we want to use nRF52833 as BLE5.1 AOA/DOA locator,here are some questions about to how to use it:
Athos.Zhang said:How many antennas are needed for direction finding/positioning? Is 6 enough? What are the maximum and minimum numbers of antennas supported?
Depends on your case. Two antennas can cover a 90-degree sector, if you need 360-degree coverage, you need at least four antennas. More antennas can improve accuracy with a good algorithm.
Maximum controlled GPIO lines is 8 - with SP4T switches, you can easy connect 16 antennas.
Athos.Zhang said:What are the requirements for isolation, polarization, and cross-polarization isolation between antennas?
IMHO absolute polarization doesn't matter, as tags may have any orientation - two sets of differently polarized antennas would improve distance but increases complexity a lot. Of course, each two antennas involving in one measurement should have equal polarization.
Athos.Zhang said:What is the fundamental theory of the direction finding/positioning algorithm? Is there a ready-made algorithm that we can use?
http://www.diva-portal.org/smash/get/diva2:1317231/FULLTEXT01.pdf gives a good overview of principles with the real evaluation.
Athos.Zhang said:Should the phase delay of each RF path be consistent? Are the amplitudes required to be consistent? What about phase error and amplitude error index ?
Not necesary, but you should account phase difference in your algorithm. With equal antennas, amplitudes should be near equal (amplitude difference can give you a hint about mixing with reflected signal).
Athos.Zhang said:Can all GPIO ports be configured to switch antenna paths?
Any GPIO that is not marked as "low drive, low frequency I/O only" in product specification.