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The total input power ratio of the antenna, said the maximum gain factor of the antenna. It is a more complete reflection of the antenna's effective use of the total RF power than the antenna directivity factor. And expressed in decibels. It can be mathematically deduced that the maximum antenna gain factor is equal to the product of the antenna directivity factor and the antenna efficiency.
It refers to the antenna radiation out of the power (that is, the effective conversion of electromagnetic wave power) and the input to the antenna active power ratio. Is constant less than 1 value.
Antenna polarized wave
When the electromagnetic wave is propagating in space, if the direction of the electric field vector remains fixed or rotates according to a certain law, this electromagnetic wave is called a polarized wave, which is also called an antenna polarized wave or a polarized wave. Generally can be divided into plane polarization (including horizontal and vertical polarization), circular polarization and elliptical polarization.
The direction of the electric field of a polarized electromagnetic wave is called the direction of polarization.
Polarized electromagnetic wave polarization direction and propagation direction of the plane formed by the plane called the polarization.
The polarization of radio waves, often with the earth as a standard surface. Any polarization plane and the earth normal surface (vertical) parallel to the polarization is called the vertical polarization. Its electric field direction and the earth vertical.
Polarized surface and normal earth surface perpendicular to the polarized wave is called the horizontal polarization. Its electric field direction and the earth parallel.
If the direction of polarization of electromagnetic waves to maintain a fixed direction, called plane polarization, also known as linear polarization. In the electric field parallel to the Earth's component (horizontal component) and perpendicular to the Earth's surface components, the spatial amplitude of any relative size, can be planar polarization. Vertical polarization and horizontal polarization are all special cases of plane polarization.
When the angle between the plane of the radio wave and the earth's normal plane changes from 0 to 360 °, that is, the size of the electric field does not change and the direction changes with time. The end of the electric field vector locates in a plane perpendicular to the propagation direction When the projection is a circle, it is called circular polarization. Circular polarization can be obtained when the amplitude of the horizontal component and the vertical component of the electric field are equal and the phases are different by 90 ° or 270 °. Circular polarization, if the polarization plane rotates with time and the direction of the electromagnetic wave into the right spiral relationship, said the right circular polarization; the other hand, if the left spiral relationship, said the left circular polarization.
If the angle between the radio wave polarization plane and the normal earth surface changes periodically from 0 to 2π and the trajectory of the end of the electric field vector is an ellipse projected on a plane perpendicular to the propagation direction, it is called elliptical polarization. When the amplitudes and phases of the vertical and horizontal components of an electric field have arbitrary values (with the exception of the two components being equal), the elliptical polarization can be obtained.
Long-wave antenna, antenna in the wave
Is working in the long wave and middle wave band transmitting antenna or receiving antenna collectively. Long, medium wave is based on ground waves and sky waves, and sky waves are continuously reflected between the ionosphere and the earth. According to this propagation characteristics, long, medium-wave antennas should be able to produce vertically polarized radio waves. In the long, medium wave antenna, a wide range of applications are vertical, inverted L-type, T-type, umbrella vertical ground antenna. Long, medium wave antenna should have a good network. Long, medium wave antenna there are many technical problems, such as effective height, radiation resistance, low efficiency, narrow passband, the directivity coefficient and so on. In order to solve these problems, the antenna structure is often very complex and very large.
Working in the shortwave transmission or receiving antenna, collectively referred to as the shortwave antenna. The shortwave is mainly transmitted by sky waves reflected by the ionosphere and is one of the important means of modern long-range radio communications. There are many forms of shortwave antennas, of which the most widely used are symmetrical antennas, in-phase horizontal antennas, multiplier antennas, angle antennas, V-shaped antennas, rhombic antennas and fishbone antennas. Compared with the long-wave antenna, the effective height of the short-wave antenna is large, the radiation resistance is high, the efficiency is high, the directivity is good, the gain is high, and the passband is wide.
