Imaging radars that can see through clouds and weather are preferred sensors for Earth monitoring and target surveillance, but are traditionally large and heavy and carried by specialized and expensive satellite and aircraft platforms.
Now scientists at Singapore’s Nanyang Technological University (NTU) have developed a miniaturized radar system-on-chip that could enable all-weather synthetic-aperture-radar (SAR) imaging sensors to be carried by small unmanned aircraft.
Fitting on a fingertip, the microchip is an integrated Ku-band frequency-modulated continuous wave (FMCW) radar transceiver, including chirp generation, radio-frequency transmitter and receiver, dechirp processor and analog-to-digital converters.
SAR sensors are becoming smaller, with
Northrop Grumman’s Vehicle-and-Dismount Exploitation Radar (Vader) and
Raytheon’s Dismount-Detection Radar designed to fly in Predator-class vehicles and
Finmeccanica’s PicoSar on Scheibel’s Camcopter small unmanned helicopter. The NTU’s chip promises far smaller radars.
The chip is produced using a 65-nanometer CMOS (complementary metal-oxide semiconductor) process, and is targeted at synthetic-aperture radar imaging for unmanned aircraft, ground vehicle and satellite applications, says Zheng Yuanjin, who is leading the research at NTU.
The single-chip SAR transmitter/receiver is less than 10 sq. mm (0.015 sq. in.) in size, uses less than 200 milliwatts of electrical power and has a resolution of 20 cm (8 in.) or better. When packaged into a 3 X 4 X 5-cm (0.9 X 1.2 X 1.5 in.) module, the system weighs less than 100 grams (3.5 oz.), making it suitable for use in micro-UAVs and small satellites.
In FMCW radar, chirp is the modulation that is imposed on the transmitted signal to help distinguish target returns from background clutter. Because high-resolution SAR imaging requires a stable platform, the NTU transceiver has a tunable chirp rate to help cope with variations in UAS altitude.
In radar, the rule of thumb is the bigger the aperture, the higher the resolution. In synthetic aperture radar, Doppler shifts—from the motion of the radar relative to the ground—are used to electronically synthesize a longer antenna for higher resolution.
NTU tested the SAR imaging performance of its miniaturized radar transceiver, combined with an antenna and processor, by moving the prototype chip along the rail on the roof of a building to emulate an unmanned-aircraft flying.
The acquired data was processed to generate a SAR image with a slant range of 108-129 meters (328-423 ft.). This clearly revealed two reflectors against a background of radar clutter from the grass, says NTU’s technical paper.
“We are now developing a phased-array radar system-on-chip for a 10 X 10 array, with each channel using this radar transceiver chip, and will hopefully get to a beamforming radar system in about 2-3 years,” Zheng says. It will be 3-6 years before the chip is ready for commercial use.
NTU says
SpaceX, Dutch semiconductor company NXP, Japanese electronics giant Panasonic and satellite maker
Thales have expressed interest in the technology. The next phase will involve research into space applications by S4TIN, a laboratory operated jointly by NTU and
Thales Alenia Space.
“The low power consumption makes [the radar chip] very suitable for microsatellites such as the X-Sat or Velox-C1 that NTU has launched,” says Low Kay Soon, director of the university’s satellite research center. Solar-power-generation limitations on smallsats preclude for the moment the use of SAR systems.