A base station antenna module comprising a frequency selective surface layer mounted on an opening in a reflector

Abstract

The technology disclosed relates to an antenna module comprising at least one array of antenna elements (101), at least one layer comprising a frequency selective surface (102; 107) configured to control the transmission and reflection of electromagnetic waves and a reflector (104) comprising an opening. According to technology disclosed, one of the at least one layer comprising a frequency selective surface (FSS) is mounted on / to the opening in the reflector (104) and antenna elements (106) mounted on the at least one FSS layer (107) is capacitively coupled to conductive reflector material surrounding the opening in the reflector (104).

Description

[0001] TITLE

[0002] A base station antenna module comprising a frequency selective surface layer mounted on an opening in a reflector

[0003] FIELD OF THE INVENTION

[0004] The technology disclosed relates to the field of wireless communications, and more particularly to an arrangement including at least one frequency selective surface (FSS) layer in an antenna module and an antenna module comprising such a FSS layer mounted to / on an opening in the reflector of the antenna module.

[0005] BACKGROUND OF THE INVENTION

[0006] In recent years, with the development of information communication technologies data traffic is continuously and exponentially increasing.

[0007] The base station antenna system is currently evolving from the fourth generation communication technology (4th-generation, 4G) to the fifth generation communication technology (5th-generation, 5G). The 5G base station antenna typically includes both passive and active antennas, and the active antennas may be, for example, massive multiple-input multiple-output (massive MIMO) 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] In order to rapidly deploy 5G communication equipment, a 5G site is often implemented by adding a 5G antenna and related equipment to the original 4G site resources. The 4G and 5G integrated active / passive base station antenna has more advantages in size, wind load and resource management, is widely accepted and applied in the 5G base station deployment process and is an important direction for future base station antenna evolution. In this connection, the use of frequency selective surfaces becomes an important choice.

[0009] For multi-band antenna modules, the above-mentioned 4G and 5G integrated active / passive base station antenna being an example of a multi-band antenna module, the use of frequency selective surfaces for controlling the transmission and reflection of electromagnetic waves in different frequency ranges becomes an important choice. However, an increased height and size for these multi-band antenna modules due to additional FSS layers is not desirable since it may limit the number of possible installation sites for the modules and therefore the number of possible use cases.

[0010] Hence, the height and size of antenna modules comprising at least one FSS layer for controlling electromagnetic radiation are critical aspects for the number of possible installation sites and use cases for the individual antenna module. There is therefore a need for antenna modules that are relatively compact in size to reduce the required space for the antenna module when installed on site. However, the free space wavelength needs to be sampled well enough and, in order to provide reliable Radio Frequency (RF) grounding, there is also a need for multiple ground points where the separation between the ground points must not be too large.

[0011] If there is no frequency selective surface, one must either arrange antennas side-by- side or in an interleaved element configuration, both of which have their disadvantages depending on the choice of design. The use of frequency selective surfaces enables the stacking of arrays of antennas, or antenna elements, in the z- direction, or beam transmission direction of the antenna elements, in an antenna configuration where the plane of the antenna elements is the x-y-plane.

[0012] The increased possibility for stacking separate antennas arrays has several advantages including reduced exposure to wind, improved visual experience, etc. In addition, the antenna modules become more modular because instead of a complicated product where several frequency band must share a common aperture, the complexity can be reduced by moving frequency bands out provided the frequency separation between the bands is large enough.

[0013] BRIEF SUMMARY OF THE INVENTION

[0014] An objective of the technology disclosed is to overcome at least part of the limitations of the state-of-the-art antenna modules by providing a relatively compact and flexible antenna module comprising at least one layer comprising a frequency selective surface (FSS), or FSS layer, configured to control and / or influence the transmission and reflection of electromagnetic waves. A general objective is to provide an improved antenna module. This objective is achieved by the proposed technology as defined in the independent claim 1.

[0015] Exemplifying embodiments of the proposed technology are defined by the dependent claims.

[0016] A particular objective of the technology disclosed is to reduce the height and size of an antenna module including at least one layer comprising a frequency selective surface, or FSS layer, where one of the at least one layer comprising a frequency selective surface is substantially reflective in the frequency band in which an array of antenna elements of the antenna module mounted to the FSS layer operates and where the layer comprising a frequency selective surface is substantially transparent in at least one frequency band outside the frequency band in which the array of antenna elements of the antenna module operates.

[0017] To achieve reliable Radio Frequency (RF) grounding, there should preferably be multiple ground points where the separation between the ground points should not be small compared to the wavelength. Another objective of the technology disclosed is therefore to provide a compact antenna module with reduced height and size in that antenna elements are arranged on a FSS layer mounted to / on an opening in the reflector of the antenna module, yet to provide a solution where the antenna elements arranged on the FSS are reliably Radio Frequency (RF) grounded through a capacitive connection between the FSS layer and the conducting reflector.

[0018] The above objective may be achieved by introducing an opening in the reflector where the opening is surrounded by the conducting material of the reflector so that the antenna elements arranged on the FSS layer may be easily and reliably grounded though a capacitive connection between the FSS layer and the reflector, for example through an insulting layer arranged between the FSS layer mounted to / on the opening and the reflector. By providing capacitive Radio Frequency (RF) grounding around the entire FSS layer, either discretely or continuously around the entire FSS layer, the FSS layer together with the reflector behaves as a continuous ground plane, meaning that ground currents do not have to take any strange detours. In particular, an objective is to provide a compact antenna module that is substantially transparent in at least one frequency band separated from the frequency band in which a first array of antenna elements of the antenna module operates. This may be achieved by introducing an opening in the reflector and replacing the conductive material with a FSS layer connected to ground where the opening is surrounded by conductive metal material of the reflector with a first subset of antenna elements operating at a first frequency band and arranged on the FSS layer. The FSS layer and the reflector are capacitively grounded, for example through an insulting layer arranged between the FSS layer mounted to / on the opening and the reflector. This provides for a continuous ground plane and thereby reliable RF grounding.

[0019] The technology disclosed addresses the above-mentioned need to reduce the size and height of an antenna module including at least one layer comprising a frequency selective surface (FSS), or FSS structure, while at the same time both keeping the transmission loss through the at least one FSS layer for electromagnetic waves in a passband frequency range small and provide for easy and reliable RF grounding for antenna elements.

[0020] The technology disclosed relates to an antenna module comprising at least one array of antenna elements, at least one frequency selective surface (FSS) layer, or FSS structure, configured to control the transmission and reflection properties of electromagnetic waves and a reflector configured to reflect electromagnetic waves transmitted by the at least one array of antenna elements and provide mechanical stability to the antenna module.

[0021] The technology disclosed relates to an antenna module comprising at least one array of antenna elements, at least one layer comprising a frequency selective surface configured to control the transmission and reflection of electromagnetic waves and a reflector comprising an opening. According to the technology disclosed, one of the at least one layer comprising a frequency selective surface (FSS) , or FSS layer, is mounted in the opening in the reflector and antenna elements mounted on the at least one FSS layer may be capacitively coupled to the reflector surrounding the opening through a capacitive connection between the FSS layer and the reflector. The technology disclosed attempts to reduce the size and height of an antenna module by introducing a (FSS) layer that is mounted on an opening in the reflector of the antenna module, while at the same time both keeping the transmission loss through the at least one FSS layer for electromagnetic waves in a passband frequency range small and provide for reliable radio frequency (RF) grounding for antenna elements mounted on the FSS layer. The wanted RF grounding is achieved by introducing, for example, an insulting layer arranged between the FSS layer mounted on the opening in the reflector.

[0022] According to exemplifying aspects of the technology disclosed, the reflector of the antenna module comprises an opening, for example a cutout in the reflector, and a FSS layer is mounted on / to the opening, for example mounted on / to the opening so that the FSS layer is covering the opening in the reflector. The opening is surrounded by the conductive material of the reflector to provide for an improved and more reliable RF grounding for the antenna elements arranged / mounted on the FSS layer. The technology disclosed thereby provides for a more reliable RF grounding in that the two grounded layers overlap, for example with an insulating layer between them, and by the fact that these layers can be easily mechanically held together, for example with a screw connection. The RF grounding that the technology disclosed provides is therefore more reliable than previous RF grounding solutions and does not change.

[0023] In exemplifying aspects and embodiments of the technology disclosed, the antenna elements are arranged on the FSS layer mounted in the opening in the reflector where the opening is surrounded by the conductive material of the reflector and the FSS layer is provided with conductive material arranged so that ground is provided, discretely or continuously, along the entire periphery of the FSS layer. A more reliable RF grounding is provided in that the two grounded layers overlap, for example with an insulating layer between them.

