Combination antenna arrangement for several wireless communication services for vehicles

A combination antenna arrangement is provided for at least two wireless communication services, wherein a closely tolerated directional diagram is configured for the first wireless service, in a frequency range assigned to it. Antenna conductor parts are provided only for the function of the additional wireless communication services, and are radiation-coupled with the antenna assigned to the first wireless communication service. The conductor parts are divided into segments forming interruption points designed to be smaller than ⅜ λ for this first wireless service. The interruption points are bridged by low-loss, frequency-dependent reactance circuits (8), in order for the combination antenna arrangement to function. These circuits possess a sufficiently high impedance in the frequency range of the first service and an impedance that is predetermined for proper functioning for the frequency range of the frequency range of the additional communication services.

BACKGROUND OF THE INVENTION

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 service1, the combination of satellite antennas and antennas for other wireless communication services2in 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 service1, 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.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an antenna affixed in the close proximity of a first antenna for the first wireless communication service having a closely permissible antenna directional diagram, or combined with this antenna, for additional wireless communication services, which avoid the disadvantages of distortion of the antenna directional diagram of the antenna for the first wireless communication service.

The great advantage of antenna arrangements according to the invention consists in concentrating combination antennas for several wireless communication services for vehicles in an extremely small space, without having to accept impermissible diagram distortions for the first wireless communication service, while adhering to particularly stringent requirements with regard to a reference directional diagram.

According to the invention, a high-precision antenna for SDARS (first wireless communication service1) can be combined with two combination antennas for AMPS and PCS cell phone (other wireless communication services2), in a housing having the dimensions of about 12 by 5 cm (corresponding to only about 1 λ times 0.4 λ, with reference to the wavelength of the SDARS service), whereby the antennas for these additional functions have a distance of about 0.3 λ, with reference to the wavelength of the SDARS service, from the center of the SDARS antenna. Moreover, a patch antenna for GPS is also integrated into the housing. This distance of only 0.3 λ is possible in that only 5 cm was selected as the height of the telephone radiators, and these were divided twice, whereby the maximum distance between two interruption points only amounts to 2 cm, corresponding to 0.16 λ, with reference to the wavelength of the SDARS service.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1a, there is shown a first antenna14in the form of a λ/4 antenna20, with an antenna connection point22for the first wireless communication service1. The effects of its radiation coupling with an additional antenna15for an additional wireless communication service2on the directional diagram of the first wireless communication service1, will be explained as a function of the division of additional antenna15into parts. In order to reduce the radiation coupling, segments4, are formed by providing a series of interruption points10spaced apart by a segment length5. A coax line30is coupled to antenna15through an inductance8.

FIG. 1bis a detail circuit of the interruption point of the antenna arrangement ofFIG. 1awith an inductance8coupled between antenna segments3in separation11.

FIG. 1cshows a typical impedance and reactance diagram of the reactance circuit ofFIG. 1bwith respect to frequency f.

FIGS. 2ato2d′ show the diagram distortions of antenna14, in dB, that result from the presence of additional antenna15. In this connection,FIG. 2ashows the maximal influence of an antenna15having a total length of λ, which is divided into two segments4having a length of λ/2 as shown inFIG. 2a′. For use in a vehicle, for the case of an SDARS antenna, distances of 0.5<d/λ<3 are of interest. The accompanying deviations between +3.5 dB and −6.5 dB for d/λ=0.5 dB, and +1.5 dB and −2.5 dB for d/λ=3, respectively, are completely unsuitable for use of a closely tolerated antenna for the first wireless communication service.

It is of great advantage of the present invention that the design permits a maximal segment length5of 3λ/8, as shown inFIG. 2b′, for each division, thereby reducing the corresponding distortion as shown inFIG. 2bto the range between +/−1.5 dB (d/λ=0.5) and +/−0.8 dB (d/λ=3). With more divisions, i.e. with a segment length5that becomes shorter, the distortion of the directional diagram decreases significantly. This is evident fromFIGS. 2cand2d, where the corresponding distortion is reduced to the range between +/−0.5 dB or +/−0.2 dB, or to a maximum of +/−0.2 dB at a segment length of λ/8. The present invention therefore requires selecting segment length5to be sufficiently small and, where additional antenna15is used for the additional wireless communication services2to bridge interruption points10, as shown inFIG. 1b, with reactance circuits8, so that the impedance that is active between interruption points10is sufficiently great.

