Surrey Cuts NovaSAR cost with GaN Technology

New British Satellite Puts SAR in Reach | Paris Air Show 2015 content from Aviation Week

NovaSAR-S - DigitalCommons@USU

“We've been trying for many years to do small satellites with SAR,” says Surrey Satellites' director of earth observation and science, Luis Gomes, in a separate interview. “We have a customer base, usually around developing countries and developing space nations, that want to move from optical to SAR. Many of them are in the equatorial belt, where you tend to need something that can see through clouds. The problem was that SAR was very difficult to do on small satellites.”

That was until Martin Cohen of Astrium and his colleagues in Portsmouth began to apply gallium nitride (GaN) technology to the problem. Previous SAR systems, such as the ASAR payload carried on the European Space Agency's huge Envisat satellite, improved on earlier capabilities by using an active-phased array antenna in preference to earlier systems' passive arrays. The passive array requires one large amplifier supplying power across the entire antenna, while the active array divides the antenna into smaller elements, each of which needs its own smaller amplifier. On ASAR there were 320 elements.

“The engineering effort that's involved in building, testing and integrating 320 of everything is just enormous,” says Cohen. “It's not compatible with a low-cost program. But gallium nitride can deliver 100 watts rather than 10 watts. So the idea was, what if we had 10 times fewer building-blocks on the antenna?”

The resulting system delivers many of the benefits of an active array – principally, different SAR modes, and a steerable beam – but without requiring so many antenna elements as to defeat the low-cost objective. The final NovaSAR antenna configuration uses 18 elements in a six-by-three layout, each with a 100W GaN amplifier.

“It's vastly cheaper than ASAR but it's got a 6-meter resolution while ASAR had 30 meters,” says  Cohen. “We can look at a 20-km swath at 6-meter resolution, or a 100-140-kilometer swath at 20- to 30-meter resolution in Scan SAR mode. It's also got an experimental maritime-surveillance mode, with a swath width of something like 400 km."