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EP-4740270-A1 - A BASE STATION ANTENNA MODULE COMPRISING A FREQUENCY SELECTIVE SURFACE LAYER MOUNTED ON AN OPENING IN A REFLECTOR

EP4740270A1EP 4740270 A1EP4740270 A1EP 4740270A1EP-4740270-A1

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).

Inventors

  • SOHL, Christian

Assignees

  • Kaelus AB

Dates

Publication Date
20260513
Application Date
20240620

Claims (15)

  1. 1. 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. 2. The antenna module of claim 1, wherein said opening is a rectangular cutout in the reflector.
  3. 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 of antenna elements mounted on the FSS layer thereby are capacitively coupled to ground.
  4. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.
  15. 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.

Description

TITLE A base station antenna module comprising a frequency selective surface layer mounted on an opening in a reflector FIELD OF THE INVENTION 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. BACKGROUND OF THE INVENTION In recent years, with the development of information communication technologies data traffic is continuously and exponentially increasing. 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. 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. 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. 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. 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. 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. BRIEF SUMMARY OF THE INVENTION 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. Exemplifying embodiments of the proposed technology are defined by the dependent claims. 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