Patent Application
20150091759
The present embodiments relate generally to antennas, and specifically to antennas that provide polarization diversity, radiation diversity, and spatial diversity.
Wireless communication devices, such as access points (APs) and/or mobile stations (STAs), may employ multiple-input and multiple-output (MIMO) technology to improve data throughput, to improve channel conditions, and/or to increase range. In general, MIMO may refer to the use of multiple antennas in a wireless device to achieve antenna diversity. Antenna diversity may allow the wireless device to transmit and/or receive signals from a set of multiple paths through the wireless channel, which in turn may reduce the impact of multipath interference and increase channel diversity, for example, to provide well-conditioned wireless channels.
Antenna diversity may be achieved by providing polarization diversity, pattern diversity, and/or spatial diversity. Polarization diversity may be achieved by using multiple antennas with different polarizations to transmit or receive radio frequency (RF) signals. For example, a horizontally polarized antenna may be used to transmit and receive horizontally polarized signals, and a vertically polarized antenna may be used to transmit and receive vertically polarized signals. It is noted that a horizontally polarized antenna may not harvest sufficient energy from vertically polarized signals to successfully receive the vertically polarized signals, and a vertically polarized antenna may not harvest sufficient energy from horizontally polarized signals to successfully receive the horizontally polarized signals.
Pattern diversity may be achieved by using multiple antennas, each having a unique radiation pattern and/or radiation direction, to transmit or receive RF signals. More specifically, to achieve omni-directional signal transmission and reception coverage, multiple antennas may be positioned in different directions so that their corresponding radiation patterns are oriented in different directions. For example, a horizontally positioned dipole antenna and a vertically positioned dipole antenna may be arranged in a “cross” configuration to provide an omni-directional radiation pattern. However, because the horizontally positioned dipole antenna has a figure-8 radiation pattern in the azimuth plane, cross-dipole antennas may not provide omni-directional signal coverage in the azimuth plane for horizontally polarized signals. As a result, cross dipole antennas may not be suitable for use in WLAN applications (e.g., in access points and mobile stations) for which omni-directional signal coverage in the azimuth plane is desired for different polarization angles. Similarly, because the vertically positioned dipole antenna has a figure-8 radiation pattern in the vertical plane, cross-dipole antennas may not provide omni-directional signal coverage in the vertical plane vertically polarized signals.
Spatial diversity may be achieved by spacing the multiple antennas apart from one another. Due to the small size and form factor of many wireless devices (e.g., APs and STAs), spatial diversity may be difficult to achieve in such wireless devices.
Thus, there is a need for a compact antenna structure that provides omni-directional coverage in the azimuth plane for signals of various (e.g., horizontal and vertical) polarizations.
This Summary is provided to introduce in a simplified form a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.
An antenna structure is disclosed that provides polarization diversity at all angles on the horizon (e.g., in the azimuth plane of the Earth) while occupying less space than conventional antenna structures having orthogonally positioned antennas (e.g., cross dipole antennas). For some embodiments, the antenna structure includes a first antenna, a second antenna, a first parasitic element, and a second parasitic element. The first and second parasitic elements may be formed on opposite sides of a surface of a substrate. The first antenna, which is mounted on the first parasitic element and extends from the substrate in a vertical direction, may provide an omni-directional radiation pattern in the azimuth plane for vertically polarized signals. The second antenna, which is formed on the substrate and positioned between the first and second parasitic elements (e.g., such that the second antenna, the first parasitic element, and the second parasitic element are co-planar with respect to the substrate), may provide an omni-directional radiation pattern in the azimuth plane for horizontally polarized signals. Accordingly, the antenna structure may provide an omni-directional radiation pattern, in the azimuth plane, that includes both horizontal polarization and vertical polarization at all angles of incidence on the horizon.
For some embodiments, the first parasitic element may serve as a ground plane of the first antenna, and both the first and second parasitic elements may be magnetically coupled to the second antenna while being electrically isolated from the second antenna. For at least some embodiments, the first and second parasitic elements may absorb and re-radiate electromagnetic waves emanated from the second antenna, for example, in a manner that may operate to fill nulls in the radiation pattern of the second antenna that lie alongside the first and second parasitic elements.