The transmitting and receiving antennas working in the ultra-short wave band are called ultrashort wave antennas. Ultrashort wave mainly by space wave propagation. There are many forms of such an antenna, of which Yagi antennas, disk cones, double conical antennas and "batwing" television transmitting antennas are the most widely used.
Work in the rice, decimeter, centimeter, millimeter wave band transmitting or receiving antenna, collectively referred to as the microwave antenna. Microwave mainly by space wave propagation, in order to increase the communication distance, antenna set up higher. In the microwave antenna, the more widely used parabolic antenna, horn parabolic antenna, horn antenna, lens antenna, slotted antenna, dielectric antenna, periscope antenna.
Directional antennas are antennas that transmit and receive electromagnetic waves that are particularly strong in one or a few specific directions while transmitting and receiving electromagnetic waves in other directions with zero or very little. The purpose of using directional transmit antennas is to increase the effective utilization of radiation power and increase confidentiality. The main purpose of using directional receive antennas is to increase the anti-interference ability.
Not directional antenna
Antennas that radiate or receive electromagnetic waves uniformly in all directions are called non-directional antennas, such as whip antennas for small communication machines.
Directional, impedance and polarization characteristics of a wide band in almost the same antenna, known as the wideband antenna. Early broadband antenna with a rhombic antenna, V-shaped antenna, Echo antenna, dish cone antenna, the new broadband antenna has a logarithmic periodic antenna.
Tune the antenna
Antennas that have a predetermined directivity only within a narrow band of frequencies are called tuned antennas or tuned directional antennas. In general, the tuning antenna maintains its directivity only in the 5% band around its tuning frequency, whereas on other frequencies the directivity changes so dramatically that communications are destroyed. Tuning antenna is not suitable for short-wave communication with variable frequency. The same phase level antenna, equivalent to the antenna, winding antenna, etc. belong to the tuned antenna.
Vertical antenna refers to the antenna placed perpendicular to the ground. It has two forms of symmetry and asymmetry, while the latter is widely used. Symmetrical vertical antennas are often fed from the center. Asymmetric vertical antenna is fed between the bottom of the antenna and the ground, the maximum radiation direction in the case of less than 1/2 wavelength, concentrated in the ground direction, it is adapted to broadcast. Asymmetric vertical antenna, also known as vertical ground antenna.
L inverted antenna
One end of a single horizontal wire connected to a vertical lead wire antenna formed. Because of its shape like the English letter L upside down, so that inverted L-shaped antenna. The Γ word of the Russian alphabet happens to be the inverse of the English letter L. So called Γ antenna more convenient. It is a form of vertical ground antenna. In order to improve the efficiency of the antenna, its horizontal part can be composed of a few wires arranged in the same horizontal plane, this part of the radiation is negligible, radiation is the vertical part. Inverted L antenna is generally used for long-wave communications. Its advantages are simple structure, easy to set up; the disadvantage is the large area, poor durability.
In the horizontal wire in the center, connected to a vertical lead wire, the shape of the English letter T, so called T antenna. It is the most common kind of vertically grounded antenna. Its horizontal part of the radiation is negligible, the radiation is the vertical part. In order to improve efficiency, the horizontal part can also be composed of multiple wires. T-shaped antenna features the same inverted L-shaped antenna. It is generally used for long-wave and medium-wave communications.
In the top of a single vertical wire, in several directions down a few inclined conductor, so the shape of the antenna like an open umbrella, so called umbrella antenna. It is also a form of vertical ground antenna. Its characteristics and uses inverted L-shaped, T-shaped antenna the same.
A whip antenna is a bendable vertical rod antenna that typically has a length of 1/4 or 1/2 wavelength. Most whip antennas do not use ground wire to ground. Small whip antenna often use small radio for the metal shell for the network. Sometimes in order to increase the effective height of the whip antenna, the whip antenna can be added at the top of some small radial blades or whip antenna in the middle of the inductor and so on. Whip antenna can be used for small communication machines, walkie talkies, car radios and so on.
