A TV antenna is a device for improving the quality of wave reception. TV channels. The signal received with its help is transmitted to the TV via, which provides minimal distortion. Antennas can be used to receive an analog, digital or satellite signal, depending on their design features. At the moment, in Russia, the most common are antennas analog television. It is broadcast by the Ostankino Tower, using meter and decimeter waves.
Types of television antennas
The device is very common, since almost no TV will be able to work without an antenna, with the exception of those that are connected to cable TV. Different settlements have different distances from the repeater. Some houses can be located hundreds of kilometers away, while others are just a few steps away. This factor directly affects the power of the antenna, which will allow you to receive a signal of acceptable quality, compensating for the distance. All TV antennas can be divided into 3 categories:
- Room.
- Street.
- Satellite.
Indoor TV Antenna
These devices are installed indoors. They are the cheapest, and besides this, they do not require complex installation. When choosing in their favor, you do not have to lay a coaxial cable outside, making a through hole in the facade wall or window frame. The major disadvantage of this design is weak signal. In this regard, they are installed only in areas with a distance of up to 30 km from a television center or repeater. At a longer distance, the received signal will have a strong distortion, which will not allow you to view a high-quality TV picture.
Indoor antennas can also be equipped with a signal amplifier. The farther from the repeater, the more powerful amplifier will be required. These devices are divided into two types by design:
- Rod.
- Framework.
Rod
These are the weakest room devices. They have 2 or 4 telescopic mustache-vibrators, which pick up the signals. Their length usually does not exceed 1 m. They are connected to a special stand, which has a matching transformer inside, which transmits the signal to the coaxial cable and further to the TV. Using this design has its advantages. It is lightweight, and thanks to the telescopic mustache, it can be compactly folded for transportation.
If the signal repeater is close, the mustache can be made short so that it does not take up useful space. When the TV tower is far away, their height is set to the maximum, which allows you to compensate for the distance. Often, a rod TV antenna comes with a TV. To most, it is known by the popular name "horns". Such antennas well receive waves in the meter range. To carry out their adjustment, it is necessary to change not only the height, but also the distance between the whiskers, for which their fastening with the help of hinges is provided. The big disadvantage of the rod antenna is the lack of universal setting. Having set the position of the mustache for good reception of one channel, the second will begin to be broadcast on the screen with interference.
Framework
More or less perfect are frame-type devices. They pick up signals in the decimeter range. These devices have a metal outline, made in the form of a frame, which is fixed on a stand. Such equipment is still better than rod equipment, but still far from ideal. It cannot be used at a considerable distance from the repeater or TV tower.
outdoor TV antenna
More powerful are outdoor antennas for receiving a television signal. They are installed on a hill in areas of open visibility. Often such antennas can be seen on the roofs of multi-storey buildings. Residents of the private sector install them on top of a tall metal pipe fixed vertically. In this case, an elevation of 10-15 m is provided, which makes it possible to compensate for the distortion of waves by the walls of houses and tree branches. In fact, the more signal obstructions around, the higher the distance you need to raise the antenna.
These devices come in various external designs, but they are all divided into 2 types according to the principle of operation:
- Active.
- Passive.
active design
Such a TV antenna has, which allows you to receive signals much better and compensate for interference. Such devices are selected if the repeater is far away, and there are serious signal-scattering obstacles in front of the antenna, such as houses, forest areas and power lines. Also, an active device will be required if the installation is carried out on a lowland, when there is no direct line of sight between the broadcast source and the receiving point.
Active antennas can transmit a signal to several TVs. To do this, you just need to use a special tee for coaxial cable. The amplifier they use requires a separate power supply. For this, a step-down block of 12 volts is provided. It connects to a coaxial cable at the TV and supplies voltage to the receiving point to the vibrating antennae, near which there is an amplifier board hidden in a sealed case.
Passive devices
Such antennas are cheaper, but they can only be chosen if there is a line of sight without obstacles between the receiving point and the broadcast equipment. In such conditions, the use of an amplifier is not necessary. Residents of individual houses may live too close to the broadcast tower, so they need just such an antenna. But even she can receive a signal with distortion from the fact that it is too strong. In this case, you will need to install special equipment - an attenuator. It allows you to compensate for this shortcoming by reducing the signal strength to an acceptable level for the TV.
Satellite antenna
Of course, the best equipment for receiving a television signal is a satellite TV antenna. It picks up the broadcast not from a TV tower located on the ground, but from a satellite. This is a massive structure, which is many times more expensive than outdoor and even more so indoor devices. The antenna consists of a large white painted metal dish that acts as a screen for focusing the satellite broadcast. The waves that hit it are captured by a converter, which is made in the form of a small head a little smaller than a fist. It tunes in to a specific satellite and receives all the TV channels that it transmits. The number of converters on the antenna differs depending on the region, but rarely exceeds 3 pieces.
The signals of conventional broadcasters on the ground and satellite ones are different, so the TV cannot perceive them. In this regard, a receiver is installed between the inverter and the television screen. He is small device, the dimensions of which are slightly smaller than DVD set-top boxes. Its task is to transform the satellite signal into a standard TV signal.
Usually, if there are two TVs in the house, then each of them will require a separate TV antenna, which is due to the specifics of the converter. When receiving one channel from a satellite, it cannot process another channel at the same time. In other words, if you make such a connection, then all TVs will show one TV channel.
Relatively recently this problem has been resolved. Universal converters have appeared that allow you to connect to two TVs, while maintaining the ability to view different channels. Their design provides two inputs for connecting a coaxial cable. Unfortunately the design is not perfect. When choosing such a converter, one TV antenna will be used, but you still need to connect a receiver to each TV.
Satellite devices transmit a much better signal to the TV than terrestrial stations, therefore they are very popular, especially in regions where broadcasters are very far away. Even with very difficult terrain, you will be able to watch television programs with a perfect picture, which would be impossible with an outdoor antenna. Satellite broadcast interference may occur only in the event of a severe thunderstorm or heavy snowfall.
Satellite dishes have a lot of advantages. They are certainly better than other types, but they also have a drawback. In addition to being more expensive, they require skilled maintenance. It is unlikely that you will be able to install them yourself, because you need to initially check the signal quality and set the dish in the right direction at the right angle. In addition, for the receiver to work correctly, it is necessary to record the frequencies of the broadcast channels, which change periodically. After the firmware, it will be possible to view all the channels for several months, after which some of them will begin to disappear until only a few of the hundreds remain. You will need to re-flash again. Doing it yourself is difficult because you need a special cable and software with channel codes. You will have to periodically contact specialized service centres whose services are not free.
