Researchers in the USA have built and tested a tracking solution for small drones that uses a network of phased array radars able to calibrate themselves with radar measurements and GPS data.
Tracking of small drones is set to become more important as their use increases, particularly in urban and restricted areas. Traditional radar systems are powerful but cannot effectively detect low-flying aircraft below 400ft.
Engineers at Brigham Young University (BYU), Utah used a set of phased array low-cost radars connected to multiple ground station computers to detect moving objects within their field of view during their tests.
When a radar unit identifies an object, it records the position of that object in addition to the radar unit itself. This information is then converted to a global coordinate frame to be shared with other ground stations to create a comprehensive, time-varying picture of air traffic in the area.
This conversion allows all ground stations to interpret the object's position. To achieve a dynamic air traffic picture, each radar unit must be calibrated or provided with the necessary data to convert from the local frame to the global frame.
“Each radar has a field of view as it’s pointed up at the sky,” said BYU professor of mechanical engineering at BYU. “You want the radars to be calibrated so they all see an individual aircraft at the same place in the sky,”
Cammy Peterson, professor of electrical and computer engineering at BYU said, “The effectiveness of the system could be compromised due to weather or an object that bumps into a physical radar unit, causing it to move and point in an unintended direction. But an online calibration process allows the radar units to adjust for an inadvertent change in its position as it is collecting data and to correct for any problems.”
The radars can correct for a unit’s new position in 10 seconds using a mathematical equation that combines the radar and GPS data and performs the online calibration. The research team demonstrated that this dynamic calibration technique showed clear improvements over methods that used recorded batch data.
The small radars could be installed on structures such as light posts or cell towers. Using this approach the radar units could also be swapped out or more could be added, allowing for different capabilities depending on the needs.
“Radar has been around for a long time,” said Karl Warnick, BYU professor of electrical and computer engineering. “Instead of having a $10 million spinning dish like you’d see at an airport, we have a simple thing that could be built for a few hundred dollars.
“The small radars don’t have all the capabilities of a higher-end radar, but a network of small radars can work together effectively.”
While the BYU researchers testing used three radars — each able to track a circular airspace about 500ft across — the technology could be scaled to a broader network with many radars.
“One company can’t take the whole airspace for an hour.” Peterson said. “To be cost-effective you need to allow multiple vehicles from different companies to travel through the same area during the same time window. If you want to be safe, you’ll want to know where the other drones are at.”