Modeling a mm-Wave Imaging System with a 2.5D BiCGS-FFT Volume Integral Equation technique

In this contribution we present an exact forward solver for a two-dimensional (2D) inhomogeneous dielectric object embedded in a homogeneous background medium. The object is illuminated with a given three-dimensional (3D) time-harmonic incident field. The 3D scattered field is computed in a number of points surrounding the object.
The size of the scattering objects can be very large with respect to the wavelength, leading to an extremely high number of unknowns. Therefore a 2.5D configuration is adopted, since it reduces the computational cost while it maintains the capability of accurately studying the system performance.

The vector fields are calculated by discretizing a contrast source integral equation with the Method of Moments. The resulting linear system is solved iteratively with a stabilized biconjugate gradient Fast Fourier Transform (BiCGS-FFT) method [1][2]. Simulation and validation results for a number of test objects are shown.

Simulation results for test objects will be compared to measurements performed at the VUB, where a free-space active mm-wave imaging system is being developed. The system presently consists of a mm-wave vector network analyzer [3] operating in the 75 to 300 GHz range. It measures the S-parameters in amplitude and phase with a dynamic range of more than 80 dB. At the transmitting side, a horn antenna emits an incident Gaussian beam, which is focused by a lens at the object location. At the receiving side the scattered field is focused by a lens for image formation at a receiving horn antenna. The total distance between transmitting and receiving sides is typically 75 cm.