Advantages and disadvantages of horn antennas. Horn antenna: description, design, properties and use. E-plane sectorial horn
At 2.45 GHz, the WiFi signal wavelength is 122 mm. Polarization is vertical. The network provides an interesting diagram of a biquadrat curved around a copper pipe with a diameter of 10 cm. It turns out that the radiation pattern of such an antenna is distorted and stretched in azimuth. There are no MMANA models to see exactly what happens, but amateurs argue that this move is not the best (we'll look at that later). Horn antennas are suitable for high frequencies, but are too bulky for low frequencies. Is it possible to make an antenna for a router with your own hands in the form of a speaker. In exceptional cases (imitation of the voice of a lake duck), definitely yes.
Few people think about the physical meaning of the antenna. The average person will answer that an antenna is necessary to amplify the signal, but it is a passive, non-amplifying device. It collects a signal from a large area and sends it to a small one, where the receiver cable is located. All antennas do this without exception. What can a vibrator collect? Suffice it to remember that a wave vibrator (a piece of wire equal to the wavelength) is better than a half-wave vibrator, which has an advantage over a quarter-wave vibrator (equal to a quarter of the wavelength). The longer the vibrator, the more effective. In this case, certain proportions are observed. This is dictated by the wave laws of nature.
It is known that an opera singer, after hitting a high note, breaks a crystal glass. How it's done. The singing master hits the instrument lightly and listens to what note flows from the vessel. This is the resonant frequency of the object. By playing the same note with a trained voice, the singer evokes a response from the container. The oscillations accumulate, intensify, and do not die out. As a result, the glass breaks into pieces. Exactly the same thing happens in the antenna. Collects and transmits waves that are resonant. And this is the fundamental frequency and harmonics (multiplied by two, four, etc. frequencies). A homemade antenna for a router will help weed out the unnecessary. The signal will be concentrated in the right place.
It is important to connect the wire to the antenna correctly. Reception of waves and harmonics will make it possible to produce a harmonic antenna that receives frequencies whose half-waves are multiples of the dimensions of the device.
For example, frequencies related as 1: 2: 4: 6, etc. A properly drawn line will allow you to catch several waves at the same time. If you break the rules, the device will not work. Here's how to do it:
- Draw a schematic diagram of a vibrator (straight line), on which the laws of distribution of currents and voltages for all wavelengths are schematically indicated.
- If you connect the wires at the voltage antinode point, you get voltage power supply.
- If you connect the wires at the antinode point of all currents, you get current feeding.
This is how harmonic antennas are made. To make something like this, for example, for a frequency of 3.7 MHz (HF range), you need a piece of wire 80 meters long. It is clear that such a situation may not suit you. Therefore, new designs are constantly being searched for. Not long ago they published a description of the process of constructing a ferromagnetic antenna for the 3.7 - 7 MHz range that fits in a fist. We do not claim that it will replace 80 meters of copper, but researchers have observed a positive effect from it, which is used in radio receivers.
Horn antennas for router
What will please you with a horn amplifying antenna for a router. Simple in design. Here's the theory:
- pyramidal (truncated pyramid);
- sectorial, sectorial (a sector made of a waveguide, the bottom and ceiling are parallel to each other, the sides diverge);
- conical (truncated cone);
- hybrid (the shape of the horn can hardly be called a coined word; those who have disassembled satellite converters are familiar with a horn with steps).
If horns are used in satellite communications at frequencies above 5 GHz, then they are also suitable for WiFi. How to make an antenna for a router. Horns belong to the class of microwave devices. The antenna is made of steel plated inside. This improves conductivity conditions, allows the wave to move freely inside, and gives the walls hardness. In practice, cardboard covered with foil inside is suitable for a glazed loggia. Foil, as you know, is made of aluminum; copper has the best qualities. Some people assemble horn antennas from PCB. Then the surface is polished, for example, with an eraser, and varnished. Seal the horn antenna portal with dielectric, plastic, foam, etc.
Important! Without foil, the horn will not work for obvious reasons. A dielectric cannot reflect electromagnetic radiation.
The joints, in the case of PCB, are soldered, the cardboard is glued. It's probably better to take plywood, because the correct geometry is important for the antenna. And the veneer sheet holds its shape better. The inside needs to be glued at the seams, and the outside needs to be coated with a primer that prevents moisture from penetrating inside. Next, it is painted and hung anywhere. If desired, it is possible to attach a bird feeder at the top. Cover the inside of the structure with foil, as evenly as possible (the evenness of the pasting will not affect the operation of the antenna). We suggest making a pyramidal horn, which is simpler and will provide an acceptable radiation pattern and elevation in case strangers want to get into our network.
