This is a 2 dBi omni-directional 900 MHz dipole antenna with an RP-SMA plug. Omni-directional antennas radiate equally well in all directions and are best used to spread a signal uniformly over some area. Unlike a directional or semi-directional antenna, an ideal omni-directional antenna does not favor any direction in particular. For a general purpose application, omni-directional antennas are usually the antenna of choice and directional or semi-directional antennas are used when the application and node locations are well defined.
The dBi rating of an antenna specifies the amount of gain the antenna has in a particular direction. An antenna gain of 0dBi specifies an antenna that radiates all power uniformly over a sphere. Any antenna that has a gain greater than 0 dBi in some direction means that it has less gain somewhere else so that the total RF energy remains constant.
For a dipole antenna, the radiation pattern is toroidal and signal transmission and reception is best on the broad side of the antenna (ie: horizontally placed from the antenna). The higher the gain of a dipole antenna, the stronger the signal is in the horizontal directions and the weaker the signal will be in the vertical (elevated) directions. Hence a high gain dipole antenna may not be ideal for a multi-story building but it will be good to disperse a signal omni-directionally across a single floor.
+2 dBi 900 MHz Dipole Antenna Datasheet