In the world around us, it is often very important that a person cannot do without a large amount of necessary and timely information. This information can be both peaceful and military in nature, but it is intended primarily to facilitate human activities.
Antennas are one of the types of devices used to receive and transmit information.
This course work will consider the calculation of the antenna that meets the specified technical requirements.
2. The purpose of the work
The aim of the work is to study the helical antenna of the DTsMV range, which implies the calculation of the geometric dimensions of the antenna, its radiation characteristics.
3. Brief overview of helical antennas
Helical antennas belong to the class of traveling wave antennas. They are a metal spiral fed by a coaxial line. There are quite a few varieties of helical antennas, but almost all can be reduced to the following three types:
a) cylindrical (see figure 3.1);
b) conical (see figure 3.2);
c) flat (see figure 3.3).
Figure 3.1 - Cylindrical antenna.
Figure 3.2 - Conical antenna.
Figure 3.3 - Flat antenna.
Depending on the number of spiral branches, they can be single-start (one branch), double-start (two branches), etc.
The principle of operation of helical antennas
The spiral antenna (Fig. 4.1) consists of a wire spiral powered by a coaxial line. The inner wire of this line is connected to the spiral, and the outer sheath to the metal disk.
Helical antennas form a radiation pattern consisting of two lobes located along the axis of the spiral on opposite sides of it. In practice, one-sided radiation is usually required, which is obtained by placing it in front of a screen (disk). In addition, the helical antenna disk serves to reduce currents on the outer sheath of the coaxial line, to reduce fluctuations in the input resistance in the working one. The disk diameter is chosen on the order of (0.8-1.5)l, where l is the length of the helix. The disc does not have to be made from a solid sheet, it can be made from a system of radial and circular wires.
4. The basis of the operation of a cylindrical helical antenna
Detailed studies have shown that several types of current simultaneously exist on a radiating cylindrical spiral, differing from each other in amplitude and the number of periods, which fit along the axis of the spiral with their own attenuation and with their own phase velocity. However, the shape of the directivity diagram of the spiral depends mainly on only one, the dominant wave, the type of which is determined by the ratio between the length of the spiral coil and the operating wavelength.
Let us introduce the following notation:
Operating wavelength in free space;
T q - current wave in the coil of the q-th type; q=0,1,2…. An integer indicating how many periods of the current wave fit along one turn of the spiral;
V q - the speed of propagation of the current wave T q along the wire of the spiral;
C is the speed of light in free space;
D is the diameter of a coil of a cylindrical spiral.
Three modes of operation of a cylindrical helical antenna are known:
When the length of the spiral turn is less than 0.65 (the wavelength is >5D), the T0 wave dominates on it, which is characterized by a change in the current phase within 3600 over several turns. Wave T 0 from the end of the spiral leads to the formation of standing waves, which form the radiation pattern of the antenna. Wave T 1 has a very small amplitude and does not participate in the radiation. The maximum radiation for this case is obtained in a plane perpendicular to the axis of the spiral (Fig. 4.2a) and it is not directed in this plane.
If the length of the coil lies in the range from 0.75-1.3 (wavelength, respectively = 4D-2.2D), the T 1 wave prevails on it, the phase velocity of which is less than the speed of light V 1 0.82 C. The T 1 wave is intensely emitted by all the coils, therefore, in the spiral a traveling current wave is established, which forms a radiation maximum along the axis of the spiral (Fig. 4.2 b). The wave T 0 also present on the helix quickly decays along the length of the helix and its contribution to the radiation pattern is small.
The axial radiation mode is the main, most used mode for the operation of helical antennas, therefore the T 1 wave, which is predominant when the length of the spiral coil wire is approximately equal to the operating wavelength, is called the main one.
With a coil length greater than 1.5 (in this case<2D), на цилиндрической спирали помимо основного типа волны Т 1 возникают волны Т 2 , Т 3 и т.д. Волна Т 1 становится затухающей, в то время как Т 2 имеет постоянную амплитуду и является определяющей в излучении. Максимальное излучение получается в направлениях, образующих острый угол относительно оси антенны, и пространственная диаграмма получается в форме конуса
Figure 4.1 - Helical antenna excitation circuit.
Figure 4.2 - spirals having different diameters and their corresponding radiation patterns.
5. Calculation of the parameters of a cylindrical antenna
The parameters of the cylindrical spiral are:
n is the number of turns of the helix,
Helix angle,
R - spiral radius,
l - axial length of the spiral,
S - helix pitch,
L is the length of the helix.
There are the following relationships between the specified parameters (see Figure 5.1):
Figure 5.1
The diameter of the helix turns and the winding pitch should be chosen so that each turn has a polarization close to circular and maximum radiation in the direction of the helix axis (Z axis). In addition, it is necessary that the strengths of the fields created by the individual turns in the direction of the Z axis add up at the reception point in phase or with a slight phase shift. According to the traveling wave antenna theory, the maximum directivity is obtained when the phase shift A1 between the field strength generated by the first (from the source) turn and the field strength generated by the last turn is equal.
To ensure circular or close to it polarization of the field, as well as to ensure intense radiation of each loop in the direction of the Z axis, it is necessary that the length of the loop be close to k. The above can be explained as follows. Assume that the coil pitch is infinitely small, then the coil forms a flat frame. As is known, in a helical antenna, the KBV turns out to be close to unity. Let us therefore assume that the traveling wave regime takes place in the helical antenna. Let us also assume that the speed of current propagation along the coil is equal to the speed of light. In this case, the phase shift between the current at the beginning and at the end of the coil is equal.