[0024] In exemplifying aspects and embodiments of the technology disclosed, antenna elements are arranged on the FSS layer mounted in the opening in the reflector. The opening may have a rectangular shape and be surrounded by conductive material of the reflector to thereby provide improved and reliable RF grounding for the antenna elements arranged / mounted on the FSS layer. In exemplifying embodiments of the technology disclosed, antenna elements are arranged on the FSS layer mounted in the opening in the reflector. The FSS layer may be a Printed Circuit Board (PCB) and the opening may have a rectangular shape so that all sides of the rectangular shaped opening are surrounded by conductive material of the reflector to thereby provide for improved and thereby reliable RF grounding for the antenna elements arranged on the FSS layer.

[0025] According to exemplifying aspects of the technology disclosed, at least a plurality of antenna elements of an array of antenna elements operating at a first frequency band Fi are mounted on the FSS layer in the opening and the FSS is configured to be substantially transparent to electromagnetic waves in a second frequency band F2, corresponding to a passband frequency range, well-separated from the first frequency band Fi.

[0026] In exemplifying embodiments, a plurality of antenna elements in the array of antenna elements are mounted on the FSS layer, or FSS structure comprising at least one FSS layer, and the conductive pattern printed on the FSS layer is configured so that the FSS layer is substantially transparent to electromagnetic waves in a second frequency band F2 and substantially reflective to electromagnetic waves in the first frequency band Fi in which the array of antenna elements mounted on the FSS layer is operating. According to aspects of the technology disclosed, at least a first subset of the antenna elements of an array of antenna elements operating at a lower first frequency band Fi are mounted on the FSS layer in the opening and a second subset of the antenna elements of an array of antenna elements also operating at the first frequency band Fi are mounted on the reflector. The FSS may then be configured to be substantially transparent to electromagnetic waves in a second frequency band F2 well-separated from the first frequency band FL

[0027] In exemplifying aspects and embodiments, the RF grounding of the FSS layer mounted on the opening of the reflector is capacitive in nature, and the FSS layer is capacitively coupled to ground along the edges of the reflector surrounding the opening so that a plurality of antenna elements mounted on the FSS layer thereby are capacitively coupled to ground. In exemplifying embodiments, a plurality of antenna elements mounted on the FSS layer is a first subset of an array of antenna elements operating at a first frequency band Fi. The antenna elements of the first subset may then be capacitively coupled to ground through a capacitive connection between the FSS layer and the reflector and a second subset of the array of antenna elements operating at the first frequency band Fi are mounted on the reflector.

[0028] In exemplifying embodiments, a plurality of antenna elements mounted on the FSS layer is a first subset of an array of antenna elements operating at a first frequency band Fi and a second subset of the array of antenna elements operating at the first frequency band Fi are mounted on the reflector. The first and second subset of antenna elements are configured to co-operate and thereby provide for improved antenna gain and / or beam-steering capabilities in that the FSS layer mounted on the opening of the reflector is capacitively coupled to ground along the edges of the opening in the reflector. Since conductive material of the reflector may be surrounding the opening in the reflector on all of its sides, each of the antenna elements in the first subset that are arranged on the FSS layer may be capacitively coupled to ground. For example, the antenna module may further comprise an insulating layer arranged between the FSS layer and the edges of the reflector that is used for capacitively coupling the antenna elements mounted on the FSS layer to ground.

[0029] In exemplifying embodiments, the antenna module further comprises a layer of insulating material arranged at least along portions of the edges of the opening in the reflector between the FSS layer and the reflector to capacitively couple a first subset of antenna elements mounted on the FSS layer to ground.

[0030] In exemplifying embodiments, the antenna module further comprises a second FSS layer physically separated from the (first) FSS layer and configured to also be substantially transparent to electromagnetic waves having wavelength X2 corresponding to a center frequency in the second frequency band F2. The first and second FSS layers may then be separated by a distance that is partly maintained during operation of the antenna module by means of at least one of spacers and a foam material arranged between the first and second FSS layer and that provides mechanical stability to external influences. For example, the at least one of spacers and a foam material may be adapted for maintaining a certain distance between the first and second FSS layers where the distance is adapted so that the combination of the two FSS layers is more transparent to electromagnetic waves having wavelength Aa than the individual two FSS layers alone.

[0031] In exemplifying embodiments, the total FSS structure of the antenna module consists solely of the first and second FSS layers and the first and second FSS layers are physically separated by a distance of about X2 / 4 to thereby enable constructive interference from electromagnetic waves with a wavelength X2 passing through the first and second FSS layers.

[0032] In exemplifying embodiments, the second frequency band F2 is a higher frequency band than the first frequency band Fi and is non-overlapping with the first frequency band Fi.

[0033] In exemplifying embodiments, the antenna module further comprises a second array of antenna elements configured to operate at a third frequency band F3 well- separated from both the first frequency band Fi and the second frequency band F2 and arranged to radiate in the same transmitting direction as the first array of antenna elements.

[0034] In exemplifying embodiments, the second frequency band F3 is a higher frequency band than the first frequency band Fi and is non-overlapping with both the first frequency band Fi and the second frequency band F2.

[0035] In exemplifying embodiments, the antenna module further comprises an additional FSS layer physically separated from said FSS layer, and the additional FSS layer is attached to and / or integrated in a backside radome of the antenna module.

[0036] In exemplifying embodiments, feed cables for feeding the antenna elements mounted on said FSS layer are routed along said FSS layer.

[0037] BRIEF DESCRIPTION OF DRAWINGS

[0038] FIG. 1 illustrates a side view of an example embodiment of an antenna module according to the technology disclosed. FIG. 2 illustrates a side view of another example embodiment of an antenna module according to technology disclosed.

[0039] FIG. 3 illustrates a side top view of an example embodiment of an antenna module according to technology disclosed.

[0040] FIG. 4 illustrates a top view of an example embodiment of an antenna module according to technology disclosed.

[0041] FIG. 5 graphically illustrates the reflection and transmission of electromagnetic waves as a function of frequency for an example embodiment of a two-layer frequency selective surface with both bandstop and bandpass filtering characteristics .

[0042] DETAILED DESCRIPTION

[0043] 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 radiation. A reflector is typically a structure that reflects electromagnetic radiation from an antenna element substantially in a given direction. A radome is typically a protective cover for one or more arrays of antenna elements. A backside radome structure is a part of the radome that is located at the backside of the antenna module.

[0044] Herein, the term bandstop is used for a bandstop filter or the process of bandstop filtering, whereas the term stopband is used for the corresponding band or frequency range. The term bandpass is used for a bandpass filter or the process of bandpass filtering, whereas the term passband is used in relation to the frequency band or frequency range.

[0045] In some contexts, a passband frequency range may be referred to as a bandpass frequency range.

[0046] In this disclosure, the wording “mounted on / to” or “arranged on / to” may include an intermediate layer, for example “FSS layer mounted on / to the reflector” may also include that an intermediate layer is arranged between the FSS layer and the reflector. According to a main aspect, there is provided an improved antenna module, also referred to as a base station antenna module. The antenna module comprises at least one array of antenna elements, a feed network for the at least one array of antenna elements, a reflector, an FSS layer configured to control the transmission and reflection of electromagnetic waves, and a radome configured to protect the at least one array of antenna elements of the antenna module from mechanical impact and weather influences. The array of antenna elements is configured to operate at a first frequency band Fi and arranged to transmit in a transmitting direction, and said FSS layer is provided with bandstop and bandpass filtering characteristics in that said FSS layer is configured to be substantially transparent to an electromagnetic wave having wavelength X2 corresponding to a center frequency in a second frequency band F2, corresponding to a passband frequency range, separate from the first frequency band Fi and in that the first frequency band Fi in which the array of antenna elements operates is within the stopband frequencies of said FSS layer. The reflector of the antenna module is provided with an opening and said FSS layer is mounted on the opening, and a plurality of antenna elements are mounted on said FSS layer in the opening so that they are surrounded by the conductive metal material of the reflector to thereby provide a reliable Radio Frequency (RF) grounding for said plurality of antenna elements mounted on the FSS layer.

[0047] It is important to understand that for all practical applications and purposes, the inventor has realized through careful analysis and simulations that the use of conventional high-pass filters is not feasible for designing this type of base station antenna module. A high-pass filter is not a bandpass filter and extensive experimentation and simulations by the inventor have shown that a high-pass filter will suffer from high transmission losses in practical applications.

[0048] On the contrary, the proposed technology employs at least one FSS layer, which is / are configured to have both bandstop and bandpass filtering properties such that the FSS layer(s) is / are substantially transparent to electromagnetic waves in a second frequency band F2, corresponding to a passband frequency range, separate from the first frequency band Fi and in that the first frequency band Fi in which the array of antenna elements operates is within the stopband frequencies of the FSS layer(s). In order to create a directional antenna, it is common to use a reflector to direct the radiation from the antenna element, so that the antenna lobe will point away from the reflector. Reflectors are often made of metal, so that they reflect all radiation. However, to create a compact setup, where a second antenna is mounted behind the first antenna, it is useful to instead use a frequency selective surface (FSS) as a reflector. The FSS may then be designed to reflect the frequencies transmitted by a first antenna and be transparent to the frequencies transmitted by a second antenna. However, the first antenna itself will partly block the transmission from the second antenna.