The second antenna may include first and second radiating elements formed on opposite surfaces of the substrate. For at least some embodiments, the first radiating element may include a first pair of substantially L-shaped radiating bodies electrically coupled to each other at a first terminal of the second antenna, and the second radiating element may include a second pair of substantially L-shaped radiating bodies electrically coupled to each other at a second terminal of the second antenna. For at least one embodiment, the first and second radiating bodies may be positioned such that ends of the first pair of substantially L-shaped radiating bodies do not overlap ends of the second pair of substantially L-shaped radiating bodies.
As described in more detail below, wireless devices such as APs and STAs that employ antenna structures of the present embodiments may transmit/receive both vertically polarized signals and horizontally polarized signals to/from any angle on the horizon using less antenna space than conventional antenna structures that include orthogonally positioned antenna elements.
The present embodiments are illustrated by way of example and are not intended to be limited by the figures of the accompanying drawings, where:
Like reference numerals refer to corresponding parts throughout the drawings.
The present embodiments are discussed below in the context of antenna structures for WLAN devices for simplicity only. It is to be understood that the present embodiments are equally applicable to other wireless communication technologies and/or standards. In the following description, numerous specific details are set forth such as examples of specific components, circuits, and processes to provide a thorough understanding of the present disclosure. The term “coupled” as used herein means connected directly to or connected through one or more intervening components or circuits. Also, in the following description and for purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present embodiments. However, it will be apparent to one skilled in the art that these specific details may not be required to practice the present embodiments. In other instances, well-known circuits and devices are shown in block diagram form to avoid obscuring the present disclosure. The present embodiments are not to be construed as limited to specific examples described herein but rather to include within their scopes all embodiments defined by the appended claims.
The terms “horizontal plane” and “azimuth plane,” as used herein, are interchangeable and refer to the two-dimensional plane parallel to the surface of the Earth (e.g., as defined by an x-axis and a y-axis). The term “vertical plane,” as used herein, refers to a two-dimensional plane perpendicular to the horizontal plane (e.g., symmetrical about a z-axis).
The term “radiation pattern,” as used herein, refers to a geometric representation of the relative electric field strength as emitted by a transmitting antenna at different spatial locations. For example, a radiation pattern may be represented pictorially as one or more two-dimensional cross sections of the three-dimensional radiation pattern. Because of the principle of reciprocity, it is known that an antenna has the same radiation pattern when used as a receiving antenna as it does when used as a transmitting antenna. Therefore, the term radiation pattern is understood herein to also apply to a receiving antenna, where it represents the relative amount of electromagnetic coupling between the receiving antenna and an electric field at different spatial locations. Thus, the term “omni-directional radiation pattern in the azimuth plane,” as used herein, means a radiation pattern that covers all angles of incidence on the horizon.
The term “polarization,” as used herein, refers to a spatial orientation of the electric field produced by a transmitting antenna, or alternatively the spatial orientation of electrical and magnetic fields causing substantially maximal resonance of a receiving antenna. For example, in the absence of reflective surfaces, a dipole antenna radiates an electric field that is oriented parallel to the radiating bodies of the antenna. The term “horizontally polarized,” as used herein, refers to electromagnetic waves (e.g., RF signals) associated with an electric field (E-field) that oscillates in the horizontal direction (e.g., side-to-side in the horizontal plane), and the term “vertically polarized,” as used herein, refers to electromagnetic waves (e.g., RF signals) associated with an E-field that oscillates in the vertical direction (e.g., up and down in the vertical plane).
Thus, although the vertically polarized antenna 111 and the horizontally polarized antenna 121 may be arranged together in a cross-configuration, the resulting cross dipole antenna structure may not be able to transmit/receive horizontally polarized signals to/from all angles on the horizon (although it may be able to transmit/receive vertically polarized signals to/from all angles on the horizon).
