Microwave Inversion of Measured S-Parameters Using a Thin-Wire Antenna Model

An imaging procedure based on the minimization of an objective function that incorporates measured S-parameters is presented. Experimentally measured S-parameters are used to link modelled incident and reflected power waves at the antenna ports. The S-parameter objective function is incorporated into the Contrast Source Inversion method. A sub-grid thin-wire model is used to model these incident and reflected power waves. The new procedure is used to image a simple breast phantom, consisting of a tumour within a homogeneous fat region, placed within an air-based quasi-resonant breast imaging chamber. Single frequency S-parameters measurements at the ports of 24 half-loop antennas on the chamber walls constitutes the inversion data. The thin-wire antenna model, which reduces modelling error, together with the new objective function, lessens the burden on calibration procedures that often fail when the objective function is formulated using field components. Experimental results show promising imaging performance over a large frequency band.