# Explanation of Polarisation Angle.

## Definition of Polarisation ( also known as skew or polarization )

Vertical polarisation is when the electric field is vertical.   When people talk about polarisation they are referring to the electric field vector.

References to 'vertical' and 'horizontal' are frequent since terrestrial antennas are normally vertical or horizontal relative to the ground.

Example 1:   Vertical polarisation is produced by a vertical dipole antenna.  At an instant the top is positive voltage and the bottom is negative voltage - so the electric field produced is vertical.

 Example 2.  Vertical polarisation is produced by the open end of a rectangular waveguide whose narrow dimension is vertical and whose broad face is horizontal.   The waveguide is typically energised by a vertical probe (like a single ended quarter-wave half dipole antenna) sticking through the broad face of the waveguide.   Inside the waveguide think in terms of voltage between the centre lines of the two broad faces.   This is the vertical electric field.   Around the two narrow sides, current flows.   It does not matter if the pin is at the top, pointing downwards, it is still vertical polarisation. Vertical polarisation

To set nominal Vertical receive polarisation the broad faces of the LNB waveguide must be on top and underneath.

Always start from the nominal position, vertical or horizontal.  Then apply the adjustment.

### Tilting the angle

In the case of satellite communications, polarisation angles are tilted over a wide range.

If you are in the northern hemisphere:   Face the equator (by looking south) and you can envisage the geostationary orbit as curved line across the sky starting in the south east, rising to say 35 deg elevation at due south and falling in the south west.  The polarisation of satellites located to the east will be tilted anticlockwise, satellites to the west clockwise.  Only a satellite due south of you will have its polarisation aligned vertical.

If you are in the southern hemisphere:   Face the equator (by looking north) and you can envisage the geostationary orbit as curved line across the sky starting in the north east, rising to say 60 deg elevation at due north and falling in the north west.  The polarisation of satellites located to the west will be tilted anticlockwise, satellites to the east clockwise.  Only a satellite due north of you will have its polarisation aligned vertical.

Important: Think in terms of the view from behind the dish, facing towards the satellite; clockwise is positive.

This figure shows Horizontal nominal polarisation (with the LNB initially on top) then with -45 deg polarisation adjustment applied.

### The calculated angle

If the calculated angle is positive you need to face towards the satellite and tilt the top of the vertical polarisation clockwise so many degrees to the right.

If the calculated angle is negative you need to face towards the satellite and tilt the top of the vertical polarisation anti-clockwise so many degrees to the left.

Horizontal polarisation adjusted by -13 deg anticlockwise, while facing the satellite.

These diagrams above show your view facing towards the satellite.  Your viewpoint is from behind the dish looking forwards towards the satellite.
You can see the feed horn window.  The rectangular LNB waveguide is shown. Note the four possible starting positions in the top row.
You then apply an adjustment, between -90, 0 and +90 deg, anticlockwise or clockwise.  A -45 deg adjustment is shown as an example.  Sometimes the LNB will hit the metal arm when you apply the adjustment; in this case start again with the alternative starting position,  on the other side.