If, under normal weather conditions, a satellite TV antenna begins to broadcast a signal with interference, then this is most likely due to the lack of a direct line of sight between the dish and the satellite. Usually this is due to the growth of trees. It is enough to cut the branches and the signal quality is restored. In addition, the problem may lie in changing the position of the converter. When mounting the antenna, it is set at the correct angle relative to the location of the satellite. If the angle changes slightly, the reception quality is distorted. Usually, during strong winds, a poorly fixed dish can turn a little, literally a few centimeters. In this case, it needs to be reconfigured. This is quite difficult to do without special diagnostic equipment.
Antennas(from the Latin word antenna - mast, yardarm) in transmitters serve to convert radio frequency electrical oscillations into the energy of an electromagnetic field (radio waves), in receivers- to convert the energy of radio waves into radio frequency currents.
Any antenna can be used for both transmission and reception, and its characteristics (frequency range, directional properties, etc.) are preserved.
This largely explains the fact that the purpose of the antenna (receiving or transmitting) usually does not reflect its symbol. The very location of the antenna symbol on the diagram uniquely determines its function (recall that the development of the diagram, as a rule, occurs from left to right).
Rice. 1. Designation of symmetrical antennas on the diagrams.
The general designation of the antenna is used in cases where it is necessary to show an asymmetric antenna, that is, an antenna connected to a transmitter or receiver with one wire (ground serves as the second wire). Such antennas are used in the ranges of long, medium and short waves. In the ultrashortwave range, as well as in the shortwave range, symmetrical antennas are used, that is, antennas with a two-wire output (or input). The general designation of a symmetrical antenna differs from those indicated by the presence of two leads (Fig. 1, a).
Purpose and features of the antenna in the most general form, they show the direction of flow propagation with signs electromagnetic energy. The symbols of the receiving, transmitting and receiving-transmitting antenna, built using these signs, are used in many schemes.
The ESKD standard provides for special signs to indicate such features of antennas as the width and nature of movement (rotation, swing) of the main lobe of the radiation pattern, the type of polarization, directivity in azimuth and height, etc. As examples of the use of such signs in Fig. 1 shows the symbols of a rotating antenna (b) and antennas with horizontal (c) and vertical (d) polarization.
To improve the efficiency of asymmetric transmitting and receiving antennas, grounding is used (in the simplest case, this is a metal sheet or pipe buried to the depth of soil water). In the diagrams, grounding is depicted with three short strokes inscribed in a right angle (Fig. 2, a). Sometimes, instead of grounding, a counterweight is used - big number wires stretched above the ground at a low height. Such a device is indicated by two parallel lines of different lengths, the larger of which symbolizes the earth (Fig. 2, 6).
Rice. 2. Designation on the grounding diagrams.
The considered symbols are constructed by the functional method. In other words, they are based on the general symbol of the antenna, and the characteristics are expressed by auxiliary signs. In radio engineering, such designations are used mainly in structural and functional diagrams, i.e., at the first stages of device development, when the characteristics of the antenna are determined, and its specific type has not yet been selected.
AT circuit diagrams more often they use conventional graphic symbols, reminiscent of extremely simplified drawings of specific types of antennas. So, the simplest antenna - an asymmetric vibrator (vertical wire, pin) is depicted as a segment of a vertical thickened line (Fig. 3). Such antennas are used in the ranges of long, medium, short and ultrashort waves.
Rice. 3. Antenna - asymmetrical vibrator in the receiver.
However, for such an antenna to work well, its length should be approximately a quarter of the operating wavelength. In the ranges of short and ultrashort waves, the length of which does not exceed several tens of meters, this requirement is easy to fulfill, but at medium and even more so at long waves, it is much more difficult, since a quarter of the wavelength in these ranges reaches hundreds of meters.
In order not to build expensive high-rise structures, one or more horizontal wires are attached to the upper end of the vertical wire (vibrator), the effect of which is to seem to lengthen the vibrator. In the diagrams, the L-shaped and T-shaped antennas are indicated by symbols that clearly convey them characteristics(Fig. 4, a, b).
Rice. 4. Designation on the diagrams of L-shaped and T-shaped antennas.
For the considered asymmetric vibrators, the vertical part serves as the emitter (receiver) of radio waves. In the ranges of short and ultrashort waves, due to the peculiarities of their propagation, antennas are usually used, in which the horizontal parts are working.
The simplest antenna in the ed bands is a symmetrical vibrator, which is two insulated horizontal conductors of the same length, between which a two-wire line is connected connecting the antenna to the receiver or transmitter. This communication line is called a feeder (from the English feeder - feeder). The total length of the vibrator is usually equal to about half the length of the operating wave. "
Symmetrical vibrator(its conventional graphic designation is shown in Fig. 5) has clearly expressed directional properties. Best of all, it receives or radiates in a plane perpendicular to its axis, worst of all - in planes passing through it. Therefore, such. the antenna (for example, for receiving television) is positioned so that its horizontal parts (shoulders) are perpendicular to the direction of the television center.
Rice. 5. Designation of the antenna "Symmetrical vibrator".
In practice, it is often required that the antenna be able to emit or receive radio waves over a sufficiently wide frequency band. Achieve this is; using several parallel wires as arms of the vibrator, connected by ends.
Antennas of this design, known as the Nadenenko dipole, have found wide application in shortwave communications. For the same purpose (expanding the frequency range) television antennas often made from pieces of thick tubes or complex vibrators, such as loop vibrators, are used.
Loop vibrator consists of two half-wave vibrators connected by ends. This design feature of the loop vibrator is also reflected in its symbol (Fig. 6).
Rice. 6. Antenna - loop vibrator.
An important condition for good antenna performance is matching its input impedance with the wave impedance of the feeder, since only in this case it can radiate or receive the greatest power. To match the antennas with the feeder, use special devices in the form of segments of two-wire lines or use the so-called shunt power supply of vibrators.
Shunt powered symmetrical vibrator is a continuous conductor with a length also equal to half the length of the will. The feeder is connected to it at two points located symmetrically with respect to its middle. By changing the places where the feeder is connected to the vibrator, it is possible to achieve equality of the input impedance of the antenna to the wave impedance of the feeder, i.e. matching. In the same way, the loop vibrators of shunt power are coordinated with the feeder. The symbol of a half-wave vibrator with shunt power is shown in fig. 7.
