What is the theory behind the Max Relative Velocity?
Along with the distance, the relative velocity of the object is another critical parameter of interest. The maximum measurable velocity in Fast FMCW modulated radars depends on the chirp cycle time – that is, the time difference between the start of two consecutive chirps. This in turn depends on how fast the frequency sweep can be performed and the minimum inter-chirp time allowed.
The faster the mmWave device can ramp the frequency, the higher the maximum unambiguous velocity. TI’s mmWave device allows a fast ramp of 100 MHz/µs. Also the closed loop PLL is designed to support a very fast settling of the frequency ramp. Hence, the time taken for the VCO to jump from the end of the ramp frequency to restart the next ramp is very low and allows for a smaller idle time (as low as 2 µsec).
Unambiguous max velocity = ƛ/4Tc
Tc →Total Chirp time ,which inlcudes chirp time+idle time
ƛ→Wavelength of the signal used
The actual measurable max velocity can be extended beyond the unambiguous max velocity using higher level algorithm.
You can determine the chirp parameters using the mmWave Sensing Estimator tool. This tool will allow you to try various different configurations and tell you whether or not these configurations are valid. If a configuration is not valid, the tool will tell you what needs to be changed in order to have a valid configuration.
