Antenna is a kind of converter, it transforms the guided wave spread on the transmission line into electromagnetic waves which transmits in the unbounded medium (usually free space) propagation, or the opposite transformation. It is also a necessary component of the radio equipment used to transmit or receive electromagnetic. The engineering system of radio communication, radio, television, radar, navigation, electronic countermeasures, remote sensing, radio astronomy, etc., all the systems that use electromagnetic waves to transmit information rely on antennas to work. In addition, in the transmission of energy by the electromagnetic waves, the non-energy radiation signal also needs the help of antenna. General antenna is reversible, that is the same pair of antennas can be used either as a transmitting antenna, can also be used as a receiving antenna. The basic parameters of a same antenna as the emission or reception features are the same. This is the antenna reciprocity theorem.
Types of WLAN antennas
When the computer has a long distance with the wireless AP or any other computers, with the weakening of the signal, or the transmission rate decreased, or it is impossible to achieve communication between the AP or other computers, at this time, it must need the help of a wireless antenna to amplify the signal received or sent. There are many types of WLAN antenna, but commonly, there are two types. One is an indoor antenna, its advantages are convenient and flexible, the disadvantage is that the amplification is small, the transmission distance is short; the other is outdoor antenna. More types of outdoor antennas are pot-shaped directional antenna, rod-shape omni-directional antenna. The advantages of outdoor antenna is that its transmission distance is very long. So it is more suitable for long-distance transmission. The antenna of the wireless device itself has a certain distance limitation, when exceeding these limits, it is necessary to use external antenna to enhance the wireless signal to reach the purpose of extending transmission distance.
Essential Antenna Parameters
The most two important parameters of the antenna is the antenna gain and directivity. Directivity refers to the directional antenna radiation and reception points, i.e., antenna signal over a certain angle is particularly sensitive and whether the radiation energy is concentrated on a certain perspective. The antenna can be divided into omni-directional antenna and directional antenna according to the different horizontal directionals. Gain refers to the antenna power magnification, the greater the value the greater the magnification of the signal, which means that the greater the gain value, the stronger and better the signal transmission quality. The WIMAX antenna sold in the market are mostly self attached with 2dbi or 3dbi antenna, users can replace 4dbi or 5dbi even 9dbi antenna according to different needs.
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