FIELD OF THE INVENTION

The present invention relates to an omnidirectional horizontally polarized antenna which offers high current protection and a dual-slant omnidirectional antenna.

BACKGROUND OF THE INVENTION

Train application antennas with high current protection and an omnidirectional ra diation pattern are known from the prior art. An example of such solution was given in W02007048258A1 . An alternative solution was also shown in US20170207539A1 . All those antennas have one or more radiating elements with vertical polarization and in some cases the system is supplemented with a GPS re ceiving antenna.

It is well-known that using dual-polarized radiators can bring significant benefit to MIMO systems. Two classical solutions are to use a combination of vertically and horizontally polarized radiators or to use a dual-slant configuration. It is state of the art to have dual polarized directional radiators and different solutions for these ex ist. When it comes to dual polarized omnidirectional radiators, it is easy only to have vertically polarized omnidirectional radiators since any monopole, which due to a rotational symmetry is omnidirectional, can be used. However, horizontal or slant polarized radiators are problematic if one wants them to be omnidirectional and 5 broadband simultaneously. Typical horizontally polarized radiators, such as e.g. loop antennas, are narrowband so a standard solution to provide omnidirectional radiation with horizontal polarization is to use several directional antennas with each of them covering one sector. Such solutions are used in e.g. US9209526B2 where a set of four broadband monopoles are placed on a printed circuit board0 (PCB) which is placed above a monopole radiator that results in a dual-polarized antenna. The monopole can be also surrounded with dipoles like in the EP2668677B1 where a monopole radiator is surrounded by four separate dipole radiators. Finally, in US9748666B2 a monopole is placed on a bended sheet metal construction which is formed into four Vivaldi antennas. Such configuration used5 in train application is presented in US9496624B2. Another, narrowband solution with horizontal dipoles and some vertical monopole is in US20160072196A1

A dual vertical/horizontal polarization can be also achieved using only printed radi ators. Such a solution is presented is US8860629B2. Another solution with mostly printed elements is in US7936314B2. Another solution is in US7310066B1 . In this0 solution the radiator is only a PCB which is placed horizontally but there are some vertical parts to provide second polarization. For a dual-slant configuration, the standard solution is also to use several sets of two crossed antennas, each covering a sector. Also dual-polarized patch antennas can be used for directional dual-slant antennas. Dual slant directional radiator crossed pairs are a standard solution in base station antennas. Such solution is shown e.g. in US20170244176A1 . Similar solution is in US9887708B2 and an other example is in US20170358842A1 .

In case of using several antennas, each covering a sector, a signal dividing/combin ing element is required. Since for each polarization a separate signal dividing/com bining network is required, this solution is complicated to design and manufacture. Another attempt, which is very common in train applications is to take two omni directional antennas and mount them on two 45 degrees inclined surfaces. How ever, the drawback of this attempt is that the real dual slant polarization is only along the top edge of the surface used to mount the antennas. In other directions the polarization is either vertical (perpendicular direction to the top edge) or ellip- tical with domination of vertical component. Other attempts which are known from literature, are based on single slant omnidirectional antennas. The drawback of all solutions is that they provide only a single slant polarization so a second radiator would be required to provide dual-slant polarization. Using a second radiator usu ally requires more space, makes the design more complicated, and the second ra- diator might obstruct field of view of the first radiator in a negative manner.

SUMMARY OF THE INVENTION Roof-top antennas especially for trains must provide so-called high current protec tion. This means that in case of a broken catenary line which e.g. touches the an tenna, the antenna must be able to short the current to the antenna ground (usu ally the mounting surface) for at least 1 25 ms and during this time the voltage on the antenna connector must remain below 50V. It is assumed that after less than 125 ms the protection circuits will kick-in and the catenary line will be de-ener- gized. This requires that the radiator is appropriately grounded and has sufficient cross-section as well as ground contact which will be able to carry current up to 40kA. Due to the mobile character of roof-top train applications, in most applications an omnidirectional radiation pattern is required to provide the coverage no matter what is the mutual position of the train and base station.

