ANTENNA

 Antenna

                           An antenna is a metallic device.This device for radiating or receiving radiowaves is known as antenna.Antenna are connecting links between the transmitter and free space and the receivers.It is optimize the radiation energy in some direction and suppress it in other direction.

An electrical device used to send or receive electromagnetic waves.In Transmission line, transformation of a guided EM wave into an EM wave freely propagating in space.Alternative, a transmitter produce a large frequency. When current applied to the terminals of  the antenna in order to covert it into an electromagnetic wave radiated into free space.Antenna used in systems such as radio and television broadcasting, two-way radio,wireless LAN, mobile telephones, radar, and satellite communication systems, live telecasting.

Antenna have depend and works on parameters and efficiency, they are

        1.Beam width

        2.CPD: It is a cross pole discrimination.When the feed is rotated to 90 degrees then the strength of  the

                    signal becomes low.

         3.C/N:It is carrier to noise ratio.This is the difference of peak and the reference X-axis.

         4. Gain:It is Electromagnetic Power gain and efficiency gain   

                     Usually the efficiency of the antenna is 65%

                 Now a days different types of antennas are available,

                  1.V-SAT (Very small aperture terminal antenna)

                  2.EARTH STATION ANTENNA

1.V-SAT(MOBILE STATION): It is very small aperture terminal antennas.these antennas have different sizes from 0.75mts to 3.8mts.these usually used for mobile antennas.the gain varies with different sizes of antennas.

more the sizes of antenna more than gain.Here the gain is less when compared to earth station antennas.and also due to the different bands the gain varies.Data rates typically from 56 K bit/s up to 4 bit/s.

VSATs access satellite in geosynchronous orbit to relay data from small remote earth stations(terminals) to other terminals master earth station "jigs".VSATs are most commonly used to transmit narrowband data or broad data(for the provision of satellite internet access to remote  locations like live videos).VSATs are also used for transportable, on-the-move or mobile maritime and also nowadays news channels are majorly  using these type of antennas.mobile station antennas are mainly using for live coverage.

V-SAT FUNCTIONING:

•E-compass is used to measure our present angle with respect to north.

•GPS gives exact latitude and longitude of current position.

•E-compass and GPS are primary inputs for ACU(Antenna control system).

•Satellite ID's are stored in the ACU manually.For transmitting and receiving of signal we should get aligned to a particular satellite, ACU gives command to motors with help of encoders.

•After getting maximum signal then antenna is peaked to the satellite.

•The Beacon frequency is entered in BTR(Beacon Tracking Receiver).BTR converts the set Beacon frequency into respective voltage.

•This BTR output voltage is given to ACU for fine tracking.

 2.EARTH STATION ANTENNA:  Earth station antenna are very large in size.This antenna size is more than V-SAT antennas.these antenna sizes from 3.8 mts to 32 mts.This antenna gain is more the beam is collected here.The resulting satellite earth station is the largest satellite communications facility in Germany.An earth station, ground station, or earth terminal is a terrestrial terminal station designed for extra planetary telecommunication with spacecraft, a reception of radio from an astronomical radio source.Earth station are located either on the surface of the earth, or within Earth's atmosphere.Earth stations communicate with spacecraft by transmitting and receiving radio waves in the super high frequency or extremely high frequency bands(e.g.,microwaves).When an earth station successfully transmits radio waves to a spacecraft, it establishes a telecommunication link.Earth station may occupy either a fixed or itinerant position.

 When a satellite is within an earth station line of sight, the earth station is set to have a view of the satellite.It is possible for a satellite to communicate with more than one earth station at the time.A pair of the earth stations are set to have a satellite in mutual view when the stations share simultaneous, unobstructed , line-of-sight contact with the satellite.This can receive the signal in any climatic conditions.