[0049] The technology disclosed provides for capacitive Radio Frequency (RF) grounding around the entire FSS layer, either discretely or continuously around the entire FSS layer, so that the FSS layer together with the reflector behaves as a continuous ground plane, meaning that ground currents do not have to take any strange detours. If there is no continuous ground, this can cause problems. To achieve reliable Radio Frequency (RF) grounding, there needs to be multiple ground points where the separation between the ground points must not be too large, and the free space wavelength needs to be sampled well enough. In order for the FSS layer to be experienced as a metal reflector, there needs to be ground along the entire periphery of the FSS layer, i.e. along the edges of the opening in the reflector, discretely or continuously. If one side of the FSS layer is left open / ungrounded, this edge will locally have a different potential than other edges connected to the homogenous reflector where the reflector acts as a large reservoir. Thus, leaving one or more of the edges ungrounded will affect the performance of the antenna elements mounted on the FSS layer, specifically if the antenna elements are placed relatively close to an ungrounded edge of the opening in the reflector.

[0050] The technology disclosed relates to an antenna module comprising at least one array of antenna elements, at least one layer comprising a frequency selective surface configured to control the transmission and reflection of electromagnetic waves and a reflector.

[0051] The technology disclosed relate to an antenna module comprising at least one array of antenna elements, at least one layer comprising a frequency selective surface configured to control the transmission and reflection of electromagnetic waves and a reflector comprising an opening. According to the technology disclosed, an FFS layer, typically a Printed Circuit Board (PCB) comprising a frequency selective surface, is mounted on the opening in the reflector and antenna elements mounted on the at least one FSS layer may be capacitively coupled to the reflector surrounding the opening through a capacitive connection between the FSS layer and the reflector.

[0052] The antenna elements mounted on a FSS layer may then operate at a first frequency band and the FSS layer is configured to be substantially transparent in at least one selected frequency band outside the first frequency band in which the array of antenna elements of the antenna module operates.

[0053] In addition to a first subset of antenna elements mounted on the FSS layer, the antenna module may comprise a second subset of antenna elements mounted on the reflector. The antenna elements of the first subset mounted on the FSS layer and the antenna elements of the second subset mounted on the reflector may then both operate at a frequency band and be capacitively coupled to each other in that the first subset of antenna elements are capacitively coupled to ground through a capacitive connection between the FSS layer mounted on the reflector and the reflector.

[0054] In aspects, the technology disclosed provides a compact antenna module with reduced height and size in that antenna elements are arranged on a FSS layer mounted on an opening in the reflector of the antenna module yet provides a solution where the antenna elements arranged on the FSS layer are reliably connected to ground through a capacitive connection between the FSS layer and a reflector which is connected to ground. As an example, the antenna elements arranged on the FSS layer may be reliably connected to ground through an insulating layer between the FSS layer and the reflector.

[0055] The technology disclosed is reducing the size and height of an antenna module including at least one layer comprising a frequency selective surface (FSS) layer, or FSS structure, while at the same time both keeping the transmission loss through the at least one FSS layer for electromagnetic waves in a passband frequency range small and provide for reliable radio frequency (RF) grounding for antenna elements mounted on the FSS layer. The reliable RF grounding is achieved by introducing an opening in a reflector connected to ground where the opening is surrounded by conductive metal material of the reflector so that the antenna elements arranged on the FSS layer may be capacitively coupled to ground though a capacitive connection between the FSS layer and the reflector, for example through an insulting layer arranged between the FSS layer mounted on the opening and the reflector. The technology disclosed provides for a more reliable RF grounding in that the two grounded layers overlap each other along the portions of the conducting reflector surrounding the opening in the reflector, for example by providing an insulating layer between them, and by the fact that these layers can be easily mechanically held together, for example with a screw connection. The RF grounding that the technology disclosed provides is therefore more reliable than previous RF grounding solutions and does not change.

[0056] FIG. 1 illustrates a side view of an example embodiment of an antenna module 100 according to the technology disclosed. The example antenna module 100 shown in FIG. l comprises one array of antenna elements 101 and two layers comprising a frequency selective surface 102, 107. In the example embodiments shown in FIG. l, the lower FSS layer 102 is arranged on the backside radome structure 103 of the radome of the antenna module. Arranging a second FSS layer on a backside radome structure 103 is only an option for the technology disclosed.

[0057] In FIG. l, the upper FSS layer 107 is mounted on the opening of the reflector 104 arranged in an opening of the reflector 104 of the antenna module 100. The array of antenna elements 101 in the example embodiments shown in FIG. l comprises a plurality of antenna elements 105 arranged on the reflector 104 and a plurality of antenna elements 106 arranged on the FSS layer 107.

[0058] Expressed slightly differently, the upper FSS layer 107 may be attached in the antenna module such that the FSS layer 107 is mounted on the opening of the reflector 104 (without imposing any directional intent). In other words, the FSS layer may be mounted in the antenna module such that the 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 and / or the FSS layer 107. In the example embodiment of an antenna module 100 illustrated in FIG. 1, the upper FSS layer 107 and the reflector 104 is capacitively coupled through a thin layer of insulating material 109 so that the plurality of antenna elements 105 arranged on the reflector 104 thereby can cooperate with the plurality of antenna elements 106 arranged on the upper FSS layer 107, for improved beamforming capabilities and antenna gain.

[0059] FIG. l also shows a support layer 108 for the upper FSS layer 107. The support layer 108 in FIG. l has the same thickness as the backside radome structure 103 on which the lower FSS layer 102 is arranged. The lower FSS layer 102 and the upper FSS layer 107 mounted to the reflector 104 in FIG. l are separated by an air gap-

[0060] In example embodiments, the technology disclosed, as illustrated by the example embodiment of an antenna module 100 shown in FIG. 1, relates to an antenna module 100 comprising at least one array of antenna elements 101, a feed network for the at least one array of antenna elements (not shown in FIG. 1), a reflector 104, two FSS layers 102, 107 configured to control the transmission and reflection of electromagnetic waves and a radome comprising a backside radome structure 103 configured to protect the antenna elements 105, 106 of the antenna module 100 from weather influences and mechanical impact.

[0061] According to aspects of the technology disclosed as illustrated by the example embodiment of an antenna module 100 shown in FIG. 1, both a first subset of antenna elements 106 and a second subset of antenna elements 105 of the array of antenna elements 101 are configured to operate at a first frequency band Fi and both the lower FSS layer 102 in FIG. 1 and the FSS layer 107 mounted to the reflector 104 comprises a plurality of elements forming at least one pattern on the material so that each of the two layers comprising a frequency selective surface 102, 107 is thereby configured to be substantially transparent to an electromagnetic wave in a second frequency band F2 that is non-overlapping with and well-separated from the first frequency band Fi.

[0062] In FIG. 1, the lower FSS layer 102 is arranged directly on the backside radome structure 103. By arranging the lower FSS layer 102 directly on the backside radome structure 103 (i.e., less than X2 / 6 from the backside radome structure 103), the lower FSS layer 102 is configured and arranged to be substantially transparent to an electromagnetic wave in a second frequency band F2. The first frequency band Fi, in which the array of antenna elements 101 in FIG. 1 operates, is within the stopband frequencies of both the lower FSS layer 102 arranged directly on the backside radome structure 103 and the upper FSS layer 107 mounted to the reflector 104.

[0063] In example embodiments of antenna module shown in FIG. 1, the antenna module 100 comprises two layers comprising a frequency selective surface, or FSS layers, 102, 107 where each of the two FSS layers comprises a plurality of elements forming at least one pattern on the material (not shown). In this example embodiment, the at least one pattern formed on each of the two FSS layers 102, 107 is configured so that each of the two layers comprising a frequency selective surface is configured to be substantially transparent to electromagnetic waves in a second frequency band F2 and substantially reflective to electromagnetic wave in a second frequency band Fi in which the array of antenna elements 101 of the antenna module 100 operates.

[0064] When more than one FSS layer is used, it is normally the combination of the FSS layers that is configured to have the above band suppression and bandpass filtering properties.

[0065] FIG. 2 illustrates a side view of an example embodiment of an antenna module 200 according to the technology disclosed. The example antenna module 200 shown in FIG. 2 comprises two arrays of antenna elements 201, 211 and two layers comprising a frequency selective surface, or FSS layers, 202, 207 where the lower FSS layer 202 in the example embodiment shown in FIG. 2 is arranged on the backside radome structure 203 of the antenna module 200. The two FSS layers, 202, 207 in FIG. 2 are configured to be substantially transparent to electromagnetic waves in a second frequency band F2 separated from and non-overlapping with both a first frequency band Fi and a third frequency band F3.

[0066] The first array of antenna elements 201 in FIG. 2 is configured to operate at a first frequency band Fi and comprises a first subset of antenna elements 206 arranged on the upper FSS layer 207 and a second subset of antenna elements 205 arranged on the reflector 204. The second array of antenna elements 211 in FIG. 2 is configured to operate at a third frequency band F3 separated from both the first and the second frequency bands Fi, F2 and comprises a first plurality of antenna elements 212 arranged on the reflector 204 and a second plurality of antenna elements 213 arranged on the upper FSS layer 207.

