BAE Systems has completed the first phase of a DARPA programme aimed at removing heat from radio frequency electronics and has been funded to continue into a second phase, work the company says could nearly triple the range of RF systems, the company stated.
The programme is called Technologies for Heat Removal in Electronics at the Device Scale, or THREADS, and is run by the Defense Advanced Research Projects Agency. It targets the temperature limits that constrain gallium nitride devices, the semiconductors that sit behind most modern military radar and electronic warfare transmitters.
Heat is what caps the output of those systems. A gallium nitride transmitter converts electrical power into radio energy and loses a proportion of it as heat within a device measured in fractions of a millimetre, and once the junction temperature rises beyond a certain point the device degrades or fails. Designers have therefore run transmitters below their theoretical maximum output, because the alternative is a shorter service life. Extracting heat closer to where it is generated would allow more power out of the same device.
Isaac Wildeson, principal investigator at BAE Systems’ FAST Labs, said: “We look forward to advancing to Phase 2 of the THREADS program. The progress we’ve made during Phase 1 validates our approach to material and process enhancements and brings us closer to unlocking the full potential of RF-based systems for our warfighters.”
According to BAE Systems, successful thermal management developed through the programme would nearly triple the range of RF systems, improving safety and engagement distances for military personnel.
Radar range scales poorly with transmitter power, detection range rises with the fourth root of the power radiated, so doubling the range of a radar requires something in the order of sixteen times the transmitted power, which is why incremental gains at device level matter more than they might appear to. The company has not set out how the range figure it cites was derived.
Work is being carried out at the company’s Microelectronics Center in Nashua, New Hampshire, a facility accredited as a Category 1A Trusted Supplier, which builds gallium nitride and gallium arsenide integrated circuits. Partners on the programme include Modern Microsystems, Penn State University, Stanford University, the University of Notre Dame and the University of Texas at Dallas.
Gallium nitride has displaced older gallium arsenide technology across radar and electronic warfare over the past fifteen years because it handles higher voltages and power densities, allowing smaller and more capable arrays. British systems using it include the Sampson radar on the Type 45 destroyers and the European Common Radar System Mark 2 being fitted to RAF Typhoons, while the United States has moved its Patriot and Aegis radars onto the material.
“detection range rises with the fourth root of the power radiated, so doubling the range of a radar requires something in the order of sixteen times the transmitted power, which is why incremental gains at device level matter more than they might appear to. The company has not set out how the range figure it cites was derived.”
That is something a basic radar textbook would tell you.
Detection range rises with the third root of the power radiated – that is the inverse cube relationship which is schoolboy physics and is simply energy dispersed over volume. This is unfixable as it is a physical reality. IRL there is a difference between full volume scanning which is fully 3rd power and more pinpoint methods which are less wasteful of brute RF power.
The fourth power if the dissipation in the junctions. Obvs going from 3rd-4th power is a very big deal in energy terms.
There are three main impacts of heat on Gallium Nitride radars.
Thermal Throttling & Power Derating
To protect transmit/receive (T/R) modules from permanent damage or premature failure, radar control units use thermal management algorithms to automatically dial back RF output power (derating) or reduce the radar’s operational duty cycle.
Because maximum radar range is governed by the radar range equation. Any thermal throttling that forces a drop in average transmitted power directly translates into a shorter detection envelope.
Elevated Noise Floor
Detection sensitivity depends on the ratio of target signal to background thermal noise.
Reduced Efficiency & Gain Compression
As the junction temperature of a GaN High Electron Mobility Transistor (HEMT) climbs:
Electron mobility and saturation velocity decrease.
The amplifier suffers from gain compression, causing a higher percentage of input DC power to convert into waste heat rather than radiated RF energy, triggering a feedback loop of thermal loss.
Removal or heavy control of all three factors can result in significant gains however obviously anything a defence contract says on these documents will exaggerate real world performance.