Rice. 7. Symbol of a half-wave vibrator with shunt power.
When using a coaxial cable as a feeder, there is a need for balancing, i.e., creating conditions under which the currents at the points of connection to the vibrator have opposite phases. In practice, the balancing device is made in the form of a piece of half-wavelength cable, bent in the form of the letter U.
Power supply through a coaxial cable with a balancing device of this kind illustrates the symbol of the loop vibrator shown in fig. 8 (the cable here is indicated by a circle with a segment of a tangent parallel to the electrical communication line, and the matching device is indicated by an arc connecting the vibrator leads).
Rice. 8. Power supply via coaxial cable with balun.
To communicate on short waves, antennas must be unidirectional, that is, they must radiate and receive radio waves from only one direction. A typical representative of such antennas is a rhombic antenna, which is a rhombus made of wire, the sides of which are about four times the wavelength. A two-wire feeder is connected to one of the sharp corners of the antenna, and an absorbing load is connected to the other, the resistance of which is equal to the wave impedances of the antenna and feeder. In the symbol of a rhombic antenna, the symbol of the resistor (absorbing load) is reduced by about half compared to the usual one. This makes the antenna designation more compact (Fig. 9).
Rice. 9. More compact designation of the antenna.
In the meter and decimeter wavelengths, antennas are often used " wave channel”, which have a significantly greater, compared with a single vibrator, directional action coefficient. Such an antenna, in addition to the main - active - vibrator, contains several passive ones. One of them, located behind the active one, is called a reflector (from Latin reflectere - to reflect), the rest (located in front of the active one) are called directors (directio - to direct). The length of the reflector is somewhat longer, and the directors are somewhat less than the length of the active vibrator. In the diagrams, this is shown by the different lengths of the corresponding symbols in the antenna symbol "wave channel" (Fig. 10).
Rice. 10. Antenna symbol "wave channel".
In order to improve the directional properties of antennas, they are also used metal reflectors in the form of corners bent from a metal sheet, paraboloids, etc. The symbol of such a reflector reproduces (of course, simplified) its profile in section. As an example, in fig. 11, the graphic symbols of an antenna with a radiator (receiver) in the form of a symmetrical vibrator and a corner reflector (a) and an antenna with a curvilinear reflector (b) are proved, the vibrator of which is fed through a coaxial cable (the balancing device is not shown for simplicity).
Rice. 11. Designations of antennas with a radiator (receiver) in the form of a symmetrical vibrator and a corner reflector (a) and an antenna with a curvilinear reflector (b).
For the transmission of electromagnetic energy in the ranges of centimeter and millimeter waves, waveguides- metal pipes, usually rectangular. The open end of the waveguide radiates electromagnetic waves. To improve the radiation, a pyramidal funnel is attached to it, which is called a horn antenna. The symbol of the latter is shown in fig. 12. Here, a corner resembling a socket of a detachable connection symbolizes an antenna horn, a rectangle on an electrical communication line attached to it - a rectangular waveguide.
Rice. 12. Antenna - pyramidal funnel.
An improvement in directional properties in these wave ranges can also be obtained by using a metal reflector by placing a horn emitter in its opening (Fig. 13). The so-called dielectric antenna. It is a solid or hollow rod made of high-quality dielectric (polystyrene, polyethylene), on the base of which a metal cup is put on, which acts as a reflector. At a distance of a quarter wavelength from the bottom of the glass, an exciting pin is fixed in the body of the antenna.
Rice. 13. Horn emitter.
Due to the special shape of the generatrix of the rod, electromagnetic waves come out of it at the same angles to the axis, as a result of which directed radiation is created. The conventional graphic designation of a dielectric antenna is a narrow triangle shaded with oblique lines with a line leading from a smaller base (Fig. 14).
Rice. 14. Conditional graphic designation of a dielectric antenna.
The so-called magnetic antennas(they do not respond to the electrical component of electromagnetic waves, like all previously considered antennas, but to the magnetic one). The simplest antenna of this type is a frame consisting of one or more turns of wire. Regardless of the shape of the turns, the loop antenna is depicted as an open square with lead lines from adjacent sides (Fig. 15).
Rice. 15. Image of a loop antenna.
Much more often, magnetic antennas with a ferrite magnetic circuit are used. In the diagrams, they are designated as one or more (according to the number of windings) inductors with a common magnetic circuit, but unlike the latter, they are always placed horizontally (Fig. 16, a).
Rice. 16. Magnetic antenna.
Belonging to antenna devices is shown with a common symbol, placing it above the middle symbol magnetic circuit. The windings of a magnetic antenna are usually used as coils of input oscillatory circuits, therefore they are designated by the code of the coils - the Latin letter L, and the possibility of adjusting their inductance (by moving along the magnetic circuit) is shown with the already familiar sign of tuning regulation (Fig. 16.6).
Literature: V.V. Frolov, Language of Radio Circuits, Moscow, 1998.
Each antenna as a passive linear device can work:
In transmission mode;
in receive mode.
In both modes, the antenna is characterized by directional, polarization properties and input impedance.
The main characteristics and parameters that describe these properties include:
Bandwidth;
input impedance;
Radiation pattern (DN);
Coefficient of directed action (KND);
Antenna gain (KU);
Antenna efficiency (efficiency);
Bandwidth
The frequency range within which the amplitude-frequency response (AFC) of the antenna is sufficiently uniform to ensure signal transmission without significant distortion of its shape.
This is the range of frequencies over which the antenna operates effectively, usually the center (resonant) frequency region. Depends on the type of antenna, its geometry.
The main parameters that characterize the bandwidth of frequencies are the bandwidth and the unevenness of the frequency response within the band.
Fig.5
The bandwidth (Fig. 5.) is usually defined as the difference between the upper and lower boundary frequencies of the frequency response section, in which the oscillation amplitude from the maximum decreases to the root of two times or the power decreases by 2 times. This level corresponds approximately to -3 dB. The bandwidth is expressed in units of frequency (eg, hertz).
The uneven frequency response characterizes the degree of its deviation from a straight line parallel to the frequency axis, expressed in decibels.
Antenna input impedance.
An antenna is a source of a signal, which is characterized by an electromotive force (EMF) and an internal resistance, which is called the input impedance of the antenna.