In the direction of the Z axis, the components of the field strength vectors Ex and Ey will be of the same magnitude. The phase shift between these components will be equal to /2. The latter follows from the fact that the currents in the coil elements oriented parallel to the X axis are phase-shifted by /2 with respect to the phase of the currents in the elements oriented parallel to the Y axis. The equality of the values of Ex and Ey and the phase shift between them, equal to /2, provides circular polarization. When the length of the coil is equal to and the speed of current propagation along the wire is equal to the speed of light, intense radiation is also provided in the direction of the Z axis. The latter can be approximately proved as follows. Consider two arbitrary coil elements located symmetrically about the center, for example, elements 1 and 2 (Fig. 5.2). Each of these elements has a maximum radiation in the direction of the Z axis. The vectors E created by these elements in the direction of the Z axis are parallel to the tangents to the circle at points 1 and 2. The phase shift between the currents in elements 1 and 2 due to the traveling wave mode is equal to. In addition, the currents in these elements have opposite directions, which is equivalent to an additional phase shift equal to. Thus, the fields of both elements in the direction of the Z-axis are added in phase. It is easy to show that any two symmetrically located elements create in-phase fields in the direction of the Z axis, which provides intense radiation in this direction.
The elementary presentation of the principle of operation of a helical antenna given here does not take into account the complexity of the processes occurring in it and, in particular, the fact that in reality there is a significant reflection of energy from the helix. In addition, the wave along the antenna propagates both directly along the wire and through the spatial connection between the turns, which creates a more complex picture of the current distribution.
Figure 5.2.
To ensure circular or close to it polarization of the field, as well as to ensure intense radiation of each loop in the direction of the Z axis, it is necessary that the length of the loop be close to.
The winding pitch and the coil diameter are chosen in such a way that the phase shift between the field strengths created by the first and last elements of the coil, then in the direction of the Z axis, circular polarization and maximum radiation are preserved. This will take place when the relation is satisfied:
2????????????????
Phase shift between the fields of the initial and final elements of the coil, determined by the difference in the path of the rays from these elements; - phase shift of the fields of these elements, determined by the phase shift of the currents of these elements.
From the above equation, we get the relationship between L and S corresponding to circular polarization:
If we choose the ratio between S and L in accordance with this formula, then the phase shift between the fields created in the Z direction by adjacent turns will also be equal to 2. Thus, the fields of all antenna turns add up in phase, which ensures maximum radiation in the Z direction. However, this mode of operation of the helical antenna does not correspond to the maximum directivity factor. The maximum directivity factor is obtained when the phase shift between the fields of the first and second turns is equal to. This requires that:
where n is the number of turns of the helix.
From (5.3) we find the relation between and S corresponding to the maximum value of the directivity factor:
If relation (5.4) is satisfied, however, a purely circular polarization is not obtained, and the level of the side lobes somewhat increases. The non-uniformity coefficient of the polarization characteristic in the direction of the spiral axis is equal to:
If these antennas are selected in accordance with formula (5.2) or (5.4), then good directional properties are maintained in a significant range, lying approximately in the range from 0.75 to 1.3, where is the wave for which the optimal ratio between L, C / V1, n and S.
Antenna calculation:
Initial data for the calculation of the antenna
Operating wavelength range: min=0.48 m
40 degree half power beamwidth
Calculation of the geometric dimensions of the antenna
Let's choose the average value of the wavelength from the given range:
On the basis of experimental studies, the following empirical formulas were obtained, valid for 5 Half power beamwidth, expressed in degrees: Coefficient of directional action (KND) in the direction of its axis: Input impedance The pitch of the helix can be found from condition (5.2), if it is necessary to obtain circular polarization, or from (5.4), to obtain the maximum directivity. Let us need circular polarization, then the pitch of the helix is Satisfies the condition 12 0<<15 0 , значит мы можем применить формулы, полученные на основании экспериментальных исследований: To find the length of the antenna, we express l=nS from (5.7) when condition (5.9) is satisfied: So the number of turns is: For further calculations, round the number n up to an integer: n=8, then l=nS=0.986m(5.14) The radius of the spiral will be equal to (see Fig. 5.1): from here The input impedance of the antenna in the axial radiation mode remains purely active, since in this mode the traveling wave mode is established in the helix wire. Let us need to get the maximum DPV, then In order for the antenna radiation to be axial, we take the length of the helix turn equal to the average wavelength of the specified range: the pitch of the helix is The winding angle of the turns will be equal to: Satisfies the condition 12 0<<15 0 , значит мы можем применить формулы, полученные на основании экспериментальных исследований: To find the length of the antenna, we express l=nS from (5.7) when condition (5.18) is satisfied: So the number of turns is: For further calculations, round the number n up to an integer: n=6, then l=nS=0.846m(5.23) The radius of the spiral will be: The length of the wire for winding the spiral will be equal to: Directional Coefficient: Input impedance For both cases: The screen disk diameter is assumed to be (0.9-1.1) sr The diameter of the wire of the spiral is selected on the order of (0.03-0.05) sr Beam calculation: Approximately, we can assume that the amplitude of the traveling wave in the spiral is constant. Then the radiation pattern of the antenna can be represented by the product of the radiation pattern of a single turn by the radiation pattern of an array of n omnidirectional radiators, where n is the number of turns: where is the angle relative to the helix axis. This approximation is valid the more, the more turns n the spiral has and the smaller the step angle. The radiation pattern of a single loop is approximately described by the expression The lattice factor is known to be Applied to a helical antenna phase shift between the currents of adjacent turns. Given that С/V1=1.22, to calculate the radiation pattern of a cylindrical helical antenna, we obtain the following approximate expression: As a result, when obtaining the maximum directivity factor, we will have radiation patterns for three values of wavelengths: min, cf, max: When obtaining circular polarization, we will have radiation patterns for three values of wavelengths: min, cf, max: Antenna matching with coaxial (Zv = 75 ohm) There are several ways to match the antenna with the coax: Coordination with a quarter-wave transformer: Coordination of an antenna with input impedance Z3=120 ohm with coax Z1=75 ohm is carried out by a piece of coax with =95 ohm, length L==0.14m, and antennas with input impedance Z3=154 ohm with coax with =110 ohm Coaxial cone line termination Coordination is carried out by non-reflecting cones, an integer number of half-waves long, by making conductors in the form of corresponding linear cones. Moreover, the longer the length of the matching link (more half-waves fit), it will be better to coordinate with the antenna. 