Patent Application
20180342807
The present disclosure relates to configurable antenna arrays with diverse polarizations.
Wireless Local Area Networks (WLANs) are utilized for providing users with access to services and/or network connectivity. As a result, compact antenna modules are desirable to provide adaptive beams and multiple beams in WLANs. Many base station or access point antennas deploy arrays of antenna elements to achieve advanced antenna functionality, e.g., beam forming, etc. Thus, solutions for reducing the profile of individual antenna elements as well as for reducing the size (e.g., width, etc.) of the antenna element arrays are desired, while maintaining key performance features such as polarization diversity, high gain in a particular direction, and wide frequency bandwidths.
Typical existing antennas face challenges in respect of the number of radio frequency streams, peak gain, polarizations and frequency bandwidths they can effectively support within a compact antenna package. Examples described herein can address one or more of these challenges in at least some applications. In at least some examples, an antenna configuration is provided that can support different frequency bands with multiple antenna units, each of which provide selectable polarization diversity.
According to one example aspect is a radio frequency (RF) antenna unit that includes a first antenna and a second antenna. The first antenna is positioned on a reflector element, and includes at least three inverted-F antenna (IFA) elements that are electrically connected to a first RF signal port and that each have an associated tunable element that controls excitation of the IFA element, the tunable elements being operative to control a polarization direction of the first antenna. The second antenna is co-located on the reflector element with the first antenna, and includes a plurality of antenna elements.
In some examples, the tunable elements are operative to control excitation of the IFA elements to enable a first mode in which the first antenna has an omni-directional polarization and a second mode in which the first antenna has a directional polarization. Furthermore, the IFA elements may be arranged symmetrically around a central axis, on a printed surface board (PCB) substrate, and are spaced apart from and parallel to the reflector element.
In some examples, the first RF port is centrally located relative to the IFA elements, each IFA element being electrically connected to the first RF signal port through the tunable element associated with the IFA element such that the tunable element can selectively couple and decouple the IFA element to the first RF signal port. In some configurations, each IFA element may have an associated gain enhancing parasitic conductor that is located adjacent the IFA element on the PCB substrate a further distance from the RF signal port than the IFA element.
In some examples, the antenna elements of the second antenna are each connected to a second RF signal port and each have an associated tunable element that controls excitation of the antenna element, the tunable elements being operative to control a polarization direction of the second antenna. The antenna elements of the second antenna may be centrosymetrically arranged around the central axis, and the antenna elements are each folded monopole antenna elements that extend perpendicular to the reflector element.
In some examples of the first aspect, the first antenna and the second antenna are configured to operate in the same frequency band, for example a 2.4 GHz band or a 5 GHz band. In some examples, the first antenna and the second antenna are configured to operate in different frequency bands, for example one in the 2.4 GHz band and one in the 5 GHz band.
In some examples, the first antenna comprises four IFA elements and the second antenna comprises four folded monopole antenna elements. In some examples, a shorting line of each monopole antenna element is connected to ground through the tunable element associated with the monopole antenna element.
In some alternative configurations, the antenna elements of the second antenna are IFA elements arranged symmetrically around the central axis, on a further PCB substrate, and are spaced apart from and parallel to the reflector element and the PCB substrate of the first antenna.
According to a further aspect, an antenna array is provided that includes a planar reflector element and first and second antenna units that respectively include a first antenna and a second antenna positioned on the reflector element. The first antenna is configured to operate in a first frequency range, and has at least three inverted-F antenna (IFAs) elements electrically connected to a first RF signal port and that each have an associated tunable element that controls excitation of the IFA element. The second antenna is configured to operate in a second frequency range and has at least three inverted-F antenna (IFAs) elements that are electrically connected to a second RF signal port. All of the IFA elements have an associated tunable element that controls excitation of the IFA element. A controller is operatively connected to the tunable elements associated with each of the IFA elements for selectively controlling polarization directions of the first antenna and the second antenna.
In some examples configurations, the tunable elements are responsive to the controller to control excitation of the IFA elements to selectively enable a first and second mode for each of the first and second antennas, wherein in the first mode the IFA elements are excited collectively to provide an omni-directional polarization and in the second mode the IFA elements are selectively excited to provide a directional polarization.
