An antenna is a device that serves as an interface between an electrical circuit and space, designed to transmit and receive electromagnetic waves in a certain frequency range in accordance with its own size and shape. It is made of metal, mainly copper or aluminum, transmitting antennas can convert electric current into electromagnetic radiation and vice versa. Each wireless device contains at least one antenna.
Wireless network radio waves
When the need for wireless communication arises, an antenna is needed. It has the ability to send or receive electromagnetic waves to communicate where a wired system cannot be installed.
The antenna is the key element of this wireless technology. Radio waves are easily created and widely used for both indoor and outdoor communications due to their ability to pass through buildings and travel long distances.
Key features of transmitting antennas:
- Because radio transmission is omnidirectional, the need for physical matchingtransmitter and receiver is required.
- The frequency of radio waves determines many transmission characteristics.
- At low frequencies, waves can easily pass through obstacles. However, their power drops with the inverse square of distance.
- Higher frequency waves are more likely to be absorbed and are reflected on obstacles. Due to the long transmission range of radio waves, interference between transmissions is a problem.
- On the VLF, LF and MF bands, wave propagation, also called ground waves, follows the curvature of the Earth.
- The maximum transmission ranges of these waves are on the order of several hundred kilometers.
- Transmitting antennas are used for low bandwidth transmissions such as AM broadcasts.
- HF and VHF band transmissions are absorbed by the atmosphere near the Earth's surface. However, part of the radiation, called skywave, propagates outward and upward towards the ionosphere in the upper atmosphere. The ionosphere contains ionized particles formed by the Sun's radiation. These ionized particles reflect sky waves back to Earth.
Wave propagation
- Line of sight propagation. Among all distribution methods, this is the most common. The wave travels the minimum distance that can be seen with the naked eye. Next, you need to use the transmitter of the amplifier to increase the signal and transmit it again. Such propagation will not be smooth if there is any obstacle in its transmission path. This transmission is used for infrared or microwave transmissions.
- Ground wave propagation from a transmitting antenna. The propagation of the wave to the ground occurs along the contour of the Earth. Such a wave is called a direct wave. The wave sometimes bends due to the Earth's magnetic field and hits the receiver. Such a wave can be called a reflected wave.
- A wave propagating through the earth's atmosphere is known as the earth wave. The direct wave and the reflected wave together give a signal at the receiving station. When the wave reaches the receiver, the delay stops. In addition, the signal is filtered to avoid distortion and amplification for clear output. Waves are transmitted from one place and where they are received by many transceiver antennas.
Antenna measurement coordinate system
When looking at flat models, the user will be confronted with indicators of the azimuth of the plane and the height of the plane of the pattern. The term azimuth usually occurs in relation to "horizon" or "horizontal", while the term " altitude" usually refers to "vertical". In the figure, the xy plane is the azimuth plane.
The azimuth plane pattern is measured when the measurement is made by moving the entire xy plane around the transceiver antenna under test. An elevation plane is a plane orthogonal to the xy plane, such as the yz plane. The elevation plan travels the entire yz plane around the antenna under test.
Samples (azimuths and elevations) are often displayed as plots in polarcoordinates. This gives the user the ability to easily visualize how the antenna radiates in all directions, as if it were already "pointed" or mounted. It is sometimes useful to draw radiation patterns in Cartesian coordinates, especially when there are multiple sidelobes in patterns and where sidelobe levels are important.
Basic communication characteristics
Antennas are essential components of any electrical circuit as they provide the interconnection between a transmitter and free space or between free space and a receiver. Before talking about the types of antennas, you need to know their properties.
Antenna Array - The systematic deployment of antennas that work together. The individual antennas in an array are usually of the same type and located in close proximity, at a fixed distance from each other. The array allows you to increase the directivity, control of the main beams of radiation and side beams.
All antennas are passive gain. Passive gain is measured in dBi, which is related to a theoretical isotropic antenna. It is believed that it transmits energy equally in all directions, but does not exist in nature. The gain of an ideal half-wave dipole antenna is 2.15 dBi.
EIRP, or the Equivalent Isotropic Radiated Power of a transmitting antenna, is a measure of the maximum power that a theoretical isotropic antenna would radiate in the directionmaximum gain. EIRP takes into account the losses from power lines and connectors and includes the actual gain. EIRP allows real power and field strengths to be calculated if the actual gain and output power of the transmitter are known.
