Patent Application
20160064830
Embodiments of the disclosure relate to the field of communications, and in particular, to a wireless network device adapted with a low profile antenna configuration for improved performance.
Over the last decade or so, electronic devices responsible for establishing and maintaining wireless connectivity within a wireless network have increased in complexity. For instance, wireless electronic devices now support greater processing speeds and greater data rates. As a by-product of this increased complexity, radio communications techniques have evolved with the emergence of multiple-input and multiple-output (MIMO) architectures.
In general, MIMO involves the use of multiple antennas operating as transmitters and/or receivers to improve communication performance. Herein, multiple radio channels are used to carry data within radio signals transmitted and/or received via multiple antennas. In comparison with other conventional architectures, MIMO architectures offer significant increases in data throughput and link reliability. MIMO architectures may utilize a “smart” antenna concept requiring multiple sets of antennas, especially for wireless network products such as an Access Point (AP). The use of smart antennas may improve the reliability and performance of MIMO communication, which may be accomplished with polarization diversity (e.g., horizontal v. vertical) and/or the spatial diversity (e.g., physical location of the antennas within the AP or beam-forming/beam-switching antennas).
However, one disadvantage of MIMO is that multiple antennas traditionally required more space within the AP, which poses some difficulties as it is preferred for indoor APs to have low visual impact as these devices are generally placed in conspicuous places such as mounted to the ceiling. When design constraints limit the area of the AP, low profile antennas may be used to satisfy one or more design constraints. Low profile antennas are placed within close proximity to a ground plane. When an antenna with a horizontally polarized component and a ground plane operate in parallel and within close proximity to each other, the ground plane effectively short circuits the electric field generated by the antenna. This lowers the feedpoint impedance of the antenna, which reduces the efficiency and bandwidth of the antenna. The ground plane also creates an opposing magnetic field that interacts with the magnetic field of the antenna. Therefore, the impact of utilizing a low profile antenna is that the proximity of the ground plane reduces the useful voltage standing wave ratio (VSWR) bandwidth and lowers the efficiency of the antenna.
It would be advantageous if the impact of the proximity of the ground plane to the low profile antenna was negated and therefore did not impact the antenna's bandwidth.
The disclosure may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the disclosure.
Embodiments of the disclosure relate to a wireless network device configured with a plurality of low profile antennas, wherein at least one horizontally or elliptically polarized antenna is electromagnetically coupled to a parasitic element.
According to one embodiment of the disclosure, the antenna array assembly comprises an antenna array and a substrate (e.g., a ground plane) onto which the antenna array is placed. The “substrate” of the antenna array assembly may comprise a thin layer of conductive material, for example, but not limited or restricted to, copper, silver and/or aluminum. Alternatively, the substrate may comprise a printed circuit board that includes multiple layers of different materials. The “antenna array” may be a collection of low profile antennas including Alford loop antennas, semi- or full-loop antennas and/or monopole antennas. Throughout the application, unless otherwise stated, the term “Alford loop antenna” should be interpreted as a low profile Alford loop antenna or any low profile antenna operating in a manner similar to an Alford loop antenna. In communication with the wireless logic (e.g., processing circuitry), these low profile antennas allow the AP to achieve a thin, inconspicuous form factor.
In one embodiment, the antenna array assembly may be encapsulated within an Access Point (AP), wherein design requirements placed on the AP may impose certain size constraints on the antenna array assembly. For example, design constraints may require that the height of any antenna included in the antenna array be a maximum height of 12 millimeters (mm) as measured from the ground plane. In a second embodiment, any antenna included in the antenna array may be limited to a maximum height of 10 mm as measured from the ground plane.
In addition, at least one antenna of the antenna array may be horizontally or elliptically polarized and electromagnetically coupled to a parasitic element. The electromagnetic coupling of the parasitic element and the horizontally polarized antenna may act to negate the impact of the close proximity of the ground plane to the Alford loop antenna and allow the Alford loop antenna to operate at full bandwidth.
In the following description, certain terminology is used to describe features of the disclosure. For example, the term “logic” is generally defined as hardware and/or software. As hardware, logic may include circuitry such as processing circuitry (e.g., a microprocessor, a programmable gate array, a controller, an application specific integrated circuit, controller, etc.), wireless receiver, transmitter and/or transceiver circuitry, semiconductor memory, decryption circuitry, and/or encryption circuitry.
A “wireless network device” generally represents an electronic unit that supports wireless communications such as an Access Point (AP), a bridge, a data transfer device (e.g., wireless network switch, wireless router, router, etc.), or the like.