In some examples, the first antenna unit includes a further antenna co-located on the reflector element with the first antenna and comprising at least three antenna elements electrically connected to a third RF signal port and that each have an associated tunable element that controls excitation of the antenna element. Similarly, the second antenna unit includes a further antenna co-located on the reflector element with the second antenna and comprising at least three antenna elements electrically connected to a forth RF signal port and that each have an associated tunable element that controls excitation of the antenna element. The controller is operatively connected to the tunable elements associated with each of the antenna elements for selectively controlling polarization directions of the further antennas of the first antenna unit and the second antenna unit.
In some embodiments of the antenna array, each of the first antenna and the second antenna have their IFA elements arranged symmetrically around a central axis, on a printed surface board (PCB) substrate, and are spaced apart from and parallel to the reflector element. For the first antenna the first RF signal port is centrally located relative to the IFA elements, and each IFA element of the first antenna is connected to the first RF signal port through the tunable element associated with the IFA element. For the second antenna the second RF signal port is centrally located relative to the IFA elements, and each IFA element of the second antenna is connected to the second RF signal port through the tunable element associated with the IFA element.
In some embodiments the antenna array includes two of the first antenna units and two of the second antenna units located symmetrically around a central area of the reflector element, enabling 8 RF signals to be independently polarized.
In some examples of the antenna array, the first antenna and second antenna each include at least four IFA elements and the further antennas of the first antenna unit and the second antenna unit each comprise at least four folded monopole antenna elements.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Multiple input and multiple output (MIMO) antenna technology produces significant increases in spectral efficiency and link reliability, and these benefits generally increase as the number of transmission antennas within the MIMO system increases. System operators require more and more capacity for multiple input and multiple output (MIMO) antennas. One way to increase the capacity of such a system is to provide an antenna array that includes multiple antenna units to support dual bands with high gain in diverse polarization directions.
In example embodiments the first antenna units 110 are configured to emit or receive wireless radio frequency (RF) signals within a first RF band and the second antenna units 120 are configured to emit or receive wireless RF signals within a second RF band. For example, in some embodiments the antenna array 100 is used to support WiFi communications, with the first antenna units 110 configured to operate in the 5 GHz frequency band and the second antenna units 120 configured to operate in the 2.4 GHz frequency band.
In the illustrated example, the antenna array 100 includes two 5 GHz antenna units 110(1), 110(2), positioned at two corners of the reflector element 114 along a diagonal of the front surface 115, and two 2.4 GHz antenna units 120(1), 120(2), positioned at the other two corners of the reflector element 114 along the other diagonal of the front surface 115. The 2.4 GHz antenna units 120 are substantially centrosymmetrical with respect to each other about the central area of the front surface 115 and the 5 GHz antenna units 110 are centrosymmetrical with respect to each other about the central area of the front surface 115, as illustrated in
In the illustrated embodiment the configuration of the 5 GHz band antenna units 110(1), 110(2) is substantially identical to that of 2.4 GHz band antenna units 120(1), 120(2), except that the dimensions of each antenna unit 120 are scaled-up compared to those of each antenna unit 110 in order to target the larger wavelength of the 2.4 GHz band as opposed to the shorter wavelength of the 5 GHz band. In this regard
The first and second antennas 310 and 320 provide independently configurable polarizations, with the four IFA elements 311 of the first antenna element 310 being configurable to emit or receive RF signals polarized with either omni-directional polarization or directional polarization, and the four monopole elements 314 of second antenna element 320 are also configurable to emit or receive RF signals polarized with either omni-directional polarization or directional polarization. Thus, both of the antennas 310, 320 of antenna unit 110, 120 can be configured into either omni-directional polarization or directional polarization modes independently of each other.
In the embodiment shown in
Accordingly, in the illustrated embodiment of
Configuring the two antennas 310, 320 of the antenna units 110, 120 to emit or receive RF signals with either omni-directional polarization or directional polarization is controlled by an antenna controller 140 (
The antenna units 110, 120 can take a number of different possible configurations. An example configuration for a horizontally oriented first antenna 310 that can be used in antenna units 110, 120 will now be described in greater detail with reference to
In examples, substrate 312 and support legs 313A and 313B are each formed from printed circuit boards (PCBs) that include a dielectric substrate that support one or more conductive regions. In at least some example embodiments, the PCBs may be 0.5 mm thick, although thicker and thinner substrates could be used. Conventional PCB materials such as those available under the Taconic™ or Arlon™ brands can be used. In some examples, the PCBs may be formed from a thin film substrate having a thickness thinner than around 600 μm in some examples, or thinner than around 500 μm, although thicker substrate structures are possible. Typical thin film substrate materials may be flexible printed circuit board materials such as polyimide foils, polyethylene naphthalate (PEN) foils, polyethylene foils, polyethylene terephthalate (PET) foils, and liquid crystal polymer (LCP) foils. Further substrate materials include polytetrafluoroethylene (PTFE) and other fluorinated polymers, such as perfluoroalkoxy (PFA) and fluorinated ethylene propylene (FEP), Cytop® (amorphous fluorocarbon polymer), and HyRelex materials available from Taconic. In some embodiments the substrates are a multi-dielectric layer substrate.
