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AWR1642BOOST: Reflection of High RCS object at the other end of Range

Santhana Raj
Expert 1765 points
Part Number: AWR1642BOOST
Other Parts Discussed in Thread: AWR1642

Hi,

I am facing a specific problem with data capture & analysis using AWR1642. The scenario has a high RCS Corner Reflector at around 1.5m (10th bin in Range FFT). This is identified as a very large peak at the same distance after taking Range FFT. My problem is, There is a small reflection at the higher range also. Considering that I have 256 range bins, I see a small peak in the FFT result at 245th bin (255-10). This reflected peak does move when I move my Corner reflector.

I call it as small peak because the amplitude value is very small compared to the Corner reflector but considering its surrounding area, the peak is significant and gets detected at CFAR.

The peak disappears when the Corner reflector is moved away from the sensor by more than 3m. As long as the reflector is within 3m, the corresponding (255-actual bin distance)th bin has a peak.

This problem is seen in the ADC dump captured using AWR1642EVM on analyzing it in Matlab.

I would like to know the reason for this reflection of high RCS object. And Any solution to avoid this.

Thanks in Advance

Santhana Raj

  • 0
    TI__Guru*** 147994 points
    Hi,

    Is this possible that this is a ghost image?

    Thank you
    Cesar
  • 0 in reply to Cesar
    Expert 1765 points

    Hi Cesar,

    I don't think so. Because

    1. The distance to this reflected image comes closer to the sensor when my actual Corner reflector is moving away.

    2. Sometimes we see Ghost object for this Corner reflector at almost double the distance.  For ex, the object at 1.5m, the ghost appears at 3-4m. And this ghost moves farther when the Corner reflector moves farther. We believe this ghost at 3-4m, is due to multi path reflection. And we are able to handle this in our use case. Evidently the reflection problem I am talking about happens at around 37m.

    3. This reflection problem is present in all environment that we have tested.

    Thanks in advance,

    Santhana Raj

  • 0 in reply to Santhana Raj
    TI__Guru 58035 points
    Hello Santhana,
    With a strong RCS corner reflector you will see the harmonics of the object because the signal reflected from the corner reflector might get reflected back and so on. So for the a 1.5m distance you might see small peaks at 3m, 4.5m. If you just tilt the corner reflector slightly it would reduce the multiple reflections.

    Regarding the other issue of small peak at 37m, can you provide more information on this? You mentioned this peak also moves with the object distance. Could you list the measurements you have done with different distances? At each distance of the corner reflect what is the distance at which the peak is observed? Can you share some plots with us?

    Regards,
    Vivek
  • 0 in reply to Vivek Dham
    Expert 1765 points

    Hi Vivek,

    Thank you for the explanation.

    I completely understand the multi-path object reflection. And as explained in my earlier reply, I am pretty sure that this issue is not because of multi path reflection.

    To be clear, I have only one issue, when a High RCS object at closer distance like 1.2m, I am able to see a small reflection at the farther most end.

    Object Position          X bin             1.5m        10th bin       1.8m      

    Extra reflection          256-X bin      37.5m      246th bin       37.2m

    where, the no of samples per chirp as 256, and the maximum 39m.

    Hope I am clear on my explanation. Please  let me now if any more details is required.

    Looking forward to your response.Thanks in advance,

    Santhana Raj

  • 0 in reply to Santhana Raj
    TI__Guru 58035 points
    Hello santhana,
    Are you using the complex1X mode? In this mode the usable bandwidth is 0.9Fs. After that there could be some small foldback of the image band. ie you need to consider only bins upto bin 230.

    Regards,
    Vivek
  • 0 in reply to Vivek Dham
    Expert 1765 points

    Hi Vivek,

    Thanks for  the explanation.

    I understand that only 0.9Fs is the usable Bandwidth. But I am not clear how there is a foldback of image  band. Can you provide me some document or explain me this phenomenon.

    Thanks & Regards,

    Santhana Raj

  • 0 in reply to Santhana Raj
    TI__Guru 58035 points
    Hello Santhana,
    There will be an aliasing from the image band and filtering on the image band very close to the DC is limited .

    Regards,
    Vivek