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4T8R MIMO System Phase Problem

Thread Summary

The user is experiencing inconsistent phase trends across different TX transmissions in a 4T8R MIMO radar system using ADF5901, ADF5904, ADF4159, and ADRF5300. The final answer suggests checking the recalibration sequence after power-up and recommends recalibrating for every 10°C temperature change. The user also inquires about output power settings and AUX BUFFER GAIN adjustments for the ADF5901, planning to connect a HMC863ALC4 power amplifier.
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Category: Hardware
Product Number: ADF4159, ADF5901, ADF5904, ADRF5300, ADF4159

Hi, I am currently using the ADF5901, ADF5904, ADF4159, and ADRF5300 to design a 4T8R MIMO radar system. Previously, I successfully verified the feasibility of a 2T4R system without using the ADRF5300. In this design, I utilized a Wilkinson power splitter to distribute the LO signal to two ADF5904 chips for achieving 8RX. Two ADRF5300 switches allow one ADF5901 to control four channels in a time-division manner.

During the design and testing phase, I found that the quality of the IF signals for all channels was acceptable; however, there were issues with angle-of-arrival estimation. After extensive validation, I suspect that the four signals generated by the ADF5901 may be problematic. Theoretically, for a 4T8R array, the phase trends of the 8-channel data obtained from each TX transmission should be consistent. However, testing revealed significant issues with this consistency. It’s not that a specific TX channel is unstable; rather, the phase trends from different TXs exhibit variations across different data collection sessions.

I would like to inquire about the potential causes of this issue. Below are the phase results from three signal acquisitions, where 1 to 8 represent the 8 RX channels, and different curves indicate the phase changes of the received signals corresponding to different TX transmissions. In the embedded control system, both RX and LO are continuously active. TX is controlled through register 0 of the ADF5901, switching channels 1 and 2, while each channel is managed by the ADRF5300 for switching to form four transmit paths, with a channel switch occurring every ten chirps. This part of the embedded control is illustrated in the diagram. The STM32 is used for control, and the history represents the ramp output from the technical ADF4159's MUXOUT. The high and low levels of PA11 and PA10 are used to control the two ADRF5300 switches.

I would appreciate your assistance in understanding why different TXs produce varying phase trends. Thank you!

Parents
  • Hi,

    Did you implement a recalibration sequence after powering up? It seems like, temperature change during operation might create different phase values.

    We recommend calling the recalibration sequence for every 10°C temperature change. 

    Thanks
    Emrecan 

  • Yes, I followed the calibration process based on the reference example from the ADF5901 datasheet, and the three tests mentioned above were conducted at different times, so the temperature difference shouldn't be that significant. Could the issue be related to switching every 10 chirps? Does the switching cause phase instability? Additionally, is it feasible to use the ADRF5300 for TX expansion in this way? The control code references the embedded section in the diagram. Thank you!

  • Hi

    I don't have much experience with RF switches and radar FEs. This might come short but I have a theory. 

    ADRF5300 is a reflective switch. Therefore, there might be disturbances while changing the load. This might create a phase mismatch. 

    How do you control chirps? It is possible to ignore the first couple of chirps and start sampling afterward. Or you can use the TXData input to start the chirp after waiting for a couple of microseconds for the switch to settle. 

    Additional note; I checked and found that ADRF5020 is a recommended non-relective switch for 24GHz FMCW arrays. 

    Thanks
    Emrecan

  • So, is it acceptable to discard the first 10 chirps after each switch toggle? Also, is the ADRF5300 unsuitable for this type of array design? Should we use the 5020 instead? Thank you.

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