Understanding Polarisation

There are two major types of polarisation: Cross Polarisation (Cross-pol) and Co Polarisation (Co-pol).

Looking at cross polarisation initially, there are two types of cross polarization namely circular and linear. Within the circular realm there is the Left Hand Circular, or LHCP, or Right Hand Circular, or RHCP. This type of polarization is used in C-Band and in X-Band. One would be hard pressed to find circular polarization on Ku, K or Ka band frequencies. Linear polarization on the other hand is used frequently on Ku and Ka band antennas. With linear there are two types: Horizontal and Vertical.

What exactly is happening in the linear world that we need to know about? Before understanding how linear is used, one must understand the device being used on the satellite dish to let one signal pass while blocking the other signal. This is called the Orthogonal Mode Transducer, or OMT for short.

To use the channels that are available for satellite broadcast as efficiently as possible, both horizontal and vertical polarization (and left- and right-hand circular polarization) can be applied simultaneously per channel or frequency. In such cases the frequency of one of the two is slightly altered, to prevent possible interference. Horizontal and vertical transmissions will therefore not interfere with each another because they are differently polarized. This means twice as many programs can be transmitted per satellite. Consequently, via one and (almost) the same frequency the satellite can broadcast both a horizontal and a vertical polarized signal (H and V), or a left- and right-hand circular polarized signal (LH and RH).

The ASTRA2Connect system uses cross polarisation and our users can use this page to check the correct polarisation of their own systems. ASTRA2Connect polarisation checker.

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