The radiation pattern of a horn antenna for a router is not original. This is a petal, 15 degrees wide (depending on the design) in azimuth and elevation. This determines the specific application. To cover the house, the antenna is placed at the height of the middle distance away. So that the main petal covers all consumers. Let's start with the dimensions of the supply waveguide, which receives little attention. There is a calculator on the website http://users.skynet.be/chricat/horn/horn-javascript.html; use it to calculate the parameters by substituting the frequency. The default is channel 6 (2437 MHz).
The bottom of the supply waveguide is pierced from below by a pin spaced from the rear wall by a quarter of the wavelength, and the length of the section is half the wavelength. Using a formula from physics, we find the wavelength: 299792458 / 2430000000 = 123 mm. This is the wavelength in free space. There is a critical wave in the waveguide; it cannot work below it. The value is equal to twice the long side of the waveguide. Let's follow the advice of the calculator and take walls 90 x 60 mm. The critical wave length will be 180 mm. Inside the waveguide, the wave moves at an angle. Consequently, the wavelength increases, equal to the quotient of the wavelength in free space divided by the cosine of the angle of motion inside.
The difficulty is finding the angle. Special formulas have been developed for the calculation; readers will find them on their own, but we will use the results. Initially, the calculator asks you to specify the dimensions of the horn. Let's give the correct values. Using the method, we find the sides of a parallelepiped that includes the opening of the horn (without a supply waveguide). It turns out:
- Length P – 60 cm.
- Width H – 25 cm.
- Height E – 10 cm.
The dimensions of the external portal are found, and the internal one is equal to the entrance to the waveguide. This will determine the geometry of the four walls. Click on Compute and you will get a ready-made template. Pay attention to the Aperture Quality column. It should contain a figure less than 1/8 of a wave (in this case, 15 mm). A quarter was published with the original data from the site, but the author is not sure of its accuracy. Do not glue the first model tightly, but test it first on the ground. Please note that we have already calculated the wavelength in the waveguide, the figure is 16.85 cm. Now we understand what to do with the rod:
- distanced from the rear blanked wall of the waveguide by 168.5 / 4 = 42.125 mm;
- the waveguide section has a length of 84 mm;
These are important parameters and should be strictly followed. Here the signal is removed from the pin. How to set up a site. The pin protrudes from the bottom to a certain length, this is a quarter of a wave in free space (31 mm). You need to take the SWR meter and move it in different directions until you get a value in the unity area. If it doesn’t work for a long time, then tilt the rod slightly towards the back wall.
Well, the external antenna of the WiFi router is ready. Next there will be a conversation about microwave technologies.
The article for translation was proposed by alessandro893. The material is taken from an extensive reference site, describing, in particular, the principles of operation and design of radars.
An antenna is an electrical device that converts electricity into radio waves and vice versa. The antenna is used not only in radars, but also in jammers, radiation warning systems and communications systems. During transmission, the antenna concentrates the energy of the radar transmitter and forms a beam directed in the desired direction. When receiving, the antenna collects the returning radar energy contained in the reflected signals and transmits them to the receiver. Antennas often vary in beam shape and efficiency.
On the left is an isotropic antenna, on the right is a directional antenna
Dipole antenna
A dipole antenna, or dipole, is the simplest and most popular class of antennas. Consists of two identical conductors, wires or rods, usually with bilateral symmetry. For transmitting devices, current is supplied to it, and for receiving devices, a signal is received between the two halves of the antenna. Both sides of the feeder at the transmitter or receiver are connected to one of the conductors. Dipoles are resonating antennas, that is, their elements serve as resonators in which standing waves pass from one end to the other. So the length of the dipole elements is determined by the length of the radio wave.
Directional pattern
Dipoles are omnidirectional antennas. For this reason, they are often used in communication systems.Antenna in the form of an asymmetric vibrator (monopole)
An asymmetrical antenna is half of a dipole antenna, and is mounted perpendicular to the conducting surface, a horizontal reflecting element. The directivity of a monopole antenna is twice that of a double-length dipole antenna because there is no radiation underneath the horizontal reflective element. In this regard, the efficiency of such an antenna is twice as high, and it is capable of transmitting waves further using the same transmission power.