Further, when multiple antennas having different polarizations are collocated on the same device, undesirable coupling between the multiple antennas may cause the multiple antennas to interfere with each other. For example, if antenna 111 of
The first antenna 210, which may operate as a monopole antenna, is mounted over the first parasitic element 211. The first antenna 210 extends outwardly from the substrate 205 in the vertical direction (e.g., along the z-axis), and is perpendicular to the first parasitic element 211 (and thus perpendicular to the substrate 205). The first parasitic element 211 is formed on a surface of substrate 205 using a conductive material. For at least some embodiments, the first parasitic element 211 may act as a ground plane and/or as a reflecting surface for the first antenna 210 (e.g., in a manner that causes the radiation pattern of the first antenna 210 to resemble the radiation pattern of a dipole antenna). For such embodiments, the first feed point FP1 may include a positive terminal to provide signal connections to first antenna 210, and may include a negative terminal to provide ground connections to the first parasitic element 211. In this manner, the first antenna 210 and the first parasitic element 211 may operate together, for example, in a manner similar to a dipole antenna.
The first antenna 210 is vertically polarized, and may primarily radiate and/or absorb vertically polarized components of electromagnetic waves. The radiation pattern of the first antenna 210 is a toroid that is symmetrical about the z-axis and is omni-directional in the azimuth plane (e.g., as defined by the x-axis and the y-axis). Thus, the first antenna 210 provides omni-directional coverage on the horizon for vertically polarized signals.
The second antenna 220, which may exhibit at least some of the radiating characteristics of a cross-dipole antenna, includes a first radiating element 221 and a second radiating element 222. As shown in
For the exemplary embodiment shown in
For some embodiments, the first end portions 221A and 222A of corresponding radiating elements 221 and 222 extend in opposite directions (e.g., such that first end portions 221A and 222A do not overlap each other), and the second end portions 221B and 222B of corresponding radiating elements 221 and 222 extend in opposite directions (e.g., such that second end portions 221B and 222B do not overlap each other). Note that the main portions 221C and 222C of radiating elements 221 and 222 overlie each other. Further, for some embodiments, the end portions 221A-221B of first radiating element 221 and the end portions 222A-222B of second radiating element 222 may be of a “flared” shape (e.g., as depicted in
The second antenna 220 is horizontally polarized, and thus may primarily radiate and/or absorb horizontally polarized components of electromagnetic waves. The radiation pattern of the second antenna 220 is symmetrical about the z-axis and is omni-directional in the azimuth plane (e.g., as defined by the x-axis and the y-axis). Thus, the second antenna 220 provides omni-directional coverage on the horizon for horizontally polarized signals.
The second parasitic element 231, which may be similar in size and shape to the first parasitic element 211, is formed on a surface of substrate 205 using a conductive material. For some embodiments, the first parasitic element 211 and the second parasitic element 231 are oriented in parallel with each other, and in parallel with the main portions 221C and 222C of radiating elements 221 and 222 (e.g., as depicted in
The first antenna 210, the radiating elements 221-222 that form the second antenna 220, and the parasitic elements 211 and 231 may be formed using any suitable conductive material, and may be formed on substrate 205 using any suitable fabrication technique. For some embodiments, the first radiating element 221 may be a microstrip conductor printed onto or otherwise attached to the top surface 205T of substrate 205, and the second radiating element 222 may be a microstrip conductor printed onto or otherwise attached to the bottom surface 205B of substrate 205. Further, for some embodiments, the first parasitic element 211 may be a microstrip conductor printed onto or otherwise attached to the bottom surface 205B of substrate 205, and the second parasitic element 231 may be a microstrip conductor printed onto or otherwise attached to the bottom surface 205B of substrate 205. For other embodiments, the first and second parasitic elements 211 and 231 may be formed on the top surface 205T of substrate 205.
In accordance with the present embodiments, the first parasitic element 211 may operate not only as a ground plane for first antenna 210 but also to re-radiate electromagnetic waves radiated from the second antenna 220. In this manner, the first parasitic element 211 may form a portion of both the first antenna 210 and the second antenna 220. The ability to use the first parasitic element 211 as a portion of both the first antenna 210 and the second antenna 220 may reduce the area consumed by the antenna structure 200. In addition, by mounting the first antenna 210 over the first parasitic element 211 and positioning the first antenna 210 adjacent to the horizontally oriented second antenna 220, the cross-sectional area of antenna structure 200 is, at least in the azimuth plane, similar to the cross-sectional area of the second antenna 220. In this manner, the addition of the first antenna 210 to the second antenna 220 may allow for dual polarizations in the azimuth plane with minimal increase in cross-sectional area (e.g., as compared with only the second antenna 220).