FIGS. 2e, f, andgshow the typical effects on directional diagrams of antenna14for the first wireless communication service1. In all three cases, the horizontal diagrams are shown for vertical polarization, which react with particular sensitivity, and the antennas are arranged on a conductive surface that extends infinitely.FIG. 2eshows the circular, angle-independent diagram of antenna14in the absence of conductor parts3of the additional wireless communication services. This diagram is therefore the reference diagram for the deviations that result in the presence of conductor parts3of the additional wireless communication services.

FIG. 2frelates to a combination antenna arrangement according toFIG. 2a′, in other words to an embodiment of additional antenna15that is not in accordance with the invention, for a distance d/λ=0.5. The diagram distortion is definitely impermissibly great. In contrast to this, the diagram according toFIG. 2gdemonstrates only comparatively slight changes as compared with that ofFIG. 2e.FIG. 2grelates to the antenna arrangement ofFIG. 2c′, and again applies for a distance d/λ=0.5. In accordance with the invention, the influences can be further reduced if either the distance d/λ is increased, while keeping the division of conductor parts3the same, or if the additional antenna15is divided more frequently, as inFIGS. 2d,2d′ by reducing the maximal dimensions5of segments4.

In the most general case, it is a requirement for the reactance circuits8that the frequency progression of the reactance circuits8is configured as inFIG. 1cand possesses a pole position in the frequency range6of the first wireless communication service1, and is sufficiently great, in terms of amount, over the frequency bandwidth13of the range, and that the reactance X in the frequency ranges9of the additional wireless communication services2is sufficiently small. For the required values for reactance8within frequency range6, it turns out that the impedance should not go below about 1 kΩ for conductor parts3of the additional wireless communication service that are divided into segments having a length of λ/4, for example, whereby the capacitative effects between the two adjacent segments must also be taken into consideration.

InFIG. 3b, the segments of additional antenna15according to the invention are configured in a flat manner, and their maximal dimension5must also be selected to be less than 3λ/8. Here, the widths11of interruption points10must be selected to be small in comparison with maximal dimension5, and reactance circuits8must be configured so that impedances7that are in effect between interruption points10essentially possess the frequency behavior of a parallel resonance circuit16in frequency range6of the first wireless communication service. The configuration of these flat segments can preferably be implemented, for example, in printed or stripline circuits, including the parallel resonance circuits16as shown in the structure ofFIG. 3c.FIG. 3ctherefore shows a particularly cost-effective, reliable printed circuit embodiment of a parallel resonance circuit16for a combination antenna arrangement according to the invention, which can be produced with only slight production variations.FIG. 3ashows an electrically equivalent circuit approximation to the total surface according to the circuit ofFIG. 3b, by means of linear structures17.

FIG. 4shows an additional antenna15for an additional wireless communication service2placed in the close proximity of a first antenna14for a first wireless communication service1having a closely tolerated antenna directional diagram. As an example, a first antenna14is shown in the drawing as an antenna as indicated in U.S. Pat. No. 6,653,982 B2. An antenna known as an inverted F is shown as an additional antenna15. In order to adhere to the strict tolerance provisions of the directional diagram for first antenna14, the flat elements of the additional antenna15are divided in accordance with the rules stated in connection with the antenna ofFIG. 3b.

FIG. 5shows a first antenna14in combination with additional antennas15affixed in close proximity to the former, structured as linear antennas. Additional antennas15are provided for wireless communication services such as AMPS, GSM 900, PCS, GSM 1800 or UMTS. With a satellite radio antenna as a first antenna14, the directional diagram of this antenna cannot be tolerated, due to the presence of additional antenna15, without the proposed measures. In an advantageous embodiment of the present invention, parallel resonance circuits16are therefore introduced into additional antennas15, which are structured as monopoles. In order to avoid resonance currents in the conductor parts of the additional antennas15, the connections to them are also separated by means of parallel resonance circuits16affixed in the lower part of the radiators.

