Multiband antenna apparatus

Abstract

A multiband antenna apparatus is disclosed, comprising a first radiating element (110a-d) and a second radiating element. The first radiating element (110a-d) is configured to operate at a first frequency band and arranged on an upper support plane (150a) of a support arrangement (150) at a first distance to a reflector plate. The second radiating element is configured to operate at a second frequency band and arranged on a lower support plane of the support arrangement (150) at a second distance to the reflector plate, wherein the second distance is smaller than the first distance and the second frequency band is higher than the first frequency band. Moreover, the multiband antenna apparatus (100) comprises a plurality of metallic structures (130a-d) not connected to, e.g. not in the current path of the first radiating element (110a-d), wherein the plurality of metallic structures (130a-d) are arranged on or close to the upper support plane (150a) of the support arrangement (150) and each have a size being smaller than the largest wavelength of the second frequency band for increasing the transparency of the first radiating element (110a-d) in the second frequency band by down-converting a frequency behavior of the transparency of the first radiating element (110a-d).

Description

[0001] Multiband antenna apparatus

[0002] TECHNICAL FIELD

[0003] Generally, the present invention relates to the field of wireless communications and antenna technology. The present invention relates to a multiband antenna apparatus and a method for providing such a multiband antenna apparatus.

[0004] BACKGROUND

[0005] Modem mobile communication networks typically use frequency bands that are licensed by network providers for data communication. The mobile communication networks include several base stations, wherein each base station is usually equipped with several antennas. Such an antenna includes an antenna body and a radome which is a top cover of the antenna. The radome protects the antenna from external influences, such as severe weather conditions. The antenna body includes antenna radiators, often dipole radiators, to radiate power for data transmission.

[0006] Regulations within different countries concerning the size of base station antennas often make it necessary that new improved antenna generations have the same or at least a similar size as legacy antennas. Moreover, in order to be able to keep an already installed mechanical support structure for a base station, the wind load of a new antenna should be equivalent or at least similar to legacy antennas. Because of these factors more and more antenna arrays are being integrated under the same radome sharing the same area. Among many other technical design strategies, one of the key points to fulfill these requirements, is that radiating elements designed, for instance, for low-band (LB), mid-band (MB), high-band (HB) and C-band (CB) arrays should be electrically transparent with respect to each other. Mutual transparency is achieved when placing a radiating element of one frequency band in the vicinity of other of a different frequency band does not affect the performance of either. At the same time, new arrays try to cover as much spectrum as possible (broad and ultra broad band arrays) which requires the use of specific techniques such as rings around the elements or elements occupying large areas.

[0007] SUMMARY OF THE INVENTION

[0008] It is an objective of the present disclosure to provide an improved multiband antenna apparatus and a method for providing such a multiband antenna apparatus.

[0009] The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

[0010] According to a first aspect a multiband antenna apparatus is provided, comprising a first radiating element configured to operate at a first frequency band and arranged on a first upper support plane, (e.g. a substrate) of a support arrangement at a first distance to a reflector plate and a second radiating element configured to operate at a second frequency band and arranged on a second lower support plane (e.g. substrate) of the support arrangement at a second distance to the reflector plate, wherein the second distance is smaller than the first distance and wherein the second frequency band is higher than the first frequency band. Moreover, the multiband antenna apparatus comprises a plurality of metallic structures (e.g. metallic elements not connected to the first radiating element, e.g. not in the current path of the first radiating element). The plurality of metallic structures are arranged on or close to the upper support plane (e.g. substrate) of the support arrangement and each metallic structure has a characteristic size d being smaller than the largest wavelength Amaxof the second frequency band for increasing the transparency of the first radiating element in the second frequency band by down-converting a frequency behavior of the transparency of the first radiating element. Thus, by loading the substrate (e.g. the first upper support plane) of the first radiating element with a plurality of metallic structures with a small characteristic size the transparency properties of the first radiating element may be down-converted in frequency and, thus, the transparency of the first radiating element with respect to the second frequency band can be improved. In a further possible implementation form, the plurality of metallic structures each have a characteristic size d being smaller than one tenth of the largest wavelength Amaxof the second frequency band. This allows for an improved transparency of the first radiating element with respect to the second frequency band.

[0011] In a further possible implementation form, the metallic structures of the plurality of metallic structures have at least two different shapes. This allows for an additional degree of freedom in the design of the metallic structures when canonical shapes are not possible due to any possible space limitations.

