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TELE-satellite International — The World‘s Largest Digital TV Trade Magazine
— 06-07-08/2012
Polar Mount Antennas
Motorised Antennas for
Satellite Reception
Adolf Oberhuber
If you consult the relevant literature you will find that
no or – at most – insufficient background information
is available about how this type of motorised polar
mounted antennas actually works. The same is true for
the required formulas and their derivation. The following
illustrations are meant to provide answers to all questions
in association with a polar mount. This also includes,
inter alia, various size determinations for positions as well
as calculations for the satellite orbit based on a specific
example. Altogether this report is a collection of data and
calculations which, the author believes, have hitherto been
scattered across an endless number of publications and
accounts. For the sake of completeness and reference,
technical terms and their origin will be explained in a
separate addendum at the end.
In general, if a satellite antenna is to
be rotated with a motor you would need
two motors – one for the rotating move-
ment (azimuth) to the selected satel-
lite and the other one for adjusting the
dish to account for the differing heights
above the ground (elevation). Mounting
the rotation axis in parallel to the rota-
tions axis of the earth, i.e. in a pole-to-
pole direction, alleviates this problem so
that only one motor is required. How-
ever, this can only be achieved with a
more complicated and extremely precise
installation and alignment of the rotation
Dealing with the installation of satel-
lite receptions systems – both in theory
and practice – requires gaining an
understanding of sizes and proportions
relating to different sizes. As even the
relevant sizes and their derivations are
hard to come by, the following will estab-
lish all relevant data.
Before performing any calculations it
is paramount to recall the interdepend-
encies between the earth and satellites.
This may also provide a welcome oppor-
tunity to correct some common miscon-
The earth
Due to its rotation the diameter of the
earth at the equator is larger than the
distance between the north pole and the
south pole, which means the earth does
not have an exact spherical shape. How-
ever, the differences associated with this
fact can be neglected for our calcula-
tions, so that we accept the established
median radius of the earth of 6,731 km
as given.
Historically and depending on the
purpose, positions and directions are
Without exception, all calculations
and remarks are for the northern hemi-
sphere. If you live south of the equator
you need to interpret them accordingly,
such as antenna alignment to the north
instead of the south, inclination of the
rotation axis towards the south instead
of north and so on. For all calculations
you merely need a standard 10-digit
electronic calculator capable of per-
forming trigonometric operations. If you
intend to receive several satellites at
once you may choose one of the follow-
ing set-ups:
1. Several antennas:
Usually, such a set-up is only chosen for
commercial applications as it requires a
lot of space and also is more costly than
other solutions.
2. A single antenna with two or more
This design is intended for multi-user
layouts that have to make sure each user
has unrestricted access to all transmis-
sions of all satellites at any time. Natu-
rally, if several LNBs are attached to a
single antenna they cannot all be in the
precise focus of the parabolic dish, which
means that they are slightly out of focus.
However, reception is only possible if the
satellites are rather close to each other
and if the antenna has a certain (larger)
3. Polar mount antennas:
For single users interested in maxing
out their reception possibilities a polar
mounted motorised antenna is an inter-
esting solution. As the name implies, the
axis around which the antenna rotates is
mounted in a pole-to-pole direction, i.e.
in parallel to the axis of the earth. Such
a set-up does not restrict the number
of receivable satellites, provided they
can be ‘seen’ from the location of the
antenna. It is no big deal to receive 15 to
20 satellites without exceedingly elabo-
rate equipment.
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