The present disclosure addresses two main aspects. The first one is how to provide a horizontally polarized omnidirectional radiator with high current protection for train applications. In a preferred variation, this radiator is suitable to be used with another, vertically polarized, radiator in order to provide dual polarized train roof top antenna but could be used alone as well. Up to now, no horizontally polarized radiator with high current protection is known from the prior art. All radiators men tioned above in the section background of the invention, are either not fully grounded or made by using materials like PCB or relatively thin metal which are inappropriate for this application. These materials cannot be used to provide high current protection, where all the exposed parts must be grounded and made out of electrically conductive material (usually metal) that is thick enough to guide in cer tain variations up to 40kA of current for at last 1 25 milliseconds. Therefore, the present disclosure addresses as a first aspect the problem of providing a horizon tally polarized omnidirectional radiator which offers high current protection. De- pending on the field of application, this radiator can be used together with a verti cally polarized omnidirectional radiator with high current protection to provide a dual-polarized antenna with high current protection. If appropriate, the horizon tally polarized radiator can be used alone. Furthermore, the horizontally polarized radiator can be used to cover only one or several sectors. As a second aspect the present disclosure provides a dual slant polarized antenna arrangement with e.g. omnidirectional radiation. While there are numerous exam ples of dual polarized vertical-horizontal radiator antennas, there are no omnidi rectional dual slant antennas known so far. Since most of the base station antennas use dual slant polarization diversity, a dual slant antenna would load both channels of a MIMO receiver equally and provide polarization matching which is attractive to increase the throughput. This aspect is addressed by adopting a vertical-horizon tal dual-polarized antenna pair into dual-slant configuration. It is important to note that the disclosed approach can be used with any pair of vertically/horizontally po larized radiators. However, it can be also used with the antenna proposed above which would result in a dual-slant omnidirectional antenna for train applications, i.e. with high current protection. On top of this, such approach could be applied to directional radiators as well. The proposed approach can be used to obtain dual- slant polarized directional radiators. Therefore, the herein after in more detail pre sented dual slant polarized antenna arrangement should thus be considered a sep arate inventive concept, which may be made subject of one or several divisional patent applications. In a variation of the first aspect, a set of Vivaldi radiators which are made of thick metal is provided in order to provide simultaneously horizontal polarization, omni directional patterns, and high current protection. The horizontal polarization with omnidirectional patterns can e.g. be achieved by 3 to 6 Vivaldi antennas arranged in a horizontal plane, evenly distributed around an antenna center point and feed- ing them by a power divider and thereto interconnected PCB stubs as described hereinafter in more detail. The high current protection is obtained by a radiating element (radiator) which is made of a sufficiently thick plate of conductive material to provide enough volume for conducting high current. The radiating element is placed on one or several sufficiently massive legs, made of a conductive material, which provide distance to a ground plate that is required for efficient horizontally polarized radiation and are able to carry the high current to the ground. A feeding cable is preferably guided behind or through one of the legs e.g. in order to protect it from the contact with the catenary line. If present, a power divider PCB is prefer ably placed vertically below the radiator such that it is better protected by the mas- sive radiator arranged vertically above. Good results can be achieved, when the feeding cable is guided through a trench in the top of the radiator so it is not ex posed for a contact with the catenary line. Good results can be achieved when a right angle connector, similar to the one proposed in patent application US20170207539A1, is used in order to connect feeding cable and Vivaldi PCB without exposing any "hot" part (e.g. cable or PCB connection interface) to a po tential contact with the catenary line. In a preferred variation, the antenna assembly comprises an omnidirectional hori zontally polarized Vivaldi-type first antenna comprising an omnidirectional hori zontally polarized first radiator, extending (in a mounted position) in an essentially horizontal plane, having a flower-shaped outline with several leaves separated from each other by several tapered slots which are arranged distributed around a radiator center. Depending on the field of application and the characteristics to be achieved, the number and the arrangement of the tapered slots may vary. E.g. the tapered slots can be designed to provide an oriented characteristic. The tapered slots are preferably extending horizontally with respect to the radiator center in an outward direction. Vertically the tapered slots are usually extending perpendicular to the essentially horizontal plane by a certain thickness. A base plate is usually ar ranged in general parallel at a certain distance below the radiator which is galvani cally interconnected to the radiator by at least one post. Good results can be achieved, when the at least one post is arranged at a leave to which it is e.g. at tached by a bolt. The at least one post and the radiator can be made from one piece. A power divider and (per tapered slot) a feeding stub are preferably arranged be tween the base plate and the first radiator. Depending on the field of application and the design, they can be arranged above the radiator. They are interconnected electromagnetically to the first radiator for coupling radio signals into the first radi ator. The first radiator is preferably made at least partially from solid metal, such that it can withstand high current easily as described herein above. Good results can be achieved, when the first radiator is essentially plate-shaped. For omnidirec- tional radiation, the several tapered slots are preferably arranged evenly distributed around the radiator center. The tapered slots are preferably arranged in radial out ward directions with respect to the radiator center. Depending on the field of ap plication, other arrangements are possible. In a preferred variation, the power di vider and the feeding stubs are arranged as at least one electrical conductor on a printed circuit board attached to the bottom of the first radiator. In a preferred var iation, the power divider has a star like design starting from the center of the radi ator and comprising several branches. The feeding stubs are curved in a forward direction from an outer end of each branch and extending across a tapered slot arranged in a coupling distance from each feeding stub and each tapered slot end. The at least one post may be galvanically interconnected to the first radiator suita ble to receive a high current from a catenary line of a railway track as mentioned herein above. A feeding cable may extend at least partially through the first radia tor. Thereby a compact and robust design with a low overall height may be achieved. The feeding cable can at least partially be arranged in a trench of the first radiator. In a preferred variation, the feeding cable extends at least partially through the at least one post. The feeding cable can be interconnected to the power divider by a connector arranged at least partially in the first radiator. Usually, the connector is arranged in the radiator center. The center conductor of the connector or the center conductor of the feeding cable is preferably soldered or electrically connected by other means to the power divider.