As shown in
In example embodiments, the tunable element 412 may selectively couple or decouple the IFA elements 311 by creating a virtual, RF open circuit or closed circuit, such as with the use of PIN diodes. Alternatively, in example embodiments, the tunable element 412 may selectively couple or decouple the IFA elements 311 by creating a physical open circuit or closed circuit, such as with the use of MEMS devices.
In example embodiments, the ground plane 406 is centrosymmetrical about and electrically isolated from the central RF port 401. In the illustrated embodiment, the ground plane 406 is rectangular and includes slots that extend inward on each of its four sides in order to reduce coupling between the IFA elements 311. Each side edge of the ground plane 406 runs parallel to the elongate resonating element of a respective IFA element 311.
The IFA elements 311 and the microstrip signal paths 414 may be formed from conductive material such as copper or a copper alloy, or alternatively, aluminum or an aluminum alloy, that have been printed onto the first surface 402 of the substrate 312. Additionally, the centrosymmetrically shaped ground plane 406 may be formed from conductive material such as copper or a copper alloy, or alternatively, aluminum or an aluminum alloy, that have been printed onto the second surface 404 of the substrate 312. In example embodiments, tunable elements 412 may include PIN diodes or Micro-Electro-Mechanical System (MEMS) devices.
In an example embodiment, the vertical support legs 313A and 313B have cooperating slots along the central axis A1 that allows them to connect to each other, and they also each include centrally located a downwardly opening void or slot 424 that allows the structure of the first antenna 312 to be placed over a central part of the structure of the second antenna 320. The ground planes, control lines 420 and RF signal path 422 on the substrate 400 of the support legs 313A, 313B are electrically isolated with respect to each other, and may be formed from conductive material such as copper or a copper alloy, or alternatively, aluminum or an aluminum alloy, that have been printed onto the substrate of the antenna support legs 313A, 313B.
Accordingly, in example embodiments, each of the four IFA elements 311 of the antenna 310 are connected to a common RF line (for example RFL(1)) through a respective tunable element 412. The four tunable elements 412 are in turn each individually connected to controller 140, such that each of the four IFA elements 311 of the antenna 310 can be selectively activated by coupling them to or decoupling them from the RF signal line, enabling the antenna 310 to be controlled to emit or receive RF signals using all of the IFA elements 311 together in an omnidirectional mode or selectively using the IFA elements 311 in a directional mode. In the illustrated example, controller 140 is used to control a connection between each IFA element 311 and the central RF port 401, exciting the IFA elements 311 to emit or receive signals with diverse polarization in either omni-directional polarization direction or directional polarization. As illustrated by the electric field polarization arrows 408, the four symmetrical IFA elements 311 facilitate electric field vectors that form a circle, cancelling the radiation in the direction normal to the ground plane of the reflector element 114 as well as increasing radiation at angles close to the ground plane of the reflector element 114. Such a configuration can be beneficial for increasing antenna radiation range.
Referring to
An example embodiment of second antenna 320 will now be described in greater detail with reference to
Conductive region 501 includes two identical portions that extend in opposite directions outward from central connector 506. Each portion forms one of the folded ¼ wavelength monopole antenna elements 314, with each antenna element 314 including: a first elongate RF signal line 512 that extends along surface 503 generally parallel to back edge 511 to a RF resonating section 514 that extends at a right angle from the first section 512 towards a top edge 516 of the substrate 504 to a connecting line section 518 that extends generally parallel to the front edge 516. The connecting line section 518 extends to a shorting line 520 that folds back to extend to the back edge 511 of the substrate 502A. In example embodiments, RF resonating section 514 has a height H2 of about ¼ of the operating wavelength λ1, and each U-shaped leg 320A has a width of about ½ of the operating wavelength λ1.
Leg 320B has a similar configuration to leg 320A, with the exception of the central regions of the legs that are respectively slotted to cooperate with each other so that the legs can bisect each other at a perpendicular angle along central axis A1. In this regard, as seen in
Antenna elements 314 and the other conductive portions on legs 320A, 320B may be formed from a conductive material such as copper or a copper alloy, or alternatively, aluminum or an aluminum alloy, that have been printed onto the substrate 502A, 502B.
