EP0679318A1

EP0679318A1 - Uhf-waveband radio-antenna assembly for vehicles

Info

Publication number: EP0679318A1
Application number: EP95900076A
Authority: EP
Inventors: Heinz Lindenmeier; Jochen Hopf; Leopold Reiter; Rainer Kronberger
Original assignee: Fuba Automotive GmbH and Co KG; Hans Kolbe and Co
Current assignee: Fuba Automotive GmbH and Co KG
Priority date: 1993-11-16
Filing date: 1994-11-11
Publication date: 1995-11-02
Anticipated expiration: 2014-11-11
Also published as: DE4339162A1; DE59409715D1; WO1995014354A1; EP0679318B1; ES2156202T3

Abstract

The invention concerns a vehicle-mounted radio-antenna assembly for UHF communications links with land stations. A first antenna element with the character of an electric monopole or dipole with an essentially vertical polarization component is mounted on a first surface, made of essentially homogeneous material, on the vehicle body. Its azimuthal omndirectional properties are considerably affected by the environment formed by the vehicle body. In addition to the first antenna element (3), the assembly includes at least one additional antenna element (8) with monopole or dipole character. Each additional antenna element is mounted either on the first (11) or another (12) surface, and the antenna elements together form an antenna assembly with respect to the antenna-connection point (6). At least one of the antenna elements is directly fed and the other(s) are either directly fed or indirectly fed (passive). The clearance (9) between two adjacent antenna elements is set so that it is smaller than one free-space wavelength.

Description

Radio antenna arrangement for the decimeter wave range on one

Motor vehicle

The invention relates to a radio antenna arrangement for the decimeter wave range according to the preamble of claim 1. Such a radio antenna arrangement can advantageously be used, e.g. for the radio systems of mobile communication (car phone in the D or E network or for trunked radio systems).

Such antennas are known from daily radio practice and are usually rod-shaped antennas with the character of an electrical monopole or dipole and are either on the vehicle roof, on one of the fenders or, if no mounting hole is to be made in the vehicle body, also Applied in the upper region of the vehicle rear window, the antenna element then being attached to the outside of the glass window and frequently being fed capacitively through the glass window. Such an antenna is known from the USA.

Disadvantages of these known antenna forms result from the requirement of radio practice that, with a given transmission power, no horizontal direction due to dips in the

Horizontal diagram the radiation density with vertical polarization drops below a minimum required value. At the same time, the dimensions of the antenna elements should be as small as possible. The shapes of the length λ / 4 or less are particularly desirable because of their small dimensions. o In practice, the characteristic of the horizontal diagrams aimed for motor vehicle radio antennas with a radiation that is as uniform as possible in all azimuthal spatial directions is only achieved with electrically short antenna elements according to the prior art by means of rotationally symmetrical elements in the center of the vehicle roof. In this case, the vehicle roof, as an essentially flat partial surface of the body 5 with a horizontal orientation with central attachment of the antenna element, forms an environment in which, due to its size, the rotational symmetry of the radiation can develop largely undisturbed. With antennas mounted off-center on the roof, or with the antennas glued to the vehicle window or attached to the fender, the radiation coupling with the vehicle body, which acts rotationally asymmetrically with respect to the antenna in the immediate vicinity, in combination with the inhomogeneities of the antennas Body shape (edges) or the material (transition from sheet metal to window) undesirable and sometimes no longer tolerable deformations of the horizontal diagram, in particular radiation compensations, which cause strong indentations in the horizontal diagram. When attaching the antenna element in the area of the rear of the vehicle, the radiation in the solid angle area to the front is often especially inadmissibly reduced. In addition, as the frequency increases, the diagram becomes distinct. In the mini a of horizontal radiation in particular, this frequently leads to undesirably low radiation densities at the receiving location, ie to undesirably large radio field attenuation, for a given radiation power in the transmission mode. The limitation given by this coupling with regard to the possible mounting points represents a decisive disadvantage in practice. However, from the vehicle manufacturer's point of view, electrically advantageous mounting points, such as the center of the roof, are undesirable for various vehicle-technical reasons, for example because of the required one Installation space for sunroofs.

A reduction in the coupling to the vehicle body can be achieved by means of special antenna elements, the center of radiation of which is clearly distant from the body, which usually leads to very large installation heights. This technology aims to generate small currents on the body surface in order to keep the rotationally asymmetrical radiation component as small as possible. Very good degrees of decoupling from the body are often achieved by attaching antennas of length λ / 2 via a feed line at a distance of several decimeters (often more than 50 cm) above the vehicle body, which results in a disadvantageously large overall height for the entire body arrangement results. Such an antenna is known from US. When λ / 2-long antenna elements are attached to the vehicle body - be it on the conductive body panel or on the rear window pane, the rotationally asymmetrical influence of the vehicle body is mitigated by the fact that only comparatively small currents flow on the antenna element in the vicinity of the body, i.e. at the feed point . Such an antenna is known from published patent application OS 4007824.8. Such antennas therefore necessarily have a length which is significantly greater than λ / 4, namely λ / 2 or longer, which, in addition to the often inadequate rotational symmetry of the radiation, also has a serious disadvantage in practice, e.g. due to increased wind noise.

