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TIDEP-01012: Grating lobes when using Cascade radar in beam steering configuration

David Smith12
Prodigy 70 points
Part Number: TIDEP-01012

Hello,

I have two questions, first, I have been examining this document. https://www.ti.com/lit/ug/tiduen5a/tiduen5a.pdf?ts=1620076694074&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FAWR2243, specifically, these figures on page 27.

These images appear to show the presence of significant grating lobes when steering the beam to an angle of 15 degrees off boresight. My question is in regards to data processing, is there a mechanism by which these grating lobes are excluded when calculating the range angle plots? The provided beamsteering example code appears to simply sum all the Rx returns together, would this not create ambiguity about the arrival angles?

Two, I have attempted to reproduce the plots shown above using an Ansys HFSS simulation of the radar system, these results are:

This plot shows four lobes, similar to that of the reference document. However, the peaks in the Ansys simulation are split, and I am wondering what the cause might be?

I look forward to your response.

Thank you.

  • 0
    TI__Guru*** 141284 points

    Hi,

    Please give us some time to check with systems team.

    Thank you

    Cesar

  • +1 in reply to Cesar
    TI__Guru*** 141284 points

    Hi,

    Here is the response from systems team

    • The grating lobes are expected during TX beamforming as the spacing between the TX channels is 2*lambda. The impact of the grating lobes can be suppressed by RX beamforming. Please look at the function “Plot_advFraConfig_TXBF_rangeAzimuth_stich.m” which is doing RX beamforming. This function is in“<mmWaveStudioInstallDirectory>\mmWaveStudio\MatlabExamples\4chip_cascade_TxBF_example\PostProc”

    Thank you

    Cesar

  • 0 in reply to Cesar
    Prodigy 70 points

    Hi Cesar,

    Thank you for the response. I have examined the file you suggested. Could you please clarify for me what the D_RX and d variables represent in the equation: a1_az = exp(1*j*2*pi*d*(D_RX*wx));

    Thank you.

  • 0 in reply to David Smith12
    TI__Guru*** 141284 points

    I am checking with the systems team

    thank you

    Cesar

  • +1 in reply to Cesar
    TI__Guru*** 141284 points

    Hi,

    Here is the response from systems team:

    D_RX is the positions of the RX channels on the 4-chip cascade EVM (defined in “module_param.m”)

    d is the spacing between the RX channels in units of lambda. It is defined as

    d = 0.5*centerFrequency/TI_Cascade_Antenna_DesignFreq; 

    where the centerFrequency would be dependent on the chirp configuration used

    while TI_Cascade_Antenna_DesignFreq = 76.8

    Thank you

    Cesar