help to calculate phase shift in certain frequency(identified from FFT) 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.
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.