Field of the Invention
This invention relates to a combination antenna arrangement for at least two wireless communication services for vehicles, by which a closely tolerated directional diagram is configured for the first wireless communication service, in a frequency range assigned to it, at A predetermined antenna connection point.
Because of the small construction space available, there is a significant demand for compactness smallness and, in particular, for minimizing the footprint of the antenna, in the case of vehicle antennas. U.S. Pat. No. 5,973,648 describes a combined antenna design for which the telephone services of the GSM-900 system, and the GSM-1800 system (cell phone systems of the D-network and the E-network), as well as the AMPS system, which is used in the United States, are mentioned as examples of use. In addition to these telephone services, a satellite wireless communication service is supposed to be made possible, such as the Global Positioning System (GPS) or a bi-directional satellite wireless communication service with low-flying satellites (Leos), which is in the planning stage.
Particularly for satellite wireless communication services as the first wireless communication service 1, the combination of satellite antennas and antennas for other wireless communication services 2 in a confined space is problematical, because of the radiation coupling between the antennas, and the related distortion of the directional diagram of the satellite antenna. This is particularly due to the limited link budget, which can result in a breakdown of the wireless communication connection in case of a drastic distortion of the directional diagram. For example, in the case of satellite antennas according to the standard of SDARS satellite wireless communication, an antenna gain of a constant 2 dBi or 3 dBi for circular polarization is a strict requirement in the elevation angle between 25 or 30 degrees and 60 or 90 degrees, for example, depending on the operator. This demand exists for an antenna structured in the center of a level conductive base plate. This demand can only be met if the deviation from the ideal radiation characteristic does not amount to more than approximately 0.5 dB at any spatial angle.
Therefore the directional diagram has extremely close tolerances, particularly in view of the scale that is known for antennas on vehicles. U.S. Pat. No. 6,653,982 B2 indicates the construction of an antenna, for example, that allows adherence to the closely tolerated directional diagram. Using antennas having this construction, it is possible, in general, to provide the antenna gain in the region of the zenith angle without problems. In the case this antenna, the reception of terrestrially broadcast signals according to the SDARS standard is combined with a monopole antenna, thereby resulting in a small construction of the combined antenna for the first wireless communication service 1, which is advantageous for use in vehicles. A close tolerance requirement must therefore be maintained, to a great extent, for the structure on a vehicle.