Two equal length and the center disconnected and fed wire, can be used as the transmitting and receiving antenna, the antenna is composed of such a symmetrical antenna. Because the antenna is sometimes called a vibrator, a symmetrical antenna is also called a symmetric dipole, or a dipole antenna. The total length of half the wavelength of the symmetric oscillator, called the half-wave oscillator, also known as half-wave dipole antenna. It is the most basic unit antenna, the most widely used, many complex antenna is composed of it. Half-wave dipole structure is simple, convenient feeding, more applications in close-range communication.
Is a wide band weak directional antenna. It is a hollow cylinder surrounded by a few wires instead of a single conductor in the symmetrical antenna radiation body made of, because of its radiator was cage, so called cage antenna. Cage antenna works wide band, easy to tune. It is suitable for short-range trunk communication.
Belongs to a class of symmetrical antenna, but its arms are not arranged in a straight line, and into a 90 ° or 120 ° angle, so called angle antenna. This antenna is generally a horizontal device, its directivity is not significant. In order to get wideband characteristics, the angle of the antenna can also be folded arms, cage angle antenna.
Equivalent to the antenna
The oscillator is folded into parallel to each other's symmetrical antenna called folded antenna. There are two folded antenna, three folded antenna and multi-line folded antenna in several forms, bending, the corresponding point should be the current of each line in the same phase, from a distance, the antenna as a symmetrical antenna. However, the equivalent of the antenna compared with the symmetrical antenna, radiation enhancement. Input impedance increases, easy to couple with the feeder. Equivalent to the antenna is a tuned antenna, the working frequency is narrow. It is widely used in shortwave and ultrashortwave bands.
Is composed of two conductors at an angle to each other, shaped like an English letter V an antenna. Its terminal can be open, you can also receive a resistor, the size of the resistor is equal to the antenna's characteristic impedance. V-shaped antenna has a unidirectional, the maximum emission direction in the direction of the bisector of the vertical plane. Its disadvantage is inefficient, large area.
Is a wideband antenna. It consists of a horizontal diamond hanging on the four pillars formed, an acute angle rhombus connected to the feeder, and the other acute angle connected with a characteristic impedance of the diamond antenna terminal resistance equal. In the direction of the terminal resistance direction of the vertical plane, with a one-way.
The advantage of rhombic antenna is high gain, strong directivity, wide band of use, easy to set up and maintain; the disadvantage is the large area. After deformation of the rhombic antenna, there are two diamond antenna, feedback diamond antenna and folded rhombus antenna in three forms. Diamond antenna is generally used for large and medium-sized short-wave reception radio.
Is an ultrashort wave antenna. At the top of a disc (ie, radiator), by the coaxial line feed the heart, below a conical, coaxial outer conductor. The role of the cone and the infinite ground similar to changing the cone tilt angle, you can change the maximum antenna radiation direction. It has a very wide frequency band.
Fish bone antenna
Fish bone antenna also known as side-fired antenna, is a dedicated short-wave receiving antenna. It consists of a symmetrical oscillator connected at regular intervals on both sets of lines, all connected to the assembly line through a very small capacitor. At the end of the assembly line, that is, one end facing the communication direction, connect a resistor with the same characteristic impedance as that of the integration line, and the other end is connected to the receiver through the feeder. Compared with the rhombus antenna, the advantage of the fishbone antenna is that the sidelobes are small (that is, the receiving direction of the main lobe is strong, and the weaker ones are received in other directions), and the mutual influence between the antennas is small and the area is small. The disadvantage is that the efficiency Low, installation and use are more complicated.
Also called to the antenna. It has a few metal rods, one of which is a radiator, radiator behind a longer for the reflector, the first few short is the director. Radiators usually use a folded half-wave dipole. The maximum radiation direction of the antenna is the same as that of the director. Yagi antenna has the advantages of simple structure, light and sturdy, convenient feeding; shortcomings narrow band, poor immunity. Application in ultrashort wave communication and radar.