[0012] In a further possible implementation form, the metallic structures of the plurality of metallic structures have the same shape and are arranged in an irregular or random pattern on or close to the upper support plane of the support arrangement to increase the transparency of the first radiating element in the second frequency band. This allows for an additional degree of freedom in the design of the metallic structures.

[0013] In a further possible implementation form, the metallic structures of the plurality of metallic structures have at least two different characteristic sizes d and d’ and are arranged on or close to the upper support plane of the support arrangement to increase the transparency of the first radiating element in the second frequency band, wherein the at least two different characteristic sizes d and d’ are smaller than the largest wavelength Amaxof the second frequency band. Granularity in the shapes provides allows tuning the transparency in a finer way.

[0014] In a further possible implementation form, the metallic structures of the plurality of metallic structures comprises one or more metallic structures with a hollow or filled (e.g. solid) square shape one or more metallic structures with a hollow or filled, solid circular shape, and / or one or more metallic structures with a hollow or filled cross shape. This allows for an additional degree of freedom in the design of the metallic structures.

[0015] In a further possible implementation form, the first radiating element comprises one or more coils for providing wideband transparency at a frequency band which is down-converted by the plurality of metallic structures. This allows for broadband transparency.

[0016] In a further possible implementation form, the metallic structures of the plurality of metallic structures are arranged on the upper support plane of the support arrangement or on a further support plane of the support arrangement substantially in parallel with the upper support plane of the support arrangement, wherein the distance between the upper support plane and the further support plane of the support arrangement is smaller than one tenth of the largest wavelength Amaxof the second frequency band. This allows for further degrees of freedom with respect to the arrangement of the plurality of metallic structures relative to the first radiating element.

[0017] In a further possible implementation form, the multiband antenna apparatus further comprises a third radiating element configured to operate at a third frequency band and arranged on a third lower support plane of the support arrangement at a third distance to the reflector plate, wherein the third distance is smaller than the second distance and the third frequency band is higher than the second frequency band. The multiband antenna apparatus further comprises a further plurality of metallic structures, e.g. elements not connected to the first radiating element, e.g. not in the current path, wherein the further plurality of metallic structures are arranged on or close to the lower support plane of the support arrangement and each have a characteristic size being smaller than the largest wavelength of the third frequency band for increasing the transparency of the first radiating element in the third frequency band by down-converting a frequency behavior of the transparency of the first radiating element. This allows for transparency of the first radiating element with respect to multiple frequency bands. In a further possible implementation form, each of the plurality of metallic structures has a characteristic size being smaller than the largest wavelength of the third frequency band for increasing the transparency of the first radiating element in the third frequency band by down-converting a frequency behavior of the transparency of the first radiating element.

[0018] In a further possible implementation form, the number of the plurality of metallic structures may be selected based on a desired degree of the down-conversion of the frequency behavior of the transparency of the first radiating element. This allows to adjust the number of the metallic structures based on the desired transparency behavior of the first radiating element.

[0019] In a further possible implementation form, the first radiating element is a first dipole radiating element with a plurality of arms. This allows for an efficient implementation of the first radiating element.

[0020] In a further possible implementation form, the metallic structures of the plurality of metallic structures are arranged within a region defined by the plurality of arms of the first dipole radiating element. This allows for an improved transparency of the first radiating element with respect to the second frequency band.

[0021] According to a second aspect a method for providing a multiband antenna apparatus is provided. The method according to the second aspect comprises the steps of: providing a first radiating element configured to operate at a first frequency band and arranged on a first upper support plane of a support arrangement at a first distance to a reflector plate; providing a second radiating element configured to operate at a second frequency band and arranged on a second lower support plane of the support arrangement at a second distance to the reflector plate, the second distance being smaller than the first distance, and the second frequency band being higher than the first frequency band; and providing a plurality of metallic structures (e.g. electrically conductive elements not connected to the first radiating element, e.g. not in the current path of the first radiating element), wherein the plurality of metallic structures are arranged on or close to the upper support plane of the support arrangement and each have a characteristic size d being smaller than the largest wavelength Amaxof the second frequency band for increasing the transparency of the first radiating element in the second frequency band by down-converting a frequency behavior of the transparency of the first radiating element.