The dimensions of the first antenna 210, the dimensions of the second antenna 220, and/or the dimensions of the parasitic elements 211 and 231 may be of any suitable values, and may be sized (e.g., with respect to an absolute scale and/or with respect to each other) to provide one or more desired antenna operating characteristics (e.g., operating frequencies, frequency responses, frequency bandwidths, antenna impedance, antenna gains, etc.). For some embodiments, a length of the first antenna 210 may be approximately equal to one-fourth of the wavelength of a desired operating frequency of the antenna structure 200, and a length of the radiating elements 221-222 of the second antenna 220 may be approximately equal to one-half of the wavelength of the desired operating frequency of the antenna structure 200.
As mentioned above, embodiments of the antenna structure 200 may provide omni-directional coverage in the azimuth plane for both horizontally polarized signals and vertically polarized signals. In this manner, the antenna structure 200 may be able to transmit/receive both vertically polarized signals and horizontally polarized signals to/from any direction in the azimuth plane without reduction in gain. Further, the relative position, orientation, size, and/or shapes of the conductors that form the first antenna 210, the first parasitic element 211, the first radiating element 221, the second radiating element 222, and the second parasitic element 231 may isolate the first and second antennas 210 and 220 from each other. In this manner, the first antenna 210 and the second antenna 220 may dominantly radiate or receive vertically and horizontally polarized signals, respectively. More specifically, by minimizing the cross polarization levels of the first antenna 210 and the second antenna 220, any relatively small horizontally polarized signals undesirably radiated from the first antenna 210 may minimally interfere with the second antenna 220's radiation of horizontally polarized signals, and any relatively small vertically polarized signals undesirably radiated from the second antenna 220 may minimally interfere with the first antenna 210's radiation of vertically polarized signals.
For example,
The radiation pattern 320 of the second antenna 220, which is horizontally polarized and is co-planar with the azimuth plane (e.g., as defined by the x-axis and the y-axis), includes a desired co-polar radiation pattern 321 and an undesirable cross-polar radiation pattern 322. The desired co-polar radiation pattern 321 is a toroid that provides omni-directional coverage in the azimuth plane for horizontally polarized signals (E). The undesired cross-polar radiation pattern 322 is a lobe at approximately 30 degrees. The isolation between the desired co-polar radiation pattern 321 and the undesirable cross-polar radiation pattern 322 may be on the order of approximately 18 dB, thereby allowing the horizontally polarized second antenna 220 to receive horizontally polarized signals with minimal interference from any inadvertently received vertically polarized signals.
By providing approximately 13-14 dB of isolation between the co-planar pattern 311 and the cross-planar pattern 312 of first antenna 210 and providing approximately 18 dB of isolation between the co-planar pattern 321 and the cross-planar pattern 322 of second antenna 220, the antenna structure 200 of
As described above with respect to
The radiation pattern 420 of the second antenna 220, which is horizontally polarized and is co-planar with the azimuth plane (e.g., as defined by the x-axis and the y-axis), includes a desired co-polar radiation pattern 421 and an undesirable cross-polar radiation pattern 422. The desired co-polar radiation pattern 421 is a toroid that provides omni-directional coverage in the azimuth plane for horizontally polarized signals (E). The undesired cross-polar radiation pattern 422 may be described as a figure-8 pattern having maximum gains at approximately 120 degrees and 300 degrees, and having nulls at approximately 30 degrees and 210 degrees. The isolation between the desired co-polar radiation pattern 421 and the undesirable cross-polar radiation pattern 422 may be on the order of approximately 18 dB, thereby allowing the horizontally polarized second antenna 220 to receive horizontally polarized signals with minimal interference from any inadvertently received vertically polarized signals.
As described above with respect to
The radiation pattern 520 of the second antenna 220, which is horizontally polarized and is co-planar with the azimuth plane (e.g., as defined by the x-axis and the y-axis), includes a desired co-polar radiation pattern 521 and an undesirable cross-polar radiation pattern 522. The desired co-polar radiation pattern 521 is a toroid that provides omni-directional coverage in the azimuth plane for horizontally polarized signals (E). The undesired cross-polar radiation pattern 522 may be described as a cardioid having maximum gains at approximately 120 degrees and 300 degrees, and having a null at approximately 45 degrees. The isolation between the desired co-polar radiation pattern 521 and the undesirable cross-polar radiation pattern 522 may be on the order of approximately 18 dB, thereby allowing the horizontally polarized second antenna 220 to receive horizontally polarized signals with minimal interference from any inadvertently received vertically polarized signals.
