The emergence of ultra-small, micro-UAVs (Unmanned Aerial Vehicles) has driven researchers to try and shrink many of the electronics systems required to carry out the tasks given to these drones. The most recent system to receive the down-sizing treatment is Synthetic Aperture Radar (SAR), which combines signal phase and amplitude information from several time-adjacent radar pulses to create a high-resolution image.
An illustration of how SAR works made by the MIT Lincoln Laboratory (PDF)
Unlike optical cameras, which cannot work well at night due to a lack of light or cloudy conditions, radar uses microwaves (X-band or Ku-band) for its imaging, so it can operate well in all weather conditions. SAR devices, which usually weigh between 50kg and 200kg and are anywhere from a half meter to two and a half meters in length, are typically carried aloft by large satellites and/or aircraft and are employed to generate detailed images of the Earth's surface. They can cost more than US $1 million and consume as much power as a typical household air-conditioning unit.
In order for an SAR payload to be suitable for micro-UAVs, it must have a transceiver smaller than 10mm2 in size with less than 300mW power consumption and produce images with greater than 20cm resolution. Recently, scientists at Nanyang Technological University (NTU) in Singapore unveiled a chip that promises to enable the development of palm-sized SAR devices, a hundred times smaller than current units, producing images claimed to be of the same quality if not better than their larger cousins. The mini-radars should also be also cheaper to produce and use much less power.
Fitting on a fingertip, the NTU microchip is an integrated Ku-band frequency-modulated continuous wave (FMCW) radar transceiver, including chirp generation (chirp refers to a signal in which the frequency increases or decreases with time. In FMCW radar, chirp is the modulation imposed on the transmitted signal to help distinguish target returns from background clutter), a de-chirp processor and analog-to-digital converters.
Professor Zheng Yuanjin with the radar chip on his finger
Information about NTU's new radar chip was first presented at last month’s International Solid-State Circuits Conference (ISSCC). The researchers, led by Assistant Professor Zheng Yuanjin (pictured above) reported that the chip was fabricated in a 65nm CMOS process and consumes 259.4mW at 1.2V (including 41mW for the synthesizer, 136mW for the power amp, 4.8mW PGA, and 1.3mW ADC). When packaged into a 3 X 4 X 5-cm module, the system weighs less than 100 grams.
Potential applications include environmental monitoring of disasters like forest fires, volcano eruptions, and earthquakes as well as monitoring cities for traffic congestion. Driverless cars using mini-SAR systems will be able to better scan the environment around them to avoid collisions and navigate more accurately than current laser and optical technologies in all weather conditions.
NTU’s research team says its new technology has attracted the attention of a number of multinational corporations, among them the U.S. aerospace company Space X; the Netherlands semiconductor company NXP; Japan’s electronics giant Panasonic, and the French satellite maker Thales Alenia Space.
Asst. Prof Zheng’s team is now developing a phased-array radar system-on-chip for a 10 X 10 array, with each channel using the new radar transceiver chip. The researchers expect to develop a beamforming radar system in about 2 to 3 years. They estimate it will be 3 to 6 years before the chip is ready for commercial use.