Next-gen radars: Seeing through the clutterStory
February 07, 2013
Next-generation radar systems are improving accuracy in high-clutter environments such as littoral waters, wind farm locations, and slow-moving ground objects ? and at faster than ever speeds, reducing the sensor to shooter cycle.
Military radar systems remain ever vigilant in their mission to detect superfast, incoming missiles and supersonic enemy fighter jets. High-speed threats are not going away, but military officials today also want radar systems to detect slower-moving objects on the ground or in shallow, littoral waters, requiring complex algorithms and signal processing techniques.
“Radar capability demands are trending toward dismount detection technology to detect people moving on the ground,” says John Fanelle, Program Director, Radar Systems, Reconnaissance Systems Group at General Atomics Aeronautical Systems Inc. (GA-ASI) in San Diego. “We have incorporated this capability into our Lynx Block 20A Multi-mode Radar and also added a maritime capability to cross-cue the Electro-Optic/Infrared (EO/IR) ball on the Predator B/MQ-9 Reaper Remotely Piloted Aircraft (RPA) fleet to detect shorter-range maritime targets. A maritime mode for the radar is currently being developed to detect specific small items in the water. For the maritime mode we can leverage different algorithms that are available now. It’s just a matter of getting them to work in real time.”
Accurate, real-time information from radar and other sensors brought together in one picture helps save lives by reducing the sensor to shooter cycle – the time it takes for sensor data to reach a shooter, such as a UAS, fighter jet, tank, sniper, and so on, so it can eliminate a threat. “The trends are to more automation, smaller crews, radars that do multiple things, and radars that can talk to other sensors on the battlefield,” says Lee Flake, Program Director for counterfire target acquisition radar programs at Lockheed Martin Mission Systems and Training. The AN/TPQ-53 (Q-53) counterfire target acquisition radar from Lockheed Martin is that type of radar. The system – which has 360- or 90-degree modes – reduces sensor to shooter time by acquiring the projectiles such as mortars, rockets, and artillery while they are in the air, and sends information on their point of origin immediately, enabling it to destroy the object before it hits its intended target, Flake adds. “It all takes place in seconds.”
The system, already operating in Iraq and Afghanistan, can be rapidly deployed, automatically leveled, and remotely operated as far as a kilometer away with a laptop computer or from a fully equipped climate-controlled command vehicle. “The radar uses a custom signal processing system designed by our partner, Syracuse Research Corp. (SRC) in Syracuse, NY,” Flake says. “We designed the wireless component for the system. This approach is cutting edge and what the Army wants their sensors to do. When designing it, we started thinking ‘What else can we add to this radar – what technology can we insert?’ We are only beginning to attack the capability of this radar, which will be around for decades.”
Adding capability without overhauling the system enables cost-effective and quick enhancements for meeting urgent requirements. “The beauty of our Lynx Block 20A is that it has enough capability to add these modes without redesigning the radar,” Fanelle says (Figure 1). The multifunction radar functions in high-resolution Synthetic Aperture Radar (SAR) and Ground Moving Target Indicator (GMTI) modes. Lynx provides photographic-quality images through rain, clouds, rain, smoke, dust, and fog, day or night. It flies on manned and remotely piloted platforms and has a range as long as 100 kilometers. In radar systems, situational awareness also is enhanced through 3D images. “Lynx has the ability to do 3-Dimensional (3D) targeting using radar imagery,” Fanelle says. “With 3D targeting, you need longitude, latitude, and altitude. If you look at a target such as a ship at sea, longitude and latitude would suffice, but if the target is also high up in the mountains, on a plane, or a plateau, then you need to factor in altitude as well to properly fix the crosshairs on the target. Very high precision is associated with 3D targeting, which enables the use of small weapons that minimalize collateral damage.”
Figure 1: Photographic-quality imagery is generated by the multimode Lynx Block 20A radar system from General Atomics Aeronautical Systems, Inc. (GA-ASI).
(Click graphic to zoom)
Military radar users want quickly deployable systems that have more capability in smaller packages, that can run on less power, and that have more agility in how they are deployed – airborne, ground vehicle, man portable, and so on, says Pierre Poitevin, General Manager at FLIR Radars in Montreal. Time to market can be a challenge today because radar products are more complex and to deploy a system as quickly as possible requires a delicate balance between functionality in the product versus how soon a customer might want it. FLIR engineers developed a dual-mode ground surveillance radar – the Ranger R3D – that has a fast camera mode and a Doppler mode in a small form factor – about 15 inches in height by 18 inches in diameter and less than 30 lbs. It consumes only 30 W and can be used in ground vehicles or man-portable applications for persistent surveillance.
