The invention relates to an antenna reflector support which, in the radiation field, supports the passive parabolic reflector on an omnidirectional antenna for a microwave transmitter and consists in a cylindrical wall coaxial with the reflector.
Originally the parabolic reflector of such an antenna was supported by two or more metal posts. These posts, however, affected the homogeneity of the field, so that the radiation diagram was no longer rotation-symmetrical. In order to overcome this difficulty the posts were replaced by a cylindrical wall of dielectic material.
A reflector support of this type is described in publication A454 TBr 5 of the German Post Office Telecommunications Research Institute, January 1969. Such a dielectric support provides, on the one hand, a sufficient rigidity of the support and, on the other, a protection of the antenna components from the influence of the weather.
However the use of a dielectric material for this support has the drawback that, due to ultra-violet irradiation, it becomes brittle, owing to which its strength decreases, so that frequent maintenance of the usually difficulty accessible antenna is necessary. Moreover, owing to the change of the dielectric properties of the material, the reflection increased, to the detriment of the quality of the antenna.
On the other hand utilization of a wall made of a good conductor for electricity and provided with slots as active elements was known in itself, e.g. from the so-called waveguide slot antennae, in which, however, the wall is the outer conductor of a closed transmission line and, as such, an active current-carrying element. In that case the waves travel lengthwise through the space enclosed by the wall. Moreover, the wall has no supporting function.