Different types of satellite antennas

There are many options that can be found in the evolution of satellite or satellite dishes, and they vary according to the requirement in which they are to be used and the area even in which they are to be installed. Each has a specific function. In the following, we will explain what each antenna is about.

Dipole antenna

It is said that an antenna is of rectilinear polarization when the electric vector of the irradiated wave is always oriented in the same direction. This is the case of a dipolar antenna that is the simplest and most functional type of antennas.

Dipole receiver

On the contrary, the electric and magnetic vectors of the wave irradiated by the antenna rotate, changing direction continuously, the polarization is elliptical or circular, which we could well compare with certain galaxies and their characteristics. (See article: Elliptical galaxies).

At reception, when the direction of the electrical component of the incident field is not parallel to the direction of polarization of the antenna, the absorbed power decreases, and is canceled when both directions are orthogonal.

To achieve good electrical efficiency, the dimensions of the satellite or satellite dishes must be of the order of the length of the radiated or received waves. Therefore, given the wide range of wavelengths used for communications, from kilometers to centimeters and millimeters, the types of antennas used are very different.

Meaning of Onda

wave in satellite or satellite dishes

As we see in both the previous and the following graph, an electromagnetic wave is defined as the disturbance that propagates outward from any electric charge and away from the charge, electric and magnetic fields are formed that move at the speed of light and are perpendicular to each other and to the direction of movement.

That is to say, what we call disturbance in the graph is manifested as the lines in the form of waves that go from one end to the other, that are produced when receiving the electric charge, and after that impact the electric and magnetic drives are also generated. by the speed of light and let themselves be carried away by the movement where they are going.

electromagnetic wave

They cross the non-metallic bodies and although their intensity decreases according to the square of the distance, they can be captured very far by means of high sensitivity devices.

https://youtu.be/cF1fYetYDcs?t=14

They cross the non-metallic bodies and although their intensity decreases according to the square of the distance, they can be captured very far by means of high sensitivity devices.

Among the electromagnetic waves, for which special names, such as radio waves or microwaves, are used, depending on their frequency, are those used in broadcasting communications, radar television, infrared, visible light, ultraviolet radiation and X-ray, gamma and cosmic.

Wave phenomena are important not only in mechanics but also in electromagnetism and in atomic physics. The existence of a material medium for the propagation of a wave is not strictly necessary, the clearest example is in the propagation of electric and magnetic fields in space: the so-called electromagnetic waves are capable of traveling in a vacuum.

"wave

All these explanations, although they seem very technical, allow us to venture into a topic of considerable importance, if we decide in some way to try to understand the meaning and operation of the satellite or satellite dishes. Although we will not become experts in the field, basic knowledge will give us a certain level of understanding that will be appreciated and valued in the future.

Continuing with the topic of the definitions of satellite or satellite dishes, and their elements; for the wavelength and even longer wavelengths, the antenna is a vertical half-pole, the other half is constituted by the ground that, for the purposes of irradiation, behaves like a reflecting mirror.

For hectometric wavelengths, used in local radiocommunications, the terrain is no longer quite reflective and therefore a grid of metallic wires is usually available around the antenna in order to increase the conductivity of the terrain; while for the reception the called frame or frame antennas formed by turns of conductors that act as a magnetic dipole are used.

"dipole

Frame antenna

It is the type of receiving antenna, sometimes used as a transmitter, equivalent to a magnetic dipole, whose effective area is increased in normal radio receivers, because the turns are wrapped around a core of high permability material.

frame antenna

Spiral are called some satellite or satellite dishes.

For wavelengths of the order of the meter or shorter, the spiral antenna (logarithmic or Archimedes spiral) can be used, which consists of two coiled wires or conductive coils on a flat insulating surface.

