The main goal of 'Phase Array Imaging Toolbox' is to implement different
millimeter wave imaging ... system using different array sizes and antenna
spacing.
User Guide to Phase Array Imaging Toolbox Murat Torlak and Sujeet Patole Texas Analog Center of Excellence (TXACE) University of Texas at Dallas Richardson, TX 75080 Revision Date: Nov 5, 2012
Introduction
The main goal of ‘Phase Array Imaging Toolbox’ is to implement different millimeter wave imaging algorithms and to contrast between their performances. In addition, we consider presence of several RF impairments and noise during this reconstruction. Thus, toolbox enables user to model end-‐to-‐end phase array imaging system using different array sizes and antenna spacing. Following sections illustrate selection of different parameters in the toolbox.
Method of Reconstruction Toolbox includes following methods, 1. Switched Array Method (Original) 2. Switched Array Method (Using Matched Filtering) 3. Beam Steering Method Switched Array Method (Original) is explained in reference [1]. Deficiencies in this method are rectified using ‘Matched Filtering Approach’. In the third method, all the antennas in an array are simultaneously put into operation and image is reconstructed using beam steering method.
Array Geometry Following parameters define antenna array geometry 1. Array Size 2. Antenna Spacing Toolbox uses square grid (16×16, 16×16 selected using dropdown menu) with uniform spacing for the positioning antennas in an array. Antenna spacing is multiple of wavelength and can be varied from 0.1 to 1 times wavelength using the slider. Imaging system uses narrowband 5mm source.
Focus Distance
As seen in figure I, the object is separated by distance 𝑧! (100mm for toolbox) from the antenna array. This introduces phase difference in the reflected wave data, which is compensated by electronic focusing. The focusing distance can be varied from 50𝑚𝑚 to 150𝑚𝑚 using the focus slider. In the toolbox this distance is indicated as a multiple of wavelength.
Figure I Geometry of Imaging System
RF Impairments and Noise 1. Number of bits for quantization of beam steering weights 2. SNR When using beam steering method for reconstruction, complex beam steering weights are used to introduce phase shift at each transmitting and receiving antenna. In practice, this phase shift has finite resolution. Toolbox includes one bit, two bits, three bits and no quantization options selected using drop down box. To verify the performance improvement by employing beam steering, noise can be added at each receiver before reconstruction. Different SNR values can be selected from drop down menu.
Target Object Selection Different target geometries can be used. Toolbox includes ‘T’ shaped object and two reflectors. Two reflectors can be placed at broadside and off-‐ broadside position to illustrate shift-‐varying resolution of the imaging system.
Working with the Toolbox
After selecting reconstruction method, target object and array size hit the UPDATE push button to see results. Antenna spacing and focus distance can be varied this time to see their effect on the reconstruction. After introducing noise or phase quantization again hit UPDATE push button again to view new results.
Figure II Phase array Imaging toolbox showing reconstruction in the presence of noise and phase quantization (© Developed by Prof. Murat Torlak, Dept. of Electrical Engineering, University of Texas at Dallas)
Video demonstration of the toolbox can be found in reference [2].
References
1. D. M. Sheen, D. L. McMakin, and T. E. Hall, “Three-‐Dimensional Millimeter-‐ Wave Imaging for Concealed Weapon Detection,” IEEE Trans. On Microwave Theory and Techniques, vol. 49, no. 9, Sept. 2001, pp. 1581-‐1592
2. http://www.utdallas.edu/~smp106120/toolbox.mp4
