A base station antenna module having at least one frequency selective surface (FSS) layer

Abstract

The proposed technology relates to a base station antenna module (100) comprising a plurality of antenna elements, a reflector (104) and at least one Frequency Selective Structure, FSS, layer (102; 107). The reflector (104) of the antenna module is provided with an opening and a first FSS layer (107) is arranged to at least partially overlap with the opening of the reflector (104). A first set of antenna elements (106) is mounted on the first FSS layer (107) and is configured to operate in a first frequency band F1. More importantly, said at least one FSS layer (102; 107) is configured to have both frequency suppression and multi-passband properties such that i) the first frequency band F1 is within a suppression band of said at least one FSS layer, and ii) said at least one FSS layer is configured to be substantially transparent to electromagnetic waves in at least two disjunct frequency bands, including at least a second frequency band F2 and a third frequency band F3, that are separate from the first frequency band F1.

Description

[0001] TITLE

[0002] A base station antenna module having at least one Frequency Selective Surface (FSS) layer

[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 manufactured and installed so as to keep up with the increased demands on 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 updated base station technology, a communications site is often updated 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 technical solution has been to place the new active antenna unit behind the passive antenna unit to build an integrated base station antenna system comprising both an active module and a passive 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. First, 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 therefore reinforcements may not be necessary.

[0010] 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.

[0011] WO 2023 / 029431 Al relates to a base station antenna that includes at least one passive internal grid reflector operating as an FSS with an array of low band radiating elements projecting forward of a front one of the at least one grid reflector. A mMIMO antenna array resides behind a back one of the at least one grid reflector and is configured to transmit signal through the grid reflector and out a front radome of the base station antenna.

[0012] EP 4195413 Al relates to a multi-band antenna system and a base station, and implementation of a multi-band architecture. The multi-band antenna system includes: a plurality of radiating element arrays, feeding networks separately corresponding to the plurality of radiating element arrays, at least one layer of a frequency selective surface, and a reflection panel, where 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 frequency selective surface 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 frequency selective surface, or the feeding network corresponding to the at least one radiating element array is integrated on the at least one layer of the frequency selective surface.

[0013] The addition of one or more FSS layers and related structural elements typically translates into an undesirable increase in height and / or size of these multi-band antenna modules. This may limit the number of possible installation sites for the antenna modules and therefore the number of possible use cases.

[0014] There is thus a need for antenna modules that are relatively compact in size to reduce the required space for the antenna module when installed on site. It is also important to provide a design solution that enables good radio frequency performance and does not impose unreasonable transmission losses.

[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.

[0018] It is also an object to provide an improved antenna system for base station applications in cellular communication networks.

[0019] These and other objects may be achieved by one or more embodiments of the proposed technology.

[0020] 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 at least one Frequency Selective Surface, FSS, layer. The reflector of the antenna module is provided with an opening and a first FSS layer is arranged to at least partially overlap with the opening of the reflector. A first set of antenna elements are mounted on the first FSS layer and configured to operate in a first frequency band F 1. More importantly, said at least one FSS layer is configured to have both frequency suppression and multi-passband properties such that: i) the first frequency band F 1 is within a suppression band of said at least one FSS layer, and ii) said at least one FSS layer is configured to be substantially transparent to electromagnetic waves in at least two disjunct frequency bands, including at least a second frequency band F2 and a third frequency band F3, that are separate from the first frequency band F 1.

[0021] According to a second aspect of the invention, there is provided an antenna system for base station applications in cellular communication networks. The antenna system comprises a base station antenna module according to the first aspect, combined with a separate multi-band antenna unit having antenna elements configured to operate in said at least two disjunct frequency bands, including at least a second frequency band F2 and a third frequency band F3, wherein the multi-band antenna unit is arranged on the opposite side of said at least one FSS layer relative to the first set of antenna elements that are mounted on the first FSS layer and configured to operate in the first frequency band Fl.

[0022] In this way, improved antenna modules and antenna systems for base station applications is provided. In particular, the proposed technology enables advanced multi-band antenna systems to be designed compactly and to cater for minimal transmission losses.

[0023] BRIEF DESCRIPTION OF DRAWINGS

[0024] The embodiments, together with further objects and advantages thereof, may best be understood by referring to the following description taken together with the accompanying drawings, in which:

[0025] FIG. 1 is a schematic cross-sectional diagram illustrating an example of a base station antenna module according to an embodiment of the invention.

[0026] FIG. 2 is a schematic cross-sectional diagram illustrating another example of a base station antenna module according to an embodiment of the invention. FIG. 3 is a schematic cross-sectional diagram illustrating yet another example of a base station antenna module according to an embodiment of the invention.

[0027] FIG. 4 is a schematic cross-sectional diagram illustrating still another example of a base station antenna module according to an embodiment of the invention.

[0028] FIG. 5 is a schematic cross-sectional diagram illustrating another example of a base station antenna module according to an embodiment of the invention.

[0029] FIG. 6 is a schematic cross-sectional diagram illustrating an example of a base station antenna module combined with a multi-band antenna unit according to an embodiment of the invention.

[0030] FIG. 7 is a schematic cross-sectional diagram illustrating an example of a base station antenna module having an integrated multi-band antenna sub-system according to an embodiment of the invention.

[0031] FIG. 8 is a schematic cross-sectional diagram illustrating another example of a base station antenna module having an integrated multi-band antenna sub-system according to an embodiment of the invention.

[0032] FIG. 9 is a schematic cross-sectional diagram illustrating yet another example of a base station antenna module having an integrated multi-band antenna sub-system according to an embodiment of the invention.

