N211-042 TITLE: Sensitivity and Resolution Improvements for Small-Aperture Marine RADAR
RT&L FOCUS AREA(S): Directed energy
TECHNOLOGY AREA(S): Sensors
OBJECTIVE: Achieve higher detection sensitivity and angular resolution in small-aperture marine RADAR applications.
DESCRIPTION: Modern submarine navigation systems leverage commercial off-the-shelf (COTS) magnetron RADAR technology to detect moving vessels and distant shorelines. In this architecture, long-range detection sensitivity is limited by the effective radiated power (ERP) of commercially available RADAR products, many of which have been discontinued or experienced power reduction in recent years due to the emergence of low-cost broadband and pulse compression devices. Furthermore, submarine surface navigation RADAR systems must operate within a pressure proof volume (i.e., "pod") that remains permanently mounted on a penetrating mast. There are acquisition and shipbuilding advantages to using smaller pod volumes, and therefore smaller antennas, but this comes at the expense of angular resolution, which degrades with shorter diameters. The use of large and powerful open array marine RADARs is not practical in these applications, yet International Electromagnetic Commission (IEC) standards still require strict RADAR performance against small, distant and closely spaced contacts. This puts IEC compliance out of reach for these small-aperture RADAR systems.
The Navy seeks innovative concepts that increase detection sensitivity and angular resolution of small aperture RADARs without breaking the pod-based sensor model. Reliable detection and resolution of navigation buoys (5 m2), small vessels (2.5 m2) and channel markers (1 m2) is required at IEC compliant ranges. The challenge is to overcome physical sensor limitations by using new architectures, innovative apertures, or digital processing to improve detection and resolution performance on these required targets. Doppler beam sharpening (DBS) algorithms can improve bearing resolution and are now available digitally in commercial marine RADAR products. Further resolution improvement is attainable using knowledge-aided DBS techniques. Sensitivity improvements are achievable using minor modifications to COTS devices. For example, the incorporation of low-noise amplifiers, coherent processing threads, or multi-static/netted sensor architectures all offer sensitivity advantages. The use of frequency and phase-modulated waveforms is shown to provide predictable improvements in processing gain and range resolution. The technology introduced by this topic will help retain navigation RADAR performance for the warfighter without forfeiting the cost and shipbuilding advantage of small and COTS-based designs. This technology is also applicable to the commercial RADAR industry as a means of reducing sensor size and improving the standard for safe navigation.
In the submarine application, the available volume for a rotating antenna is less than 20" in diameter and 8" in height. Analog-to-digital conversion must be performed within the sensor pod using a commercial RADAR processor assembly or similar small form factor device that would fit in a 20" diameter by 3" high volume. Digital RADAR video and data processing outputs will be distributed from the pod to inboard processors, so low network speeds (10 GbE or less) are preferred to enable integration with legacy platforms. Solutions that rely on commercially available components are preferred because of cost and availability, but not required. Digital processing capabilities must be implemented on Government-furnished servers or field-programmable gate arrays (FPGA) using open interface standards to allow periodic and modular software/firmware upgrades.
PHASE I: Conduct innovative research, design, and modelling to demonstrate the proof of concept. Evaluate the feasibility of using the concept to improve sensitivity and resolution of small-aperture X-band RADAR. The concept shall include simulated performance analysis, performance estimates for achievable angle resolution, and range of first detection of required targets identified in the Description Section. Develop system architecture diagrams to identify technical challenges, risks, and any cost/performance trades associated with the technology. The Phase I Option, if exercised, will include development of the capability description, design specifications, and performance requirements for a Phase II prototype.
PHASE II: Mature the concept by building and testing a functional prototype based on the Phase I design and the Phase II Statement of Work (SOW). Conduct demonstrations and collect measurements in simulated and over-water environments to validate the prototype. Ideally, Phase II testing will consist of field measurements that demonstrate the ability to meet Phase I performance predictions and applicable IEC 62388 performance metrics in a relevant over-water environment. Controlled laboratory experiments may also be used to verify and validate performance estimates where field measurements are not practical. Develop a transition plan for technical insertion on Navy platforms, and report on the overall commerciality and suitability of the prototype for tactical fielding. Transition the final solution to appropriate platforms and end users.
PHASE III DUAL USE APPLICATIONS: Assist the Navy to transition the concept from prototype development to full production. The final design will be produced with tactical form, fit and function. Factory acceptance testing is expected to formally verify system performance and survivability against MIL-STD-167-1A, MIL-STD-461F, MIL-STD-464C, and MIL-STD-810G environmental standards.
The targeted platforms for Phase III transition are VIRGINIA and COLUMBIA class submarines, and so a temporary alterations (TEMPALT) fielding may also be used to reduce production technical risks. While the primary motivation for this technology is to improve performance of military marine RADARs, commercial applications also exist in any industry where a sensor aperture is limited by physical constraints, for example, small aperture RADARs are used in modern automobiles to automatically detect and resolve moving objects, predict collisions, and assist in driver decision making. Similarly, the use of commercial unmanned aerial vehicles (UAVs), or drones, has gained interest in many service industries. The technology described in this topic can be used to improve the performance of electromagnetic sensors in these non-military applications.
KEYWORDS: Marine RADAR; Beam sharpening; Frequency Modulate Continuous Wave; FMCW; Collison Avoidance; Coherent integration; Field-programmable gate arrays; FPGA
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