Few Typical Characteristics Of An Antenna

An earth station is a terrestrial terminal station designed for extraterrestrial telecommunication with spacecraft and radio waves from an astronomical radio source. The typical characteristics of  antenna that should be known are:

Radiation Pattern

It is the main characteristics of antenna. The antenna pattern is a graphical representation in three dimensions of the radiation of antenna as a function of angular direction. The pattern involves a main lobe and several minor lobes. A side lobe on the direction opposite to the main lobe is called black lobe.

Antenna Gain

Antenna gain is a measure for antenna efficiency. It is the ratio of the maximum radiation to that of reference antenna in a given direction for equal input power. Gain is generally measured in decibels above isotropic. Antenna gain depends on the mechanical size, the effective aperture area, the frequency band and the antenna configuration.

Antenna Lobes

There are different antenna lobes. Main lobe is the radiation lobe containing the direction of maximum radiation. Other than this there are side lobes, and back lobes.

Half-power beam width

The half power beamwidth is the angle between the points on the main lobe that are lower than 3dB in gain compared to the maximum.

Polarization

The propagation of the electric field vector is polarization. Antennas used in cellular communications are either vertically polarized or cross polarized.

Front-to-back ratio

Front to back ratio is the ratio of the maximum directivity of an antenna to its directivity. The antenna with a high front to back ratio is generally used.

First Null Beamwidth

The first null beamwidth is the angular span between the first pattern nulls nearby to the main lobe.

Frequency bandwidth

VSWR of an antenna is the main bandwidth limiting factor.

The earth station antenna requires maintenance to reduce the antenna failure probability and extend the antenna life.

Types of Satellite Communication System

Satellite communication system uses satellite technology for communications. The services provided by satellite communications are internet, voice and video calling, fax, radio channels, military applications and television.

In satellite communication, transferring of signal between the receiver and sender is done with the help of satellite. The signal is a beam of modulated microwaves sent towards the satellite. Then the signal is amplified by satellite and sent back to the antenna of the receiver present on the earth’s surface.This type of communication is called space communication.

Satellite communications can provide communication capabilities spanning long distances and can operate under conditions which are inoperable for other forms of communication.There are around 2,000 communications satellites present in Earth’s orbit, used by both government and private organizations.

Two types of satellites which are used commonly in satellite communication are active and passive satellites:-

Passive satellites: It is like a plastic balloon with a metal coated over it. This sphere reflects the microwave signals coming from one location of the earth to another one. This is also called passive sphere. Moon is passive satellite of the earth.

Active satellites: It basically amplifies the microwave signals coming. In active satellites a receiver, an antenna system, power supply, transmitter is used. These satellites are also called as transponders. Microwaves are generated by the transmitters fitted on the earth.

These rays are then received by the transponders attached to the satellite. After amplifying, these signals are then transmitted back to earth. This sending can be done at the same time or after some delay. These amplified signals are later stored in the memory of the satellites, when earth faces the satellite. Afterwards satellite sends the signals to earth.

Some active satellites also have recording and programming features. Then these recordings can be easily watched. The signals that come from the satellite are of very low intensity. Their receivers then amplify these signals themselves. After amplification they become available for further use.