[0022] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

[0025] Fig. la and lb show a schematic side view and a schematic top view of a multiband antenna apparatus according to an embodiment;

[0026] Fig. 2a shows a perspective view of a dual polarized dipole radiating element of a multiband antenna apparatus according to an embodiment with a plurality of square-shaped metallic structures for improving the transparency of the dual polarized dipole radiating element;

[0027] Fig. 2b shows the perspective view of figure 2a without the plurality of square-shaped metallic structures;

[0028] Fig. 3 shows a perspective view of a dual polarized dipole radiating element of a multiband antenna apparatus according to an embodiment with a plurality of circular metallic structures for improving the transparency of the dual polarized dipole radiating elements; Fig. 4a shows a perspective view of a dual polarized dipole radiating element with coils of a multiband antenna apparatus according to an embodiment with a plurality of square-shaped metallic structures for improving the transparency of the dual polarized dipole radiating element;

[0029] Fig. 4b shows the perspective view of figure 4a without the plurality of square-shaped metallic structures;

[0030] Fig. 5 illustrates a schematic side view of a multiband antenna apparatus according to an embodiment, where the plurality of metallic structures are vertically spaced from the dipole radiating element;

[0031] Fig. 6 shows a perspective view of a dual polarized dipole radiating element of a multiband antenna apparatus according to an embodiment with a plurality of square-shaped metallic structures with different sizes for improving the transparency of the dual polarized dipole radiating element;

[0032] Fig. 7 shows a perspective view of a dual polarized dipole radiating element of a multiband antenna apparatus according to an embodiment with a plurality of metallic structures with different shapes for improving the transparency of the dual polarized dipole radiating element; and

[0033] Fig. 8 shows a flow diagram illustrating steps of a method according to an embodiment for providing a multiband antenna apparatus according to an embodiment.

[0034] In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0035] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] In the following description, reference is made to the accompanying figures, which form part of the disclosure, which illustrate specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0037] For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically noted otherwise.

[0038] Figures la and lb show a schematic side view and a schematic top view of a multiband antenna apparatus 100 according to an embodiment. The multiband antenna apparatus 100 comprises one or more first radiating elements 1 lOa-d configured to operate at a first frequency band and arranged on an upper support plane 150a, e.g. substrate 150a of a support arrangement 150 at a first distance to a reflector plate 140. In an embodiment, the support arrangement may further support feeding lines for the one or more first radiating elements 1 lOa-d as well as further components for operating the one or more first radiating elements 1 lOa-d, such as one or more baluns. In an embodiment, the one or more first radiating elements 1 lOa-d may comprise one or more first dipole radiating elements 1 lOa-d with a plurality of arms. Figures 2a and 2b illustrate an embodiment of the first radiating element 1 lOa-d in the form of a dual polarized dipole radiating element 1 lOa-d with a first dipole 110a, c and a second orthogonally polarized dipole 110b,d, wherein each dipole comprises a plurality of arms. For instance, the dipole 110a,c comprises a first arm defined by the elements I l la, 112a, 113a, 114a and a second arm defined by the elements 111c, 112c, 113c, 114c, as illustrated in the embodiment shown in figure 2b. The plurality of elements I lla, 112a, 113a, 114a, 111c, 112c, 113c, 114c of the dipole arms may be implemented with a “bow-tie” configuration. In an embodiment, the plurality of elements I l la, 112a, 113a, 114a, 111c, 112c, 113c, 114c of the dipole arms may define a square-shaped area bounded by the plurality of elements I l la, 112a, 113a, 114a, 111c, 112c, 113c, 114c of the dipole arms of the dual polarized dipole radiating element HOa-d.

[0039] As illustrated in figures la and lb, the multiband antenna apparatus 100 further comprises one or more second radiating elements 120a-d (in the embodiment shown in figures la and lb four second radiating elements 120a-d), wherein each second radiating element 120a-d is configured to operate at a second frequency band and arranged on a lower support plane, e.g. substrate of the support arrangement 150 at a second distance to the reflector plate 140, wherein the second distance is smaller than the first distance (e.g. each second radiating element 120a-d is closer to the reflector plate than each first radiating element 1 lOa-d) and wherein the second frequency band is higher than the first frequency band (e.g. the first radiating element 1 lOa-d is operating in a lower frequency band than the one or more second radiating elements 120a-d).

