A base station antenna module having a frequency selective surface (FSS) component

Abstract

The proposed technology relates to a base station antenna module (100) comprising a plurality of antenna elements (101), a reflector (102) and a Frequency Selective Surface, FSS, component (103). The reflector (102) of the antenna module is provided with an opening and the FSS component (103) is arranged to at least partially overlap with the opening of the reflector. The FSS component (103) is configured to have both frequency suppression and bandpass characteristics. Furthermore, the FSS component (103) is a stacked multi-layered component. The FSS component (103) comprises at least one layer of conductive material, wherein said at least one layer of conductive material is configured to have predetermined frequency filtering properties. The FSS component (103) further comprises at least two layers of dielectric material, arranged on opposite sides of said at least one layer of conductive material for embedding at least a substantial part of said at least one layer of conductive material in dielectric material to thereby contribute to and / or influence the frequency suppression and bandpass characteristics of the FSS component.

Description

[0001] TITLE

[0002] A base station antenna module having a Frequency Selective Surface (FSS) component

[0003] FIELD OF THE INVENTION

[0004] The invention generally relates to radio antenna technology, and more particularly to a base station antenna module as well as an antenna system for base station applications in cellular communication networks.

[0005] BACKGROUND OF THE INVENTION

[0006] In recent years, with the development of radio communication technologies, data traffic is continuously and exponentially increasing. The number of users is constantly rising and the capacity demanded from each user is also increasing. Thus, there has been an increase in the number of new frequency bands available for radio communication and these new frequency bands require new base stations to be installed to keep up with the increased demands for data traffic. This incurs additional costs as the installation of new base stations with new and / or improved capabilities require more installation space. There is also a larger number of base station antennas installed in close proximity of each other, e.g., passive and active base station antennas operating in multiple frequency bands, and they may at times negatively affect each other through radio frequency interference.

[0007] By way of example, base station antenna technology is currently evolving from the fourth generation communication technology (4th-generation, 4G) to the fifth generation communication technology (5th-generation, 5G). A 5G base station antenna typically includes both passive and active antennas, and the active antennas may be, for example, massive multiple-input multiple-output (mMIMO) antennas utilizing beamforming technology. The number of 5G base stations is rapidly increasing and the problem of shortage of site resources is increasingly appearing.

[0008] To effectively deploy new and / or upgraded base station technology, a communications site is often upgraded by adding new equipment to an existing base station site, e.g., adding a new active 5G antenna unit and related equipment to an original 4G site having an existing passive antenna unit. In particular, a promising technical solution is to place the new active antenna unit behind the passive antenna unit to build an integrated base station antenna system comprising both an active antenna module and a passive antenna module.

[0009] There are several advantages with the integration of an active antenna unit behind a traditional passive antenna unit compared to arranging them side-by-side. There is normally not enough available space in existing radio masts or towers, and it is quite expensive to rent new radio mast locations. In addition, the wind load is significantly reduced with an integrated solution. High wind load is a severe problem that typically requires costly structural reinforcements of the radio masts. An integrated solution has the same projected cross-section area in the forward direction as a traditional base station antenna, and, as a consequence, reinforcements may not be necessary.

[0010] There is a general need for antenna modules that are relatively compact in size to reduce the required installation space. If the antenna modules occupy too much space, the number of possible installation sites for the antenna modules may be limited and therefore the number of possible use cases. Cell-site space is already constrained, and operators do not want to go through the lengthy process of gaining permission to occupy more tower space, which, in turn, increases maintenance costs.

[0011] For multi-band antenna modules such as the aforementioned 4G and 5G integrated active / passive base station antenna units the use of frequency selective surfaces (FSS) becomes an important choice.

[0012] WO 2023 / 029431 Al relates to a base station antenna that includes at least one passive internal grid reflector operating as a high-pass filtering FSS with an array of low-band radiating elements in front of the grid reflector. A mMIMO antenna array resides behind a back one of the at least one grid reflector and is configured to transmit radio frequencies through the grid reflector and out a front radome of the base station antenna.

[0013] EP 4195413 Al relates to a multi-band antenna system and implementation of a multi-band architecture. The multi-band antenna system includes: a plurality of radiating element arrays, feeding networks corresponding to the plurality of radiating element arrays, at least one layer of an FSS, and a reflection panel. The plurality of radiating element arrays are located above the reflection panel and all or some of the plurality of radiating element arrays are stacked. The at least one layer of the FSS is located between the stacked radiating element arrays and a feeding network corresponding to at least one radiating element array in the stacked radiating element arrays is electrically connected to the at least one layer of the FSS, or the feeding network corresponding to the at least one radiating element array is integrated on the at least one layer of the FSS.

[0014] When building compact multi-band antenna modules such as the aforementioned 4G and 5G integrated active / passive base station antenna units, the frequency filtering properties and performance of the FSS component becomes critical to provide an overall base station antenna solution that enables good radio-frequency performance.

[0015] BRIEF SUMMARY OF THE INVENTION

[0016] A general object of the proposed technology is to overcome at least part of the limitations of the state-of-the-art antenna modules and to provide improvements with regard to antenna modules and antenna systems for base station applications.

[0017] It is a particular object to provide an improved base station antenna module. It is also an object to provide an improved antenna system for base station applications in cellular communication networks.

[0018] These and other objects may be achieved by one or more embodiments of the proposed technology.

[0019] According to a first aspect of the invention, there is provided a base station antenna module comprising a plurality of antenna elements, a reflector and an FSS component. The reflector of the antenna module is provided with an opening and the FSS component is arranged to at least partially overlap with the opening of the reflector. The FSS component is configured to have both frequency suppression and bandpass characteristics. Furthermore, the FSS component is a stacked multi- layered component. The FSS component comprises at least one layer of conductive material, wherein said at least one layer of conductive material is configured to have predetermined frequency filtering properties. The FSS component further comprises at least two layers of dielectric material(s) arranged on opposite sides of said at least one layer of conductive material for embedding at least a substantial part of said at least one layer of conductive material in dielectric material to thereby contribute to and / or influence the frequency suppression and bandpass characteristics of the FSS component. The at least one layer of conductive material is configured as a two-dimensional array of recurrent filter elements for providing the predetermined frequency filtering properties. The sum of the thickness of the two outermost layers of dielectric material of the stacked multi-layered FSS component corresponds to at least a substantial part of half a wavelength, as measured in any of the dielectric material(s), at a center frequency of a specified passband of the FSS component.

[0020] Accordingly, said at least two layers of dielectric material in combination with said at least one layer of conductive material give said FSS component its intended frequency suppression and bandpass characteristics.

[0021] The inventor has realized that for the purpose of designing a base station antenna module the concept of at least partially embedding or encapsulating the conductive layer(s) of the FSS component in dielectric material enables the FSS component to have a passband with improved bandpass characteristics. As an example, it may be desirable to improve the stability or robustness of the passband and / or increase the frequency bandwidth of the passband. For example, it may be beneficial to obtain a passband with a frequency bandwidth that is substantially stable with respect to incident direction and / or polarization of an impinging electromagnetic wave in the sense that the passband does not shift substantially in frequency with varying incident direction and / or polarization.

[0022] The present invention may be regarded as a technical enabler for building multiband antenna systems in a compact and efficient manner and to cater for minimal transmission losses in the operating frequency bands as will be explained in more detail later on.

[0023] According to a second aspect of the invention, there is provided an antenna system for a base station application in a cellular communication network. The antenna system comprises a base station antenna module according to the first aspect, and a radio antenna unit.

[0024] BRIEF DESCRIPTION OF DRAWINGS

[0025] The embodiments, together with further objects and advantages thereof, may best be understood by referring to the following description together with the accompanying drawings, in which:

[0026] FIG. 1 is a schematic cross-sectional diagram illustrating an example of a base station antenna module according to an embodiment of the invention.

