The antenna is an essential part of a radiocommunication system, coupling the energy of the output of a transmitter to the free space or of the free space towards a receiver, which is why it is known as a reciprocal device since it maintains its characteristics both in transmission as in reception. It can be understood as a device that transforms electrical signals (voltage and current of a transmission line) into electromagnetic waves (electric and magnetic fields), or vice versa
Round or square, small, long, or gigantic. In a few radio equipment, there is as much variety as in the antennas. Infinity of models for an immensity of uses.
9 Different Types of Antennas:
1. SIMPLE DIPOLE ANTENNA
In general, we call the main element of the antenna dipole, which radiates the waves. This type of antenna is the simplest that exists and the easiest to manufacture.
It is a cable or conductor element split in half to which the coaxial cable that arrives from the transmitter is connected. In question 6 we talked about the wavelength and said that this magnitude is fundamental in the construction of the antennas. Here is the reason. The dipole or conductor cable has to measure half the wavelength of the frequency at which we want to transmit.
The wavelength is obtained by dividing the speed of light by the frequency. Since this dipole is half the wavelength, we can leave the formula in this way to calculate a 20 Mhz dipole antenna:
Dipole length = 142.5 / F (in Megahertz)
L = 142.5 / 20 Mhz = 7.125 meters
The 7 meters is the total length of the dipole. Now, we will have to divide it in half and connect each part to one of the two ends of the coaxial cable that arrives from the transmitter, the negative and the positive.
This type of single dipole antennas can be used for HF transmissions that are long-distance communications. Simple dipole antennas are also used for FM stations. In this case, is much higher frequencies, much smaller dipoles are used. Instead of half-wave, they are a quarter. The dipoles of an FM, depending on their frequency, have an approximate size of one meter.
The dipole antennas for FM or communications with Walkie-Talkie can be purchased adjusted to a certain frequency or multiband that serves all bands. There are also tunable ones, where the dipoles come with a screw system that allows you to adjust them to the frequency of our equipment.
2. YAGI TYPE ANTENNAS
They are used in FM as receiving antennas or for radio links, although most of the Yagis that we see on the rooftops are antennas to receive TV channels.
The particularity of this type of antennas is that they have several elements. This brings two advantages: they are very directive, since the additional elements, called precisely directors, have the mission of directing the signal to a single place; The other advantage is its gain that increases with the managing elements.
In Yagi antennas, the greater the number of elements, the greater directivity and the greater the gain. But the construction of these antennas with respect to the size and separation distance of each element is not random, as you can see in the image.
These are made up of an array of independent antenna elements, where only one of them transmits radio waves. The number of elements (specifically, the number of director elements) determines the gain and directivity. Yagi antennas are not as directional as satellite dishes, but they are more directive than panel antennas.
3. VERTICAL ANTENNA
They are the antennas used to transmit in AM. The tower is separated from the concrete base by an insulator, usually ceramic, which completely isolates the tower from the ground.
Before the cable reaches the tower it has to go through the tuning box. This box contains a series of coils for adjustment or impedance matching.
There are different types of vertical antennas, from the most basic where the cable that arrives from the coupling box is connected to the tower and with it forms the radiator assembly, to models such as the folded monopole. In this case, 6 tensioned cables rise parallel to the tower forming the antenna.
Therefore, for simple vertical antennas, height is not random. The tower, in this case, receives the cable, and together they form the transmission system. Therefore, we will calculate its height based on the wavelength and frequency, in the same way as in the simple dipole.
For example, a 560 Khz station will have an antenna of more than 250 meters. While at the other end of the dial, an antenna at 1330 Khz will have an approximate height of 100 meters, unless we use models such as the folded monopole, where the height that counts is that of the 6 cables, not so much that of the tower.
But the AM antenna is not just the erect conductor that is seen 100 meters above the ground. Underground the secret of these transmissions is hidden. For electricity to flow there must be two poles. Therefore, every antenna has a positive and a negative plane. The negative is usually the same land. Many times, this earth is not conducive enough for the radio signal to come out with good quality. Therefore, we manufacture a “ground plane” by burying bare copper wires connected to the negative or ground of the tuning box under it, about 25 cm. These cables are known as radials.
These types of antennas are omnidirectional, therefore they have no gain. The power with which we transmit is the nominal power of the transmitter.
“Invisible” antennas
In the past, cell phones brought an antenna that we had to stretch to listen better. Now, almost no cell phone or wireless phone has external antennas, but they all carry their own inside. The advantage is that, since cell phones work at very high frequencies, the wavelength is very small. This allows the antennas to be too and the same phone to act as if it were one.
