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Can I simply increase the distance of antennas to improve the angle resolution?

Jun Fang
Prodigy 170 points

Hi,

In angle estimation of mmWave radar, Angle resolution is inversely proportional to the length of TX antennas, which is defined by number N of antennas and their distance d. I find that current document usually assume that the distance d is fixed, and increase N to improve angle resolution. I am wondering if I can increase d to achieve it.

For example, a device with four RX antennas (d = 0.5mm) has an angle resolution of about 30 degree. If I let d = 10mm, then I have an angle resolution of 1.5 degree? Compare with increase of N, this method can avoid the computation problem, so it looks like a better solution if we have enough space. Is there something wrong? or Are there some additional restrictions for the distance d?

Thanks.

  • 0
    TI__Genius 16540 points

    Hello,

    Thank you for reaching out to Texas Instruments. Increasing the inter-element distance by more than 0.5λ does seem like a good option to increase angular resolution, but this comes with a major tradeoff. This increase would narrow the main lobe (narrower HPBW) and introduce several side lobes almost equal in size to the main lobe. Based on these effects, 0.5λ is observed to be the perfect spacing. 

    Hope this helps,

    -Shareef

  • +1
    TI__Expert 8275 points

    Hi,

       We have tested for 'd', distance between the antenna as large as lambda/2. If you keep on increasing the d between antenna, at some point aliasing might happen in the antenna domain. Please note that FOV also reduces if you keep on increasing 'd'. So it is advisable to use d to be as long as lambda/2.

      Let me know if you have any questions

    Thanks and Regards,

    Akshay 

  • 0 in reply to E. Shareef
    Prodigy 170 points
    Hi,Thanks for your reply. 
    I made a typos in the question, the d is the distance of RX antennas instead of TX antennas.
    For your reply,  I know side lobe effect exist in TX antenna, does it exist in RX antenna as well?
    Furthermore, as I know, the side lobe decrease the directivity and radiation intensity of the antenna, so the detection distance becomes shorter. If I can accept shorter detection distance, such as decrease from 100m to 20m, can I enlarge antenna distance d to improve the angle resolution? Is there any other negative effect except for shorter detection distance?
    Thanks.
  • 0 in reply to Akshay Kumar Chandrasekaran
    Prodigy 170 points

    Hi,

    Thanks for your reply. I made a typos in the question, the d is the distance of RX antennas instead of TX antennas.

    Could you give me more information about the aliasing and FOV reduction when increasing distance of RX antennas. Thanks.