In particular, shorter, essentially vertically polarized monopole antenna elements with a length of λ / 4 or less carry strong currents in the feed point and, with regard to their radiation diagram, are dependent on their structure on an electrically conductive partial body area which has an azimuthal direction in all directions Distance of at least two wavelengths is largely flat and oriented horizontally. If this condition is not fulfilled because the antenna element is attached, for example, in the vicinity of a bend line of the body, that is to say in the vicinity of the edge of a partial area where this partial area of the vehicle body collides with another partial area with a different inclination, then the result is as described undesirable rotational asymmetry of the Radiation. Similar relationships result, for example, if the antenna element is attached in the vicinity of the boundary line of two partial surfaces made of different materials, such as, for example, body panel and window glass.

Even a uniformly curved conductive body surface e.g. in the rear area as a mounting surface leads to rotationally asymmetrical radiation properties, because the partial area surrounding the antenna element acts as a flat partial area with respect to the radiation only in a too small area, and this partial area is generally inclined with respect to the horizontal. In all these cases, the azimuthal omnidirectional characteristic of the antenna element is significantly disturbed by the surrounding vehicle body. A preferred mounting point for antenna elements in terms of vehicle technology is, for example, in the center of the vehicle on the roof of the vehicle near the rear edge of the roof or at the upper edge of the rear window pane. In both cases, the antenna element is mounted on a partial surface of the body in such a way that the rotational symmetry of the radiation from the vehicle body is disturbed. The object of the invention is therefore to provide a radio antenna arrangement according to the preamble of claim 1, in which despite the existing radiation coupling to the vehicle body, the lowest flat radiation density occurring in the horizontal diagram is as large as possible.

This object is achieved in a generic radio antenna arrangement by the characterizing features of claim 1.

The invention is therefore based on the idea of reducing or avoiding the disruptive influence of the vehicle body on the radiation with the aid of a group antenna arrangement designed for this vehicle body and for a given installation location. By achieving the object according to the invention, a radiation characteristic is designed such that the roundness of the azimuth diagram is also set in the best possible way. In the present invention, the group antenna is adapted to the vehicle body in such a way that the desired radiation properties of the arrangement of vehicle and antenna elements are obtained by superimposing the electromagnetic radiation generated by the usually strongly structured vehicle body and the antenna elements of the group.

In the case of the technology according to the invention, in order to generate the suitable amplitude and phase relationships of the antenna currents, it is also possible to use further fed and / or radiation-excited antenna elements in addition to a fed antenna element. The clear distance between adjacent antenna elements should not be chosen too large. Often you get with intervals of about a quarter length favorable conditions. Distances larger than one wavelength are unfavorable due to the jittering of the directional diagrams.

The antenna elements can either be fed in a simple manner via a common network with defined phase and amplitude relationships of the antenna currents, or the antenna elements can be excited by coordinating the radiator geometry, by reactivating the resistance and by selecting the distance, also by radiation, so that a group antenna with only a fed antenna element can be realized if all other antenna elements are radiation-excited. It is essential here that the setting of the phase and amplitude relationships forces the inclusion of the shape of the vehicle body.

The mode of operation of the invention can be illustrated using the example of three antenna elements, the azimuthal individual diagrams of which are shown in FIGS. 14a to 14c. Due to the influence of the vehicle body, the individual diagrams, in contrast to the diagram of the group antenna in FIG. 14d, are strongly direction-dependent. The advantages that can be achieved with the invention can be realized for motor vehicles, in particular at frequencies above about 600 MHz, and above all consist in the possibility of enabling short and optically inconspicuous antennas at vehicle mounting points that are particularly favorable in terms of vehicle technology, that is to say optically with a high performance of the antenna system and to be able to implement an extremely attractive solution from a vehicle-specific point of view.

In the meter wave range, in which the vehicle dimensions of the cars are in the order of a few wavelengths, it is less the fine structure of the vehicle shape in the vicinity of the mounting point of the antenna than the overall shape of the vehicle that has a significant influence on the radiation characteristics of a radio antenna. In contrast to this, the near range determining the radiation properties is an im

Decimeter wave range of much smaller radio antenna elements by an order of magnitude smaller, so that the fine structure of the vehicle body and its nature in the immediate vicinity of the antenna element also have a significant influence on the radiation properties. This effect is more pronounced the higher the frequency. Due to the smallness of the wavelength in the decimeter wave range, the attachment according to the invention of a plurality of antenna elements coupled to one another to achieve the object of the invention is well possible in a relatively narrow area, which is small compared to the vehicle dimensions.

The use of a plurality of antenna elements allows for a specific generation of current distributions on the antenna elements for a given positioning of the group antenna on the vehicle that is suitable from a vehicle-specific point of view. elements of the group antenna according to amount and phase in such a way that including the radiation coupling with this vehicle body

- On average, there is an increased concentration of the radiation in the vertical direction in favor of small elevation angles and - the smallest possible indentation of the horizontal radiation diagram occurs, which has the effect that the lowest flat radiation density occurring in the entire horizontal area is as large as possible.

