Elliptical satellite dish antenna orientation
In satellite communications, elliptically shaped dishes are often used in order to achieve a narrow main beam pattern and low side lobe levels in a particular directions. The alternative is to use larger circular dishes, but smaller dishes are preferred as they less obstrusive.
It is desired to minimise the side lobes in the direction towards other satellites, adjacent either side along the geostationary orbit. This minimises interference to and from those satellites. In the case of exceptionally small satellite dishes, as used for satellite TV, the width of the main beam itself and the locations of the adjacent satellite are of importance and it may be possible to make the width of the elliptical dish such that the locations of the probable adjacent satellites fall in the null between the main beam and the first sidelobes.
When installing an elliptical dish it may be possible to alter the orientation of the ellipse by tilting the entire dish clockwise or anticlockwise while facing the satellite.
In the case where the wanted satellite is on approximately the same longitude as the satellite, the satellite is at the top of the geo orbit arc as seen across the sky. The top of the geo orbit is horizontal and it is appropriate in this case that the wide dimension of the elliptical dish be sideways. The broad width of the dish is thus aligned parallel with the orbit.
This image illustrates the case of a satellite some way away from the highest point on the geo arc. The dish needs tilting so that its minimum sidelobes line up with the adjacent satellite.
The dish is tilted clockwise, viewed in the direction towards the satellite and its larger diameter is roughly parallel with the line of the nearby satellites.
The appropriate angle is the same as the skew or polarisation angle as calculated using the dish pointing calculator
The diameter of the main beam is smaller with large diameter dishes. In the case of an elliptical dish the main beam shape is normally also elliptical with the narrow dimension sideways, if the broad dimension of the dish is also sideways.
Page started 21 Nov 2007, amended 4 August 2015