Electromagnetic Analysis of Radiometer Calibration Targets Using Dispersive 3D FDTD

Accurate electromagnetic and thermal analysis is essential for designing wideband radiometer calibration targets as well as for understanding the electromagnetic wave interaction with these highly absorbing structures. To serve this purpose, a three dimensional dispersive finite difference time domain (FDTD) engine has been developed. We present the various aspects associated with this FDTD formulation, including modeling of dispersive lossy media using piecewise linear recursive convolution (PLRC) and application of uniaxial perfectly matched layer (UPML) absorbing boundary condition and symmetry/periodic boundary conditions to provide high accuracy using moderate computational resources. Time domain modeling of the dispersive radar absorbent material is performed by fitting the measured complex permittivity and permeability data to a series of Debye like terms using genetic algorithm (GA) optimization. The broadband reflectivity spectrum of the calibration target is obtained by transient plane wave excitation. The reflectivity spectra of pyramidal calibration targets in the frequency range [6, 200] GHz is obtained and compared to the geometrical optics limit and a finite element solution. The spectrum depends significantly on the height to base ratio and coating thicknesses of the absorbent material.