When future hypersonic vehicles are tested far above the Pacific Ocean, the telemetry signals they transmit will be captured by a new type of modular antenna system developed by the Georgia Tech Research Institute (GTRI) in collaboration with prime contractor AV (formerly Blue Halo). 
 

Known as Advanced Phased Array Antenna Technology (APAT), the system uses Radio Frequency System on Chip (RFSoC) technology to process the signals directly on the antenna’s elements, allowing multiple signals to be tracked simultaneously in different directions. Both ground-based and airborne versions of the antenna technology have been built and tested for capturing the telemetry data sent from the vehicles to monitor flight factors and conditions.
 

Built for the Pentagon’s Test Resource Management Center (TRMC), APAT uses commercial-off-the-shelf components paired with bespoke antenna elements and a custom system architecture to create a novel system with unparalleled operational flexibility. It is believed to be the largest all-digital antenna system ever designed by GTRI, which has been developing and building antennas for more than 25 years.
 

“We’re combining RF-efficient aperture design with an intelligently-selected RF front-end that goes directly to digital so that when they’re tracking these telemetry streams, they can track multiple streams simultaneously,” said Kevin Cook, a GTRI principal research engineer who is co-principal investigator on the project. “In earlier analog systems, you’d have to just pick a stream or split the array (or multiple arrays) and lose signal gain. But with digital, you can track as many streams as you want, limited only by the system’s processing power.”
 

GTRI and AV have so far collaborated to deliver one airborne system designed to fly on a large UAV platform. A ground-based system with additional computing power for broader test applications is now being tested prior to installation on San Nicolas Island, which is located off the Southern California coast. A second airborne system is also in the works.
 

Beyond the ability to simultaneously track multiple signal sources – as many as 24 with the ground-based system – the digital array maintains high signal quality with limited noise, said Todd Lee, a GTRI principal research engineer and the program’s principal investigator.
 

“The signal-to-noise ratio is set when you go to digital,” he explained. “It’s the same as when you make a copy of a digital music file. The music sounds exactly the same every time it is copied and played because it is exactly the same. The flexibility and stability from a noise perspective are probably the two biggest advantages of going directly to digital with APAT.”
 

The ground-based system, which is about the size of a small room, has much in common electronically with the smaller airborne system – a cost savings for the test community. “It really reduces the cost if you can reuse the electronics, even if the antennas look different,” said Lee. “These antennas are unique, but the sort of electronics we used in the background are pretty common.”
 

Both systems use commercially available RFSoCs that combine multiple components to move digital processing to individual elements of the arrays – in contrast to earlier analog systems, where the processing was done off the antenna. The APAT arrays include as many as 500 elements.
 

The cost implications go much farther than the antenna arrays themselves. Testing on the Pacific Range currently requires that U.S. ships be positioned along flight test routes to capture telemetry data that is beyond the reach of land-based stations. Once the new antennas are deployed on UAVs, those ships will no longer be needed to monitor flight tests.
 

APAT was one of three hypersonic antenna projects developed by different vendors for the TRMC, which will use them to carry out a broad range of testing. 
 

Development of the antennas required expertise from three of GTRI’s eight specialized laboratories, in addition to engineers at AV. Testing was done in GTRI research facilities in Atlanta and at AV’s Maryland facilities. The ground system was tested by another contractor before being shipped to California for final acceptance testing. Engineers from the Georgia Tech Research Institute (GTRI) dedicated several weeks on-site at government facilities in California to support the integration and execution of flight tests. 
 

Robert Case, a senior research engineer within the Electro-Optical Systems Laboratory (EOSL), noted, "The field testing of these systems was actively supported and observed by government RF experts prior to their deployment in real-world scenarios. This process provided the government with increased confidence in the capabilities these systems deliver."
 

GTRI researchers say the technologies developed for APAT could have both commercial and defense applications beyond flight testing. 
 

“We have built something with flexible technology that can be easily reprogrammed,” Lee said. “We’re now looking at different places where this technology could be used. For instance, the airborne system could potentially be repackaged into a pod to operate under the wing of an aircraft.”
 

The project builds on GTRI’s long-term experience with antennas and related technology.
 

“Antenna design is something that has been fine-tuned within GTRI for the past 25 years,” Lee added. “Processes have gotten faster, computers have gotten better, and we’ve gotten more advanced with them throughout the years. We keep building on the same fundamental approaches, making improvements every time.”

Writer: John Toon (john.toon@gtri.gatech.edu)
GTRI Communications
Georgia Tech Research Institute
Atlanta, Georgia USA

About the Georgia Tech Research Institute (GTRI)
The Georgia Tech Research Institute (GTRI) is the nonprofit, applied research division of the Georgia Institute of Technology (Georgia Tech). Founded in 1934 as the Engineering Experiment Station, GTRI has grown to more than 3,000 employees, supporting eight laboratories in over 20 locations around the country and performing more than $919 million of problem-solving research annually for government and industry. GTRI's renowned researchers combine science, engineering, economics, policy, and technical expertise to solve complex problems for the U.S. federal government, state, and industry.