Directional pattern
Wave channel antenna, Yagi-Uda antenna, Yagi antenna
Directional pattern
Corner antenna
A type of antenna often used on VHF and UHF transmitters. It consists of an irradiator (this can be a dipole or a Yagi array) mounted in front of two flat rectangular reflective screens connected at an angle, usually 90°. A sheet of metal or a grating (for low-frequency radars) can act as a reflector, reducing weight and reducing wind resistance. Corner antennas have a wide range, and the gain is about 10-15 dB.
Directional pattern
Vibrator log-periodic (logarithmic periodic) antenna, or log-periodic array of symmetrical vibrators
A log-periodic antenna (LPA) consists of several half-wave dipole emitters of gradually increasing length. Each consists of a pair of metal rods. The dipoles are attached closely, one behind the other, and connected to the feeder in parallel, with opposite phases. This antenna looks similar to the Yagi antenna, but it works differently. Adding elements to a Yagi antenna increases its directivity (gain), and adding elements to an LPA increases its bandwidth. Its main advantage over other antennas is its extremely wide range of operating frequencies. The lengths of the antenna elements relate to each other according to a logarithmic law. The length of the longest element is 1/2 the wavelength of the lowest frequency, and the shortest is 1/2 the wavelength of the highest frequency.
Directional pattern
Helix antenna
A helical antenna consists of a conductor twisted into a spiral. They are usually mounted above a horizontal reflective element. The feeder is connected to the bottom of the spiral and the horizontal plane. They can operate in two modes - normal and axial.
Normal (transverse) mode: The helix dimensions (diameter and inclination) are small compared to the wavelength of the transmitted frequency. The antenna operates in the same way as a shorted dipole or monopole, with the same radiation pattern. The radiation is linearly polarized parallel to the axis of the spiral. This mode is used in compact antennas for portable and mobile radios.
Axial mode: the dimensions of the spiral are comparable to the wavelength. The antenna works as a directional one, transmitting the beam from the end of the spiral along its axis. Emits radio waves of circular polarization. Often used for satellite communications.
Directional pattern
Rhombic antenna
A diamond antenna is a broadband directional antenna consisting of one to three parallel wires fixed above the ground in the shape of a diamond, supported at each vertex by towers or poles to which the wires are attached using insulators. All four sides of the antenna are the same length, usually at least the same wavelength, or longer. Often used for communication and operation in the decameter wave range.
Directional pattern
Two-dimensional antenna array
Multi-element array of dipoles used in the HF bands (1.6 - 30 MHz), consisting of rows and columns of dipoles. The number of rows can be 1, 2, 3, 4 or 6. The number of columns can be 2 or 4. The dipoles are horizontally polarized and a reflective screen is placed behind the dipole array to provide an amplified beam. The number of dipole columns determines the width of the azimuthal beam. For 2 columns the width of the radiation pattern is about 50°, for 4 columns it is 30°. The main beam can be tilted 15° or 30° for maximum coverage of 90°.
The number of rows and the height of the lowest element above the ground determines the elevation angle and the size of the serviced area. An array of two rows has an angle of 20°, and an array of four has an angle of 10°. The radiation from a two-dimensional array usually approaches the ionosphere at a slight angle, and due to its low frequency, is often reflected back to the earth's surface. Since radiation can be reflected many times between the ionosphere and the ground, the antenna's action is not limited to the horizon. As a result, such an antenna is often used for long-distance communications.
Directional pattern
Horn antenna
A horn antenna consists of an expanding horn-shaped metal waveguide that collects radio waves into a beam. Horn antennas have a very wide range of operating frequencies; they can operate with a 20-fold gap in its boundaries - for example, from 1 to 20 GHz. The gain varies from 10 to 25 dB, and they are often used as feeds for larger antennas.
Directional pattern
Parabolic antenna
One of the most popular radar antennas is the parabolic reflector. The feed is located at the focus of the parabola, and the radar energy is directed to the surface of the reflector. Most often, a horn antenna is used as a feed, but both a dipole and a helical antenna can be used.
Since the point source of energy is at the focus, it is converted into a wavefront of constant phase, making the parabola well suited for use in radar. By changing the size and shape of the reflective surface, beams and radiation patterns of various shapes can be created. The directivity of parabolic antennas is much better than that of a Yagi or dipole; the gain can reach 30-35 dB. Their main drawback is their inability to handle low frequencies due to their size. Another thing is that the irradiator can block part of the signal.