Antenna gain in directions
It is defined as the ratio of the power gain in a given direction to the power gain of the reference antenna in the same direction. It is standard practice to use an isotropic radiator as the reference antenna. In this case, an isotropic emitter will be lossless, radiate its energy equally in all directions. This means that the gain of an isotropic radiator is G=1 (or 0 dB). It is common to use the dBi (decibels relative to an isotropic radiator) unit for gain relative to an isotropic radiator.
The gain, expressed in dBi, is calculated using the following formula: GdBi=10Log (GNumeric / GISotropic)=10Log (GNumeric).
Sometimes a theoretical dipole is used as a reference, so the unit dBd (decibels relative to dipole) will be used to describe the gain relative to the dipole. This block is typically used when it comes to amplifying higher gain omnidirectional antennas. In this case, their gain is higher by 2.2 dBi. So if the antenna has a gain of 3 dBu, the total gain will be 5.2 dBi.
3 dB beamwidth
This beamwidth (or half-power beamwidth) of the antenna is usually specified for each of the principal planes. The 3 dB beamwidth in each plane is defined as the angle between main lobe points that are reduced from maximum gain by 3 dB. Beamwidth 3 dB - the angle between the two blue lines in the polar area. In this example, the 3 dB beamwidth in this plane is about 37 degrees. Wide beamwidth antennas typically have low gain, while narrow beamwidth antennas have higher gain.
Thus, an antenna that directs most of its energy into a narrow beam, in at least one plane, will have a higher gain. The front-to-back ratio (F/B) is used as a measure of merit that attempts to describe the level of radiation from the back of a directional antenna. Basically, the front-to-back ratio is the ratio of the peak gain in the forward direction to the gain 180 degrees behind the peak. Of course, on a DB scale, the front-to-back ratio is simply the difference between the forward peak gain and the gain 180 degrees behind the peak.
Antenna classification
There are many types of antennas for various applications such as communications, radar, measurement, electromagnetic pulse simulation (EMP), electromagnetic compatibility (EMC), etc. Some of them are designed to operate in narrow frequency bands, while othersdesigned to emit/receive transient pulses. Transmitting Antenna Specifications:
- Physical structure of the antenna.
- Frequency bands.
- App Mode.
The following are the types of antennas according to the physical structure:
- wire;
- aperture;
- reflective;
- antenna lens;
- microstrip antennas;
- massive antennas.
The following are the types of transmitting antennas depending on the frequency of operation:
- Very Low Frequency (VLF).
- Low frequency (LF).
- Mid frequency (MF).
- High frequency (HF).
- Very High Frequency (VHF).
- Ultra High Frequency (UHF).
- Super High Frequency (SHF).
- Microwave wave.
- Radio wave.
The following are transmitting and receiving antennas according to application modes:
- Point-to-point connection.
- Broadcast applications.
- Radar communications.
- Satellite communications.
Design features
Transmitting antennas create radio frequency radiation that propagates through space. Receiving antennas perform the reverse process: they receive radio frequency radiation and convert it into the desired signals, such as sound, image in television transmitting antennas and a mobile phone.
The simplest type of antenna consists of two metal rods and is known as a dipole. One of the most common types isa monopole antenna consisting of a rod placed vertically to a large metal board that serves as a ground plane. Mounting on vehicles is usually a monopole and the metal roof of the vehicle serves as a ground. The design of the transmitting antenna, its shape and size determine the operating frequency and other radiation characteristics.
One of the important attributes of an antenna is its directivity. In communication between two fixed targets, as in communication between two fixed transmission stations, or in radar applications, an antenna is required to directly transmit the transmission energy to the receiver. Conversely, when the transmitter or receiver is not stationary, as in cellular communications, a non-directional system is required. In such cases, an omnidirectional antenna is required that receives all frequencies uniformly in all directions of the horizontal plane, and in the vertical plane the radiation is uneven and very small, like a HF transmitting antenna.
Transmitting and receiving sources
The transmitter is the main source of RF radiation. This type consists of a conductor whose intensity fluctuates over time and converts it into radio frequency radiation that propagates through space. Receiving antenna - a device for receiving radio frequencies (RF). It performs the reverse transmission performed by the transmitter, receives RF radiation, converts it into electrical currents in the antenna circuit.
Television and radio broadcasting stations use transmitting antennas to transmit certain types of signals that travel through the air. These signals are detected by receiving antennas, which convert them into signals and are received by an appropriate device such as TV, radio, mobile phone.
