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Classification of radio wave propagation application antenna telescopic mast

Time：2021-07-09 View：

Basic Classification
Radio wave propagation is basically classified according to the research object. Since radio wave propagation is the process of studying the action between radio wave and medium, both radio wave and medium are the research objects. In this way, two types are divided by radio frequency (band) and by medium. According to frequency classification, there are extremely long wave propagation, ultra long wave propagation, long wave propagation, medium wave propagation, short wave propagation, ultra short wave propagation, microwave propagation and millimeter wave propagation; According to medium classification, there are underground radio wave propagation, ground wave propagation, Stratosphere radio wave propagation, ionosphere radio wave propagation and magnetosphere electromagnetic wave, etc. These two categories are basically "parallel" and corresponding to each other, but they are intersecting (see figure).
Due to different media structures and wave wavelengths, the physical mechanisms of radio wave propagation vary. Some are mainly scattering propagation, while others are mainly Waveguide propagation. Different physical mechanisms lead to different communication theories and methods. From this perspective, there are random medium propagation theory (scattering theory), layered medium propagation theory, waveguide mode propagation theory, diffraction propagation theory, magnetic ion theory and inversion theory, etc.
Relationship with other disciplines the basic theoretical starting point of radio wave propagation is electromagnetic theory, namely Maxwell equations and electrodynamics derived from physics. The Earth, the Earth's atmosphere and even the outer space are the media of radio wave propagation, and various media produce rich and colorful radio wave propagation content. In order to study different types of radio wave propagation, we must understand the physical structure and motion changes of different media. For example, studying ground waves requires understanding the Earth's crust, especially the geoelectric characteristics. To study the propagation of the tropopause, we need to know the dielectric properties and their changes in the tropopause, so as to understand the structure and changes of temperature, humidity and pressure, stratification and turbulent motion, etc, we also need to know all kinds of air components, especially oxygen and water vapor molecules, their interaction with radio waves, cloud and mist precipitation, etc. However, the study of ionosphere propagation needs to know the ionosphere electron concentration, geomagnetic and its changes, as well as the influence of sunspot, magnetic storm, Aurora and nuclear explosion. In the study of earth-air radio wave propagation, the physical characteristics of magnetosphere and outer space certainly need to be understood. Therefore, radio wave propagation is based on geophysics, meteorology, atmospheric physics and space physics.
Radio wave propagation is a branch of electronics, which is closely related to other branches of electronics. First of all, radio wave propagation detection requires the use of communication, radar, radio navigation, antenna and other technical equipment, while data processing and test control require the use of electronic computers, the research results of radio wave propagation also serve the design, operation and parameter prediction of these systems.
Because radio waves always carry the information of the transmission medium, reflecting the physical state and changes of the Earth, atmosphere and even outer space, radio wave propagation has now become Geophysical, meteorological, atmospheric physics, one of the commonly used and extremely important observation methods in space physics and astronomy. Ground detection and top detection of ionosphere, magnetosphere, etc. almost all use radio waves. Radio waves are used in meteorology and astronomy, forming a new discipline-Radio meteorology and radio astronomy. In addition to providing means, the detection data and analysis results of radio wave propagation in media are also contributions to the corresponding physics disciplines.
Radio wave propagation theory is particularly closely related to mathematics. It not only uses the latest results in field theory, mathematical physics methods and mathematical statistics, but also promotes the development of these aspects.
Basic form
Ground wave diffraction propagation.
The transmitting antenna is located on the ground, and the electromagnetic wave propagates along the ground surface by diffraction, which is called ground wave diffraction propagation. Due to the difference of dielectric characteristics and radio frequency on the ground surface, the ground wave receives different degrees of attenuation in the propagation process. In the case of close distance, the ground wave field strength can be calculated by using the schulekin-Van der Bohr formula, however, when considering the influence of the earth curvature, the diffraction formula should be used for calculation. ITU-R P.526 gives the transmission loss calculation model of smooth spherical surface radio wave diffraction propagation commonly used in engineering, which is also applicable to smooth sea surface with small roughness.
Line-of-sight propagation.
The transmission mode in which the radio wave is transmitted directly from the transmitting antenna to the receiving antenna or reaches acceptance point after being reflected by the ground. That is to say, the transmitting antenna and the receiving antenna are limited to propagation within the line-of-sight distance that is "seen" from each other. Land mobile communication, personal communication and paging communication are all spread in this way. For ground communication, the height of antenna installation is much higher than the wavelength. Due to the influence of the curvature of the Earth, the longest distance of the radio wave propagation between the transmitting and receiving antennas can be determined by the antenna height.
Scattering propagation.
The radio wave is scattered to acceptance point through the uneven distribution medium in the stratosphere or ionosphere, so that the radio wave reaches the place outside the line of sight. The tropopause is about 10~18 kilometers above the Earth's surface, which is a heterogeneous medium. The reflection index decreases with the increase of height. The applicable wave band and sight distance propagation of scattering propagation are basically the same but far away (for example, ionosphere scattering can reach 2,000 kilometers), so it is over-sight distance propagation for ground communication.
Waveguide propagation. In layered media, there may be a propagation mode similar to that in metal waveguide between layers, which is called Waveguide propagation. This kind of waveguide is a waveguide existing under natural conditions, or other waveguide that is not specially used to propagate radio waves (such as underground tunnels). The propagation of radio waves in the offshore evaporation waveguide belongs to this kind of propagation form. Evaporation waveguide is an abnormal atmospheric structure formed by the rapid decline of water vapor along the offshore surface with the increase of height. It has a high probability of occurrence and a long existence time in a certain sea area. Evaporation waveguide can trap electromagnetic waves of a certain frequency in the waveguide structure to form over-the-horizon propagation of radio waves.
Basic applications