One embodiment of the invention relates to an antenna for reception of circularly polarized satellite radio signals.
With satellite radio systems, what is important is the efficiency of the transmission output emitted by the satellite, and the efficiency of the reception antenna. Satellite radio signals are generally transmitted with circularly polarized electromagnetic waves, because of polarization rotations on the transmission path. In many cases, program contents are transmitted, for example, on separate frequency bands that lie close to one another in frequency. This is done, using the example of SDARS satellite radio, at a frequency of approximately 2.33 GHz, in two adjacent frequency bands, each having a bandwidth of 4 MHz, at a distance between the center frequencies of 8 MHz. The signals are emitted by different satellites, with an electromagnetic wave that is circularly polarized in one direction. Accordingly, circularly polarized antennas are used for reception in the corresponding direction of rotation. Such antennas are known, for example, from DE-A-4008505 and DE-A-10163793 which was also published as U.S. Pat. No. 6,653,982 on Nov. 25, 2003, the disclosure of which is hereby incorporated by reference in its entirety. This satellite radio system is additionally supported by means of the transmission of terrestrial signals, in certain areas, in another frequency band having the same bandwidth, disposed between the two satellite signals. Similar satellite radio systems are currently in a planning stage. The satellites of the Global Positioning System (GPS) also emit waves that are circularly polarized in one direction, at a frequency of about 1575 MHz, so that the aforementioned antenna shapes can fundamentally be configured for this service.
The antenna known from DE-A-4008505 is built up on a conductive base surface that is essentially or substantially oriented horizontally, and consists of crossed horizontal dipoles having dipole halves that consist of linear conductor parts inclined downward in V shape, which are mechanically fixed in place at an azimuthal angle of 90 degrees, relative to one another, and are affixed at the upper end of a linear vertical conductor attached to the conductive base surface. The antenna known from DE-A-10163793 is also built up above a conductive base surface that is generally oriented horizontally, and consists of crossed frame structures that are mounted azimuthally at 90° relative to one another. With both antennas, in order to produce the circular polarization, the antenna parts that are spatially offset by 90° relative to one another, in each instance, are interconnected and shifted by 90° relative to one another in terms of the electrical phase.
It is true that both antenna shapes are suitable for reception of satellite signals that are emitted by high-flying satellites—so-called HEOS. By means of an increase in the cross-polarization suppression in an elevation angle range that is as great as possible, however, the reception of temperature noise can be clearly reduced, in comparison with the reception of the satellite signals.
In addition, there is the difficulty of forming antennas having a smaller construction volume, which is compulsory for mobile applications, in particular. As further antennas of this type, patch antennas are known, according to the state of the art, but these are also less powerful with regard to reception at low elevation angles, and because of the use of dielectric materials, they demonstrate losses that clearly impair the signal-to-noise ratio.
For reception of all the radio services mentioned, however, efficiency in production of the antennas, which are produced in large volume, is of decisive importance.
For the production of antennas that are known from DE-A-4008505 and DE-A-10163793, there are problems resulting from the situation that the individual antenna parts are placed on planes that intersect at a right angle, and that these planes additionally stand perpendicular on the conductive base plane. Such antennas cannot be produced in sufficiently economically efficient manner, as desired, for example, for use in the automobile industry. This particularly holds true for the frequencies of several gigahertz that are usual in the case of satellite antennas, for which particularly great mechanical precision is required in the interests of polarization purity, impedance adaptation, and reproducibility of the directional diagram in the mass production of the antennas. Likewise, the production of patch antennas is generally relatively complicated, due to the close tolerances of the dielectric.