Definition Radar
Radar is short for Radio detection and ranging and stands for a contactless sensor technology to detect moving and static objects. A radar emits an electromagnetic wave in the microwave range, which is reflected by objects in the field of view. The reflected waves are then received and processed by the radar. There are different types of radar, which mainly differ in the modulation of the transmitted high-frequency signal.
Comprehensive data per object
Depending on the type, a radar can measure speed, direction of movement, distance and angle in up to two dimensions per object.
3D measurement
A radar can measure data in multiple dimensions. Based on the modulation used and the antenna arrangement, it is even possible to generate a 3D point cloud of its surroundings.
Anonymous
Radar is completely anonymous and does not take pictures like a camera. Thus, the technology can also be used in environments where privacy is important.
Environmental robustness
Radar doesn’t care if it’s day or night. Furthermore, the measured values are independent of temperature fluctuations and environmental influences such as humidity, fog, rain or even snow. Radar is therefore perfectly suited for harsh environments.
Material penetration
Radar sensors can see through a variety of materials including plastics. Compared to optical systems, a radar can be hidden directly in the product case without the need for an optical lens, which gives more flexibility in product design.
Radar in comparison to other technologies
There are different sensor technologies to detect objects, each with its
advantages and disadvantages. Compared to other technologies, radar is
a very flexible and robust technology with a lot of design freedom.
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Technology vs. Feature
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Radar
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Infrared
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Ultrasonic
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TOF
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Laser/Lidar
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Camera
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Detection range
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High
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Low
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Low
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Low
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Medium
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Low
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Range Accuracy
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High
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Low
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High
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High
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High
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Medium
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Angle Accuracy
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Medium
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Low
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Low
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Low
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High
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High
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Object separation
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High
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Low
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High
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High
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High
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High
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Environmental robustness
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High
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Low
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Low
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Medium
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Medium
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Low
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Material penetration
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High
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Low
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Low
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Low
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Low
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Low
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Design flexibility
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High
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Low
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Medium
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Medium
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Medium
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Low
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Cost
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Medium
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Low
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Low
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Medium
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High
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Low
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Radar parameters
Radar sensors are available in different versions and price ranges to cover different applications. Basically, the sensors can be distinguished by the following parameters:
There are three common types of radar modulation (CW, FSK, and FMCW) that differ primarily in the data that can be measured. Continuous Wave (CW) is the simplest and isn‘t really a modulation as it works at a fixed frequency, while Frequency Shift Keying (FSK) uses square wave modulation to jump between two frequencies. Frequency Modulated Continuous Wave (FMCW) works with continuous frequency sweeps and a triangle or sawtooth modulation over a defined bandwidth. Modern radars are able to generate fast FMCW triangle chirps what gives the option to create a range Doppler map for better object separation and further processing.
The following table provides an overview of the various modulations and possible measurements:
Frequency band
The emission of electromagnetic waves is regulated by national authorities like CEPT for Europe or FCC for the USA and international associations like the ITU. There are different frequency bands available for different applications in the range of 10 to 120 GHz.
There are global and regional efforts to harmonize frequency bands for worldwide use. There are so called ISM bands which can be used license free in industrial, science and medical applications which
mainly differ in the usable bandwidth. Two interesting ISM bands for radar are at 24 or 61 GHz, whichare used by RFbeam for their standard sensors.
The two bands differ mainly in the usable bandwidth and the maximum detection distance. 61 GHz allows a higher bandwidth to be used compared to 24 GHz, resulting in better range resolution when using FMCW modulation. On the other hand, 24 GHz allows a higher detection range due to less attenuation in the air.
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Measurement vs. modulation
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CW
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FSK
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FMCW sawtooth
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FMCW triangle
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FMCW fast chirp
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Velocity (Speed and direction)
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Distance of moving objects
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Distance of static objects
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Antenna pattern
The antenna pattern defines the area covered by a radar. A narrower beam width has the advantage of longer detection distances and the ability to focus on an area of interest. A wider beam is better suited to cover a large area with one sensor, at the expense of shorter detection distances.
Number of antennas
Simple radar devices work with a transmitting (TX) and a receiving antenna (RX) in combination with one of the modulations mentioned above. By using two RX antennas it is possible to measure the angle of arrival of an object horizontally or vertically. More complex radar sensors use multiple TX and RX antennas to create so called virtual antenna arrays by the use of MIMO technology. This has the advantage that, in addition to measuring the angle, it is also possible to separate objects via the angle.
Object Separation
A radar can separate objects from each other based on modulation and number of antennas. An FSK radar for example can measure the velocity and distance of moving objects but a separation is only possible by velocity. This means that it is not possible to separate objects with the same speed and direction.
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Separation vs. modulation
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CW
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FSK
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FMCW sawtooth
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FMCW triangle
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FMCW fast chirp
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Velocity (Speed and direction)
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Distance of moving objects
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Distance of static objects
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Further it is possible to separate objects also via angle. The more but here a minimum of 4 antennas per axis is needed. With 2 antennas it is possible to measure the angle and with 4 antennas it is already possible to separate objects measure the angle of an object with two RX antennas but it is not possible to separate the objects via angle. To separate objects via angle a minimum of 4 antennas per axis is needed
