A 3-D Dual-Polarized Near-Field Microwave Imaging System

A novel 3-D dual-polarized microwave imaging system based on the modulated scattering technique (MST) is presented. The system collects the magnitude and phase of the scattered field using 120 MST probes and 12 transmitter/collector antennas distributed around an object-of-interest in the near-field region. The 12 antennas form a middle circumferential layer while the printed MST probes are arranged on three circumferential layers including the middle layer. The antennas are linearly polarized double-layer Vivaldi antennas, each fixed inside its own cylindrical conducting cavity and slanted with respect to the vertical axis of the imaging chamber. The MST probes are etched on both sides of a thin substrate and loaded with five evenly distributed p-i-n diodes along their length. These are positioned vertically and horizontally so that the z- and φ-components of the electric field is measured. Field data are collected using MST, calibrated, and then inverted using a multiplicatively regularized finite-element contrast source inversion algorithm. The system performance is evaluated by collecting and inverting data from different 3-D targets.

I. Introduction

The use of microwave imaging (MWI) to noninvasively estimate the dielectric properties within an object-of-interest (OI) is an alternative as well as a complementary option to existing imaging modalities. MWI is relatively low cost, portable, and uses nonionizing microwave radiation (for biomedical applications, frequencies in the range of 1–6 GHz are used). The objective of MWI is to obtain a dielectric “map” of an OI providing qualitative information regarding the shape and location of the OI's internal features, as well as some quantitative electromagnetic properties of those features [1], [2]. It has been applied to various civil, military, and biomedical imaging applications, e.g., see [3]–[10], and the references therein. Biomedical imaging is the main motivation for the work presented herein.