Justin J. McCombe

Microwave Holography Using Point-Spread Functions Measured With Calibration Objects

Microwave holography requires knowledge of the incident field and the Green tensor of the background medium. In near-field imaging, analytical models of these are inadequate and the use of electromagnetic simulations has been previously proposed. In practice, however, the fidelity of such simulations may also be insufficient. Here, we propose a measurement method for the acquisition of this information, thus eliminating the need to estimate it analytically or numerically. We validate the approach through simulated data acquisitions as well as through experiments. It is shown that this approach characterizes the measurement system more reliably than simulations leading to significant improvement of the image quality.

Microwave Holographic Imaging Using the Antenna Phaseless Radiation Pattern

In this letter, we propose a three-dimensional microwave holographic imaging approach for the cases where the object is in the far zone of the antenna but the measurements are performed in the near zone of the scattering object. Typical applications include concealed weapon detection, through-the-wall imaging, etc. In the proposed approach, the phaseless radiation pattern of the antenna, acquired through measurements, is employed to improve the quality of the image reconstruction results. We demonstrate the performance of the proposed approach via a full-wave simulation example and an experiment and compare the images to the previously proposed holographic imaging approaches.

Three-Dimensional Microwave Holographic Imaging Employing Forward-Scattered Waves Only

We propose a three-dimensional microwave holographic imaging method based on the forward-scattered waves only. In the proposed method, one transmitter and multiple receivers perform together a two-dimensional scan on two planar apertures on opposite sides of the inspected domain. The ability to achieve three-dimensional imaging without back-scattered waves enables the imaging of high-loss objects, for example, tissues, where the back-scattered waves may not be available due to low signal-to-noise ratio or nonreciprocal measurement setup. The simulation and experimental results demonstrate the satisfactory performance of the proposed method in providing three-dimensional images. Resolution limits are derived and confirmed with simulation examples.

Quantitative imaging of dielectric objects based on holographic reconstruction

We present a technique to perform quantitative microwave holographic reconstruction in quasi-real time. Both the real and the imaginary parts of the permittivity distribution of a dielectric target are recovered quantitatively. The method relies on a calibration measurement of a known electrically small target. The initial validation of the approach is done with simulations of an F shaped dielectric bar.

SNR assessment of microwave imaging systems

A method to assess the signal-to-noise ratio (SNR) of microwave imaging acquisition systems is proposed. The method can be used to automatically discriminate between high- and low-quality responses acquired with a given setup or to compare acquisition hardware. The approach uses the measurements of a known calibration object, which are often available from the calibration of the microwave acquisition system.

Sensitivity of Microwave Imaging Systems Employing Scattering-Parameter Measurements

The physical contrast sensitivity of microwave imaging systems employing scattering-parameter measurements is defined. Methodologies are proposed for its evaluation through measurements and through simulations. This enables the estimation of the smallest detectable target permittivity contrast or size for the system under evaluation. The outcomes of the proposed simulation-based and measurement-based methods are compared for the case of a realistic tissue-imaging system. The agreement between the simulated and measured sensitivity estimation validates the proposed methods. The intention of the proposed methodology is to provide common means to quantify and compare the sensitivity performance of microwave systems used in tissue imaging as well as the antennas used as sensors. We emphasize that the proposed method targets the performance of the hardware and it is not concerned with the image-reconstruction algorithms.

Range resolution in microwave imaging with forward-scattered waves only

In the microwave imaging of lossy dielectric objects, the back-scattered target signatures are often too weak. In comparison, the forward-scattered signals are much more sensitive to a target since it is likely to affect their attenuation. On the other hand, the ability of current imaging algorithms to achieve good range resolution depends critically on the availability of back-scattered signals. Here, we propose a method to achieve good range resolution with forward-scattered signals only.