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Stepped-Frequency Distributed Radar for Through-the-Wall Sensing

A technical analysis of the effectiveness of distributed radar for through-the-wall sensing applications.

The image shows a stepped-frequency radar transceiver: (a) RFSoC by Xilinx with radar firmware by Alion/ HII, and (b) custom transmitter/receiver (Tx/Rx) filter-and-amplifier PCBs powered by 28 VDC. (Image: Army Research Laboratory)

The authors are studying the application of distributed radar to through-the-wall sensing. The intended operational scenario for this technology is detection and identification of personnel and weaponry located inside of a building from a (safe) remote standoff distance outside of that building.

The radar architecture and signal-processing algorithms used for this study are similar to the designs implemented by the U.S. Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory (ARL) for buried-and concealed-surface target detection; the current radar transmits and receives higher frequencies. For this study, experiments were conducted at ARL’s Adelphi Laboratory Center (ALC) in Building 507 (the “sandbox” area) using the indoor low-metal two-story plywood structure. The controlled environment used to test the distributed radar is the same as the low-metal environment used to test ARL’s harmonic radar against electronic targets.

The radar transceiver was developed by Alion Science & Technology, recently acquired by Huntington Ingalls Industries (HII). The waveform generation-and-capture core of the radar is the Zynq UltraScale+ radio-frequency system-on-a-chip (RFSoC) manufactured by Xilinx. The RFSoC evaluation board, packaged by Alion/HII and controllable by a graphical user interface (GUI) over Ethernet, is shown in Fig. 1a. The GUI is labeled “non-linear radar” because the hardware and firmware were originally developed with the ability to transmit a (lower) band of frequencies while receiving a harmonic (higher) band of frequencies. Two such PCBs are visible in Fig. 1b; both are powered from a single 28-VDC power supply.

The RFSoC-based radar transmits and captures stepped-frequency pulses, appending a single file with two channels of received pulses, for as long as the user desires. Short data collections, when no targets were present or moving in the scene, lasted under 1 minute. Longer data collections, when both authors walked back and forth inside of the building, lasted about 8 minutes.

For the experiments reported here, the radar was always run in “linear” mode (i.e., the transmitted and received frequencies were identical). The radar captures data as in-phase and quadrature modulation on the instantaneous stepped carrier (I/Q data), and it computes an inverse fast Fourier transform (iFFT) to generate individual range profiles.

The data collected in this study indicates that antenna pairs looking into a low-metal building and at right angles to each other are able to detect multiple moving targets when those targets are otherwise not visible from outside the building. Mapping distance over time reveals the path that a target follows, ambiguity regarding a target’s path tracked in one channel may be mitigated by tracking the same target on another channel.

Work remains to coherently combine the IQ amplitudes from the simultaneous data collections to resolve multiple targets. One goal is to map target locations on a 2-D (down-range and cross-range) image, presented perhaps as a video animation overlaid on an overhead view of the scene (i.e., a typical floorplan for the building being imaged). It remains to be determined whether a bistatic pairing of transmitter and receiver antennas provides an advantage (over the standard mono-static transmitter-antenna pairing) when imaging moving targets.

This work was performed by Gregory Mazzaro for the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at mobilityengineeringtech.com/tsp  under the Sensors category. ARL-9627

Topics:
Radar/LiDAR Systems Aerospace Antennas Electronic equipment Identification Ingestibles and Lab-on-a-Chip People and personalities Personnel RF & Microwave Electronics Radar Research and development Sensors Transmitters/Receivers
This Brief includes a Technical Support Package (TSP).
Document cover
Stepped-Frequency Distributed Radar for Through-the-Wall Sensing

(reference ARL-9627) is currently available for download from the TSP library.

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    Aerospace & Defense Technology Magazine

    This article first appeared in the April, 2023 issue of Aerospace & Defense Technology Magazine (Vol. 8 No. 2).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document titled "Stepped-Frequency Distributed Radar for Through-the-Wall Sensing: Resolution of Moving Targets by Orthogonal Antenna Pairs" presents research on a novel radar technology aimed at enhancing the detection and identification of personnel and weaponry located inside buildings from a safe distance outside. The study focuses on the application of distributed radar systems, which utilize multiple antennas to improve target resolution and tracking capabilities.

    The introduction outlines the operational scenario for this technology, emphasizing the need for effective through-the-wall sensing in various defense and security contexts. The authors detail the hardware and test environment used in their experiments, which are crucial for validating the performance of the radar system. The document includes a comprehensive analysis of data collected during tests, specifically range profiles plotted over time, which illustrate the radar's ability to detect and track moving targets.

    A significant portion of the report discusses the creation of false alarms that can still track real targets, addressing a common challenge in radar systems where distinguishing between actual threats and non-threatening objects is critical. The authors explore the concept of bistatic distributed radar, which involves using multiple transmitters and receivers to enhance detection capabilities and improve the overall effectiveness of the system.

    The conclusion summarizes the findings and suggests follow-on work to further refine the technology. The report emphasizes the potential applications of this radar system in military and security operations, highlighting its ability to provide situational awareness in complex environments.

    Overall, the document serves as a technical report detailing the development and testing of a stepped-frequency distributed radar system, showcasing its innovative approach to through-the-wall sensing and the resolution of moving targets. The research contributes to the ongoing efforts to enhance radar technologies for defense applications, providing valuable insights into the challenges and solutions associated with detecting threats in urban settings.

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