(57) the invention relates to a mode coupler which, for example is included in an angle
tracking system of a satellite to establish a telecommunication between the transmitting
and the receiving ground stations. The mode coupler is realized through a circular
main wave guide (1) which also can include the feeding horn of the satellite antenna
in which a basic mode, for example the TE11-mode of the incoming circular polarized wave guide field appears and which procures
two communication channels (f1-f2 and f3-f4 respectively), as well as a beacon frequency (fb). To the main wave guide four rectangular wave guide arms (2a-2d) are connected via
the associated apertures (3a-3d). The main wave guide is dimensioned as a mode filter
for filtering away the non-desired higher modes TE21 and TM", and the wave guide arms are dimensioned as a frequency filter for filtering
away the frequency bands of the communication channels. From the higher modes TE2,
and TM01, the difference- and the sum signals are created in known way to provide a measure
of the angle error of the satellite antenna.
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