A 1-GHz 64-Channel Cross-Correlation System for Real-Time Interferometric Aperture Synthesis Imaging

Abstract

We present a 64-channel 1-bit/2-level cross-correlation system for a passive millimeter wave imager used for indoor human body security screening. Sixty-four commercial comparators are used to perform 1-bit analog-to-digital conversion, and a Field Programmable Gate Array (FPGA) is used to perform the cross-correlation processing. This system can handle 2016 cross-correlations at the sample frequency of 1GHz, and its power consumption is 48.75 W. The data readout interface makes it possible to read earlier data while simultaneously performing the next correlation when imaging at video rate. The longest integration time is up to 68.7 s, which can satisfy the requirements of video rate imaging and system calibration. The measured crosstalk between neighboring channels is less than 0.068%, and the stability is longer than 10 s. A correlation efficiency greater than 96% is achieved for input signal levels greater than −25 dBm.

Calibration of Visibility Samples for Real-Time Passive Millimeter Wave Imaging

“…It can be seen that with the increase of adjustment times, the normalized threshold offset is approaching zero. After 80 adjustments, the maximum value of normalized threshold offset is about 0.0011<0.01, which satisfies the system requirements [11].…”

“…where ε(k) is the measurement error of V m,n raw at each phase state. Rewriting (10) in matrix form is: V = X * β + ε (11) where , , ,…”

“…To verify the ability to detect concealed objects and validate the advantages of high imaging rate and large FOV, consecutive generations of two-dimensional (2-D) interferometric aperture synthesis demonstrators have been developed by Beihang University [9]- [10]. However, a 2-D interferometric aperture synthesis PMMW imager with satisfactory radiometric sensitivity and spatial resolution at the video imaging rate needs several hundred antenna-receiver channels with a bandwidth of 1GHz or larger, which brings an enormous challenge to the hardware design [11]. Hence, Beihang University takes radiometric sensitivity, spatial resolution, and hardware design complexity into consideration, develops an improved PMMW imager using 1024 antenna-receiver channels with 1GHz bandwidth.…”

Indoor Full-Body Security Screening: Radiometric Microwave Imaging Phenomenology and Polarimetric Scene Simulation

“…Realization of a radiometric imaging technology whereby all regions of the human body can be in focus in the nearfield regime of a security screening portal is possible using an aperture synthesis imaging system [11]. However, such a system can only be realized by accessing low-cost multichannel radiometric digital receivers interfaced with digital cross-correlators [12], [13], [14].…”

“…The results of the modeling and experiments are presented as tabulated numerical values and illustrated by scene simulation to show the phenomenology. This knowledge is important for the design of the next generation of aperture synthesis portal screening systems [11] which will use emerging powerful digital cross-correlators [12], [13], [14].…”