6. Conclusions on the work done helical antenna radiation polarization In the process of completing the course project, a single-pass cylindrical helical antenna was calculated: the geometric dimensions of the antenna and the radiation characteristics of the antenna. Since the operation of a helical antenna is based on circular polarization, this type of antenna is referred to as a wide-range antenna. Below are the results: helix pitch S = 0.053 m; length of the spiral turn = 0.192 m; spiral radius = 0.03 m; spiral length Lz = 0.567 m; directivity factor D = 30 dB; antenna input impedance Rin = 31.7 Ohm; the number of turns of the spiral N = 6; helix winding angle = 16 degrees; antenna disk diameter = 0.652 m; working wavelength = 0.175 m. List of sources used Aizenberg G.Z., Yampolsky V.G., Tereshin O.N. Antennas VHF.- M.: Svyaz, 1971. In 2 parts. Zhuk M.S., Molochkov Yu.B. Design of lens, scanning, wide-range antennas and feeder devices. - M.: Energy, 1973.- 440 p. Voskresensky D.I. Calculation and design of antenna arrays and their radiating elements Yurtsev OA,... Spiral antennas. - M.: Soviet radio, 1974. - 224 p. "Transmission lines of centimeter waves", part I-II. Per. from English, ed. G.A. Remeza. Publishing house "Sov.radio", 1961 This type of antenna is well suited for long-range reception of a digital television signal. The simplicity of the product captivates, there are only two main parts: a reflector from a snow shovel and a spiral from a coil of power wire. Not a single solder joint, everything is screwed and twisted. There are no complex matching elements. However, the gain of the design reaches more than 10 dB, which allows it to be used in some cases without an amplifier. It was on this antenna without an amplifier that I received a digital television signal outside the city. I want to remind you that any decimeter antenna is suitable for a digital broadcast channel, the difference will be only in the reception range. But not every antenna will provide the maximum gain and matching exactly at the desired frequency. No matter how complex the antenna is, it has gain dips and peaks throughout its entire range of received frequencies. It was the spiral antennas that followed the flight of the first cosmonaut Yuri Gagarin. When the first Soviet lunar rovers, orienting the spirals, plowed the surface of the Moon, I dreamed of making the same space antenna. There is nothing worse than unfinished business. As a basis, I choose the simplest of all types of helical antennas. This is a single-start, spiral, cylindrical (sometimes also conical), regular, that is, with a constant winding pitch or the same distance between the turns. Thus, the name of the antenna already speaks of its design. It was this design that was first proposed by Kraus J.D. Helical beam antenna. - Electronics, 1947. V 20, N 4. R. 109. I recommend the best reference book for radio amateurs "Antennas", edition 11, volume 2. By Carl Rothhammel. The book contains a lot of practical material for almost all types of antennas. Characteristics, parameters, practical calculations, recommendations. From this edition, I give the characteristics of a helical antenna. You need to find out at what frequency digital broadcasting is in your region and convert the value of this frequency to meters. Wavelength in meters = 300 / F (frequency in MHz). For Moscow broadcasting frequencies of two digital packages, I chose an average frequency of 522 MHz, which corresponds to a lambda wavelength of 57 cm. In this case, the coil diameter is D = 17.7 cm, the distance between the coils is 13.7 cm, the distance from the screen to the coil is 7 .4 cm, and the width of the screen must be within 35 cm. As a screen (reflector), I needed the wrong snow shovel made of beautiful shiny stainless steel, constantly bending under the weight of snow. Practice shows that the reflector does not have to be round, and it makes no sense to make the side of the square more than two diameters of the spiral turn. I made the spiral from a network power wire with a diameter of about 2 mm, using one of its cores, without removing the insulation from it, since it is transparent for radio waves, and the copper wire does not oxidize in it under the influence of the external environment. In practice, the thickness of the wire turned out to be almost 5 times less than the theoretical one, which is why the antenna range turned out to be narrow. In the decimeter range, the antenna will receive well only a few television stations of analog broadcasting, however, two digital packages located side by side in frequency will fit perfectly in its amplification band. You will also need a 75-ohm coaxial cable with a connector. I do not recommend getting carried away with the length of the cable, especially if the antenna is without an amplifier, since 0.5 to 1 dB of gain is lost in each meter and a long cable will need a matching device. In my design, I used 3 meters of cable. Just something to do, wind the spiral, connect the cable to the conductor of the spiral and attach it all to the blade of the shovel. But I did not have a dielectric cylinder of the required diameter for fixing the wire of the spiral, and therefore I used rails and a sheet of dry plywood as a frame, transferring the dimensions of the antenna from the sketch to it. It would have been cooler if shovels were used instead of slats and plywood, but I only assembled the layout, and it was convenient for me to do everything on plywood. When the shell began to be wrapped in wire, the homemade product looked like the body of an aircraft. From the outside, it looked less harmless if I began to bend coils from a copper tube, as I wanted before. As I have already said, it is convenient to hide such an antenna under the ridge of a house with a roof made of soft roofing, andulin or slate, transparent to radio waves. To test the antenna, I used the attic room, where I lifted the homemade closer to the ceiling with the help of a ladder. This place