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OBJECTIVE: Develop low-cost, small-size multiple-input multiple-output (MIMO) radar at millimeter-wave frequencies capable of analyzing target micro-Doppler signatures for detection, classification and tracking of unmanned aerial systems (UASs) in highly cluttered environments. DESCRIPTION: Proliferation of UASs, more commonly referred to as drones, is emerging as one of the largest threats to the US Army's mission. These systems could provide US adversaries with a low-cost means of conducting intelligence, surveillance, and reconnaissance missions against or even attacking US forces. Many small UASs cannot be detected by traditional air defense systems due to their size, construction material, and flight altitude. Conventional microwave systems for detecting small airborne threats, such as counter rocket and mortar (C-RAM) radars, rely on high target speed to reject clutter but face challenges for low, slow, small UASs. The greater Doppler sensitivity and narrower radar beamwidths can be achieved at millimeter-wave (MMW) (30-300 GHz) frequencies could potentially enable detection and resolution of slower objects in more complex terrain. Larger radar bandwidths allow high range resolution, which can facilitate the classification and tracking of slow moving objects. MMW offers additional advantages over optical and infrared parts of the electromagnetic spectrum. MMW has good penetration characteristics in the presence of fog, smoke or dust. Radars are active sensors that operate independently of external lighting and the time of day, allowing day/night/all-weather operation. On the system side, recent advances in low cost RF-CMOS technology have significantly lowered the cost of MMW systems, and enabled the commercialization of these systems such as automotive radars. Building on low power RF-CMOS technology, low cost single-chip collision avoidance radars at 77 GHz have become widely available. Besides offering high range resolution, they also include multiple transmitters and receivers in a single-chip form factor that can be electronically configured into coherent beam forming mode for MIMO (multiple-input, multiple-output) radar mode with enhanced angular resolution. MMW radars operating in MIMO mode are particularly attractive for tracking UASs. A reliable UAS radar system must be able to discriminate quadcopters, fixed-wing drones, from birds and slow-moving ground objects. Micro-Doppler is generated due to the organic motion of the various components within a target, such as propeller blade rotation for a drone or wing flapping for a bird. Because these motions result in distinct time-Doppler-frequency patterns, micro-Doppler is more useful than RCS or bulk speed for unique identification of small UAS targets. Higher frequencies at MMW band could be advantageous by providing better Doppler resolution from ground clutter in a shorter time, therefore reducing the minimum detectable target velocity. When combined with artificial neural networks or other machine learning algorithms, these micro-Doppler features can be used to train a radar to detect and classify an UAS. Despite the potential advantages of MMW radar for counter UAS detection, many challenges exist in hardware and software. Hardware at MMW frequencies remains expensive and low efficiency, resulting bulky systems with high power consumption. Fully utilization of micro-Doppler features will require development in low phase-noise sources as well as classification algorithms that can operate with limited training data. The goal of this STTR topic is overcoming these challenges to achieve systems with both high spatial resolution and classification performance using micro-Doppler extracted from MMW MIMO radar returns. PHASE I: Establish a MMW MIMO radar simulation testbed for detection, classification and tracking of small UASs. Determine system architecture and radar system parameters. Determine radar system hardware specifications and perform trade study between system size, architecture, operating frequency, antenna structure, range, power consumption, etc. Perform design of a prototype radar based on optimized parameters selected from the trade study. Initiate development of signal processing algorithms for the prototype radar. Machine learning techniques are encouraged for processing micro-Doppler signatures for identification and classification of UAS targets. The prototype radar design should demonstrate detection ranges up to 500 m, altitudes between from 10 to 200 ft., and radial speeds between 2 10 m/s, and demonstrate simulated classification accuracy > 90% for discrimination of small UAS versus birds, pedestrians, and road vehicles. PHASE II: Improve prototype radar design developed in Phase I and build a hardware prototype based on the improved design to realize a low power MMW MIMO radar testbed for detection, classification, and tracking of small UASs in complex terrain. Integrate radar system hardware, signal processing software, and user display to demonstrate small UAS detection at ranges up to 1 km, altitudes between 10 and 400 ft., and radial speeds between 2 30 m/s in government-defined complex terrain. Establish training data requirements to achieve classification accuracy > 95% for discrimination of small UAS versus birds, pedestrians, and road vehicles. Identify promising approaches to extend detection ranges up to 3 km in potential Phase III research. PHASE III DUAL USE APPLICATIONS: A low-cost, small-size MMW MIMO radar for detection, classification and tracking of UASs in highly cluttered environments will fill a critical technology gap for the Army. Phase III commercialization of the compact MMW radar developed in this STTR project, if successful, will provide an effective tool for developing strategies for countering potential hostile UAS threats. Phase III efforts will include ruggedizing the radar package and further capability enhancements such as extending detection ranges. Similarly, the MMW radars can be used for detecting and classify intruding UASs for civilian applications. REFERENCES: 1. J. Wang, Y. Liu, and H. Song, Counter-Unmanned Aircraft System(s) (C-UAS): State of the Art, Challenges and Future Trends, arXiv, 2020; 2. R.Z. Syeda, et. al., Design of a mm-wave MIMO radar demonstrator with an array of FMCW radar chips with on-chip antennas, Proceedings of the 16th European Radar Conference, 2019; 3. D. Tahmoush, Review of micro-doppler signatures, IET Radar, Sonar & Navigation, vol. 9, no. 9, pp. 1140 1146, 2015; 4. S. Rahman and D.A. Robertson, Radar micro-Doppler signatures of drones and birds at K-band and W-band, Scientific Report, 8, 17396 (2018) KEYWORDS: RADAR, MIMO, micro-Doppler, millimeter-wave, unmanned aerial systems (UASs)
