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Customers using our certified sensors do not need to test their equipment regarding to radio emissions in the K-Band.
There is no general rule for sensor selection. Each application has its own requirements. Please contact RFbeam to discuss the optimal solution for your specific needs.
K-band stands for the radio frequency range of 18...27GHz. A portion of this range from 24...24.250GHz is a so called ISM (Industrial, Science and Medical) radio band. RFbeam sensors use the ISM K-band. The ISM K-band allows operating our sensors in nearly all countries worldwide. For more details on ISM bands please refer to http://en.wikipedia.org/wiki/ISM_band.
Doppler Radar is used to detect moving objects and evaluate their velocity. A reflective moving object in sight of the sensor generates a low frequency sine wave at the sensor output, that is proportional to the object speed. The amplitude depends on the distance and the reflectivity of the moving objects. The output frequency is proportional to the object speed: 158Hz per m/s or 44Hz per km/h for a radial moving object. Some RFbeam sensors are “stereo” senors with 2 outputs, called I (In phase) and Q (Quadrature). These sensors allow detecting the moving direction (approaching, receding). For more details, please refer to the application note “AN01 Radar Sensor Basics”.
FMCW stands for Frequency Modulated Continuous Wave Radar. FMCW is used to detect distances (ranging) of stationary and moving objects.
This type of Radar uses a frequency modulated carrier. Typically, the carrier frequency is changed linearly by applying a sawtooth or a triangle waveform. At the output of the Radar transceiver we get low frequency signal called beat frequency. This is the result of mixing (=multiplying) transmitted and received frequencies.
Most RFbeam sensors have an analog FM input. Some types can also be modulated under digital control.
In K-Band (24GHz), maximum allowed frequency modulation depth is < 250MHz. We also have to take in account tolerances and temperature influences. This limits the usable frequency shift to typically 150MHz. This results in a resolution (and a minimum distance) of 1m.
FSK stands for Frequency Shift Keying. FSK allows distance measurements (ranging) of moving objects. FSK allows a better resolution than FMCW and uses less bandwidth. FSK uses switching between two discrete carrier frequencies fa and fb, while FMCW uses linear ramps.
This technique is based on the Doppler signals generated by reflective moving objects. Due to the very small step fa - fb a moving target will appear at the nearly the same Doppler frequency at both carriers, but with a different phase. This phase is proportional to the distance of the moving object.
For more Details, please refer to the application note “AN01 Radar Sensor Basics”.
Speed can be measured with so called Doppler sensors. These sensors deliver a low frequency sine wave that is proportional to the object speed. Nearly all RFbeam sensors allow measuring speed. For more details see question "What does Doppler sensor mean?"
This depends on the sensor output bandwidth and on the data processing bandwidth. Speed of a K-Band Doppler sensor is calculated by output frequency / 44Hz per km/h. Please refer to the data sheet (parameter IF frequency range) for the specific sensor.
K-MC1 high gain output bandwidth = 40Hz to 15kHz → speed range 1km/h to 340km/h
This is nearly the same task as measuring distances of objects. With FMCW, you may “learn” the environment (the “background”) without the object. If an object is in place, FMCW output will become different from the learned curve. For more details on FMCW see What is FMCW Radar?
For stationary objects, FMCW is the most used technology for distance measurement. Please refer to What is FMCW Radar?
For moving objects, most used technology is FSK. Please find more information in What is FSK?
RFbeam defines antenna pattern (also called beam width) as the angular width of beam, where the (Doppler) output signal amplitude drops to 50% (-6dB). K-LC1 example 80° x 35°: This is an asymmetrical beam. Sometimes, horizontal beam width is called azimuth, vertical beam width is called elevation. These expressions are misleading, because the sensor can be mounted in either direction.
Most RFbeam sensor antennas are so called patch antennas. Each single patch (rectangle) builds a small antenna. In a combination, they build an array, that focus the beam. The more patches, the narrower the beam:
The broader the antenna, the narrower the beam. Most RFbeam sensors have 2 antennas, one for transmitting and one for receiving signals. For transceivers, antenna pattern designates the resulting combination of transmitter and receiver characteristics. In this example, both antennas have the same characteristics.
RFbeam K-MCx sensors have a built-in RSW (Rapid Sleep Wakeup) that allows saving more than 90% of the full current consumption. Special considerations on pulsing and data acquisition are described in the corresponding data sheet. Current saving with K-LCx sensors may accomplished by pulsing the power supply. External sample & hold circuitry is needed. This technique allows saving of up to 99% of the normal current consumption. For more details, please refer to the application note “AN02 Noise and Pulsed Operation”.
Unlike other sensor technologies, Radar sensors may be completely hidden. Of course, the microwaves must be able to pass the cover with losses as low as possible. Therefore, metal covers are not appropriate! Radar antenna covers are also called Radom (derived from Radar Dome).
Every cover has some influence on the shape of detection field and the achievable maximum distance. Radar can „view“ through plastic and glass of any color. This makes a high degree of design freedom. Nevertheless, some rules should be considered.