[0033] FIG. 10 is a schematic cross-sectional diagram illustrating still another example of a base station antenna module having an integrated multi-band antenna subsystem according to an embodiment of the invention.

[0034] FIG. 11 is a schematic graph illustrating an example of the reflection and transmission coefficients of electromagnetic waves in power scale as function of frequency for an example embodiment of a two-layer FSS having frequency suppression and bandpass filtering characteristics with multi-passband properties. FIG. 12 is a schematic cross-sectional diagram illustrating an example of an antenna module according to an embodiment of the invention.

[0035] FIG. 13 is a schematic cross-sectional diagram illustrating another example of an antenna module according to an embodiment of the invention.

[0036] FIG. 14 is a schematic cross-sectional diagram illustrating yet another example of an antenna module according to an embodiment of the invention.

[0037] FIG. 15A-B are schematic diagrams illustrating two different conceptual examples of an FSS unit cell from which a structured FSS component may be built.

[0038] FIG. 16A is a schematic top-view diagram illustrating an example of a smaller cutout of a conceptual FSS component with a grounded metal foundation in the center cell at which an antenna element may be arranged.

[0039] FIG. 16B is a schematic diagram illustrating an example of a coaxial line that may be used for electrically feeding antenna elements mounted on the first FSS layer.

[0040] FIG. 17 is a diagram illustrating a perspective view of an example of an antenna module according to an embodiment.

[0041] FIG. 18 is a diagram illustrating a top view of an example of an antenna module according to an embodiment.

[0042] FIG. 19 is a diagram illustrating a top view of another example of an antenna module according to an embodiment.

[0043] FIG. 20 is a diagram illustrating a perspective view of an example of an antenna system according to an embodiment.

[0044] FIG. 21 is a diagram illustrating a side view of an example of an antenna system according to an embodiment. FIG. 22 is a diagram illustrating an exploded view of an example of relevant parts of an antenna system according to an embodiment.

[0045] FIG. 23 is a diagram illustrating another exploded view of the antenna system of FIG. 22 according to an embodiment.

[0046] DETAILED DESCRIPTION

[0047] In the following, the proposed technology will be described with reference to nonlimiting examples of the proposed technical design concept for a new base station antenna module and antenna system.

[0048] 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 that acts as a filter for electromagnetic waves, allowing certain frequencies to pass through while reflecting or attenuating others. In antenna applications, FSS structures are mostly used to enhance performance by filtering out unwanted frequencies and improving the antenna unit's bandwidth and efficiency. 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.

[0049] 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 at least one FSS layer. The reflector of the antenna module is provided with an opening and a first FSS layer is arranged to at least partially overlap with the opening of the reflector. A first set of antenna elements are mounted on the first FSS layer and configured to operate in a first frequency band Fl. More importantly, said at least one FSS layer is configured to have both frequency suppression and multi-passband properties such that: i) the first frequency band F 1 is within the suppression band of said at least one FSS layer, and ii) said at least one FSS layer is configured to be substantially transparent to electromagnetic waves in at least two disjunct frequency bands, including at least a second frequency band F2 and a third frequency band F3, that are separate from the first frequency band F 1.

[0050] 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 multiband antenna systems in a compact and efficient manner and to cater for minimal losses in the operating frequency bands.

[0051] By way of example, the technology disclosed herein provides a compact antenna module and the benefits of the antenna module lie in the combined overall system and its functionality, with special emphasize on the application to base station antennas, rather than isolated, individual Radio Frequency (RF) features.

[0052] 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 comprises a plurality of antenna elements 101, a reflector 104 and at least one FSS layer 107; 102.

[0053] As mentioned, the antenna module 100 is based on a reflector 104 in which an opening has been defined. The opening may be fully or partially surrounded by the reflector. The antenna module 100 further comprises at least one FSS layer. In the example of FIG. 1, there is provided a first FSS layer 107, which is arranged to at least partially overlap with the opening of the reflector. Optionally, at least one additional FSS layer such as a second FSS layer 102 may be incorporated in the antenna module to form an overall “FSS structure” or “FSS component”. Such an optional, additional FSS layer such as the FSS layer 102 may be physically separated from and arranged substantially in parallel with the first FSS layer 107.

[0054] As can be seen in FIG. 1, a first set of antenna elements 106 are mounted on the first FSS layer 107. The antenna elements 106 are configured to operate in a first frequency band Fl. The FSS layer(s) 107; 102 is / are configured to have both suppression and multi-passband properties. Sometimes the suppression characteristics of the FSS layer(s) are referred to as bandstop characteristics, implying that the overall FSS component has both bandstop and bandpass filtering characteristics. The bandpass filtering part of the FSS component is configured to have multi-passband properties.

[0055] To start with, the first frequency band Fl should be within the suppression band of the FSS layer(s). In other words, the FSS layer(s) 107; 102 is / are configured to be substantially reflective to electromagnetic waves in the first frequency band Fl. This radio frequency reflection of frequency band Fl is schematically indicated by a turning arrow in FIG. 1.

[0056] Additionally, the FSS layer(s) should be configured to be substantially transparent to electromagnetic waves in at least two disjunct frequency bands, including at least a second frequency band F2 (corresponding to a passband frequency range) and a third frequency band F3 (corresponding to another passband frequency range), that are separate from the first frequency band Fl. This radio frequency transparency is schematically indicated in FIG. 1 by dashed lines that extend through the FSS layer(s) 107; 102, where transparency in the context of RF normally refers to minimum or at least low transmission losses with respect to scattering by an incident electromagnetic wave.

[0057] In other words, the at least one FSS layer provides bandpass filtering characteristics for at least two disjunct passbands, each of which corresponds to a respective passband frequency range.

