I am designing a 24ghz doppler radar, with 1TX 2RX. Four adc channel are recording at 25khz, applying 256point FFT on adc of both of RX I and Q, I could identify the target in certain doppler frequency(speed) . The next step is to calculate the phase shift to get the angle of the target, that's where I stuck. Since I locate the target on FFT, how to trace it back to the time domain and calculate the phase shift between the different RXs. Any input will be very welcomed. I am a computer engineer with limited knowledge of dsp though, but facinated about radar.
Since you are able to trace the target back in FFT, no need to trace it back to time domain. What does the phase information of the FFTs say?
The signal incident at antenna 2 $y_2$ has traversed distance $L$ more than signal incident on antenna 1 $y_1$. Due to the difference in distance traversed, the phase difference between $y_2$ and $y_1$ is $2\pi L/\lambda$, where $L = d/\cos(\theta)$. Here $\theta$ is the angle of arrival. If you could give info on what info you found in phase would be great. Also see these tutorials : https://training.ti.com/node/1139153
Phase shift in time domain translates to frequency shift in the Fourier transform.
$FT of exp(j2πf0t)x(t) = X(f−f0).$
If there is a phase shift in time, the Fourier transform that you take is already shifted in frequency. Find the shift in frequency f0 and you should get the phase change.