IWR6843ISK: The changing rangeFFT in a static environment when use IWR 6843ISK+ DCA1000evm

Tool/software:

Hi Team,

I put a strong reflector in a static environment, and I am using IWR6843ISK + DCA1000evm to get the raw ADC data. During the experiment, I captured more than 1500 frames, and did Range FFT for the raw data. The strongest peak is indeed by the corner reflector is static, but it looks like the range bins from the environment are not static. However, I am pretty sure that nothing was moved during the measurements in the FoV of the radar. 

So I have some questions,

1. It is normal to expect something like this? I changed the frame time to longer (longer interframe time), but still the time-varied behavior is there.

2. Is there any solution to solve the problem? It will be more difficult for us to understand the static environment since the Range FFT is changing with time.

The configuration for the chirp and frame is followed.

"rlProfiles": [
{
"rlProfileCfg_t": {
"profileId": 0,
"pfVcoSelect": "0x2",
"pfCalLutUpdate": "0x0",
"startFreqConst_GHz": 60.0,
"idleTimeConst_usec": 5.0,
"adcStartTimeConst_usec": 3.0,
"rampEndTime_usec": 20.0,
"txOutPowerBackoffCode": "0x0",
"txPhaseShifter": "0x0",
"freqSlopeConst_MHz_usec": 50.0,
"txStartTime_usec": 0.0,
"numAdcSamples": 212,
"digOutSampleRate": 12500,
"hpfCornerFreq1": 0,
"hpfCornerFreq2": 0,
"rxGain_dB": "0x1E"
}
}
],
"rlChirps": [
{
"rlChirpCfg_t": {
"chirpStartIdx": 0,
"chirpEndIdx": 0,
"profileId": 0,
"startFreqVar_MHz": 0.0,
"freqSlopeVar_KHz_usec": 0.0,
"idleTimeVar_usec": 0.0,
"adcStartTimeVar_usec": 0.0,
"txEnable": "0x1"
}
}}



"rlFrameCfg_t": {
"chirpEndIdx": 1,
"chirpStartIdx": 0,
"numLoops": 222,
"numFrames": 0,
"framePeriodicity_msec": 11.888,
"triggerSelect": 1,
"numDummyChirpsAtEnd": 0,
"frameTriggerDelay": 0.0}

So this is the range FFT of different frames. 

And if I zoom in to check other peaks than the strongest peak, you can see that the areas that are circled are becoming different when the frame number is increasing.

Best,

Bei