This question appears in Mumbai University > Satellite Communication and Network subject

Marks: 5 M

Year: Dec 2013, May 2013

Spot Beam & Use in Satellite Communication

1. A spot beam is a focused , conical shaped pattern of electromagnetic waves directed from the antenna of a communication satellite towards a specific region on the ground.
2. Multiple beam antennas may take the following forms:
3. Separate antenna
4. Multiple feed single reflector
5. Phase shift array
6. Usage of separate antennas for each beam, each pointing to an appropriate area, gives maximum isolation between feeds and little beam interference at the satellite as seen in fig below.

Separate Antenna

1. Multiple beams generated from a single reflector or microwave lens by using multiple feeds is illustrated in the fig below. The feeds simultaneously illuminate a common parabolic dish, which focuses the entire feed in the given direction. By offsetting the fields and positioning each point to a different section of the dish, the reflected fields can be spatially separated, producing the desired spot beams.

Multiple feed single reflector

1. In phased antenna arrays, by properly phasing a modulated carrier, the field can be transmitted as seen in fig below.

Phase Shift Array