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Near field correction

Kishor KS10
Prodigy 60 points

Hi,

In Near filed correction doc [ti/mmwave_sdk_01_02_00_05/packages/ti/demo/xwr16xx/mmw/docs/doxygen/html/index.html],

For r = 5cm and theta = 0 degree, Correction phase mentioned in Doc is 177.8 degree. But I am getting 158.22 degree.

For calculation of phase correction, I considered lamda = c/fc, c = 3*10^8 m/s, fc = 77*10^9 Hz.

Can anyone please verify this.

Regards,

Kishor KS

  • 0
    TI__Guru*** 149104 points
    Hi

    Can you please provide details of your computation?

    thank you
    Cesar
  • 0 in reply to Cesar
    TI__Expert 7215 points
    Hi Kishor,

    Looks like your estimation is correct for theta = 0 and r = 5. Let me check why there is discrepancy in estimated result and the table.

    Regards,
    Kaushal
  • 0
    TI__Expert 5235 points

    Yes your calculation is correct, we will correct the table entries in future release, thanks.

  • 0 in reply to Piyush_
    TI__Expert 5235 points
    FYI, the current table entries were based on boresight (point B in the picture) choice of 2*lambda whereas the code and the picture shows B at lambda. So it is a mismatch between code and document, and the document will be fixed as I mentioned. The choice of boresight is somwhat arbitrary because in TDM-MIMO, each tx antenna is transmitting separately in time so there is no one right choice. User can change this position in the code (and rebuild) as indicated below (in file dss_data_path.c):

    /* B can be changed to position the desired reference (boresight) in the geometry */
    #define MMWDEMO_NEAR_FIELD_B (MMWDEMO_XWR16XX_EVM_77GHZ_LAMBDA) //((((2 + 0.75) * MMWDEMO_XWR16XX_EVM_77GHZ_LAMBDA)) + 8.7)

    Boresight is the direction of max gain so when Tx1 is transmitting, it is the direction of tx1 and when tx2 is transmitting, it is tx2 but because we are alternating, one might consider the middle of the two as the boresight. So it is a matter of reference, but it does not affect much the end objective of doing near field correction.