The measures taken according to the invention do not prevent the undesired radiation of the vehicle body excited by radiation coupling. By means of suitable current distributions on the antenna elements of the group antenna according to magnitude and phase, a wave field is superimposed by the plurality of radiators, which in total results in radiation properties according to the object of the invention.

Exemplary embodiments of the invention are shown in the drawings 1 to 14 and are described in more detail below.

Show it:

Fig. L: inventive group antenna on the rear roof edge with a further antenna element 8 and a network 4 below the roof with concentrated blind elements. Fig.2: Group antenna according to the invention on the rear roof edge with another

Antenna element 8 and a network 4 on the roof, which is realized with stripline circuits.

3a: Group antenna according to the invention on the rear roof edge with a further antenna element 8, which is only radiation-excited with the first antenna element 3 and suitably connected with a blind element.

3b: Group antenna according to the invention on the rear roof edge with a further antenna element 8, which only excites radiation with the first antenna element and whose length is suitably selected.

Fig.4: Group antenna according to the invention on the rear roof edge with a further antenna element 8 and antenna elements each with roof capacitances and

Extension coils under a radome and with the connection cable routed along the roof and in the area of the window adhesive inside. 5: Group antenna according to the invention in the area of the rear roof edge with a first antenna element 3 just above the pane and a further radiation-excited antenna element 8 on the roof.

Fig. 6: Group antenna according to the invention in the area of the rear roof edge and the upper area of the rear window with a first antenna element 3 on the window and two further only radiation-excited antenna element 8 on the metal surface above the window and on the roof.

7: Group antenna according to the invention on the vehicle window 1 with a further antenna element 8 and a network 4 with stripline circuits. Fig. 8: Group antenna according to the invention on the vehicle window similar to Fig. 7, but with a screen 29 printed on the window to form a counterweight and to reduce the RF radiation in the passenger compartment.

Fig. 9: Group antenna according to the invention on the vehicle window, among others. with radial and ring-shaped wire-shaped conductors on the disc to form a transparent, larger ground surface

10a: Group antenna according to the invention on the vehicle window with a first antenna element 3, which projects approximately normally away from the window, and three further antenna elements 8 arranged in the window plane: sectional view.

Fig.10b: Group antenna according to the invention as Fig.10a, but in a perspective view.

11a: sectional view of a group antenna according to the invention on the vehicle window with a first antenna element 3 lying in the window plane and two further antenna elements 8 arranged in the window plane.

11b: Group antenna according to the invention as in FIG. 11a, but in a perspective view.

12: Group antenna according to the invention, completely mounted inside the vehicle, and with a wire-shaped first antenna element 3 and a further antenna element 8, each with roof capacitance, and a metallic cavity 31 open to the pane. Group antenna according to the invention, mounted completely inside the vehicle, and with a first antenna element 3 and a further antenna element 8, both mounted in the plane of the window, and with a metallic cavity 31.

Fig. 14: Measured directional diagrams with the three antenna elements and measured directional diagram of the optimized group antenna. 1 shows the basic structure of a group antenna according to the invention with a first antenna element 3, which is mounted on the roof of the vehicle near the rear roof edge 10 in the center of the vehicle and is powered by an opening in the roof. A further antenna element 8 is attached at a distance 9 in the direction of the rear roof edge, which is likewise fed in the same way through an opening in the roof. Both

Because of their small relative spacing, antenna elements are radiation-coupled to one another and to the body. In the example of FIG. 1, the antenna connection point 6 is inside the vehicle, a network 4 conducts the high-frequency signal from the antenna connection point 6 to the two antenna elements. The network 4 distributes the power via a low-loss feed network, which in the example in FIG. 1 is made up of concentrated low-loss dummy elements, the network 4 forming a further high-frequency coupling path between the two antenna elements in addition to radiation coupling through the field .

Each of the two antenna elements 3 and 8, if used alone as a radio antenna, ie in the absence of the respective other antenna element, would be an inadequate one

Distribution of the high-frequency power in the horizontal plane, because there is a strong inhomogeneity of the environment due to the proximity of the rear roof edge 10. The first partial surface 11, which is homogeneous in terms of material and position in space, extends from the rear roof edge 10 to the front and to the side, in each case up to the other edges of the roof surface.

However, the homogeneity of this partial area is not required for antennas according to the invention over such large areas. What is important for the electrical function is essentially the closer environment around the antenna elements in which the radio field is formed. In practice, this range is shown to be approximately two wavelengths in size. In FIG. 1, therefore, the distance between the first antenna element 3 is less than approximately two

Wavelengths to the rear roof edge, the homogeneity of the partial surface 11 is not sufficient for antennas according to the invention and the radiation characteristic is consequently unsatisfactory. The sheet metal surface which bends downwards at an angle 26 represents an adjoining further partial surface 12. The two partial surfaces have in common the boundary line 13, which in this example is therefore also the rear roof edge 10. In this example, the inhomogeneity of this area is further increased by the fact that the body part sloping downwards is short and merges into the rear window, which is made of non-high-frequency conductive material.

