The present invention relates to a method of assembling a radiocommunication antenna comprising a reflector connected to a subreflector via a circular section waveguide extending along a longitudinal axis. According to the invention, such a method comprises the following steps: the step of pivoting the waveguide about its longitudinal axis to determine a position such that an offset of the plane of propagation of a polarized electromagnetic field transmitted by this guide is limited, the step of marking this position on the waveguide, and the step of fitting the waveguide to the reflector as a function of this mark.