used to work Place test too. Vladimir region, 90 km east of Ostankino. Now a helical antenna without an amplifier works here. She “sees” the television center through: lining, glassine, 10 cm of basalt wool, lathing board, OSB plywood, bedding carpet, soft roof scales and a clot of nails of different lengths. layout. To improve the parameters of the antenna, it does not hurt to use a matching device - a transformer that provides a transition from an antenna resistance of 180 ohms to a coaxial cable with a resistance of 75 ohms. This is a plate of thin copper in the form of a triangle, expanding towards the screen. I picked up the place of attachment of the plate and its dimensions experimentally, using two plastic clothespins. At home, this is easy to do with a TV, lowering the antenna to a lower level, at which the image will be "snowy". It is necessary to move, turning the plate, and by ear, by reducing the noise level in the audio channel when receiving an analog signal that is close in frequency to the digital package, determine its location. Then solder. The power supply of the amplifier itself may fail, since, as a rule, it is always energized and its resource is limited. Another advantage is that the range of this antenna with an amplifier will be greater, by how much, check for yourself. Addition. Changing the design of the antenna. This year (2015) I decided to refine the self-made design of the spiral antenna, using a metal-plastic tube (metal-plastic) with a diameter of 16 mm instead of a wire. Previously assembled antennas have already undergone a similar operation and noticeably revived. The spiral antenna has also undergone recovery, but don't be fooled, the increase in signal level was only 10 percent, and the signal quality remained at the same 100 percent level. For a long time I wanted to make an antenna using a tube as a material. The similarity with the moonshine still and the high cost stopped. But now the material has been found and already tested on simple antennas. It is an easily bendable tube made of high quality aluminum covered with plastic on all sides, sold in all construction markets for laying water pipes. Economic antenna calculation. I had to do this complicated calculation when I went to the "Everything for the Home" store, on the very outskirts of the Moscow region, and saw a metal-plastic at a price of 45 rubles. Wavelength, broadcast frequencies, circle length, number of turns, antenna gain…. I blurted out 4 meters at the checkout, summing up the economic part of the project. The prime cost of the antenna must not exceed the minimum excise value of a bottle of vodka. Antenna calculation. Purely for economic reasons, it turned out 6.5 turns, half a turn less than the previous homemade wire. I also took a distance between the turns equal to the fourth part of the wavelength. Similarly, I calculated the length of one turn, but for practical reasons, already having experience in the manufacture of simple loop antennas, I corrected the frequency dependence of the metal layer, reduced the length of the turn by 1.5 cm. I also calculated the diameter of the mandrel, dividing the adjusted length of the turn by 3.14 . Taking into account the thickness of the tube, the diameter of the mandrel took 8 mm less. Adjustment. It consisted in measuring the SWR (standing wave ratio). Initially, I measured the old homemade. Strange, but the device claimed excellent matching with a 50 ohm load (SWR = 1.5). Everything coincided with the modified antenna, however, when powered from the edge of the canvas. But constructively, later, I used the cable in the center and the SWR dropped to 2. A simple home-made SWR meter, combined with a home-made generator tuned to digital broadcast frequencies, turned out to be very useful. With its help, I was able not only to determine the SWR of the antenna, but also to check its performance, when each turn reacted to the brought lid from the saucepan by swinging the needle of the microammeter. Results. The design change added a gain of 10 percent, and this despite the fact that the antenna has half a turn less. In general, it receives programs in the decimeter range, operating in analog mode, no worse than a wave channel antenna (Uda-Yagi), which includes 12 directors and an amplifier with a declared gain of at least 26 dB. Both antennas are located in the same conditions at the same level from the ground. The only difference is that the operation of a purchased antenna, when receiving an over-the-air digital signal, depends on the weather and time of day, simulating a deterioration in the passage of radio waves with a characteristic quacking sound and freezing of television pictures, or even a complete absence of an image. Radio reception with a homemade antenna is always constant. But in general, I was dissatisfied with this design, because I expected something more from it, solely based on its dimensions and the money spent. Comparing this helical antenna with the previous design ,
consisting of only two phased rings of identical diameter, made of the same material, I did not find a significant gain when comparing them in terms of reception levels. Two phased rings and six helical rings give theoretical gains of 6dB and 10dB. Two rings in the open air and 6.5 rings under the roof, at the same level from the ground and at almost the same level of gain in percentage. Maybe the roof ate a difference of 4 dB, or maybe it's really hard to notice this difference? At the same time, do not put this coil on the street, opening this topic for unnecessary talk. Have I lost heart? No! Amateur radio is a source of pleasure. Take up amateur radio, it's interesting. Perhaps your results will be better. Most likely, I will return to this spiral antenna, because it didn’t fall asleep, when the “wave channel” antenna stopped receiving the air. At frequencies above 300 MHz and above, cylindrical helical traveling wave antennas are widely used. One of the variants of the spiral antenna is shown in Fig.1. It is a spiral with a diameter D and winding step S, and a metal reflector made in the form of a disk or a square with a size of ≈ 2D. Depending on the geometric parameters (electrical length of the perimeter of the coil With and electric length of the helix pitch S) of a helical antenna, various types of waves (modes) can be excited in it. The phase relationship between adjacent turns of the spiral has the greatest significance on the nature of the radiation of the antenna. We are interested in the T1 wave (Fig. 2), which is characterized by a 360-degree difference in the phase of the currents on neighboring turns. Wave T1 is formed when the electrical length of the perimeter of the coil is close to the wavelength λ
, while the helical antenna operates in the axial radiation mode (the radiation maximum coincides with the axis of the helix). Optimal dimensions of the helical antenna: Antenna input impedance, subject to 12°≤α≤15°, 0.75λ<с<1,33
λ
and the number of turns n>3 equals: RA ≈140 s/λ(ohm) Main lobe width at half power level: θ0.5 =52· λ/s· √nS/λ
