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MMWCAS-RF-EVM: Far Field in TDM MIMO Mode

Malte Müller
Prodigy 40 points
Part Number: MMWCAS-RF-EVM

Hello,

I'm wondering how I'm correctly calculate the distance to far field in TDM MIMO Mode. Do I consider a single antenna patch as aperture since there is only one TX-antenna active at time or

do I have to consider the whole 86 virtual antennas?

1. Single Antenna: 

      D = ca. 4 mm

      Rff = 2 * D ^ 2/lambda = ca. 8 mm

2. Whole virtual antenna array:

     D = 85 * lambda/2 = 165 mm

      Rff = 2 * D ^ 2/lambda = ca. 13 m

Second Question: Are there any known drawbacks working in near field with this evaluation board?

 Thanks,

M. Mueller

  • 0
    TI__Guru*** 148804 points

    Hi,

    We don't have any experience working with this board at a few cm distance. Our use case for cascade device is longer ranges: >50m.

    Let me check with systems team how the near field range should be computed

    Thank you

    cesar

  • +1
    TI__Intellectual 790 points

    Hello Mueller.

    The far field should be computed based on the total aperture size in the MIMO system. In other words, when you use the entire 86 channels in your angle estimation blocks, the far field should be computed according to the  D = 85 * lambda/2.

    Using the far-field algorithms (assuming planar waves) in near-field imaging will result in degraded imaging quality and wrong angle estimations imposed by the spherical nature of the actual signal.

    Yo can refer to the following paper for near-field imaging concepts/artifacts/algorithms when using the 4-chip cascade board:

    https://ieeexplore.ieee.org/document/9136646

    Regards.

    Muhammet