The value of the input impedance of the antenna must be known in order to correctly match the antenna with the feeder and receiver (transmitter): only under this condition does the greatest power enter the input. With proper matching, the input impedance of the antenna should be equal to the input impedance of the feeder, which, in turn, must be equal to the input impedance of the receiver (transmitter). The input impedance (impedance) of the antenna is rarely equal to the impedance of the feeder line. Matching devices are used for matching.
The input impedance of the antenna also depends on objects located near the antenna and affecting the distribution of the field in space, which must be taken into account when installing the antenna.
The dependence of the input impedance of the antenna on frequency is called frequency response: the less the input impedance of the antenna changes with the change in frequency, the wider its bandwidth.
Receiving antenna radiation pattern.
This is a graph that characterizes the dependence of the EMF induced in the antenna by an electromagnetic field on its orientation in space.
The antenna pattern gives graphic representation dependence of the antenna gain or antenna directivity on the direction of the antenna in a given plane. A radiation pattern is built in polar, spherical (Fig. 4) or in rectangular coordinate systems in two characteristic planes (horizontal and vertical).
When the antenna is rotated in one direction or another from the zero direction, the values corresponding to the E/Emax ratio are plotted on the diagram. If we square the relative EMF values, corresponding to different directions of signal arrival, then it is possible to construct a radiation pattern in terms of power (Fig. 7).
Fig.7.
antenna range radio wave feeder
The main parameter of the radiation pattern is the opening angle (width) of the main lobe, within which the power drops to a level of 0.5 of the maximum.
The lobe corresponding to the maximum signal or the zero direction is called the main or main lobe, the rest are side or rear (depending on the location in relation to the main lobe).
The width of the main lobe is used to judge the directional properties of the antenna. The smaller this width, the greater the directivity of the antenna.
The shape of the radiation pattern depends on the type and design of the antenna. For example, the radiation pattern of a half-wave vibrator in the horizontal plane resembles a figure eight, and in the vertical plane it resembles a circle.
In some cases, the diagram is built in two mutually perpendicular E and H planes. The polar diagram shows the direction in which the energy of the corresponding component is concentrated. An example of a polar pattern in the E-plane is shown in fig. 8. The value of the amplitude of the emitted field is plotted along the radius, normalized to the value of the amplitude in the main maximum.
Fig.8
Antenna directivity.
This number indicates how many times the power received at the receiver input when received on a directional antenna is greater than the power that can be obtained when received on an omnidirectional antenna (at the same field strength).
The directivity properties of the antenna are characterized by the directivity pattern discussed above (Fig. 5).
Antenna Gain
The ratio of the power at the input of the reference antenna to the power supplied to the input of the antenna under consideration, provided that both antennas create in a given direction at the same distance equal values field strength or the same power flux-density.
The antenna gain shows how many times it is necessary to increase the power at the antenna input (transmitter output power) when replacing this antenna with an ideal non-directional antenna so that the value of the power flux density of the electromagnetic field emitted by the antenna at the observation point does not change. It is assumed that the coefficient of performance (COP) of an omnidirectional antenna is equal to one.
Antenna gain is a dimensionless quantity and can be expressed in decibels (dB).
Antenna efficiency
This is a parameter that characterizes the power loss in the antenna and is the ratio of the radiation power to the power that is supplied to the antenna from the transmitter.
The power lost in the antenna consists of losses in the ground, antenna wires, insulators used to suspend the antenna web, in the ropes supporting the antenna. The main energy losses are losses in the ground.
By virtue of the principle of antenna reversibility, the efficiency of a receiving antenna is estimated by the efficiency that it will have when used as a transmitting one.
Since the power of the received radio waves is very small, the efficiency of the receiving antenna may be low, but not less than 10-15%.
Conclusion
During the creation of this work, I studied:
Appointment of antenna-feeder devices;
The range of radio waves used in radio engineering;
Types of antennas;
Basic parameters of antennas.
Bibliography
G.A. Erokhin, O.V. Chernov, N.D. Kozyrev, V.D. Kocherzhevsky "Antenna-feeder devices and propagation of radio waves";
V.F. Vlasov "Course of radio engineering" - Moscow, 1962
Chapter 4 - Antennas - "windows" to other worlds
From the electronic version of the printed edition of the book by A. Pois: "Our World and We", part 1 - "The World and Us"(Series of the publication: "The search for truth", M. ICSTI - International Center scientific and technical information. OOO " Mobile communications", 2004), posted on the website www.pois.ru
Chapter 4 - Antennas - "windows" to other worlds.... 1
Purpose and directional properties of antennas .. 1
different types antennas.. 6
Antennas not called antennas. 24
Space scale antennas.. 25
Cosmic inhomogeneous dielectric lenses and gravity. 26
Egyptian pyramids as irradiators of a lens antenna named "Earth". 30
Galaxies, interstellar nebulae, planetary shells and black holes as antennas.. 32
Earth scale antennas.. 36
Antennas of the microworld.. 44
Some artificial forms like antennas.. 50
Common parameters real and field antennas .. 55
Conclusions.. 57
Antennas, as you know, are a very "narrow" scientific direction, but they are used so widely that almost every person uses one or another antenna in his daily life, without thinking, as a rule, either about the principles of their operation or about their properties. Antennas belong to that field of science, without which further knowledge of the world is impossible, since they are the devices I/O energy, allowing the exchange of information, including through huge intervals of space-time. They are always located on the outer surface of the environment, the "windows" of which they are, and therefore they are easy to detect. In addition, all the basic information about the antennas themselves, as well as about ourselves, is “written on the face” and can be read quite easily by the relevant specialists. The theory of antennas, which is based on the theory of the electromagnetic field, is so universal that it can be used in various fields of science. Below is the basic information about antennas. And although its primary sources -, - and - are designed for students of higher educational institutions and narrow specialists, it is given here in the most general form and is presented, if possible, in a popular way, therefore it can be understood by a fairly wide range of readers. In addition to antennas created by man, this chapter discusses natural antennas, and some artificial structures, which, as a rule, are not considered antennas, although in fact they are. Among the antennas created by Nature itself, you can find analogues to all antennas created by man.
Purpose and directional properties of antennas
Antenna- a device designed for radiation (emission, "sputtering") and reception (absorption, "trapping") electromagnetic waves. However, similar devices are also used when working with elastic waves, especially sound waves.
