NEAR-FIELD MICROWAVE IMAGING OF BIOLOGICALLY-BASED MATERIALS USING A MONOPOLE TRANSCEIVER SYSTEM

A prototype monopole-transceiver microwave imaging system has been imp lemented, and initial single and multitarget imaging experiments invol ving biologically relevant property distributions have been conducted to evaluate its performance relative to a previously developed wavegui de system. A new, simplified, but more effective calibration procedure has also been devised and tested. Results show that the calibration p rocedure leads to improvements which are independent of the type of ra diator used, Specifically, data-model match is found to increase by 0. 4 dB in magnitude and 4 degrees in phase for the monopoles and by 0.6 dB in magnitude and 7 degrees in phase for the waveguides (on average) on a per measurement basis when the new calibration procedure is empl oyed, Enhancements are also found in the reconstructed images obtained with the monopole system relative to waveguides. Improvements are obs erved in: 1) the recovered object shape; 2) the uniformity of the back ground; 3) edge detection; and 4) target property value recovery. Anal yses of reconstructed images also suggest that there is a systematic d ecrease of approximately 10% in the reconstruction errors for the mono pole system over its waveguide counterpart in single-target experiment s and as much as a 20% decrease in multitarget cases, Results indicate that these enhancements stem from a better data-model match for the m onopoles relative to waveguides which Is consistent across the type of calibration procedure used, Comparisons of computations and measureme nts show an average improvement in data-model match of approximately 0 .25 dB in magnitude and near 7 degrees in phase in favor of the monopo les in this regard. Beyond this apparent imaging performance enhanceme nt, the monopole system offers economy-of-space and low construction-c ost considerations along with computational advantages (as described h erein) which make it a compelling choice as a radiator/receiver elemen t around which to construct a clinically viable near-field microwave i maging system.