[0027] FIG. 2 is a schematic cross-sectional diagram illustrating an example of a base station antenna module for co-operation with an optional radio antenna unit / sub- system according to an embodiment of the invention.

[0028] FIG. 3 is a schematic cross-sectional diagram illustrating an example of a base station antenna module for co-operation with an optional integrated radio antenna sub-system according to an embodiment of the invention.

[0029] FIG. 4 is a schematic cross-sectional diagram illustrating another example of a base station antenna module for co-operation with an optional external radio antenna unit according to an embodiment of the invention.

[0030] FIG. 5 is a schematic cross-sectional diagram illustrating yet another example of a base station antenna module for co-operation with an optional external radio antenna unit according to an embodiment of the invention.

[0031] FIG. 6 is a schematic cross-sectional diagram illustrating still another example of a base station antenna module for co-operation with an optional external radio antenna unit according to an embodiment of the invention.

[0032] FIG. 7 is a schematic cross-sectional diagram illustrating a particular example of a base station antenna module according to an embodiment of the invention. FIG. 8 is a schematic cross-sectional diagram illustrating another particular example of a base station antenna module according to an embodiment of the invention.

[0033] FIG. 9 is a schematic cross-sectional diagram illustrating yet another particular example of a base station antenna module according to an embodiment of the invention.

[0034] FIG. 10 is a schematic cross-sectional diagram illustrating still another particular example of a base station antenna module according to an embodiment of the invention.

[0035] FIG. 11 is a schematic cross-sectional diagram illustrating an example of an FSS component according to an embodiment of the invention.

[0036] FIG. 12 is a schematic cross-sectional diagram illustrating another example of an FSS component according to an embodiment of the invention.

[0037] FIG. 13 is a schematic cross-sectional diagram illustrating yet another example of an FSS component according to an embodiment of the invention.

[0038] FIG. 14 is a schematic cross-sectional diagram illustrating an example of an FSS component according to an embodiment of the invention.

[0039] FIG. 15 is a schematic cross-sectional diagram illustrating another example of an FSS component according to an embodiment of the invention.

[0040] FIG. 16 is a schematic cross-sectional diagram illustrating yet another example of an FSS component according to an embodiment of the invention.

[0041] FIG. 17 is a schematic cross-sectional diagram illustrating still another example of an FSS component according to an embodiment of the invention.

[0042] FIG. 18 is a schematic cross-sectional diagram illustrating another example of an FSS component according to an embodiment of the invention. FIG. 19 is a schematic cross-sectional diagram illustrating an example of an FSS component showing an extension to an arbitrary higher number of layers according to an embodiment of the invention.

[0043] FIG. 20 is a schematic cross-sectional diagram illustrating an example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0044] FIG. 21 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0045] FIG. 22 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0046] FIG. 23 is a schematic cross-sectional diagram illustrating yet another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0047] FIG. 24 is a schematic cross-sectional diagram illustrating still another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0048] FIG. 25 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0049] FIG. 26 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 27 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0050] FIG. 28 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0051] FIG. 29 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0052] FIG. 30 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0053] FIG. 31 is a schematic cross-sectional diagram illustrating yet another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0054] FIG. 32 is a numerical example illustrating the reflection and transmission coefficients in logarithmic power scale as function of frequency for an example embodiment of an FSS component having both frequency suppression and bandpass characteristics.

[0055] FIG. 33 is a schematic diagram illustrating an example of relevant parts of a base station antenna module pertaining to the reflector and the FSS component according to an embodiment of the invention.

[0056] FIG. 34 is a diagram illustrating a top view of an example of a base station antenna module according to an embodiment.

[0057] FIG. 35 is a diagram illustrating a top view of another example of a base station antenna module according to an embodiment. FIG. 36 is a schematic diagram illustrating a top view of an example of a reflector unit according to an embodiment.

[0058] FIG. 37 is a schematic diagram illustrating an example of relevant parts of an antenna element and its relation to a layer of conductive material and associated layer of dielectric material.

[0059] FIG. 38 is a schematic diagram illustrating another example of relevant parts of an antenna element and its relation to a layer of conductive material and associated layer of dielectric material.

[0060] FIG. 39 is a diagram illustrating a perspective view of an example of an antenna system according to an embodiment.

[0061] FIG. 40 is a diagram illustrating a side view of an example of an antenna system according to an embodiment.

[0062] FIG. 41 is a diagram illustrating an exploded view of an example of relevant parts of an antenna system according to an embodiment.

[0063] DETAILED DESCRIPTION

[0064] In the following, the proposed technology will be described with reference to nonlimiting examples of the proposed design concept for a new base station antenna module and antenna system.

[0065] The below description generally refers to time-harmonic waves in the frequency domain.

[0066] Some terminology that is used throughout this document will now be presented. An “antenna element” typically refers to a structure that is capable of emitting and receiving electromagnetic waves. A “reflector” is typically a structure that substantially reflects electromagnetic waves launched by an antenna element in a given direction. A “Frequency Selective Surface”, or “FSS” for short, is a physical structure or component that acts as a filter for electromagnetic waves, allowing certain frequencies to pass through while reflecting others. A “radome” is typically a protective cover for the overall antenna module. A “backside radome” is a part of the radome that is located at the “backside” of the antenna module.

[0067] According to a first aspect of the invention, there is provided a base station antenna module comprising a plurality of antenna elements, a reflector and an FSS component. The reflector of the antenna module is provided with an opening and the FSS component is arranged to at least partially overlap with the opening of the reflector.

[0068] The FSS component is configured to have both frequency suppression and bandpass characteristics.

[0069] Furthermore, the FSS component is a stacked multi-layered component comprising: at least one layer of conductive material, wherein said at least one layer of conductive material is configured to have predetermined frequency filtering properties; and at least two layers of dielectric material, arranged on opposite sides of said at least one layer of conductive material for embedding at least a substantial part of said at least one layer of conductive material in the dielectric material(s) to thereby contribute to and / or influence the frequency suppression and bandpass characteristics of the FSS component.

[0070] It should be understood that said at least two layers of dielectric material in combination with said at least one layer of conductive material give the FSS component its intended frequency suppression and bandpass characteristics.

[0071] FIG. 1 is a schematic cross-sectional diagram illustrating an example of a base station antenna module according to an embodiment of the invention. The base station antenna module 100 typically comprises a plurality of antenna elements 101, a reflector 102, and an FSS component 103.

[0072] FIG. 1 shows a longitudinal side view of the base station antenna module 100, like many of the following cross-sectional diagrams. The reflector 102 of the antenna module 100 is provided with an opening and the FSS component 103 is arranged to at least partially overlap with the opening of the reflector. The opening may be fully or partially surrounded by the reflector 102. By way of example, it should also be understood that the reflector may be manufactured or built as a single piece or as a multi-component unit comprising at least two separate components for providing the reflector functionality and defining the opening of the reflector.

[0073] The FSS component 103 is configured to have both frequency suppression and bandpass characteristics.

[0074] The FSS component is generally a stacked multi-layered component. The FSS component comprises at least one layer of conductive material wherein said at least one layer of conductive material is configured to have predetermined frequency filtering properties.

[0075] The FSS component further comprises at least two layers of dielectric material arranged on opposite sides of said at least one layer of conductive material for embedding at least a substantial part of said at least one layer of conductive material in the dielectric material(s). The dielectric layers, or at least a subset thereof, thereby contribute to and / or influence the frequency suppression and bandpass characteristics of the FSS component.

[0076] As mentioned, it is the combination of said at least one layer of conductive material and said at least two layers of dielectric material that provides the intended frequency suppression and bandpass characteristics of the overall FSS component. In a particular example, at least a subset of said at least two layers of dielectric material may be configured to have a thickness configuration that provides and / or ensures predetermined frequency suppression and bandpass characteristics of the FSS component.

[0077] More specifically, said at least one layer of conductive material may be configured as a two-dimensional array of recurrent filter elements for providing the intended frequency filtering properties. For example, each conductive layer may be a two- dimensional periodic metallic pattern layer as will be explained in more detail later on.

