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Radar technology has grown a great deal over the last century. The principle of a radar system has not changed—sending out timed, pulsed signals and charting the direction and timing of their return reflections to learn more about what is causing those reflections—but the technology is now enhanced by advances in digital technology, in particular, modern data converters such as analog-to-digital converters and digital-to-analog converters. By digitizing and processing radar return signals, modern radar systems can perform any number of functions in support of different applications, including search, surveillance, target tracking, fire control, and weather monitoring.

By leveraging the signal processing possible with improved analog and digital components, modern radar receivers can increase sensitivity and overcome performance degradation from traditional problems such as clutter. As an example, the U.S. Navy is benefitting from a new multimode maritime surveillance radar on board the MQ-8B Fire Scout (Fig. 1), which is an unmanned helicopter developed by Northrop Grumman. The improved radar system helps drastically improve the long-range imaging and search capabilities of these unmanned aerial vehicles (UAVs). According to George Vardoulakis, vice president for Medium Range Tactical Systems, Northrop Grumman Aerospace Systems, “This modernized radar complements Fire Scout's other sensors and systems to provide the Navy with increased visibility far beyond the horizon, while collecting vital imaging for maritime operations.”

Fire Scout

Essentially, Northrop Grumman modified an AN/ZPY-4 multi-mode maritime surveillance radar system from Telephonics Corp. that is normally used on manned aircraft and adapted it for effective use on the unmanned MQ-8B Fire Scout. The MQ-8B Vertical Take-Off and Landing Tactical Unmanned Aerial Vehicle is part of the U.S. Navy’s Fire Scout radar Rapid Deployment Capability program. On board an MQ-8B, the radar is configured for broad-area intelligence, surveillance, and reconnaissance missions and it is designed for remote control from the ground or at sea by Navy controllers. The MQ-8B has a range of about 110 nautical miles and is available in a larger version, the MQ-8C, with a slightly larger range of about 150 nautical miles and larger payload capacity. Both UAVs are based on a Bell 407 helicopter certified by the Federal Aviation Administration for such missions.

The Fire Scout provides the Navy with warning signals by means of conventional application of radar technology. But not all applications for radar are conventional, or through the air. The U.S. Army, for example, has been exploring new applications for ground-penetrating-radar (GPR) systems. GPR technology has been used by law-enforcement professionals to find hidden graves, while military professionals have long applied GPR systems for detection of mines, tunnels, and unexploded ordnance. The U.S. Army Contracting Command (Alexandria, Va.) recently announced a $7.3 million contract to Non-Intrusive Technology to develop a real-time version of the company's VISOR GPR system.

GPR systems usually operate with antennas in contact with the ground but can also operate with air-launched antennas above the ground. Higher frequencies do not penetrate as far through the ground as lower frequencies, but do provide better resolution. Good depth penetration is achieved in ice, where it can reach several hundred meters and is also possible in dry sandy soils. Good GPR depth penetration cannot be achieved in high-conductivity materials such as clay, where the radar pulses are dissipated as heat.

In addition to advances in digital technology, GPR systems are leveraging improvements in RF/microwave technology, such as a system developed by US Radar. The firm’s Quantum Imager is said to be the world’s first three-frequency GPR system. The use of three frequencies promises to improve imaging at increased ground penetration depths compared to single- and dual-frequency GPR systems. The firm’s earlier GPR systems have developed excellent reputations for their capabilities in locating plastic land mines underground, so it would appear that applications for GPR systems are only beginning to spread.

Perhaps the best-known name in radar, Raytheon Co., has been exploring multiple capabilities for its radar systems for some time. The firm recently received an $8.5 million base contract from the U.S. Office of Naval Research (ONR) to design the Flexible Distributed Array Radar (FlexDAR), a multiple-mission system capable of numerous functions, including surveillance, communications, and electronic warfare (EW). The company hopes to apply digital beam forming among other techniques to support different applications from a common radar platform. As Paul Ferraro, vice president of Raytheon Integrated Defense Systems Advanced Technology Programs, explains, “Migrating digital technologies closer to the front end of radars will allow for more reconfigurability and ultimately more flexible radars resulting in game-changing improvements.” The FlexDAR system is being developed under ONR’s Integrated Topside (InTop) Program to explore the use of novel technologies for the diversification of radar platforms.

Raytheon has long been an innovator in terms of applying new technologies. The firm has been using high-power gallium-nitride (GaN) semiconductor technology for more than 15 years, developing the technology in partnership with the U.S. Defense Advanced Research Projects Agency (DARPA). The company fabricates and studies GaN devices at its Radio Frequency Components Foundry in Andover, Mass. The GaN devices are capable of higher output-power levels than GaAs devices at microwave and even millimeter-wave frequencies, helping to extend the operating ranges of different radar systems and enabling them to function well even with smaller antenna arrays. As Ferraro observes, “We are charged with creating a pipeline of technologies to fuel business growth for years to come. GaN is the biggest winner we’ve delivered so far.”

Somewhat smaller radar-developing companies such as Mercury Systems are contributing to steady advances in radar technology with their modules and their simulation tools (Fig. 2). The company recently received a $8.8 million order from a leading defense prime contractor for signal-processing subsystems for a ship-borne radar application. According to Didier Thibaud, president of Mercury’s Commercial Electronics business unit, “Mercury’s commitment to providing the most advanced and reliable high-performance signal processing subsystems has ensured our continued participation in this mission-critical defense program.” The company’s Radar Environmental Simulator tools have also proven to be reliable simulation and test tools for developing and evaluating radar systems.

Compact radar function modules

Mercury has been involved for some time in the improvement of synthetic aperture radar (SAR) techniques, such as circular SAR, to enhance the images created by different radar systems from the return signals they receive. According to Mercury, the processor-intense part of radar is image formation, which requires significant numbers crunching. These are computer- and processor-intensive applications that attempt to create high-resolution images from received return signals. Circular SAR involves flying a radar system around an area of interest and performing repetitive signal capture, collecting enough signal data to build a 3D image of the area based on successive layers of radar data.

Lockheed Martin has developed its own version of a 3D radar system, its Three Dimensional Expeditionary Long-Range Radar (3DELRR) prototype system. The technology is intended for the U.S. Air Force's next-generation mobile, long-range surveillance and ballistic missile defense radar, providing 3D imaging in place of the existing AN/TPS-75 air surveillance radar system. The U.S. Marines also are evaluating the system as a replacement for its AN/TPS-59 ballistic missile defense radar system.

The system moves the radar beam rather than the antennas, by means of phased-array technology. By controlling the phase relationships of multiple beams from fixed scanning antennas, the system can switch the directions of tracking beams within microseconds. Historically, phased-array radar systems have suffered loss of imaging resolution when attempting to track multiple targets simultaneously. Lockheed Martin’s efforts on the new system have included enhancements to allow tracking multiple targets at the same time without losing resolution, with each target followed by a dedicated tracking beam.

The company is also developing its radar technology for the Space Fence program, meant to alter the way that the U.S. Air Force tracks and identifies objects in space. Space Fence is based on the use of ground-based S-band radars to provide uncued detection, tracking, and measurement of objects in outer space, mainly in low-earth orbit. Space Fence is being designed with specific placement of S-band systems to achieve detection of much smaller microsatellites and debris than current systems. The Space Fence system will allow operators to detect space events and debris that might pose problems for the International Space Station as well as GPS satellites. This new system, which will replace the VHF Fence currently in use since the 1960s for this purpose, is scheduled to come online by 2017.

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