Directional pattern
Cassegrain antenna
A Cassegrain antenna is very similar to a conventional parabolic antenna, but uses a system of two reflectors to create and focus the radar beam. The main reflector is parabolic, and the auxiliary reflector is hyperbolic. The irradiator is located at one of the two foci of the hyperbola. The radar energy from the transmitter is reflected from the auxiliary reflector onto the main one and focused. The energy returning from the target is collected by the main reflector and reflected in the form of a beam converging at one point onto the auxiliary one. It is then reflected by an auxiliary reflector and collected at the point where the irradiator is located. The larger the auxiliary reflector, the closer it can be to the main one. This design reduces the axial dimensions of the radar, but increases the shading of the aperture. A small auxiliary reflector, on the contrary, reduces shading of the opening, but it must be located away from the main one. Advantages compared to a parabolic antenna: compactness (despite the presence of a second reflector, the total distance between the two reflectors is less than the distance from the feed to the reflector of a parabolic antenna), reduced losses (the receiver can be placed close to the horn emitter), reduced side lobe interference for ground radars. Main disadvantages: the beam is blocked more strongly (the size of the auxiliary reflector and feed is larger than the size of the feed of a conventional parabolic antenna), does not work well with a wide range of waves.
Directional pattern
Antenna Gregory
On the left is the Gregory antenna, on the right is the Cassegrain antenna
The Gregory parabolic antenna is very similar in structure to the Cassegrain antenna. The difference is that the auxiliary reflector is curved in the opposite direction. Gregory's design can use a smaller secondary reflector compared to a Cassegrain antenna, resulting in less of the beam being blocked.
Offset (asymmetric) antenna
As the name suggests, the emitter and auxiliary reflector (if it is a Gregory antenna) of an offset antenna are offset from the center of the main reflector so as not to block the beam. This design is often used on parabolic and Gregory antennas to increase efficiency.
Cassegrain antenna with flat phase plate
Another design designed to combat beam blocking by an auxiliary reflector is the flat plate Cassegrain antenna. It works taking into account the polarization of waves. An electromagnetic wave has 2 components, magnetic and electric, which are always perpendicular to each other and the direction of movement. The polarization of the wave is determined by the orientation of the electric field, it can be linear (vertical/horizontal) or circular (circular or elliptical, twisted clockwise or counterclockwise). The interesting thing about polarization is the polarizer, or the process of filtering the waves, leaving only waves polarized in one direction or plane. Typically, the polarizer is made of a material with a parallel arrangement of atoms, or it can be a lattice of parallel wires, the distance between which is less than the wavelength. It is often assumed that the distance should be approximately half the wavelength.
A common misconception is that the electromagnetic wave and polarizer work in a similar way to an oscillating cable and a plank fence - that is, for example, a horizontally polarized wave must be blocked by a screen with vertical slits.
In fact, electromagnetic waves behave differently than mechanical waves. A lattice of parallel horizontal wires completely blocks and reflects a horizontally polarized radio wave and transmits a vertically polarized one - and vice versa. The reason is this: when an electric field, or wave, is parallel to a wire, it excites electrons along the length of the wire, and since the length of the wire is many times greater than its thickness, the electrons can easily move and absorb most of the energy of the wave. The movement of electrons will lead to the appearance of a current, and the current will create its own waves. These waves will cancel out the transmission waves and behave like reflected waves. On the other hand, when the electric field of the wave is perpendicular to the wires, it will excite electrons across the width of the wire. Since the electrons will not be able to actively move in this way, very little energy will be reflected.
It is important to note that although in most illustrations radio waves have only 1 magnetic field and 1 electric field, this does not mean that they oscillate strictly in the same plane. In fact, one can imagine that electric and magnetic fields consist of several subfields that add up vectorially. For example, for a vertically polarized wave from two subfields, the result of adding their vectors is vertical. When two subfields are in phase, the resulting electric field will always be stationary in the same plane. But if one of the subfields is slower than the other, then the resulting field will begin to rotate around the direction the wave is moving (this is often called elliptical polarization). If one subfield is slower than the others by exactly a quarter of a wavelength (the phase differs by 90 degrees), then we get circular polarization:
To convert linear polarization of a wave into circular polarization and back, it is necessary to slow down one of the subfields relative to the others by exactly a quarter of the wavelength. For this, a grating (quarter-wave phase plate) of parallel wires with a distance between them of 1/4 wavelength, located at an angle of 45 degrees to the horizontal, is most often used.
For a wave passing through the device, linear polarization turns into circular, and circular into linear.