[0078] Also, the sum of the thickness of the two outermost layers of dielectric material of the stacked multi-layered FSS component corresponds to at least a substantial part of half a wavelength, as measured in any of the dielectric materials, at a center frequency of a specified passband of the FSS component.

[0079] Various implementational examples of FSS component designs will be described later on.

[0080] The term “bandpass” is normally used for a bandpass filter or the process or characteristics of bandpass filtering, whereas the term “passband” is normally used for describing the corresponding frequency band or frequency range.

[0081] Sometimes the suppression characteristics of the FSS component are referred to as “bandstop” characteristics, implying that the overall FSS component has both bandstop and bandpass filtering characteristics.

[0082] As mentioned, said at least two layers of dielectric material are arranged on opposite sides of said at least one layer of conductive material for embedding at least a substantial part of said at least one layer of conductive material in dielectric material. An important design option is to embed the entire layer or layers of conductive material in dielectric material. By way of example, in the case of two or more layers of conductive material, each layer of conductive material may be embedded completely in dielectric material. The layers of dielectric material may be of the same type of dielectric material or different materials.

[0083] The inventor has realized that for the purpose of designing a base station antenna module the concept of at least partially embedding or encapsulating the conductive layer or layers of the FSS component in dielectric material enables the FSS component to have a passband with improved bandpass characteristics. As an example, it may be desirable to improve the stability or robustness of the passband and / or increase the frequency bandwidth of the passband compared to available prior art within the field of base station antenna technology. For example, it may be beneficial to obtain a passband with a frequency bandwidth that is substantially stable with respect to incident direction and / or polarization of an impinging electromagnetic wave in the sense that the passband does not substantially shift in frequency with varying incident direction and / or polarization.

[0084] By way of example, this allows the base station antenna module to interwork effectively with an optional external radio antenna unit or an integrated radio antenna sub-system that operates in one or more frequency bands that are within the passband of the FSS component. In other words, the FSS component may be configured to be substantially transparent to electromagnetic waves in this or these frequency bands.

[0085] Existing prior art predominantly focuses on FSS components with high-pass filtering characteristics. By way of example, the proposed technology allows for improved stability or robustness of the passband with respect to varying direction and polarization of the incident electromagnetic wave and / or allows for an increased frequency bandwidth of the passband.

[0086] As an example, the technology disclosed herein provides a compact antenna module and at least some of the benefits of the antenna module lies in the combined overall system functionality, with special emphasis on the application to base station antennas rather than individual Radio Frequency, RF, features.

[0087] The antenna elements 101 are typically connected to a feeding network (not shown in FIG. 1). The feeding network, including electrical power circuitry, and the electrical feeding lines, also referred to as feeding cables, may be of any standard type within the field of base station antennas.

[0088] By way of example, the FSS component 103, with said at least one layer of conductive material and said at least two layers of dielectric material, is configured to be substantially reflective to electromagnetic waves in a first frequency band, Fl, and configured to be substantially transparent to electromagnetic waves in at least one other frequency band, separate from the first frequency band Fl. In other words, Fl is within the suppression band of the FSS component 103, and the FSS component 103 has bandpass characteristics in said at least one other frequency band.

[0089] It should be understood that at least part of the antenna elements 101 of the base station antenna module 100 may be configured to operate in the first frequency band F 1.

[0090] FIG. 2 is a schematic cross-sectional diagram illustrating an example of a base station antenna module for co-operation with an optional radio antenna unit / subsystem according to an embodiment of the invention.

[0091] The base station antenna module 100 can interwork with an external radio antenna unit or an integrated radio antenna sub-system, collectively designated by reference 110 in FIG. 2, and individually designated by reference 110a for the integrated radio antenna sub-system and 110b for the external radio antenna unit in FIG. 3 to FIG. 6.

[0092] For example, the external radio antenna unit or integrated radio antenna subsystem operates in said at least one other frequency band, assuming that i) the antenna elements operating in the first frequency band Fl on one hand, and ii) the external radio antenna unit or integrated radio antenna sub-system operating in said at least one other frequency band on the other hand, are arranged on opposite sides of the FSS component.

[0093] Expressed differently, the antenna elements operating in the first frequency band Fl may be located on the front side of the base station antenna module, assuming that the front side corresponds to the main transmit direction of the antenna elements. The external radio antenna unit or integrated radio antenna sub-system operating in said at least one other frequency band may then be located behind the FSS component, which allows electromagnetic waves from the external radio antenna unit or integrated radio antenna sub-system to pass through the FSS component substantially unperturbed. In this way, an improved antenna module for base station applications is provided. The present invention may be regarded as a technical enabler for building compact multi-band antenna systems with minimal losses in the operating frequency bands, as will be explained in more detail later on.

[0094] By way of example, at least a subset of the antenna elements of the base station antenna module that are configured to operate in the first frequency band F 1 may be substantially transparent to electromagnetic waves in said at least one other frequency band.

[0095] For example, said at least one other frequency band is a band of higher frequency than the first frequency band F 1.

[0096] As schematically indicated in FIG. 1 and FIG. 2, a set of antenna elements may be mounted in or on the FSS component 103. Alternatively, or complementary, a set of antenna elements may be arranged on the reflector 102. At least part of the antenna elements are configured to operate in the first frequency band F 1.

[0097] Typically, the reflector 102 is RF grounded and at least part of the FSS component 103 is arranged to be coupled to the reflector 102 to provide RF grounding for the set of antenna elements that are mounted in or on the FSS component 103.

[0098] For example, at least part of the FSS component 103 may be capacitively or galvanically coupled to the reflector 102 along at least part of the perimeter that defines the opening of the reflector 102.

[0099] By way of example, another set of antenna elements may be mounted on the reflector 102 and also configured to operate in the first frequency band Fl . The set of antenna elements mounted in or on the FSS component 103 may be configured to co-operate with the set of antenna elements mounted on the reflector 102 as an array of antenna elements.

[0100] FIG. 3 is a schematic cross-sectional diagram illustrating an example of a base station antenna module for co-operation with an optional integrated radio antenna sub-system according to an embodiment of the invention. In this particular example, the base station antenna module 100 comprises an integrated radio antenna sub-system 110a which is located within an at least partially enclosing radome 107 / 108 of the base station antenna module 100. The integrated radio antenna sub-system 110a is configured to operate in at least one other frequency band separate from the first frequency band F 1.

[0101] As depicted in FIG. 3, the integrated radio antenna sub-system 110a and at least part of the antenna elements 101 of the base station antenna module 100 that are configured to operate in the first frequency band F 1 are arranged on opposite sides of the FSS component 103.

[0102] The radome elements 107 and 108 shown in FIG. 3 may be separated or part of the same radome. By way of example, the radome may be a planar radome, a tube radome, and / or a sleeve radome.

[0103] FIG. 4 is a schematic cross-sectional diagram illustrating another example of a base station antenna module for co-operation with an optional external radio antenna unit according to an embodiment of the invention.

[0104] In this particular example, the base station antenna module 100 is configured for enabling interoperability with an external radio antenna unit 110b which is located outside an at least partially enclosing radome 107 / 108 of the base station antenna module 100. The external radio antenna unit 110b is configured to operate in at least one other frequency band separate from the first frequency band F 1.

[0105] The external radio antenna unit 110b and at least part of the antenna elements 101 of the base station antenna module 100 that are configured to operate in the first frequency band Fl are arranged on opposite sides of the FSS component.

[0106] The base station antenna module 100 and the external radio antenna unit 110 may form an overall base station antenna system 150 with application in a cellular communication network. FIG. 5 is a schematic cross-sectional diagram illustrating yet another example of a base station antenna module for co-operation with an optional external radio antenna unit according to an embodiment of the invention.

[0107] In this particular example, the radome 108 is attached to the FSS component 103, or rather suitable parts thereof such as one of the layers of dielectric material.