An antenna converts vibrations into free waves (or vice versa) and radiates (receives) these waves in certain directions (from certain directions) in accordance with its radiation pattern. The waves between the antenna and the generator (receiver) propagate along the feeder line ( power line) in the form of connected, "running" along it, waves.
By the transmitting antenna, the coupled waves coming from the exciter of oscillations - the generator, are converted free, which are then emitted ("sputtered") and propagated in free space. The receiving antenna performs reverse actions- captures free waves and converts them into coupled ones, which are then transmitted to the receiver, where they are again converted into oscillations.
Strictly speaking, absolutely there are no free waves, just as there is no absolutely free space. Therefore, propagating even in supposedly free space, the waves are associated with the medium, although to a disproportionately lesser extent than with the energy guide.
If any UNITY is indeed a particle-wave, then the "catchers" and "sprayers" any particle-waves, and not just electromagnetic ones, can also be called antennas.
An antenna, in principle, can be any, and not only a material and visible, but also a field and invisible form, capable of "catching" - receiving or "spraying" - emitting energy of one kind or another. But it can only capture energy blank, "empty", a form having flaw this type of energy. And "spray" - only crowded a form that has an excess of energy. The unfilled and overfilled form is, as has already been shown, a kind of energetic "concavity" and "convexity", respectively. In the first, the density of energy of a certain type is less than in the space communicating with it, and in the second - more.
Energy Conduits used in antenna technology are shown in fig. 4.1 (pos.1).
Many devices created by Nature and man have a similar form. And although most of them are not called energy conduits, they can actually become them if the kind of energy that they are able to direct appears in their environment. In principle, natural and artificial elements that have not only a similar design, but also many other forms can serve as energy conduits.
Man-made structures capable of serving as energy conduits include many building elements, including various pipes and rolled profiles. To natural - riverbeds; roots, trunks and branches of plants; caves and much more, including layers of the atmosphere of different density, which, as you know, are atmospheric waveguides for a certain range of waves (see Fig. 4.1, pos. 2).
Any the power guide always acts as an antenna, although the gain of such an antenna can be infinitely small. This is a consequence of the fact that absolutely closed systems have not been created either by man or by Nature, and any system, at least a little ajar for energy of one kind or another, is already an antenna. A good antenna is an open power cable, for example, oscillatory circuit. In a closed circuit, energy, changing with a certain frequency in time, oscillates in a small space interval. But if the circuit is “opened”, then these oscillations will “stretch” in space, forming waves, and the oscillatory circuit will turn into an antenna.
Free electromagnetic wave, as already mentioned, is a system of closed circuits (see Fig. 2.1, pos. 2), inside which circulates electricity is the flow of electrons. Electrical circuits create around themselves a closed magnetic field, consisting of many magnetic "rings" located in a plane perpendicular to the plane of the electrical circuit. Magnetic "rings", in turn, create electrical, etc. As a result, a moving field is formed, consisting of "stringed" on each other and located in mutually perpendicular planes of "rings". Each of these "rings" can be considered as a closed circuit in which standing waves "beat", creating bulges and concavities on its surface. The formation of single “rings” visible to us that “breathe” can be demonstrated by an experienced smoker, sharply exhaling smoke. Similar particle-waves can also be "knocked out" from the "Theta" apparatus.
The Theta apparatus is wooden box, in which instead of one wall a dense matter (membrane) is stretched, and a hole is cut out on the opposite wall. With a sharp blow to the membrane, air (it should be tinted to make it visible) is ejected from the hole in the form rotating ring.
Directional properties of antennas- the ability to concentrate (amplify) particle-waves in certain directions by creating narrow beams (beams) or other, sometimes very complex, forms from them, as is known, manifest themselves when their dimensions significantly exceed the wavelength. However, almost any antenna has a directivity, at least a small one. Directional properties are subject to reciprocity principle, from which it follows that directional properties antennas during operation in transmit and receive mode are the same. The directional emission of particle-waves allows, without increasing the transmitter power by tens, hundreds, thousands and even millions of times, to increase the concentration of particle-waves in certain directions and (or) without increasing the sensitivity of the receiver, amplify the signal attenuated by the same number of times coming from the same directions . The directional properties of an antenna are determined by its radiation pattern.
An analogue, albeit a distant one, of directional "antennas" can be large enterprises. During peak hours, they “catch” or “emit” a large number of people, increasing the density of human flows in certain directions. In this case, the principle of reciprocity is also implemented - the flows of people, both when they are “captured” by the enterprise, and when they are “emitted”, will be approximately the same, but directed in opposite directions.
Directional pattern (DN) determines the nature of the distribution in space of the power of the electromagnetic field emitted (received) by the antenna.
It follows from the definition that, in the general case, the RP determines the distribution of energy in space, the direction of its movement, i.e., directional properties. It is a kind of distribution network. Therefore, DN has any a system capable of directing (distributing) certain types of energy, particle-waves of a certain range in a certain way. Any network of power lines also is kind DN.
Ocean and air currents; orbits, comets, planets, stars, etc.; way to work and back; a network of all kinds of lines of force, including magnetic ones; and many other networks are a kind of NAM. For cars, this is a network of roads, and for trains, it is a network of railways. For water - a network of reservoirs and voids in the earth's crust, including caves and underground rivers, a water supply network, etc. For aircraft - air routes. For electric current and gas - electric and gas network, respectively. For the energy that ensures the vital activity of humans and animals, it is mainly the nervous, circulatory, lymphatic and digestive systems. All these systems (and not only them), like a water or gas network or a road system, at certain intervals of space-time can be filled particles-waves of one kind or another, but may or may not be filled. DN defines only possibility the movement of energy through a particular distribution network, and not the energy itself and its movement.
The radiation pattern is, as you know, one of the main characteristics of the antenna. The shape of the DN and the "length" ( range) of its individual petals, first of all, determined, as is known, configuration and density working surface of the antenna, as well as its size in wavelengths (“specific interacting surface”). It also depends on the spatial orientation of the wave (polarization), on the parameters of the environment, on the type of the wave itself, and much more. An infinite number of forms of RPs are known, corresponding to certain antennas when they operate at certain wavelengths. Many of them can be calculated with great accuracy, but what is invisible to us, the RP, "filled" with energy, including the RP of antennas designed to receive and transmit electromagnetic waves, remains not entirely clear. Therefore, let's try to figure it out, taking into account the assumption made earlier that the charges that determine the distribution of energy in space are energy "bulges" and "concavities".