[0067] In the example embodiment of an antenna module 200 illustrated in FIG.2, the reflector is connected to ground (not shown) and the upper FSS layer 207 mounted to the reflector 204 and the reflector 204 are capacitively coupled through a thin layer of insulating material 209 so that the plurality of antenna elements 205 of the first array of antenna elements 201 arranged on the reflector 204 thereby can cooperate with the plurality of antenna elements 206 arranged on the FSS layer 207 mounted to the reflector 204, for improved beamforming capabilities and antenna gain for the first array of antenna elements 201. The upper FSS layer 207 mounted to / on the opening in the reflector 204 is capacitively coupled to the reflector 204 through the thin layer of insulating material 209 so that the plurality of antenna elements 212 of the second array of antenna elements 211 arranged on the reflector 204 thereby cooperate with the plurality of antenna elements 213 of the second array of antenna elements 211 arranged on the FSS layer 207 mounted to / on the opening in the reflector 204, for improved beamforming capabilities and antenna gain for the second array of antenna elements 211.

[0068] FIG. 2 also shows a support layer 208 for the FSS layer 207 mounted to / on the opening in the reflector 204. The support layer 208 has the same thickness as the backside radome structure 203 on which the lower FSS layer 202 is arranged. In the example embodiment in FIG. 2, the lower FSS layer 202 and the FSS layer 207 mounted to / on the opening in the reflector 204 are separated by an air gap maintained by means of three spacers 210.

[0069] In FIG. 2, the upper layer 207 is mounted to / on the opening in the reflector 204 of the antenna module 200. As illustrated in FIG. 2, both the first array of antenna elements 201 and the second array of antenna elements 211 comprises a plurality of antenna elements 205, 212 arranged on the reflector 204 and a plurality of antenna elements 206, 213 arranged on the upper layer 207 mounted to / on the opening in the reflector 204. According to aspects of the technology disclosed, the lower FSS layer 202 is arranged less than X2 / 6 from the backside radome structure 203, so that the lower layer 202 and the backside radome structure 203 are arranged and configured to be substantially transparent to electromagnetic waves in a frequency range including a second frequency band F2. The lower FSS layer 202 is then configured and arranged to be substantially reflective to electromagnetic waves in two separate frequency bands Fi and F3 in which the respective array of antenna elements 201, 211 of the antenna module 200 is configured to operate.

[0070] FIG. 3 illustrates a side top view of an example embodiment of an antenna module 300 according to technology disclosed. In FIG. 3, the example antenna module comprises one array of antenna elements 301 (two antenna elements shown in FIG. 3) and two FSS layers 302, 303 including a lower layer 302 and an upper layer 303 arranged in an opening 304 of a reflector 307 and mounted to the reflector 307. The distance between the first and second FSS layer 302, 303 is in FIG. 3 maintained by means of spacers 305.

[0071] The example antenna module illustrated in FIG. 3 further comprises a plurality of lateral support beams 306 configured to both give the antenna module 300 structural strength and to maintain a distance of about X2 / 4 between the lower FSS layer 302 and the upper FSS layer 303 mounted to the reflector 307. Some of the lateral support beams 306 illustrated in FIG. 3 are mechanically connected to the upper FSS layer 303.

[0072] FIG. 4 illustrates a top view of an example embodiment of an antenna module 400 according to the technology disclosed. The example antenna module 400 illustrated in FIG. 4 comprises an array of antenna elements 401. The array of antenna elements 401 comprises a plurality of antenna elements 402 arranged on the reflector 404 and a plurality of antenna elements 403 arranged on the FSS layer 405 mounted to the reflector 404. The plurality of antenna elements 403 arranged on the FSS layer 405 mounted to the reflector 404 are capacitively coupled to the reflector 404 for improved beamforming capabilities and antenna gain for the array of antenna elements 401. The opening in reflector 404 is surrounded by conductive material of the reflector 404 to thereby provide an improved and more reliable Radio Frequency (RF) grounding for the plurality of antenna elements 403 mounted on the FSS layer 405 to enable cooperation with the plurality of antenna elements 402 arranged on the reflector 404 in terms of antenna gain and beamforming. FIG. 5 graphically illustrates the reflection and transmission of electromagnetic waves as a function of frequency for an example embodiment of a dual layer frequency selective surface provided with both bandstop and bandpass filtering characteristics .

[0073] In various embodiments of the technology disclosed where the antenna module comprises a plurality of FSS layers, where at least one of the plurality of FSS layers is arranged on a support layer and each of the plurality of FSS layers typically comprises a conductive pattern. In example embodiments of the technology disclosed, the conductive pattern may be at least one of printed on a thin plastic film, etched on a Printed Circuit Board (PCB) and etched directly on the support layer. The conductive pattern is typically periodic in the xy-plane with the z-axis pointing in the normal direction of the antenna structure, i.e. with the z-axis pointing in the direction of maximum radiation of the at least one array of antenna elements.

[0074] In example embodiments and as mentioned above, the lower FSS layer may typically be attached to and / or integrated in the backside radome of the antenna module. In certain embodiments, the antenna module may then have a rectangular indentation. Antenna elements mounted on the upper FSS layer may then typically provide an RF extension of antenna elements mounted on the conductive reflector. As an example, the reflector may have a rectangular cutout with typically the same shape, but not necessarily the same dimensions, as the indention in the backside radome.

[0075] The RF grounding of the upper FSS layer may then be capacitive in nature. A proper RF grounding is essential to populate the second or uppermost FSS layer with radiating elements operating in the stopband Fstop.

[0076] The technology disclosed addresses a need to provide improved and more reliable Radio Frequency (RF) grounding for a plurality of antenna elements mounted on a FSS layer attached to the reflector of an antenna module and to reduce the size and height of an antenna module comprising at least one layer comprising at least one frequency selective surface, while at the same time keeping the attenuation or transmission loss small. The technology disclosed thereby provides a compact antenna module and the benefits of the antenna module lies in the composite system and its function rather than the individual RF details with special emphasize on the application to base station antennas.

[0077] In aspects, the opening is surrounded by the conductive material of the reflector and the FSS layer is provided with conductive material arranged so that ground is at least one of discretely and continuously provided along the entire periphery of the FSS layer. Within Radio Frequency (RF) grounding, there needs to be multiple ground points where the separation between the ground points must not be too large. By providing capacitive RF grounding around the entire FSS layer, either discretely or continuously, the FSS layer together with the reflector behaves as a continuous ground plane, meaning that ground currents do not have to take any strange detours. This provides for more reliable RF grounding compared to prior art solutions.

[0078] According to the technology disclosed, a reflector of the antenna module is provided with an opening surrounded by the reflector and the mounted FSS layer in the opening. A plurality of antenna elements of said first set of antenna elements are mounted on the FSS layer in the opening so that they are surrounded by the conductive material of the reflector to thereby provide an improved and / or more reliable Radio Frequency (RF) grounding for the plurality of antenna elements mounted on the FSS layer. The technology disclosed provides for a more reliable RF grounding in that the two grounded layers overlap, for example with an insulating layer between them, and by the fact that these layers can be easily mechanically held together, for example with a screw connection. By providing capacitive RF grounding around the entire FSS layer, either discretely or continuously around the entire FSS layer, the FSS layer together with the reflector behaves as a continuous ground plane, meaning that ground currents do not have to take any strange detours. The RF grounding that the technology disclosed provides is therefore more reliable than previous RF grounding solutions and does not change.

[0079] The plurality of antenna elements mounted on the FSS layer may then be a first subset of the first array of antenna elements, and a second subset of the first array of antenna elements comprising a plurality of antenna elements operating at the first frequency band Fi are mounted on the reflector. The first and second subset of antenna elements may then be configured to co-operate with each other in that the FSS layer mounted on the opening of the reflector is capacitively coupled to RF ground along the edge of the reflector to the opening.

[0080] In embodiments, the antenna module further comprises a layer of insulating material arranged at least along portions of the edge of the opening in the reflector between the FSS layer and the reflector to capacitively couple the first subset of antenna elements mounted on the FSS layer to ground for improved antenna gain and beam-steering capabilities between the first subset of antenna elements mounted on the FSS layer and the second subset of antenna elements mounted on the reflector.

[0081] The antenna element (or array of antenna elements) of the technology disclosed is typically placed on top of an FSS of bandstop type, where the bandstop FSS is operating similar to a reflecting conducting reflector with respect to the antenna element(s) frequency band of operation, giving the antenna element(s), a direction of maximum radiation orthogonal to the surface of the FSS.