[0108] FIG. 6 is a schematic cross-sectional diagram illustrating still another example of a base station antenna module for co-operation with an optional external radio antenna unit according to an embodiment of the invention.

[0109] In this particular example, the FSS component 103, or rather suitable parts thereof such as one of the layers of dielectric material, forms part of or is integrated with the radome 108 of the antenna module.

[0110] It should be understood that the integrated radio antenna sub-system 110a and the external radio antenna unit 110b normally includes power circuitry, electrical feeding, structural support elements and other components according to well- established radio antenna technology.

[0111] FIG. 7 is a schematic cross-sectional diagram illustrating a particular example of a base station antenna module according to an embodiment of the invention.

[0112] In this example, a set of antenna elements 101 are mounted in or on the FSS component 103 and configured to operate in a first frequency band Fl . As mentioned earlier the FSS component 103 is configured to be substantially reflective to electromagnetic waves in the first frequency band F 1. The reflection of frequency band Fl is schematically indicated by a turning arrow in FIG. 7. This notation also extends to other figures. Expressed differently, the first frequency band Fl is within the suppression band of the FSS component 103.

[0113] By way of example, the reflector 102 may be RF grounded and at least part of the FSS component 103 may be arranged to be coupled to the reflector 102 to provide RF grounding for the set of antenna elements 101 that are mounted in or on the FSS component 103. Various detailed implementations will be described later on. It should be understood that the reflector 102 is itself RF grounded through a suitable ground connection using well-established technical solutions.

[0114] For example, at least part of the FSS component 103 may be capacitively or galvanically coupled to the reflector 102 along at least part of the perimeter that defines the opening of the reflector 102.

[0115] In a particular example, the FSS component 103 and the reflector 102 may be capacitively coupled through a thin layer of insulating material so that the antenna elements arranged on the FSS component 103 may be effectively RF grounded, as will be discussed in more detail later on.

[0116] Additionally, the FSS component 103 is configured to be substantially transparent to electromagnetic waves in at least one other frequency band, preferably a higher frequency band, where transparency refers to minimum or low transmission losses with respect to scattering by an incident electromagnetic wave. This allows operational co-existence and interoperability with the optional radio antenna unit / sub-system 110, such as an external radio antenna unit or an integrated radio antenna sub-system, operating in said at least one other frequency band.

[0117] Thus, signals in said at least one other frequency band are allowed to pass through the FSS component 103 substantially unperturbed and to be received / transmitted by the optional radio antenna unit / sub-system 110.

[0118] The optional radio antenna unit / sub-system 110 includes power circuitry and electrical feeding, and may be an antenna sub-system or a complete multi-band radio unit, configured for operation in one or more frequency bands with reference to any relevant radio communication standard.

[0119] Optionally, at least a subset of the antenna elements 101 of the base station antenna module 100 that are configured to operate in the first frequency band Fl are configured to be substantially transparent to electromagnetic waves in said at least one other frequency band, as schematically indicated by the dashed arrows passing through one of the antenna elements 101 in FIG. 7. This notation also extends to other figures described below. FIG. 8 is a schematic cross-sectional diagram illustrating another particular example of a base station antenna module according to an embodiment of the invention.

[0120] In this example, a set of antenna elements 101 are mounted on the reflector 102, but extend into the space over the FSS component 103 and at least partially overlap with the opening of the reflector 102. This is an alternative antenna element configuration within the base station antenna module 100. At least part of these antenna elements 101 are configured to operate at the first frequency band F 1.

[0121] The alternative antenna element configuration illustrated in FIG. 8, where a set of antenna elements 101 are mounted on the reflector 102 but extend into the space over the FSS component 103 and at least partially overlap with the opening of the reflector 102, is merely an example of how such a configuration can be implemented. The skilled person realizes that other forms and orientations of feed arms or feed stalks may be used to achieve a similar technical effect.

[0122] As mentioned, the FSS component 103 is configured to be substantially transparent to electromagnetic waves in at least one other frequency band separate from the first frequency band F 1 to allow for efficient operational co-existence and interoperability with the optional radio antenna unit / sub-system 110 operating in said at least one other frequency band.

[0123] FIG. 9 is a schematic cross-sectional diagram illustrating yet another particular example of a base station antenna module according to an embodiment of the invention.

[0124] In this example, the base station antenna module comprises a plurality of antenna elements 101, including a set of antenna elements 104 mounted on the reflector 102 and a set of antenna elements 105 mounted on or in the FSS component 103. Both sets of antenna elements 104 and 105 are configured to operate in the first frequency band F 1. By providing suitable RF coupling, the set of antenna elements 105 mounted in or on the FSS component 103 may effectively co-operate with the set of antenna elements 104 mounted on the reflector 102 as a unified array of antenna elements, e.g., to improve the radiation pattern and enhance the antenna gain.

[0125] As mentioned, the reflector 102 may be RF grounded and at least part of the FSS component 103 may be arranged to be coupled to the reflector 102 to provide RF grounding for the set of antenna elements that are mounted in or on the FSS component 103.

[0126] FIG. 10 is a schematic cross-sectional diagram illustrating still another particular example of a base station antenna module according to an embodiment of the invention.

[0127] In this example, the base station antenna module 100 comprises a plurality of antenna elements 101, including a set of antenna elements 104 mounted on the reflector 102 and arranged to be placed over the reflector 102, and a set of antenna elements 106 mounted on the reflector 102 but extending into the space over the FSS component 103 and at least partially overlapping with the opening of the reflector 102. Both sets of antenna elements 104 and 106 operate in the first frequency band Fl and may be configured to co-operate, e.g., to improve the radiation pattern and enhance the antenna gain.

[0128] Both sets of antenna elements 104 and 106 are RF grounded via the reflector 102 which in turn has a suitable ground connection.

[0129] In the following, a number of examples of multi-layered FSS components will be described with reference to FIG. 11 to FIG. 19.

[0130] Common for the examples in FIG. 11 to FIG. 19 is the concept of at least partially encapsulating or embedding at least a substantial part of at least one layer of conductive material in dielectric material.

[0131] FIG. 11 is a schematic cross-sectional diagram illustrating an example of an FSS component according to an embodiment of the invention. In this example, the FSS component 103 comprises a layer 201 of conductive material and a first layer 202 of dielectric material and a second layer 203 of dielectric material, wherein the first layer 202 of dielectric material and the second layer 203 of dielectric material are arranged on opposite sides of the layer 201 of conductive material, at least partially embedding the conductive layer 201 in dielectric material. By embedding the conductive layer 201 in dielectric material a contribution to and / or influence of the frequency suppression and bandpass characteristics of the FSS component can be obtained.

[0132] In the following, the layer(s) of conductive material is / are sometimes referred to as conductive layer(s), and the layers of dielectric material are sometimes referred to as dielectric layers.

[0133] Although a symmetrical design with respect to the thickness of the first dielectric layer 202 and the thickness of the second dielectric layer 203 is preferable, this is not a requirement.

[0134] It should be understood that the layers 202 and 203 of dielectric material can be of the same type of material or different materials.

[0135] FIG. 12 is a schematic cross-sectional diagram illustrating another example of an FSS component according to an embodiment of the invention.

[0136] FIG. 12 is similar to FIG. 11, except for the presence of support layer 204 such as a carrier layer or a Printed Circuit Board, PCB, substrate layer. Specifically, the layer 201 of conductive material may be supported by such a carrier layer or PCB substrate layer 204.

[0137] FIG. 13 is a schematic cross-sectional diagram illustrating yet another example of an FSS component according to an embodiment of the invention. FIG. 13 is similar to FIG. 12, except for a different orientation of the support layer 204.

[0138] FIG. 14 is a schematic cross-sectional diagram illustrating an example of an FSS component according to an embodiment of the invention. In this example, the FSS component 103 comprises a first layer 301 of conductive material and a second layer 302 of conductive material, and a first layer 303 of dielectric material, a second layer 305 of dielectric material and a third intermediate layer 304 of dielectric material.