A Cassegrain antenna with a flat phase plate operating on this principle consists of two reflectors of equal size. The auxiliary reflects only horizontally polarized waves and transmits vertically polarized waves. The main one reflects all waves. The auxiliary reflector plate is located in front of the main one. It consists of two parts - a plate with slits running at an angle of 45°, and a plate with horizontal slits less than 1/4 wavelength wide.
Let's say the feed transmits a wave with circular polarization counterclockwise. The wave passes through the quarter-wave plate and becomes a horizontally polarized wave. It is reflected from horizontal wires. It passes through the quarter-wave plate again, on the other side, and for it the plate wires are already oriented mirror-image, that is, as if rotated by 90°. The previous change in polarization is reversed, so that the wave again becomes circularly polarized counterclockwise and travels back to the main reflector. The reflector changes polarization from counterclockwise to clockwise. It passes through the horizontal slits of the auxiliary reflector without resistance and leaves in the direction of the targets, vertically polarized. In receive mode, the opposite happens.
Slot antenna
Although the described antennas have fairly high gain relative to the aperture size, they all have common disadvantages: high side-lobe susceptibility (susceptibility to nuisance reflections from the earth's surface and sensitivity to targets with a low effective scattering area), reduced efficiency due to beam blocking (small radars, which can be used on aircraft, have a problem with blocking; large radars, where the problem with blocking is less, cannot be used in the air). As a result, a new antenna design was invented - a slot antenna. It is made in the form of a metal surface, usually flat, in which holes or slots are cut. When it is irradiated at the desired frequency, electromagnetic waves are emitted from each slot - that is, the slots act as individual antennas and form an array. Since the beam coming from each slot is weak, their side lobes are also very small. Slot antennas are characterized by high gain, small side lobes and low weight. They may have no protruding parts, which in some cases is their important advantage (for example, when installed on aircraft).
Directional pattern
Passive phased array antenna (PFAR)
Radar with MIG-31
Since the early days of radar development, developers have been plagued by one problem: the balance between accuracy, range and scan time of the radar. It arises because radars with a narrower beam width increase accuracy (increased resolution) and range at the same power (power concentration). But the smaller the beam width, the longer the radar scans the entire field of view. Moreover, a high-gain radar will require larger antennas, which is inconvenient for fast scanning. To achieve practical accuracy at low frequencies, the radar would require antennas so huge that they would be mechanically difficult to rotate. To solve this problem, a passive phased array antenna was created. It relies not on mechanics, but on the interference of waves to control the beam. If two or more waves of the same type oscillate and meet at one point in space, the total amplitude of the waves adds up in much the same way as waves on water add up. Depending on the phases of these waves, interference can strengthen or weaken them.
The beam can be shaped and controlled electronically by controlling the phase difference of a group of transmitting elements - thus controlling where amplification or attenuation interference occurs. It follows from this that the aircraft radar must have at least two transmitting elements to control the beam from side to side.
Typically, a PFAR radar consists of 1 feed, one LNA (low noise amplifier), one power distributor, 1000-2000 transmitting elements and an equal number of phase shifters.
Transmitting elements can be isotropic or directional antennas. Some typical types of transmission elements:
On the first generations of fighter aircraft, patch antennas (strip antennas) were most often used because they were the easiest to develop.
Modern active phase arrays use groove emitters due to their wideband capabilities and improved gain:
Regardless of the type of antenna used, increasing the number of radiating elements improves the radar's directivity characteristics.
As we know, for the same radar frequency, increasing the aperture leads to a decrease in beam width, which increases range and accuracy. But for phased arrays, it is not worth increasing the distance between the emitting elements in an attempt to increase the aperture and reduce the cost of the radar. Because if the distance between the elements is greater than the operating frequency, side lobes may appear, significantly degrading the radar's performance.
The most important and expensive part of the PFAR is the phase shifters. Without them, it is impossible to control the signal phase and beam direction.
They come in different types, but generally they can be divided into four types.
Phase shifters with time delay
The simplest type of phase shifters. It takes time for a signal to travel through a transmission line. This delay, equal to the phase shift of the signal, depends on the length of the transmission line, the frequency of the signal, and the phase velocity of the signal in the transmitting material. By switching a signal between two or more transmission lines of a given length, the phase shift can be controlled. Switching elements are mechanical relays, pin diodes, field-effect transistors or microelectromechanical systems. Pin diodes are often used because of their high speed, low loss, and simple bias circuits that provide resistance changes from 10 kΩ to 1 Ω.
Delay, sec = phase shift ° / (360 * frequency, Hz)
Their disadvantage is that the phase error increases with increasing frequency and increases in size with decreasing frequency. Also, the phase change varies with frequency, so they are not applicable for very low and high frequencies.
Reflective/quadrature phase shifter
Typically this is a quadrature coupling device that splits the input signal into two signals 90° out of phase, which are then reflected. They are then combined in phase at the output. This circuit works because signal reflections from conductive lines can be out of phase with respect to the incident signal. The phase shift varies from 0° (open circuit, zero varactor capacitance) to -180° (shorted circuit, infinite varactor capacitance). Such phase shifters have a wide range of operation. However, the physical limitations of varactors mean that in practice the phase shift can only reach 160°. But for a larger shift it is possible to combine several such chains.
Vector IQ modulator
Just like a reflective phase shifter, here the signal is split into two outputs with a 90-degree phase shift. The unbiased input phase is called the I-channel, and the quadrature with a 90-degree offset is called the Q-channel. Each signal is then passed through a biphasic modulator capable of shifting the phase of the signal. Each signal is phase shifted by 0° or 180°, allowing any pair of quadrature vectors to be selected. The two signals are then recombined. Since the attenuation of both signals can be controlled, not only the phase but also the amplitude of the output signal is controlled.
Phase shifter on high/low pass filters
It was manufactured to solve the problem of time delay phase shifters not being able to operate over a large frequency range. It works by switching the signal path between high-pass and low-pass filters. Similar to a time delay phase shifter, but uses filters instead of transmission lines. The high-pass filter consists of a series of inductors and capacitors that provide phase advance. Such a phase shifter provides a constant phase shift in the operating frequency range. It is also much smaller in size than the previous phase shifters listed, which is why it is most often used in radar applications.
To summarize, compared to a conventional reflective antenna, the main advantages of PFAR will be: high scanning speed (increasing the number of tracked targets, reducing the likelihood of the station detecting an radiation warning), optimization of the time spent on the target, high gain and small side lobes (difficult to jam and detect), random scan sequence (harder to jam), ability to use special modulation and detection techniques to extract signal from noise. The main disadvantages are high cost, the inability to scan wider than 60 degrees in width (the field of view of a stationary phase array is 120 degrees, a mechanical radar can expand it to 360).
Active phased array antenna
Outside, AFAR (AESA) and PFAR (PESA) are difficult to distinguish, but inside they are radically different. PFAR uses one or two high-power amplifiers to transmit a single signal, which is then divided into thousands of paths for thousands of phase shifters and elements. An AFAR radar consists of thousands of reception/transmission modules. Since the transmitters are located directly in the elements themselves, it does not have a separate receiver and transmitter. The differences in architecture are shown in the picture.
In AFAR, most of the components, such as a weak signal amplifier, a high-power amplifier, a duplexer, and a phase shifter, are reduced in size and assembled in one housing called a transmit/receive module. Each of the modules is a small radar. Their architecture is as follows:
Although AESA and PESA use wave interference to shape and deflect the beam, the unique design of AESA provides many advantages over PFAR. For example, a small signal amplifier is located close to the receiver, before the components where part of the signal is lost, so it has a better signal-to-noise ratio than a PFAR.
Moreover, with equal detection capabilities, AFAR has a lower duty cycle and peak power. Also, since individual APAA modules do not rely on a single amplifier, they can transmit signals at different frequencies simultaneously. As a result, AFAR can create several separate beams, dividing the array into subarrays. The ability to operate on multiple frequencies brings multitasking and the ability to deploy electronic jamming systems anywhere in relation to the radar. But forming too many simultaneous beams reduces the radar's range.
The two main disadvantages of AFAR are high cost and limited field of view to 60 degrees.
Hybrid electronic-mechanical phased array antennas
The very high scanning speed of the phased array is combined with a limited field of view. To solve this problem, modern radars place phased arrays on a movable disk, which increases the field of view. Do not confuse the field of view with the width of the beam. Beam width refers to the radar beam, and field of view refers to the overall size of the area being scanned. Narrow beams are often needed to improve accuracy and range, but a narrow field of view is usually not necessary.
Application of horn antennas
A stand-alone horn antenna is used mainly in cases where a sharp radiation pattern is not required and when the antenna must have sufficient range. In practice, using a horn antenna, you can cover approximately twice the wavelength range. Strictly speaking, the range of an Electromagnetic horn antenna is limited not by the horn, but by the waveguide feeding it.
The large range of horn antennas and simplicity of design are significant advantages of this type of microwave antennas, thanks to which they are widely used in antenna measurements and measurements of electromagnetic field characteristics.
horns are also widely used as feeds for lens and mirror antennas, as well as elements of antenna arrays.
