US: NASA has awarded USD 2.4 million to Georgia Institute of Technology (GIT) in Atlanta to develop a new type of radar system that will be used to study the Earth’s ice and snow formations from the air. The system could provide new information about the effects of global climate change. The research aims to create a small, lightweight, low-cost phased-array radar that uses silicon-germanium (SiGe) chips in tandem with radio-frequency micro-electromechanical systems (RF MEMS). The system being developed could be mounted on aircraft or satellites to enable high-quality mapping of ice and snow formations.
John Papapolymerou, a professor in Georgia Tech’s School of Electrical and Computer Engineering, project’s principal investigator, said, “This aerial approach would greatly facilitate environmental remote sensing of ice, allowing us to map larger areas of interest to better understand location, quantity and composition. This mapping ability is very important because we need to know about ice accumulation, consistency and stability.”
Phased-array radar technology uses fixed, interconnected antenna elements to send and receive multiple radar signals almost simultaneously. This approach employs the technique of phase-shifting to electronically steer the radar-signal beam. By contrast, a conventional radar antenna changes the direction of the signal beam mechanically; the antenna moves physically among set positions, sending and receiving signals at each position. The serial approach used by conventional radar generally offers slower and less-effective performance than the more parallel technique of phased-array radar.
The basic sub-array unit under development consists of a flat grid with eight antenna elements on a side (64 elements in total). These sub-arrays, measuring about 8.5 inches by 7 inches, can be combined to create a far larger radar array capable of high-quality 3D mapping. To date, the researchers have produced and tested an eight-by-two-element sub-array mounted on a multi-layer substrate. This substrate consists of a layer of liquid crystal polymer (LCP), which is a robust organic polymer, and a layer of a composite material called duroid.
The LCP/duroid substrate houses the SiGe integrated circuits, which transmit and receive the radar signals via the sub-array’s multiple interconnected antenna elements. “The researchers chose SiGe because it offers high-performance signal amplification that is also low in noise and in power consumption,” said Cressler, who is a Ken Byers Professor in the School of Electrical and Computer Engineering.
“Using MEMS devices for electro-mechanical switching results in less signal loss than integrating the transmit-receive switching function within a SiGe chip electronically,” Cressler said. “And while MEMS switching is a bit slower than a purely electronic approach, it offers both better signal performance and the ability to handle higher signal-output power.”
The system under development uses the X band (microwave frequencies of 8–12GHz), which is especially effective for scanning within ice and snow deposits and remotely mapping them in three dimensions.