1. Field of the Invention
The present invention relates to a method of assembling a radiocommunication antenna, a radiocommunication antenna assembled by such a method, and a device adapted to implement such an assembly method.
2. Description of the Prior Art
A radiocommunication antenna 10 (FIG. 1) may comprise a main reflector 12 the shape whereof, for example that of a circular symmetry paraboloid, focuses the received or transmitted electromagnetic waves at a subreflector 14.
That subreflector 14 is connected to the feeder device 11 of the antenna 10 via a waveguide 16 of generally circular section.
Such a circular section waveguide 16 may have imperfections that cause a modification of the plane of propagation of a polarized electromagnetic field transmitted by the waveguide, as explained hereinafter with the assistance of FIG. 2a. 
FIG. 2a is a front view of the waveguide 16 described above, this representation foregrounding the elliptical shape of certain sections of the waveguide 16.
These elliptical sections cause an offset between the plane of propagation of a polarized electromagnetic field 17 entering the guide 16 and the plane of propagation of the electromagnetic field 18 leaving the guide 16.
Such an offset between the planes of propagation of the electromagnetic fields entering and leaving the guide is undesirable since it may cause interference between adjacent antennas. In fact, each antenna is defined by an ‘ideal’ transmission plan along which the transmitted signals theoretically propagate, the use of this ideal plane enabling different adjacent antennas to be allocated separate propagation planes in order to limit the interference between antennas.
Consequently, the offset introduced by a waveguide in the plane of propagation of a polarized electromagnetic field can limit the number of antennas that may be placed in the same vicinity.
This is why an antenna manufacturer is obliged to limit the offset of the plane of propagation of the polarized electromagnetic field transmitted, which offset can be evaluated by a parameter such as the transverse discrimination of the antenna, also called the cross polar discrimination (XPD).
More precisely, the XPD of an antenna fed by a plane electromagnetic field corresponds to the ratio in dB between the power Pc transmitted by the antenna in the component coplanar with the electromagnetic field provided and the power Pt transmitted by the antenna in the component transverse to, i.e. at a right-angle or 90° to, the electromagnetic field supplied, in accordance with the following formula:G=−10 log(Pc/Pt)these powers being measured over a particular angular aperture as a function of the standards concerned.
To limit the offset introduced by a waveguide, it is known to use precise, and therefore long and costly, machining techniques so that the imperfections of the waveguide are limited.
The present invention results from the observation that a circular section waveguide in practice, and despite its imperfections, exhibits circular symmetry about its longitudinal axis and, because of this, it is possible to fix the waveguide to a reflector at any position obtained by pivoting the cylindrical waveguide relative to its longitudinal axis.
The invention is also a result of the observation that, as described hereinafter with the assistance of FIG. 2b, the offset electromagnetic field 18 may be considered as the sum of an electromagnetic field 18a propagating in a plane coplanar with the incoming electromagnetic field and an electromagnetic field 18b propagating in a plane transverse to or perpendicular to that incoming electromagnetic field.