Index and classification of 45 kinds of antennas
1. Maximum gain coefficient of antenna
The ratio of the total input power of the antenna is called the maximum gain coefficient of the antenna. It is more comprehensive than the antenna directivity coefficient to reflect the effective utilization of the antenna to the total RF power. And expressed in decibels. It can be mathematically proved that the maximum gain coefficient of the antenna is equal to the product of the antenna directivity coefficient and the antenna efficiency.
2. Antenna efficiency
It refers to the ratio of the power radiated by the antenna (that is, the power of effectively converting the electromagnetic wave part) to the active power input to the antenna. Is a value that is always less than 1.
3. Antenna polarization wave
When the electromagnetic wave propagates in space, if the direction of the electric field vector remains fixed or rotates according to a certain law, this electromagnetic wave is called polarization wave, also known as antenna polarization wave, or polarization wave. Generally, it can be divided into plane polarization (including horizontal polarization and vertical polarization), circular polarization and elliptical polarization.
4. Polarization direction
The electric field direction of polarized electromagnetic wave is called polarization direction.
5. Polarization surface
The plane formed by the polarization direction and propagation direction of polarized electromagnetic wave is called polarization surface.
6. Vertical polarization
The polarization of radio waves often takes the earth as the standard plane. Any polarization wave whose polarization plane is parallel to the geodetic normal line plane (vertical plane) is called vertical polarization wave. Its electric field direction is perpendicular to the earth
7. Horizontal polarization
The polarization wave whose polarization plane is perpendicular to the geodetic normal line plane is called horizontal polarization wave. Its electric field direction is parallel to the earth.
8. Planar polarization
If the polarization direction of electromagnetic wave remains in a fixed direction, it is called plane polarization, also known as linear polarization. In the component of the electric field parallel to the earth (horizontal component) and perpendicular to the earth surface, the spatial amplitude has any relative size, and the plane polarization can be obtained. Both vertical polarization and horizontal polarization are special cases of plane polarization.
9. Circular polarization
Circular polarization is called when the angle between the polarization plane of radio wave and the geodetic normal line plane changes periodically from 0 to 360 °, that is, the electric field size remains unchanged, the direction changes with time, and the trajectory at the end of the electric field vector is projected into a circle on the plane perpendicular to the propagation direction. Circular polarization can be obtained when the amplitudes of the horizontal and vertical components of the electric field are equal and the phase difference is 90 ° or 270 °. Circular polarization, if the polarization surface rotates with time and forms a right spiral relationship with the propagation direction of electromagnetic wave, it is called right circular polarization; On the contrary, if it forms a left spiral relationship, it is called left circular polarization.
10. Elliptical polarization
If the included angle between the radio wave polarization surface and the geodetic normal line surface changes periodically from 0 ~ 2 π, and the trajectory at the end of the electric field vector is an ellipse projected on the plane perpendicular to the propagation direction, it is called elliptical polarization. Elliptical polarization can be obtained when the amplitude and phase of the vertical and horizontal components of the electric field have arbitrary values (except when the two components are equal).
11. Long wave antenna and medium wave antenna
It is a general term for transmitting antenna or receiving antenna working in long wave and medium wave band. Long and medium waves propagate as ground waves and sky waves, while sky waves are continuously reflected between the ionosphere and the earth. According to this propagation characteristic, long and medium wave antennas should be able to produce vertically polarized radio waves. Among the long and medium wave antennas, vertical, inverted L, t and umbrella vertical grounding antennas are widely used. Long and medium wave antennas shall have good grounding grid. Long and medium wave antennas have many technical problems, such as small effective height, small radiation resistance, low efficiency, narrow passband, small directivity coefficient and so on. In order to solve these problems, the antenna structure is often very complex and huge.
12. Short wave antenna
Transmitting or receiving antennas working in the short wave band are collectively referred to as short wave antennas. Short wave is mainly transmitted by the sky wave reflected by the ionosphere. It is one of the important means of modern long-distance radio communication. There are many forms of short wave antenna, among which the most widely used are symmetrical antenna, in-phase horizontal antenna, wave doubling antenna, angle antenna, V-shaped antenna, diamond antenna, fishbone antenna and so on. Compared with the long wave antenna, short wave antenna has large effective height, large radiation resistance, high efficiency, good directivity, high gain and direct bandwidth.