[0058] The multi-passband properties implies bandpass characteristics for two or more disjunct passbands.

[0059] The term “bandpass” is used for a bandpass filter or the process or characteristics of bandpass filtering, whereas the term “passband” is used for describing the frequency band or frequency range.

[0060] When more than one FSS layer is used, it should be understood that it is normally the combination of the FSS layers that is configured to have the above frequency band properties. It is important to understand that for practical applications, the inventor has realized through analysis and simulations that the use of high-pass filters is not feasible for designing this type of base station antenna module. A single high-pass filter cannot cater multiple, disjunct passbands without introducing unacceptable high transmission losses.

[0061] In a particular example, at least a subset of the antenna elements of the first set of antenna elements 106 mounted on the first FSS layer 107 are also configured to be substantially transparent to electromagnetic waves in said at least two disjunct frequency bands, including at least the second frequency band F2 and the third frequency band F3. This is schematically indicated in FIG. l by a dashed line that extends through the antenna elements arranged on the first FSS layer 107. In this way, the overall design allows electromagnetic waves in said at least two disjunct frequency bands to pass through the FSS layer(s) 107; 102 and also pass through antenna elements 106 arranged on the first FSS layer 107. This solution represents a highly efficient overall antenna module design.

[0062] Expressed slightly differently, the first FSS layer 107 may be attached in the antenna module such that the first FSS layer 107 is mounted on the opening (without imposing any directional intent) of the reflector 104. In other words, the first FSS layer 107 may be mounted in the antenna module such that the first FSS layer 107 is arranged substantially in parallel with the opening of the reflector and at least partially overlapping with the opening. As clear to the skilled person, any suitable support elements or substrates of the antenna module 100 may be used for providing physical support for the reflector 104 as well as the FSS layer(s) 107; 102. By way of example, the second FSS layer 102 may be attached to and / or integrated with the backside radome (not explicitly shown in FIG. 1) of the antenna module. In the example of FIG. 1, the reflector 104 and the first FSS layer 107 may be coupled to each other in various ways, e.g., galvanically or capacitively, as will later be discussed in more detail. As an example, the reflector 104 and the first FSS layer 107 may be mechanically held together, for example by a screw connection. In particular, the antenna module 100 may comprise a support in the form of a structure configured to support the reflector 104 and / or the first FSS layer 107 mounted on the opening of the reflector. Preferably, the reflector 104 is Radio Frequency, RF, grounded and the first FSS layer 107 is arranged to be coupled to the reflector 104 to provide RF grounding for the first set of antenna elements 106 mounted on the first FSS layer 107. It should be understood that the reflector 104 is itself RF grounded through a suitable ground connection using well-accepted technical solutions.

[0063] By way of example, the first FSS layer 107 may be capacitively or galvanically coupled to the reflector 104 along at least part of one or more of the edges that define the opening in the reflector 104.

[0064] The above design configuration allows the first set of antenna elements mounted on the first FSS layer to cooperate with an additional set of antenna elements arranged on the reflector in order to improve radiation patterns and enhance the antenna gain.

[0065] Optionally, the antenna elements mounted on the first FSS layer may be surrounded by the conductive metal material of the reflector to provide a highly reliable RF grounding for the antenna elements on the first FSS layer.

[0066] In a particular example, feed cables for feeding the antenna elements mounted on the first FSS layer may be routed along the FSS layer as will later be discussed in more detail. As an example, the feed cables may be coaxial cables or microstrip transmission lines that are aligned with the inductive grid lines on the FSS layer.

[0067] FIG. 2 is a schematic cross-sectional diagram illustrating another example of a base station antenna module according to an embodiment of the invention. In this particular example, the first FSS layer 107 and the reflector 104 are capacitively coupled through a thin layer of insulating material 109 so that the antenna elements 106 arranged on the first FSS layer 107 may be effectively RF grounded.

[0068] FIG. 3 is a schematic cross-sectional diagram illustrating yet another example of a base station antenna module according to an embodiment of the invention. FIG. 3 is similar to FIG. 2 except for an additional set of antenna elements 105 that are arranged or mounted on the reflector 104 and configured to operate in the first frequency band Fl. By way of example, the first set of antenna elements 106 mounted on the first FSS layer 107 may be configured to cooperate with the second set of antenna elements 105 mounted on the reflector 104 as a unified array of antenna elements. The insulating material 109 capacitively couples the first FSS layer 107 with the reflector 104, which itself is connected to ground, to provide for an effective RF grounding of the combined array of antenna elements 105, 106.

[0069] FIG. 4 is a schematic cross-sectional diagram illustrating still another example of a base station antenna module according to an embodiment of the invention. In this example, yet another FSS layer 111 is illustrated. Any suitable number of FSS layers may be employed in the overall design with trade-off considerations between larger bandwidth on one hand and lower transmission losses on the other hand.

[0070] For example, with a first FSS layer and a second FSS layer, as previously discussed, it is a combination of the first FSS layer and the second FSS layer that is configured to be substantially transparent to electromagnetic waves in said at least two disjunct frequency bands, including at least the second frequency band F2 and the third frequency band F3.

[0071] More generally, when the antenna module 100 includes the first FSS layer and at least one additional FSS layer, which is physically separated from and arranged substantially in parallel with the first FSS layer, it is the combination of the first FSS layer and said at least one additional FSS layer that is configured to have the above-discussed frequency suppression and multi-passband properties.

[0072] By way of example, the FSS layers may be aligned in a stacked, parallelized configuration.

