Available Radar Modules

Doppler Radar Modules for speed detection
Doppler Radar modules are emitting microwaves at 24.125 GHz. If the radiation is reflected at a moving object, the reflected radiation shows a slightly different frequency compared to the incident radiation. The patch antenna of the module collects the reflected radiation and the antenne signal is mixed with the original frequency in a mixer unit. The output IF of the mixing unit is an AC signal with a frequency which is the difference of the emitting and reflecting radar frequencies. This frequency is a measure of the velocity of the moving object. Calculating this frequency for a moving object could be easily found that it is 44Hz for an object speed of 1 km/h and is grown linearly with the speed of the object (only valid for moving direction parallel to a line between radar source and object. Otherwise a factor cos a has to be taken into account).
For typical velocities of the reflecting object (human beings or cars) this frequency is below 10 kHz. The frequency spectrum of IF could be evaluated by a Fast Fourier Transformation (digital evaluation) or with analog technics by counting the number of zero-crossings of the IF signal.
Our K-LC3 Radar module is suitable for simple movement detectors without direction detection.

Doppler Radar Modules with direction detection
It is possible to use two mixer units in one doppler radar sensor module which are shifted by 90°. Comparing the phase shift of both outputs IF and Q, allows to decide whether the object is approaching or departing relative to the sensor. The speed of the object can also be determined by measuring the frequency of the outputs IF or Q.
Our K-LC2 Radar module is suitable for simple movement detectors with direction detection.

FM-Radar Modules for distance measurements
Two different methods of detecting the distance of objects with radar can be applied to our K-LC1:
FMCW-methode
Using the so-called Frequency-Modulated-Continuous-Wave-method (FMCW) radar modules can be used for detecting the distance to stationary targets. In those modules the frequency of the emitting microwave radiation is not constant, but changed periodically e.g. like a saw-tooth- or tringular pattern (driven by the FM-input). Regulated by law, the maximum allowed modulation range is 250 MHz in the K-band. The emitted radiation needs some time to reach the target and to be reflected back to th radar sensor. Since the object is stationary there is no frequency-shift after the reflection. When the reflected radiation reaches then radar module the emitting frewuency has changed in the meantime due to the saw-tooth-pattern of the frequency modulation. Mixing both frequencies in the mixing unit will result in a different frequency at the output IF. For a saw-tooth modulation the distance of the object is a linear function of the differential frequency. Using this method, the minimum detectable distance and resolution at 24 GHz is about 2-3m. Signal processing of FMCW is typically accompolished by FFT algorithms and requires relatively powerful processors.
FSK-methode
FSK (Frequency Shift Keying) is a method to detect distances of moving objects with high resolution. As opposed to FMCW, FSK works by switching between two frequencies with a very small frequency shift (10 MHz as an example). The smaller the FM amplitude, the higher the detecable unambiguous distance. FSK is not usable for static objects however. Frequency shifting is generated by a rectangular signal with a frequency of some kHz at the FM input. The IF output is sampled synchronous with the FM signal. This results for moving objects in two Doppler signals with very similar frequency, but with a different phase. Distance is derived from the phase difference between the two Doppler signals. Resolution depends mainly on signal processing and noise conditions. With a K-LC1 sensor and a maximuin distance of 12m, a resolution of 10cm and better is achievable. FSK is simpler regarding the hardware requirements, but requires more computing powr than FMCW.