The determination of dielectric constant and conductivity profiles at microwave frequencies

A novel method for determining the relative dielectric constant or the conductivity profile for nonhomogeneous media at microwave frequencies is presented. The profiles are assumed to be changing along the direction of propagation of electromagnetic energy inside a rectangular waveguide. The waveguide cross section is completely filled with the nonhomogeneous medium, which has a finite thickness, and the sample should be placed inside the waveguide in a plane perpendicular to the waveguide axis. The waveguide will be terminated by a variable short-circuit line, so that the load on the waveguide output port will be a variable reactance depending on the length of the variable short-circuit termination. The magnitude and/or the phase of the input reflection coefficient is measured at the input reference plane for different values of the load termination at a fixed frequency. Its shown that the formation of the objective function to be used in the optimization process as well as the prior information about the behavior of the dielectric constant or the conductivity profiles is very important in determining the correct coefficients of the polynomial