outer diameter coaxial airline were made for known isotropic specimens as well as an anisotropic lossy material specimen. This technique provides the material measurement community with a mechanism to characterize a single specimen of complex shape and biaxial dielectric anisotropy at low frequencies covering multiple rectangular waveguide bands simultaneously and represents a significant advance in the current measurement state-of-the-art particularly at frequencies below 100 MHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1864–1868, 2015