The circuit arrangement in the network 4 and the resulting impedance coupling of the first antenna element 3 to the further or the further antenna elements 8 can also consist of a stripline circuit (FIG. 2) or a combination of stripline circuits and concentrated blind elements. At a Realization of the network 4 with strip lines are then used according to the state of the art printed lines corresponding wave resistances. Such circuits allow particularly advantageous and inexpensive the targeted setting of the required currents on the antenna elements 3 and 8 according to the amount and phase and the adaptation to the waves resistance of the feed cable. Another and particularly great advantage of the stripline circuit is the precisely reproducible arrangement, which is particularly suitable for large-scale production of such antenna arrangements according to the invention.

In each of the cases discussed, the resulting radiation characteristic results with respect to the antenna connection point 6, taking into account the radiation coupling of the antenna elements and their feeding and the radiation coupling to the body of the vehicle. The network 4 is thus designed so that there is a defined and fixed phase and amplitude relationship between the base point feed currents of the antenna elements 3 and 8. The horizontal diagram of the antenna arrangement according to the invention is influenced in the desired advantageous manner via this defined phase and amplitude relationship and is improved compared to the radiation characteristics of each of the individual antennas.

The example in FIG. 2 shows a similar arrangement with regard to the antenna elements. In contrast to FIG. 1, the network 4 is attached to the top of the roof with the advantage that only a single breakthrough through the roof skin is required. This arrangement lends itself particularly well to networks 4 which use stripline circuits, since these are very flat by design and can therefore be attached flat to the outside of the body. Fig. 2 shows a vertical stripline circuit only for easier illustration. In the arrangement according to FIG. 1, as many breakthroughs through the sheet metal of the body are required as there are antenna elements 3 and 8 fed via the network, which is certainly a disadvantage from the vehicle-specific point of view. On the other hand, installation in the interior is cheaper in that the functionality of the network only has to be ensured under the climatic conditions of the interior.

In a particularly simple embodiment of a group antenna according to the invention, the network 4 can also be designed in accordance with FIG. 3a so that the coupling of the first antenna element 3 and the further antenna element (s) 8 takes place exclusively via field coupling between the radiators, that is to say due to the radiation coupling of the antenna elements 3 and 8. In this case, only the first antenna element 3 is connected to the antenna connection point 6 on the network 4 via a high-frequency line. The radiation characteristic of the overall arrangement, however, will essentially formed by the entirety of the radiation-coupled antenna elements 3 and 8, including the effect of the vehicle body.

In order to achieve the current and amount required for an optimal horizontal diagram in each of the further antenna elements 8 with pure radiation coupling, e.g. the length of the further antenna element 8 is chosen appropriately. For a good

Radiation coupling requires resonance lengths. For example, an antenna element 8 can advantageously be chosen to be approximately 1/4 wavelength long if it is connected to the body in a high-frequency conductive manner at its lower end. The phase position is then suitably set with the exact length around the λ / 4 resonance. Shorter or longer further antenna elements 8 can also be used if the base point of the element is connected to a corresponding blind element (FIG. 3a). As is known, for antenna elements that are shorter than λ / 4, an inductance at the base point is required; for longer antenna elements, a capacitance is correspondingly necessary.

In this way, in the case of antennas according to the invention, at least one further antenna element 8, which is coupled to the first antenna element 3, can be a considerable one

Improvement of the radiation characteristics can be effected in the horizontal. The horizontal directional characteristic of each of the antenna elements 3 and 8 therefore exhibits undesirable deviations from the ideal radiation characteristic even in the case of group antennas according to the invention. In addition, the individual diagrams of the individual antenna elements are not the same as each other, because the shading by the body and the coupling to it are not the same because of the different mounting points. The radiation coupling between the antenna elements is essentially determined by their length and their distance from one another.

The desired improvement in the radiation characteristic in antennas according to the invention can therefore also be achieved by exclusive radiation coupling between the first antenna element 3 and further antenna elements 8. The required high degree of coupling, however, requires a not too large distance 9 between the individual radiators. A value of approximately λ / 4 can be set as the upper limit for this distance 9, the current on the antenna element 8 or, respectively, by suitable choice of the length of the antenna element 8 or antenna elements 8 and / or by connection to a blind element at the base point. can be set on the antenna elements 8 according to the prior art. Figure 3a shows an example of this. In such cases, the network 4 then only serves to feed the first antenna element 3, for example to adapt to the characteristic impedance of the connecting cable 28 to the radio, which is connected to the antenna connection point 6. Here, as is generally the case with radio systems, a sufficiently low standing wave ratio is required at the antenna connection point 6 of the group antenna for the respective useful frequency band, as is known from RF interfaces of other radio systems.

