# 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.

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
$$FT of exp(j2πf0t)x(t) = X(f−f0).$$