Basics of Antenna and its Characteristics

Communication:

• It is the process where information is shared from one place or person to another with the help of a medium.
• When we normally talk we communicate with the help of sound waves passing through the air.

Long-distance Communication:

• In long-distance communication, the most common means of communication is mobile or wireless communication.
• The information here is transferred through electromagnetic waves.

ANTENNA:

• It is a device that converts electrical signals into EM waves and transmits them.
• ANTENNA helps to transmit information at a long distance wirelessly through EM waves.

Working of Antenna

• The information here is converted into electrical signals.
• These electrical signals can be transmitted wirelessly when a transmitter converts the signals into electromagnetic signals.
• The power applied to the antenna is in the form of radio frequency.

There are two antennas:

Transmitter Antenna:

• It converts electrical signals into electromagnetic waves and transmits them.
  The transmission antenna is the basic source of radiofrequency (RF) radiation and the basic element of radio technology.
• This type of antenna is composed of a conductor that carries an electric current whose intensity fluctuates over time and converts it into radiofrequency radiation that propagates in space.

Receiver Antenna:

• it receives the information in the form of electromagnetic waves which was transmitted by the transmitter and converts these waves back into electrical form.
• Receiving antenna is a device for the reception of radiofrequency (RF).
• It performs the reverse of the process performed by the transmission antenna. It receives radiofrequency radiation and converts it into electric currents in an electric circuit connected to the antenna.

Characteristics of Antenna

1) Radiation Pattern

• A practical antenna cannot radiate energy in all directions with equal strength.
• Radiation from an antenna is usually found to be maximum in one direction whereas it is minimum or almost zero in other directions.
• Field Strength is the quantity that is used to represent the radiation pattern of an antenna. It is usually measured at a point located at a particular distance from the antenna.

2) Directivity

• Antennas can be designed to radiate energy equally in all directions or primarily along a single direction.
• Directivity D is a unitless measure of the uniformity of the radiation pattern plot.
• It is defined as the ratio of the maximum power density over the average power density.
• An antenna that radiates equally in all directions is called isotropic. An antenna that radiates equally in two, but not the third, directions are called omnidirectional direction.
• Isotropic antennas have
  D=1
  All other antennas have
  D>1.

3) Polarisation

• The direction of the electric field radiating from the antenna in areas sufficiently distant from the antenna (a distance of several wavelengths).
• A radio wave may be non-polarized or polarized (linear or circular/elliptical polarization).

4) Efficiency

• The ratio between the total power radiated by the antenna and the net electric power fed to the antenna.
• An ideal antenna has 100% antenna efficiency i.e., it transmits all the power fed to it. But in the real world, a good antenna radiates only 50 to 60% of the power supplied to it.

5) Bandwidth

• The width of a range of frequencies at which the antenna transmits its maximal radiation and intensity.

6) Antenna Array

• A systematic deployment of antennas that operate together. The individual antennas in an array are usually of the same type and are situated nearby and at a fixed distance from one another.
• An antenna array enables increasing the directionality and control of the main radiation beams and the lateral beams.