Principle and main parameters of microwave antenna
What is a microwave antenna
Microwave antenna is a kind of antenna device used in the field of microwave (meter wave, decimeter wave, centimeter wave, millimeter wave, etc.) communication as a feeder for reflective surface communication. Now it is also used to calibrate and measure other communications .
Principle of microwave antenna
Microwave antenna consists of three parts: primary radiator, sub-reflector and main reflector. The principle of a microwave antenna is similar to that of an optical astronomical telescope. When the antenna is used for launch, electromagnetic energy is radiated from the phase center point P of the horn, and radiated to the secondary reflecting surface in the form of a spherical surface. The device is corrected to a plane wave so that the energy is emitted more concentratedly.
The main parameters of microwave antenna
1. Directivity diagram: The basic function of the antenna is to transform the electromagnetic wave transmitted by the feeder into an electromagnetic wave propagating in free space. The directional diagram of the antenna characterizes the distribution of electromagnetic wave energy (or field strength) at various points in space when the antenna radiates. Describe one of the main transmissions of the antenna. The antenna pattern is a three-dimensional pattern. Its characteristics can be described by directional graphs in two mutually perpendicular planes (E plane and H plane).
2. Directivity coefficient: Although the above-mentioned directivity diagram reflects the antenna radiation state to a certain extent, it is a relative value. In order to quantitatively describe the degree of antenna concentrated radiation, the concept of directivity coefficient is introduced. The directivity coefficient is defined as: at the same distance and the same radiation conditions, the radiation power density Smax (or field strength square E2max) and the radiation power density S0 (or field strength) of a non-directional antenna (point source) at the maximum radiation directivity of an antenna The ratio of square E20) is represented by D.
3. Antenna efficiency: Generally speaking, the conductor and insulating medium constituting the antenna have certain energy loss. The power input to the antenna cannot be completely converted into the radiated power of free space electromagnetic waves. We take the ratio of the antenna radiated power Pr to the antenna input power Antenna efficiency
4. Gain coefficient: abbreviated as gain, which is defined as: under the condition of the same distance and the same input power, the radiation power density Smax (or field strength square E2max) of a certain antenna in the maximum radiation direction and the non-directional antenna (ideal Point source) the ratio of the radiant power density S0 (or field strength squared E20), represented by G
5. Antenna impedance: refers to the input impedance of the antenna input port in the direction of the antenna radiation port. It depends on the antenna structure and operating frequency. The conversion efficiency of the antenna is the highest only when the input impedance of the antenna is well matched with the impedance of the feeder. Otherwise, reflections will occur on the input port of the antenna and a standing wave will be formed on the feeder, thereby increasing the transmission loss.
6. Antenna polarization refers to the orientation of the electric field strength (E) vector in the maximum radiation direction of the antenna. Linear polarization is a more common way of polarization. Linear polarization can be divided into "vertical polarization and horizontal polarization". The electric field vector of the former is perpendicular to the ground, and the latter is parallel to the ground.
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