[0073] The FSS layers may be separated by a fixed distance that is maintained during operation of the antenna module, e.g., by means of spacers and / or a suitable core or foam material inserted between the FSS layers, to ensure proper functionality of the combined FSS layers and / or to provide mechanical stability. Principally, to support a specific passband, the nominal distance between two FSS layers should be a quarter of a wavelength at the center frequency of the passband. In practice, it is necessary to also consider the change of transmission phase through the conductive metal pattern of each FSS layer, and hence the distance between two FSS layers deviates slightly from the above-mentioned rule of thumb. For multiple passbands, a trade-off has to be made between the different passbands with regard to determining a suitable distance between the FSS layers.

[0074] In a particular example, for a compact and efficient overall design, the FSS layer 102 that is located farthest away from the first FSS layer 107 may be attached to and / or integrated with a radome of the antenna module. Preferably, the FSS layer 102 is integrated in the backside radome of the antenna module. By way of example, a support layer to which the FSS layer 102 is attached may act as at least part of the backside radome.

[0075] FIG. 5 is a schematic cross-sectional diagram illustrating another example of a base station antenna module according to an embodiment of the invention. FIG. 5 is similar to FIG. 3, except for the placement of the first FSS layer 107. In this particular example, the first FSS layer is located on the other side of the opening of the reflector 104. With more than one FSS layer, the first FSS layer 107 is arranged on the opposite side of the opening of the reflector 104 in relation to the additional FSS layer or layers, here illustrated by a second FSS layer 102.

[0076] It should be understood that the above-described base station antenna module 100 normally cooperates with and / or includes 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.

[0077] FIG. 6 is a schematic cross-sectional diagram illustrating an example of a base station antenna module combined with a multi-band antenna unit according to an embodiment of the invention. In this example, a multi-band antenna unit 120 being configured for operation in said at least two disjunct frequency bands, including at least the second frequency band F2 and the third frequency band F3, is arranged in relation to the antenna module 100 to form an overall base station antenna system 150. Possibly, the multi-band antenna unit 120 may be integrated with the antenna module 100 as part of the base station antenna module 100, as will be described later.

[0078] It should be understood that any of the above-described embodiments of the base station antenna module may be combined with a multi-band antenna unit to form an overall base station antenna system.

[0079] As can be seen in FIG. 6, the multi-band antenna unit 120 is arranged on the opposite side of the at least one FSS layer 107 relative / compared to the first set of antenna elements 106 that are mounted on the first FSS layer 107 and configured to operate in the first frequency band F 1.

[0080] As indicated, the multi-band antenna unit 120 may be provided as a separate antenna unit for combination with the antenna module 100 to form an overall base station antenna system 150 or integrated as a multi-band antenna sub-system in the antenna module 100.

[0081] In the following, some examples of different implementations of a multi-band antenna sub-system for integration in the base station antenna module will be described briefly with reference to FIGs. 7-10.

[0082] FIG. 7 is a schematic cross-sectional diagram illustrating an example of a base station antenna module having an integrated multi-band antenna sub-system according to an embodiment of the invention. In this example, the antenna module 100 further comprises two additional sets of antenna elements 121; 122 arranged on a second reflector 124. Each set of antenna elements is configured to operate in a respective frequency band F2 / F3. The FSS layers 107; 102 are configured as a combined structure to be substantially transparent to electromagnetic waves in frequency bands F2 and F3.

[0083] As can be seen in FIG. 7, the multi-band antenna sub-system, including the second reflector 124 and the additional sets of antenna elements 121, 122, is arranged on the opposite side of said at least one FSS layer relative to the first set of antenna elements 106 that are mounted on the first FSS layer 107 and configured to operate in the first frequency band Fl. By way of example, the second reflector 124 and the corresponding additional sets of antenna elements 121, 122 is arranged substantially in parallel with the FSS layer(s) 107; 102 and the first reflector 104.

[0084] In the particular example of FIG. 7, the two additional sets of antenna elements 121, 122 are distributed over the second reflector 124 in an aperture-divided pattern in relation to the opening of the first reflector 104 so as to cover different parts of the aperture or opening of the first reflector 104, but usually with a partial overlap of the different antenna element sets.

[0085] FIG. 8 is a schematic cross-sectional diagram illustrating another example of a base station antenna module having an integrated multi-band antenna sub-system according to an embodiment of the invention.

[0086] In this particular example, the antenna elements of the additional sets of antenna elements 121, 122 are interleaved with each other, with an antenna element operating in frequency band F2 alternately arranged with an antenna element operating in frequency band F3.

[0087] FIG. 9 is a schematic cross-sectional diagram illustrating yet another example of a base station antenna module having an integrated multi-band antenna sub-system according to an embodiment of the invention.

[0088] In this example, the multi-band antenna sub-system involves three sets of antenna elements 121, 122, 123 operating at frequency bands F2, F3 and F4, respectively. Correspondingly, the FSS layers 107; 102 are configured as a combined structure to be substantially transparent to electromagnetic waves in frequency bands F2, F3 and F4.

[0089] In the particular example of FIG. 9, the additional sets of antenna elements 121, 122 123 are distributed over the second reflector 124 in an aperture-divided pattern in relation to the opening of the first reflector 104 so as to cover different parts of the aperture or opening of the first reflector 104, but usually with a partial overlap of the different antenna element sets. FIG. 10 is a schematic cross-sectional diagram illustrating still another example of a base station antenna module having an integrated multi-band antenna subsystem according to an embodiment of the invention.

[0090] In this particular example, the antenna elements of the additional sets of antenna elements 121, 122, 123 are interleaved with each other on the second reflector 124.