The antenna radiates, with good efficiency, in a wide range of wavelengths, which varies from near the length of the maximum circumference of the spiral to the distance between the power terminals.

spiral antennas

Undoubtedly, many of the fields of industry, telecommunication or simply for the work of daily life, inventions related to technology for the improvement of the functions of devices for the use of the individual in their daily lives, are contingent and originated in both forms and process of evolution of the celestial spheres, movements of the planets, etc,

In this case, the spiral antenna is inspired by the galaxy that bears the same name, which at first glance the shape of its composition leads us to easily resemble it, strengthening the relationship of the universe with the human being, then, the individual with his eagerness to constantly seek answers in the cosmos, finds true foundations for its evolution. (See article: Spiral galaxies).

A spiral antenna can also rest on a non-flat surface, for example, spherical as in the case of the spiral satellite antenna Transit, whose arrangement provides the most uniform emission possible in all directions.

spiral galaxy antenna comparison

The spiral antenna is, in reality, a directivity scale, but radiates with circular polarization along the axis around which it is wound; Such a feature is useful to limit the weakness of the signal received on the ground due to ionospheric effects. This antenna is part of what are called frequency independent antennas.

Satellite or satellite dishes for reflection

It is the optical type system used to obtain high directivity values, or also to achieve, with shorter wavelengths, special type radiation patterns. One type of reflector widely used is the paraboloid of rotation. A low directivity antenna, for example; a dipole or a tube is placed in the focus of a metal surface that is shaped like a paraboloid of rotation.

antenna types

The antenna is mounted in such a way that it radiates, as evenly as possible, to the metal surface. This reflects the incident radiation and concentrates them in the direction of the paraboloid axis, in a radiation lobe that can be very narrow.

Parabolic reflectors, or in other ways, are also used in radar apparatus; It is always to obtain a radiation diagram with a sufficiently narrow lobe, in order to obtain good angular determination sensitivity.

Dipole

In previous paragraphs we had invested some in describing what a dipole antenna was about, but it is important to know in depth the term that names this antenna; so we have that the dipole is a system of two specific electric or magnetic charges of equal magnitude, but of opposite electric charge. The product of the load is called the electric dipole moment.

antenna dipole

What is paraboloid?

It is a figure that can give a parabolic section at any of its points when cut by a plane, as it can also be defined as the figure that can make a parabola when it rotates around its axis of symmetry.

"paraboloid

Rhombic antenna

It is a directive receiving antenna consisting of four equal conductors and arranged parallel to the ground, according to the sides of a rhombus. It has the characteristic of being aperiodic, that is, suitable for a wide frequency field, provided that the wavelengths do not exceed that of the half of the rhombus side.

Satellite or satellite curtain type antennas

The curtain antennas are constituted by a set of dipole, each of length equal to the wavelength or a semi wavelength, arranged parallel to one or more alignments. This arrangement leads to better directivity than with a single dipole.

Curtain antennas

Indeed, for two half-wave dipoles, parallel and separated by half-wavelength, fed in phase, that is, so that the maximum of the input current occurs simultaneously for the two dipoles, all points of the middle plane They are at the same distance as both poles.

Therefore, the waves irradiated in phase by the two antennas also arrive in phase with each other. The intensity of the field is the sum of the intensities, instead the points located in inclined planes with respect to the middle plane are at different distances from the dipoles, and therefore, the path traveled by the waves to reach one or the other of the Antennas is different.

dipole distance

When the angle of inclination is such that the difference in travel BA ’is equal to λ2, the waves reach B’ in a perfectly opposite phase and cancel each other out; The magnetic field is null. This type of alignment is designated as broad-side array.

The same two half-wave poles, parallel but located at a distance equal to a quarter of a wavelength and fed with a phase difference of a quarter of a period of oscillation, produce a maximum intensity, due to the part of the dipole fed with phase in delay.

Lens antenna

lens antenna

For microwaves, metal lenses are used to increase the directivity of the antenna. In the optical field, the properties of a lens depend on the various propagation characteristics of light waves in a vacuum and in the medium that constitutes the lens. In particular, the index of refraction of the two media is different.