Absolutely "empty" space, as has been repeatedly noted, has not been found in nature. Any space, including vacuum, with one or another density is filled with both relatively stable (“resting”) and unstable (acting, moving, changing) particles-waves, majority of which remains for us invisible. Therefore, any form introduced into any space, like any body lowered into water, in a completely definite way of its distorts- redistributes the particles and quasi-particles filling it. In general, it redistributes energy. As a result, new energy flows and new energy forms are formed - “bulges” and “concavities”, which are immediately filled with the energy available in environment until the system reaches a state of static or dynamic equilibrium. If in a given space-time interval there is no type of energy capable of filling this energy network, but it appears over time, then this energy is distributed in accordance with the "voids" suitable for it and communicating with each other, capable of absorbing it, i.e., according to a certain radiation pattern. And it does not depend on which side this energy "flows" - from inside or outside. The same applies to antennas. DN, "filled" with electromagnetic or any other field particles-waves, in turn, is also a kind of energy form - invisible antenna. It also bends space, redistributing its energy (particles-waves) and creating new energy "bulges" and "concavities" - another distribution network, DN of the next order. Etc.
Hypothesis 4.1 : The radiation pattern, in general, is a certain energy form created by the body by changing the curvature of space, creating energy "bulges" and "concavities" by redistributing resting and (or) moving real and field particles and quasi-particles of various shapes, sizes and configuration. The form blank radiation patterns determined by location communicating spatio-temporal energy"voids" (filled - by the arrangement of seals), the size of which is commensurate with the size of certain particles-waves or more, and energy the spatio-temporal density of the surface (or volume) that bounds these voids does not allow these particle-waves to pass through it completely freely.
An example visible us "concavity", limited by a surface opaque for certain particles-waves, can serve as a "dish" of the NTV antenna, as well as the most ordinary plate or colander. In order for an antenna (and not only an antenna) having one or another RP to turn from “dead” into “alive” (active), it is necessary to breathe a “soul” into it - fill it with particles-waves. And not any, but those with which she is able to interact - to capture and emit, and in a certain way.
The radiation pattern image can be spatial or flat (in polar or rectangular coordinate system). With a planar image, DNs are most often produced in the most characteristic sectional plane or in two main mutually perpendicular planes. The spatial image is very complex and time-consuming, therefore, a planar image is more often used.
On fig. 4.2 shows a spatial and planar (in polar and Cartesian coordinates) image of a needle and fan pattern (pos.1), as well as several spatial patterns of various shapes (pos.2-4), which are similar to many well-known real forms, including the shape of some antennas.
On fig. 4.3 shows a schematic representation and planar DN of several types of antennas -: a vertical quarter-wave vibrator located above the screen (pos.1); a thin angular vibrator (half-wave and wave) having a different angle between the arms (pos. 2); three cylindrical helical antennas (pos.3) having different sizes in wavelengths; a symmetrical vibrator having different sizes in wavelengths and different thicknesses (pos. 4); a biconical antenna having a different size in wavelengths (pos.5); a thick angular vibrator having a different size in wavelengths (pos.6); dielectric rod antenna (pos.7); wire rhombic antenna (pos. 8); an antenna consisting of a vertical vibrator and three radial wires (pos. 9), an antenna of four radial vibrators located on the surface of the cylinder (pos. 10); and also (bottom) RPs of different antennas, the shape of which is most typical. The corresponding spatial MDs are, as a rule, the body of rotation of a planar MD around the axis of symmetry.
The directional properties of many antennas are highly dependent on the presence or absence of a shield. If, for example, a horizontal or vertical vibrator is placed at a certain distance from a conducting screen, then this is equivalent to the appearance of another (virtual) vibrator, which, being only mirror reflection first, affects the distribution of the field in a very real way. As a result, the pattern is obtained as if it were a system consisting of two real vibrators. The reflective screen, especially at long and medium wavelengths, is often the ground; at short and ultrashort wavelengths, metal screens are most often made, which can be solid or mesh. Sometimes they are made and radiant. Most often, screens are used to create one-way radiation. The directional properties also depend heavily on the screen size. For example, the DN of a quarter-wave vertical vibrator shown in Fig. 4.3 (pos. 1) in the presence of an infinite screen is a continuous funnel-shaped body (dotted line). At the final screen, this body consists of several layers (petals) and resembles the cup of a multi-petal flower in shape.
If you mentally imagine the spatial forms of the given planar RPs, then many of them will turn out to be similar to certain visible objects of the world around us, and multi-petal RPs, most often, look like flowers. The variety of flower forms is known to everyone, and the variety of DN forms is generally incalculable. However, even among a small number of RPs shown in Fig. 4.2 and 4.3, one can find DNs very close in form, although they belong constructively different antennas.
The fundamental difference between antennas from many other devices, as already mentioned, is that antennas are energy input-output devices, i.e., a kind of windows. Therefore, they, as a rule, are located on the border of environments ("worlds") and are open for viewing. Moreover, even one external The type of antenna an experienced specialist can often determine many of its parameters, including the main ones - the possible operating range and directional properties.
If any UNITY is really a transceiver for particle-waves of various types and ranges, then it is also an antenna, most often an infinite set of antennas. Therefore, it is the antennas that will help us most quickly determine the main parameters of each UNITY. But for this, from the infinite variety of antennas, it is necessary to single out those that are of interest to us in each specific case, since any antenna, at least a little open system. But since absolutely closed systems in the real world are not discovered and not created by man, then the antennas are all EXISTING.
Various types of antennas
Modern antenna devices divided into the following main types: wire, slotted, superficial waves, acoustic type (horn), spiral, log-periodic and optical type (mirror and lens). In addition, a separate group is usually distinguished elementary radiators (dipoles), which can also be "elementary" structural elements of more complex antennas.
Elementary Emitters- this is an elementary electric vibrator (a small straight piece of conductor), an elementary magnetic vibrator (frame) and their slot counterparts, as well as a Huygens emitter.
Elementary wire and slot (rectilinear and circular) emitters and DN, which for wire vibrators and their corresponding slot "brothers" has the same shape, are shown in Fig. 4.4 (pos. 1 and 2, respectively). The theoretical DN of the imaginary Huygens element (pos. 3) is also shown there, as well as the RP (pos. 4, left) of its close real analogue - a cardioid antenna (pos. 4, right), consisting of a rectilinear element and a circular frame.
