An electromagnetic (radio) wave (satellite signal) consists of two components.
- A magnetic field
- An electric field.
These two fields oscillates (vibrates) in the same direction on the same (parallel) axis 90 degrees apart. See figure 1.
- Signals transmitted by satellite can be polarized in one of four different ways:
- linear horizontal
- linear vertical
- left-hand circular
- right-hand circular
- Vertically polarized
An antenna is vertically polarized when its electric field is perpendicular to the Earth’s surface. Vertically polarized signals oscillate from top to bottom. Signals are transmitted in all directions. Therefore vertical polarization is used for ground-wave transmission, allowing the radio wave to travel a considerable distance along the ground surface with minimum attenuation.
- Horizontally polarized
Horizontally polarized antennas have their electric field parallel to the Earth’s surface. Horizontally polarized signals oscillate from left to right. Horizontal polarization frequencies are parallel to and touch the earth. Since the earth acts as a good conductor at low frequencies, it shorts some of the frequencies and prevents the signals from traveling very far.
- Circular polarization
Circular polarization is most often use on satellites. The polarization of the signals is rotating. Due the position of the Earth with respect to the satellite, geometric differences may vary. Circular polarization will keep the signal constant regardless of anomalies.
- FSS (Fixed Service Satellites) satellites use horizontal and vertical polarization. FFS are used for:
- telephone calls
- data transmission
- TV signals for broadcasting
- cable organizations (cable TV networks)
The low power FSS requiring a larger antennas with the advantage that more programs can be broadcast.
- DBS (Direct Broadcasting Satellite) satellites use left- and right-hand circular polarization. DBS are especially designed used for:
- TV programs
Because of its high power, its signals can be received with smaller antennae and received much easier
- MPS (Medium Powered Satellite) which is a satellite with more power than a FSS and its signals can therefore be received much easier. Although it has less power than a DBS, it broadcast more programs. The ASTRA satellite is an example.
Horizontal and vertical polarized signals will not interfere with each another because they are differently polarized (90 degrees apart). This means twice as many programs can be transmitted per satellite.
There are 2 elements (antennae) in a LNB. One element is to receive horizontal polarized signals only and one element to receive vertical polarized signals only. If your LNB is not set up correctly, you will not receive the signal at all. It is very important to adjust the LNB that the horizontal element lines up with the horizontal polarized signal and the vertical element with the vertical polarized signal.