Antenna and antenna program
An antenna is a device that radiates to space or receives electromagnetic waves from space in a radio transceiver system. It is an essential part of the radio communication system. Such as in the long, medium and short wave segment, wire is generally used to form the antenna, T-shaped, inverted L-shaped, annular, diamond, fishbone shape, cage antenna and so on.
In the microwave band, horn antenna, paraboloid antenna, slotting crack antenna on the metal surface and lens antenna arranged by metal or dielectric strip are made of metal plates or nets.
The antenna has five basic parameters: directionality coefficient, antenna efficiency, gain coefficient, radiation resistance and antenna effective height.
Directionality of the antenna
The ability of an antenna to radiate electromagnetic waves in a certain direction. Directionality is one of the important factors to evaluate the advantages and disadvantages of antenna. With the directionality of antenna, it can improve the efficiency of transmitter or receiver to some extent, and make it have certain confidentiality and anti-interference.
The directionality diagram is a characteristic curve representing the directionality of an antenna, that is, a graph showing the ability of an antenna to transmit or receive electromagnetic waves in all directions.
Sometimes called beamwidth. Refers to the width of the main lobe of the directionality diagram. Generally refers to the half - power lobe width. Therefore, the smaller the lobe width, the stronger the directionality, the stronger the confidentiality and the smaller the possibility of interfering with the adjacent station.
Coefficient of directivity
The directionality coefficient is a parameter used to express the degree of electromagnetic wave radiation concentrated by the antenna in a certain direction (i.e. the sharpness of the directionality pattern).
In the medium and short wave bands, the directionality coefficient is about several to dozens. In the range of meters wave, about tens to hundreds; In the centimeter-wave band, it can be as high as thousands or even tens of thousands.
The ratio of the radiated power of the transmitting antenna to the square of the effective current at the feeding point is called the radiation resistance of the antenna.
The radiation resistance depends on the size and shape of the antenna and the wavelength of the feed current. Since the task of transmitting antennas is to radiate electromagnetic waves, the size and shape of antennas are always chosen appropriately to make the radiation resistance as large as possible.
Effective antenna height
Vertical antenna less than a quarter wavelength: Assume that there is a uniform distribution of current on a vertical antenna. The uniform current is equal to the maximum current on the actual antenna, and the generated radiation field intensity is the same as that of the actual antenna. The length of the assumed vertical antenna is the effective height of the actual antenna.
Maximum gain coefficient of antenna
Usually also referred to as antenna maximum gain or antenna gain. It refers to the ratio of the total input power of the standard antenna (without direction) to the total input power of the directional antenna under the condition that the electric field intensity is equal at a point in the direction of the maximum field intensity, and is called the maximum gain coefficient of the antenna.
The efficiency of the antenna
It is the ratio of the power radiated by the antenna (that is, the power that effectively converts the electromagnetic wave part) to the active power input to the antenna. It's always less than 1.
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