[0082] The antenna element operates at a frequency band Fi, within the stopband frequencies of the FSS. Outside the stopband, the FSS is typically more or less transparent with respect to electromagnetic waves. Both the antenna element (which could be a part of an array) and the FSS are typically transparent with respect to out of band frequencies, for example with respect to frequencies 3: 1 above the frequency band of operation of the transparent element(s). Thus, another antenna element, or array of antenna elements, operating at a frequency band F2 where the FSS is transparent, could be placed beneath the FSS, the antenna element or array of elements, having an antenna lobe, or maximum direction of radiation, pointing in the direction of the (at these frequencies) transparent FSS. Thus, the two antennas (arrays) share the same aperture and considerable area can be spared compared to if two separate arrays would be considered. The FSS, which is a bandstop filter for certain frequencies, typically comprises a periodic pattern of one or more layers of interlaced inductive and capacitive grids, wires and patches, respectively.

[0083] In embodiments, the antenna module comprises a support layer (layer) separated from the (first) layer comprising a frequency selective surface by a distance and configured to be functioning as a frequency selective layer in that a frequency selective pattern is printed on the support layer. The frequency selective pattern may be printed directly on the support layer, for example by means of Printed Circuit Board (PCB) etching, Screen Printing or Laser Direct Structuring (LDS) technology. The frequency selective pattern printed on the support layer may be configured so that the support layer is substantially transparent to electromagnetic waves in a selected frequency range including a second frequency band F2.

[0084] The array of antenna elements of the at least one array of antenna elements may be configured to operate at a lower first frequency band F 1 and the layer comprising a frequency selective surface mounted on the reflector may be configured to be substantially transparent to electromagnetic waves in a higher second frequency band F2 where the second frequency band F2 is typically well-separated from the first frequency band Fi. In embodiments, the layer comprising a frequency selective surface mounted on the reflector may be substantially transparent to electromagnetic waves in a second frequency band F23.3 - 3.8 GHz. The frequency selective pattern may then be further adapted so that the layer comprising a frequency selective surface mounted on the reflector is substantially reflective to electromagnetic waves in a first frequency band Fi 694 - 960 MHz.

[0085] In embodiments, the antenna module comprises a second array of antenna elements operating in a third frequency band F3 which is well-separated from both the first frequency band Fi and the second frequency band F2 and the frequency selective surface may further be configured so that the layer comprising a frequency selective surface mounted on the reflector is also substantially reflective for electromagnetic waves in a third frequency band F3 in which the second array of antenna elements is configured to operate where the third frequency band F3 is separated from the first and second frequency bands. The layer comprising a frequency selective surface is provided with a frequency selective pattern, for example a periodically arranged conductive pattern, configured so that the layer is substantially transparent to electromagnetic waves in the second frequency band F2. In embodiments, the first frequency band Fi in which the array of antenna elements mounted on the FSS layer is configured to operate is in the frequency range 610 - 980 MHz, and the FSS layer is configured to be substantially reflective to electromagnetic waves in the frequency range 610 - 980 MHz and is further configured to be substantially transparent to electromagnetic waves in at least one of the frequency ranges 1.4 - 2.7 GHz, 3.3 - 4.2 GHz and 4.8 - 7.2 GHz. In embodiments, the first frequency band Fi in which the array of antenna elements mounted on the FSS layer is configured to operate is in the frequency range 610 - 980 MHz, and the FSS layer is configured to be substantially reflective to electromagnetic waves in the frequency range 610 - 980 MHz and is further configured to be substantially transparent to electromagnetic waves in at least one of the frequency ranges 3.3 - 4.2 GHz and 4.8 - 7.2 GHz.

[0086] In certain embodiments, the antenna module comprises a second array of antenna elements operating in a third frequency band F3 and the FSS layer mounted on the reflector is substantially transparent to both a second frequency band F23.3 - 3.8 GHz and a third frequency band F34.8 - 7.2 GHz. The frequency selective pattern of the FSS layer may then be further adapted so that the layer comprising a frequency selective surface mounted on the reflector is substantially reflective to electromagnetic waves in a first frequency band Fi 610 - 980 MHz.

[0087] In certain embodiments, the antenna module comprises a second array of antenna elements operating in a third frequency band F3 4.8 - 7.2 GHz and the FSS layer mounted on the reflector is substantially transparent to a second frequency band F2 3.3 - 3.8 GHz. The frequency selective pattern of the FSS layer may then be further adapted so that the layer comprising a frequency selective surface mounted on the reflector is substantially reflective to electromagnetic waves in both a first frequency band Fi 694 - 960 MHz in which a first array of antenna elements is operating and a third frequency band F3 4.8 - 7.2 GHz in which the second array of antenna elements is operating.

[0088] In embodiments, the frequency selective conductive pattern may be directly printed on the layer comprising a frequency selective surface, for example by means of Screen Printing, Printed Circuit Board (PCB) etching or Laser Direct Structuring (LDS) technology. The conductive pattern printed on the layer comprising a frequency selective surface may then be configured so that the layer comprising a frequency selective surface is substantially transparent to electromagnetic waves in the second frequency band Fa.

[0089] As an example, the array of antenna elements of the at least one array of antenna elements is configured to operate at a first frequency band Fi and the layer comprising a frequency selective surface is configured to be substantially transparent to an electromagnetic wave having a wavelength X2 corresponding to a center frequency in the second frequency band F2 which is well-separated from the first frequency band Fi, and is further configured to be substantially reflective for electromagnetic waves in the first frequency band F 1 in which the array of antenna elements is configured to operate. The layer comprising a frequency selective surface is typically provided with a conductive pattern configured so that the layer is substantially transparent to electromagnetic waves in the second frequency band F2 and substantially reflective to electromagnetic waves in the first frequency band Fi in which the at least one array of antenna elements is configured to operate.

[0090] In embodiments, the layer comprising a frequency selective surface is arranged less than X2 / 6 from the backside radome structure and is provided with a periodic conductive pattern so that the layer of frequency selective surface and the backside radome structure are configured and arranged to be substantially transparent to electromagnetic waves in a second frequency band F2 which is a frequency band well-separated from the frequency band Fi in which an array of antenna elements of the antenna module operates.

[0091] In embodiments, the layer comprising a frequency selective surface is arranged less than X2 / 6 from the backside radome structure and is provided with a periodic conductive pattern so that the layer of frequency selective surface and the backside radome structure are thereby configured and arranged to be substantially transparent to electromagnetic waves in a second frequency band F2. The second frequency band F2 is then typically well-separated from the frequency band Fi in which an array of antenna elements of the antenna module operates.

[0092] In embodiments, the at least one frequency selective surface comprises a plurality of layers comprising a frequency selective surface where a lower layer comprising a frequency selective surface is arranged less than X2 / 6 from the backside radome structure. Each of the plurality of layers comprising a frequency selective surface is provided with a periodic conductive pattern configured so that the complete structure including the layers comprising a frequency selective surface is configured and arranged to be substantially transparent to electromagnetic waves in a second frequency band F2. The second frequency band F2 is typically well-separated from the frequency band Fi in which an array of antenna elements of the antenna module operates and at least the uppermost FSS layer among the plurality of FSS layers is configured to be substantially reflective to electromagnetic waves in the first frequency band Fi.

[0093] In certain embodiments, the layer comprising a frequency selective surface may be at least one of attached to and integrated into the backside radome structure so that the layer comprising a frequency selective surface and the backside radome structure are configured and arranged to be substantially transparent to electromagnetic waves in a frequency range including the second frequency band F2.

[0094] In aspects of the technology disclosed, the second frequency band F2for which the layer comprising a frequency selective surface is substantially transparent is typically a higher frequency band, for example a frequency band in the range 3.3 - 3.8 GHz, than the operating frequency band Fi of the array of antenna elements, which for example may be a frequency band in the lower frequency range 694 - 960 MHz, and is non-overlapping with the first frequency band Fi, i.e. the two frequency bands Fi and F2are separated in frequency.

[0095] In various embodiments of the technology disclosed, the layer comprising a frequency selective surface is arranged directly onto the backside radome structure. In example embodiments, the layer comprising a frequency selective surface is at least one of taped and glued to the backside radome structure.

[0096] In other example embodiments, the backside radome structure may comprise an indentation or recess and the layer comprising a frequency selective surface may then be arranged in the indentation or recess, for example by being at least one of taped and glued to the bottom of the indentation or recess.

[0097] The at least one layer comprising a frequency selective surface may typically comprise a plurality of elements forming at least one periodic conductive pattern on the material. In embodiments, the layer comprising a frequency selective surface is made of a plastic material including a periodic conductive pattern or periodic conductive tracks printed on the plastic material. Typically, the layer comprising a frequency selective surface may then comprise a periodic conductive pattern, for example a periodically arranged pattern made of relatively thin conductive tracks. In example embodiments where two FSS layers are used, the first layer comprising a frequency selective surface and the second layer comprising a frequency selective surface are typically separated by a distance of about Aa / 4. When more FSS layers are used, the separate distance between individual FSS layers may be different than about A2 / 4.

