Any Cisco Aironet antenna can be used with Cisco Wireless LAN Controllers and Lightweight Access Points as long as the Cisco or Aironet antenna is 6 dBi or less (6 DBI per Threaded Naval Connector (TNC). Two 6-dBi antennas can be installed, but one 12-dBi antenna can not be used).
Note : dBi is used to compare the power level of a given antenna to the theoretical isotropic antenna. For more information on dBi, refer to dBi.
Some of the 6dBi antenna's are :
AIR-ANT1729 Wall Mount Antenna
AIR-ANT2012 Diversity Patch
For more information on antennas, refer to these documents: