Shielded antenna device

Abstract

The present disclosure relates to an antenna device (1) for railway applications comprising, a base plate (2) which has an upper surface (3) and a lower surface (4). An antenna layer (5) is arranged on the upper surface (3) of the base plate (2) and comprises at least one antenna element (6). An electrically conductive shielding (7) is mounted on the upper surface (3) of the base plate (2), is electrically connectable to a ground potential and permeable to electromagnetic radiation at an operating frequency of the antenna element (6). The antenna layer (5) is arranged between the shielding (7) and the upper surface (3) of the base plate (2) and is electrically isolated from the shielding (7).

Description

[0001] Shielded Antenna Device

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to an antenna device comprising an antenna layer arranged on an upper surface of a base plate.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] Train application antennas with high current protection and an omnidirectional radiation pattern are known from the prior art. An example of such a solution is provided in W02007048258A1 , published on 03.05.2007 in the name of the applicant, showing radiating elements with vertical polarization. In some cases, this system is supplemented with a GPS receiving antenna.

[0006] WO2021116265A1 published on 17.06.2021 in the name of the applicant is directed to an antenna assembly comprising a horizontally polarized Vivaldi-type first antenna. The first antenna comprises a horizontally polarized first radiator extending in a horizontal plane having a flower-shaped outline comprising several tapered slots arranged distributed around a radiator center. The first radiator is horizontally extending with respect to the radiator center in an outward direction. In vertical direction, the radiator extends by a certain thickness. A base plate arranged at a certain distance below the radiator interconnected to the radiator by at least one post. A power divider and a feeding stub per tapered slot are arranged between the base plate and the first radiator, interconnected to the first radiator for coupling radio signals into the first radiator. W02016008607A1 published on 21.01.2016 in the name of the applicant is directed to an antenna arrangement, which comprises a baseplate that is at least partially electrically conductive and has a top surface which defines a top level and a bottom surface which defines a bottom level. The antenna arrangement further comprises a first and a second cup-shaped antenna radiating element that have an apex which is arranged nearby to the top level of the baseplate and opposite to the apex an opening that is arranged distal to the top level of the baseplate. The antenna radiating elements are arranged above the baseplate and are spaced apart with respect to each other by a spacing, electrically interconnected to the baseplate. According to this disclosure, the first antenna radiating element is electrically interconnected in the region of its apex to an inner conductor of a first coaxial cable, said inner conductor being arranged in the region of the apex above said bottom level. The second antenna radiating element is electrically interconnected in the region of its apex to an inner conductor of a second coaxial cable, said inner conductor being arranged in the region of the apex above said bottom level. The baseplate further comprises at least one port arranged in a bottom surface of the baseplate.

[0007] WO2019024355A1 published on 07.02.2019 in the name of X TRIP INF Tech. Co LTD is directed to a frequency selective surface radome, comprising a radome body and a base. An electromagnetic wave incident surface of the radome body consists of a frequency selective surface structure. The frequency selective surface structure comprises an upper dielectric layer, an air dielectric layer, and a lower dielectric layer. The upper dielectric layer comprises a first dielectric slab and a second dielectric slab. A metal wire grid is separately etched on the upper surface of the first dielectric slab and the lower surface of the second dielectric slab. A resonant layer is etched on the upper surface of the second dielectric slab. The resonant layer comprises multiple hybrid resonators. Each of the hybrid resonators comprises a metal sheet and a Jerusalem cross unit. The Jerusalem cross unit comprises one cross hollowed slot etched on the metal sheet and eight spiral slit structure units. The left and right sides of each tail end of the cross hollowed slot are separately vertically connected to one spiral slit structure unit. The upper dielectric layer is cascaded with the lower dielectric layer by means of the air dielectric layer. The frequency selective surface radome provided has good frequency selective characteristics and polarization stability.

[0008] SUMMARY OF THE DISCLOSURE

[0009] Besides known train application antennas with high current protection and omnidirectional radiation pattern for telecommunication applications, as known from the prior art, also satellite communication is desired. Satellite communication antennas are enabling the transmission and reception of signals to and from satellites orbiting the Earth. Among these, steerable active antennas possess the ability to dynamically direct their beam patterns towards specific communication satellites, even as those satellites move across the sky. This agility is crucial for maintaining a stable and reliable communication link.

[0010] Active antennas incorporate electronic components that amplify and process signals directly at the antenna site, enhancing signal strength and quality. The 'active' aspect refers to the antenna's capability to electronically control the amplitude and phase of the signal it transmits or receives, allowing for real-time adjustments in beam direction and shape. This is in contrast to 'passive' antennas, which have no signal processing capabilities of their own and rely on external devices.

[0011] Roof-top antenna devices, especially for trains, must provide so-called high current protection. This means that in case of a broken catenary line which e.g. touches the antenna device, the antenna device must be able to short the current to the antenna ground (usually via the mounting surface) for at least 125 ms. 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-energized. This requires that the antenna device is appropriately grounded and has sufficient cross-section as well as ground contact, which will be able to carry currents 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.

[0012] Known solutions, which provide so-called high current protection, comprise radiating elements which are typically fully metallic and heavy, since they have to be milled or casted to have the appropriate cross sections. This is because the antenna elements are required to provide for the high-current protection, in case the catenary line drops on the roof-top. For this the antenna elements typically carry the high current to the grounding to which they are connected by a stand instead of allowing the current to travel through the antenna cable or PCB and destroy the electronics, and possibly also causing a fire inside of the vehicle. To be able to provide the needed functionality, these heavy metallic antenna elements are very costly to produce due to their complex shapes. One objective of the present disclosure can be seen in providing an antenna device, which provides high current protection, has a low overall height and is versatile regarding the antenna element to be used.

[0013] An antenna device according to the present disclosure for automotive or railway applications comprises a base plate, which has an upper surface and a lower. The upper surface can define an upper pane and the lower surface can define a lower plane. The base plate may function as a ground plate being configured to ground the antenna device to a ground potential. The base plate is typically configured to be attached to a cabin or roof of a train, vehicle or building in an electrically conductive manner. To be able to discharge high currents or voltages, the base plate is may be designed as a plate shaped element. The antenna device is preferably designed for vehicles, which are connected to a catenary line / power transfer from the top side. The antenna device must therefore be mechanically robust to survive the impact of a catenary line.

[0014] The antenna element can be in form of a patch antenna, which is arranged on a printed circuit board (PCB). To be able to protect the antenna device from mechanical damage, lightening and / or high currents or voltages as caused by a failing catenary line, e.g. a broken overhead line of a railway network, an electrically conductive shielding is mounted on the upper surface of the base plate, is electrically connectable to a ground potential and permeable to electromagnetic radiation at an operating frequency of the antenna element. To protect the sensitive antenna layer and prevent lightning or an arc from striking through the antenna device into the interior of the vehicle, the antenna layer is arranged between the shielding and the upper surface of the base plate, electrically isolated from the shielding. An antenna layer is arranged on the upper surface of the base plate, which comprises at least one antenna element. Besides passive antennas also antennas with active capabilities e.g. antennas with some extra circuitry for MIMO operation or multiplex or beam steering can be used.

[0015] The base plate can be at least partially electrically conductive and connectable to the ground potential. The antenna layer is preferably electrically isolated from the base plate. The antenna layer can be arranged on the base plate via isolating posts or patches to be electrically isolated from the base plate. The base plate can comprise at least one port for feeding the at least one antenna element. The base plate can be directly mounted on the cabin roof. Typically, the dimensions of the base plate depend on the number of antenna elements that are arranged on the antenna layer. For multiple input multiple output (MIMO) applications typically eight antenna elements are placed on one antenna layer. The dimensions of the base plate may also depend on the antenna gain, since the gain is proportional to the area the antenna element occupies. The dimensions typically depend on these two parameters. In the case of an antenna device for satellite communication, high gain antennas are required which can provide high data rates. In a variation of an antenna device with a download rate > 100 Mbps, the base plate can preferably have a width of 500 mm and a length of 500 mm. For a download rate of 20 Mbps the base plate can preferably have a width of 100 mm and a length of 100 mm.