[0098] In embodiments, the second layer comprising a frequency selective surface is substantially transparent to electromagnetic waves in a second frequency band F2 3.3 - 3.8 GHz. The second layer comprising a frequency selective surface may further be substantially reflective to electromagnetic waves in a first frequency band Fi 694 - 960 MHz in which an array of antenna elements of the antenna module is configured to operate. At least some of the antenna elements of the array of antenna elements may be arranged on the second layer comprising a frequency selective surface.

[0099] In embodiments, the conductive pattern may be directly printed on the second layer comprising a frequency selective surface, for example by means of Screen Printing or Laser Direct Structuring (LDS) technology. The conductive pattern printed on the FSS layer mounted on the opening of the reflector may be configured to be substantially transparent to electromagnetic waves in a frequency range including the second frequency band F2. In embodiments, at least a plurality of antenna elements of the at least one array of antenna elements is arranged on the FSS layer mounted on the opening of the reflector (some of the antenna elements may be arranged on the reflector) and another second FSS layer is arranged less than A2 / 6 from the backside radome structure, for example is the second FSS layer directly attached to the backside radome structure.

[0100] In embodiments, the plurality of antenna elements arranged / mounted on the reflector are operating at the same frequency band as the plurality of antenna elements mounted on the FSS layer and configured to be co-operating with the plurality of antenna elements arranged / mounted on the FSS layer mounted on the opening of the reflector. The plurality of antenna elements arranged on the FSS layer mounted on the opening of the reflector on which some of the antenna elements are arranged / mounted may then be configured to be substantially transparent to electromagnetic waves in at least one frequency range including a second frequency band F2. Moreover, the plurality of antenna elements arranged on the reflector may be configured to be substantially transparent to electromagnetic waves in at least one frequency range including a second frequency band F2.

[0101] In aspects of the technology disclosed, the FSS layer mounted on the opening of the reflector is configured and arranged to provide an RF extension of the reflector in that the FSS layer is capacitively coupled to the reflector. The antenna module may then further comprise a thin layer of insulating material arranged between conducting portions of the FSS layer mounted on the opening of the reflector and conducting portions of the reflector. The FSS layer mounted on the opening of the reflector may thereby be capacitively coupled to the reflector through a thin layer of insulating material so that the plurality of antenna elements arranged on the reflector cooperate with the plurality of antenna elements arranged on the FSS layer mounted on the opening of the reflector to improve antenna gain.

[0102] In example embodiments of an antenna module comprising two layers of frequency selective material, the feeding network for feeding the (first) array of antenna elements is arranged on the FSS layer mounted on the opening of the reflector, i.e. feed cables for feeding the array of antenna elements is routed along the FSS layer mounted on the opening of the reflector.

[0103] In embodiments, the antenna module further comprises a support layer for the FSS layer mounted on the opening of the reflector. According to certain embodiments of the technology disclosed, the support layer is typically made of the same material as the backside radome structure and further typically has a thickness corresponding essentially to the thickness of the backside radome structure.

[0104] In embodiments, the antenna module comprises a multi-layer structure and at least two spacers. The at least two spacers may then be configured and mechanically connected to at least one of the layers of the multi-layer structure to maintain an air gap of about X2 / 4 between the FSS layer mounted on the opening of the reflector and another FSS layer of the antenna module.

[0105] In embodiments, the at least two spacers are mechanically connected to a layer comprising a frequency selective surface which is attached to the backside radome structure and are further also mechanically connected to the uppermost FSS layer mounted on the opening of the reflector, the support layer and the reflector. In various embodiments of the technology disclosed, the at least one frequency selective surface of the technology disclosed comprises at least three separate layers comprising a frequency selective surface, each layer comprising a periodic pattern and where the at least three layers are separated from each other by a distance. One of the FSS layers may then be arranged a close distance from the backside radome structure and the other at least two layers may be arranged between the layer and the at least one array of antenna elements. One of the two other FSS layers may then be mounted on the opening in the reflector. In embodiments, the antenna module comprises a multi-layer structure including at least one layer of frequency selective surface, or FSS layer. At least one of the at least one FSS layers may be a printed circuit board (PCB) mounted on the opening in the reflector.

[0106] In embodiments, the antenna module further comprises a second array of antenna elements operating at a different frequency band than the antenna elements arranged on the FSS layer mounted on the opening in the reflector. In certain embodiments, both the feed cables for feeding the first array of antenna elements and the feed cables for feeding the second array of antenna elements may be routed along the FSS layer mounted on the opening in the reflector. According to certain embodiments of the technology disclosed, a second FSS layer is arranged on, or close to, the backside radome structure and a support layer for the FSS layer mounted to / on the opening in the reflector is typically made of the same material as the backside radome structure of the antenna module and further typically has a thickness corresponding essentially to the thickness of the backside radome structure. The reflector of the antenna module may have an opening and the support layer for the FSS layer is then typically also arranged in the opening of the reflector.

[0107] In embodiments, the antenna module may comprise a foam material arranged between the FSS layer mounted on the opening in the reflector and a second FSS layer. The foam material may then be configured to maintain a distance, for example of about Aa / 4, between the FSS layer mounted on the opening in the reflector and the other FSS layer.

[0108] In embodiments, the antenna module may comprise at least two spacers configured and mechanically connected to maintain a distance, for example an air gap distance, of about Xa / 4 between the FSS layer mounted on the opening in the reflector and a second FSS layer.

[0109] In embodiments, the antenna module may comprise at least two lateral support beams configured to both give the antenna module structural strength and to maintain a distance, for example an air gap distance, of about X2 / 4 between the FSS layer mounted on the opening in the reflector and the second FSS layer. In example embodiments of an antenna module comprising two layers of frequency selective material, a feeding network for feeding the array of antenna elements is arranged on the FSS layer mounted on the opening of the reflector, i.e. feed cables for feeding the array of antenna elements is routed along the first FSS layer.

[0110] In embodiments, the antenna module may comprise a structure comprising a foam material configured to both give the antenna module structural strength and to maintain a distance, for example a distance of about Xa / 4, between a FSS layer mounted on the opening of the reflector and a second FSS layer.

[0111] In embodiments, the antenna module may comprise at least two lateral support beams configured to both give the antenna module structural strength and to maintain a distance, for example an air gap distance, of about X2 / 4 between a first layer comprising a frequency selective surface and a second layer comprising a frequency selective surface. The at least two lateral support beams may then be mechanically connected to at least one of the first layer comprising a frequency selective surface, the second layer comprising a frequency selective surface, the support layer for the second FSS layer and the reflector.

[0112] In embodiments, the antenna module may comprise at least one spacer and at least one lateral support beam configured to both give the antenna module structural strength and to maintain a distance, for example an air gap distance, of about X2 / 4 between the first layer comprising a frequency selective surface and the second layer comprising a frequency selective surface. At least one of the at least one spacer and the at least one lateral support beam may then be mechanically connected to at least one of the FSS layer mounted on the opening of the reflector and the second FSS layer. In embodiments, the first array of antenna elements of the antenna module is configured as a 5G antenna, and the second array of antenna elements of the antenna module is configured as a non-5G antenna. According to aspects of the technology disclosed, the second layer comprising a frequency selective surface is arranged less than X2 / 6 from the backside radome structure, and the layer comprising a frequency selective surface is further configured so that the total transmission loss through the backside radome structure and the second layer comprising a frequency selective surface is reduced to a minimum or close to 0, for example less than 1.0 dB in for all incident electromagnetic waves in a second frequency range F2. As an example, the second frequency band F2 is in the frequency range 3.3 - 4.2 GHz and the layer comprising a frequency selective surface is arranged less than 10 mm from the backside radome structure. In certain example embodiments, the second layer comprising a frequency selective surface may then be arranged on a support layer positioned between the layer comprising a frequency selective surface and the backside radome structure and the support layer has a thickness of less than X2 / 6.

[0113] In embodiments, the (lower) second FSS layer is at least one of attached to and integrated in the backside radome structure. As examples of embodiments, the second FSS layer is directly joined to the backside radome structure. In embodiments, the center frequency of the second frequency band F2 is about 3.5 GHz and the at least one second FSS layer is arranged less than 5 mm from the backside radome structure.

[0114] In embodiments, the first frequency band Fi in which the antenna elements arranged on the FSS layer mounted on the opening of the reflector is configured to operate is in the frequency range 610 - 980 MHz. The FSS layer mounted on the opening of the reflector may then be configured to be substantially reflective to electromagnetic waves in the frequency range 610 - 980 MHz and may be further configured to be substantially transparent to electromagnetic waves in at least one of the frequency ranges 1.4 - 2.7 GHz, 3.3 - 4.2 GHz and 4.8 - 7.2 GHz.