[0091] It should be understood that the above-described multi-band antenna sub-systems normally includes power circuitry, electrical feeding, structural support elements and / or other components according to well-established radio antenna technology.

[0092] FIG. 11 is a schematic graph illustrating an example of the reflection coefficient (dashed line) and transmission coefficient (solid line) as a function of frequency for an example embodiment of a two-layer FSS having suppression and bandpass filtering characteristics with multi-passband properties. The scattering parameters (S-parameters) are shown on a logarithmic power scale for the case of 45 degrees slant linear polarization and incident tilt angle 6.5 degree. As can be seen in the example of FIG. 11 , frequency suppression is achieved for a desired lower frequency band (shaded area below 1 GHz), and multi-passband properties are achieved, here in two disjunct frequency bands (shaded areas centered at 2.5 GHz and 3.65 GHz, respectively).

[0093] In general, the at least two disjunct frequency bands, including at least the second frequency band F2 and the third frequency band F3, are higher frequency bands than the first frequency band Fl. In other words, the overall FSS structure that includes at least one FSS layer has a frequency suppression band at a lower frequency range and at least two disjunct passbands at relatively higher frequency bands.

[0094] By way of example, the Fl frequency band may be 600- 1000 MHz, or a subset of that frequency range, and the F2 frequency band may be 2300-2700 MHz, or a subset thereof and the F3 frequency band may be 3300-4200 MHz, or a subset thereof. In a non-limiting example embodiment, the first frequency band Fl in which the antenna elements arranged on the first FSS layer are configured to operate is in the frequency range 617-960 MHz. The overall FSS structure comprising at least one FSS layer may then be configured to be substantially reflective to electromagnetic waves in the frequency range 617-960 MHz and may further be configured to be substantially transparent to electromagnetic waves in the at least two disjunct frequency bands or ranges such as 2300-2690 MHz (F2) and 3300-4000 MHz (F3).

[0095] In the following, non-limiting example embodiments will now be described with reference to FIGs. 12-23.

[0096] FIG. 12 illustrates a side view of an example embodiment of a base station antenna module 100 according to the technology disclosed. The example base station antenna module 100 shown in FIG. 12 comprises a plurality of antenna elements 101 and at least two FSS layers including a first FSS layer 107 and a second FSS layer 102. In the example embodiments shown in FIG. 12, the FSS layer furthest away from the antenna elements 106 is arranged on the backside radome 103 of the radome of the base station antenna module 100 or on a corresponding support layer. Arranging the second FSS layer 102 on the backside radome 103 is an option for the technology disclosed. By way of example, the second FSS layer 102 may be glued or taped onto the inside of the backside radome 103. Alternatively, the second FSS layer 102 is arranged on a support layer, which in turn is arranged in relation to the backside radome in a suitable manner, either directly on the backside radome or slightly distanced from the backside radome.

[0097] In FIG.12, the first FSS layer 107 is arranged to substantially cover or at least partially overlap with the opening of the reflector 104 of the base station antenna module 100. The plurality of antenna elements 101 in the example embodiments shown in FIG. 12 comprises a first set of antenna elements 106 arranged on the first FSS layer 107 and a second set of antenna elements 105 arranged on the reflector 104. The first set of antenna elements 106 and the second set of antenna elements 105 do not necessarily have to be of the same type and / or design.

[0098] In the example embodiment of a base station antenna module 100 illustrated in FIG. 12, the first FSS layer 107 and the reflector 104 may, by way of example, be capacitively coupled through a thin layer of insulating material 109 so that the second set of antenna elements 105 arranged on the reflector 104 can cooperate with the first set of antenna elements 106 arranged on the first FSS layer 107, for improved radiation patterns and antenna gain. Alternatively, the first FSS layer 107 and the reflector 104 may be galvanically coupled to obtain a common radio frequency grounding between the first set of antenna elements 106 and the second set of antenna elements 105.

[0099] By way of example, the reflector is normally a metallic reflector, e.g., comprising aluminum or various alloys thereof. The introduction of a thin layer of insulating material 109 may also provide the technical effect of avoiding unwanted voltage effects between the first FSS layer 107 and the first set of antenna elements 106 on one hand, and the metallic reflector 104 and the second set of antenna elements 105 on the other hand.

[0100] FIG. 12 also illustrates a support layer 108 for the first FSS layer 107. The support layer 108 in FIG. 12 has substantially the same thickness as the backside radome 103 on which the second FSS layer 102 is arranged. In the particular example of FIG. 12, the second FSS layer 102 and the first FSS layer 107 mounted in the opening of the reflector 104 are separated by an air gap.

[0101] The support layer 108 may typically be made of the same material, for example plastic material, as the backside radome 103 and further typically has a thickness corresponding to the thickness of the backside radome. The thickness of the support layer and the thickness of the backside radome is typically in the range 1.5 to 4 mm. The backside radome 103 provides structural support for the antenna module and protects the interior components of the base station antenna module from environmental conditions and mechanical impact.

[0102] By way of example, each of the FSS layers 107; 102 may be implemented as a Printed Circuit Board (PCB) comprising a FSS layer.

[0103] Normally, each FSS layer comprises a conductive pattern. In example embodiments of the technology disclosed, the conductive pattern may be printed on a thin plastic film, etched on a PCB and / or etched directly onto a support layer. The conductive pattern is typically periodic in the x-y-plane with the z-axis pointing in the normal direction of the FSS layer 107, i.e., with the z-axis pointing in the direction of maximum radiation of the antenna elements 101.