The antenna is operated in accordance with regulatory documentation, which stipulates the timing of routine maintenance. Routine work is a list of necessary actions to check the accuracy of the antenna and its parameters, as well as mechanical and electrical properties.
External inspection must be carried out constantly for the presence of mechanical and electrical damage. Regularly clean the antenna from dirt and dust and check the feeder path.
Conclusion
During the course work, the main dimensions of the antenna were calculated, and the parameters of the feed line were calculated. Based on the calculations made, a radiation pattern was constructed and a sketch of the antenna was made.
Based on the shape of the radiation patterns and the calculated efficiency value, we can conclude that the main parameters of the antenna correspond to the specified values.
Antenna efficiency: 0.84
The requirements for the horn antenna in the technical specifications are met with some power reserve.
horn antenna feeder directivity
Literature and sources of information
1. Sazonov D. M. Antennas and microwave devices. - M.: Higher School, 1988. - 432 p.
2. Nechaev E. E. Methodological instructions for completing coursework in the discipline “Antennas and RVR”. M.: MGTUGA, 1996. -106 p.
3. Kocherzhevsky G.N., Erokhin G.A., Antenna-feeder devices. M.: Radio and communication, 1989. - 352 p.
4. A.Z. Fradin. Antenna-feeder devices. Tutorial. M.: Svyaz, 1997.
Calculation of the director antenna……………………………………………3
Calculation of a horn antenna……………………………………………………………10
Calculation of a single-mirror parabolic antenna………………………17
Conclusions on the calculation work……………………………………………..24
List of references……………………………………………………….25
Vibrator antennas are used in the millimeter, centimeter, decimeter, meter and longer wavelength ranges and are straight conductors excited at certain points. Vibrator antennas, depending on the design, have a directivity factor from several units to tens of thousands and are used in radio communication systems, radio navigation, television, telemetry and other areas of radio engineering.
To increase the directivity, a vibrator with a reflector and one or more directors is used. Such an antenna is called a director antenna and is widely used in various fields of radio communications in the VHF range. The more directors, the greater the KND and already the main petal of the DN. Typically, the efficiency of director antennas is 10...30, but designs of director antennas with efficiency = 80...100 are known.
Drawing 1.1 - General view of the director antenna
The figure shows an active vibrator with a length of , a reflector with a length of , a director with a length of , a boom, a mast and an antenna mounting box, as well as the distances from the vibrator to the reflector, from the vibrator to the director, and the length of the antenna itself.
Theoretical calculation of antenna parameters.
In a director antenna, the length of the active vibrator is made equal to the resonant length:
With such a length, the input resistance has a reactive part close to zero. The reflector length must be longer than the resonant length:
The length of the directors is made less than the resonant length:
Moreover, the length of the directors decreases from the first to the last.
For a vibrator-reflector system, the optimal distance, from the point of view of maximum efficiency, is selected within the limits:
For the system, the vibrator is the first director:
The distance between neighboring directors is taken within the limits:
The wavelength is determined using the formula:
Where is the speed of light, and is the frequency of the channel. Because we are given 5 - 6 television channels, then we take the average frequency of the occupied frequency bands of these two channels: , then the wavelength from formula (1.7) will be equal to:
Let's calculate the lengths of the antenna vibrators and the distance between them using formulas (1.1 – 1.6):
We will take the total length of the antenna and its image in Figure 1.2 from the VIBRAT program.
Drawing 1.2 - General view of the calculated director antenna
To find the directional pattern of the director antenna in the plane, we use formula (1.8):
Where is the number of vibrators, k is the wave number, and is the average distance between the vibrators.
Substituting (1.9) and (1.10) into (1.8) and numerical values, we obtain an expression for finding the pattern of a given director antenna:
We will construct a normalized radiation pattern using the Mathcad package. Because it is symmetric about zero, then we will construct it for:
Drawing 1.3 - DN in plane
From the graph you can determine the width of the main lobe and the maximum level of the side lobes: .
The directivity factor and the width of the main lobe are determined by formulas (1.10-1.11):
Coefficients and are determined from the graph in Figure 1.4:
Drawing 1.4 - Odds chart
Let's determine the wavelength of the antenna:
Knowing the wavelength of the antenna and using Figure 1.4, we determine that . Then:
Let us compare the obtained calculation results with the results of the calculated director antenna modeled in the program. The results have a slight discrepancy due to the fact that the formulas used are approximate and do not take into account a number of factors.
