How does an antenna works ? In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electrical currents in metal conductors used with a transmitter or receiver.
In transmission, the radio transmitter provides electrical current to the terminals of the antenna and the antenna emits energy from the current as electromagnetic waves (radio waves).
In reception, in order to generate an electrical current at its terminals, an antenna intercepts some of the power of a radio wave, which is applied to a receiver to be amplified. Antennas are components of all radio equipment that are necessary.
An antenna is an array of conductors (elements) that are electrically connected to the receiver or transmitter. Antennas may be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas) or preferably in a particular direction (directional or high-gain or “beam” antennas).
An antenna may include components not connected to the transmitter, parabolic reflectors, horns or parasitic elements used to direct radio waves into a beam or other desired pattern of radiation.
Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field. Radio waves are electromagnetic waves which carry signals through the air (or through space) at the speed of light with almost no transmission loss.
How Antenna Works
In transmission, the information signal will first be modulated with an analog signal having a higher frequency and then amplified to a certain power level. This modulated and amplified signal is what is being fed into the antenna. The antenna is usually made of metal that is a conductor.
When the antenna receives electrical energy, the antenna converts it into electromagnetic waves and releases it into the air. Electromagnetic radiation is a combination of electrical and magnetic fields that oscillate and propagate through space and carry energy from one place to another.
In the receiver, the electromagnetic wave radiation in the air that is received by the antenna will cause the electron movement in the antenna element to produce electrical waves. The electrical signal generated depends on the strength of the radiation received and will be transmitted to the existing system. In general, it will be amplified, filtered and demodulated to obtain information.
Antenna Parameters or Characteristics
Radiation patterns
The radiation pattern of the antenna is a plot of the relative field intensity of the radio waves emitted by the antenna at various angles in the far field. The graph or the polar plots of the horizontal and vertical cross-sections usually reflect this. It is represented.
This model will look like a sphere, an ideal isotropic antenna that irradiated equally in all directions. Many non directional antennas, like monopole and dipole, emit equal power in all horizontal directions, with power flowing at the higher and lower angles, this is called the omnidirectional pattern.
Field Regions
The space surrounding the antenna can be divided into three concentric regions:
- the near-field (also known as the near-field inductive),
- the near-field (Fresnel region) and
- the far-field (Fraunhofer) regions.
These regions are useful for identifying the field structure in each region, although the transitions between them are gradual and there are no precise boundaries.
The far-field region is far enough from the antenna to ignore its size and shape: it can be assumed that the electromagnetic wave is merely a radiating plane wave (electric and magnetic fields are in phase and perpendicular to each other and to the direction of propagation).
Gain
Gain (directive gain) is an antenna characteristic related to the ability of the antenna to direct or receive signals from a certain direction.
Gain is not a quantity that can be measured in general physical units, such as watts, volts or others, but rather a form of comparison. The amount of antenna gain is affected by the number and arrangement of the antenna and the frequency used.
Polarization
Polarization is defined as the orientation of the electrical field. Identifying polarization of the antenna is very useful in telecommunications systems, in particular to achieve maximum efficiency in signal transmission.
The polarization of the antenna refers to the orientation of the electrical field of the radio wave transmitted by the antenna and is determined by the physical structure of the antenna and its orientation.
For example, a vertically-oriented antenna consisting of a linear conductor (such as a dipole or whip antenna) will result in vertical polarization; if the antenna is turned on its side, the polarization of the same antenna will be horizontal.
In the most general case, polarization is elliptical, meaning that over each cycle the electric field vector traces out an ellipse.
Types of antenna
Based on the functionality
Based on its function, the antenna is divided into
- A transmitting antenna
- A receiver antenna and
- A transmitting and receiving antenna.
- On the basis of gain
Based on the amount of gain
The antenna is divided into VHF and UHF antennas that are usually used on TVs.
In most countries, very high-frequency (VHF) television broadcasts from 47 to 68 MHz, called VHF low band or I band in Europe; 174 to 216 MHz, called VHF high band or III band in Europe; and in ultra-high-frequency (UHF) bands from 470 to 698 MHz, called IV and V bands in Europe.
The boundaries of each band vary slightly in different countries.
Based on the polarization process
Based on the polarization of the antenna, it can be divided into two, i.e.
- Dipole Antennas and
- Monopole antennas.
Dipole antennas have vertical linear polarization, while monopole antennas polarize only in one direction
The directional antenna is an antenna with a directional radiation pattern, so that the radio transmission is only in one direction, while the omnidirectional antenna can emit waves in all directions.
A half-wave dipole antenna receiving a radio wave. The antenna consists of two metal rods connected to a receiver R. The electric field (E, green arrows) of the incoming wave pushes the electrons in the rods back and forth, charging the ends alternately positive (+) and negative (−).
Since the length of the antenna is one half the wavelength of the wave, the oscillating field induces standing waves of voltage (V, represented by red band) and current in the rods.
The oscillating currents (black arrows) flow down the transmission line and through the receiver (represented by the resistance R).
On the basis of the shape
Antennas based on their shape include:
Microstripe Antennas
Microstrip or Patch antennas have become the favorites of antenna designers due to their versatility and the advantages of a flat profile, ease of manufacture, compatibility with integrated circuit technology and conformability to a shaped surface.
They can be printed directly on the circuit board. Microstrip antennas are becoming very widespread in the mobile phone market. Patch antennas are low cost, low profile and easy to manufacture.
Parabolic Antennas
A parabola antenna uses a parabolic reflector to direct the radio waves, which means a curved surface with a cross-sectional form of a parabola. The most common form is shaped like a dish and is commonly referred to as a dish antenna or a parabolic dish.
The main advantage of the parabolic antenna is its high directivity. Similarly, a searchlight or flashlight reflector can be used to direct radio waves in a narrow beam, or to receive radio waves in a single direction only.
Parabolic antennas have some of the highest gains, which means they can produce the narrowest beam widths of any type of antenna.
how antenna works
Inverted vee antenna
An inverted vee antenna is like a horizontal dipole but with the two sides bent down to the ground, producing a standard angle between the dipole legs of 120 or 90 degrees.
Usually it is used in areas with limited space because its footprint can be greatly reduced without any noticeable effect on the efficiency of the antenna.
From the foot, the English letter “V” appears to have turned upside-down. Antennas used by amateur radio stations and on board sailing ships that need better HF output than a short whip antenna.
Horn Antennas
How Does a Helix Antenna works
An antenna consisting of one or more conducting wires wound in the shape of a helix is a helical antenna. A helical antenna made of a single helical wire is called monofilar, the most common form, whereas antennas with two or four wires are called bifilar or quadrifilar in a helix, respectively.
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