It has two types of metal plate and metal wire. Among them, the fan-shaped metal plate is a fan-shaped metal wire. This antenna due to increased antenna cross-sectional area, so widen the antenna band. Line sector antenna can use three, four or five metal wire. Sector antenna for ultrashort wave reception.
Double conical antenna
The double cone antenna consists of two cones with opposite cones, fed at the cone top. Cone can be metal surface, metal wire or metal mesh composition. Just like a cage antenna, the antenna band broadens as the cross-sectional area of the antenna increases. Double conical antenna is mainly used for ultrashort wave reception.
A parabolic antenna is a directional microwave antenna consisting of a parabolic reflector and a radiator mounted on the focal point or focal axis of a parabolic reflector. Electromagnetic waves emitted by the radiator through the parabolic reflection, the formation of highly directional beam.
Parabolic reflector made of metal with good conductivity, mainly in the following four ways: rotating paraboloid, cylindrical paraboloid, cut truncated paraboloid and elliptical edge paraboloid, the most commonly used is rotating paraboloid and cylindrical paraboloid. Radiators generally use half-wave oscillator, open waveguide, slotted waveguide.
Parabolic antenna has the advantages of simple structure, strong directivity and wide working frequency band. Disadvantages are: due to the radiator is located in the electric field of the parabolic reflector, and thus the reflector reaction to the radiator is large, the antenna and the feeder is difficult to get a good match; back radiation larger; poor protection; production of high precision. This antenna is widely used in microwave relay communications, troposcatter communications, radar and television.
Speaker parabolic antenna
The horn parabolic antenna consists of a horn and a paraboloid. Parabolic cover speaker, and the horn is located in the focus of the parabola. Speaker is a radiator, which radiates electromagnetic waves to the paraboloid, electromagnetic waves through parabolic reflection, focused into a narrow beam emitted. The advantages of the horn parabolic antenna are: the reflector has no adverse effect on the radiator, the radiator has no shielding effect on the reflected radio wave, the antenna matches the feeding device better, the back radiation is smaller, the protection degree is higher, the working frequency band is very wide, and the structure is simple. The horn parabolic antenna is used extensively in trunk relay communication.
Also called Horn antenna. It consists of a uniform waveguide and a section of slowly increasing trumpet-shaped waveguide components. There are three types of horn antenna: fan horn antenna, horn cone horn antenna and cone horn. Horn antenna is one of the most commonly used microwave antenna, generally used as a radiator. The advantage is the wide frequency band; the disadvantage is the larger size, and the same caliber, its direction less than the parabolic antenna sharp.
Horn lens antenna
By the speaker and mounted on the horn diameter lens composition, it is called the horn lens antenna. The principle of the lens see the lens antenna, this antenna has a fairly wide operating band, and has a higher degree of protection than the parabolic antenna, it is widely used in the microwave channel communications with more channels.
In the centimeter band, many optical principles can be used in the antenna area. In optics, the use of the lens enables the spherical wave radiated from the point light source placed on the focal point of the lens to become a plane wave after being refracted by the lens. The lens antenna is made using this principle. It consists of a lens and a radiator placed at the focus of the lens. Lens Antenna There are two kinds of media deceleration lens antenna and metal acceleration lens antenna. The lens is made of low-loss, high-frequency media with a thick center and a thin periphery. The spherical wave emitted from the radiation source is slowed down through the dielectric lens. Therefore, the spherical wave is slowed down in the middle of the lens and shorted in the surrounding portion. Therefore, the spherical wave becomes a plane wave after passing through the lens, that is, the radiation becomes directional. The lens is made of many metal plates of different lengths in parallel. The metal plate is perpendicular to the ground, the shorter the metal plate closer to the center. Radio waves in the parallel metal plate
In the spread of accelerated. As the spherical wave from the source passes through the metal lens, the nearer the edge of the lens is, the longer the path is accelerated and the faster the path is accelerated in the middle. Therefore, after passing through the metal lens, the spherical wave becomes a plane wave.
