iMac 21 2011 AirDrop Card

[mba.user]

Hi , im owning an 2011 21.5 inch iMac running macOS High Sierra , when i go to the AirDrop in Finder there i cant see any of my apple devices even if they are haveing AirDrop on (my iPhone, iPad , MacBook) what wifi or bt card should i buy do i need any adapters to plug in new card , what do i do to make it work ? i really need AirDrop and Continue option , pls for help (-;
i am not sure what wi fi is already in my Mac i have no idea sorry