[0104] Further example embodiments, as illustrated in FIG. 12, relate to a base station antenna module 100 comprising at least a plurality of antenna elements 101, a feed network 130 for the plurality of antenna elements, a reflector 104, at least two FSS layers 102, 107 configured to filter and control electromagnetic waves and a radome comprising a backside radome 103 configured to protect interior components of the base station antenna module 100 such as the first and second sets of antenna elements 106, 105 from environmental factors and mechanical impact.

[0105] As illustrated by the example embodiment of the base station antenna module 100 shown in FIG. 12, both a first subset of antenna elements 106 and a second subset of antenna elements 105 of the plurality of antenna elements 101 are configured to operate at a first frequency band Fl. The first and second FSS layers 107, 102 comprises a plurality of FSS elements forming at least one pattern so that the combination of the FSS layers 102, 107 is configured to act as a RF bandpass filter that is substantially transparent to an electromagnetic wave in at least a second frequency band F2, and a third frequency band F3, wherein both bands are nonoverlapping with the first frequency band Fi. Further, the second frequency band F2 and the third frequency band F3 are disjunct in relation to each other. The first and second FSS layers 102, 107 are also configured to have one or more suppression bands and at least one of these suppression bands comprises the first frequency band Fl, thereby providing substantial reflection of electromagnetic waves in the first frequency band Fl.

[0106] In the example of FIG. 12, the second FSS layer 102 is arranged directly onto the backside radome 103 or a support layer, or separated therefrom by a suitable, small distance. The second FSS layer 102 may even be integrated with the backside radome to provide for a streamlined and efficient implementation. For example, if the second FSS layer is implemented as a metallic pattern etched on a substrate such as a PCB or any other suitable support layer, the substrate may then act as the backside radome.

[0107] It should though be understood that the second FSS layer 102 may be arranged on a substrate or support layer that is not necessarily acting as the backside radome. This means that a backside radome separate from the second FSS layer 102 may be provided, e.g., with an air gap between the second FSS layer 102 and the backside radome.

[0108] In the particular example of FIG. 12, the base station antenna module 100 comprises two FSS layers 102, 107, where each of the two FSS layers comprises a plurality of FSS elements forming at least one pattern (not shown in FIG. 12 but illustrated in FIG. 15A-B). In this example embodiment, the at least one pattern formed on each of the two FSS layers 102, 107 is configured so that the functional combination of the two layers is configured to be substantially transparent to electromagnetic waves in at least a second frequency band F2 and a third frequency band F3, and substantially reflective to electromagnetic waves in a first frequency band Fl in which the plurality of antenna elements 101 of the base station antenna module 100 operates.

[0109] Thus, signals in the frequency bands F2 and F3 are allowed to pass through the FSS layers 102, 107 and to be received / transmitted by an optional multi-band antenna unit 120 arranged opposite to the backside radome 103.

[0110] The multi-band antenna unit 120 may also include an electrical feeding network and may be a pure antenna unit or a complete multi-band radio unit, configured for operation in multiple disjunct frequency bands with reference to any relevant radio communication standard.

[0111] FIG. 13 illustrates a side view of an example embodiment of a base station antenna module 100 according to the technology disclosed. The example base station antenna module 100 additionally comprises one or more insulating spacers 110 arranged to maintain a fixed distance, e.g., an air gap, between the FSS layers 102, 107. In the example of FIG. 13, the spacers 110 are mechanically connected to the second FSS layer 102 that is attached to the backside radome 103 or directly to the radome via holes in the second FSS layer 102, and the spacers 110 are further also mechanically connected to the support layer 108, thereby providing indirect structural support for the first FSS layer 107 and / or the reflector 104. In other words, the first FSS layer 107 and the second FSS layer 102 are here separated by an air gap maintained by means of the insulating spacers 110. FIG. 14 is a schematic diagram illustrating a side view of yet another example of an antenna module according to an embodiment of the invention. In this particular example, the antenna module comprises an insulating core material or foam material 112 configured to give the antenna module structural strength and to maintain a fixed distance between the first FSS layer 107 and the second FSS layer 102. The core material or foam material is substantially transparent to electromagnetic waves in at least frequency band F2 and frequency band F3.

[0112] FIG. 15A-B are schematic diagrams illustrating two different conceptual examples of an FSS unit cell or FSS element 200-A / 200-B from which a structured FSS component may be designed.

[0113] Designing an FSS component based on a set of FSS unit cells involves selecting appropriate materials and the shape and geometry of the FSS unit cells, defining the periodic arrangement of the FSS unit cells, and optimizing the design through 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.

[0114] Normally, the FSS unit cells are arranged on a base substrate and each unit cell is part of a larger periodic array.

[0115] The FSS unit cell may be defined by slots and / or patches of various geometrical shapes of metal and / or dielectric material, e.g., slots in a metallic screen and / or metallic patches.

[0116] 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 given multiple passbands while keeping a sufficiently high attenuation in the frequency suppression band. The FSS design is validated against the entire scan range for which the beamforming multi-band radio operates.

[0117] By way of example, the FSS unit cell may be composed of one FSS layer or several FSS layers separated by a distance. Often the geometry of the FSS unit cell is the same for the different FSS layers, but this is not always the case. The FSS unit cell geometry should preferably obey certain symmetry requirements, typically reflection symmetry with respect to two orthogonal planes with respect to the center of the unit cell, in order to minimize cross-polarization of the transmitted electromagnetic wave. The core material used to separate the different FSS layers as well as the materials building up the individual FSS layers must be accurately modeled from an RF point of view and included in the design process.

[0118] One challenge in the design of the overall FSS component is to obtain low transmission losses in a wide passband over a large range of scan angles. The extension from a single passband to multiple passbands adds additional complexity to the geometry of the FSS unit cell.