(degrees) Figure 3 shows the result of calculating the radiation pattern of a helical antenna in the vertical and horizontal planes using the MMANA program. Fig.3 Directional pattern of a helical antenna. Cylindrical helical antennas operating in the T1 wave mode have circular polarization. When a signal is received by an antenna with linear polarization (vertical or horizontal), the signal will be attenuated by 3dB (twice). To avoid this, you can use a system of two helical antennas with opposite helix winding and fed in-phase, located at a distance of 0.5 λ or 1.5 λ (Fig. 4). The input impedance of such an antenna system will be 67.6 ohms, which is in good agreement with the wave impedance of the coaxial cable (SWR 1.1 and 1.35 for 75 and 50 ohm cable, respectively). Wave impedance of a single-wire line (Fig. 5) section ab must match the input impedance of the helix antenna (≈140 ohm). To do this, it is necessary to maintain the ratio e/d equal to ≈2.75. To match a single antenna or an antenna system consisting of three or more antennas, in this case, you can use an exponential matching transformer, which is structurally made in the form of a strip line (Fig. 6). For an exponential line, the wave resistance varies along its length according to the law: Z 0 (x) \u003d Z 01 e bx, Where Z01- line impedance at the input Z 0 (x)- wave impedance of the line in the section located at a distance X from its beginning b- parameter showing the rate of change of the wave impedance of the line Depending on the SWR and the known ratio Z02 /Z01 of the wave impedances at the end and at the beginning of the line, its minimum length is calculated by the formula: Figure 7 shows an exponential matching transformer, designed to match 140 ohms and 50 ohms at a frequency of 2450 MHz with an SWR of 1.2. Distance e equal to 7 mm, dielectric - air (ε=1), material thickness d 1 mm. Due to the high gain and stability of electrical parameters, due to the low sensitivity to external factors and deviations in geometry, cylindrical helical antennas can be widely used in communication and security systems for organizing long-distance communications. Sazonov D.M. Antennas and microwave devices. Benkovsky Z., Lipinsky E. Amateur HF and VHF antennas. Uronov L.G. TechnoSphere LLC, 2011 Introduction The current state of radio communication technology cannot be imagined without helical antennas. This type of antenna systems is used due to its characteristic qualities: broadband, elliptical field polarization with small dimensions and simple design. Helical antennas are used both independently and as elements of an antenna array, feed, for example, a reflector antenna, which adds directivity to the advantages of helical antennas. Due to the property of elliptical polarization, helical antennas have found application in space communications technology, since, in some cases, the polarization of the received signal can be random, for example, from objects whose position in space changes or can be arbitrary (these objects can be: aircraft, rockets, satellites etc.) In radar, antennas with rotating polarization can reduce the interference created by reflections from precipitation and from the Earth's surface, due to the fact that the direction of the electric field strength vector is reversed. A field with a rotating polarization can also be used when the same antenna is transmitting and receiving to increase the isolation between the channels (in this case, the emitted and received fields must have the opposite direction of rotation). Currently, helical antennas are widely used as antennas for personal communication devices. A significant proportion of cell phones, trunk devices, and mobile radios contain helical antennas in their design, operating in the mode perpendicular to the radiation axis. At the present time I am going to study the radiation patterns of flat spiral and cylindrical SAs, analyze their dependence on length, trace the change in directivity with changing antenna parameters. Also compare the characteristics of the SA with each other and with other types of antennas. At the beginning of each section, a specific type of CA is taken. And then the results of computer analysis for different modes and types will go on. All calculations and plotting will be carried out in MathCAD 2001i. It is supposed to include in the applications of programs the simplest calculation of the characteristics of a helical antenna. A feature of the SA theory is the complexity of calculating the antenna field. Of the various designs of elliptical polarized band antennas, the helical antenna proposed by Kraus in 1947 and its various modifications have received the greatest use. In order to be able to calculate the listed characteristics and parameters of the SA in a wide frequency range, it is necessary to establish the dependence of the phase velocities of the current waves propagating along the wire in the helix on the geometry and frequency of the voltage that excites the helix. Many works are devoted to calculating the phase velocity of a current wave propagating along the wire of a spiral, and establishing the dependence of phase velocities on the geometry and frequency of the voltage that excites the spiral, the first attempt to solve this problem belongs to Pocklington, who back in 1897, having solved the problem of determining the phase velocity of an electromagnetic wave, propagating along a straight wire and along a ring, tried to consider the propagation of an electromagnetic wave along a spiral. He managed to do this in a number of special cases. With the exception of individual works in this direction, related to the propagation of an electromagnetic wave in coils, interest in this topic arose in the late 40s in connection with the widespread use of spirals as slowing down structures. Chapter 1 Helical Antenna Types 1.1 Types of helical antennas Among the various types of broadband antennas, various helical antennas occupy an important place. Helical antennas are low- and medium-directional broadband antennas of elliptical and controllable polarization. They are used as independent antennas, exciters of waveguide-horn antennas of elliptical and controlled polarization, elements of antenna arrays. Helical antennas are surface wave antennas. According to the type of guide (delaying system) and the method of ensuring operation in a wide frequency range, they can be divided into: regular cylindrical, in which the geometric parameters (pitch, radius, wire diameter) are constant along the entire length and the broadband is due to the presence of phase velocity dispersion; equiangular or frequency-independent (conical, flat); Irregular, which include all other types of helical antennas. Fig.1.1. 