Antennas are the radiating element in a radio frequency communication system and work by focusing the broadcasted energy. There are several common types of antennas including ¼ wave monopole antennas, ½ wave dipole antennas and various types of printed circuit board or patch and gain antennas. Gain and patch antennas tend to be the most expensive as they are designed for fixed outdoor installation, whereas the PCB, monopole and dipole antennas are designed with cost and portability in mind.
The XBee radio family is available with three separate antenna options. The modules are available with a PCB chip antenna, a ¼ monopole integrated whip antenna, or a U.FL. antenna connector that allows for connection to a dipole or other external antenna. The chip and integrated whip antennas are suited for any application, but are especially useful in embedded applications. Since the radios do not have any issue radiating through plastic cases or housings, the antennas can be completely enclosed in those types of applications.
The U.FL. connector is used in conjunction with an adapter cable that can allow connection to a dipole or gain antenna if the housing is metal or if that solution is more desirable mechanically. Range can differ somewhat with different antenna types, so that should be a consideration when choosing what type of antenna you want to use.