From the prior art no omnidirectional horizontally polarized antennas with radiator high current protection are known. Therefore, the present disclosure is a preferred proposal for train applications if horizontal polarization is desired. By using several sub-radiators, good omnidirectional behavior is achieved while a certain thickness of the cross-sections, which is required for high current protection, is obtained.

With respect to the second aspect of the disclosure, a slant polarization can be gen erated by adding a vertically polarized radiation to a horizontally polarized radia- tion. If the amplitudes of V/H polarizations are equal, a 45-degree slant polariza tion is generated. An orthogonal slant polarization can be generated by applying a 180-degree phase shift to the horizontally polarized component. Thus if one can have a system with two radiators, one with vertical polarization and one with hori zontal polarization, both having similar patterns and gain, and could feed them with signals in which one is divided equally between both radiators and in-phase and a second is divided equally between both radiators but with a horizontal com ponent out of phase ( 180-degree phase difference), it is possible to generate dual slant, orthogonal polarization. This is achieved by a microwave device comprising a first input and a second input and a first output and a second output. The micro wave device providing the following properties: - The micro wave device is splitting between both outputs a first signal re ceived by the first input into two signals exiting at the first and the second output which are equal and in-phase (0-degree phase difference) with re spect to each other. - The micro wave device is splitting between both outputs a second signal re ceived by the second input into two signals exiting at the first and the second output which are equal to each other but in counter-phase (i.e. out-of- phase, 180 degrees phase difference).

- The inputs are isolated from each other. - A microwave device is reciprocal so the signals which are exciting the first and second signal outputs are added in-phase at the first signal input and in counter-phase at the second signal input.