3 Irregular helical antennas: a - flat with a constant winding pitch (Archimedean); b - conical with a constant winding pitch; (c) on the surface of an ellipsoid of revolution with a constant winding angle. Fig.1.1.4 Irregular cylindrical helical antenna (variable pitch) According to the number of passes (branches) and the method of their winding, helical antennas can be single- and multi-entry with one-sided or two-sided (opposite) winding. The absence or presence of additional deceleration of the phase velocity and the method of its implementation make it possible to divide helical antennas into the following types: from a smooth wire in a homogeneous dielectric (air), from a wire with its own slowdown (impedance helical antennas), from a wire with its own slowdown and with a dielectric (impedance spiral-dielectric antennas). Rice. 1.1.5 Helical antennas with additional deceleration: a - impedance; b, c – spiral-dielectric; d - impedance spiral-dielectric. One of the main properties of helical antennas is their ability to operate in a wide frequency band with an coverage factor of 1.5 to 10 or more. All helical antennas are traveling wave antennas, but one circumstance does not in itself cause helical antennas to operate in the frequency range with such an overlap ratio. The operation of single-pass regular cylindrical helical antennas and their modifications in the frequency range is possible due to their dispersion properties, due to which, in a wide frequency range, the phase velocity of the field along the axis of the helix is close to the speed of light, the reflection from the free end of the helix is small, the wavelength in the wire of the helix is approximately equal to the length coil. In multi-pass cylindrical helical antennas, the operating range is further expanded due to the suppression in them of the nearest lower and higher types of waves that distort the radiation pattern of the main type. Helical antennas with one-sided winding radiate a field with an elliptical, close to circular, polarization. The direction of rotation of the field vector corresponds to the direction of the spiral winding. To obtain linear and controlled polarization, helical antennas with two-sided (opposite) winding are used. Fig.1.1.6. Equiangular helical antennas with two-sided (opposite) winding: a - conical four-way; b - flat three-way. The form of frequency-independent (flat and conical equiangular) helical antennas is determined only by the angles. Each wavelength within the operating range corresponds to a radiating section of a constant shape and constant electrical dimensions. Therefore, the beamwidth and input impedance remain approximately constant over very wide frequency ranges (10:1 ...20:1). To obtain unidirectional radiation with elliptical polarization in smaller frequency ranges (2:1 ... 4:1), there is no need to strictly maintain the shape of the antenna in accordance with the condition of frequency independence. If, during the transition from one wavelength to another, the shape and electrical dimensions of the radiating element are repeated at least approximately, the antenna operates in the frequency range with less constancy of characteristics and parameters. Following this, it is possible to build a very wide family of antennas that does not exactly obey the principle of frequency independence in the form of single- or multi-start spirals wound (according to different winding laws) on various surfaces of rotation. Sometimes such antennas are called quasi-frequency independent. Quasi-frequency-independent helical antennas for obtaining controlled and linear polarization are also made with double-sided winding. To obtain controlled, linear and circular polarization, various (cylindrical, equiangular, etc.) two-way helical antennas can also be used. Fig.1.1.7. Quasi-frequency-independent helical antennas with double-sided (opposite) winding and constant pitch: a - conical four-wire; b - hemispherical four-way; c - ellipsoidal four-way. Buying a good antenna for the country is not always advisable. Especially if it is visited from time to time. It's not so much the cost, but the fact that after a while it may not be in place. Therefore, many people prefer to make an antenna for giving their own. The cost is minimal and the quality is good. And the most important point - a do-it-yourself TV antenna can be made in half an hour or an hour and then, if necessary, it can be easily repeated ... Digital television in DVB-T2 format is transmitted in the UHF range, and there is either a digital signal or it is not. If the signal is received, then the picture is of good quality. Due to this. any decimeter antenna is suitable for receiving digital television. Many radio amateurs are familiar with the TV antenna, which is called "zigzag" or "eight". This do-it-yourself TV antenna is assembled in just a matter of minutes. To reduce the amount of interference, a reflector is placed behind the antenna. The distance between the antenna and the reflector is selected experimentally - according to the "purity" of the picture Making it is very simple, the material is any conductive metal: tube, rod, wire, strip, corner. She accepts, despite the simplicity, well. It looks like two squares (rhombuses) connected to each other. In the original, a reflector is located behind the square - for more confident signal reception. But it is more needed for analog signals. To receive digital television, it is quite possible to do without it or install it later if the reception is too weak. Optimum for this homemade television antenna, copper or aluminum wire with a diameter of 2-5 mm is suitable. In this case, everything can be done in just an hour. You can also use a tube, a corner, a strip of copper or aluminum, but you will need some kind of device to bend the frames of the desired shape. The wire can be bent with a hammer, fixing it in a vise. You will also need a coaxial antenna cable of the required length, a plug suitable for the connector on your TV, some kind of mount for the antenna itself. The cable can be taken with a resistance of 75 ohms and 50 ohms (the second option is worse). If you make a TV antenna with your own hands for installation on the street, pay attention to the quality of the insulation. Mounting depends on where you are going to hang a homemade antenna for digital television. On the upper floors, you can try to use it as a home and hang it on curtains. Then you need large pins. In the country or if you take a home-made television antenna to the roof, you will need to attach it to a pole. For this case, look for suitable clamps. To work, you will also need a soldering iron, sandpaper and / or a file, a needle file. To receive a digital signal, there is no need to count the wavelength. It is simply desirable to make the antenna more broadband - in order to receive as many signals as possible. To do this, some changes have been made to the original design (pictured above) (further in the text). You can do the calculation if you want. To do this, you need to find out on which wave the signal is broadcast, divide by 4 and get the required side of the square. To get the required distance between the two parts of the antenna, make the outer sides of the diamonds a little longer, the inner ones