[0040] As illustrated in figure 2a and as will be described in more detail below, the multiband antenna apparatus 100 further comprises a plurality of metallic structures 130a-d, for instance, square-shaped metallic structures 130a-d, wherein the plurality of metallic structures 130a-d are arranged on or close to the upper support plane 150a, e.g. substrate 150 of the support arrangement 150 also supporting the first radiating element 1 lOa-d, in particular first dipole radiating element 1 lOa-d, but not connected to the first radiating element 1 lOa-d, e.g. not in the current path of the first radiating element 1 lOa-d. In an embodiment, as illustrated in figure 2a, the plurality of square-shaped metallic structures 130a-d are arranged within the square-shaped region defined by the elements I lla, 112a, 113a, 114a, 111c, 112c, 113c, 114c of the dipole arms of the first dual polarized dipole radiating element 1 lOa-d. As will be appreciated from figure 2a, the location of the plurality of square-shaped metallic structures 130a- d may be randomly distributed or distributed in an irregular way within the area defined by the arms of the first dipole radiating element HOa-d.

[0041] Each of the plurality of square-shaped metallic structures 130a-d shown in figure 2a has a characteristic size being smaller than the largest wavelength Amaxof the second frequency band for increasing the transparency of the first radiating element 110a- d in the second frequency band by down-converting a frequency behavior of the transparency of the first radiating element HOa-d. In an embodiment, the plurality of metallic structures 130a-d each have a characteristic size being smaller than one tenth of the largest wavelength Amaxof the second frequency band. Thus, by loading the substrate, e.g. the first upper support plane 150a supporting the first radiating element 1 lOa-d with a plurality of metallic structures with a small characteristic size, the transparency properties of the first radiating element HOa-d may be down-converted in frequency and, thus, the transparency of the first radiating element 1 lOa-d with respect to the second frequency band may be improved. Figure 2b shows the perspective view of figure 2a without the plurality of square-shaped metallic structures 130a-d for better illustrating the first dual polarized dipole radiating element 1 lOa-d.

[0042] The multiband antenna apparatus 100 may be configured to radiate electromagnetic signals in low band (LB, e.g. e.g. 618 to 960 MHz), high band (HB, e.g. e.g. 1.7 to 2.69 GHz), and C-band (CB, e.g. 3.3 to 4.99 GHz). As already described above, the first radiating element 1 lOa-d is operated at a lower frequency band, e.g. 618 to 960 MHz, while the second radiating elements 120a-d may be a high band radiator operating, for instance, in the frequency band 1.7 to 2.69 GHz. The multiband antenna apparatus 100 may be used to facilitate wireless communication between a user equipment device and a network. Such wireless communication systems may comprise, but are not limited to base transceiver station (BTS) antennas (such as an Evolved Node B (eNB), or a Next Generation NodeB (gNB)), a repeater device, or other customized telecommunication hardware. The multiband antenna apparatus 100 may further include a radome configured to cover the first and second radiating elements 1 lOa-d, 120a-d. In general, the radome may be a structural, weatherproof enclosure that protects the radiating elements from damage and is constructed from different kinds of materials, such as fiberglass, polytetrafluoroethylene (PTFE)-coated fabric, that minimally attenuate the electromagnetic signal transmitted or received by the multiband antenna apparatus 100.

[0043] Figure 3 shows a perspective view of a further embodiment of the multiband antenna apparatus 100 with the plurality of metallic structures 130a-d having a circular shape. As in the case of the embodiment shown in figure 2a, the location of the plurality of circular-shaped metallic structures 130a-d may be randomly distributed or distributed in an irregular way within the area defined by the arms of the first dipole radiating element 1 lOa-d.

[0044] Figure 4a shows a variant of the embodiment shown in figure 2a, wherein the first dual polarized dipole radiating element 1 lOa-d of the multiband antenna apparatus 100 comprises one or more coils. More specifically, in the embodiment shown in figure 4a, a respective portion of the elements I lla, 112a of the first arm of a first dipole of the dual polarized dipole radiating element 1 lOa-d may be configured with a coil shape. Also in this embodiment, the location of the plurality of square-shaped metallic structures 130a-d may be randomly distributed or distributed in an irregular way within the area defined by the arms of the first dipole radiating element 1 lOa-d. Figure 4b shows the perspective view of figure 4a without the plurality of squareshaped metallic structures 130a-d for better illustrating the coil-shaped configuration of portions of the arms of the first dipole radiating element HOa-d.

[0045] Figure 5 illustrates a schematic side view of the multiband antenna apparatus 100 according to an embodiment, where the plurality of metallic structures 130a-d are vertically spaced from upper support plane 150a, e.g. substrate 150a supporting the dipole radiating element 1 lOa-d. In an embodiment, the distance z between the upper support plane 150a and a further support plane of the support arrangement 150 supporting the plurality of metallic structures 130a-d is smaller than one tenth of the largest wavelength of the second frequency band.