An “interconnect” is generally defined as a communication pathway established over an information-carrying medium. This information-carrying medium may be a physical medium (e.g., electrical wire, optical fiber, cable, bus traces, etc.), a wireless medium (e.g., air in combination with wireless signaling technology), or a combination thereof.
The term “parasitic element” should be defined as a conductive element of an antenna, such as a strip of metal that is not electrically connected to any other portion of the antenna but located in close proximity to one or more dipoles of the antenna. The lack of a physical connection may result in a coupling, e.g., electromagnetic coupling, between the two circuit elements. For example, a parasitic element may be a parasitic resonator located within close proximity to an antenna element wherein the parasitic resonator is electromagnetically coupled to the antenna element (e.g., the dipole of an antenna). Throughout the specification and claims, the terms “parasitic element” and “parasitic resonator” are used interchangeably.
The term “circular polarization” of an antenna may be defined as the polarization of an antenna having a radiofrequency (RF) signal that is split into two equal amplitude components that are in phase quadrature (at 90 degrees) and are spacially oriented perpendicular to each other and to the direction of propagation.
The term “elliptical polarization” of an antenna may be defined as the polarization of an antenna having a RF signal that has deviated from being circularly polarized. For example, an elliptically polarized antenna may transmit a RF signal having two components that are not equal in amplitude, are not in phase quadrature and/or are not spacially orthogonal.
The term “linear polarization” of an antenna may be defined as the polarization of an antenna having a RF signal wherein the phase difference of one component of the RF signal is equal to zero. The term “vertical polarization” of an antenna may be defined as a linearly polarized antenna having an electric field that is directed 90 degrees away from the earth's surface. In contrast, the term “horizontal polarization” of an antenna may be defined as a linearly polarized antenna having an electric field that is directed parallel to the earth's surface. A linearly polarized antenna may have an electric field that is directed at an angle other than 90 degrees away from the earth's surface (for example, 88 degrees away from the earth's surface).
Lastly, the terms “or” and “and/or” as used herein are to be interpreted as inclusive or meaning any one or any combination. Therefore, “X, Y or Z” or “X, Y and/or Z” mean “any of the following: X; Y; Z; X and Y; X and Z; Y and Z; X, Y and Z.” An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.
Certain details are set forth below in order to provide a thorough understanding of various embodiments of the disclosure, albeit the invention may be practiced through many embodiments other that those illustrated. Well-known logic and operations are not set forth in detail in order to avoid unnecessarily obscuring this description.
Referring to
As shown in this embodiment, AP 110 comprises logic, implemented within a cover 120, that controls wireless communications with other wireless network devices 1301-130r (where r≧1, r=3 for this embodiment) and/or wired communications over interconnect 140. Although not shown, interconnect 140 further provides connectivity for network resources such as servers for data storage, web servers, or the like. These network resources are available to network users via wireless network devices 1301-130r of
More specifically, for this embodiment of the disclosure, each AP 110-112 supports bi-directional communications by receiving wireless messages from STAs 1301-130r within its coverage area. For instance, as shown as an illustrative embodiment of a network configuration, wireless network devices 1301 may be associated with AP 110 and communicates over the air in accordance with a selected wireless communications protocol. Hence, AP 110 may be adapted to operate as a transparent bridge connecting together a wireless and wired network.
Of course, in lieu of providing wireless transceiver functionality, it is contemplated that AP 110 may only support unidirectional transmissions thereby featuring only receive (RX) or transmit (TX) functionality.
The antenna array assembly 150 is shown to include a plurality of antennas, illustrated as dashed rectangular objects. The configuration of the antennas on the antenna array assembly 150 comprises one embodiment of locations in which each antenna of the plurality of antennas may be placed.
Referring now to
In one embodiment, both the base section 230 and the cover section 240 may be made of a heat-radiating material in order to dissipate heat by convection. For example, this heat-radiating material may include aluminum or any other metal, combination of metals or a composite that conducts heat.