[0115] In embodiments, the first frequency band Fi in which the array of antenna elements arranged on the FSS layer mounted on the opening in the reflector is configured to operate is in the frequency range 1.4 - 2.7 GHz, and the FSS layer mounted on the opening in the reflector is configured to be substantially reflective to electromagnetic waves in the frequency range 1.4 - 2.7 GHz and substantially transparent to electromagnetic waves in at least one of the frequency ranges 3.3 - 4.2 GHz and 4.8 - 7.2 GHz. In embodiments, the antenna module may comprise a support in form of a support layer configured to support the FSS layer mounted to / on the opening in the reflector. In certain embodiments, feed cables for feeding the array of antenna elements mounted on the first FSS layer are routed along grounded grid lines of the FSS layer mounted to / on the opening in the reflector.

[0116] In embodiments, the antenna module further comprises a support layer for the first FSS layer. The support layer may be selected to be of the same material, for example a plastic material, and have essentially the same thickness as the backside radome structure having the second FSS layer arranged thereon. The first FSS layer may then be a plastic structure comprising a periodic conductive pattern printed on the plastic structure.

[0117] In embodiments, the antenna module may comprise a multi-layer structure and spacers. A certain distance between a second layer comprising a frequency selective surface attached and / or integrated in the backside radome structure and the first FSS layer arranged in an opening of the reflector may be maintained by means of at least two spacers that are mechanically connected to at least one of the layers of the multi-layer structure. The at least two spacers may be mechanically connected to the second layer comprising a frequency selective surface or the backside radome structure (through holes in the first FSS layer) and may be further mechanically connected to at least one of the first FSS layer, the support layer for the first FSS layer and the reflector.

[0118] According to aspects of the technology disclosed, the reflector of the antenna module may be provided with an opening (window) and the (first) FSS layer may be arranged in the opening of the reflector, for example arranged on and / or be attached / joined to an inside edge of the opening of the reflector. In embodiments, the antenna elements of the array of antenna elements are configured to operate at a first frequency band F i and are further arranged on the first FSS layer, for example attached to and / or joined to ground grid lines of the first FSS layer.

[0119] In embodiments, the array of antenna elements comprises a plurality of antenna elements arranged on the reflector and a plurality of antenna elements arranged on the (upper / first) FSS layer mounted to / on the opening of the reflector. By providing a thin layer of insulating material between portions of the (upper / first) FSS layer and portions of the reflector, the (upper / first) layer and the reflector is capacitively coupled through a thin layer of insulating material so that the plurality of antenna elements arranged on the reflector may cooperate with the plurality of antenna elements arranged on the (upper / first) layer comprising a frequency selective surface.

[0120] In another example embodiment of the technology disclosed, the second frequency band F2 is in the frequency range 3.3 - 4.2 GHz and the attenuation through a structure including the backside radome structure and the layer comprising a frequency selective surface (attached to and / or integrated in the backside radome structure) is less than 1.0 dB for electromagnetic waves first on the surface of the backside radome structure and which are transmitted by an antenna device external to the antenna module configured to operate at a frequency band in the frequency range F2.

[0121] In aspects of the technology disclosed, the layer comprising a frequency selective surface is typically provided with both bandstop and bandpass filtering characteristics in that the layer comprising a frequency selective surface is configured to be essentially transparent to electromagnetic waves with wavelength X2 corresponding to the center frequency of a second frequency band F2, for example a center frequency of 3.5 GHz, and in that the first frequency band Fi in which the array of antenna elements operates is within the stopband frequencies of the layer comprising a frequency selective surface.

[0122] In aspects and embodiments, the second layer comprising a frequency selective surface is arranged at a distance less than X2 / 6 from the backside radome structure so that the combined structure of the layer comprising a frequency selective surface and the backside radome structure is configured to be essentially transparent to electromagnetic waves with wavelength X2 corresponding to the center frequency of a second frequency band F2.

[0123] Arranging the layer comprising a frequency selective surface at a close distance from or directly joined to the backside radome structure, for example directly joined to and / or integrated in an indentation of the backside radome structure, reduces the overall height of the antenna module and thereby makes the antenna module more compact. As mentioned above, the metallic reflector of the antenna module has an opening, for example a rectangular cutout, and the layer comprising a frequency selective surface is arranged in the opening of the reflector. The array of antenna elements may typically comprise a plurality of antenna elements arranged on the reflector, and which are co-operating with a plurality of antenna elements arranged on the second layer comprising a frequency selective surface in the opening of the reflector.

[0124] The plurality of antenna elements arranged on the second layer comprising a frequency selective surface typically need to be capacitively grounded to the same ground (reference) potential of the antenna module.

[0125] The reflector of the antenna module may have an opening and the layer comprising a frequency selective surface may be arranged in an opening of the reflector. The array of antenna elements may typically comprise a plurality of antenna elements arranged / mounted on the metallic reflector, for example made of aluminum, and which are co-operating with a plurality of antenna elements arranged / mounted on the layer comprising a frequency selective surface in the opening of the reflector. At least the plurality of antenna elements arranged on the layer comprising a frequency selective surface may be configured to be substantially transparent to electromagnetic waves in at least one frequency range including a second frequency band F2. For the two sets of antenna elements to be able to co-operate to improve the total gain of the array of antenna elements (and in order to reduce or avoid unwanted voltage effects), the plurality of antenna elements arranged on the reflector and the plurality of antenna elements arranged on the layer comprising a frequency selective surface need to be capacitively grounded to the same ground (reference) potential of the antenna module.

[0126] In aspects of the technology disclosed, the layer comprising a frequency selective surface mounted to / on the opening in the reflector is configured and arranged to provide an RF extension of the reflector. For example, the antenna module may then further comprise a relatively thin layer of insulating material arranged between conducting portions of the second layer comprising a frequency selective surface and conducting portions of the reflector. The second layer comprising a frequency selective surface may then be capacitively coupled, or capacitively grounded, to the reflector through the thin layer of insulating material so that the plurality of antenna elements arranged on the reflector and the plurality of antenna elements arranged on the layer comprising a frequency selective surface are capacitively grounded to the same ground (reference) potential of the antenna module to be able to co-operate for improved antenna gain.

[0127] In aspects of the technology disclosed, the second layer comprising a frequency selective surface is configured and arranged to provide an RF extension of the reflector. The antenna module may then further comprise a thin layer of insulating material arranged between conducting portions, for example copper lines, of the layer comprising a frequency selective surface and conducting portions of the reflector, for example is the reflector made of aluminum or alloys thereof. The layer comprising a frequency selective surface may be capacitively coupled, or capacitively grounded, to the reflector through the thin layer of insulating material so that the plurality of antenna elements arranged on the reflector cooperates with the plurality of antenna elements arranged on the layer comprising a frequency selective surface to improve the gain of the antenna module.

[0128] The introduction of this thin layer of insulating material arranged between conducting portions of the layer comprising a frequency selective surface that is mounted to / on the opening and the reflector, in addition, provides the technical effect of reducing or avoiding unwanted voltage effects, yet the plurality of antenna elements arranged on the reflector and the plurality of antenna elements arranged on the layer comprising a frequency selective surface are both capacitively grounded to the same ground (reference) potential of the antenna module to be able to cooperate for improved antenna gain.

[0129] In embodiments, the layer comprising a frequency selective surface and the second layer comprising a frequency selective surface are separated by a distance of about X2 / 4 to provide constructive interference from the electromagnetic waves passing through the two layers. Preferably, in order to reduce or avoid transmission losses, the first layer comprising a frequency selective surface and the second layer comprising a frequency selective surface are separated by an air gap of about Xa / 4. However, in certain embodiments the two layers may also be separated by a layer of foam material that is configured to maintain a distance corresponding to a travel distance in air of about Xa / 4, yet the layer of foam material may provide the necessary mechanical stability to the antenna module. The layer of foam material may then itself have a thickness corresponding to a travel distance in air of about A2 / 4.

[0130] In embodiments, the antenna module further comprises a support layer for the second layer comprising a frequency selective surface. The support layer for the second layer comprising a frequency selective surface is typically made of the same material, for example plastic material, as the backside radome structure and further typically has a thickness corresponding essentially to the thickness of the backside radome structure. The thickness of the support layer for the second layer comprising a frequency selective surface and the thickness of the backside radome structure is then typically in the range 1.5 to 3 mm to thereby minimize the transmission loss for electromagnetic waves having a frequency band F2in a passband frequency range for both the layer of frequency selective material and the second layer of frequency selective material (i.e. substantially no attenuation through the two layers), yet the backside radome structure provides the necessary stability for the antenna module and the support layer does not add to much to the total height of the antenna module (typically 1 to 2 mm compared to a state-of-the- art support layer). Typically, and in order to avoid reflections between surfaces for the wave, the (first) layer of frequency selective material is arranged, for example attached, directly on the backside radome structure and the second layer of frequency selective material is arranged directly on its support layer.

[0131] In embodiments, the antenna module comprises a multi-layer structure and at least two spacers. The at least two spacers may be configured and mechanically connected to at least one of the layers of the multi-layer structure to maintain an air gap distance of about X2 / 4 between the layer comprising a frequency selective surface and the second layer comprising a frequency selective surface.