Basically, it can be seen that when the antenna elements are fed via the network and if the distances between the radiators are too great, the radiation directional diagrams tend to form strong indents. In the case of preferred antenna arrangements, the maximum distance between two antenna elements is therefore chosen to be no greater than about a free space wavelength, also in the interest of a simple design of the network 4.

The phase and amplitude states of the electrical quantities on the antenna elements that are required to achieve the object of the invention are thus essentially dependent on their shape and position with respect to one another and on the radiation coupling to the conductive vehicle body. There are thus a multitude of favorable arrangements of antenna groups according to the invention for each vehicle, which each result in advantageous radiation properties by optimizing the network 4 specifically for this purpose. The radiator shapes used for this can be freely selected within certain limits.

Instead of simple rod-shaped antenna elements, e.g. antenna elements with a capacitive roof load can be used and in the interest of further shortening e.g. can be connected with dummy elements, which are usually designed in the form of an extension coil (FIG. 4). Even with longer antenna elements with a length between λ / 4 and λ / 2, the current assignments on the antenna elements can be influenced in a suitable manner. In the example of FIG. 4 of a radio antenna arrangement according to the invention, the antenna elements, which are minimized in length by the use of a roof capacitance and an extension coil, are accommodated under a plastic radome 32. FIG. 4 also shows a particularly advantageous feed for the antenna connection point 6 via the feed line, which does not require a breakthrough through the roof skin. For this purpose, a very thin coaxial cable or a flexible triplate strip line circuit is led through the area of the adhesive bead of the rear window and is thus sealed by the window adhesive.

Because of the increased losses of thin cables, in the sense of a high efficiency of a corresponding antenna arrangement according to the invention, the section with a small cross section should be as short as possible. In the example in FIG. 4, this section is relatively long since the radio antenna arrangement is arranged on the vehicle roof and therefore a comparatively long distance has to be bridged along the sheet metal part which is bent downwards. 5 shows a more advantageous antenna arrangement according to the invention, in which the first antenna element 3 is attached to this inclined surface, which consequently forms the first partial surface 11, and approximately normal to it. The other radiator 8 is only coupled by the radiation field and sits on the further partial surface 12, which is formed by the approximately horizontal surface of the roof.

In the example in FIG. 6 of a radio antenna arrangement according to the invention, the first antenna element 3 is attached in the upper region of the rear window and is capacitively fed in a known manner through the window through the network 4. The first partial surface 11 here forms the pane, the inhomogeneity arises at the transition to the sheet metal of the body at the upper edge of the pane. If the sheet metal strip is wide above the pane up to the roof edge, which is usually approximately evenly but spatially arranged in the extension of the pane, there is a further partial area 12b corresponding to this sheet metal strip. The roof area then forms a further partial area 12a.

With this arrangement and wide sheet metal strip, there would then be too great a distance between the further antenna element 8a on the roof, so that the radiation coupling may be too low. In such cases, it is advisable for radio antenna arrangements according to the invention to have a further antenna element 8b on the further partial surface 12b, e.g. essentially normal to her to attach. In this way, the distance between two antenna elements 8 is approximately halved, with the advantage of a significantly increased coupling. The shading to the front, which is provided when the first radiator 3 is only present, can be significantly reduced according to the invention by this chain of two further antenna elements 8. Further embodiments of radio antenna arrangements according to the invention result if all antenna elements are mounted on or in the vehicle window, as shown in FIGS. 9 to 13.

The disc 1 is inclined at an angle 26 to the horizontal. In today's vehicles, this angle is between approximately 10 degrees (sports cars) and approximately 80 degrees (station wagons). At not too large angles 26, despite the inclination of the disc and also at normal to

Antenna elements mounted on the pane surface (examples of FIGS. 7 and 8), the preferably radiated polarization vertically, since the essentially horizontally oriented sheet metal surfaces of the vehicle, namely the roof and the trunk lid, guide the shaft in such a way that essentially a vertical electrical field component runs towards the far field. The alignment of the E vector is therefore not necessarily identical to that

Location of the antenna elements in the room, but is determined by the surface of the body.

However, the shadowing to the front and thus the impairment of the radiation distribution in the horizontal increases when the pane is steeper. In antenna arrangements according to the invention, this can be counteracted by a larger number of radiators, since the possibilities of shaping the diagram then become greater. Particularly good radiation properties with one or two further antenna elements 8 in the sense of achieving the object of the invention are achieved in vehicles in which the angle of inclination 26 of the window pane with respect to the horizontal is not greater than approximately 60 degrees. Basically, measurements show that the greater the angle of inclination 26 of the window pane 1, the more advantageous it is to arrange the radiators near the upper edge of the window pane.

7 shows an antenna arrangement according to the invention, in which the first antenna element 3 and one or more further antenna elements 8 are attached to the vehicle window 1. The antenna elements are all arranged substantially normal to the surface of the pane and are fed through the pane from below. The network 4 is attached inside the pane. The inhomogeneity of the first partial surface 11, which represents the window surface, is given by its upper edge and the transition to the metallic body. In the example shown, the connection between the antenna elements 3 and 8 and the network 4 takes place via a hole through the glass. In order to avoid such an unfavorable bore, capacitive coupling through the disk is also possible, as is shown in FIG. 8 for another antenna arrangement according to the invention.