[0016] The antenna element may have an operating frequency band between 10 GHz and 15 GHz, which is a typical frequency band for satellite communications. The shielding can be implemented as a so-called frequency-selective surface (FSS). Such frequency selective surfaces (FSS) are spatial filters, manipulating electromagnetic (EM) waves in a frequency-dependent manner. These surfaces are typically composed of periodic arrays of conductive elements, e.g. in form of stay sections of metallic materials like Aluminum or steel. The periodic arrays of conductive elements can be arranged on a dielectric substrate.

[0017] The fundamental principle behind FSS is their ability to selectively transmit, reflect, or absorb electromagnetic waves according to their frequency. This selective behavior is due to the resonance of the array elements, which can be designed to correspond to specific frequencies of interest. The operation of an FSS is akin to that of optical filters, but it is tailored for the EM spectrum, particularly in the radio frequency range. When an EM wave encounters an FSS, its frequency is compared against the resonant frequency of the surface elements. If the frequencies match, the wave is either allowed to pass through (passband) or is reflected back (stopband). This is analogous to how certain materials can be transparent to visible light but opaque to ultraviolet light, depending on their molecular structure.

[0018] The shielding can be in form of a one- or two-dimensional lattice, formed by stay sections with gaps in between them. The two-dimensional lattice can have a unit cell, which is selected from the group consisting of a parallelogram, a rectangle, a square and a rhombus. A unit cell is a repeating unit formed by the vectors spanning the points of a lattice. The unit cell can have a first side length and / or a second side length in the range between A / 20 to 2 and an angle a from 0° to

[0019] 90°. c = speed of light in m / s f = operating frequency of the antenna element in 1 / s

[0020] With the wavelength and speed of light being the wavelength and speed of light in air, if no dielectric is used, or the wavelength and speed of light in the dielectric substrate if one is used. The gaps can have a shape, which is selected from circular, polygonal, in particular triangular, squared and hexagonal, rectangular and cross-shaped.

[0021] The shielding is typically at least partially metallic and comprises a sufficiently thick cross section in order to absorb and discharge high currents and voltages effectively. The thickness may be chosen to be able to also resist mechanical impacts, e.g. of a falling catenary line of a railway network. For an adequate electrical and mechanical protection, the stay sections may have a diameter / thick- ness of at least 1.25 mm. The shielding and in particular the stay sections may be designed to surviving an impact as simulated by a hammer test as defined in DIN EN 60068-2-75: 2015-08, VDE 0468-2-75:2015-08.

[0022] A shielding with gaps in form of a honeycomb have proven to be advantageous. Such a shielding has good angular transmission characteristics, even under different incident wave angles up to 45 degrees in theta, with theta being the angle deviating from the vertical direction towards the horizontal direction. Transmis- sion with an operating frequency between 10 GHz and 15 GHz.. It has been observed that any form of shielding which has a good transmission response with respect to high wave incident angle can be used.

[0023] Transmission at 0 GHz, i.e. DC, is blocked from the antenna element, meaning that the shielding is able to give a DC block protection function and ground the antenna device. The same practically applies for alternating current (AC; for instance 50 Hz) used in typical power transmission lines. The shielding can be connected to the base plate by posts. These posts typically have a diameter / thick- ness of at least 3 mm or 4 mm. Good results regarding filter functionality and high voltage / current protection can be achieved when at least 15% of the area in the unit cell are solid to reach enough robustness, preferably 15% to 35%. Each gap may have a largest diameter, which is in the range of between A / 20 to 2 and an angle a from 0° to 90° ( being the wavelength in air if no dielectric is employed and the wavelength in the dielectric substrate if present) and / or the stay sections having a dimeter and / or thickness between 1 mm and 4 mm. The stay sections may have a staggered arrangement. The stay sections are typically made from a conductive metallic material, e.g. Aluminum or steel.

