Numerical Vector Green’s Function for S-Parameter Measurement With Waveport Excitation

We present a numerical vector Green’s function that directly links the object material property within the electric field volume integral equation (VIE) to the scattered S-parameters. This Green’s function is particularly useful for microwave inverse scattering applications in which S-parameter measurements are used to reconstruct the dielectric properties of unknown objects in an inhomogeneous background where the Green’s function does not have an analytic form. Unlike the dyadic Green’s function in a standard VIE, which relates the fields in the object domain (vector) to the scattered fields (vector), this vector Green’s function kernel relates the object domain fields (vector) to the measured S-parameters (scalar). Also this new vector Green’s function uses a waveport source method, which accurately accounts for the measured scattered S-parameters between antenna feeds of arbitrary impedance and modes. A detailed derivation is presented, and simulated and experimental examples are provided to validate this vector Green’s function for the prediction of scattered S-parameters.