A similar antenna arrangement according to the invention is shown in FIG. 8, in which the network 4 is mounted on the outside of the pane. The coupling of the high-frequency signal through the disk takes place in this example only at a single point and therefore particularly simply and advantageously capacitively, the antenna connection point 6 is given by the inner coupling surface and by the surrounding mass. In this case, too, the capacitive connection can be included in the network 4 in a technologically cost-effective manner if it is constructed as a stripline circuit.

Antenna arrangements as shown in FIG. 7 have the disadvantage that some of the field lines that begin on the antenna elements run through the interior of the vehicle and lead to undesired high field strengths there. At the same time, this results in an increased inhomogeneity for the first partial surface 11 and an increased asymmetry, which results in an increased shadowing of the radiation to the front.

A temporally invariant antenna counterweight is furthermore advantageous for the antenna array according to the invention for each antenna element. This can be designed as a high-frequency conductive surface 29 on the window pane, as shown in FIG. In the interest of the transparency of this area, it is advantageously designed as a radiation-shaped structure which consists of wire-shaped conductors radially extending from the network 4 (FIG. 9). The network 4 itself is advantageously equipped with a conductive outer surface, which in the center of the group antenna is part of the antenna. forms a counterweight for the antenna elements. The radiating conductors 20 are connected to this conductive outer surface at a high frequency. These beams can be supplemented by a ring 20 attached around the group antenna to a high-frequency conductive mesh network (Fig. 9). In the case of radio antennas on the rear window of vehicles, large field strengths naturally occur in the immediate vicinity of the transmitting antenna, which could endanger people in the passenger compartment. The formation of the antenna counterweight 29 as a high-frequency conductive surface has a very advantageous shielding effect against electromagnetic fields which otherwise penetrate into the passenger compartment. The requirement for a defined antenna counterweight can thus advantageously be combined with the requirement for a field weakening of the hazardous electromagnetic radiation.

There are often horizontally attached heating conductors on the rear window. Points of the same DC voltage potential can be galvanically connected to one another without influencing the heating current flow. By introducing connecting landings, the heating field can also be designed as a high-frequency, largely shielding surface and act as an extended antenna counterweight. In order to enable high-frequency currents between the ground surface in the group antenna via the heating field without influencing the heating currents, a direct current-impermeable, frequency-selective connection in the wire-shaped conductors is advantageous. Such frequency-selective connections are also necessary if parts of the antenna counterweight are used as antenna parts for other radio services, which are also attached to the window pane. An example of this is given for antennas, which e.g. act as an AM-FM antenna. Capacitive structures are mainly used as frequency-selective connecting elements. A coplanar line structure of approximately λ / 4 length for the radio frequency is also very advantageous.

10a and b show an antenna arrangement according to the invention, in which the first antenna element 3 is oriented essentially normal to the pane surface. The further antenna elements 8 are arranged in the plane of the disk and e.g. printed on the inside. FIG. 10 a shows this arrangement as a section, FIG. 10 b shows a perspective view. 1 a and b show an antenna arrangement according to the invention (FIG. 1 a as a section,

11b as a perspective view), in which all antenna elements are arranged in the plane of the pane surface. This arrangement leads to satisfactory radiation characteristics if the pane is steep and the antenna elements 3 and 8 are therefore oriented essentially perpendicularly in space. Further and particularly advantageous embodiments of antenna arrangements according to the invention are shown in FIGS. 12 and 13. The advantage of these arrangements results from the fact thing that no components of the radio antenna arrangement are arranged on the outside of the vehicle body. For this purpose, a metallic cavity 31 is used, which is open towards the pane and which serves as a ground plane and as a rear shield for the antenna elements 3 and 8, respectively. In the example of FIG. 12, the antenna elements 3 and 8 are oriented essentially normal to the pane surface and normal to the rear of the cavity 31 and are fed by the network 4, which is advantageously attached to the rear of the cavity 31 facing the pane . The distance between the back of the cavity and the pane should be chosen as small as possible in the interest of a low construction height. Therefore, with such an antenna arrangement according to the invention, antenna elements with roof capacitance and extension coil are advantageously used, with which the length of the antenna elements can be made as short as possible. As a lower limit for the height of the cavity, a value of approximately 1/20 of the free space length is useful, since otherwise the transmission efficiency is known to be too low. Fig. 13 shows a similar arrangement, in which all antenna elements 3 and 8 are arranged in the plane of the disc.

The effect achieved with the invention is shown impressively in Figures 14a to 14d. In the horizontal diagrams shown in FIGS. 14a to 14c, the radiation properties of three antenna elements on the rear window of a sedan are shown in a triangular arrangement near the upper window edge.

