Radar sensor - BGT24MTR11 - difference between I and Q signals

[Ali_Afsari]

Hi,

     Our design consists of two boards. First is an antenna shield board with BGT24MTR11 on it and it connects to the main board that has the rest of the circuitry (RF, MCU, LDO...).  the quadrature IF signals (I and Q) are connected to two stages of amplification and filtering. The I & Q lines that are coming from the antenna board are differential pairs.

My question is, when I observe the two lines of I and Q at the High-gain output of the RF stage I notice a mismatch in amplitude between the I and Q signals.

  1. What could be the reason for this mismatch?

  2. Will it have a noticeable effect on the detection process (doppler)? I think determining the object movement direction will get more complex as we will get two peaks on the spectrum rather than one.

Thank You,

Ali

[Yashraj_P]

Hi @Ali_Afsari ,

What is the difference between the peak-amplitudes of I & Q signals? Can you please, share the I and Q signals in the same plot?

Thanks and regards,
Yashraj

[Ali_Afsari]

Hi @Yashraj_P ,

    The difference is not fixed as it appears. There is clipping because my hand is too close when I wave in front of it. Maybe I should also coma pare the low-gain signal for better view.  This is how the two signals look line under the oscilloscope.

Note,

After cutting one of the differential pair pins for each signal, this is how it looked:

Thank You,

Ali

[Yashraj_P · Accepted solution]

Hi @Ali_Afsari ,

1. There will be some imbalance of phase and amplitude between I & Q signal, cause the quadrature phase-shifter isn't a perfect one. The imbalances are taken in account as given per data-sheet., in the RX section 2.4.3. 
Non-linear effects of close targets and the TX and RX cross-talk also aggravates the imbalances.

2. You would require I and Q both data only in Doppler radar to measure the direction of motion. The phase imbalance won't have much impact here.

Thanks and regards,
Yashraj.

[Ali_Afsari]

Hi @Yashraj_P ,

                Thank you for the response. in point to, you suggest that I reply on I signal for speed detection and I+Q for direction? We are trying to improve the performance by detecting multiple targets moving in opposite directions.

Is the sample and hold (S&H) mechanism implemented by Sense2GoL and Distance2GoL meant to overcome issues like this?

Thank You,

Ali

[Yashraj_P]

Hi @Ali_Afsari ,

Some clarifications: Sense2GoL and Distance2GoL use BGT24LTR11 shield. And Demo Sense2GoL is a discontinued product.
S&H is implemented to enable duty-cycling and carry out (pulsed) Doppler detection with low power consumption.
For detecting multiple targets moving in different directions, may I ask what principle are you using?

Thanks and regards,
Yashraj

[Ali_Afsari]

Hi @Yashraj_P ,

I am aware that the two Kits use BGT24LTR11 but I assume the principle and mechanism remains the same, correct?

We are also converting IF signal to Digital signal. Is there an advantage of implementing an external S&H circuit ? I know that many SAR ADCs implement S&H internally but the Kits rely on the XMC4700 internal ADC.

for multiple target detection, we will be using doppler . Concurrent target tracking algorithm will be implemented for the range of speed bins. There will be limitations as Overlapping Objects (same speed) will be treated as one but it is a compromise with the current hardware we have.

Thank you,

Ali

[Yashraj_P]

Hi @Ali_Afsari,

Sense2GOL uses Pulsed Doppler for motion, speed and direction of motion of target. Not for multiple targets. The Pulsed Doppler is implemented using S&H. Please go through User Manual of Sense2GoLPulse, Section 4.4.1. 

Distance2GoL uses software controlled FMCW for detecting distance of multiple target. Also capable of motion, speed and direction of target. Please go through User Manual of Distance2GoL.

Thanks and regards,
Yashraj

[Yashraj_P]

Hi @Ali_Afsari ,

We will be locking this thread  due to inactivity. If you have further queries, please create a new thread.

Thanks and regards,
Yashraj