History of the cross dipole antenna in Mainflingen
The German religious broadcaster
represented by its director for technical devolopement and marketing, Hartmut Diehl, was always annoyed that broadcasting from the vertical antenna in Mainflingen caused a fading zone during night time in "his" main coverage area. The fading zone is defined as an area where the difference of levels between groundwave and skywave field strength is less than 6 dB.
Due to different phases of these field strengths - the path along the ionosphere is longer than along the ground- distortions of reception occur.
Hence the idea came up to install an horizontally polarized antenna at the same site, which radiates the whole power towards the ionosphere. There it is reflected towards the earth where now nearly everywhere the skywaves are much stronger than the groundwaves. In addition complaints about bad TV reception in the villages close to the vertical antenna never stopped. This problem could be also solved when using an horizontally polarized antenna which radiates nearly the full energy to the sky.
The cross dipole antenna is a very efficient horizontally polarised antenna because of its additional circular polarisation. This is due to a particular behaviour of the ionosphere.
With the correct sense of rotation of the waves entering the E or F layers the whole energy is reflected and nearly no losses are occuring at the ionosphere.
At that time the only cross dipole antenna in operation was in Arganda
near Madrid. Mr. Diehl himself checked the effectiveness of this antenna by driving through whole Spain in order to measure the field strengths.