The microwave metal lenses are based on the fact that the programming speed of the guided electromagnetic waves between metal sheets can also be significantly higher than the speed of the same vacuum waves.

These metal lenses can be placed on the mouth of a tube. The radiation beam that is obtained is noticeably narrower than what would be obtained with the tubes without a lens.

Lens antenna

Satellite or satellite dishes called helical

It is an antenna constructed by a metallic wire wound along or along a cylinder or a cone trunk. The power line is connected to a conductor by one end of the propeller and the other connected to ground or a flat metal plate perpendicular to the axis of the helix.

Irradiation occurs, in the opposite direction to the plate of the two characteristic modes; in one of them, called axial or axial, the main radiation lobe is directed along the axis of the propeller, with circular polarization according to the winding direction of the turns.

helical antennas

This form of radiation is preponderant, with good values ​​of electrical efficiency and directivity, when the length of each turn is of the order of λ and the total length of the antenna in the axial direction is of the order of one or more wavelengths.

When the axial length of the propeller is small with respect to the wavelength, irradiation occurs transversely to the axis with rectilinear polarization, for example, for a magnetic dipole consisting of one or more turns traveled by an oscillating current.

This type can be used as a transmitting antenna for metric or shorter wavelengths, while for longer wavelengths it is preferably used as a receiving antenna.

Tube antenna

Horn antennas

The electromagnetic, decimetric, centimeter and millimeter waves can propagate through the waveguides. kind of tubes, generally rectangular, circular or elliptical section, and conductive walls. If the guide is truncated in a certain section, a part of the energy radiates to the surrounding space and the truncated guide functions as an antenna.

In order to improve the adaptation between the guide and the outer space and prevent an even considerable potion of the energy from reaching the mouth of the guide from being reflected back inwards, the section of the terminal part of the mentioned part is gradually widened guide, thus obtaining the so-called horn or horn.

Slit are called some satellite or satellite dishes

Some satellite or satellite dishes are called slit because they consist of a very large metal plate that has a thin rectangular slit; An electromotive force is applied between the larger sides of the rectangle: the assembly functions as an electric dipole of length equal to that of the grid and arranged perpendicularly to it.

Slit

As with the dipoles, grid arrangements can be made, each fed with the convenient phase, so that special radiation characteristics are obtained.

The slits are specially constituted for decimetric and shorter wavelength radiation. For propagation with waveguide, slits are made on the walls of the guide. The wave or the waves that propagate in said guide feed the slits, each with a phase that also depends on the wavelength.

wave propagation in slit antenna

The radiation pattern of the slot alignment can have a main lobe, the direction of which depends on the frequency of feeding and is a function of the phases of the slits. If the frequency is varied, the direction in which the antenna radiates or the direction in which this antenna receives its maximum power is changed.

Satellite dish

A satellite dish consists of a spring of electromagnetic waves (illuminator) located in the focus of a conductive parabolic surface. By virtue of the properties of the parabola, the totality of the emerging rays of the focus are reflected in the form of a beam parallel to the axis thereof, the normal planes to said axis are equiphasic.

satellite dish

This class of antennas has to act in two different angular directions, due to which they are composed of different types of grouped reflectors. Theoretically, the radiation pattern of a satellite dish should extend only in the direction of the axis of the parabola, (infinite directivity), but this would only occur if the radiant spring was perfectly punctiform and the parabola extended indefinitely.

Under real conditions, both the antenna and the illuminator have finite dimensions, and the radiation pattern will depend on the reflector and the type of illuminator chosen.

Satellite dish

Depending on the frequency of the regime, the reflectors can be made of iron or metallic cloth and even of metallic material. its dimensions depend on the desired directivity, in relation to the frequency of the regime. The illuminator is projected in such a way that the radiated energy is concentrated almost entirely on the reflector.

The use of parabolic antennas is frequent in the field of application of microwaves when good directivity is of interest, as in the case of radar, which we will explain later.

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