The lens antenna has the following advantages:
1, side lobe and small flap, so the direction is better;
2, the manufacturing accuracy of the lens is not high, so manufacturing more convenient. The disadvantage is the low efficiency, complex structure, expensive. The lens antenna is used in microwave relay communication.
One or a few narrow slots in a large metal plate are fed with coaxial or waveguides. The antenna formed in this way is called a slotted antenna, also called a cracked antenna. In order to obtain unidirectional radiation, the back of the metal plate is made into a cavity which is fed directly by the waveguide. Slotted antenna structure is simple, there is no bulge, it is particularly suitable for use on high-speed aircraft. Its disadvantage is the difficulty of tuning.
Antenna Antenna is a round rod made of low loss, high frequency dielectric material (usually polystyrene), one end of which is fed by a coaxial line or waveguide. 2 is an extension of the inner conductor of the coaxial line to form a vibrator for exciting the electromagnetic wave; 3 is a coaxial line; 4 is a metal sleeve. The role of the sleeve in addition to clamping the dielectric rod, the more important is the reflection of electromagnetic waves, so as to ensure that by the coaxial inner conductor excitation electromagnetic waves, and to the free end of the dielectric rod propagation. The advantage of the dielectric antenna is small size, sharp directivity; the disadvantage is that the media have loss, and therefore inefficient.
In microwave relay communications, the antenna is often placed on a tall rack, so feeding the antenna requires a long feed line. Excessive feeding creates many difficulties such as complex structures, large energy losses, distortions due to energy reflections at the feeder joints, and the like. To overcome these difficulties, a periscope antenna can be used. The periscope antenna consists of a lower mirror radiator mounted on the ground and an upper mirror reflector mounted on the bracket. Under the mirror radiator is generally a parabolic antenna, mirror reflector for the metal plate. Under the mirror emit electromagnetic radiation upwards, reflected out through the metal plate. The periscope antenna has the advantages of low energy loss, low distortion and high efficiency. Mainly used for microwave relays with small capacity.
Is an antenna with a spiral shape. It consists of a metal helix with good electrical conductivity and is usually fed by a coaxial line whose center line is connected to one end of a helix. The outer conductor of the coaxial line is connected to a grounded metal mesh (or plate) connection. The helical antenna radiation direction and helix circumference related. When the helix's circumference is much smaller than one wavelength, the direction of the strongest radiation is perpendicular to the helix axis; the strongest radiation appears in the direction of the helix axis when the circumference of the helix is on the order of one wavelength.
An impedance matching network that connects a transmitter to an antenna is called an antenna tuner. The antenna input impedance varies greatly with frequency, and the transmitter output impedance is constant. If the transmitter is directly connected to the antenna, the impedance mismatch between the transmitter and antenna reduces the radiation when the transmitter frequency changes power. Using an antenna tuner, you can match the impedance between the transmitter and the antenna so that the antenna has the highest radiated power at any frequency. Antenna tuner is widely used in the ground, car, shipborne and shortwave airborne radio.
Log periodic antenna
Is a wideband antenna, or a frequency-independent antenna. Among them, is a simple logarithmic periodicity antenna, its dipole length and interval accord with the following relation: The τ dipole is fed by a uniform two-wire transmission line, the transmission line needs to change position between adjacent dipoles . This antenna has one characteristic: where the characteristic at f frequency is repeated at all frequencies given by τⁿf, where n is an integer. These frequencies are equally spaced on the logarithmic scale, and the period equals the logarithm of τ. Logarithmically periodic antenna is the result of this. Log periodic antennas only repeat radiation patterns and impedance characteristics periodically. However, the antenna of such a structure, if τ is not much less than 1, then its characteristics change very little over one period and thus are essentially frequency-independent. There are many types of logarithmic periodic antennas, such as logarithmic periodic dipole and monopole, log periodic resonant V-shaped antenna, logarithmic periodic helical antenna and the like. The most common one is a logarithmic periodic dipole antenna. These antennas are widely used in the shortwave and shortwave band above.
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