I obtained the IQ signal samples and stored each in a separate array, then I applied the following formula to obtain the phase difference delta_phase = arctan2(Q_samples(t)/I_samples(t)). Then what should I do to obtain the distance ?
The fs = 1953 Hz
The buffersize for storing the values = 64
The freq of the radar = 61 GHz.
The phase method of measuring distances is based on determining the phase difference between the sent and received modulated signals. In this case , the distance is calculated by the formula
R=φ*c/4*π*f,
where φ is the phase difference between the reference and the operating signal; f is the modulation frequency.
In the absence of modulation, you can measure distance within half a wavelength, with an ambiguity that is a multiple of half a wavelength.
Distance=(Wavelengtn/2)*((Phase/360o)+n); n=0,1,2,3,...
In your case Wavelengtn=c/f=300mm/61GHz=4.9mm.
You need to use FM, for example
Vladimir Kubov thank you for your answer. I actually did exactly what you mentioned, but as I plot the distance against time and moving my hands back and forth against the radar, the distance keeps on fluctuating between certain numbers in my case was 0.34 and 0.36mm which is also give me another questiom that I didn't change the units I left it as it is when I calculated the distance based on the formula that you've mentioned. Should I expect that the distance keeps on changing and once I get close to the radar the distance goes to zero or Im missing something. Again thank you for your answer.
The spatial period of standing waves for a frequency of 61GHz is about 2.46mm. And it is impossible to obtain smaller periods - this is the so-called diffraction limit of spatial resolution.
I wonder how you can get spatial fluctuations with a scale of 0.34-0.36mm. Perhaps these are not spatial, but temporal fluctuations.
What sensor and what measurement scheme are you using?
The phase difference method of measuring phase is subject to two major limitations that render it impractical in most cases.
1 It is subject to 2*pi ambiguity for every wavelength of propagation i.e. every half-wavelength of range and,
2 It can only give an indication if there is only one target present. If these is more than one target, including any mis-match reflections from the antenna not previously corrected for, then the phase shift does not relate to the range of either target.
One has to use some form of frequency or phase modulation to recover range in CW radars.
CW radars can, however, measure relative velocity. By integrating the relative velocity you can obtain the difference in range over the duration of your measurement. By knowing the initial range (from some other sensor), you can then deduce range at any time afterwards.
Best regards,
Clive Alabaster
Clive Alabaster
thank you for your answer. The thing Is that I only want to use the CW radar to do everything without using other sensors. For obtaining the velocity I need the doppler freq shift, but all I got is the freq of the rada which is 61GHz and the obtained I Q signal from the ADC after being sampled. Is there any idea how then to obtain the relative velocity ?
Vladimir Kubov
the sensor that Im using is the infineon BGT60LTRAIP radar sensor which has a range up to 7m and an open angle for the Antenna with a 12 degree value.
Look at the theory of operation of continuous-wave radar
https://en.wikipedia.org/wiki/Continuous-wave_radar
You can use two methods:
1- measure the frequency of signal change by one of the quadratures (I or Q). It's just the Doppler frequency.
2 - measure the rate of phase change (dPhi/dt=360o/TDoppler). The time it takes for the phase to change 360 degrees corresponds to the period of the Doppler frequency (FDoppler=1/TDoppler).
Seif, you obtain the relative velocity from the Doppler shift, however, your best strategy is the use FM or phase modulation to measure range.
- Badges
- Science topic
- Similar topics
- Philosophy
- Esthetics
- Interpretation