Radar sensors make use of radio waves, or shorter wavelength microwaves, to determine the relative distance and position of an object to the sensor. RADAR stands for ‘radio detection and ranging’. As radar sensors can be robust, reliable and work in a variety of weather and light conditions, radar sensors have become a popular choice in many machine vision and automation applications.
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Radar Sensors: A History
Radar sensing relies on the principle of reflection of electromagnetic waves by surfaces. A very early patent from 1904 was filed for creating a system that could be used to detect ships in fog at distances up to 3 km.1 While the system lacked the range information of a full radar system, as the ‘radar sensor’ was simply a bell that rang with no timing information, it relied on the same operating principles as more sophisticated radar sensors.
One of the first recorded statements of a true radar system was made by Marconi in 1922.2 Marconi had already had a great deal of success in pioneering wireless technologies and proposed a scheme incorporating a radar transmitter and receiver (a radar sensor) that could be used to translocate an object.
Much of the underlying theory of wave reflection was already known, but he had the vision of using a timed system so that the radar sensor would also be able to calculate the distance information of the detected object.
The biggest accelerator of early radar sensor development was the outbreak of World War 2. Planes already had acoustic sensing to try and locate guns and defend against possible air attacks, but these techniques had many inadequacies.2 Radar sensors and systems meant pilots could now carry out missions at night and significantly improved target tracking systems.
While modern radar sensor development has perhaps slowed from the period during this World War, modern radar sensors development is now focusing on aspects such as a move to transmission and detection of higher frequencies to improve the spatial resolution in object recognition for gesture recognition and automation systems.3
What is a Radar Sensor?
A radar sensor is any device that can convert radio or microwaves into an electrical signal. Most radar sensors also incorporate a number of signal-processing electronics to process phase information about the detected waves that can be converted into information about object distance and angle. Recent developments have also made the construction and use of 2D radar sensors possible.4
Most radar sensors are made from semiconductor materials such as silicon germanium. Bipolar silicon germanium chips are being used to extend the sensor detection range to higher frequencies.5 A full radar sensor may have several layers of materials, including several protective layers to prevent damage to the chip and adhesives to hold the device together. There may also be thermally conductive materials to ensure the sensor can operate under a constant temperature.
How Does a Radar Sensor Work?
A radar sensor works on the detection of transmitted and reflected electromagnetic radiation. A timed electromagnetic pulse is sent to the object, and the time taken to receive the reflected signal is measured. As the speed of the transmitted radiation is known, this can be converted into a distance.
Radar can also be used to locate moving objects using the Doppler principle, where the radar sensor detects a frequency change with respect to the transmitted wave. This frequency change can then be converted into a velocity. Doppler radar sensors are at the heart of radar-based speed cameras and traps.
Where Are Radar Sensors Used?
The widespread appeal of radar sensors in many applications is their robustness, ability to be used in a variety of light levels, unfavorable weather conditions and low power draw. The latter has made radar a popular choice for machine vision applications on unmanned aerial vehicles (UAVs), where power consumption is a significant consideration.
Many detection and tracking systems for vehicles, whether land-based or aerospace, make use of radar sensors. Some earthquake detection devices are based on radar sensors and other remote sensing applications in the environment. Air traffic control and navigation systems both incorporate radar sensors.
Radar Sensors: Commercial Landscape
Recent developments in radar sensing include the availability of commercial 2D radar sensors and a widespread interest in radar sensors for machine vision applications.4 Automation and machine vision applications are proving to be one of the largest growth areas for radar sensors and their development.
Alongside LiDAR systems, radar sensors are a useful complement for autonomous vehicles to allow them to navigate in weather conditions or environments that LiDAR finds challenging.
Most demand for radar sensors remains in areas such as airplane navigation. However, airports are increasingly looking to invest in radar sensors to detect drones and enhance security. As developments in radar sensor technologies make higher resolving powers possible, radar will likely remain a popular and cost-effective sensing technology.
References and Further Reading
Hulsmeyer, C. (1904) Patent, https://commons.wikimedia.org/wiki/File:DE165546.pdf
James, R. J. (1989). A history of radar. IEEE Revview, 35(9), pp.343–349. https://doi.org/10.1049/ir:19890152
Antonucci, A., Corra, M., Ferrari, A., Fontanelli, D., Fusari, E., Macii, D., & Palopoli, L. (2019). Performance Analysis of a 60-GHz Radar for Indoor Positioning and Tracking. 2019 International Conference on Indoor Positioning and Indoor Navigation (IPIN), pp.1–7. doi.org/10.1109/IPIN.2019.8911764
Weber, C., Eggert, M., Rodrigo-Comino, J., & Udelhoven, T. (2022). Transforming 2D Radar Remote Sensor Information from a UAV into a 3D World-View. Remote Sensing, 14(7), p.1633. https://doi.org/10.3390/rs14071633
Agethen, R., Pourmousavi, M., Forstner, H. P., Wojnowski, M., Pressel, K., Weigel, R., Kissinger, D., Technologies, I., Campeon, A., Technologies, I., & Chipdesign, A. (2013). 60 GHz Industrial Radar Systems in Silicon-Germanium Technology. 2013 IEEE MTT-S International Microwave Symposium Digest (MTT), pp.1–3. doi.org/10.1109/MWSYM.2013.6697731