Each of the diagrams has strong intolerable indentations or shading areas. Although the antenna elements used are each rotationally symmetrical, slender elements that are normally mounted to the window surface, the non-roundness of the diagrams results as a result of the radiation coupling to the conductive vehicle body. The directional diagram shown in FIG. 14d is achieved by connecting a suitable network 4, which feeds the antenna elements in the correct phase and amplitude and whose characteristics have been calculated by using mathematical optimization methods specifically for the antenna elements measured on the specific vehicle , which has much lower indents. If a group antenna according to the invention is intended for several radio systems, e.g. the D-

Network and the E-network are designed equally, the antenna elements can be designed so that they are functional in both frequency ranges. If the network 4 is designed in such a way that it ensures the required phase and amplitude conditions for the individual radiators in the two frequency ranges, the group antenna can be used in both frequency ranges. Another possibility is to use at least partially separate antenna elements for both frequency ranges. In order to ensure the best possible connection of the signals in the network 4, a certain amount of measurement is necessary to determine the antenna properties of the radiators on the vehicle. This is done by assigning a connection gate 27 to each antenna element at a defined interface. The wave parameters of this antenna element network can be determined with the aid of modern network analyzers. In addition, when a wave comes in from a certain direction, the excitations at the connection gates 27 can be measured in terms of magnitude and phase. With knowledge of the properties of the radiator network and its excitation by the incident wave at the various connection gates 27, a network 4 which is optimal for this can be designed with the aid of modern computer systems using suitable optimization strategies.

For the transmission case, the radio antenna should always work according to the object of the invention. In the case of reception, however, antenna diversity operation is generally preferable due to the Rayleigh scattering of the received waves. The network 4 can be designed so that with the help of switching diodes different signal combinations of the

Beam received individual signals are formed at the antenna connection point 6. With the aid of an antenna diversity device, the switching diodes can be controlled in such a way that the signal combination appears at every moment at the antenna connection point, which effects the best possible reception. The design of the radio antenna as a group antenna thus offers the advantage of being usable simultaneously as a diversity antenna.

Claims

claims

1. Radio antenna arrangement for vehicles for radio connections with terrestrial radio stations in the frequency range of the decimeter wave range, in particular above 600 MHz, with a first antenna element with the character of an electrical monopole or dipole with an essentially vertical polarization component, each of which consists of a first partial area essentially homogeneous material of a vehicle body is attached, whose azimuthal omnidirectional characteristic is substantially disturbed by the surrounding vehicle body, characterized in that in addition to the first antenna element (3) at least one further antenna element (8) with a monopole or dipole character is available and each further antenna element is attached either to the first (11) or a further partial surface (12) and the antenna elements form a group antenna with respect to the antenna connection point (6), at least one of which is fed and the other o which the others are either fed or excited by radiation and the group antenna is designed in such a way that suitable relationships between the currents on the individual antenna elements are set in terms of magnitude and phase and the clear distance (9) between two adjacent antenna elements is chosen smaller than a free space wavelength.

2. Radio antenna arrangement according to claim 1, characterized in that all antenna elements are dimensioned such that they do not protrude beyond the vehicle body over a vertical distance which is appreciably smaller than half a free space wavelength.

3. Radio antenna arrangement according to claim 2, characterized in that the antenna element (3) and the further antenna element (8) or the further antenna elements (8) in the vicinity of the boundary line (13) or the boundary lines of two or more aufeinandertref¬ fender first (11) and adjoining partial surfaces (12) of the vehicle body (5) are attached.

. Radio antenna arrangement according to claim 3, characterized in that the boundary line (13) is formed by one of the roof edges.

5. Radio antenna arrangement according to claim 4, characterized in that the first partial surface (11) is formed by the roof surface of the vehicle.

6. Radio antenna arrangement according to claim 5, characterized in that the first antenna element (3) and the one or more antenna elements (8) are all mounted on the same first partial surface (11) (FIGS. 1, 2, 3 a, 3b, 4).

7. Radio antenna arrangement according to claim 5, characterized in that the first antenna element (3) on the first partial surface (11) and the further antenna element (8) or at least one of the further antenna elements (8) on an adjacent partial surface (12) ¬ is brought (Fig.5).

8. Radio antenna arrangement according to one of claims 1 to 3, characterized in that a network (4) is present and the first (3) and at least one further antenna element (8) via the network (4) fed and with the antenna connection point ( 6) are connected at high frequencies and the network is designed such that the required currents are adjusted according to amount and phase on the first antenna element (3) and on the further antenna elements (8) fed by the network (4) (FIG .1,2,4).

9. Radio antenna arrangement according to one of claims 1 to 3, characterized in that only the first antenna element (3) is connected via the network (4) to the antenna connection point (6) and the further antenna elements (8) are excited by radiation, such that the required currents according to amount and phase on the further antenna element or the further antenna elements (8) by radiation coupling and by a suitable choice of the length of the further antenna elements (8) and / or by a suitable circuit at the base are set (Fig.3a, 3b, 5,6).