In a particularly advantageous embodiment of the present invention, reactance circuit8is configured, in each case, so that they possess a zero point at a frequency f2in the frequency range9of an additional wireless communication service2, and a pole in the frequency range6of the first wireless communication service1as shown inFIGS. 6aand6b. Thus, a sufficiently low-ohm impedance7exists over the frequency bandwidth21of an additional wireless communication service2, and a sufficiently high-ohm impedance exists over the frequency bandwidth13of the first wireless communication service1.

FIGS. 6a′ and6a″ show two possible reactance circuits where the frequency range6of the first wireless communication service1is higher in frequency than frequency range9of the additional wireless communication service2.FIGS. 6b′ and6b″ show corresponding reactance circuits8for the case where the frequency range9is higher than the frequency range6.

FIGS. 6c′ and6c″ show types of reactance circuits8if additional wireless communication services2are present, whereby the frequency range6of the first wireless communication service lies between the two frequency ranges9a,9b, of the additional wireless communication services2in their frequencies f2a, f2bas inFIG. 6c.FIGS. 6d′, and6d″ show types of reactance circuits8if two frequency ranges9a,9bof the additional wireless communication services2exist, which as shown inFIG. 6d, are lower in their frequencies, f2a, f2bor, as inFIG. 6e, higher in frequency than the frequency range6of the first wireless communication service1, with corresponding reactance circuits6e′ and6e″.

InFIG. 7a, a linear antenna15is shown for the cell phone services AMPS and PCS, and placed in close proximity of an antenna14according to the SDARS standard. The interruption points10of additional antenna15are each configured with a parallel resonance circuit16, the reactance progressions of which are shown as a function of the frequency inFIG. 7b. At the frequency f1in the frequency range6of the first wireless communication service1, the impedance X1(f) forms a pole at the bottom end of the monopole, and is at sufficiently high impedance over the frequency bandwidth13of the first wireless communication service1, in order to practically not impair the directional diagram of first antenna14, and is selected to be sufficiently low in the indicated frequency ranges of PCS and AMPS. The reactance X2(f) at the interruption points10in the upper third of additional antenna15is configured in similar manner, and because of its high impedance, it causes the upper part in the frequency range PCS to be shut off at full effectiveness in the frequency range of AMPS. The impedance progression Z(f) shown in the chart ofFIG. 7c, in the foot point of additional antenna15, shows the adaptation that has been achieved in the two cell phone services.

In another advantageous embodiment of the invention, the combination antenna arrangement is configured as a first antenna14for satellite radio reception according to the SDARS standard, as the first wireless communication service1, and for additional antennas15according to the AMPS and PCS standard as additional wireless communication services2aand2b. In this connection, first antenna14according to the SDARS standard is configured with rotational symmetry, as an antenna on an essentially horizontal conductive surface, with reference to its vertical centerline. As described in U.S. Pat. No. 6,653,982 B2, a vertical combined monopole for the AMPS standard and the PCS standard is introduced into its centerline. This is switched with a suitable reactance circuit8at suitably selected interruption points10, as inFIG. 8cor8d. InFIG. 8a,FIG. 8b, as well asFIG. 8d, the monopole is loaded or burdened with a roof capacitor, which is provided with radial interruption points10shown inFIG. 8a, for small diameters of the circular roof plate, to avoid distortions of the directional diagram for the SDARS service. InFIG. 8b, additional circular interruption points10with reactance circuits8are inserted in antenna15.

FIG. 9shows another advantageous use of the invention wherein an AM/FM antenna affixed on a rod-shaped plastic or flexible support, and configured in the close proximity of first antenna14for the first wireless communication service1, e.g. an SDARS antenna. The length of this an antenna is generally selected to be between 0.4 m and 0.9 m. Applying the invention, the AM/FM monopole antenna is formed by an essentially wire-shaped conductor25. In order to produce the high impedance state of the antenna for the frequency range6of the first wireless communication service1, it is advantageous if it is provided with a series of coils24at the necessary intervals. These can be formed from the same wire, by means of close winding, or by means of a meander structure, so that the winding capacitor that results from this forms a parallel resonance circuit16with the coil. In another possible embodiment, the wire is structured as a wire coil essentially continuously wound over the length of the rod-shaped plastic support26, which forms a sufficiently high impedance structure for the frequency range6of the first wireless communication service.

Accordingly, while several embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.