shorter. Drawing of the G8 antenna for receiving digital TV Due to the difference in lengths, the distance between the squares is formed (they should not be connected). The two extreme sections are made 1 cm longer - so that you can roll the loop to which the coaxial antenna cable is soldered. If you count all the lengths, you get 112 cm. We cut off the wire or the material that you have, take the pliers and the ruler, and begin to bend. The angles should be at 90° or so. With the lengths of the sides, you can make a little mistake - this is not fatal. It turns out like this: Actually the antenna frame is ready. If everything was done correctly, a distance of 1.5-2 cm was obtained between the two halves in the middle. There may be slight discrepancies. Next, we clean the loops and the place of the inflection to bare metal (treat with fine-grained emery), tin. Connect two loops, compress with pliers to hold tight. We take the antenna cable, carefully clean it. How to do this is shown in a step-by-step photo. Strip the cable on both sides. One end will be attached to the antenna. Here we clean it so that the wire sticks out 2 cm. If it turned out more, the excess (later) can be cut off. Twist the screen (foil) and braid into a bundle. It turned out two conductors. One is the central monocore of the cable, the second is twisted from a multitude of braid wires. Both are needed and need to be tinned. Solder the plug to the second edge. There is enough length of 1 cm or so. Also form two conductors, tin. The plug in those places where we will carry out soldering, wipe it with alcohol or a solvent, clean it with emery (you can use a needle file). Put the plastic part of the plug on the cable, now you can start soldering. We solder a monocore to the central outlet of the plug, and a stranded twist to the side outlet. The last thing is to crimp the grip around the insulation. Then you can simply wind the plastic tip, you can fill it with glue or non-conductive sealant (this is important). While the glue / sealant has not hardened, we quickly assemble the plug (we wind the plastic part), remove the excess composition. So the plug will be almost eternal. Now it remains to connect the cable and frame. Since we were not tied to a specific channel, we will solder the cable to the midpoint. This will increase the bandwidth of the antenna - more channels will be received. Therefore, we solder the second cut end of the cable to the two sides in the middle (those that were stripped and tinned). Another difference from the “original version” is that the cable does not need to be looped around the frame and soldered at the bottom. This will also expand the reception range. The assembled antenna can be checked. If the reception is normal, you can finish the assembly - fill the soldering points with sealant. If the reception is bad, try to find a place where you can catch better first. If there are no positive changes, you can try replacing the cable. For ease of experiment, you can use ordinary telephone noodles. She's worth every penny. Solder the plug and the frame to it. Try with her. If it "catches" better, it's a bad cable. In principle, you can work on "noodles", but not for long - it will quickly become unusable. It is better, of course, to put a normal antenna cable. To protect the junction of the cable and the antenna frame from atmospheric influences, the soldering points can be wrapped with ordinary electrical tape. But this is not a reliable way. If you remember, you can put on a few heat shrink tubes before soldering to insulate with their help. But the most reliable way is to fill everything with glue or sealant (they should not conduct current). As a "case" you can use covers for 5-6 liter water bottles, ordinary plastic covers for cans, etc. We make recesses in the right places - so that the frame “lays down” in them, do not forget about the cable outlet. Fill with sealing compound, wait until it seizes. Everything, a do-it-yourself TV antenna for receiving digital television is ready.
This is a narrowband antenna, which is used when you need to receive a weak signal. It can even help if a weaker signal is "clogged" by a stronger one. The only drawback is that you need an exact orientation to the source. The same design can be done to receive digital television. The advantages of this design are that the reception will be confident even at a considerable distance from the repeater. Only it will be necessary to specifically find out the frequency of broadcasting, to withstand the dimensions of the frames and the matching device. Make it from tubes or wire: The double square antenna consists of two frames connected by two arrows - upper and lower. The smaller frame is a vibrator, the larger one is a reflector. An antenna consisting of three frames gives a greater gain. The third, smallest, square is called the director. The upper arrow connects the middle of the frames, it can be made of metal. The lower one is made of insulating material (textolite, gettinax, wooden plank). Frames should be installed so that their centers (crossing points of the diagonals) are on the same straight line. And this line should be directed to the transmitter. The active frame - the vibrator - has an open circuit. Its ends are screwed to a textolite plate measuring 30 * 60 mm. If frames are made from a tube, the edges are flattened, holes are made in them and the lower arrow is attached through them. The mast for this antenna must be wooden. In any case, the upper part of it. Moreover, the wooden part should begin at a distance of at least 1.5 meters from the level of the antenna frames. All dimensions for the manufacture of this TV antenna with your own hands are shown in the tables. The first table is for the meter range, the second is for the decimeter range. In three-frame antennas, the distance between the ends of the vibrator (middle) frame is made larger - 50 mm. Other dimensions are given in the tables. Since the frame is a symmetrical device, and you need to connect it to an unbalanced coaxial antenna cable, you need a matching device. In this case, a balancing short-circuited loop is usually used. It is made from pieces of antenna cable. The right segment is called the “loop”, the left one is called the “feeder”. A cable is attached to the junction of the feeder and the cable, which goes to the TV. The length of the segments is selected based on the wavelength of the received signal (see table). A short piece of wire (loop) is cut at one end by removing the aluminum screen and twisting the braid into a tight bundle. Its center conductor can be cut to insulation, as it does not matter. Divide and feeder. Here, too, the aluminum screen is removed and the braid is twisted into a bundle, but the central conductor remains. Further assembly goes like this: This matching device allows you to get rid of interference, a blurry contour, a second blurry image. It is especially useful at a great distance from the transmitter, when the signal will be clogged with interference.
