An antenna is a device that is made to efficiently radiate and receive radiated electromagnetic waves. There are several important antenna characteristics that should be considered when choosing an antenna for your application as follows:

• Antenna radiation patterns
• Polarization
• Directivity
• Power Gain

Antenna Radiation Patterns
An antenna radiation pattern is a 3-D plot of its radiation far from the source. Antenna radiation patterns usually take two forms, the elevation pattern and the azimuth pattern. The elevation pattern is a graph of the energy radiated from the antenna looking at it from the side as can be seen in Figure 1a.

The azimuth pattern is a graph of the energy radiated from the antenna as if you were looking at it from directly above the antenna as illustrated in Figure 1b. When you combine the two graphs you have a 3-D representation of how energy is radiated from the antenna in Figure 1c.





















Polarization
Polarization is the orientation of electromagnetic waves far from the source. There are several types of polarization that apply to antennas. They are Linear, which comprises, Vertical, Horizontal and Oblique, and circular, which comprises, Circular Right Hand (RHCP); Circular Left Hand (LHCP), Elliptical Right Hand and Elliptical Left Hand.

Polarization is most important if you are trying to get the maximum performance from the antennas. For best performance you will need to match up the polarization of the transmitting antenna and the receiving antenna.

Directivity
The directive gain of an antenna is a measure of the concentration of the radiated power in a particular direction. It may be regarded as the ability of the antenna to direct radiated power in a given direction. It is usually a ratio of radiation intensity in a given direction to the average radiation intensity.

Power Gain
The power gain of an antenna is a ratio of the power input to the antenna to the power output from the antenna. This gain is most often referred to with the units of dBi, which is logarithmic gain relative to an isotropic antenna. An isotropic antenna has a perfect spherical radiation pattern and a linear gain of one.