13. Ultrashort wave antenna
The transmitting and receiving antennas working in the ultrashort wave band are called ultrashort wave antennas. Ultrashort wave mainly propagates by space wave. There are many forms of this antenna, among which the most widely used are Yagi antenna, disk conical antenna, double conical antenna, "bat wing" TV transmitting antenna and so on.
14. Microwave antenna
The transmitting or receiving antennas working in the wave bands of meter wave, decimeter wave, centimeter wave and millimeter wave are collectively referred to as microwave antennas. Microwave mainly depends on space wave propagation. In order to increase the communication distance, the antenna is erected higher. Among microwave antennas, paraboloid antenna, horn paraboloid antenna, horn antenna, lens antenna, slotted antenna, dielectric antenna, periscope antenna and so on are widely used.
15. Directional antenna
Directional antenna refers to an antenna that transmits and receives electromagnetic waves in one or several specific directions, while transmitting and receiving electromagnetic waves in other directions are zero or minimal. The purpose of using directional transmitting antenna is to increase the effective utilization of radiation power and increase confidentiality; The main purpose of using directional receiving antenna is to increase the anti-interference ability.
16. Non directional antenna
Antennas that uniformly radiate or receive electromagnetic waves in all directions are called non directional antennas, such as whip antennas for small communication machines.
17. Broadband antenna
The antenna whose directivity, impedance and polarization characteristics remain almost unchanged in a wide band is called broadband antenna. The early broadband antennas include diamond antenna, V-shaped antenna, wave doubling antenna, disk conical antenna, etc. the new broadband antennas include log periodic antenna, etc.
18. Tuning antenna
An antenna that has a predetermined directivity only in a very narrow frequency band is called a tuned antenna or a tuned directional antenna. Usually, the directivity of the tuning antenna remains unchanged only in the band of 5% near its tuning frequency, while in other frequencies, the directivity changes very much, resulting in the destruction of communication. The tuning antenna is not suitable for HF communication with variable frequency. In phase horizontal antenna, folded antenna and zigzag antenna belong to tuned antenna.
19. Vertical antenna
Vertical antenna refers to the antenna placed perpendicular to the ground. It has two forms of symmetry and asymmetry, and the latter is widely used. Symmetrical vertical antennas are often center fed. The asymmetric vertical antenna feeds between the bottom of the antenna and the ground, and its maximum radiation direction is concentrated in the ground direction when the height is less than 1 / 2 wavelength, so it is suitable for broadcasting. Asymmetric vertical antenna is also called vertical grounding antenna.
20. Inverted L antenna
An antenna formed by connecting a vertical downlead at one end of a single horizontal conductor. Because its shape is like the English letter L, it is called inverted L-shaped antenna. Russian alphabetic Γ The word is just the reverse of the English letter L. Hence the name Γ Type antenna is more convenient. It is a form of vertical grounding antenna. In order to improve the efficiency of the antenna, its horizontal part can be composed of several wires arranged on the same horizontal plane. The radiation generated by this part can be ignored, and the radiation generated by the vertical part. Inverted-L antenna is generally used for long wave communication. Its advantages are simple structure and convenient erection; The disadvantages are large floor area and poor durability.
21. T-shaped antenna
In the center of the horizontal conductor, a vertical down lead is connected, which is shaped like the English letter T, so it is called T-shaped antenna. It is the most common type of vertically grounded antenna. The radiation of its horizontal part is negligible, and the radiation is generated by the vertical part. In order to improve efficiency, the horizontal part can also be composed of multiple wires. The characteristics of T-shaped antenna are the same as those of inverted L-shaped antenna. It is generally used for long wave and medium wave communication.
22. Umbrella antenna
At the top of a single vertical conductor, several inclined conductors are led down in all directions. In this way, the shape of the antenna is like an open umbrella, so it is called umbrella antenna. It is also a form of vertical grounding antenna. Its characteristics and uses are the same as those of inverted L-shaped and T-shaped antennas.
23. Whip antenna
Whip antenna is a flexible vertical rod antenna, and its length is generally 1 / 4 or 1 / 2 wavelength. Most whip antennas use ground grids instead of ground wires. Small whip antenna often uses the metal shell of small radio station as ground grid. Sometimes, in order to increase the effective height of the whip antenna, some small radial blades can be added at the top of the whip antenna or inductance can be added at the middle end of the whip antenna. Whip antenna can be used in small communication machines, walkie talkies, car radios, etc.
