Microwave Imaging on S-Parameters Using FEM Thin-Wire Subcell Models

A microwave imaging method that directly incorporates S-parameters into its objective function is presented. S-parameters are extracted from a time-harmonic finite-element model of an imaging system using an efficient thin-wire antenna sub-grid technique. The microwave imaging system considered is an air-based quasi-resonant imaging chamber that is excited with monopole antennas constructed using actual thin wires. Forward modelling results demonstrate the thin-wire model is accurate over the broad band of frequencies tested. A modified contrast source inversion algorithm that incorporates the measured and modelled S-parameters within its objective function is used to reconstruct the complex-valued permittivity of a simple oil-glycerin-water based breast phantom. Image accuracy metrics demonstrate that single frequency experimental inversion results using the thin-wire antenna model and S-parameter objective function improve tumour detection and artifact reduction for the tested breast phantom.