[0024] FSS can be classified depending on their electrical properties. A low-pass filter allows frequencies below a cut -off frequency to pass. This is typically realized with arrays of unconnected solid elements, which create a capacitive response. A high-pass filter allows frequencies above a cut-off to pass. This is typically realized with grids of stay sections, complementary to the low-pass filter, which create an inductive response. Band-pass filter allow an operating frequency to pass and filter out frequencies above or below the band. Typically realized with arrays of unconnected non-solid elements, which create a capacitive / inductive response. Band-rejection filters eliminate frequencies between an upper and a lower cut-off. They are typically realized with arrays of unconnected solid elements and grids of connected elements, which create an inductive / capacitive response. To create a shielding working as a band-pass filter, patches, which are isolated from the stay sections, may be arranged in in the gaps. The unit cell may then consist by at least 15% of stay sections and / or patches. The patches may have a shape which is selected from circular, polygonal, in particular triangular, squared and hexagonal, rectangular and cross-shaped.

[0025] The shielding can be in form of a plate, which is electrically connected to the base plate, preferably to the upper surface via posts for dissipating high voltage and / or currents. It can be of interest to have multiple plates to achieve a different RF performance over angle or to increase the mechanical robustness of the design. Typically, the use of multiple layers increases the bandwidth at angles close to 0° and reduces it in larger angles, being not suitable for steering applications. The distance between the layers is a variable that can be adjusted to improve the performance. In this case, the layer more proximal to the radome / outside is preferably metallic with the thickness described above to be able to carry the current.

[0026] Intermediate layers or the bottom layer can be realized in form of a printed circuit board or can contain a dielectric material. The shielding can comprise a single metallic layer of material. Alternately, the shielding can comprise at least two layers where at least a pair of them are interconnected or in form of multiple layers which are not interconnected. This brings an advantage of bandwidth at lower angles, even though it rapidly deteriorates at larger ones. The shielding can be also a sandwich layer, wherein the shielding comprises additionally substrate layers, with metallic patches being arranged thereon, which may improve angular performance.

[0027] The shielding may comprise a circumferential frame with the stay sections spanning across the frame. Additionally, to increase the robustness of the antenna device, different mounting concepts can be defined. Spacers made out of foam or elastomeric material can be added between the shielding and the base plate and / or the shielding and a radome and / or between the shielding and the antenna layer. This helps to dampen the impact in case of a mechanical impact of a heavy object, e.g. a catenary line to mitigate the forces and maintain isolation without damaging the components. Alternatively, a layer of foam material can be arranged between certain points. Foam materials have a very low relative permittivity of less than 1.1 , which have almost no impact in RF performance. Additionally the shielding can be inserted to the radome in an insertion molding process, creating a single piece.

[0028] The base plate, the antenna layer and the shielding may be arranged parallel with respect to each other. This set-up has good transmission characteristics if an essentially vertical transmission is desired. For some applications, it is desired to radiate sideways, without the need to radiate in the vertical direction. E.g. for connections to base stations on the ground at about the same height than the train. For such applications, the antenna layer and the shielding can be placed perpendicular to the base plate. This can lead to different shapes of the shielding to protect the antenna layer. The antenna layer and the shielding can be arranged perpendicular with respect to the base plate. The shielding is typically a flat surface in form of a corrugated plate. The problem of flat surfaces is that the radiation of the antenna sees a different distance and arrives at a different angle to the flat surface, then consequently the shape that the antenna sees at a given angles is distorted compared to the original one. A possible solution to this problem can be to create a shielding with a conformal shape, e.g. half sphere or concave shape with the antenna layer being placed at focal distance. This ensures that the distance and shape is similar for all angles. Rotating the individual elements wins the flat surface without creating conformal shape. The shielding may have a curved shape, in particular selected from the group consisting of an ellipsoid, in particular a sphere, a hyperboloid, an elliptical paraboloid, a hyperbolic paraboloid, an elliptical cylinder, a parabolic cylinder and a hyperbolic cylinder. The shielding can be symmetrical towards a center axis (x) perpendicular to the base plate.

