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dyang
Level 1
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5 sign-ins First reply posted First like given

Hello,

I have a question regarding the range measurement capability of the BGT60TR13C Radar Sensor.

When I measure the distance of a target to the radar sensor, the results show that the absolute error in millimeters becomes smaller with increasing distance. The measurement has been done with a custom MATLAB script using the provided MATLAB Wrappers and the Radar Fusion GUI for comparison (see image below). Both show a decline of the absolute error as mentioned above.

Screenshot 2023-01-27 085922.png

The measurement is done in the range from 100mm up to 1500mm using a 30mm x 30mm target (other targets show approximately the same results). The target itself can move along the axis towards/away from the radar sensor on the measuring track (the target is static during data acquisition and only moves to a new position after the data acquisition has been completed). The results in the picture above depict the distance measurement of the static target each 100mm, resulting in 15 static measurements total.

Below are the numerical values corresponding to the graph above:

Screenshot 2023-01-27 093519.png

For the measurement, the following device configuration has been set in the Radar Fusion GUI and MATLAB as well:

JSON Configuration saved from Radar Fusion GUI:

Screenshot 2023-01-27 094418.png

 

 

 

 

 

 

Radar Fusion GUI configuration for reference:

Screenshot 2023-01-27 092657.png

 

 

 

 

 

 

The frequency spectrum setting in the Radar Fusion GUI are default (Optimal FFT Size and Blackman Harris windowing function).

Q: Is there a reason as to why the precision of the measurement seems to improve with larger distances?

I was expecting a somewhat constant absolute error across the measurement range or at least an increase of the absolute error with larger distance.

Sincerely,

dyang

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1 Solution
Deepa_V
Moderator
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Moderator
50 likes received 250 replies posted 5 likes given

Hi @dyang ,

Another possibility for your observation could be that there is the leakage (TX-RX coupling) at low frequencies which will influence target amplitudes (DC FFT bins are leaking into the target bins). Then the peak-search will not work properly. That's normal with a simple FFT-peak search. But since the reason for your observation has not been previously analyzed at our end, please note that this is just a possibility. But one clarification, we see no relation between the sampling delay and the deviation of absolute error that you stated. 

Best Regards,

Deepa

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4 Replies
Deepa_V
Moderator
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50 likes received 250 replies posted 5 likes given

Hi @dyang ,

There is a high pass filter in the baseband, and your chosen cutoff frequency is 80kHz. If the HPF has a non-linear phase response, it will add further delay especially in the rolling up slope of the filter, hence introduce the distance measurement error. And as with the larger distance, the IF frequency will be higher, more will fall into the pass-band of the filter.

Hope this helps ! 

Best Regards,

Deepa

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dyang
Level 1
Level 1
5 sign-ins First reply posted First like given

Hello @Deepa_V 

Thanks for the reply, I will try some reconfiguration to see if the HPF impacts the measurements and get back to you.

Best regards,

dyang

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dyang
Level 1
Level 1
5 sign-ins First reply posted First like given

Hello @Deepa_V 

I have considered the aforementioned HPF and changed the configuration to 20kHz to see if any significant changes occur. Every other configuration remains the same as mentioned in the first post.
In the graphic below you'll find the updated results for the measurements of the HPF with 80kHz and 20kHz.
Screenshot 2023-02-02 093453.png

Screenshot 2023-02-02 094355.png

 

It appears that the absolute error overall remains the same, or at least the trend line of it, with minor differences at certain points.
My impression was that the HPF should not affect the measurement results if it is located in the baseband compared to when it is placed before/outside the baseband, which should have more of an impact.

 

My assumption is that the reason for the deviation of the absolute error lies in the use of the total bandwidth (f_tx_start to f_tx_end) for sampling, instead of the bandwidth from f_adc_start to f_adc_end  since the adc samples values between adc_start and adc_end (image below for reference). Therefore my guess is that the measurement error has to do with the "sampling delay" (f_tx_start to f_adc_start).

Screenshot 2023-01-20 125832.png

 

Q: Can you verify if my assumption is correct or if I am missing/misinterpreting something else?

 

Best regards

dyang

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Deepa_V
Moderator
Moderator
Moderator
50 likes received 250 replies posted 5 likes given

Hi @dyang ,

Another possibility for your observation could be that there is the leakage (TX-RX coupling) at low frequencies which will influence target amplitudes (DC FFT bins are leaking into the target bins). Then the peak-search will not work properly. That's normal with a simple FFT-peak search. But since the reason for your observation has not been previously analyzed at our end, please note that this is just a possibility. But one clarification, we see no relation between the sampling delay and the deviation of absolute error that you stated. 

Best Regards,

Deepa

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