Referring to
Accordingly, in example embodiments, the ground line 520 of each of the four folded monopole antenna elements 314 of the antenna 320 are connected to a common ground plane through a respective tunable element 530. The four tunable elements 530 are in turn each individually connected to controller 140, such that each of the four antenna elements 314 can be selectively activated by coupling them to or decoupling them from ground, enabling the antenna 314 to be controlled in an omni-directional mode or in a directional mode. In the illustrated example, controller 140 is used to control a connection between each antenna element 314 and ground, exciting the elements 314 to emit or receive signals with diverse polarization in either omni-directional polarization direction or directional polarization.
In example embodiments, the tunable element 530 may selectively couple or decouple the antenna elements 314 by creating a virtual, RF open circuit or closed circuit, such as with the use of PIN diodes. Alternatively, in example embodiments, the tunable element 530 may selectively couple or decouple the antenna elements 314 by creating a physical open circuit or closed circuit, such as with the use of MEMS devices.
As shown in
In example embodiments the antenna elements 314 of antenna unit 310, 320 are vertically oriented at a right angle relative to reflector element 114, with the pair of antenna elements 310 on leg 320A and the antenna elements on leg 320B being perpendicular planes relative to each other. The IFA elements 311 extend in a horizontal plane parallel to reflector element 114.
In the embodiment described above, the antenna array 100 can support up to 8 RF streams or channels using the four antenna units 110(1), 110(2), 120(1), 120(2), with 4 of the streams operating in a first frequency band and 4 of the streams operating in a second frequency band. Furthermore, by controlling the tunable elements that are attached to each of antenna elements 311, 314, the polarization of each RF stream can be controlled, providing independently selectable directive patterns for each RF stream and each operating frequency. In addition, configurations of the antenna array not only reduce gain at boresight but also increase high performance with high gain near horizontal plane for each stream.
In the examples described above, the selective excitability of the antenna elements is provided in first antenna 310 by the use of tunable elements that operatively connect the RF signal lines of IFA elements 311 to RF signal port, whereas in second antenna 320, the selective excitability is provided by the use of tunable elements that operatively connect the shorting lines of the folded monopole antenna elements 314 to ground. In alternative example embodiments, the location of the tunable elements in antennas 310, 320 can be changed—for example the tunable elements could be moved to the IFA element shorting line from the RF signal line in the case of first antenna 310, and from the shorting line to the RF signal line in the case of second antenna 320.
In example embodiments, the number of antenna elements used in each of the first and second antennas 310, 320 could be more then or less than four controllable antenna elements. For example, in an alternative embodiment, second antenna 320 could be formed from three folded monopole elements 314 spaced at 120 degree intervals about central axis A1. Similarly, first antenna 310 could also include only three IFA elements 311, and in this regard
As illustrated in
In the embodiments described above, each antenna unit 110, 120 has included two co-located antennas 310, 320 that both operate in the same band (for example 5 GHz for antenna unit 110 and 2.4 GHz for antenna unit 120), with the IFA elements 311 in antenna 310 being oriented in an orthogonal plane relative to the folded monopole antenna elements 314 in antenna 320. However, in alternative example embodiments the co-located antennas in each antenna unit may be configured to operate in different bands or have antenna elements that are oriented in parallel planes, or both. In this regard,
As best seen in
In the example of
In the example shown in
In example embodiments, antenna units 700 can be used to replace some or all of the antenna units 110, 120 in antenna array 100, or be added as additional antenna units in antenna array 100. In at least some configurations, embodiments of the antenna array 100 can advantageously accomplish one of more of the following: increase the capacity of a MIMO antennal; efficiently use available real estate and space; reduce the size of an antenna required; reduce gain at boresight; and detect a wide range of RF signals.
For each antenna elements of the antenna units, omni-directional radiation polarizations as well as directional radiation polarization are independently configurable on any stream. Embodiments of the invention may be applied to radar system such as automotive radar or telecommunication applications such as transceiver applications in base stations or user equipment (e.g., hand held devices) or access point (AP). In one example embodiment, antenna array 100 is incorporated into a low profile wireless local area network (WLAN) access point (AP). The dimensions described in this application for the various elements of the antenna array 100 are non-exhaustive examples and many different dimensions can be applied depending on both the intended operating frequency bands and physical packaging constraints.
While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.