[0119] In particular, a passband FSS may be defined by a periodic arrangement of slots in an otherwise conductive screen. A conceptual example of an FSS unit cell with two concentric slots is depicted in FIG. 15A, where grey indicates metal and white indicates absence of metal. This geometry supports two distinct passbands and a frequency suppression band. FIG. 15B illustrates a corresponding design with three concentric slots and thus three distinct passbands and a frequency suppression band.

[0120] Note that the exemplifying conceptual geometries in FIG. 15A-B are symmetric with respect to two orthogonal places through the center points of the FSS unit cell. This enables supporting two orthogonal polarizations with identical filtering characteristics.

[0121] FIG. 16A is a schematic top-view diagram illustrating an example of a smaller cutout of a conceptual FSS component with a grounded metal foundation in the center cell at which an antenna element may be arranged. By way of example, feed cables 208 such as coaxial cables may be arranged to provide electrical feeding from a feed network (not shown in FIG. 16A). The feed cables are at least partly aligned with the inductive grid lines of the FSS component 207.

[0122] More generally, the first set of antenna elements mounted on the first FSS layer may thus be connectable to a feed network via feed cables (e.g., coaxial cables), which are at least partly aligned with the inductive grid lines of the first FSS layer. FIG. 16B is a schematic diagram illustrating an example of a coaxial line 208 that may be used for electrically feeding the above-mentioned antenna elements mounted on the FSS layer.

[0123] FIG. 17 is a schematic diagram illustrating a perspective view of an example of an antenna module according to an embodiment. In FIG. 17, the example base station antenna module 300 comprises at least one array of antenna elements 301 (two antenna elements shown in FIG. 17), a metallic reflector 307 in which an opening is defined, and at least two FSS layers 302, 303 including a first FSS layer 303 and a second FSS layer 302. At least the first FSS layer is arranged to at least partly cover or overlap with the opening in the reflector 307. Preferably, both FSS layers are aligned in parallel with each other and partially or fully overlap with the opening in the reflector. The antenna elements 301 are typically supported by support elements 306. The base station antenna module 300 may include a radome 304 to protect the base station antenna module from environmental conditions and mechanical impact. Optionally, the second FSS layer 302 may be configured to function as a backside radome. The radome 304 together with the second FSS layer 302 (functioning as the backside radome) may then provide sufficient protection of the antenna module.

[0124] FIG. 18 is a schematic diagram illustrating a top view of an example of an antenna module according to an embodiment. The example base station antenna module 400 comprises a plurality of antenna elements 402, 403, a metallic reflector 404 in which an opening is defined and at least one FSS layer of which a first FSS layer 405 is shown. The first FSS layer 405 is mounted on the opening of the reflector 404. A first set of antenna elements 403 are arranged on the first FSS layer 405, and a second set of antenna elements 402 are arranged on the reflector 404. In this example, the opening in the reflector 404 is surrounded by the conductive material of the reflector 404 to enable, through suitable coupling between the reflector 404 and the FSS layer 405, reliable RF grounding for the first set of antenna elements 403 mounted on the FSS layer 405 and to enable cooperation with the second set of antenna elements 402 arranged on the reflector 404, e.g., in terms of improved radiation patterns and enhanced antenna gain. For example, but not necessarily, the opening may be surrounded by the conductive material of the reflector and the FSS layer may be provided with conductive material arranged so that at least part of or the entire periphery of the FSS layer 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 layer, either discretely or continuously, the FSS layer together with the reflector behaves as a continuous ground plane.

[0125] FIG. 19 is a schematic diagram illustrating a top view of another example of an antenna module according to an embodiment. The example base station antenna module 400 illustrated in FIG. 19 is similar to that of FIG. 18, except for the structural design of the opening defined in the reflector 404. In this example, the opening in the reflector 404 and the first FSS layer 405 mounted on the opening is merely partially surrounded by the reflector 404. This setting may be enough to provide sufficient RF grounding for the first set of antenna elements 403 mounted on the FSS layer 405 and to enable cooperation with the second set of antenna elements 402 arranged on the reflector 404.

[0126] FIG. 20 is a schematic diagram illustrating a perspective view of an example of an antenna system according to an embodiment. The example embodiment of FIG. 20 represents a base station antenna system 150 comprising a base station antenna module 100, various embodiments of which have been discussed herein, and a separate multi-band antenna unit or multi-band radio unit 120 arranged in connection with the antenna module 100. The multi-band antenna unit or multiband radio unit 120 is here connected in alignment with the opening in the reflector and the associated FSS layer(s) of the antenna module 100.

[0127] FIG. 21 is a schematic 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 multi-band antenna unit or multi-band radio unit 120 “behind” the FSS layer(s).

[0128] FIG. 22 is a schematic diagram illustrating an exploded view of an example of relevant parts of an antenna system according to an embodiment. In this view, the multi-band antenna or multi-band radio unit 120 and the antenna module 100 are both visible. Further, the presence of two parallel and aligned FSS layers in the antenna module 100 can more easily be seen.

[0129] FIG. 23 is a schematic diagram illustrating another exploded view of the antenna system of FIG. 22 according to an embodiment.

[0130] According to a second aspect of the invention, there is provided an antenna system for base station applications in cellular communication networks. The antenna system comprises a base station antenna module according to the first aspect, combined with a separate multi-band antenna unit (or multi-band radio unit) having antenna elements configured to operate in said at least two disjunct frequency bands, including at least a second frequency band F2 and a third frequency band F3, wherein the multi-band antenna unit (or multi-band radio unit) is arranged on the opposite side of said at least one FSS layer relative to the first set of antenna elements that are mounted on the first FSS layer and configured to operate in the first frequency band Fl.