[0139] The first layer 303 of dielectric material and the third intermediate layer 304 of dielectric material are arranged on opposite sides of the first layer 301 of conductive material. The second layer 305 of dielectric material and the third intermediate layer 304 of dielectric material are arranged on opposite sides of the second layer

[0140] 302 of conductive material.

[0141] It should be understood that the intermediate layer 304 of dielectric material does not necessarily have to be thicker than the outermost layers 303 and 305 of dielectric material. In fact, it may be beneficial to configure the FSS component in such a way that the intermediate layer 304 of dielectric material has a smaller thickness than the outermost layers 303 and 305 of dielectric material.

[0142] Although a symmetrical design with respect to the thickness of the outermost layers

[0143] 303 and 305 of dielectric material may be preferable, this is not a requirement.

[0144] It should also be understood that the layers 303, 304 and 305 of dielectric material can be of the same type of material or different materials. For convenience, the outermost layers 303 and 305 may preferably be made of the same material while it may be advantageous to use a different material for the intermediate layer 304 of dielectric material.

[0145] FIG. 15 to FIG. 18 are schematic diagrams illustrating different examples of an FSS component in which the layers of conductive material may be supported by a respective support layer such as a carrier layer or a PCB substrate layer.

[0146] Specifically, each layer 301 and 302 of conductive material may be supported by a respective support layer or carrier layer 306 and 307, respectively.

[0147] FIG. 19 is a schematic cross-sectional diagram illustrating an example of an FSS component showing an extension to an arbitrary higher number of layers according to an embodiment of the invention. It should be understood that the number of layers of conductive material may be higher than two and the number of layers of conductive material may be higher than three, as schematically indicated by the dots in FIG. 19, implying that one or more additional layers of conductive material and corresponding layers of dielectric material may be arranged in the FSS component.

[0148] In general, it should be understood that the number M of conductive layers is M > 1 and the number N of dielectric layers is N > 2, where M and N are integers.

[0149] By way of example, the FSS component 103 may comprise three layers of conductive material and four layers of dielectric material for embedding the three layers of conductive material in dielectric material.

[0150] As another example, the FSS component 103 may comprise at least four layers of conductive material and at least five layers of dielectric material for embedding the four layers of conductive material in dielectric material.

[0151] In general, the layers of the multi-layered FSS component 103 extend in parallel with the main extension of the reflector and / or the main extension of the opening of the reflector.

[0152] As previously indicated, the dielectric material thickness may be an important design parameter of the overall FSS component.

[0153] As mentioned, the sum of the thickness of the two outermost layers of dielectric material of the stacked multi-layered FSS component corresponds to at least a substantial part of half a wavelength, as measured in any of the dielectric materials, at a center frequency of a specified passband of the FSS component.

[0154] For example, the thickness of each of the outermost layers of dielectric material may be a quarter of a wavelength at a center frequency of a specified passband measured in the respective material. More generally, each outermost layer of dielectric material normally has a thickness in the range of 0.2-0.4 of the wavelength measured in the respective material. It should be kept in mind that the same or different dielectric materials may be used in the design.

[0155] For passbands of certain frequency ranges, it may be desirable to use several layers of conductive material and hence a plurality of layers of dielectric material for embedding the conductive layers. For a given number of conductive layers, the frequency bandwidth may be increased by embedding the conductive layers in dielectric material, and the stability or robustness of the passband with respect to varying angle of incidence and polarization may also be improved.

[0156] In case the FSS component includes more than one layer of conductive material, the distance between any pair of neighboring conductive layers, and hence the thickness of the intermediate layer of dielectric material, may be configured to enable a critical coupling between the conductive layers to ensure sufficient frequency selectivity.

[0157] In practice, it may also be necessary to consider the change of transmission phase through the conductive layer(s), and hence the thickness of the overall FSS component 103 may deviate from the above-mentioned rules of thumb.

[0158] Also, the choice of dielectric material may be of great importance. By way of example, the layers of dielectric material preferably involve low-loss dielectric materials, e.g., materials with an effective dielectric constant in the range between 1.1 and 1.7. In general, porous, foam-like materials, such as polystyrene or similar substances, can be used. There is a balance between having good mechanical properties and low dielectric constant. Examples of suitable dielectric materials include, but are not limited to, various closed-cell structural polymetric foams made from, e.g., polymethacrylimide (PMI), polystyrene (PS), polyvinyl chloride (PVC) and expanded polytetrafluoroethylene (PTFE) , and possibly various polymers such as polyethylene, expanded polytetrafluoroethylene, polypropylene, and polymethylpentene .

[0159] The proposed technology may come at a price in thickness of the overall FSS component but generally offers significant RF performance improvements. For example, advantages include lower frequency bandwidth variations with respect to varying angle of incidence and polarization and / or improved frequency bandwidth of the passband. The proposed invention offers the possibility of a reasonably good design even with a single layer of conductive material, which allows for a cost- effective solution.

[0160] As mentioned, the FSS component is designed to have bandpass characteristics in a specified passband, preferably a relatively wide passband. As an example, it may be desirable for the FSS component to have a passband that allows electromagnetic waves in the range 3.3-4.0 GHz or 1.69-2.69 GHz, or combinations thereof, to pass through with minimum transmission losses. This would allow for one or more telecom frequency bands to pass through the FSS component substantially unperturbed.

[0161] In the following, a set of non-limiting examples of implementations of a base station antenna module will be described with reference to FIG. 20 to FIG. 29.

[0162] FIG. 20 is a schematic cross-sectional diagram illustrating an example of relevant parts of a base station antenna module according to an embodiment of the invention. The base station antenna module 100 comprises a plurality of antenna elements 101, a reflector 102, and an FSS component 103.

[0163] As mentioned, the antenna module 100 has a reflector 102 in which an opening has been defined. The opening may be fully or partially surrounded by the reflector as seen in the main plane of the extension of the reflector. The antenna module 100 further has an FSS component 103 which may be arranged to partially or fully overlap with the opening of the reflector 102.

[0164] In this particular example, the FSS component 103 comprises a layer 201 of conductive material, and a first layer 202 of dielectric material and a second layer 203 of dielectric material, wherein the first layer 202 of dielectric material and the second layer 203 of dielectric material are arranged on opposite sides of the layer 201 of conductive material for at least partially embedding the conductive layer 201 in dielectric material. The reflector 102 and the FSS component 103 may be mechanically held together, for example by glue or a screw connection. In this example, the layer 201 of conductive material is galvanically connected to the reflector 102.

[0165] By way of example, the reflector is normally a metallic reflector, e.g., comprising aluminum or various alloys thereof.

[0166] As schematically illustrated in FIG. 20, the antenna elements 101 are mounted in or on the FSS component 103 and configured to operate in a first frequency band Fl . In a particular example, the conductive layer 201 of the FSS component 103 is galvanically connected to the reflector 102 and the antenna elements 101 are connected to the conductive layer 201.

[0167] More generally, a specific conductive layer of the FSS component is coupled to the reflector to provide for reliable RF grounding. The antenna elements mounted in or on the FSS component are preferably connected to this specific conductive layer.

[0168] By way of example, the antenna elements may be connected to the specific conductive layer through recesses in the dielectric material in at least one of the layers of dielectric material as will be described in more detail later on. For example, electrical feeding cables for the antenna elements may be at least partially submerged into cutouts in the dielectric material or arranged on top of the dielectric material.

[0169] Normally, the specific conductive layer is the conductive layer that is located closest to the reflector.

[0170] As previously discussed, the FSS component 103, with the layer 201 of conductive material and the two layers 202 and 203 of dielectric material, may be configured to be substantially reflective to electromagnetic waves in a first frequency band F 1 , and configured to be substantially transparent to electromagnetic waves in at least one other frequency band separate from the first frequency band Fl. Thus, the first frequency band Fl should be within the suppression band of the FSS component 103. This radio frequency reflection of frequency band Fl is schematically indicated by a turning arrow in FIG. 20 and other figures.

