1. Fixed
2. Mobile

• Maritime
• Aeronautical
• Terrestrial (trucks etc)

3.  Broadcasting

#)Low system noise is important for all the applications some possible options of INTELSAT earth stations are as follows First is encountered in two-way communication systems.

#)The second is the direct TV broadcast satellite systems.

#)The third is the data collection systems

Standard A earth station:

• G/T = 40.9 db/k at C-band
• Dish diameter  = 30 m
• Antenna gain = 6.4 db

Standard B earth station :

• G/T = 31.7 db/k at C-band
• Dish diameter  = 31 m
• Antenna gain = 51.5 db

Standard C earth station:

• G/T = 39 db/k at C-band (at 14/11 GHz)
• Dish diameter  = 19 m (at 14/11 GHz)
• Antenna gain = 65 db (at 14/11 GHz)

2.    Depending Upon The Application
•    Transmit and receive
•    Receive only (DBS)
•    Transmit only (DCS)

3.    Depending Upon The Type Of Size
•    Large earth station
•    Small earth stations
•    Micro earth station:
•    Very small aperture terminals (VSAT)
•    Large earth station

#)Typically for communication applications cassegrain geometry is used diameter around 30m

Small earth stations

#)Antenna size less than 60 wavelength in diameter.

#)Diameter of antenna = (say) 5m at 4GHz
= 1.6 at 11 GHz
Gain = below 44db

#)Type of parabola = Front feed parabola

#)Fixed pointing: no need of expensive auto-track system.

#)Application: TURO (TV receive only) systems, load mobile services, maritime services, Direct broadcast satellite (DBS).

Micro earth station:

#)Size: 2 to 6 feet antenna

#)Very inexpensive

#)DBS application

Very small aperture terminals (VSAT)

#)Low cost earth station. Low speed, packet data Networks applications.

#)Antenna size: 1.2 to 2.5m dia

#)G/T <15 db/k

#)LNA is uncooled GaAs FET of about 100k

#)HPA:

• 1 to 5w power also GaAsFET Low cost solution for route data communication between control host computer and a large no. of remote sites.
• Generally employs star topology. VSAT employs packet transmission with switching at the master station.
• Such networks are ideally suited for non-voice applications like computer and other forms of data communication.
• These employ spread spectrum multiple access (SSMA) techniques.
• The data transmission rates are generally limited to 19.2 bits at 4 GHz.

Applications of VSATs are

•    Data broadcasting services and
•    Two-way data services
•    News dissemination including text and graphic information
•    Transmission of charts and documents.

#)It is believed that in future, with spread spectrum technique with 20/30 GHz band, the size of the earth may come down o 12 cm, making earth stations truly portable.

#)VSAT find applications in aircrafts ships and rural areas and mobile communications.

Mobile and Transportable earth stations:

#)The small earth stations are portable and the antenna must be capable of relating in all directions.

#)Application is the communication for shipping through IMMARSAT (International Maritime Satellite Organization) satellites.

#)IMMARSAT: Earth station characteristics are

• Antenna diameter: 12 m
• Gain:23 db
• Beam width: 100
• Capacity : single duplex telephony or telegraphy.
• Frequency: 1640/1540 GHz

TURO systems

#)It has only the downlink section consists of dish (reflector), feed –horn , polarizer, LNA, down converter and TV/Video monitor.

#)The dish can be spherical or parabolic, generally the later.

#)The receiver part of TURO consists of down converter,  IF amplifier, demodulator and video/audio processor.

#)Once the video and audio are properly processed, they may be received on the monitor.