[0046] Figure 6 shows a perspective view of a further embodiment of the multiband antenna apparatus 100. In the embodiment shown in figure 6, the metallic structures of the plurality of metallic structures 130a-d have the same square shape but different sizes, namely two different characteristic sizes. According to an embodiment, the at least two different characteristic sizes are smaller than the largest wavelength Amaxof the second frequency band.

[0047] Figure 7 shows a perspective view of a further embodiment of the multiband antenna apparatus 100. In the embodiment shown in figure 7, the metallic structures of the plurality of metallic structures 130a-d have a regular arrangement, but different shapes namely, by way of example, a circular, square, and cross shape. In an embodiment, these shapes may be hollow or filled.

[0048] In an embodiment, the multiband antenna apparatus 100 may further comprise a third radiating element configured to operate at a third frequency band and arranged on a lower support plane of the support arrangement 150 at a third distance to the reflector plate 140, wherein the third distance is smaller than the second distance, and the third frequency band is higher than the second frequency band. In this embodiment, the multiband antenna apparatus 100 further comprises a further plurality of metallic structures, wherein the further plurality of metallic structures are arranged on or close to the lower support plane of the support arrangement 150 and each further metallic structure has a size being smaller than the largest wavelength of the third frequency band for increasing the transparency of the first radiating element 1 lOa-d in the third frequency band by downconverting a frequency behavior of the transparency of the first radiating element 1 lOa-d. To this end, the plurality of metallic structures 130a-d may each have a size being smaller than the largest wavelength of the third frequency band for increasing the transparency of the first radiating element 1 lOa-d in the third frequency band by down-converting a frequency behavior of the transparency of the first radiating element 1 lOa-d. In an embodiment, the number of the plurality of metallic structures 130a-d may be selected based on a desired degree of the down-conversion of the frequency behavior of the transparency of the first radiating element 1 lOa-d.

[0049] Figure 8 shows a flow diagram illustrating steps of a method 800 for providing the multiband antenna apparatus 100 according to an embodiment. The method 800 comprises a step 801 of providing a first radiating element HOa-d, in particular a first dipole radiating element 1 lOa-d configured to operate at a first frequency band and arranged on an upper support plane, e.g. substrate 150a of a support arrangement 150 at a first distance to a reflector plate 140. Moreover, the method 800 comprises a step 803 of providing a second radiating element 120a-d configured to operate at a second frequency band and arranged on a lower support plane, e.g. substrate of the support arrangement 150 at a second distance to the reflector plate 140, wherein the second distance is smaller than the first distance and the second frequency band is higher than the first frequency band. The method 800 further comprises a step 805 of providing a plurality of metallic structures 130a-d, wherein the plurality of metallic structures 130a-d are arranged on or close to the upper support plane of the support arrangement 150 and each have a size being smaller than the largest wavelength of the second frequency band for increasing the transparency of the first radiating element 1 lOa-d in the second frequency band by down-converting a frequency behavior of the transparency of the first radiating element 1 lOa-d. In an embodiment, for providing the first radiating element 1 lOa-d, in particular the first dipole radiating element 110a- d, the first dipole radiating element 1 lOa-d may be printed on a substrate 150 in the form of a PCB. In an embodiment, also the plurality of metallic structures 130a-d may be printed on the PCB.

[0050] The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

[0051] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

[0052] The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

[0053] In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

CLAIMS1. A multiband antenna apparatus (100), comprising: a first radiating element (HOa-d) configured to operate at a first frequency band and arranged on an upper support plane (150a) of a support arrangement (150) at a first distance to a reflector plate (140); a second radiating element (120a-d) configured to operate at a second frequency band and arranged on a lower support plane of the support arrangement (150) at a second distance to the reflector plate (140), the second distance being smaller than the first distance, and the second frequency band being higher than the first frequency band; and a plurality of metallic structures (130a-d), wherein the plurality of metallic structures (130a-d) are arranged on or close to the upper support plane (150a) of the support arrangement (150) and each have a size being smaller than the largest wavelength of the second frequency band for increasing the transparency of the first radiating element (1 lOa-d) in the second frequency band by down-converting a frequency behavior of the transparency of the first radiating element (1 lOa-d).

