Microwave and Millimeter Wave Imaging Development: Towards Real-Time Portable 3D Imaging Systems

Microwave and Millimeter wave signals span the frequency range of 300MHz – 30 GHz and 30 GHz – 300 GHz respectively. Signals at these frequencies can easily penetrate inside dielectric materials and composites and interact with their inner structures. At millimeter wave frequencies, the relatively small wavelengths and wide bandwidths associated with these signals enable the production of high spatial-resolution images. Imaging techniques can be primarily classified as either near-field or far-field techniques depending on the distance between the probe from the structure. Near-field imaging techniques are simple yet powerful, producing very high image resolutions with relatively inexpensive systems. On the other hand, far-field imaging coupled with synthetic aperture radar (SAR)-based 3D imaging techniques, have demonstrated sub-wavelength image resolution, and high image clarity. SAR 3D imaging techniques rely on constructively combining reflected signal data from many measurement points within the synthetic aperture (i.e., a multi-view technique) which greatly enhances the image quality. More importantly, SAR 3D imaging techniques can be implemented using imaging arrays that yield imaging results in real-time. Moreover, utilizing techniques such as non-uniform sampling, spectrum estimation, adaptive image formations, and multi-static or multiple-input multiple-output (MIMO) imaging for 3D SAR imaging are some of the methods that be utilized for the goal of enhancing image quality while reducing measurement time and hardware complexities.

This talk will present the chronology of developing portable, high-resolution, 3D and real-time millimeter wave imaging systems. These systems are developed to address the needs of several diverse and critical applications related to nondestructive testing, security, radar tracking, localization, and biomedical fields. This talk will focus on the designs of the developed imaging systems focusing on:

• The microwave and millimeter wave instrumentation and measurement techniques used in the high frequency microwave and millimeter wave transceiver and the data acquisition circuits.
• Requirements and design criteria for the dense antenna arrays such as spatial sampling requirements, antenna bandwidth, and antenna gain.
• Real-time 3D SAR imaging algorithms used with these systems.
• The effect of various design choices on the overall capabilities of the imaging system such as image resolution and dynamic range.

Finally, practical considerations for designing real-time imaging arrays will be discussed and the capabilities of each imaging system will be demonstrated.