4T8R MIMO System Phase Problem

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.

Hi, 

Depending on the application, yes it is acceptable to discard some chirps. For example, the EV-TINYRAD24G Reference design discards some chirps while setting ADC. 

Frankly, I don't know whether ADRF5020 is more suitable. 

But I know that VGA or PA are susceptible to load shift and a reflective switch might change the phase.  However, after the switch is settled, the phase should return to normal value. Thus, I proposed skipping a couple of chirps after the switch change or using the TXData input of the ADF4159 to wait for the switch to settle. 

Thanks,
Emrecan

Thanks！

Hello, I would like to ask whether the output power adjustment of the ADF5901 is controlled through Register 1, specifically DB12~DB5? Does 0 correspond to -20dBm and 255 correspond to 8dBm? Is the adjustment evenly spaced? If I want to set the output power to around 0dBm, should I set it to approximately 183?

I plan to connect a power amplifier (PA), the HMC863ALC4, to the output. This amplifier has a gain of 24dB and a P1dB output of 27dB. Therefore, setting the ADF5901 output to 0dBm seems more appropriate. Would this approach be feasible?

Additionally, do I need to adjust the AUX BUFFER GAIN in the ADF5901? What is its function?

please refer to below thread.

ADF5901 output power - Q&A - RF and Microwave - EngineerZone

ADF5901 output power issue. - Q&A - RF and Microwave - EngineerZone

Thanks,
Emrecan