[0029] The antenna element may be a planar antenna, e.g. a patch antenna, printed dipole, printed vivaldi, printed metal on a PCB substrate, etc. Antenna devices for satellite communication may comprise an antenna layer which can an phase array of patch antenna elements, having in some cases more than 1000 patches. A plurality of antenna elements may be arranged point symmetrical with regard to one common feeder. The antenna layer can comprise a printed circuit board with the at least one antenna element being arranged thereon. The antenna element is typically placed inside of a sandwich which is formed by the base plate and the shielding. The shielding can be electrically connected, preferably without air gaps to the base plate. This can be achieved by soldering, screwing some bars or by additive manufacturing (metal 3D printing). Some non-metallic spacers can be placed between the antenna layer and the base plate and / or the radome in order to avoid the direct contact, which in the case of forces pushing on the shielding, high current could make the antenna layer suffer from it. The connected structure will allow to receive a high current through a grounded to the base plate, which is e.g. connected to a vehicle. In the case of the impact of e.g. a catenary line with high voltage and current, the shielding is preferably designed to resist this impact without touching the antenna layer, since a short could e.g. create a fire inside of the vehicle.

[0030] The antenna device may comprise a radome, wherein the shielding is preferably integrally formed with the radome. Furthermore and optionally, by creating a sandwich structure, comprising radome, shielding, antenna layer and base plate, the antenna elements can be protected by the shielding and base plate forming a frequency-selective surface. The shielding can be integrated in the radome to be able use circuitry in active antennas, which provides some capabilities such as beam shaping, steering, switching or multiplexing of the signal in the form of reducing the number of connectors especially in multiple input multiple output (MIMO) setups. The radome can be painted with metallic paint, or a metallization process can be carried out. Additionally, a insertion molding process could be performed to insert metallic pieces into a plastic radome. Gluing or clamping of the metallic piece could be also performed.

[0031] It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview 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 illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS The herein described disclosure will be more fully understood from the detailed description given herein below and the accompanying drawings which should not be considered limiting to the disclosure described in the appended claims. The drawings are showing:

[0033] Fig. 1 a first variation of the antenna device in a perspective view from the side and above;

[0034] Fig. 2 the variation of the antenna device according to Fig. 1 in a perspective exploded view from the side and above;

[0035] Fig. 3 the variation of the antenna device according to Fig. 1 in a perspective partially sectional view from the side and above; Fig. 4 an enlarged view the variation of the antenna device according to Fig. 3;

[0036] Fig. 5 a schematic illustration of a variation of the two-dimensional lattice of stay sections with gaps having a honeycomb shape; Fig. 6 a schematic illustration of a second variation of the two-dimensional lattice of stay sections with gaps having a squared shape;

[0037] Fig. 7 a schematic illustration of a third variation of the two-dimensional lattice of stay sections with gaps having a squared shape; Fig. 8 a schematic illustration of a variation of an one-dimensional lattice of stay sections with gaps having a squared shape;

[0038] Fig. 9 a second variation of the antenna device in a perspective view from the side and above with unfolded radome;

[0039] Fig. 10 the variation of the antenna device according to Fig. 7 in a perspective partially sectional view from the side and above;

[0040] Fig. 11 a third variation of the antenna device in a perspective view from the side and above with unfolded radome;

[0041] Fig. 12 the variation of the antenna device according to Fig. 9 in a perspective partially sectional view from the side and above;

[0042] Fig. 13 a fourth variation of the antenna device in a perspective view from the side and above with unfolded radome;

[0043] Fig. 14 the variation of the antenna device according to Fig. 11 in a perspective partially sectional view from the side and above; Fig. 15 a fifth variation of the antenna device in a perspective view from the side and above with unfolded radome;

[0044] Fig. 16 the variation of the antenna device according to Fig. 13 in a perspective partially sectional view from the side and above;

[0045] Fig. 17 plots of the transmission performance with vertical polarization in Fig. 17a and horizontal polarization in Fig. 17b.

[0046] DESCRIPTION OF THE EMBODIMENTS

[0047] 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 different 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.