Such properties can be achieved by a so-called rat-race hybrid coupler or a magic- tee hybrid coupler. The rat-race hybrid couplers are parts which can be realized in microstrip or stripline technology while magic-tee hybrid couplers are realized in waveguide technology. Both types of couplers are well-known state-of-the-art mi crowave devices and are available as off-shelf components or one can easily design own realizations. In a preferred variation a dual polarized vertical/horizontal omni directional antenna arrangement is interconnected to such a hybrid coupler. In this way, one hybrid input will generate one slant polarization and the second input will generate an orthogonal slant polarization. This approach can help to solve several problems: If V/H polarized radiators are omnidirectional, a dual-slant omnidirec tional antenna can be build which is not possible in any other way then using two single-slant polarized omnidirectional antennas with different senses one next to another. If V/H polarized radiators are directional, this is a way to obtain a dual slant directional antenna. The advantage of this solution, with respect to simply us ing two inclined directional radiators, is that in case of a presence of the conductive ground plane, which is attenuating the horizontal component, one can place the horizontally-polarized radiator on top of the vertically-polarized one which will in- crease the distance of the horizontally polarized radiator to the ground plane (see Figure 6 below. In this way, the horizontal component of the slant polarization will be less attenuated by the presence of the ground plane so the slant polarization purity will be better. The antenna can be easily re-configured to a vertical/horizon tal radiator configuration. It is sufficient to just remove the hybrid. A very simple method was used to obtain dual-slant omnidirectional characteristics but the effect is surprisingly good and broadband. The currently existing slant om nidirectional antennas are all single-slant and in most cases have complicated ge ometry. By using a standard component, e.g. rat-race hybrid coupler or magic-tee hybrid coupler, which can be taken as off-shelf components, one can obtain both omnidirectional and dual-slant patterns. According to the best knowledge, such a solution (both omnidirectional and dual-slant) was not yet proposed in the litera- ture. Moreover, it can be applied to the antenna which consists of a standard ver tically polarized radiator with high current protection and a horizontally-polarized radiator as proposed above, so a high current protected omnidirectional dual-slant antenna is obtained. The second aspect of the disclosure can also be applied to directional antennas. The benefit of the proposed solution is that it allows to place the source of the horizontal component of the slant radiation further from a ground plane so better perfor mance will be achieved than for standard solutions when just two radiators are crossed. The disclosure can e.g. be used in the following fields of application: By the first aspect of the disclosure, a high current protected roof-top antenna for trains or trams with dual polarization and omnidirectional patterns can be achieved. In com bination with the second aspect of the disclosure it allows to have dual-slant omni directional antennas. Therefore, a dual-slant, omnidirectional, high current pro- tected antenna for train applications can be obtained. The second aspect of the disclosure offers a solution which can be used in combination with any pair of ver tical/horizontal polarized radiators with omnidirectional characteristics to obtain a dual-slant polarized omnidirectional radiation. This can be e.g. used for example in simple base station antennas for small cells or antennas for in-building coverage. The second aspect of the disclosure can be applied to directional radiators. Using vertical and horizontal-polarized radiators instead of two crossed radiators can be beneficial e.g. in train applications where a ground plane is present and strongly attenuates the horizontal component so it is desired to increase the distance be tween horizontal component and ground plane as much as possible. Therefore, this is a practical way to obtain a low-profile directional double slant antenna to be placed over conductive surfaces, e.g. a train roof. If appropriate the leafs of the first radiator may comprise a secondary slot arranged with respect to the center of the first radiator in a radial direction. This may improve the overall matching of the horizontally polarized radiator. For better performance, the horizontally polarized first antenna may comprise an impedance transformer. The impedance transformer can e.g. be designed as so-called "Klopfenstein trans- former". Preferably, the impedance transformer can be realized as PCB line which is printed on a PCB arranged inside a depression in the main radiator. The depres sion can protect the transformer from high current in case a catenary line will fall down on the radiator while PCB technology allows simple fabrication.

A GPS antenna module can form part of the antenna assembly according to the disclosure. Good results are achieved when the GPS antenna module is arranged on top of the first radiator of the first antenna. The GPS antenna module can be arranged in a depression of the first radiator. The depression of the first radiator can be configured to protect the GPS antenna module from the high current in case a catenary line falls on the radiator. In a preferred variation, the vertically polarized second radiator of the second an tenna is arranged at least partially within the ground plot (when seen from vertically above) of the first radiator of the first antenna. A very space saving and shallow arrangement can be achieved, when the first radiator comprises a recess, e.g. in the form of a lateral indentation, in which the second radiator is arranged at least partially within the ground plot of the first radiator. Preferably, the recess is de- signed such that the second radiator is spaced a distance apart from the first radi ator by a gap. The gap preferably has an essentially uniform thickness. Good results can be obtained when no post supports the respective leaf with the recess in order not to influence the vertically polarized radiator RF performance. The horizontally polarized first antenna may comprise an impedance transformer. The impedance transformer can designed as a Klopfenstein transformer. The impedance trans former may be arranged inside a depression of the first radiator where it is pro tected against high current.