2. The multiband antenna apparatus (100) of claim 1, wherein the plurality of metallic structures (130a-d) each have a size being smaller than one tenth of the largest wavelength of the second frequency band.

3. The multiband antenna apparatus (100) of claim 1 or 2, wherein the plurality of metallic structures (130a-d) have at least two different shapes.

4. The multiband antenna apparatus (100) of claim 1 or 2, wherein the plurality of metallic structures (130a-d) have the same shape and are arranged in an irregular or random pattern on or close to the upper support plane (150a) of the support arrangement (150) to increase the transparency of the first radiating element (1 lOa-d) in the second frequency band.

5. The multiband antenna apparatus (100) of any one of the preceding claims, wherein the plurality of metallic structures (130a-d) have at least two different sizes and are arranged on or close to the upper support plane (150a) of the support arrangement (150) to increase the transparency of the first radiating element (1 lOa-d) in the second frequency band, wherein the at least two different sizes are smaller than the largest wavelength of the second frequency band.

6. The multiband antenna apparatus (100) of any one of the preceding claims, wherein the plurality of metallic structures (130a-d) comprise one or more metallic structures (130a-d) with a hollow or filled square shape, one or more metallic structures (130a-d) with a hollow or filled circular shape, and / or one or more metallic structures (130a-d) with a hollow or filled cross shape.

7. The multiband antenna apparatus (100) of any one of the preceding claims, wherein the first radiating element (110a- d) comprises one or more coils (I l la, 112a).

8. The multiband antenna apparatus (100) of any one of the preceding claims, wherein the plurality of metallic structures (130a-d) are arranged on the upper support plane (150a) of the support arrangement (150) or on a further support plane of the support arrangement (150), wherein the distance between the upper support plane (150a) and the further support plane of the support arrangement (150) is smaller than one tenth of the largest wavelength of the second frequency band.

9. The multiband antenna apparatus (100) of any one of the preceding claims, wherein the multiband antenna apparatus (100) further comprises a third radiating element configured to operate at a third frequency band and arranged on a lower support plane of the support arrangement (150) at a third distance to the reflector plate (140), the third distance being smaller than the second distance, and the third frequency band being higher than the second frequency band, wherein the multiband antenna apparatus (100) further comprises a further plurality of metallic structures, wherein the further plurality of metallicstructures are arranged on or close to the lower support plane of the support arrangement (150) and each have a size being smaller than the largest wavelength of the third frequency band for increasing the transparency of the first radiating element (11 Oa-d) in the third frequency band by down-converting a frequency behavior of the transparency of the first radiating element (HOa-d).

10. The multiband antenna apparatus (100) of claim 9, wherein each of the plurality of metallic structures has a size being smaller than the largest wavelength of the third frequency band for increasing the transparency of the first radiating element (1 lOa-d) in the third frequency band by down-converting a frequency behavior of the transparency of the first radiating element (HOa-d).

11. The multiband antenna apparatus (100) of any one of the preceding claims, wherein a number of the plurality of metallic structures (130a-d) is selected based on a desired degree of the down-conversion of the frequency behavior of the transparency of the first radiating element (1 lOa-d).

12. The multiband antenna apparatus (100) of any one of the preceding claims, wherein the first radiating element (110a- d) is a first dipole radiating element (1 lOa-d) with a plurality of arms (11 la, 112a, 113a, 114a).

13. The multiband antenna apparatus (100) of claim 12, wherein the plurality of metallic structures (130a-d) are arranged within a region defined by the plurality of arms (I l la, 112a, 113a, 114a) of the first dipole radiating element (1 lOa-d).

14. A method (800) for providing a multiband antenna apparatus (100), wherein the method (800) comprises: providing (801) a first radiating element (HOa-d) configured to operate at a first frequency band and arranged on an upper support plane (150a) of a support arrangement (150) at a first distance to a reflector plate (140); providing (803) a second radiating element (120a-d) configured to operate at a second frequency band and arranged on a lower support plane of the support arrangement (150) at a second distance to the reflector plate (140), the second distance being smaller than the first distance, and the second frequency band being higher than the first frequency band; and providing (805) a plurality of metallic structures (130a-d), wherein the plurality of metallic structures (130a-d) are arranged on or close to the upper support plane of the support arrangement (150) and each have a size being smaller than the largest wavelength of the second frequency band for increasing the transparency of the first radiating element (1 lOa-d) in the second frequency band by down-converting a frequency behavior of the transparency of the first radiating element (1 lOa-d).

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