When we buy an antenna or ask a technician to manufacture it, we will look closely at all the details. The welds in the connections, the robustness of the material used for its construction, if it is protected against rust and corrosion … They seem insignificant things, but they are not in an antenna. Remember that these teams spend all the time outdoors suffering the inclemency of rain and wind. Buy robust antennas, with anticorrosive protection, good tower fixing hardware and perfect element connections.
4. The monopole antenna (single pole)
Also known as Marconi antenna, it is the simplest that can be found and used in virtually all radio and telecommunications services especially at low frequencies, it is mounted in a vertical direction similar to a rod, landed through the coupling network of the antenna.
Its operation is based on the virtual reflection generated by the ground in the opposite direction towards the direction of the antenna, using the theory known as “method of images”, that energy is reflected a greater or lesser extent depending on the physical characteristics of the Earth, especially conductivity, for this reason, clay-rich soils are used that are good conductors to reduce losses. If the ground is poorly conductive (sandy or rocky), it is necessary to improve its conductivity characteristics for which a ground plane system can be used, made with copper wires located radially below the antenna and in cases in which monopolies on vehicles need to be installed, a wire mesh is used.
The monopole antenna presents an omnidirectional radiation pattern diagram (in all directions} in the plane perpendicular to the antenna, which is generally horizontal. In the vertical sense, the gain and directivity depend on the length of the antenna, it should always be perpendicular to the ground, as the tilt angle makes the effective length is reduced and thus the antenna gain, the decrease to reflect the same.
Although the monopole can be used in virtually all technologies or in all radio services, they are the only ones that in practice are used exclusively in AM transmitters, due to their size. If observed, the AM transmitters are generally towers of great length, several hundred meters in some cases, reaching at some times to be installed as a tower
They can also be used in other types of services such as low power FM radio systems, mobile radio systems, low coverage television systems, cellular telephony in rural areas, and Wi-Fi systems. This same concept is also implemented in the bose wave music system antenna and in a digital antenna for rural areas.
5. Dipole antenna
The dipole is usually found in practically all the services that currently exist, mainly in antenna arrangements for FM radio transmitters and also in TV transmitters and mobile radio services for dispatch services, security such as police and emergencies, firefighters and ambulances. These improve FM radio reception to get better signals.
It is an antenna with two poles facing opposite directions because each pole behaves as if it were a section of the ¼ wave transmission line, so the most common length is ½ wave, as the name implies, This type of antenna is built and used for a single frequency presenting a good compromise between directivity and size. This antenna can be placed horizontally or vertically with respect to the earth’s surface depending on the requirements of the services, its radiation pattern is omnidirectional in the H plane, used for applications such as mobile communications.
6. Panel antenna
They consist of an array of dipoles in phase to obtain a radiation pattern determined by an omnidirectional covering, connected horizontally or vertically to a rectangular flattened structure, located 1’¼ of the surface that serves as a reflector and within a fiberglass panel. glass or some material transparent to electromagnetic waves.
They began to be used in cellular mobile systems, in the 800 MHz band initially, and in recent years due to the great expansion of cell phones, they are used in all bands and in different applications since they allow the antenna to be concealed quite well Regarding your surroundings.
Recently they are being used in lower frequency bands, such as the VHF band and in some of the lower parts of UHF, for conventional mobile radio services and in radiant digital TV systems.
Satellite dishes: The third type of antenna, which can be classified apart from vertical and horizontal ones, are satellite dishes. Parabolic antennas are antennas that have a parabola shape (circular curve) and are used in situations where a very high signal directionality is required.
The satellite dishes consist of two parts: a curved plate, which acts as a reflector to direct the signal, and a transmitter that is usually located at a distance above the plate. The sender sends the signal to the dish, where it is reflected and is directed towards its destination.
In general, satellite dishes are manufactured for bands 70cm down, where high power equipment is quite expensive and it is more feasible to use high gain with low power than the reverse situation. In addition, for a satellite dish to be effective, the size of the reflector used must be very similar to or greater than the wavelength used, which makes the satellite dishes too large to be used in bands of greater length.
Satellite dishes are widely used in satellite communications and high-frequency links for telecommunications. They receive little use by radio amateurs, due to their high cost and functional requirements in terms of rotors, control mechanisms, etc.