It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an over- view or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illus trate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed. BRIEF DESCRIPTION OF THE DRAWINGS

The herein described invention will be more fully understood from the detailed de scription given herein below and the accompanying drawings which should not be considered limiting to the invention described in the appended claims. The draw- ings are showing:

Fig. 1 a first antenna in a perspective view;

Fig. 2 a first variation of an antenna assembly comprising a first and a second antenna in a perspective view and partially sectionized;

Fig. 3 the first antenna in an exploded view from above; Fig. 4 the first antenna in an exploded view from below;

Fig. 5 a second variation of an antenna assembly in a perspective view;

Fig. 6 a third variation of an antenna assembly in a perspective view;

Fig. 7 schematically a hybrid coupler device;

Fig. 8 a fourth variation of an antenna assembly in a perspective view; Fig. 9 a fifth variation of an antenna assembly in a perspective view.

Fig. 10 A detailed view of the fourth variation of Fig. 8 DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many dif- ferent forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

Figure 1 shows a variation of an omnidirectional horizontally polarized Vivaldi-type first antenna 5 in a perspective view. The hidden lines are shown as dashed lines. Figure 2 shows a first variation of an antenna assembly 1 comprising a first antenna according to Figure 1 . Figure 3 shows the first antenna 5 according to Figure 1 in an exploded isometric view from above. Figure 4 shows the first antenna 5 accord ing to Figure 1 in an exploded isometric view from below. Figure 5 shows a second variation of an antenna assembly 1 comprising a first antenna according to Figure 1 . Figure 6 shows a third variation of an antenna assembly 1 comprising a first an tenna according to Figure 1 . Figure 7 schematically shows a microwave device 24 as used in connection with the second aspect of the disclosure. Figure 8 shows a fourth variation of the antenna and Figure 9 shows a fifth variation of the antenna in a perspective manner from the front and above. Figure 10 shows a sectional view of the fourth variation of the antenna (Detail D). As e.g. visible in the perspective view of Figure 1 , an antenna assembly 1 according to a first aspect of the disclosure preferably comprises an omnidirectional horizon tally polarized Vivaldi-type first antenna 5. The first antenna 5 comprises an omni directional horizontally polarized first radiator 6 arranged extending in an essen- tially horizontal plane (xy-plane) having an essentially flower-shaped outline with several leaves 17 separated from each other by tapered slots 7 arranged distributed around a radiator center 8. The tapered slots 7 are extending horizontally with re spect to the radiator center 8 in an outward direction. Vertically (z-direction) the tapered slots 7 are extending perpendicular to the horizontal plane (xy-plane) by a certain thickness (t). A base plate 9 - which in Figure 1 is only schematically indi cated - is arranged in general parallel at a certain distance (b) below the radiator 6 and interconnected to the radiator 6 by at least one post 10. In the variation ac cording to Figure 1 , the at least one post 10 is arranged at a leaf 17 to which it is attached by a bolt 29. A power divider 1 1 and - per tapered slot 7 - a feeding stub 12 are arranged between the base plate 9 and the first radiator 6. They are elec- tromagnetically coupled to the first radiator 6 for coupling radio signals into the first radiator 6. The first radiator 6 is preferably made from solid metal, such that it can withstand high currents easily as described herein above. Good results can be achieved, when the first radiator 6 is essentially plate-shaped as shown in the draw- ings. If appropriate, the first radiator may comprise at least one recess and/or open ing on the inside as long as they do not have a negative impact on the performance. The several tapered slots 7 are preferably arranged evenly distributed around the radiator center 8. The tapered slots 7 are usually arranged in radial outward direc tion with respect to the radiator center 8. Depending on the field of application, other arrangements are possible as well. In a preferred variation, the power divider 1 1 and the feeding stubs 1 2 are arranged as at least one electrical conductor 19 on a printed circuit board 13 attached to the bottom of the first radiator 6. As e.g. visible in Figure 3 and Figure 4, the printed circuit board 13 may have a circular shape. Depending on the field of application, other designs are possible.