[0171] The base station antenna module 100 may interwork with an external radio antenna unit or integrated radio antenna sub-system, collectively designated by reference 110. The overall antenna system defined by the base station antenna module 100 and the external radio antenna unit or integrated radio antenna subsystem 110 is designated by reference 150.

[0172] As mentioned, the external radio antenna unit or integrated radio antenna subsystem may operate in said at least one other frequency band, assuming that i) the antenna elements operating in the first frequency band F 1 , and ii) the external radio antenna unit or integrated radio antenna sub-system operating in said at least one other frequency band, are arranged on opposite sides of the FSS component.

[0173] The antenna elements 101 operating in the first frequency band Fl may thus be located on the front side of the base station antenna module, assuming that the front side corresponds to the main transmit direction of the antenna elements 101. The external radio antenna unit or integrated radio antenna sub-system operating in said at least one other frequency band may then be located behind the FSS component 103, which allows electromagnetic waves from the external radio antenna unit or integrated radio antenna sub-system to pass through the FSS component 103 substantially unperturbed.

[0174] Optionally, at least a subset of the antenna elements 101 that are configured to operate in the first frequency band F 1 are configured to be substantially transparent to electromagnetic waves in said at least one other frequency band, as schematically indicated by the dashed arrow passing through one of the antenna elements 101 in FIG. 20 and other figures.

[0175] FIG. 21 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 21 is similar to FIG. 20 except for an additional set of antenna elements mounted on the reflector.

[0176] In this example, the overall set of antenna elements 101 includes at least a first set of antenna elements 105 mounted in or on the FSS component 103 and a second set of antenna elements 104 mounted on the reflector 102. The second set of antenna elements 104 may also be configured to operate at the first frequency band Fl .

[0177] By way of example, the first set of antenna elements 105 mounted in or on the FSS component 103 may be configured to co-operate with the second set of antenna elements 104 mounted on the reflector 102 as a unified array of antenna elements.

[0178] The conductive layer 201 may be galvanically connected to the reflector 102, which itself has a reliable ground connection, to provide for an effective RF grounding of the combined array of antenna elements 104 and 105.

[0179] FIG. 22 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 22 is similar to FIG. 21 except for a thin layer 205 of insulating material that capacitively couples the conductive layer 201 to the reflector 102.

[0180] In this example, the FSS component 103 may be capacitively coupled to the reflector 102 to ensure reliable RF grounding of the antenna elements 105 mounted on or in the FSS component 103.

[0181] The thin layer of insulating material 205 capacitively couples the conductive layer 201 to the reflector 102, which itself has a reliable ground connection to provide for an effective RF grounding of the unified array of antenna elements 104 and 105.

[0182] FIG. 23 is a schematic cross-sectional diagram illustrating yet another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 23 is similar to FIG. 20 except that the layer 201 of conductive material is supported by an associated carrier layer 204 such as a PCB substrate. FIG. 24 is a schematic cross-sectional diagram illustrating still another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 24 is similar to FIG. 22 except that the layer 201 of conductive material is supported by an associated carrier layer 204 such as a PCB substrate.

[0183] FIG. 25 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 25 is similar to FIG. 24 except for the lack of the thin layer 205 of insulating material. Instead, a capacitive coupling is achieved by a fraction of dielectric material, here forming part of the layer 202 of dielectric material, disposed between the reflector 102 and the conductive layer 201.

[0184] FIG. 26 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0185] In this example, the base station antenna module 100 comprises a plurality of antenna elements 101, including a set of antenna elements 104 mounted on the reflector 102 and arranged to be placed over the reflector 102, and another set of antenna elements 106 mounted on the reflector 102 but extending into the space over the FSS component 103 and at least partially overlapping with the opening of the reflector 102. As an example, both sets of antenna elements 104 and 106 are configured to operate in the first frequency band Fl, and may be configured to cooperate, e.g., to improve radiation pattern and enhance the antenna gain.

[0186] Both sets of antenna elements 104 and 106 may be naturally RF grounded via the reflector 102 which in turn has a reliable ground connection.

[0187] In this particular example, the conductive layer 201 is located on the other side of the opening of the reflector 102 compared to the examples in FIG. 20 to FIG. 25.

[0188] In this example, the conductive layer 201 is also supported by an optional carrier layer 204. FIG. 27 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 27 is similar to FIG. 26 except for the thin layer 205 of insulating material that ensures a capacitive RF coupling between the conductive layer 201 and the reflector 102.

[0189] FIG. 28 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 28 is similar to FIG. 23 except for an additional layer of conductive material and an intermediate layer of dielectric material.

[0190] In the antenna module of FIG. 28, the FSS component 103 comprises a first layer 301 of conductive material and a second layer 302 of conductive material, and three layers 303, 304 and 305 of dielectric material. In this example, each of the conductive layers 301 and 302 has an associated carrier layer 306 and 307, respectively.

[0191] The antenna elements 101 are connected to the conductive layer 301, which is galvanically connected to the reflector 102 to ensure reliable RF grounding for the antenna elements.

[0192] FIG. 29 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 29 is similar to FIG. 24 except for an additional layer of conductive material and an intermediate layer of dielectric material.

[0193] The antenna elements 105 are connected to the conductive layer 301. In this example, the conductive layer 301 is capacitively coupled to the reflector 102 via a thin layer 205 of insulating material to provide reliable RF grounding for the antenna elements 105.

[0194] FIG. 30 is a schematic cross-sectional diagram illustrating another example of relevant parts of a base station antenna module according to an embodiment of the invention. FIG. 30 is similar to FIG. 25, except for an additional layer of conductive material and an intermediate layer of dielectric material. In this example, a capacitive coupling between the conductive layer 301 and the reflector 102 is achieved by a fraction of dielectric material, here forming part of the layer 303 of dielectric material.

[0195] FIG. 31 is a schematic cross-sectional diagram illustrating yet another example of relevant parts of a base station antenna module according to an embodiment of the invention.

[0196] In this particular example, the FSS component 103 comprises three layers 401, 402 and 403 of conductive material and four layers 404, 405, 406 and 407 of dielectric material.

[0197] The example in FIG. 31 also highlights that the antenna elements 105 do not necessarily have to be mounted on the uppermost conductive layer 401 , but may be connected to one of the inner layers of conductive material such as layer 402 which is galvanically or capacitively coupled to the reflector 102, possibly via an optional thin layer of insulating material 205. The connections of the antenna elements 105 may extend through holes in the uppermost conductive layer 401 in order to reach the inner layer 402 of conductive material.

[0198] It should be understood that various other implementations and / or combinations of the above-listed examples exist.

[0199] It should also be understood that the above base station antenna modules normally include electrical feeding, structural support elements as well as other components according to well-established radio antenna technology, all of which may be encompassed fully or partially within a radome that protects the base station antenna module.

[0200] As an example, it should be understood that one of the layers of dielectric material may be attached to or form part of a radome of the antenna module. For example, one of the layers of dielectric material may be attached to or form part of a backside radome of the base station antenna module. The backside radome may provide structural support for the antenna module and protect the interior components of the base station antenna module from weather influences and mechanical impact.

[0201] FIG. 32 is a numerical example illustrating the reflection and transmission coefficients as function of frequency for an example embodiment of a multi-layered FSS component having four conductive layers with periodic metallic pattern and five layers of dielectric material. The scattering parameters, S-parameters, are shown on a logarithmic power scale for the case of ±45 degree slant linear polarization and incident angles of 0, 30 and 45 degrees, respectively. As can be seen in FIG. 32, frequency suppression is achieved in a specified low-frequency range 612-960 MHz and stable wide bandpass filtering is achieved in a specified high-frequency range 1695-2690 MHz. Note that the passband 1695-2690 MHz does not shift substantially in frequency with varying incident angle of the impinging electromagnetic wave. FIG. 32 is the result of a simulation using a commercial Finite Element Method (FEM) electromagnetic solver.