Elementary vibrator- this is very short compared to wavelength a wire flowed around by an alternating (oscillating) electric current, the amplitude and phase of which can be considered the same along its entire length. Such a vibrator is called electric, and its practical model is the Hertzian dipole.
elementary frame, which is the equivalent of a magnetic vibrator, is a coil of wire of one form or another (usually round or square), through which an alternating (oscillating) current flows, and its length much smaller than the wavelength.
Electric and magnetic vibrators are conductors through which flows alternating current. Their radiation patterns are the same in shape - this is a toroid. But in the first case, the axis of the toroid coincides with the axis of the electric vibrator, and in the second, with the axis of the frame perpendicular to its plane.
Elementary slot antenna- an antenna, the work of which is associated with the emission and reception of electromagnetic waves hole, cut through in an infinite screen or in the resonator wall.
Principle of Duality, which is very well demonstrated by elementary dipole and slot antennas, expressed in the identity of the pattern of antennas of the same shape. It does not matter whether the antenna is a conductive "body" or a "hole" of the same shape, cut out in an infinite plane through which particles-waves enter. In the first case, particles-waves break away from the electric flow flowing through the conductor, and in the second case, they “splash” through a slot from a space filled with similar flows - a resonator. What matters is the presence of a flow (current), as well as the size and shape of the surface interacting with it, from which particles-waves can “break away” or through which particles-waves can “squeeze”.
Huygens Spring- this is an imaginary primary radiator of reflector antennas, the real analogue of which can be a combination of electric and magnetic radiator, an “elementary piece” of the surface, with a certain number of which, when calculating RP, sometimes replace the surface of reflector antennas. The Huygens source in its directional properties is a combination of the properties of electric and magnetic dipoles. Its calculated RP has the form of a cardioid of rotation (see Fig. 4.4, pos. 3). Cardioid antenna, consisting of a vibrator and a frame (see Fig. 4.4, pos. 4, on the right), has approximately the same shape of the DN (see Fig. 4.4, pos. 4, on the left), as does the virtual Huygens source. And both of them are shaped like a heart.
Wire and slot antennas and their antenna systems- these are the same wire vibrators and slots, but larger (in wavelengths) than elementary vibrators, and antenna systems are multi-element structures of various shapes, composed of "elementary" (or more complex) identical radiators. Antenna systems are usually formed from several (or many) dipole, slot or other antennas arranged in a certain way. The main feature of any system is an ordered (repeating) planar or spatial arrangement of homogeneous elements or identical combinations of different elements (this is also inherent in the DNA molecule), which together form one form or another. Antenna systems consisting of active elements (energy is supplied to each 
mu of them) increase, as a rule, the gain of the antenna compared to a single element by a number of times corresponding to their number.
Wire Antennas they are most often made of wires, pipes, tapes, the cross section of which can be constant or variable. In the simplest case, a wire antenna, like an elementary electric vibrator, is made from a straight wire to which a power line is connected. A vibrator having one "shoulder" (energy guide is connected to one of its ends) is called asymmetrical, and having two identical "shoulders" (energy guide is connected to the center) - symmetrical.
On fig. 4.5 shown different kinds asymmetric vertical vibrators.
On fig. 4.6 - mast and wire antennas. They differ from each other in the operating wavelength and absolute sizes, as well as the sometimes different design implementation associated with this.
On fig. 4.7 shows some (a lot of them have been created by man) symmetrical vibrators, including the bent one, which can be bent from an angle vibrator (shown in dotted line).
On fig. 4.8 shows flat single-tier and multi-tier antenna systems,,, made of wire vibrators (pos.1), a pyramidal antenna made of wires (pos.2), and antennas made of plates (pos.3).
To flat wire antennas many loop antennas (active and passive) are also included. Some of them , , , are shown in Fig. 4.9.
The natural and artificial analogues of even the antennas listed above are so numerous that everyone can independently find a lot of similar forms among the artificial and natural objects of the world around us, especially since they are absolutely exact structural similarity in order to have parameters that approximately coincide with the parameters of one or another typical antennas are not required.
slot antennas- these are slots of various sizes and configurations cut in the wall of a resonator having one shape or another.
On fig. 4.10 shows some configurations of slots cut on a rectangular and round waveguide (pos.1), resonator screens (pos.2), as well as slot antennas made on the basis of a rectangular (pos.3) and round (pos.4) waveguide, and possible shapes and location of slots on the walls of a rectangular waveguide (pos.5). In the center (pos. 6) one of the first artificial satellites is shown, equipped with antennas of various types, mostly slit ones, which really resemble windows open to another world, in this case, to outer space.
Vibrator and slot antenna systems, , are systems of several (or many) identical and ordered vibrators or slots that can be placed on bodies of very different shapes.
On fig. 4.11 shows some of the most commonly used dipole and slot antenna systems in aircraft. Among them there are systems that look like a hedgehog, a cactus, windows of buildings, and much more.
Analogues of wire and slot antennas, as well as many others, any inhomogeneities of the corresponding form, formed by the interface between two media, the conducting (transmitting) properties of which for a given type of energy differ significantly, can serve.
It can be a dam, limited by water, on which cars are able to move, and water is a forbidden zone for them. But if the dam is replaced with a canal, the water with a solid surface, and the cars with gondolas, then everything will change. Water will "pass" the gondolas, but the hard surface will not.
In the general case, analogues of certain specific wire and slotted "vibrators" are those representatives of inanimate and living nature, including man himself, whose general contours (or their individual parts) are certain moments time, at least in a weak way reminiscent of the above (and not given here) forms of vibrators and slots. Small details, the size of which is much smaller than the working wavelength, do not really matter, and the shape can be very different from the given shapes without much damage to their work.
Analogues of asymmetric vertical Vibrators can be trees, animal horns, grass stalks and much, much more, including various designs created by man for completely different purposes. Vertical "vibrators" are, for example, towers, churches, high-rise buildings. All of them, along with tall trees, are capable of catching lightning, the wavelength of which, as you know, is several tens of meters, i.e., commensurate with their size.
Analogue of symmetrical vibrators are leaves (and needles), as well as twigs of many plants, including trees, arranged symmetrically. They are known to be able to absorb and store energy, as well as process it and emit it in the form of other energy, for example, absorb carbon dioxide and, having processed it, emit oxygen.
Slot antenna analogue any ditch, rut, or depression that can be filled with any substance, the size of individual particles of which is commensurate with its size or much smaller, can serve. They also include all the "gaps" between natural objects and artificial structures, of the appropriate size and shape. The operating "slot antennas" at the level visible to us are springs, geysers, fountains, sprinklers, etc.