Radio and television receiving antennas are designed to receive radio frequency radiation only and do not produce radio frequency radiation. Cellular communication devices, such as base stations, repeaters, and mobile phones, have designated transmitting and receiving antennas that emit radio frequency energy and serve cellular networks in accordance with telecommunication network technologies.
Difference between analog and digital antenna:
- The analog antenna has a variable gain and operates in the 50 km range for DVB-T. The farther the user is from the signal source, the worse the signal.
- To receive digital TV - the user receives either a good image or an image at all. If it is far from the signal source, it does not receive any image.
- The transmitting digital antenna has built-in filters to reduce noise and improve picture quality.
- The analog signal is sent directly to the TV, while the digital signal needs to be decoded first. It allows you to correct errors as well as data like signal compression for more features like Extra Channels, EPG, Pay TV,interactive games, etc.
Dipole transmitters
Dipole antennas are the most common omnidirectional type and spread radio frequency (RF) energy 360 degrees horizontally. These devices are designed to be resonant at half or a quarter wavelength of the applied frequency. It can be as simple as two lengths of wire, or it can be encapsulated.
Dipole is used in many corporate networks, small offices and home use (SOHO). It has a typical impedance to match it with the transmitter for maximum power transfer. If the antenna and transmitter do not match, reflections will occur on the transmission line, which will degrade the signal or even damage the transmitter.
Directed focus
Directional antennas focus the radiated power into narrow beams, providing a significant gain in this process. Its properties are also mutual. The characteristics of a transmitting antenna, such as impedance and gain, also apply to a receiving antenna. This is why the same antenna can be used to both send and receive a signal. The gain of a highly directional parabolic antenna serves to amplify a weak signal. This is one of the reasons why they are often used for long distance communications.
A commonly used directional antenna is a Yagi-Uda array called Yagi. It was invented by Shintaro Uda and his colleague Hidetsugu Yagi in 1926. The yagi antenna uses several elements toforming a directed array. One controlled element, usually a dipole, propagates the RF energy, the elements immediately before and behind the driven element re-radiate the RF energy in and out of phase, amplifying and slowing down the signal respectively.
These elements are called parasitic elements. The element behind the slave is called the reflector and the elements in front of the slave are called directors. Yagi antennas have beamwidths ranging from 30 to 80 degrees and can provide more than 10 dBi of passive gain.
The parabolic antenna is the most familiar type of directional antenna. A parabola is a symmetrical curve, and a parabolic reflector is a surface that describes a curve during a 360-degree rotation - a dish. Parabolic antennas are used for long-distance links between buildings or large geographic areas.
Semi-directional sectional radiators
The patch antenna is a semi-directional radiator using a flat metal strip mounted above the ground. Radiation from the rear of the antenna is effectively clipped by the ground plane, increasing forward directivity. This type of antenna is also known as a microstrip antenna. It is usually rectangular and encased in a plastic case. This type of antenna can be manufactured by standard PCB methods.
The patch antenna can have a beam width from 30 to 180 degrees andtypical gain is 9 dB. Sectional antennas are another type of semi-directional antenna. Sector antennas provide a sector radiation pattern and are usually installed in an array. The beamwidth for a sector antenna can range from 60 to 180 degrees, with 120 degrees being typical. In a partitioned array, the antennas are mounted close to each other, providing full 360-degree coverage.
Making the Yagi-Uda antenna
During the last decades, the Yagi-Uda antenna has been visible in almost every home.
It can be seen that there are many directors to increase the directivity of the antenna. The feeder is a folded dipole. A reflector is a long element that sits at the end of a structure. The following specifications must be applied to this antenna.
| Element | Specification |
| Controlled element length | 0.458λ to 0.5λ |
| Reflector length | 0, 55λ - 0.58λ |
| Director duration 1 | 0.45λ |
| Director length 2 | 0.40λ |
| Director duration 3 | 0.35λ |
| Interval between directors | 0.2λ |
| Reflector for distance between dipoles | 0.35λ |
| Distance between dipoles and director | 0.125λ |
Below are the benefits of Yagi-Uda antennas:
- High gain.
- High focus.
- Easy handling and maintenance.
- Less energy is wasted.
- Wider frequency coverage.
The following are the disadvantages of Yagi-Uda antennas:
- Prone to noise.
- Prone to atmospheric effects.
If the above specifications are followed, the Yagi-Uda antenna can be designed. The directional pattern of the antenna is very efficient, as shown in the figure. The small lobes are suppressed and the directivity of the main beat is increased by adding directors to the antenna.