[0202] FIG. 33 is a schematic diagram illustrating an example of relevant parts of a base station antenna module pertaining to the reflector and the FSS component according to an embodiment of the invention.

[0203] The antenna module 100 may include a basic support structure, e.g., in the form of a metallic frame, configured to support the reflector 102 and the FSS component 103 arranged in the opening of the reflector. As an example, the reflector 102 and the FSS component 103 may be mechanically held together by means of a screw connection.

[0204] In this example, the FSS component 103 comprises a single layer 201 of conductive material, which is at least partially encapsulated or embedded by the two layers 202 and 203 of dielectric material.

[0205] As previously indicated, the layer 201 of conductive material may be configured as a two-dimensional array of recurrent filter elements defining a periodic conductive pattern. A recurrent filter element may sometimes be referred to as an FSS unit cell. By way of example, the design of a suitable conductive layer may involve selecting appropriate shape and geometry of the FSS unit cell and optimizing the design through iterative simulations and / or experiments. The specific design parameters for configuring the electromagnetic properties of the FSS unit cell depend on the desired frequency characteristics and application of the overall FSS component.

[0206] Normally, the FSS unit cells are arranged on a base substrate and each unit cell is part of a larger two-dimensional periodic array.

[0207] The FSS unit cell may be defined by slots and / or patches of various geometrical shapes, e.g., slots in a metallic screen and / or metallic patches, or combinations thereof.

[0208] The FSS unit cell is usually designed by means of Floquet modes. The goal in the design process is to minimize the transmission losses in the specified passband while keeping sufficiently high attenuation in the specified suppression band. The FSS design is validated against the entire scan range for which the FSS component is intended to work. Throughout the following description the term scan angle is used synonymously with the term incident angle.

[0209] An objective in the design of the overall FSS component is normally to obtain low transmission losses in a wide passband over a large range of scan angles.

[0210] By way of example, for dual operating polarizations the FSS unit cell geometry should preferably obey certain symmetry requirements, typically reflection symmetry with respect to two orthogonal planes through the center of the unit cell, in order to minimize any cross-polarization components of the transmitted electromagnetic wave.

[0211] The design of the periodic conductive pattern of the FSS component including shape, size and symmetry of the FSS unit cell typically depends on the intended frequency range and whether the radio antenna unit, to which the FSS component should be adapted, is single polarized or dual polarized and what polarization(s) the radio antenna unit supports. As previously discussed, the embedding of at least a substantial part of the conductive layers in dielectric material contributes to and / or influences the frequency suppression and bandpass characteristics of the FSS component.

[0212] FIG. 34 is a diagram illustrating a top view of an example of a base station antenna module according to an embodiment.

[0213] The base station antenna module 100 illustrated in FIG. 34 comprises a plurality of antenna elements 104 and 105, a metallic reflector 102 in which an opening is defined, and an FSS component 103 of which the uppermost conductive layer 201 is shown. The FSS component 103 is mounted in the opening of the reflector 102. A first set of antenna elements 105 are arranged in or on the FSS component 103, and a second set of antenna elements 104 are arranged on the reflector 102. In this example, the opening of the reflector 102 is surrounded by the conductive material of the reflector 102 to enable, through suitable coupling between the reflector 102 and the FSS component 103, reliable RF grounding for the first set of antenna elements 105 mounted in or on the FSS component 103 and to enable co-operation with the second set of antenna elements 104 arranged on the reflector 102, e.g., in terms of improved radiation pattern and enhanced antenna gain.

[0214] The one or more conductive layers of the FSS component are typically embedded in multiple layers of dielectric material, as previously described.

[0215] For example, but not necessarily, the opening may be surrounded by the conductive material of the reflector and the FSS component may be provided with conductive material arranged so that at least part of or the entire periphery of the FSS component is RF grounded. It is normally desirable to provide multiple grounding points where the separation between the grounding points is small compared to the operating wavelength. By providing RF grounding around most of or the entire FSS component periphery, either discretely or continuously, the FSS component together with the reflector behaves as a continuous ground plane.

[0216] In example embodiments of the technology disclosed, the conductive pattern may be printed on a thin insulating film, etched on a PCB and / or etched directly onto a carrier layer. The conductive pattern is typically periodic in the xy-plane with the z- axis pointing in the normal direction of the FSS component 103, i.e., with the z-axis pointing in the main transmit direction of the antenna elements.

[0217] FIG. 35 is a diagram illustrating a top view of another example of a base station antenna module according to an embodiment.

[0218] The base station antenna module 100 illustrated in FIG. 35 is similar to that of FIG. 34 except for the structural design of the opening defined in the reflector 102. In this example, the opening of the reflector 102 and the FSS component 103 mounted in the opening is only partially surrounded by the reflector 102. This setting may be enough to provide sufficient RF grounding for the first set of antenna elements 105 mounted on the FSS component 103 and to enable co-operation with the second set of antenna elements 104 arranged on the reflector 102.

[0219] FIG. 36 is a schematic diagram illustrating a top view of an example of a reflector unit according to an embodiment. As previously mentioned, the reflector may be manufactured or built as a single piece or as a multi-component unit. The reflector illustrated in FIG. 36 is a multi-component unit comprising two or more components 102-1, 102-2, 102-3 and 102-4 for providing the reflector functionality and defining the opening of the reflector.

[0220] For example, the reflector component 102-4 may be an optional element as illustrated by the dashed lines. This corresponds to the reflector geometry in FIG. 35.

[0221] FIG. 37 is a schematic diagram illustrating an example of relevant parts of an antenna element and its relation to a layer of conductive material and associated layer of dielectric material.

[0222] FIG. 38 is a schematic diagram illustrating another example of relevant parts of an antenna element and its relation to a layer of conductive material and associated layer of dielectric material. As illustrated in FIG. 37 and FIG. 38, the antenna element 105 may be connected, e.g., via a metallic block, to a conductive layer 201 through recesses in the dielectric material in at least one of the layers of dielectric material.

[0223] By way of example, the electrical feeding cables 109 associated with the antenna element 105 may be arranged on top of the dielectric material, c.f., FIG. 37, or at least partially submerged into cutouts or recesses in the dielectric material, c.f., FIG. 38.

[0224] As an example, the feeding cables may be coaxial cables or microstrip transmission lines that are aligned with the inductive grid lines on the uppermost conductive layer 201. The inductive grid lines is part of the FSS unit cell geometry and is a consequence of combining slots in a metallic screen and metallic patches to achieve the desired bandpass filtering.

[0225] FIG. 39 is a diagram illustrating a perspective view of an example of an antenna system according to an embodiment.

[0226] The example embodiment of FIG. 39 represents a base station antenna system 150 comprising a base station antenna module 100, various embodiments of which have been discussed herein, and an external radio antenna unit 110b arranged in connection with the antenna module 100. The radio antenna unit 110b is aligned with the opening of the reflector and the associated FSS component of the antenna module 100.

[0227] FIG. 40 is a diagram illustrating a side view of an example of an antenna system according to an embodiment. As can be seen, a compact overall solution of the antenna system 150 is obtained by proper placement of the external radio antenna unit 110b behind the base station antenna module 100 and the associated FSS component.

[0228] FIG. 41 is a diagram illustrating an exploded view of an example of relevant parts of an antenna system according to an embodiment. In this view, the external radio antenna unit 110b and the antenna module 100 are both visible. Further, a conductive layer and two parallel and aligned dielectric layers in the antenna module 100 can be seen. It should be emphasized that FIG. 41 is an exploded view and that in practice the dielectric layers are arranged for embedding the conductive layer in dielectric material. For simplicity, only one conductive layer and two dielectric layers are shown in FIG. 41.