Drawing 1.5 - Director antenna calculated in VIBRAT
Conclusion: we calculated the directivity factor, DP and DP parameters of the director antenna in a given frequency range. Using the VIBRAT program, we simulated this antenna and verified the validity of the obtained parameters.
Rice. Types of horn antennas: a) E-sectoral, b) N-sectoral, c) pyramidal, d) conical.
Properties:
Horn antennas are very broadband and match the feed line very well - in fact, the antenna bandwidth is determined by the properties of the exciting waveguide. These antennas are characterized by a low level of the rear lobes of the radiation pattern (up to -40 dB) due to the fact that there is little flow of RF currents to the shadow side of the horn. Horn antennas with low gain are simple in design, but achieving high (>25 dB) gain requires the use of wave phase-aligning devices (lenses or mirrors) in the horn aperture. Without such devices, the antenna has to be made impractically long.
Application:
Horn antennas are used both independently and as feeds for mirror and other antennas. A horn antenna, structurally combined with a parabolic reflector, is often called a horn-parabolic antenna. Horn antennas with low gain are often used as measurement antennas due to their favorable set of properties and good repeatability.
At the Holmdale radio telescope, which is a Dicke radiometer based on a horn-parabolic antenna, Arno Penzias and Robert Woodrow Wilson discovered the cosmic microwave background radiation in 1965.
Characteristics and formulas:
The gain of a horn antenna is determined by its opening area and can be calculated using the formula:
where: - horn opening area.
λ is the wavelength of the main radiation.
- 0,4....0,8 instrumentation(horn surface utilization factor), equal to 0.6 for the case when the path difference between the central and peripheral beams is less, but close to Pi/2, and 0.8 when wave phase-leveling devices are used.
Main lobe width DNA H:
Main lobe width DNA by zero radiation in the plane E:
Since with equality L E And L H DNA in the plane N turns out to be 1.5 times wider; often, to obtain the same petal width in both planes, choose:
To keep phase distortions in the horn aperture within acceptable limits (no more than Pi/2), it is necessary that the following condition be met (for a pyramidal horn):
where and are the heights of the faces of the pyramid forming the horn.
From another source:
Where L H- opening width in plane N,
L E- opening width in plane E,
R E And RH- horn length.
For such an antenna KND in a simplified form it is calculated using the formula:
D RUR = 4piνS/λ 2
Where: S = L H * L E- horn opening area;
λ
- wavelength of the main radiation;
ν
= 0.4....0.8 - surface utilization coefficient ( instrumentation);
Depending on the type of horn, horn antennas are divided into N- And E- sectorial, pyramidal and conical. Horns whose dimensions correspond to the maximum value KND are called optimal. For optimal N-sectoral horn antennas horn length R H =L H 2 /3λ, for optimal E-sectoral horn antennas R E =L E 2 /2λ. instrumentation optimal N- And E-sectoral, pyramidal horns is 0.64. If we conditionally increase the length of the horn to infinity, then instrumentation antenna will increase to 0.81.
In a conical horn, optimal length R opt. con. depends on the diameter of its opening
d:
R opt. con. = d 2 /2.4λ + 0.15λ
instrumentation optimal conical horn v=0,5.
Table 1.2. Horn radiation pattern width with optimal length.
Horn type |
Radiation pattern width in the H plane |
Radiation pattern width in plane E |
E-sectoral |
2Θ 0.7 =68λ/L H |
2Θ 0.7 =53λ/L E |
H-sectoral |
2Θ 0.7 =80λ/L H |
2Θ 0.7 =51λ/L E |
Pyramidal |
2Θ 0.7 =80λ/L H |
2Θ 0.7 =53λ/L E |
Conical |
2Θ 0.7 =60λ/d |
2Θ 0.7 =70λ/d |
If we take an elliptical horn with an ellipse axial ratio of 1.25, then we can obtain approximately the same width of the radiation pattern in all sections passing through the horn axis.
The advantage of a horn antenna is its broadband, determined by the broadband of the feeding waveguide, efficiency. horn antenna is equal to unity.
The disadvantage of horn antennas is that the horn length must be too long to obtain highly directional radiation. The optimal horn length is proportional to the square of the aperture dimensions L H or L E, and the width of the radiation pattern is inversely proportional L H or L E in the first degree. Therefore, to narrow the radiation pattern of a horn antenna in N times, the opening width should be increased by N times, and the length of the horn is in N2 once. This circumstance imposes restrictions on the width of the radiation pattern of horn antennas.