I am currently working of 24GHz FMCW radar signal processing. The Module I'm using has 2 receiving antennas and each has 2 outputs (I and Q channel). So overall I've 4 channels. I'm using combination of harware and software for the processing in frequency domain. Range and velocity is fine, if I sample any one channel out of those 4 (either I or Q) I can find the R and V values.

Now I'm interested in finding the direction of a object, when it is moving (away from sensor or towards sensor) and the position of the object (right of the sensor or left or the senor, at the best the horizontal angle).

In the datasheet of the radar sensor I read 2 lines in the features, that gives me some idea in finding the direction and location. Below are the lines:

  1. "two receiving antenna for phase comperision operation"
  2. "I/Q channels for direction of motion discrimination"

Now I'm thinking how to find out the position or the horizontal angle of the target using phase comperision of the 2 antennas. Below is the diagram I made for analysis.

enter image description here

Surely the 2 antennas receives reflection from a single target with a phase shift. Now the question is how to I find the phase shift processing the I channel (let's say) from the 2 antennas. I'm not aware of any DSP technique, so want suggestions.

Also the direction of motion, what technique can be ised with the I and Q channel of a antenna to deduce it. I'm again on poor dsp knowledge, how do I process the I and Q channel.

I appreciate any suggestion of improve my knowledge and know about more dsp techniques in signal analysis.


The way to do it is to correlate the received signal with the signal you sent out- likely a chirp or something. You correlate it with the signal from antenna 1, which will give you a time (location of the cross correlation peak) and phase (phase of the complex value of the peak). You do the same with the signal from antenna 2, getting a time and phase. If all is right the time should be the same (or, depending on your time resolution, very, very close). The phase difference is simply the difference of the phases of the cross correlation peaks from the two antennas.

  • $\begingroup$ The output of the Radar Frontend is the Intermediate Frequency, and I have the only choice to do the processing on the IF signal (25 Hz - 61 kHz) and there is no possibility to correlate with the sending signal. $\endgroup$ – dDebug Jun 17 '15 at 9:23
  • $\begingroup$ That is a minor detail. The point is to correlate the received signals with what you expect to get, so modulate the transmitted signal to the carrier frequency that you expect to receive. You will, of course, have to be able to deal with doppler offsets. $\endgroup$ – Jim Clay Jun 17 '15 at 14:02

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