On any night, hundreds of aircraft cross through the airspace above the Chesapeake Bay, northeastern Virginia and the Atlantic coast. From airliners and general aviation airplanes to stealth fighters and large tactical aircraft, they represent a convenient, diverse target set for an experimental distributed radar system being developed by the U.S. Naval Research Laboratory (NRL) and Raytheon Technologies
The system is called Flexible Distributed Array Radar (FlexDAR). As the name implies, it incorporates different radar nodes (radar sites) into an integrated system. In the case of FlexDAR, two sites are in operation, one just south of Chesapeake Beach, Maryland on the western shore of the Bay and another 75 miles southeast at NASA’s Wallops Island flight facility on Virginia’s northeastern Atlantic coast.
FlexDAR is “flexible” NRL radar division superintendent, Michael Walder, says because it is software-defined. The radar system can be “rapidly programmed to perform many functions. It can rapidly change the relationship between the nodes.”
An operator can, for instance, configure radar sites within the system to operate independently or in collaboration with each other. The phased-array antennas at each site could be tuned to be solely transmitters or solely receivers. They could even potentially focus their radiated power in directed-energy fashion though such potential is not formally being explored by the NRL research.
The operational flexibility of software-defined radars is advancing the state of the art throughout military and commercial applications. Such systems now have the edge processing power (i.e. at the site) to take advantage of advanced algorithms like super-resolution in real-time to allow them to identify and classify targets in greater detail than ever before.
The most advanced, like FlexDAR, also use their edge processing for self-awareness, collecting data on the physical, electromagnetic and environmental conditions around them, using these to adjust their performance.
NRL engineers developed the software radar signal processing and tracking algorithms for FlexDAR as well as network coordination techniques and an advanced graphical user interface. Raytheon took on the build and design of the two antenna-arrays for FlexDAR. Phased-array radars have been around for decades and Raytheon actually began work on its FlexDAR arrays in 2014.
A key differentiator for FlexDAR is that a single array can simultaneously perform multiple functions - scan for targets, communicate with other radars/sensors and even cue a response to a threat. According to Raytheon, the radar can not only look for small drones, larger aircraft and ballistic missiles, it can detect and track hypersonic missiles. If and when Hermeus flies its hypersonic drone for the Air Force, the NRL-Raytheon will surely want to take a crack at tracking it.
In addition to the edge processing software making this possible, the arrays take advantage of every-element digital beamforming (EEDBF). NRL’s Walder explains that older phased array radars form their beams in analog fashion and then use a converter to digitize them. FlexDAR and other EEDBF-enabled radars form their beams digitally in every element from the outset.
“You can form beams in different ways, in different directions based on software rather than what’s configured into the radar [hardware] when it’s built,” he says.
Each FlexDAR array consists of 1,008 elements to be exact. The array panels are approximately six feet by six feet according to Walder and judging from the photo above, each FlexDAR installation (which includes the array as well as the processing hardware and a user interface) is about the size of a couple of maritime shipping containers.
Given that the prototype system is purely experimental and not missionized, it’s reasonable to expect an operational FlexDAR installation would be smaller. That could make it adaptable to sea, land and air platforms.
“This kind of [array] can be applied anywhere,” Walder confirms. “In the commercial world, with fewer elements, it’s being adopted for cellphone technology.”
Each array-processor combination is a more effective transceiver than current systems and when multiple arrays are synchronized the result could be a multi-function radar net capable of providing a more detailed, fused picture than existing networked radars.
While the NRL/Raytheon team has yet to compile full results or evaluate all aspects of the system, it asserts that FlexDAR “demonstrates dramatic performance improvements in detection range, tracking accuracy, and electronic protection when operated in a distributed configuration.”
How much more range, accuracy and resiliency FlexDAR can offer, NRL won’t say. Walder does confirm that they’ve encountered no surprises thus far and that the FlexDAR front end (array) and back end (software, UI) were integrated without issue or disruption.
“We have a lot of work ahead of us to continue to exercise the capabilities [of FlexDAR] and discover new capabilities,” Walder says. That could take a while. There is no formal timeline for the FlexDAR evaluation which is part of the Office of Naval Research’s (ONR) Integrated Topside and Electromagnetic Maneuver Warfare Command and Control Innovative Naval Prototype programs.
Operational resiliency is not a consideration in the NRL evaluation but the distributed nature of FlexDAR and its communication flexibility suggests it could complicate efforts by an adversary to disrupt the system’s sensing ability.
Research data and lessons-learned flow from NRL up to ONR and to interested parties in the Pentagon. Those parties are already likely looking at the possibility of adding a future operational FlexDAR to the quiver of systems that will go into the military’s developing Joint All-Domain Command and Control (JADC2) framework.
The prototype FlexDAR system is a “unique capability in the U.S.” right now Walder says though he notes that tangential distributed array research is underway the University of Oklahoma’s Advanced Radar Research Center. Lockheed Martin’s
For testing purposes, Walder acknowledges that the NRL-Raytheon team may fly a controlled target in the airspace above the system in the future. Fortunately for FlexDAR, the skies over the mid-Atlantic are a “target rich environment.”