24. Symmetrical antenna
A wire whose two parts are equal in length and whose center is disconnected and fed can be used as a transmitting and receiving antenna. The antenna formed in this way is called a symmetrical antenna. Because antennas are sometimes called oscillators, symmetrical antennas are also called symmetrical oscillators, or dipole antennas. A symmetrical oscillator with a total length of half a wavelength is called a half wave oscillator, also known as a half wave dipole antenna. It is the most basic unit antenna and is widely used. Many complex antennas are composed of it. Half wave oscillator has simple structure and convenient feeding, which is widely used in short-range communication.
25. Cage antenna
It is a wide band weak directional antenna. It is formed by replacing the single wire radiator in the symmetrical antenna with a hollow cylinder surrounded by several wires. Because its radiator is in the shape of a cage, it is called a cage antenna. The cage antenna has a wide working band and is easy to tune. It is suitable for short-range trunk communication.
26. Angle antenna
It belongs to a kind of symmetrical antenna, but its two arms are not arranged in a straight line, but form an angle of 90 ° or 120 °, so it is called angular antenna. This kind of antenna is generally installed horizontally, and its directivity is not significant. In order to obtain the wide-band characteristics, the two arms of the angular antenna can also adopt the cage structure, which is called the angular cage antenna.
27. Folding antenna
Bending the oscillator into symmetrical antennas parallel to each other is called folded antenna. There are two-wire folded antenna, three wire folded antenna and multi wire folded antenna. When bending, the current at each corresponding point on each line shall be in phase. From a distance, the whole antenna is like a symmetrical antenna. However, compared with the symmetrical antenna, the radiation of the converted antenna is enhanced. The input impedance increases to facilitate coupling with the feeder. The folded antenna is a kind of tuned antenna with narrow working frequency. It is widely used in short wave and ultrashort wave band.
28. V-shaped antenna
It is an antenna composed of two wires at an angle to each other and shaped like the English letter v. Its terminal can be open circuit or connected with resistance, and its resistance is equal to the characteristic impedance of the antenna. The V-shaped antenna is unidirectional, and the maximum transmission direction is in the vertical plane in the direction of the angle dividing line. Its disadvantages are low efficiency and large floor area.
29. Diamond antenna
It is a broadband antenna. It consists of a horizontal diamond hanging on four pillars. One acute angle of the diamond is connected to the feeder, and the other acute angle is connected to a terminal resistance equal to the characteristic impedance of the diamond antenna. It is unidirectional in the vertical plane pointing to the direction of terminal resistance.
Diamond antenna has the advantages of high gain, strong directivity, wide band, easy erection and maintenance; The disadvantage is that it covers a large area. After deformation, the rhombic antenna has three forms: Double rhombic antenna, feedback rhombic antenna and folded rhombic antenna. Diamond antenna is generally used for large and medium-sized short wave receiving radio stations.
30. Disk conical antenna
It is an ultra short wave antenna. The top is a disk (i.e. radiator), which is fed by the center line of the coaxial line, and the bottom is a cone, which is connected to the outer conductor of the coaxial line. The function of the cone is similar to the infinite ground. Changing the inclination angle of the cone can change the maximum radiation direction of the antenna. It has an extremely wide frequency band.
31. Fishbone antenna
It is another kind of short wave receiving antenna, which is called fish bone antenna. It is composed of a symmetrical oscillator connected at a certain distance between the two assembly lines. These symmetrical oscillators are connected to the assembly line through a small capacitor. At the end of the assembly line, that is, the end facing the communication direction, connect a resistance equal to the characteristic impedance of the assembly line, and the other end is connected to the receiver through a feeder. Compared with diamond antenna, fishbone antenna has the advantages of small side lobe (i.e. strong reception ability in the main lobe direction and weak reception in other directions), small interaction between antennas and small land occupation; The disadvantage is low efficiency and complex installation and use.
32. Yagi antenna
Also called directional antenna. It consists of several metal rods, one of which is a radiator, the longer one behind the radiator is a reflector, and the shorter ones in front are deflectors. The radiator usually uses a folded half wave oscillator. The maximum radiation direction of the antenna is the same as that of the deflector. Yagi antenna has the advantages of simple structure, light weight, firmness and convenient feeding; Disadvantages: narrow frequency band and poor anti-interference. Application in ultrashort wave communication and radar.
