Why antenna is used

It may be considered as the capability of an antenna to direct radiated power in a given direction. It can also be noted as the ratio of the radiation intensity in a given direction to the average radiation intensity. Bandwidth is one of the desired parameters to choose an antenna.

It can be defined as the range of frequencies over which an antenna can properly radiate energy and receives energy. Polarization: An electromagnetic wave launched from an antenna may be polarized vertically and horizontally.

If the wave gets polarized in the vertical direction, then the E vector is vertical and it requires a vertical antenna. If vector E is in a horizontal way, it needs a horizontal antenna to launch it. Sometimes, circular polarization is used, it is a combination of both horizontal and vertical ways.

Effective Length: The effective length is the parameter of antennas that characterizes the efficiency of the antennas in transmitting and receiving electromagnetic waves. Effective length can be defined for both transmitting and receiving antennas. The effective length of the transmitter can be defined as the length of the free space in a conductor, and current distribution across its length generates the same field intensity in any direction of radiation.

Polar Diagram: The most significant property of an antenna is its radiation pattern or polar diagram. In the case of a transmitting antenna, this is a plot that discusses about the strength of the power field radiated by the antenna in various angular directions as shown in the plot below.

A plot can also be obtained for both vertical and horizontal planes — and, it is also named as vertical and horizontal patterns, respectively.

Till now we have covered the properties of antennas, and now we will discuss different types of antennas that are used for different applications. A log-periodic antenna is also named a log-periodic array. It is a multi-element, directional narrow beam antenna that works on a wide range of frequencies. This antenna is made of a series of dipoles placed along the antenna axis at different space intervals of time followed by a logarithmic function of frequency.

A log-periodic antenna is used in a wide range of applications where variable bandwidth is required along with antenna gain and directivity. A bow-tie antenna is also known as a Biconical antenna or Butterfly antenna. Biconical antenna is an omnidirectional wide-band antenna. According to the size of this antenna, it has low- frequency response and acts as a high-pass filter. As the frequency goes to higher limits, away from the design frequency, the radiation pattern of the antenna gets distorted and spreads.

Most of the bow-tie antennas are derivatives of biconical antennas. The discone is a type of half-biconical antenna. The bow-tie antenna is a planar, and therefore, a directional antenna. The most common type of antenna used in wireless communication technology is a log-periodic dipole array that fundamentally comprises a number of dipole elements. These dipole-array antennas reduce in size from the back end to the front end.

The leading beam of this RF antenna comes from the smaller front end. The element at the back end of the array is large in size with the half-wavelength operating in a low-frequency range. The spacing of the element gets reduced towards the front end of the array wherein the smallest arrays are placed. During this operation, as the frequency varies, a smooth transition takes place along the array of the elements, which leads to forming an active region.

Wire antennas are also known as linear or curved antennas. These antennas are very simple, cheap, and are used in a wide range of applications. These antennas are further subdivided into four as explained below. A dipole antenna is one of the most straightforward antenna alignments. This dipole antenna consists of two thin metal rods with a sinusoidal voltage difference between them.

The length of the rods is chosen in such a way that they have a quarter length of the wavelength at operational frequencies. These antennas are used in designing their own antennas or other antennas. They are very simple to construct and use. The dipole antenna consists of two metallic rods through which current and frequency flow.

This current and voltage flow makes an electromagnetic wave and the radio signals get radiated. The antenna consists of a radiating element that splits the rods and makes current flow through the center by using a feeder at the transmitter out that takes from the receiver.

This electrical signal is then provided to the transmission line. Thus we can say that it serves the role of a transitional element between free space and transmission line guiding device.

In simple words, antennas are transducers that change RF electrical signal into an electromagnetic wave of similar frequency. The figure below illustrates the transmission and reception of radio waves in free space:. The electromagnetic wave emitted from antennas propagate in free space with speed of light i. We have already discussed that antennas are considered to be the basic building block of a wireless communication system.

As signal in free space propagates in the form of an electromagnetic wave then it requires some transmitting as well as receiving ends.

So, an antenna allows the propagation of electromagnetic waves from one end to another, in the form of EMW without the need for a wiring system. It acts as a transducer that converts RF signal into EM wave at the transmitter and EM wave back to an electrical signal at the receiver. Antennas do so by producing electric and magnetic field from the applied signal and combinedly the two fields form an electromagnetic wave.

As the two fields show perpendicularity with respect to each other. In our day to day life, we regularly come across the use of wireless communication. As it includes signals arriving at the television for watching numerous programs to communicating with any person on a mobile network, everything is associated with wireless communication.

There are several reasons as to why we need or why we use antennas, but an important reason as to why we use antennas is that they provide a simple way to transfer signals or data where other methods are impossible. For example, take the case of an aeroplane. The pilot needs to frequently communicate with the ATC personnel. If would not make any sense if we tie up a cable of dynamically variable length to the tail of the plane and connect it to the ATC.

Wireless communication is the only feasible option and Antennas are the gateway for that. There are many situations or applications where cables are preferred over wireless communication with antennas like high speed ethernet or the connection between gaming console and the T. Now that we have seen a little bit about antennas in general and why do we use antennas, let us proceed further and take a look as different types antennas.

There are several types of antennas and each literature work has its own classification of antennas. Let us now briefly see about few of these different types of antennas. One of the most commonly used antennas are wire antennas. They can be found in vehicles automobiles , ships, aircrafts, buildings etc. Wire Antennas come in different shapes and sizes like straight wire Dipole , Loop and Helix.

Perhaps the simplest of all antennas is the Short Dipole Antenna. It is a special case of the Dipole antenna. In its simplest form, it is basically an open circuit wire with the signal being fed at the centre. For a typical Short Dipole Antenna, the length of the wire les less than the tenth of the wavelength of the frequency of operation. A Dipole Antenna is made up two conductors in the same axis and the length of the wire need to be small compared to the wavelength.

A Loop antenna is formed by a single or multiple turn of wire forming a loop. The radiation produced by loop antenna is comparable to a short dipole antenna.

A special case of Dipole antenna is the monopole antenna i. A class of directional antennas, Aperture Antennas have an opening in the surface. Usually, aperture antenna consists of Dipole or Loop Antenna in a guiding structure with an opening to emit radio waves.

The designing of this is done in such a way that its radiated power is maximum in the required direction, then the other, which introduces the concept of directivity.

The antenna gain is mathematically expressed as. The efficiency takes into account the loss due to any faults like the manufacturing faults, resistance, VSWR, etc. Bandwidth: The bandwidth of the device is a range of frequencies on which it can operate correctly.

It is the range in Hz for which the SWR is less than 2. Polarization: The polarization of the antenna refers to the polarization of the fields that are transmitted by the device. The waves that are launched by the device are polarized differently. Some of this is horizontal, so the EM vector is also horizontal, and the horizontal devices are required to receive them. The same is the case with vertical polarization. Sometimes the circular polarization can be done, which the mixture of vertical waves and the horizontal waves.

Effective length: This length is measured for both receiver and transmitter. By this factor, the efficiency of this is measured. The free space length in any conductor is referred to as the effective length. The radiation pattern of the device is referred to as the polar diagram, and it is the most important property of the antenna. This plot describes the power field strength in the different angles on the vertical and horizontal planes. It is responsible for the transmission and collection of electromagnetic radiation.