A NEW APPROACH TO ESTIMATE COMPLEX PERMITTIVITY OF DIELECTRIC MATERIALS AT MICROWAVE-FREQUENCIES USING WAVE-GUIDE MEASUREMENTS

In this paper, a simple waveguide measurement technique is presented t o determine the complex dielectric constant of a dielectric material, The dielectric sample is loaded in a short-circuited rectangular waveg uide, Using a network analyzer, the reflection coefficient of the wave guide is measured, Using the finite-element method (FEM) the exact ref lection coefficient of this;configuration is determined as a function of the dielectric constant. The measured and calculated values of the reflection coefficient are then matched using the Newton-Raphson metho d to estimate the dielectric constant of a material, A comparison of e stimated values of the dielectric constant obtained from simple wavegu ide modal theory and the FEM approach is presented, Numerical results for dielectric constants of Teflon and Plexiglas measured at the X- an d Ku-bands are presented. Numerical inaccuracies in the estimate of th e dielectric constant due to: 1) the presence of airgaps between sampl e and sample holder waveguide surfaces and 2) inaccuracy in the sample dimensions are also discussed.