In order not to connect a short-circuited loop, the triple square antenna vibrator is made elongated. In this case, you can connect the cable directly to the frame as shown in the figure. Only the height at which the antenna wire is soldered is determined in each case individually. After the antenna is assembled, “tests” are carried out. The cable is connected to the TV, the center conductor and the braid are moved up / down, achieving a better picture. In the position where the picture will be most clear, the antenna cable taps are soldered, the soldering points are isolated. The position can be any - from the bottom jumper to the transition to the frame. Sometimes one antenna does not give the desired effect. The signal turns out to be a weak image - black and white. In this case, the standard solution is to install a TV signal amplifier. To make this television antenna, in addition to the cable, you will only need two aluminum or tin cans and a piece of wooden plank or plastic pipe. Banks must be metal. You can take beer aluminum, you can - tin. The main condition is that the walls are even (not ribbed). Banks are washed and dried. The end of the coaxial wire is cut - by twisting the strands of the braid and cleaning the central core from insulation, two conductors are obtained. They are attached to banks. If you know how, you can solder. No - take two small self-tapping screws with flat caps (you can use “fleas” for drywall), twist a loop at the ends of the conductors, thread a self-tapping screw with a washer installed on it, screw it to the bank. Just before that, you need to clean the metal of the can - removing the plaque with fine-grained sandpaper. Banks are fixed on the bar. The distance between them is selected individually - according to the best picture. You should not hope for a miracle - there will be one or two channels in normal quality, or maybe not ... It depends on the position of the repeater, the "cleanliness" of the corridor, how correctly the antenna is oriented ... But as an exit in an emergency - this is a great option. An antenna for receiving a Wi-Fi signal can also be made from improvised means - from a tin can. This do-it-yourself TV antenna can be assembled in half an hour. This is if everything is done slowly. The jar should be made of metal, with smooth walls. Tall and narrow cans are great. If you put a homemade antenna on the street, find a jar with a plastic lid (as in the photo). The cable is taken antenna, coaxial, with a resistance of 75 ohms. In addition to the can and cable, you will also need: The Wi-Fi transmitters operate on the 2.4 GHz frequency with a wavelength of 124 mm. So, it is advisable to choose a jar such that its height is at least 3/4 of the wavelength. For this case, it is better that it be more than 93 mm. The diameter of the jar should be as close as possible to half the wavelength - 62 mm for a given channel. There may be some deviations, but the closer to the ideal, the better. When assembling, a hole is made in the bank. It must be placed exactly at the right point. Then the signal will be amplified several times. It depends on the diameter of the selected can. All parameters are given in the table. Measure exactly the diameter of your jar, find the right line, have all the right sizes. The procedure is as follows: You can do without an RF connector, but with it everything is much simpler - it is easier to set the emitter vertically upwards, connect the cable that goes to the router (router) or Wi-Fi card.
Photo 2.
Rice. 1.
Rice. 2.
Photo 3. Antenna layout test.
Photo 5. Size and pitch of the previous ones
antenna designs are almost the same.
Photo 7. Old antenna.
Photo 8. Design change.
Photo 10. New design.
Photo 9. Bank - mandrel.
,
Where 
;
Literature
You can attach foil to the glass and get a good signal .... 
Copper tube or wire is the best option, it bends well, it is easy tomaterials
Do you need a calculation
Frame making
Cable preparation
DIY DVB-T2 TV antenna: assembly
Homemade antenna double and triple square
You can make five frames - for a more confident reception 
It is undesirable to paint or varnish - reception worsens. This is possible only in close proximity to the transmitter. 
Construction and materials
Dimensions
Connecting an active frame (vibrator) via a short-circuited loop
Another variant of the triple square
The simplest antenna for giving - from metal cans
A simple Wi-Fi antenna from a metal can
Dimensions and Assembly
D - diameter Lower limit of attenuation Upper damping limit LG 1/4 LG 3/4 LG
73 mm 2407.236
3144.522
752.281
188.070
564.211
74 mm 2374.706
3102.028
534.688
133.672
401.016
75 mm 2343.043
3060.668
440.231
110.057
330.173
76 mm 2312.214
3020.396
384.708
96.177
288.531
77 mm 2282.185
2981.170
347.276
86.819
260.457
78 mm 2252.926
2942.950
319.958
79.989
239.968
79 mm 2224.408
2905.697
298.955
74.738
224.216
80 mm 2196.603
2869.376
282.204
070.551
211.653
81 mm 2169.485
2833.952
268.471
67.117
201.353
82 mm 2143.027
2799.391
256.972
64.243
192.729
83 mm 2117.208
2765.664
247.178
61.794
185.383
84 mm 2092.003
2732.739
238.719
59.679
179.039
85 mm 2067.391
2700.589
231.329
57.832
173.497
86 mm 2043.352
2669.187
224.810
56.202
168.607
87 mm 2019.865
2638.507
219.010
54.752
164.258
88 mm 1996.912
2608.524
213.813
53.453
160.360
89 mm 1974.475
2579.214
209.126
52.281
156.845
90 mm 1952.536
2550.556
204.876
51.219
153.657
91 mm 1931.080
2522.528
201.002
50.250
150.751
92 mm 1910.090
2495.110
197.456
49.364
148.092
93 mm 1889.551
2468.280
194.196
48.549
145.647
94 mm 1869.449
2442.022
191.188
47.797
143.391
95 mm 1849.771
2416.317
188.405
47.101
141.304
96 mm 1830.502
2391.147
185.821
46.455
139.365
97 mm 1811.631
2366.496
183.415
45.853
137.561
98 mm 1793.145
2342.348
181.169
45.292
135.877
99 mm 1775.033
2318.688
179.068
44.767
134.301
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