33. Sector antenna
It has two forms: metal plate type and metal conductor type. Among them, it is fan-shaped metal plate and fan-shaped metal conductor. This antenna widens the antenna frequency band because it increases the cross-sectional area of the antenna. The linear sector antenna can use three, four or five metal wires. Sector antenna is used for ultrashort wave reception.
34. Biconical antenna
The biconical antenna is composed of two cones with opposite cone tops, which are fed at the cone tops. The cone can be made of metal surface, metal wire or metal mesh. Just like the cage antenna, the antenna frequency band is widened due to the increase of the cross-sectional area of the antenna. Biconical antenna is mainly used for ultrashort wave reception.
35. Paraboloid antenna
A paraboloid antenna or reflector that is mounted on the focal point of the antenna. The electromagnetic wave emitted by the radiator is reflected by the paraboloid to form a beam with strong directivity.
Paraboloid reflector is made of metal with good conductivity. There are mainly four ways: rotating paraboloid, cylindrical paraboloid, cutting rotating paraboloid and elliptical edge paraboloid. The most commonly used are rotating paraboloid and cylindrical paraboloid. Radiators generally use half wave oscillators, open waveguides, slotted waveguides, etc.
Parabolic antenna has the advantages of simple structure, strong directivity and wide working frequency band. The disadvantages are: because the radiator is located in the electric field of the paraboloid reflector, the reaction of the reflector to the radiator is large, and it is difficult to get a good match between the antenna and the feeder; Large back radiation; Poor degree of protection; High manufacturing accuracy. This antenna is widely used in microwave relay communication, tropospheric scattering communication, radar and television.
36. Horn paraboloid antenna
Horn paraboloid antenna consists of horn and paraboloid. The paraboloid covers the horn, and the vertex of the horn is located at the focus of the paraboloid. The horn is a radiator, which radiates electromagnetic waves to the paraboloid. The electromagnetic waves are reflected by the paraboloid, focused into a narrow beam and sent out. The advantages of horn paraboloid antenna are: the reflector has no reaction to the radiator, the radiator has no shielding effect on the reflected wave, and the antenna matches well with the feeding device; Small back radiation; High degree of protection; The working frequency band is very wide; Simple structure. Horn paraboloid antenna is widely used in trunk relay communication.
37. Horn antenna
Also known as angle antenna. It is composed of a uniform waveguide and a horn waveguide with slowly increasing cross section. There are three types of horn antenna: sector horn antenna, pyramid horn antenna and conical horn antenna. Horn antenna is one of the most commonly used microwave antennas, which is generally used as a radiator. Its advantage is wide working frequency band; The disadvantage is that the volume is large, and for the same aperture, its directivity is not as sharp as that of paraboloid antenna.
38. Horn lens antenna
It is composed of horn and lens installed on the diameter of horn, so it is called horn lens antenna. See lens antenna for the principle of lens. This antenna has a fairly wide working frequency band and higher protection than paraboloid antenna. It is widely used in microwave trunk communication with a large number of channels.
39. Lens antenna
In the centimeter band, many optical principles can be used in antennas. In optics, the spherical wave radiated by the point light source placed on the focus of the lens can be changed into a plane wave after being refracted by the lens. Lens antenna is made from this principle. It consists of a lens and a radiator placed on the focus of the lens. There are two kinds of lens Antennas: dielectric deceleration lens antenna and metal acceleration lens antenna. The lens is made of low loss high-frequency medium, thick in the middle and thin around. The spherical wave emitted from the radiation source is decelerated when it passes through the dielectric lens. Therefore, the path of spherical wave decelerated in the middle part of the lens is long, and the path of spherical wave decelerated in the surrounding part is short. Therefore, after passing through the lens, the spherical wave becomes a plane wave, that is, the radiation becomes directional. The lens is composed of many metal plates of different lengths placed in parallel. The metal plate is perpendicular to the ground, and the closer it is to the middle, the shorter it is.
Electric waves are accelerated as they travel through parallel metal plates. When the spherical wave emitted from the radiation source passes through the metal lens, the closer it is to the edge of the lens, the longer the path of acceleration, and the shorter the path of acceleration in the middle. Therefore, the spherical wave passing through the metal lens becomes a plane wave.
