Active electronically scanned array (AESA) radars are playing increasingly critical roles today, protecting warfighters and civilians as part of air and missile defense systems. They are also critical tools on modern test and training ranges, allowing aircrews to train against realistic simulations of real-world threats. 
 

To accelerate modernization of these systems, researchers at the Georgia Tech Research Institute (GTRI) have developed a novel, fully-integrated compact X-band polarization-diverse AESA testbed known as XPAT. The system was developed for operation in airborne and ground-based AESA applications that require a reconfigurable software-defined radio frequency (RF) aperture to meet a variety of requirements and mission sets. 
 

Now being tested in GTRI antenna ranges, XPAT consists of eight-element transmit-receive (T/R) modules, liquid-cooled cold plates that are optimized to reduce thermal gradients between high power amplifiers (HPAs), power/control electronics, electromagnetic interference (EMI) lids for improved isolation between channels, and a 64-element radiator. The system is designed as a building block for arrays of any planar size and shape, and to allow ease of assembly and maintenance using blind-mate interfaces for power, control, cooling, and RF connections.
 

The XPAT system is aimed at filling a gap in GTRI’s radar portfolio by establishing a path forward for packaging a high-power, digital phased-array architecture with polarization control. For specific applications, XPAT offers a broader range of capabilities than earlier passive electronically-scanned arrays.
 

“XPAT could ultimately replace an existing test asset with a more advanced version that will not only provide more capability now, but also provide the flexibility to address future scenarios, perhaps even representing systems that we may not be aware of,” said Maxwell Tannenbaum, a GTRI senior research engineer who leads the project. “There are a lot of forward-thinking applications in which XPAT could be leveraged.”
 

XPAT includes a scalable aperture design that allows ease of assembly and maintenance, and distributes coolant evenly for effective thermal management. XPAT is designed for maximum reliability and reduced system downtime as a result of field-replaceable subarrays. 
 

“The active electronically-scanned array approach basically combines the transmitter and receiver with the phase-shifting electronically-scanned antenna,” Tannenbaum said. “Every one of the elements has a built-in transmitter and receiver. That means there’s not a single point of failure for the system, which allows it to degrade gracefully.”
 

Depending on their size, systems built from the modular units can withstand the loss of certain components.
 

“You can lose a handful of elements – depending on how large the system is – and still be able to operate within specification,” he added. “But everything has a mean time to failure, so we are designing with serviceability and maintenance in mind.”
 

For example, subarrays can be replaced by loosening a handful of fasteners and disengaging the drip-free, quick-disconnect coolant fittings.
 

“There’s a lot of forward thought here, not only about getting something to work on the laboratory bench, but also how it is going to be put together and used in the field,” Tannenbaum said. “This effort leverages a lot of lessons learned from earlier antenna projects and feedback from our sponsors.”
 

The high-power operation of the system required a robust thermal management approach that uses a series of cold plates to uniformly cool electronic components. The researchers used advanced additive manufacturing techniques to build the plates, then machined them to provide clearance for all the components. GTRI has a patent pending for this technology.
 

Because XPAT was developed with an enhanced field of view for potential airborne applications, space utilization needs drove much of the design.
 

“We had to navigate around not only fluid passages in the cold plate, but also all the components on the integrated printed circuit boards (PCBs),” said Dante Dimenichi, a GTRI senior research engineer who leads the mechanical design team on the project. “We have built several large systems that operate at lower frequencies, but the scale and space constraints at X-band are much more challenging.”
 

While XPAT is designed to work at X-band frequencies, GTRI is also working on designs that would operate with a broader range of frequencies in order to potentially represent multiple types of systems with varying performance requirements.
 

For large-scale simulators used on training ranges, 150 to 200 blocks could be combined. Smaller systems could be built with 50 to 60 of the blocks. The modular nature of the system – with each block having its own T/R elements – allows aperture size flexibility.
 

“The building block is designed to be both scalable and modular,” Tannenbaum added. “You could make an antenna of any size based on that building block as long as you’ve got the power and coolant to support it. There are a lot of potential applications.”
 

The three-year project to develop XPAT was supported by GTRI’s Independent Research and Development (IRAD) program. In addition to those already mentioned, the XPAT development team included Jacob Allman, Dinal Andreasen, Thomas Beard, David Chung, Charlotte Cline, Nathan Fairlie, Wiley Holcombe, Jacob Houck, Paul Jo, Kevin Leon, Brandon Lovelace, Erick Maxwell, Ross Pettingill, Tyler Russell, Javier Sarabia, and Travis Turner. The project was also supported by the efforts of Bill Blackwell, Ken Boyle, Duston Cline, Chris Cohran, Taryn Hampton, Steven Johnston, Kay Lindsey, Zach Malone, and Parker Singletary.
 

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.