IEEE Engineering 360, 10/16/2017
Millimeter wave sensing is a radar-based technology that detects range, velocity and angle of an object with high precision. The millimeter wavelength region of the electromagnetic spectrum corresponds to the frequency bands between 30 and 300 GHz. It is designated as an extremely high-frequency band (EHF) by the International Telecommunication Union (ITU), with associated wavelengths that range from ten to one millimeter. While EHF has been studied for some time, practical use of millimeter wave sensors for radio detection and ranging in automotive applications has only been in development since the turn of the century.
Millimeter waves propagate by line-of-sight paths with a narrow beam width. They allow for small antennas and have a high-frequency reuse potential. High reuse potential is possible as the narrowband and limited transmission distance allow for a higher concentration of transmitters in a geographical area than is possible at lower frequencies.
They were first investigated in the 1890s by Jagadish Chandra Bose, a Bengali-Indian scientist. He found this band to exhibit high atmospheric attenuation, which limited its use in the field of radar when it was first developed; however, as the field of remote sensing has evolved, the possibilities of millimeter wave sensing have been realized.
Modern millimeter wave-sensing technology avoids peak absorption wavelength, concentrating on bandwidths that exhibit much lower atmosphere attenuation. The effective range of measurement is approximately 250 m, but the emphasis in automotive applications has been on bandwidth availability, sensor size and performance advantages, and not so much on extended sensing range.
Manufacturers have been able to produce sensing technology with unprecedented accuracy that also exhibits little to no adverse effects from inclement weather and water vapor. Use of short-range vehicular radars (SRR) and long-range vehicular radars (LRR) that operate in the 76-81 GHz range helps avoid peak absorption of associated atmospheric gases and exhibits much lower atmospheric attenuation overall when compared to higher frequencies.
Short-range vehicular radar that operates in the 77-81 GHz range is set to take the stage as an industry standard. The increased bandwidth compared to LLR, which operates in the 76-77 GHz range, allows for unprecedented accuracy and is being used for a number of advanced driver assistance systems (ADAS) including blind spot detection, lane departure warning systems and collision avoidance sensors.
The 77-81GHz bandwidth is slightly greater than earlier millimeter wave sensors that were developed for LRR applications, such as adaptive cruise control that operates in the 76-77 GHz band. Collectively, both bands have enhanced the performance of vehicular radar. Each band dominates its respective field with superior measurement accuracy and reproducibility in adverse environmental conditions.
The industrial movement has shifted from the use of 24 GHz vehicular radar towards the use of millimeter wave sensors. The high reuse potential, improved performance and small footprint all help support the growing number of advanced safety features and autonomous driving technologies that are expected to flood the market in the coming years.
In 2004, the European Commission ruled in favor on the harmonization of radio spectrum in the 79 GHz range for the use of automotive short-range radar equipment. Several initiatives, including the Radar on Chip for Cars (RoCC) project and the 79 GHz coordination and support action, were launched and completed by 2014 to support the European 79 GHz frequency rules of the EC. The Federal Communications Commission (FCC) of the United States followed suit and global spectrum harmonization of LRRs at 76-77 GHz and SRRs at 78-81 GHz have been supported. With the support from United States, Brazil, China, India and the European Union, development of millimeter wave radar for automotive applications helps to reduce costs and encourage deployment of automotive radars in low-cost vehicles.
Key industrial manufacturers like Texas Instruments (TI) have come to the market with single-chip millimeter-wave (millimeter wave) sensors that exemplify the capabilities of millimeter wave technology sensors. Their millimeter wave sensors implement fast frequency modulated continuous waveform (FMCW), providing for robust operation, rapid sensing and reduced ambiguity in dense scenes. They are able to sense both range and velocity simultaneously and at greater accuracy than competing technologies.
The integration of radar system components in a single-chip package is a giant step towards reducing costs, streamlining production and supporting the 79 GHz initiative. The anticipated growth in ADAS along with an estimated 10 million fully autonomous vehicles on the road by 2020 have created demand, while innovative suppliers like TI have answered with single-chip automotive millimeter wave sensors.