[0132] The at least two spacers are typically mechanically connected to the layer comprising a frequency selective surface and are further mechanically connected to at least one of the first layer comprising a frequency selective surface, the support layer and the reflector. In embodiments, the antenna module comprises a multilayer structure including at least one layer comprising a frequency selective surface.

[0133] In embodiments, the antenna module further comprises a second array of antenna elements arranged, from a top view, below the array of antenna elements but above the second layer of frequency selective material. The second array of antenna elements may then be configured to operate at a third frequency band F3 separate from and non-overlapping with the frequency bands Fi and F2, and the second layer of frequency selective material is configured to be substantially reflective to electromagnetic waves in a frequency range including the third frequency band F3 According to embodiments of the technology disclosed, the reflector of the antenna module may be provided with an opening (window) and the second (upper) layer comprising a frequency selective surface may be arranged in the opening of the reflector, for example arranged on and / or be attached / joined to an inside edge of the opening of the reflector. In embodiments, the antenna elements of the array of antenna elements are configured to operate at a first frequency band Fi and are further arranged on the (upper / first) layer comprising a frequency selective surface, for example attached to and / or joined to ground grid lines of the (upper / first) layer comprising a frequency selective surface.

[0134] In embodiments, the array of antenna elements comprises a plurality of antenna elements arranged on the reflector and a plurality of antenna elements arranged on the (upper / first) layer comprising a frequency selective surface in the opening of the reflector. By providing a thin layer of insulating material between portions of the (upper / first) layer comprising a frequency selective surface and portions of the reflector, the (upper / first) layer comprising a frequency selective surface and the reflector is capacitively coupled through a thin layer of insulating material so that the plurality of antenna elements arranged on the reflector cooperate with the plurality of antenna elements arranged on the (upper / first) layer comprising a frequency selective surface.

[0135] According to embodiments of the technology disclosed, the reflector of the antenna module may be provided with an opening (window) and the (upper / first) layer comprising a frequency selective surface may be arranged in the opening of the reflector, for example arranged on and / or be attached / joined to an inside edge of the opening of the reflector. In embodiments, the antenna elements of the array of antenna elements are configured to operate at a first frequency band F 1 and are arranged on the (upper / first) layer comprising a frequency selective surface, for example attached to and / or joined to ground grid lines of the (upper / first) layer comprising a frequency selective surface. In embodiments, the array of antenna elements comprises a plurality of antenna elements arranged on the reflector and a plurality of antenna elements arranged on the (upper / first) layer comprising a frequency selective surface in the opening of the reflector. By providing a thin layer of insulating material between portions of the (upper / first) layer comprising a frequency selective surface and portions of the reflector, the (upper) layer comprising a frequency selective surface and the reflector is capacitively coupled through a thin layer of insulating material so that the plurality of antenna elements arranged on the reflector may cooperate with the plurality of antenna elements arranged on the (upper / first) layer comprising a frequency selective surface.

[0136] According to some aspects, the technology disclosed relates to an antenna element (or array of antenna elements) placed on top of a Frequency Selective Surface (FSS) of bandstop type. The bandstop FSS is operating similar to a reflecting conducting ground plane with respect to the frequency band of operation of the antenna element(s), giving the antenna element(s) a lobe, a maximum direction of radiation orthogonal to the surface of the FSS. The antenna element operates at a frequency band Fi, within the stopband frequencies of the FSS. Outside the stopband, the FSS of the technology disclosed is typically more or less transparent with respect to electromagnetic waves. Both the antenna element (which could be a part of an array) and the FSS are typically transparent with respect to out of band frequencies, for example with respect to frequencies 3: 1 above the band of operation of the transparent element(s). In embodiments, the radiating parts of the antenna element may essentially consist of four essentially identical quadrants where each quadrant essentially comprises a conducting loop with narrow line width. Two oppositely placed (diagonally placed) loops may then be fed in pairs by exciting them by a voltage source in the middle of the element. Thus, a pair of loops behave as a broad band dipole. Since there are four loops, each element can operate as a dual polarized two port antenna. The four conducting element loops are typically printed on one side of a dielectric substrate.

[0137] The two pairs of element loops may be fed in various ways. Typically, they can be fed by slot-lines implemented on crossed printed circuit boards (PCBs). The crossed boards may be mounted on a small PCB with the same size as that of a cell in the periodic structure to thereby give a small footprint. The small PCB may further be arranged in the center of a patch in the periodic cell, perturbing no more than one periodic cell. Coaxial feed lines (or other transmission lines) may be connected to micro-strip-lines on the small PCB. The coaxial lines are typically close to and aligned with the inductive grid lines on the FSS to thereby perturb the FSS to a minimum. 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. An antenna module, comprising: at least one array of antenna elements, a feed network for the at least one array of antenna elements, a reflector, a frequency selective surface (FSS) layer configured to control the transmission and reflection of electromagnetic waves and a radome configured to protect the at least one array of antenna elements of the antenna module from mechanical impact and weather influences, wherein an array of antenna elements is configured to operate at a first frequency band Fi and arranged to transmit in a transmitting direction, and said FSS layer is provided with bandstop and bandpass filtering characteristics in that said FSS layer is configured to be substantially transparent to an electromagnetic wave having wavelength X2 corresponding to a center frequency in a second frequency band F2 corresponding to a passband frequency range, separate from the first frequency band Fi and in that the first frequency band F 1 in which said array of antenna elements operates is within the stopband frequencies of said FSS layer, and wherein the reflector of the antenna module is provided with an opening and said FSS layer is mounted on the opening, and wherein a plurality of antenna elements are mounted on said FSS layer in the opening so that they are surrounded by the conductive metal material of the reflector to thereby provide a reliable Radio Frequency (RF) grounding for said plurality of antenna elements mounted on the FSS layer.

2. The antenna module of claim 1, wherein said opening is a rectangular cutout in the reflector.

3. The antenna module of any of claims 1 and 2, wherein the RF grounding of said FSS layer mounted on the opening of the reflector is capacitive in nature, and wherein said FSS layer is capacitively coupled to ground along the edges of the reflector surrounding the opening so that said plurality ofantenna elements mounted on the FSS layer thereby are capacitively coupled to ground.

4. The antenna module of any of claims 1 to 3, wherein said plurality of antenna elements mounted on said FSS layer is a first subset of said array of antenna elements, and wherein a second subset of said array of antenna elements comprising a plurality of antenna elements operating at the first frequency band Fi are mounted on the reflector.

5. The antenna module of claim 4, wherein said first and second subset of antenna elements are configured to co-operate in that the FSS layer mounted on the opening of the reflector is capacitively coupled to ground along the edges of the reflector to the opening.

6. The antenna module of any of claims 3 to 5, wherein the antenna module further comprises a layer of insulating material arranged along at least portions of the edges of the opening in the reflector between the FSS layer and the reflector to capacitively couple said first subset of antenna elements mounted on said FSS layer to ground so that said first subset of antenna elements can co-operate with said second subset of antenna elements mounted on the reflector, thereby providing for improved antenna gain for the array of antenna elements.

7. The antenna module of any of claims 1 to 6, wherein the antenna module further comprises a second FSS layer physically separated from said (first) FSS layer mounted on the opening of the reflector and configured to also be substantially transparent to electromagnetic waves having wavelength X2 corresponding to a center frequency in the second frequency band F2.

8. The antenna module of claim 7, wherein the first and second FSS layers are separated by a distance that is partly maintained during operation of the antenna module by means of a foam material arranged between the first and second FSS layer and that provides mechanical stability to external forces.

9. The antenna module of any of claims 7 and 8, wherein the first and second FSS layers are separated by a distance so that the combination of the two FSS layers is configured to be substantially transparent in at least one frequency band F2 outside the frequency band Fi in which the array of antenna elements of the antenna module operates.

10. The antenna module of any of claims 1 to 9, wherein the opening is surrounded by the conductive material of the reflector, and wherein the FSS layer is provided with conductive material arranged so that ground is at least one of discretely and continuously provided along the entire periphery of the FSS layer.

11. The antenna module of any of claims 1 to 10, wherein the second frequency band F2 is a higher frequency band than the first frequency band Fi and is non-overlapping with the first frequency band Fi.

12. The antenna module of any of claims 1 to 11, wherein the antenna module further comprises a second array of antenna elements configured to operate at a third frequency band F3 well-separated from both the first frequency band Fi and the second frequency band F2, and wherein at least some of the antenna elements of the second array of antenna elements are also arranged on the (first) FSS layer and configured to transmit in the same transmitting direction as the first array of antenna elements.

13. The antenna module of claim 12, wherein the second frequency band Fs is a higher frequency band than the first frequency band F 1 and is nonoverlapping with both the first frequency band Fi and the second frequency band F2.

14. The antenna module of any of claims 1 to 13, wherein the antenna module further comprises an additional FSS layer physically separated from said FSS layer, and the additional FSS layer is attached to and / or integrated in the backside radome of the antenna module.

5. The antenna module of any of claims 1 to 14, wherein feed cables for feeding the antenna elements mounted on said FSS layer are routed along said FSS layer.

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