ommunications antenna

May 19, 2022

The antenna is a passive body, it does not need to provide power or energy, and will not amplify the input wireless signal. On the contrary, due to the signal attenuation caused by the feeder and the connector, the wireless energy released will be less than the energy input to the antenna contact. In fact, the antenna only plays the role of a directional amplifier, so that the sending and receiving energy is concentrated in a specific area of the space, and changing the energy distribution area to the place where it is needed is the only purpose of the antenna. If the energy is distributed to some places without wireless devices, Or over-distributing energy to a certain area is a waste. According to the law of constant energy, increasing the energy in one direction means reducing the energy in other areas.
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gain

Gain is a general representation method of antenna characteristics. It refers to the intensity gain in a certain area relative to the following two ideal standard transceiver modes. The ideal standard transceiver mode is based on the energy of the radiator emitted from an isotropic antenna. It is an equal The square radiator radiates in any direction in space, and the gain can only be used as a reference for selecting an antenna. It can only display the gain in the direction with the strongest energy, and does not provide any energy distribution.

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Half power lobe width

Since not all users can understand the radiation pattern, it is customary to use another simplified and effective parameter to describe the distribution of energy. The calculation method is the width between the two emission directions at half of the highest power. Call this radiation the "main lobe".
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Antenna polarization

"Antenna polarization" refers to the direction of the electric field vector in the radiated wave, where "linear polarization" refers to the energy part in a certain plane and "circular polarization" is a circular rotation. For losses due to matching, the receiving antenna must maintain the same polarization direction as the received radio signal.
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VSWR

The "Voltage Standing Wave Ratio" (VSWR) of an antenna is the ratio of the reflected power to the input power, which is mainly affected by the matching degree between the input impedance of the antenna terminal and the characteristic impedance of the transmission line. Reflected waves will reduce the energy transmitted to the antenna, thereby reducing the effective gain of the antenna, ideally a ratio of 1:1
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