[0048] Figures 1 to 4 show a first variation of the antenna device 1 . The shown antenna device 1 comprises a base plate 2, which has an upper surface 3 defining an upper plane P1 and a lower surface 4 defining a lower plane P2. The shown base plate 2 functions as a ground plane. The base plate 2 is configured to be attached to a cabin or roof of a train, vehicle or building in an electrically conductive manner. To be able to discharge high currents or voltages, the shown base plate 2 is designed as a massive plate shaped element. The shown antenna layer 5 is arranged on the upper surface 3 of the base plate 2 and comprises several antenna elements 6 in form of PCB / patch antennas 15. The shown antenna elements 6 are in form of a patch antennas, which is arranged on a printed circuit board 17. An electrically conductive shielding 7 is mounted on the upper surface 3 of the base plate 2 and is electrically connectable to a ground potential and permeable to electromagnetic radiation at an operating frequency of the antenna element 6. To protect the sensitive antenna layer 5 and prevent lightning or an arc from striking through the antenna device 1 into the interior, the antenna layer 5 is arranged between the shielding 7 and the upper surface 3 of the base plate 2 electrically isolated from the shielding 7.

[0049] The shown base plate 2 is electrically conductive and connectable to the ground potential. The antenna layer 5 is electrically isolated from the base plate 2. The base plate 2 comprises at least one port 21 for feeding the shown antenna elements 6. The shown shielding 7 is in the form of a metallic frequency-selective surface (FSS), which is transparent for the operating frequencies of the antenna device 1 . The base plate 2, the antenna layer 5 and the shielding 7 are arranged parallel with respect to each other. This set-up has good transmission characteristics if an essentially vertical transmission is desired.

[0050] The shown antenna device 1 comprises a radome 14. By creating a layered structure, comprising the radome 14, shielding 7, antenna layer 5 and base plate 2, the antenna elements 6 are protected by the shielding 7 and the base plate 2 forming a faraday cage. Figures 5 to 8 show schematic illustrations of variations of a two-dimensional lattice of stay sections 8 and a one-dimensional lattice of stay sections 8, with gaps 9 having a honeycomb shape in Figure 5, squared shape in Figure 6, round stay sections 8 in Figure 7 and longitudinal stay sections 8 in Figure 8. The shown shielding 7 is in both variations in form of a two-dimensional lattice, formed by stay sections 8 with gaps 9 in between them. The two-dimensional lattices each have a unit cell U, which is selected from the group consisting of a parallelogram, a rectangle, a square and a rhombus.

[0051] Each unit cell U is a repeating unit formed by the vectors spanning the points of a lattice. The unit cell U is defined by a first side length L1 and a second side length L2 and an angle a between L1 and L2. The gaps 9 have a shape, which is hexagon in Figure 5 and a square in Figure 6. The dimensions of the unit cell U are chosen to create gaps that are transmissive for the operating frequency. Especially the lattice shown by Figure 5 in form of a honeycomb have proven to be advantageous. Such a shielding has good angular transmission characteristics, even under different incident wave angles up to 45 degrees in theta. Transmission with an operating frequency between 10 GHz and 15 GHz band is close to 0 dB at and incidence theta and phi angle.

[0052] Figures 9 and 10 show an antenna device 1 with a non-planar shielding 7. The shown shielding 7 is in form of a plate, which is electrically connected to the upper surface 3 of the base plate 2 via posts 12 for dissipating high voltage and / or currents. The shown shielding 7 is in form of a curved and corrugated plate. The problem of flat surfaces is that the radiation of the antenna sees a different distance and arrives at a different angle to the flat surface, then consequently the shape that the antenna sees at a given angle is distorted compared to the original one. A possible solution to this problem is the shown shielding 7 with a conformal shape. Then the distance and shape is similar for all angles.

[0053] Figures 11 and 12 show, similar to Figures 9 and 10, an antenna device 1 with a non-planar shielding 7. The shown shielding 7 is symmetrical towards a center axis x running perpendicular to the base plate. The shown shielding 7 has a elliptical paraboloid shape.

[0054] Figures 13 and 14 show an alternative variation of the antenna device 1 , wherein the antenna layer 5 and the shielding 7 are arranged perpendicular with respect to the base plate 2. For applications where it is desired to radiate sideways, without the need to radiate in the vertical direction, e.g. for connections to base stations on the ground at are about the same height than the train, such a design is favorable. The shown antenna elements 6 are patch antennas 15, in the shown variation a number of patch / planar antennas 15 are used, arranged point symmetrical with regard to one common feeder.

