AWR1843BOOST: What is the difference of AWR1843 and AWR1843AOP?

I find AOP stands for antenna-on-package (AoP) . But could not find more information about the description of AOP version. 

What is the difference between AWR1843 and AWR1843 AOP? When I use mmwave visualizer to communicate with my AWR1843Boost, I need to select platform xWR1843 but not xWR1843_AOP, otherwise will get a warning message.

Thanks