10. Radio antenna arrangement according to one of claims 8 or 9, characterized in that the first partial surface (11) through the vehicle rear window (1) is formed ge and that the first antenna element (3) and all other antenna elements (8) on this Vehicle rear window (1) are attached (Fig. 7,8,9, 10a, 10b, 11a, 11b).

11. A radio antenna arrangement as claimed in claim 10, characterized in that the first antenna element (3) and all further antenna elements (8) are arranged substantially normal to the pane surface (1) and on the outside of the pane (FIGS. 7, 8, 9).

12. Radio antenna arrangement according to claim 11, characterized in that the network (4) on the inside of the vehicle window (1) is brought an¬ (Fig.7).

13. Radio antenna arrangement according to claim 11, characterized in that the network (4) on the outside of the vehicle window (1) is brought an¬ (Fig.8).

14. Radio antenna arrangement according to one of claims 11, 12 or 13, characterized in that on the disc surface inside or outside a largely impermeable to the frequencies of the radio service flat screen (29) for reducing the electromagnetic fields in the vehicle interior evaporated or printed which is optically transparent (Fig. 8).

15. A radio antenna arrangement according to one of claims 11, 12 or 13, characterized in that the flat screen (29), which is largely impervious to the frequencies of the radio service, consists of radial and concentric printed conductors (20) (FIG. 9 ).

16. Radio antenna arrangement according to one of claims 14 or 15, characterized in that in addition to structures of the flat screen (29) other antenna structures (30), e.g. for disk antennas for other radio services, are mounted on the disk and the flat screen (29), which is largely impervious to the frequencies of the radio service in the decimeter wave range, also partially consists of these antenna structures (30) and these antenna structures (30) for the frequencies of the radio service in the decimeter wave range of the radio antenna arrangement are selectively coupled to the structures of the flat screen (29) with high frequency and low impedance.

17. Radio antenna arrangement according to claim 10, characterized in that the first antenna element (3) is arranged substantially normal to the Schei¬ ben surface (1) on the disc and the or the other antenna elements (8) along the top of the disc or between the is attached to both panes of a laminated glass pane (Fig.lOa, 10b).

18. A radio antenna arrangement according to claim 10, characterized in that both the first antenna element (3) and the one or more antenna elements (8) are attached along the upper pane or between the two panes of a laminated glass pane (FIG. 13). .

19. Radio antenna arrangement according to claim 18, characterized in that in the region of the structures for the first antenna element (3) and for or for the further antenna elements (8) a cavity (31) with an electrically conductive edge, the opening to the glass ¬ pane has and placed on the inside of the pane and its edge is high-frequency conductive with the metallic body (5) and optionally also with the flat screen (29) on the pane (1) (Fig. 12, 13).

20. A radio antenna arrangement according to claim 19, characterized in that between the conductive rear wall of the cavity (31) and the glass pane are designed as monopoles antenna elements are attached, the rear wall of the cavity with the network (4) possibly attached to it Stripline technology serves as an electrical counterweight (Fig. 12).

21. Radio antenna arrangement according to claim 20, characterized in that the monopolies are designed to shorten their design as capacitively loaded and optionally provided with extension coils antenna elements (Fig. 12).

22. Radio antenna arrangement according to one of claims 19, 20 or 21, characterized in that the cavity (31) has a clear height of at least 1/20 of the free space wavelength.

23. Radio antenna arrangement according to one of claims 1 to 3, characterized in that the antenna elements are mounted on the horizontal of a fender and the boundary line (13) is formed by one of the fender edges.

24. Radio antenna arrangement according to one of claims 1 to 23, characterized in that the radio antenna arrangement is designed for a plurality of radio systems in the decimeter wave range with relatively narrow-band frequency ranges of different frequencies and the antenna elements (3) or (8 ) and possibly the network (4) and the other frequency-dependent parts of the radio antenna arrangement are designed to be multi-frequency.

25. A radio antenna arrangement according to claim 24, characterized in that separate or only separate antenna elements (3) or (8) are used to cover the different frequency ranges.

26. Radio antenna arrangement according to one of claims 1 to 25, characterized in that connection gates are formed in the antenna elements (3) or (8), the complex overall matrix of which describes the relationships between the electrical quantities at these connection gates (27 ) of the network (4) is determined in terms of amount and phase and its excitation, for example in the case of reception, is detected by a horizontally incident, vertically polarized reception wave for all azimuthal angles according to magnitude and phase to one another, so that the parameters for describing the electrical quantities are present the connection gates (27), based on the incident receiving wave, are known for all azimuth angles and favorable amplitude and phase values for driving the matrix are determined by variation calculation in the sense of the solution of the object of the invention and these values are connected to the network ( 4) and / or if necessary by wiring the gates with reactors (14) in the Group antenna are set.

27. Radio antenna arrangement according to one of claims 1 to 26, characterized in that the network (4) is designed such that with the help of electronic switches, which are controlled by an antenna diversity device, the signals of the antenna elements when received ( 3) and (8) are used in different combinations for the formation of antenna diversity signals for forwarding to the receiver.