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Antenna Types
Antennas are used to transmit or receive radio waves and play an important role in a WLAN. The following describes how antennas are classified based on different criteria.
Antenna Classification by Horizontal Radiation Pattern
Antennas can be classified into the following types based on the horizontal radiation pattern:
- Omnidirectional antenna
- The goal of an omnidirectional antenna is to radiate energy equally in all directions in a plane (azimuth plane), with a directional pattern in any orthogonal plane.
- The radiation pattern of an omnidirectional antenna is similar to that of an incandescent lamp, which radiates visible light in all directions in a plane.
- Directional antenna
- A directional antenna radiates its energy more effectively in one (or some) direction than others. Typically, these antennas have one main lobe and several minor lobes.
- The radiation pattern of a directional antenna is similar to that of a flashlight, which radiates visible light towards a specified direction. With the same radio energy, a directional antenna provides a longer coverage distance than an omnidirectional antenna in a particular direction.
- Smart antenna
- A smart antenna supports multiple directional radiation patterns and one omnidirectional radiation mode on a horizontal plane.
- A smart antenna receives signals from transmitters in omnidirectional mode. Based on the received signals, the smart antenna algorithm can determine the location of a transmitter and control the CPU to send control signals to the transmitter in the directional radiation pattern with the direction of the maximum radiation.
Antenna Classification by Polarization Mode
By polarization mode, antennas are classified to single-polarized antennas and dual-polarized antennas. Single polarization and dual polarization are essentially linear polarization, allowing antennas to be horizontally or vertically polarized.
- Single-polarized antenna: supports only one polarization mode. Such an antenna can only receive or transmit signals in either the horizontal or vertical plane at a time. Therefore, more installation space and maintenance workload are required.
- Dual-polarized antenna: supports the horizontal and vertical polarization modes. Such an antenna can both receive and transmit signals.