Analogues of "frame" emitters are any constructs of the corresponding configuration. Loop antennas can be jewelry in the form of chains, rings, bracelets, earrings. These include patterns and lines of appropriate configuration.
"Painted" antennas(and not only antennas) are widely used, as you know, in printed circuits.
The antennas listed above by both Nature and man can be made by the most different ways, for example, in the form of recesses, drawn with a pencil (by the way, graphite conducts electricity) or formed by a metal coating.
Human(as well as its individual parts and organs) is the owner of many antennas. A person standing at attention can serve as an analogue of a vertical vibrator, spreading his arms to the sides, he turns into a symmetrical horizontal “vibrator”, and by bringing and spreading his arms and legs, he changes (regulates) the DN of his “corner vibrator antennas”, formed hands and feet. Some (of the countless) "human" antennas will be discussed in more detail in the second part.
Almost all objects and subjects of our world can act as single vibrator and loop antennas and their slot "brothers". All of them are able to concentrate around or within themselves a certain type of field (if it has a place to be) in accordance with their own RP. And everything that falls into the zone of action of this RP will be in a field with an increased concentration of this type of energy. If the density of the internal energy of the system connected to the antenna exceeds the density of the same energy in the surrounding space, then it will begin to emit it with an increased concentration in those directions that coincide with the "petals" of its RP.
good example The "antennas" working for transmission can serve, as already mentioned, operating watering installations. Some of them are able to spray water in a circle, others in a certain sector, and still others are a kind of locator, they rotate. If necessary, it is possible to create in a certain direction a highly directed DN - a “beam”, by directing a thin but powerful jet of water there.
Analogues antenna systems - these are crystals, snowflakes, polyatomic molecules, multimolecular compounds of organic substances, etc. They also include much of what is created by human hands, but is not considered by him as antenna systems. These are windbreaks, and windows of buildings, if they are arranged in an orderly manner, and streets that have the same and orderly located houses. On some of these streets, as you know, the wind can constantly “walk”, for which they are energy conduits. Tree branches, especially conifers, can serve as natural analogs of multi-element systems; their needles, as already mentioned, are typical "wire" vibrators. But there will be a more detailed discussion about trees later.
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Surface wave antennas- these are guiding systems (Fig. 4.12), along which surface electromagnetic waves propagate. Guides (pos. 1-7) can be metal surfaces coated with a dielectric layer, ribbed metal structures, surfaces consisting of layers with different electrical properties, dielectric and metal rods, and much more. The radiation of plane antennas of surface waves (pos. 1 and 2, on the right) is directed approximately parallel to the surface, and rod antennas (pos. 2, on the left and pos 6) - mainly along their axis. Therefore, they are respectively called surface wave antennas and axial radiation antennas.
In the general case, surface wave antennas are a surface of homogeneous (identical) inhomogeneities, along which the electromagnetic wind "blows". Surface wave antennas can be compared to a road covered with a "viscous" top layer. Particle-waves in this "viscous" layer, as it were, "get entangled" and cannot "fly away" upwards, but they can move along it.
On fig. 4.12 (pos.1, 2, 5) shows the methods of excitation of the electromagnetic "wind" in some types of surface antennas,, using a primary radiator of one kind or another. A multi-element grid can be made from dielectric pins having a round, square or rectangular screen (pos. 6, bottom, right).
Analogues of surface antennas waves (planar) are the cerebral cortex, sand dunes in deserts, layers of the earth's crust with different parameters, forests, stratus clouds and much more. Rod - in fact, anything that has a similar configuration, including slightly spread apart four fingers of the palm (quadruple dielectric pins are very similar to them, see Fig. 4.12, pos 6), as well as the spine of humans and animals (it is similar to a rod made from individual washers). But about the "human" antennas, a more detailed discussion will be in the second part.
Antennas acoustic type- horn, , , , , , , - are shown in fig. 4.13.
Directional properties of horn antennas determined mainly by the size opening- the width of the "window" and the angle solution mouthpiece.
Opening angle is the angle formed by its opposite walls or generators, and opening- a plane perpendicular to the axis of the horn and passing through its edges.
At small opening angles of the horn, the width of the RP is determined mainly by its opening size in wavelengths, and at large angles, by the opening angle. The opening angle is not related to the wavelength, and therefore the directional properties of such a horn remain practically unchanged over a very wide wavelength range. All wide-angle antennas are, as a rule, also wide-range, since their phase center(focus) at different wavelengths is located approximately in the same place.
The main types of antennas.
Naturally, first of all, divide the antennas into transmitting and receiving - the main electrical characteristics of each antenna in the operating modes for receiving and transmitting are the same.
All antennas can be conveniently divided into two large groups:
Linear antennas;
aperture antennas.
In addition, more complex antenna systems are widely used - antenna arrays, the elements of which are either linear or aperture radiators.
A linear antenna is a thin metal wire in which an alternating electric current is excited, as well as a narrow slot in a metal screen, between the edges of which an alternating electric voltage is applied. According to the equivalence theorem, the electric field in the gap in its effect on the outer space is equivalent to some alternating magnetic currents flowing along the gap. Thus, linear antennas are any radiating systems of small (compared to length) transverse size and with alternating currents flowing along the axis of the system. For linear antennas, the cross-sectional size is much smaller than the wavelength.
A characteristic of linear antennas is that the current distribution along their axis depends little on the configuration of the wire. Therefore, linear antennas include not only straight antennas, but also curved, bent and coiled wires and slots, if their transverse dimensions are much smaller than longitudinal and smaller than the wavelength: symmetrical and asymmetrical vibrators and antennas, frame antennas, wire antennas. traveling wave (including spiral), thin slotted ant. standing and traveling waves.
Aperture antennas - they can define some limited imaginary surface through which the entire flow of radiated (received) electromagnetic energy passes - an aperture or aperture, often represented as a plane. The opening dimensions are usually much larger than the wavelength. Examples: pyramidal horn antenna, reflective parabolic antenna, lens antennas, open radiating ends of waveguides.
Antenna array - an antenna consisting of several radiators of the same type, located in space in a certain way and excited by one generator or several coherent generators. Here it is possible to obtain both the required spatial distribution of the radiated energy and the necessary control over this distribution. A typical antenna array is a VHF director antenna - a linear array of half-wave symmetrical vibrators.
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