Referring to
In one embodiment, the semi-loop antennas 3101-3104 may be vertically or elliptically polarized, the monopole antennas 3201-3204 may be vertically or elliptically polarized and the Alford loop antennas 3401-3404 may be horizontally or elliptically polarized. The determination of the number of horizontally and/or elliptically polarized antennas included in the antenna array 305 compared to the number of vertically or elliptically polarized antennas may be made based on several factors, including the size of the antennas. In one embodiment, as seen in
Each semi-loop antenna 3101-3104 includes a top surface 3121-3124, a first leg 3141-3144, a base member 3161-3164 and a second leg 3181-3184. The base member 3161 connects the semi-loop antenna 3101 to the ground plane 306 of the antenna array assembly 150. The first leg 3141 connects the top surface 3121 to the base member 3161. In the current embodiment, the length of the base member 3161 is smaller than that of the top surface 3121. The second leg 3181 is attached to the top surface 3121 but does not come in contact with the ground plane 306 of the antenna array assembly 150. The power cable 330 connects to the second leg 3181 to supply power to the semi-loop antenna 3101. For each semi-loop antenna 3101-3104, the power cables 330 are configured such no connection is established between the second legs 3181-3184 and the ground plane 306 through a physical medium.
Each monopole antenna 3201-3204 includes a vertical surface 3221-3224, a second leg 3241-3244 and a base member 3261-3264. The base member 3261 connects the monopole antenna 3201 to the ground plane 306 of the antenna array assembly 150. The second leg 3241 connects the vertical surface 3221 to the base member 3261. The second leg 3241 is positioned above the ground plane 306. In one embodiment, the second leg 3241 may be positioned one millimeter above the ground plane 306. The power cable 330 connects to the vertical surface 3221 to supply power to the monopole antenna 3201.
In the embodiment shown in
In one embodiment, the semi-loop antennas 3101-3104 may be vertically or elliptically polarized and configured to operate on the 2.4 GHz frequency band, the monopole antennas 3201-3204 may be vertically or elliptically polarized and configured to operate on the 5 GHz frequency band and the Alford loop antennas 3401-3404 with the parasitic elements may be horizontally or elliptically polarized and configured to operate on the 5 GHz frequency band. Alternative embodiments may comprise an assortment of combinations of the antennas having different polarizations and/or operating on different frequency bands (e.g., the semi-loop antennas 3101-3104 may be configured to operate on the 5 GHz frequency band).
Referring to
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As discussed above, the close proximity of a low profile antenna to the ground plane (e.g., a horizontally or elliptically polarized Alford loop antenna 500 having a maximum height of 12 mm as measured from the ground plane) acts to short circuit the dipoles 5101-5104 of the Alford loop antenna 500 by generating capacitance between the Alford loop antenna and the ground plane. The generated capacitance narrows the bandwidth of the Alford loop antenna 500 and also decreases its efficiency.
When parasitic elements 5301-5304 are placed in close proximity to the dipoles 5101-5104 of the Alford loop antenna 500 and are void of any direct power connections, the parasitic elements 5301-5304 will electromagnetically couple to the Alford loop antenna 500 (specifically, the dipoles 5101-5104 of the Alford loop antenna 500). The combination of the capacitance generated by the dipoles 5101-5104 of the Alford loop antennas and the changing current across the dipoles 5101-5104 results in the electromagnetic induction of the parasitic elements 5301-5304. When the parasitic elements 5301-5304 are electromagnetically coupled to the Alford loop antenna 500, the parasitic elements 5301-5304 pull the electric field generated by the dipoles 5101-5104 of the Alford loop antenna 500 away from the ground plane thereby allowing the antenna 500 to operate with normal bandwidth radiating in a radial manner away from the AP.
The electromagnetic coupling may also increase the aperture of the antenna 500 therefore increasing the antenna's bandwidth. In addition, the electromagnetic coupling may also provide the ability to tune the antennas off frequency in relation to the parasitic elements, which may also increase the bandwidth of the antenna 500. In one embodiment, tuning the Alford loop antennas off frequency in relation to the parasitic elements may produce a frequency wave having double the bandwidth as opposed to the embodiment in which the antennas and parasitic elements are in tune by keeping the first resonance low.
In addition to pulling the electric field of the Alford loop antenna 500 away from the ground plane, the parasitic elements 5301-5304 are also able to establish polarization diversity within the AP through the creation of elliptical or linear polarization. This is accomplished by (i) rotating the parasitic resonators out of the plane containing the driven elements (the dipoles of the antennas), (ii) spacing the parasitic resonators, and/or (iii) choosing an appropriate width for the parasitic resonators.
The principle embodied in the example illustrated in
Referring back to
The impedance presented at the feedpoint 540 from each feed line 5201A-5204A can be set by configuring one or more of several factors of each feed line 5201A-5204A including, but not limited or restricted to, the width of, the length of and/or the separation between the feed lines 5201A-5204A in the particular dielectric constant medium in which the feed line is located.
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Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as determined by the appended claims and their equivalents. The description is thus to be regarded as illustrative instead of limiting.