7. Quad or Cubical Antenna:
The quadratubic antenna (cubical antenna) is an antenna derived from the loop antenna. In general, it consists of an irradiating loop, with reflecting loops behind and directing loops in front. It is, in a way, a yagi antenna made from loops.
An advantage of the quadratubic one is that it occupies less space than a yagi antenna, and is generally manufactured with a single irradiating element and reflector element. Its gain is similar to that of a yagi, and it can be manufactured in multiband type without significantly affecting its dimensions.
Additionally, the quadratubic antenna has the advantage of absorbing less noise than other antennas, due precisely to the closed-circuit that forms its irradiating / receiving element.
8. The half wave dipole:
The simplest antenna to manufacture, and the most popular among beginner radio amateurs, turns out to be the half-wave dipole.
The half-wave dipole is an antenna formed by two quarter-wavelength arms (giving the total half-wavelength), which can be placed horizontally or tilted down (these positions give the names “dipole of clothesline »and« inverted V »respectively).
The arms are isolated from each other by some non-conductive material. If the antenna is manufactured using an aluminum pipe, this material is usually PVC or wood pipe, while ceramic or plastic insulators are widely used in antennas made of conductive wire.
The total length that a half-wave dipole must have is calculated using the following formula:
Where l is in meters and f in MHz. If we want the length of each arm, we must divide the previous result by 2.
The above formula turns out to be precisely the basic wavelength formula, modified by a factor of 0.475. This factor of 0.475 is composed of two numbers:
The explanation of the number 2 is simply that the dipole measures half a wavelength long. The length equation gives us the full wavelength, and we must divide it by two to get the half wave.
0.95 is a factor that is introduced to correct an electrical effect that occurs in the dipole, known as the tip effect. The tip effect is an effect that makes the wire length for the radio signal than it really is, usually at a value that is around 5%. 0.95 precisely seeks to subtract that 5% excess from the calculated length and give the correct resonant length.
It may or may not be necessary to include the factor 0.95 when making a dipole antenna, depending on the conditions and location given to the antenna. The best thing is, when calculating the length of the arms, cut them to an uncorrected length, and then trim them if necessary to achieve the desired resonance. It is preferable to make an “electrically correct” antenna and then find that it is too short, and with no way of lengthening it to achieve adjustment.
The dipole, as a horizontal antenna, should be located at half a wavelength above the ground, or optimally at a full wavelength. Normally its impedance is close enough to 50 ohms to avoid having to use impedance coupling systems.
Flat Panel
Antennas: The flat panel antennas as their name says are a square or rectangular-shaped panel. and are configured in a patch type format. Flat Panel type antennas are very directional since most of their radiated power is only one direction in either the horizontal or vertical plane. In the elevation pattern (Fig. 4) and in the azimuth pattern (Fig. 5) you can see the directivity of the Flat Panel antenna. Flat Panel antennas can be manufactured in different gain values according to their construction. This can provide excellent directivity and considerable gain.
9. Satellite dishes:
The third type of antenna, which can be classified apart from vertical and horizontal ones, are satellite dishes. Parabolic antennas are antennas that have a parabola shape (circular curve) and are used in situations where a very high signal directionality is required.
Satellite dish size should be good in order to achieve very high gain and directionality. These antennas use a reflector plate in the shape of a parabola to focus the radio waves received by the antenna to a focal point.
The parabola also works to capture the energy radiated by the antenna and focus it on a narrow beam when transmitting. As can be seen in Figure 5, the satellite dish is very directional. By concentrating all the power that reaches the antenna and focusing it in only one direction, this type of antennas is capable of providing very high gain and are the best antenna for a heavily wooded area. But for that, make sure your Satellite Dish Installation is perfect.
Parabolic Lift Pattern
In general, satellite dishes are manufactured for bands 70cm down, where high power equipment is quite expensive and it is more feasible to use high gain with low power than the reverse situation. In addition, for a satellite dish to be effective, the size of the reflector used must be very similar to or greater than the wavelength used, which makes the satellite dishes too large to be used in bands of greater length.
Satellite dishes are widely used in satellite communications and high frequency links for telecommunications. They receive little use by radio amateurs, due to their high cost and functional requirements in terms of rotors, control mechanisms, etc.
Multi-Element Dipole Antennas:
Multi-element dipole antennas have some of the general characteristics of the simple dipole. They have an elevation and azimuth pattern similar to that of the simple dipole antenna. The clearest difference between the two is the directionality of the antenna in the elevation plane, and the increase in gain due to the use of multiple elements.