The at least one post 10 may be electrically galvanically interconnected to the first radiator 6 suitable to receive a high current from a catenary line of a railway track as mentioned herein above. A feeding cable 14 preferably extends at least partially through the first radiator 6. Thereby a compact and robust design with a low overall height may be achieved. The feeding cable 14 can at least partially be arranged in a trench 1 5 of the first radiator 6. In a preferred variation, the feeding cable 14 extends at least partially through the at least one post 10. The feeding cable 14 can be interconnected to the power divider 1 1 by a connector 16 arranged at least par tially in the first radiator 6. Preferably, the power divider 1 1 and the feeding stub 12 are arranged as at least one electrical conductor 19 on a printed circuit board 13. Especially with respect to the high current protection, the power divider 1 1 and the feeding stub 1 2 are preferably attached to the bottom of the first radiator 6. As shown in the drawings, the power divider 1 1 may have a star like design starting from the center 8 of the radiator 6 and comprising several branches 18. Good re sults can be achieved, when the feeding stubs 1 2 are curved in a forward direction from an outer end of each branch 18 and extending across a tapered slot 7 ar ranged in a coupling distance from each feeding stub 1 2 and each tapered slot 7 end. Usually, the connector 16 is arranged in the radiator center 8. For save con nectivity, the connector 16 can be interconnected to the electrical conductor 19 by soldering.

Good results can be achieved, when the first antenna 5 is combined with an omni directional vertically polarized second antenna 20 with at least one omnidirectional vertically polarized second radiator 21. Preferably, the second radiator 21 is ar ranged on the same base plate 9 as the first radiator 6. In a preferred variation, the second radiator 21 is cup-shaped. Depending on the field of application, different arrangements are possible: The second radiator 21 can be arranged vertically above and/or below and/or horizontally next to the first radiator 6. The base plate 9 may encompass a hollow space suitable to receive a cabling!. i ] for the several el ements of the antenna assembly 1 . To obtain a dual slant antenna, the first 5 and the second antenna 20 may be interconnected to each other by microwave device as schematically shown in Figure 7. Good results can be achieved by a microwave device 24 in form of a rat-race hybrid coupler and/or a magic-tee hybrid coupler.

In the fourth variation according to Figure 8 and Figure 10 and fifth variation ac cording to Figure 9 of the antenna assembly 1 both horizontally as well as vertically polarized first and second antennas 5, 20 are integrated. In comparison to the var iations described above, the first antennas 5 are considerably bigger to also cover low frequency bands, such as e.g. 5G 700 MHZ band. The housings 22 are shown in an unfolded state above the base plate 9. In Figure 8 the first radiator 6, the printed circuit board 13, as well as certain posts 10 in the front of the drawing are shown in a section view to offer better visibility on the structure underneath. The feeding stub 12 which is normally arranged underneath the printer circuit board 13 is shown uncut.