[0055] The shown antenna layer 5 comprises a printed circuit board 17 with the at least one antenna element 6 being arranged thereon. The antenna layer 5 is placed inside of a layered structure, which is formed by the base plate 2 and the shielding 7. The shown box-shaped shielding 7 is electrically connected, preferably without air gaps to the base plate 2. This can be achieved by soldering, screwing some bars or by additive manufacturing (metal 3D printing) and / or welding. Figures 15 and 16 show an antenna device 1 with a shielding 7, which comprises several layers which are arranged as a stack. This brings an advantage of bandwidth at lower angles, even though it rapidly deteriorates at larger ones. The shown shielding 7 can be also a loaded layer wherein the shielding 7 comprises additionally substrate layers, which load the metal pieces and may improve angular performance or reduce metal size. In addition to several layers, patches 10 are arranged in the gaps 9 of the stay sections 8. The shown radome 14 can be painted with metallic paint, or a metallization process can be carried out. Additionally, insertion molding can be performed to insert the patches 10 into the shown plastic radome 14.

[0056] The patches 10 are isolated from the stay sections 8 and are arranged in the gaps 9. In this example, the unit cell U consist by at least 15% of stay sections 8 and / or patches 10. The patches 10 generally have a shape, which is selected from circular, polygonal, in particular triangular, squared and hexagonal, rectangular and cross-shaped. In the shown variation, the patches 10 are squared. It can be of interest to have multiple shielding 7 layers to achieve a different RF performance over angle or to increase the mechanical robustness of the design. Typically the use of multiple layers of FSS increase the bandwidth at angles close to 0°, and reduces in larger angles, being not suitable for steering applications.

[0057] The shown shielding 7 comprises a circumferential frame 13 with the stay sections 8 spanning across the frame 13. Additionally, to increase the robustness of the whole structure, different mounting concepts can be defined. Spacers made out of foam or elastomer material can be added between the shielding 7 and the base plate 2 and / or the radome 14 or between the shielding 7 and the antenna layer 5. This helps in case of an impact of a heavy object (catenary line) to mitigate the forces and maintain isolation, without damaging the components. An alternative can be to have a layer of foam material between certain points. Foam materials have a very low epsilon which have no impact in RF performance. Ad- ditionally the shielding 7 can be inserted to the radome 14 in an insertion molding process, creating a single piece.

[0058] Figure 17 shows plots of the transmission performance with vertical polarization in Figure 17a and horizontal polarization in Figure 17b. The shown transmission plots are exemplary for a shielding with hexagonal gaps (honeycomb). As it can be obtained from the plots, the shielding has good angular transmission characteristics under different incident wave angles up to 45 degrees in theta. From Figure 17a it can be obtained that transmission between 10-15 GHz band is close to 0 dB at and incidence theta and phi angle. A shielding according to the present disclosure has good transmission response even under high wave incident an- gles. Transmission at 0 GHz, i.e. DC, is minus infinite, meaning that is able to give a DC block protection function

[0059] Rather, 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 disclosure. LIST OF DESIGNATIONS

[0060] 1 Antenna device 17 Printed circuit board

[0061] 2 Base plate 20 (PCB) 3 Upper surface 18 Spacer

[0062] 4 Lower surface 19 Seal

[0063] 5 Antenna layer 20 Fixation means

[0064] 6 Antenna element 21 Port

[0065] 7 Shielding 25 P1 Upper plane 8 Stay sections P2 Lower plane

[0066] 9 Gaps U Unit cell

[0067] 10 Patch L1 First side length (Unit cell)

[0068] 11 Plate (shielding) L2 Second side length (Unit

[0069] 12 Post 30 cell) 13 Frame (shielding) a Angle (unit cell)

[0070] 14 Radome DG Diameter (gap)

[0071] 15 Patch / planar antenna DS Diameter / Thickness (stay

[0072] 16 Feeder section)

[0073] 35 X center axis

Claims

PATENT CLAIMS1. An antenna device (1 ) for railway applications, comprising a. a base plate (2) which has an upper surface (3) and a lower surface (4); b. an antenna layer (5) arranged on the upper surface (3) of the base plate (2), comprising at least one antenna element (6); and c. an electrically conductive shielding (7) which is mounted on the upper surface (3) of the base plate (2) and is electrically connectable to a ground potential and permeable to electromagnetic radiation at an operating frequency of the antenna element (6), wherein the antenna layer (5) is arranged between the shielding (7) and the upper surface (3) of the base plate (2) electrically isolated from the shielding (7).