[0229] According to a second aspect of the invention, there is provided an antenna system for a base station application in a cellular communication network. The antenna system comprises a base station antenna module according to the first aspect in combination with a radio antenna unit.

[0230] By way of example, the base station antenna module may be at least partially surrounded by a radome and the radio antenna unit may be arranged externally outside of the radome.

[0231] The embodiments described above are merely given as examples and it should be understood that the proposed technology is not limited thereto. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the invention. In particular, different part solutions in the different embodiments can be combined in other configurations where technically possible.

Claims

CLAIMS1. A base station antenna module (100) comprising a plurality of antenna elements (101), a reflector (102) and a Frequency Selective Surface, FSS, component (103), wherein the reflector (102) of the antenna module (100) is provided with an opening and said FSS component (103) is arranged to at least partially overlap with the opening of the reflector (102), wherein said FSS component (103) is configured to have both frequency suppression and bandpass characteristics, wherein said FSS component (103) is a stacked multi-layered component comprising: at least one layer (201; 301, 302) of conductive material, wherein said at least one layer (201; 301, 302) of conductive material is configured to have predetermined frequency filtering properties; and at least two layers (202; 203; 303; 304; 305) of dielectric material, arranged on opposite sides of said at least one layer (201; 301, 302) of conductive material for embedding at least a substantial part of said at least one layer (201; 301, 302) of conductive material in dielectric material to thereby contribute to and / or influence the frequency suppression and bandpass characteristics of the FSS component (103), wherein said at least one layer (201; 301, 302) of conductive material is configured as a two-dimensional array of recurrent filter elements for providing said predetermined frequency filtering properties, and wherein the sum of the thickness of the two outermost layers (202, 203; 303, 305) of dielectric material of the stacked multi-layered FSS component (103) corresponds to at least a substantial part of half a wavelength, as measured in any of the dielectric material(s), at a center frequency of a specified passband of the FSS component (103).

2. The base station antenna module (100) of claim 1, wherein at least a subset of said at least two layers (202; 203; 303; 304; 305) of dielectric material are configured to have a thickness configuration that provides and / or ensurespredetermined frequency suppression and bandpass characteristics of said FSS component (103).

3. The base station antenna module (100) of any of the claims 1 to 2, wherein said FSS component (103), with said at least one layer (201; 301, 302) of conductive material and said at least two layers (202; 203; 303; 304; 305) of dielectric material, is configured to be substantially reflective to electromagnetic waves in a first frequency band, Fl, and configured to be substantially transparent to electromagnetic waves in at least one other frequency band separate from the first frequency band F 1.

4. The base station antenna module (100) of claim 3, wherein at least part of the antenna elements (101) of the base station antenna module (100) are configured to operate in the first frequency band F 1.

5. The base station antenna module of claim 4, wherein said base station antenna module (100) further comprises an integrated radio antenna sub-system (110a), located within an at least partially enclosing radome of said base station antenna module (100), configured to operate in said at least one other frequency band, separate from the first frequency band Fl, and wherein i) said radio antenna subsystem (110a), and ii) the antenna elements (101) of the base station antenna module (100) that are configured to operate in the first frequency band Fl, are arranged on opposite sides of said FSS component (103).

6. The base station antenna module of claim 4, wherein said base station antenna module (100) is configured for enabling interoperability with an external radio antenna unit (110b) located outside an at least partially enclosing radome of said base station antenna module (100), configured to operate in said at least one other frequency band separate from the first frequency band F 1 , and wherein i) said external radio antenna unit (110b), and ii) the antenna elements (101) of the base station antenna module (100) that are configured to operate in the first frequency band Fl, are arranged on opposite sides of said FSS component (103).

7. The base station antenna module of any of the claims 4 to 6, wherein at least a subset of the antenna elements (101) of the base station antenna module (100),configured to operate in the first frequency band Fl, are substantially transparent to electromagnetic waves in said at least one other frequency band.

8. The base station antenna module (100) of any of the claims 3 to 7, wherein said at least one other frequency band is a band of higher frequency than said first frequency band F 1.

9. The base station antenna module (100) of any of the claims 3 to 8, wherein a first set of antenna elements (101; 105) are mounted in or on said FSS component (103) and configured to operate in said first frequency band Fl.

10. The base station antenna module (100) of claim 9, wherein said reflector (102) is Radio Frequency, RF, grounded and at least part of said FSS component (103) is arranged to be coupled to the reflector (102) to provide RF grounding for said first set of antenna elements (101; 105) mounted in or on said FSS component (103).

11. The base station antenna module of claim 10, wherein at least part of said FSS component (103) is capacitively or galvanically coupled to the reflector (102) along at least part of the perimeter that defines the opening of said reflector (102).

12. The base station antenna module of claim 10 or 11, wherein a second set of antenna elements (104) are mounted on the reflector (102) and configured to operate in said first frequency band Fl, and the first set of antenna elements (105) mounted in or on the FSS component (103) are configured to co-operate with the second set of antenna elements (104) mounted on the reflector (102) as an array of antenna elements.

13. The base station antenna module (100) of any of the claims 10 to 12, wherein a specific conductive layer (201; 301) of said FSS component (103) is coupled to the reflector (102) to provide for reliable RF grounding and said first set of antenna elements (105) are connected to said specific conductive layer (201; 301).

14. The base station antenna module (100) of claim 13, wherein said specific conductive layer (201; 301) is the conductive layer (201; 301) that is located closest to the reflector (102).

15. The base station antenna module (100) of claim 13 or 14, wherein said first set of antenna elements (105) are connected to said specific conductive layer (201; 301) through recesses in the dielectric material in at least one of said at least two layers (202; 203; 303; 304; 305) of dielectric material.

16. The base station antenna module (100) of claim 15, wherein electrical feeding cables for said first set of antenna elements (105) are at least partially submerged into cutouts in the dielectric material or arranged on top of the dielectric material.

17. The base station antenna module (100) of any of the claims 1 to 16, wherein said FSS component (103) comprises a first layer (301) of conductive material and a second layer (302) of conductive material, and a first layer (303) of dielectric material, a second layer (305) of dielectric material and a third intermediate layer (304) of dielectric material, wherein said first layer (303) of dielectric material and said third intermediate layer (304) of dielectric material are arranged on opposite sides of said first layer (301) of conductive material, and wherein said second layer (305) of dielectric material and said third intermediate layer (304) of dielectric material are arranged on opposite sides of said second layer (302) of conductive material.

18. The base station antenna module (100) of any of the claims 1 to 16, wherein said FSS component (103) comprises three layers of conductive material and four layers of dielectric material for embedding said three layers of conductive material in dielectric material.

19. The base station antenna module (100) of any of the claims 1 to 16, wherein said FSS component (103) comprises at least four layers of conductive material and at least five layers of dielectric material for embedding said layers of conductive material in dielectric material.

20. The base station antenna module (100) of any of the claims 1 to 19, wherein said at least one layer (201; 301, 302) of conductive material is supported by acarrier layer (204; 306, 307) or a Printed Circuit Board, PCB, substrate layer (204; 306, 307).

21. The base station antenna module (100) of any of the claims 1 to 20, wherein one of said at least two layers (202; 203; 303; 304; 305) of dielectric material is attached to or forms part of a radome of said antenna module.

22. The base station antenna module (100) of claim 21, wherein one of said at least two layers (202; 203; 303; 304; 305) of dielectric material forms part of a backside radome of said base station antenna module.

23. The base station antenna module (100) of any of the claims 1 to 22, wherein the reflector (102) of the antenna module (100) is a multi-component unit comprising at least two individual components for providing reflector functionality and defining said opening of the reflector (102).

24. An antenna system (150) for a base station application in a cellular communication network, said antenna system (150) comprising a base station antenna module (100) of any of the claims 1 to 25, and a radio antenna unit (110b).

25. The antenna system of claim 24, wherein said base station antenna module (100) is at least partially surrounded by a radome (107, 108) and said radio antenna unit (110b) is arranged outside of said radome.

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