[0131] In a particular example, the base station antenna module is at least partly surrounded by a radome and the separate multi-band antenna unit is arranged outside of the radome. By way of example, with two or more FSS layers, the FSS layer located farthest away from the first FSS layer may be attached to and / or integrated with the backside radome of the base station antenna module. The multi-band antenna unit would then be separately arranged on the outside of the backside radome. In other words, the first FSS layer, or an additional FSS layer physically separated from the first FSS layer, may be integrated into the backside radome.

[0132] 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

AMENDED CLAIMS received by the International Bureau on 22 September 2025 (22.09.2025).

1. A base station antenna module comprising a plurality of antenna elements, a reflector and at least one Frequency Selective Surface, FSS, layer, wherein the reflector of the antenna module is provided with an opening and a first FSS layer is arranged to at least partially overlap with the opening of the reflector; wherein a first set of antenna elements are mounted on the first FSS layer and configured to operate in a first frequency band Fl; wherein said at least one FSS layer is configured to have both frequency suppression characteristics and bandpass filtering characteristics with multipassband properties such that: i) the first frequency band F 1 is within a suppression band of said at least one FSS layer, and ii) said at least one FSS layer is configured to be substantially transparent to electromagnetic waves in at least two disjunct frequency passbands, including at least a second frequency band F2 and a third frequency band F3, that are separate from the first frequency band Fl, wherein said at least one FSS layer provides bandpass filtering characteristics for said at least two disjunct passbands, each of which corresponds to a respective passband frequency range.

2. The base station antenna module of claim 1, wherein said at least one FSS layer is configured to be substantially reflective to electromagnetic waves in said first frequency band F 1.

3. The base station antenna module of claim 1 or 2, wherein at least a subset of antenna elements of the first set of antenna elements mounted on the first FSS layer are configured to be substantially transparent to electromagnetic waves in said at least two disjunct frequency bands, including at least the second frequency band F2 and the third frequency band F3.

4. The base station antenna module of any of the claims 1 to 3, wherein said first FSS layer is attached in said antenna module such that said first FSS layer is mounted on the opening of the reflector.

5. The base station antenna module of any of the claims 1 to 4, wherein said first FSS layer is mounted in said antenna module such that said first FSS layer is arranged substantially in parallel with the opening of the reflector and at least partially overlapping with the opening.

6. The base station antenna module of any of the claims 1 to 5, wherein said reflector is Radio Frequency, RF, grounded and said first FSS layer is arranged to be coupled to the reflector to provide RF grounding for said first set of antenna elements mounted on said first FSS layer.

7. The base station antenna module of claim 6, wherein said first FSS layer is capacitively or galvanically coupled to the reflector along at least part of one or more of the edges that define the opening in said reflector.

8. The base station antenna module of claim 6 or 7, wherein a second set of antenna elements, configured to operate in said first frequency band Fl, are mounted on the reflector, and the first set of antenna elements mounted on the first FSS layer are configured to cooperate with the second set of antenna elements mounted on the reflector as an array of antenna elements.

9. The base station antenna module of any of the claims 1 to 8, wherein said at least one FSS layer includes said first FSS layer and a second FSS layer that is physically separated from and arranged substantially in parallel with said first FSS layer, wherein a combination of said first FSS layer and said second FSS layer is configured to be substantially transparent to electromagnetic waves in said at least two disjunct frequency bands, including at least said second frequency band F2 and said third frequency band F3.

10. The base station antenna module of any of the claims 1 to 9, wherein said at least one FSS layer includes said first FSS layer and at least one additional FSS layer physically separated from and arranged substantially in parallel with said first FSS layer, wherein a combination of said first FSS layer and said at least one additional FSS layer is configured to have said frequency suppression and multipassband properties.

11. The base station antenna module of claim 10, wherein the FSS layer of said at least one additional FSS layer that is located farthest away from said first FSS layer is attached to and / or integrated with a radome of said antenna module.

12. The base station antenna module of claim 11, wherein the FSS layer of said at least one additional FSS layer that is located farthest away from said first FSS layer is integrated with a backside radome of said antenna module.

13. The base station antenna module of any of the claims 1 to 12, wherein said first set of antenna elements mounted on the first FSS layer are connected to a feed network via coaxial cables, which are at least partly aligned with the inductive grid lines of said first FSS layer.

14. The base station antenna module of any of the claims 1 to 13, wherein said at least two disjunct frequency bands, including at least said second frequency band F2 and said third frequency band F3, are higher frequency bands than said first frequency band F 1.

15. The base station antenna module of any of the claims 1 to 14, wherein said antenna module further comprises a multi-band antenna sub-system having antenna elements configured to operate in said at least two disjunct frequency bands, including at least said second frequency band F2 and said third frequency band F3, wherein said multi-band antenna sub-system is arranged on the opposite side of said at least one FSS layer relative to said first set of antenna elements that are mounted on said first FSS layer and configured to operate in said first frequency band Fl.

16. An antenna system for base station applications in cellular communication networks, said antenna system comprising a base station antenna module of any of the claims 1 to 14, combined with a separate multi-band antenna unit having antenna elements configured to operate in said at least two disjunct frequency bands, including at least a second frequency band F2 and a third frequency band F3, wherein said multi-band antenna unit is arranged on the opposite side of said at least one FSS layer relative to said first set of antenna elements that are mounted on said first FSS layer and configured to operate in said first frequency band Fl.

17. The antenna system of claim 16, wherein said base station antenna module is at least partly surrounded by a radome and said separate multi-band antenna unit is arranged outside of said radome.

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