Cisco Cisco Aironet 350 Wireless Bridge 데이터 시트

 

 

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Unlike isotropic antennas, dipole antennas are real antennas. Dipole antennas have a different radiation pattern 

compared to isotropic antennas. The dipole radiation pattern is 360 degrees in the horizontal plane and 75 degrees 

in the vertical plane (assuming the dipole antenna is standing vertically) and resembles a donut in shape. Because 
the beam is “slightly” concentrated, dipole antennas have a gain over isotropic antennas of 2.14 dB in the 

horizontal plane. Dipole antennas are said to have a gain of 2.14 dBi (in comparison to an isotropic antenna). 

Some antennas are rated in comparison to dipole antennas. This is denoted by the suffix dBd. Hence, dipole 

antennas have a gain of 0 dBd (= 2.14 dBi). 

Note that the majority of documentation refers to dipole antennas as having a gain of 2.2 dBi. The actual figure is 

2.14 dBi, but is often rounded up. 

Types of Antennas 

Cisco offers several different styles of antennas for use with access points and bridges in both 2.4-GHz and 5-GHz 

products. Every antenna offered for sale has been FCC-approved. Each type of antenna will offer different 

coverage capabilities. As the gain of an antenna increases, there is some tradeoff to its coverage area. Usually 

high-gain antennas offer longer coverage distances, but only in a certain direction. The radiation patterns below will 

help to show the coverage areas of the styles of antennas that Cisco offers: omnidirectional, Yagi, and patch 

antennas. 

An omnidirectional antenna (Figure 1) is designed to provide a 360-degree radiation pattern. This type of antenna 

is used when coverage in all directions from the antenna is required. The standard 2.14-

dBi “Rubber Duck” is one 

style of omnidirectional antenna. 

Figure 1.    Omnidirectional Antenna 

 

Directional antennas come in many different styles and shapes. An antenna does not offer any added power to the 

signal; it simply redirects the energy it receives from the transmitter. By redirecting this energy, it has the effect of 

providing more energy in one direction, and less energy in all other directions. As the gain of a directional antenna 

increases, the angle of radiation usually decreases, providing a greater coverage distance, but with a reduced 

coverage angle. Directional antennas include patch antennas (Figure 2), Yagi antennas (Figure 3), and parabolic 

dishes. Parabolic dishes have a very narrow RF energy path, and the installer must be accurate in aiming these 

types of antennas these at each other.