Quickly deployable systems with an architecture that can accommodate future capability upgrades need to leverage Commercial Off-the-Shelf (COTS) hardware and software as well as common standards. The use of common standards with products with high Technical Readiness Levels (TRLs) also reduces risk by encouraging interoperability.
“We leverage open architectures, and our radar compute engines use COTS components,” Fanelle says. “Graphics Processing Units (GPUs) are creating a compute engine in the gaming industry that can do amazing stuff, and we are evaluating these devices to harness some of that power. The one thing the gaming industry doesn’t have is environmental restrictions on its devices. We need to take a gaming GPU and make sure it can function within the environmental constraints in military applications.”
“Implementing open architectures and common standards as part of our design process has allowed us to greatly reduce the number of parts for the same mission we were doing 30 years ago,” says Rick Herodes, Business Manager for FPS-117/TPS-77 Radar at Lockheed Martin Mission Systems & Training in Syracuse, NY. “All three of our surveillance radar products – TPS-77, the TPS-59 Marine Expeditionary Radar, and the FPS-117 long-range surveillance radar for the Air Force all use the same signal processing architecture. Treating all three as a product line enables us to leverage investment and support costs across multiple customers. For example, we use exactly the same parts in the TPS-77 as in the other radars such as the WILDFIRE FPGA boards from Annapolis Microsystems.” (For more on COTS signal processing trends, see this edition’s Mil Tech Trends coverage, beginning on page 20.)
Mitigating wind farm challenges
High-clutter littoral waters are not the only tough environment vexing radar designers. The areas around wind farms, cause quite a few headaches for radar operators. Engineers at Lockheed Martin Mission Systems & Training say their TPS-77 portable long-range radar is mitigating many of the false alarms caused by wind farms through its architecture and signal processing techniques that leverage COTS computing systems.
“The basic problem with wind turbines is they are large and keep getting larger, are semi-metallic to protect the turbines from getting struck by lightning, and are high velocity. With the new generation of turbines, blade tip velocity can approach hundreds of miles an hour,” says Chris Atherton, Technical Director for Long-Range Radar at Lockheed Martin Mission Systems & Training in Syracuse, NY. “These are all characteristics radar systems are designed to see, so they end up generating radar signatures that are orders of magnitude larger than a 747. Wind farms create complex clutter returns – zero Doppler (non-moving) from the tower and nacelle and non-zero Doppler (moving) from blade movement. The clutter returns can increase false alarms and report aircraft where there are none. This clutter can also desensitize the radar such that it cannot detect aircraft in the vicinity of wind farms. The turbines also are typically located in the same areas as radars – high up and visible to get as much wind as possible. One mitigation technique used has been to prevent wind farms from being built in ‘line of sight’ with radars – causing conflict with wind farms development.”
“To solve the wind farm challenges, we deploy a pencil beam radar system architecture in the TPS-77 transportable radar as opposed to a stack beam system,” Herodes says. “The TPS-77 has the capability to produce a usable air picture within two hours of touching down at any given radar site to a range of 250 nautical miles. Many other long-range radars use multiple stacked beams to detect a target and estimate its height. Since stacked beam transmission is simultaneous, wind farms interfere with all the beams, confusing the radar’s signal processing. Stack beam systems illuminate a much larger area – as large as a horizon to 40,000 feet. Comparing that to a pencil beam illumination is like comparing a flood light to a laser beam.”
“A pencil beam system like the TPS-77 focuses energy very narrowly while illuminating the targeted vicinity,” Atherton says. “It localizes the wind farm and enables proper detection of an aircraft immediately around the wind farm. Because it is using focused energy, it is less likely to pick up the false alarms associated with the wind farm signatures. Transmission and processing are independent, preventing clutter in one beam from affecting another. An important result of the pencil beam architecture is the ability to detect uncooperative aircraft such as those that turn their transponders off so they cannot be seen. The fundamental architecture of pencil beam separates the returns and differentiates aircraft from the clutter returns.
“The TPS-77 3D Scanning Pencil Beam Phased Array system uses advanced clutter reduction techniques such as full monopulse processing, range adaptive MTI/Doppler processing, and advanced clutter mapping,” Atherton continues. “Advanced signal processing techniques such as monopulse processing are necessary for detecting objects in littoral clutter and water/land transitions, which can change clutter characteristics fairly dramatically. Monopulse processing breaks a single beam into three beams and compares the results to determine target location. From the same transmission you can get many different looks, in many different pieces, and then integrate those pieces to get a better view of the returns. We only need a single return to get full stated accuracy of a radar system with monopulse processing. Other radars use multiple returns and employ averaging techniques, whereas monopulse is one hit, which is important for high-clutter environments around wind farms. Adaptive MTI and Doppler are excellent at suppressing targets of different speeds and velocities – like wind turbine blades.”