Each first radiator 6 is preferably fed using an electric conductor 19 in the form of a microstrip line 19, which is printed on the printed circuit board 13 which is placed on the bottom side of the Vivaldi radiator 6. The microstrip lines 19 are fed using a power divider/combiner 1 1 as mentioned herein above in more detail. The power divider 1 1 input is connected to a feeding cable 14, which in the shown variation is embedded inside the Vivaldi radiator 6. The feeding cable 14 is not directly con nected to the power divider 1 1 on the bottom side of the first radiator 6. Instead it is first connected by a coaxial connector 16 to an impedance transformer 30. As best visible in Figure 10, in the shown variation, the impedance transformer 30 is designed as an electric conductor 31 arranged on a printed circuit board 32 which is arranged in a depression 33 on the upper side of the first radiator 6. In the center area of the first radiator 6 the impedance transformer 30 is interconnected to the power divider 1 1 arranged on the bottom side of the first radiator 6 by a connector 34 arranged in a bore 35 of the first radiator 6. The connector 34 comprises a con- nection pin 36 surrounded by a sleeve 37 made from a dielectric material. The ad vantage of an impedance transformer 30 is that the input impedance of the power divider 1 1 is comparatively low (in the range of 20-30 Ohm) due to the fact that several Vivaldi feeding stubs 1 2 - in the shown variation five - are connected in parallel to the power divider 18 output. Also the connection pin 34 and the sleeve 35 arranged inside the Vivaldi radiator 6 are preferably matched to this low imped ance. The impedance transformer 30 is preferably adapted to the standard 50 Ohm impedance which is used in the coaxial adapter and coaxial cable. Good results can be achieved, when the impedance transformer 30 is designed as so-called "Klopfenstein transformer". However, any other design of impedance transformer (quarter-wavelength, multi-section, Chebyshev, maximally-flat, exponential, etc.) would be applicable if it fulfils performance and bandwidth requirements. In the "leafs" of the first radiator 6 additional secondary slots 38 are integrated in order to mitigate the mutual coupling between single, neighbouring first radiators 6. The secondary slots extend in radial direction with respect to the center 8 of the first radiator 6. This may improve the overall matching of the horizontally polarized radiator. To safe space the vertically polarized second radiator 21 of the second antenna 20 is arranged at least partially within the ground plot of the first radiator 6 of the first antenna 5. In view of the often limited height and the need to eliminate the detun ing of the vertically polarized radiator by the proximity of the Vivaldi first radiator leafs 17, the herein shown fourth and fifth variations comprise a recess 39 in at least one leaf 17. The recess 39 is designed such that it is spaced a distance apart from the cup-shaped second radiator 21 . Good results can be obtained when no post 10 supports the respective leaf 17 with the recess 39 in order not to influence the vertically polarized radiator RF performance.

If appropriate a GPS antenna module 40 can be integrated in the antenna assembly 1 . In the shown variation, there are two possible options for positioning the GPS antenna module 40. It can be either integrated in the antenna baseplate 9 or in a respective recess 41 in a leaf 17 of the first radiator 6. Integrating the GPS antenna module in the baseplate 9 is simpler from the mechanical point of view but some part of the module field of view is covered by the other elements. This might limit the GPS signal reception performance. An alternative solution is to mount the GPS antenna module 40 at less restricted position. The GPS antenna module 40 is pref erably arranged such that it does not protrude above the top surface of first radiator 6. This is still to provide high current protection to the GPS antenna module 40. If the top surface of GPS antenna module 40 is below the top surface of the first ra diator 6, a damaged catenary line will stop on the first radiator 6 which is well grounded as described above.

The variation according to Figure 9 is optimized to fit an existing antenna platform. The horizontally polarized first radiator 6 is adjusted in order to fit into a smaller housing 22. Therefore, some sections of the Vivaldi radiator leafs 17 have been re moved. Also the height of the posts 10 was reduced. The resulting antenna assem- bly 1 is more compact and uses existing elements. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

LIST OF DESIGNATIONS

I Antenna assembly 20 Second antenna (omnidirec

5 First antenna (omnidirec tional vertically polarized) tional horizontally polarized 25 21 Second radiator (omnidirec Vivaldi-type) tional vertically polarized)

6 First radiator (omnidirec 22 Housing (radome) tional horizontally polar 23 Hollow space (in base plate) ized) 24 Microwave device

7 Tapered slots 30 25 First signal input 8 Radiator center 26 Second signal input

9 Base plate 27 First signal output

10 Post 28 Second signal output

I I Power divider 29 Bolt

12 Feeding stub 35 30 Impedance transformer 13 Printed circuit board (PCB) 31 Electric conductor (imped

14 Feeding cable (coaxial) ance transformer)

1 5 Trench 32 Printed circuit board (im

16 Connector pedance transformer)

17 Leaf (first radiator) 40 33 Depression (for impedance 18 Branch (power divider) transformer)

19 Electric conductor (printed 34 Connector circuit board) 35 Bore (first radiator) Connection pin 5 39 Recess (in leaf of first radia Sleeve (connection pin) tor) Secondary Slot (in leaf of 40 GPS Antenna Module first radiator) 41 Recess (for GPS antenna module)