Doppler radar phase shift sign convention

1. What is Doppler phase shift?
2. Can Doppler shift be negative?
3. How is Doppler shift measured?
4. What is Doppler FFT?

What is Doppler phase shift?

With the "Doppler shift", the sound pitch of an object moving toward your location is higher due to compression (a change in the phase) of sound waves. As an object moves away from your location, sound waves are stretched resulting in a lower frequency.

Can Doppler shift be negative?

Notice that the Doppler shift is negative when the object is moving away (opening range) from the radar and is positive when the object is moving toward the radar (closing range).

How is Doppler shift measured?

The Doppler shift can be determined after performing the range Fourier transform (range FFT) first. For a target of interest, we can repeat the range FFT until we have enough data to perform the second level of FFT.

What is Doppler FFT?

FFT Plot (Range-Doppler Plot): The FFT is used to convert radar time domain data to frequency domain. Detected objects and their Doppler signature are plotted in an FFT Plot. The x-axis represents the Doppler Frequency (which can be converted to Doppler Speed), and the y-axis is range.