The lens antenna has the following advantages:
1. The side lobe and back lobe are small, so the pattern is better;
2. The precision of manufacturing lens is not high, so it is convenient to manufacture. Its disadvantages are low efficiency, complex structure and high price. Lens antenna is used in microwave relay communication.
40. Slotted antenna
One or several narrow slots are cut on a large metal plate and fed by coaxial line or waveguide. The antenna formed in this way is called slotted antenna, also known as slot antenna. In order to obtain unidirectional radiation, the back of the metal plate is made into a cavity, and the slot is directly fed by the waveguide. The slotted antenna has simple structure and no protruding part, so it is especially suitable for high-speed aircraft. Its disadvantage is that it is difficult to tune.
41. Dielectric antenna
Dielectric antenna is a round rod made of low loss and high frequency dielectric material (generally polystyrene), one end of which is fed by coaxial line or waveguide. 2 is the extension of the inner conductor of the coaxial line to form a vibrator to excite electromagnetic waves; 3 is coaxial line; 4 is a metal sleeve. The function of the sleeve is not only to clamp the dielectric rod, but also to reflect the electromagnetic wave, so as to ensure that the electromagnetic wave is excited by the inner conductor of the coaxial line and propagated to the free end of the dielectric rod. The advantages of dielectric antenna are small size and sharp directivity; The disadvantage is that the medium has loss, so the efficiency is not high.
42. Periscope antenna
In microwave relay communication, the antenna is often placed on a high support, so it needs a long feeder to feed the antenna. Too long feeder will cause many difficulties, such as complex structure, large energy loss, distortion caused by energy reflection at feeder joint, etc. In order to overcome these difficulties, a periscope antenna can be adopted. The periscope antenna is composed of a lower mirror radiator arranged on the ground and an upper mirror reflector installed on the support. The lower mirror radiator is generally a paraboloid antenna, and the upper mirror reflector is a metal plate. The lower mirror radiator emits electromagnetic waves upward and reflects them through the metal plate. Periscope antenna has the advantages of low energy loss, low distortion and high efficiency. It is mainly used in microwave relay communication with small capacity.
43. Helical antenna
It is an antenna with spiral shape. It is composed of metal helix with good conductivity, which is usually fed by coaxial line, the center line of coaxial line is connected with one end of helix, and the outer conductor of coaxial line is connected with grounded metal mesh (or plate). The radiation direction of spiral antenna is related to the circumference of spiral line. When the circumference of the helix is much smaller than a wavelength, the direction of the strongest radiation is perpendicular to the helix axis; When the circumference of the helix is in the order of one wavelength, the strongest radiation appears in the direction of the helix axis.
44. Antenna tuner
An impedance matching network connecting a transmitter and an antenna is called an antenna tuner. The input impedance of the antenna changes greatly with the frequency, while the output impedance of the transmitter is certain. If the transmitter is directly connected with the antenna, when the frequency of the transmitter changes, the impedance between the transmitter and the antenna does not match, which will reduce the radiation power. Using the antenna tuner, the impedance between the transmitter and the antenna can be matched, so that the antenna has the maximum radiation power at any frequency. Antenna tuners are widely used in ground, vehicle, shipborne and aviation short wave radios.
45. Log periodic antenna
It is a broadband antenna, or an antenna independent of frequency. Among them, it is a simple log periodic antenna, and its dipole length and spacing comply with the following relationship: τ The dipole is fed by a uniform two-wire transmission line, and the position of the transmission line should be changed between adjacent dipoles. This kind of antenna has one characteristic: all the characteristics at f frequency are determined by τ All frequencies given by F will repeat, where n is an integer. These frequencies are drawn on a logarithmic scale at equal intervals, and the period is equal to τ Logarithm of. The name of log periodic antenna comes from this. The log periodic antenna only repeats the radiation pattern and impedance characteristics periodically. However, if an antenna with such a structure τ If it is not much less than 1, the change of its characteristics in a cycle is very small, so it is basically independent of frequency. There are many kinds of log periodic antennas, including log periodic dipole antenna and monopole antenna, log periodic resonant V-shaped antenna, log periodic helical antenna and so on, among which the most common is log periodic dipole antenna. These antennas are widely used in short wave and above.