2. The antenna device (1 ) according to claim 1 , wherein the shielding (7) forms a one- or two-dimensional lattice of stay sections (8) with gaps (9) in between them.

3. The antenna device (1 ) according to claim 2, wherein the two-dimensional lattice has a unit cell (U), which is selected from the group consisting of a parallelogram, a rectangle, a square and a rhombus.

4. The antenna device (1 ) according to claim 3 wherein the unit cell (U) has a first side length (L1 ) and / or a second side length (L2) in the range of A / 20 to 2 mm.

5. The antenna device (1 ) according to at least one of claims 2 to 4, wherein the gaps (9) have a shape, which is selected from circular, polygonal, in particular triangular, squared and hexagonal, rectangular and cross-shaped or a combination thereof.

6. The antenna device (1 ) according to at least one of claims 2 to 5, wherein each gap (9) has a largest diameter (DG) in the range of A / 20 to 2*A and / or the stay sections (8) have a dimeter and / or thickness (DS) between 1 mm and 4 mm.

7. The antenna device (1 ) according to at least one of claims 2 to 6, wherein the stay sections (8) have a staggered arrangement.

8. The antenna device (1 ) according to at least one of claims 2 to 7, wherein patches (10), which are isolated from the stay sections (8), are arranged in in the gaps (9).

9. The antenna device (1 ) according to claim 8, wherein the patches (10) have a shape which is selected from circular, polygonal, in particular triangular, squared and hexagonal, rectangular and cross-shaped or a combination thereof.

10. The antenna device (1 ) according to claim 8 or 9, wherein the unit cell (U) consists by at least 15% of stay sections (8) and / or patches (10).

11. The antenna device (1 ) according to at least one of the preceding claims, wherein the base plate (2) is at least partially electrically conductive and connectable to the ground potential and the antenna layer (5) is electrically isolated from the base plate (2).

12. The antenna device (1 ) according to at least one of the preceding claims, wherein the shielding (7) is electrically connected to the base plate (2), preferably to the upper surface (3) via posts (12) for dissipating high voltage and / or currents or directly to the upper surface (3).

13. The antenna device (1 ) according to claim 12, wherein the shielding (7) comprises a circumferential frame (13) with the stay sections (8) spanning across the frame (13).

14. The antenna device (1 ) according to at least one of the preceding claims, wherein the antenna device (1 ) comprises a radome (14), wherein the shielding (7) is preferably integrally formed with the radome (14).

15. The antenna device (1 ) according to at least one of the preceding claims, wherein a. the base plate (2), the antenna layer (5) and the shielding (7) are arranged parallel with respect to each other, and / orb. the antenna layer (5) and the shielding (7) are arranged perpendicular with respect to the base plate (2).

16. The antenna device (1 ) according to at least one of the preceding claims, wherein the shielding (7) has a curved shape, in particular selected from the group consisting of an ellipsoid, in particular a sphere, a hyperboloid, an elliptical paraboloid, a hyperbolic paraboloid, an elliptical cylinder, a parabolic cylinder and a hyperbolic cylinder.

17. The antenna device (1 ) according to at least one of the preceding claims, wherein the shielding (7) is symmetrical towards a center axis (x), which center axis (x) is perpendicular to the base plate (2).

18. The antenna device (1 ) according to at least one of the preceding claims, wherein the antenna element (6) comprises least one patch / PCB antenna (15), wherein preferably a plurality of patch / PCB antennas (15) are arranged point symmetrical with regard to one common feeder (16).

19. The antenna device (1 ) according to at least one of the preceding claims, wherein the antenna layer (5) comprises a printed circuit board (17) with the at least one antenna element (6) being arranged thereon.

20. The antenna device (1 ) according to at least one of the preceding claims, wherein the antenna device (1 ) is configured for satellite communications, whereby the antenna element (6) has preferably an operating frequency band between 10 GHz and 15 GHz.

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