With the use of multiple elements in the construction of the antenna, it can be configured for different gains, which allows designs with similar physical characteristics.
As can be seen in the elevation pattern of fig. 2, multiple dipole antennas are very directional in the vertical plane. Because the dipole antenna radiates equally well in all directions of the horizontal plane, it is capable of operating equally well in a horizontal configuration.
Slot Antenna: Slot
antennas have radiation characteristics very similar to those of dipoles, such as elevation and azimuth patterns, but their construction consists only of a narrow groove in a plane.
As well as the microstrip antennas mentioned below, the slot antennas provide little gain and do not have high addressability, as evidenced by their radiation patterns and their similarity to that of the dipoles. Its most attractive feature is the ease of construction and integration into existing designs, as well as its low cost. These factors compensate for their poor performance.
Microstrip Antennas:
These antennas can be made to emulate any of the different types of antennas mentioned above. Microstrip antennas offer several details that should be considered. Because they are manufactured with printed circuit tracks, they can be very small and light.
This has the cost of not being able to handle a lot of power as is the case with other antennas, they are also made for very specific frequency ranges. In many cases, this limitation of operating frequency can be beneficial for radio performance. Due to their characteristics, microstrip antennas are not very suitable for broadband communication equipment.
Characteristics of the Antennas
An antenna is a device made to transmit (radiate) and receive radio waves (electromagnetic). There are several important characteristics of an antenna that should be considered when choosing a specific one for your application:
- Radiation pattern
- Gain
- Directivity
- Polarization
Radiation Patterns:
The radiation pattern of an antenna can be represented as a three-dimensional graph of the radiated energy seen from outside it. Radiation patterns are usually represented in two ways, the elevation pattern and the azimuth pattern. The elevation pattern is a graph of the energy radiated by the profile view antenna.
The azimuth pattern is a graph of radiated energy seen directly from above. By combining both graphs you have a three-dimensional representation of how the energy is really radiated from the antenna. Also readout Characteristics of Parabolic Dish.
Radiation patterns
a) Elevation pattern of a generic dipole b) Azimuth pattern of a generic dipole c) 3D radiation pattern
Gain:
The gain of an antenna is the relationship between the power that enters an antenna and the power that comes out of it. This gain is commonly referred to in dBi’s, and refers to the comparison of how much energy comes out of the antenna in question, compared to what would come out of an isotropic antenna. The anisotropic antenna is one that has a perfect spherical radiation pattern and a linear unit gain.
Directivity:
The directivity of the antenna is a measure of the concentration of the radiated power in a particular direction. It can also be understood as the ability of the antenna to direct the radiated energy in a specific direction. It is usually a ratio of radiation intensity in a particular direction compared to the isotropic average intensity.
Polarization:
It is the orientation of the electromagnetic waves when leaving the antenna. There are two basic types of polarization that apply to the antennas, such as Linear (includes vertical, horizontal, and oblique) and circular (which includes right circular, left circular, right elliptical, and left elliptical). Do not forget that taking into account the polarity of the antenna is very important if you want to get the most out of it. The transmitting antenna must have the same polarity of the receiving antenna for maximum performance.
Conclusion:
From this basic introduction to the antennas, we can obtain a simple understanding of the types of antennas and their applications. For example, dipole antennas even when they do not provide much gain offer the best flexibility in terms of antenna orientation. Flat-panel antennas offer greater addressability and are a good option for fixed installations. The parabolic antenna with its high gain and great addressability is very good for providing point-to-point links over long distances, with permanently installed antennas. Finally, the slot and microstrip antennas are correct for moderate performance applications that need to integrate the antenna into the radio and OEM applications. Additionally, it is possible to use different types of antenna in the same system. For example, A flat panel antenna can be mounted on a wall near an access point. When a piece of equipment with a dipole antenna near the access point, the system could update statistics immediately on the equipment.
To assist in choosing the correct antenna for your application, Table 1 is provided as a means of comparison between the different types:
| Radiation pattern | Gain | Directivity | Polarization | |
| Dipole | Large | Low | Low | Linear |
| Multi-Element Dipole | Large | Low / Medium | Low | Linear |
| Flat Panel | Large | Half | High average | Linear / Circular |
| Parabolic Dish | Large | high | high | Linear / Circular |
| Yagi | Endfire | High average | High average | Linear |
| Groove | Large | Low / Medium | Low / Medium | Linear |
| MicroStrip | Enfire | Half | Half | Linear |