As described above with respect to
As mentioned above, the antenna structure 200 of the present embodiments may be provided within wireless devices, for example, to provide MIMO functionality and/or to provide polarization diversity in all directions on the horizon. The wireless devices that employ antenna structure 200 of the present embodiments may include wireless access points, wireless stations, and/or other wireless communication devices. For example,
The stations STA1-STA3 may be any suitable Wi-Fi enabled wireless devices including, for example, network-enabled sensors, memory tags (RFID tags), smart meters, cell phones, personal digital assistants (PDAs), tablet devices, laptop computers, or the like. For at least some embodiments, stations STA1-STA3 may include a transceiver circuit, one or more processing resources, one or more memory resources, and a power source (e.g., battery). The memory resources may include a non-transitory computer-readable medium (e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, etc.) that stores instructions for performing a variety of different operations.
The AP may be any suitable device that allows one or more wireless devices to connect to a network (e.g., a LAN, WAN, MAN, and/or the Internet) via the AP using Wi-Fi, Bluetooth, or any other suitable wireless communication standards. For at least one embodiment, the AP may include a transceiver circuit, one or more processing resources (e.g., a baseband processor), and one or more memory sources. The memory resources may include a non-transitory computer-readable medium (e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, etc.) that stores instructions for performing a variety of different operations.
For some embodiments, the transceiver 710 may select (e.g., via a switch and other circuitry) either the first antenna 210 or the second antenna 220 of the corresponding antenna structure ANT1 or ANT2 for transmission or reception of RF signals. For other embodiments, the transceiver 710 may transmit/receive the same signals to/from both the first antenna 210 and the second antenna 220 of the corresponding antenna structure 200 for transmission or reception of RF signals. Because the first antenna 210 and the second antenna 220 of each of antenna structures ANT1-ANT2 200 may provide vertical polarization and horizontal polarization, respectively, for all angles in the azimuth plane, full polarization diversity may be achieved for MIMO performance in the device 700.
The transceiver 710 may be used to communicate with other wireless communication devices or a WLAN server (not shown) associated with WLAN 610 of
Thereafter, the first antenna 210 may transmit signals associated with a vertically polarized electric field (806), and the second antenna 220 may transmit signals associated with a horizontally polarized electric field (808). As described above, the first antenna 210 may be characterized by a first radiation pattern that is omni-directional in an azimuth plane of the Earth, and the second antenna 220 may be characterized by a second radiation pattern that is omni-directional in the azimuth plane. For at least some embodiments, the first and second parasitic elements 211 and 231 may absorb and re-radiate energy (e.g., electromagnetic waves) radiated from the second antenna 220, for example, in a manner that may fill in nulls N1 and N2 in the radiation pattern of the second antenna 220 that lie alongside the first and second parasitic elements 211 and 231, for example, as described above with respect to
For example, some embodiments may include a method of operating a communication device including an antenna structure that includes a first antenna extending from a substrate in a vertical direction, a second antenna formed on the substrate, a first parasitic element formed on the substrate, and a second parasitic element formed on the substrate, the method comprising: radiating a vertically polarized electric field at all angles in an azimuth plane from the first antenna; radiating a horizontally polarized electric field at all angles in the azimuth plane from the second antenna; absorbing, into the first and second parasitic elements, electromagnetic waves radiated from the second antenna; and re-radiating the electromagnetic waves from the first and second parasitic elements. The method may further comprise: transmitting signals associated with the vertically polarized electric field from the first antenna; and transmitting signals associated with the horizontally polarized electric field from the second antenna. For at least one embodiment, the second antenna, the first parasitic element, and the second parasitic element are coplanar with the substrate. For at least one embodiment, the second antenna comprises a first radiating element formed on a top surface of the substrate; and a second radiating element formed on a bottom surface of the substrate. For at least one embodiment, the first radiating element comprises a first pair of substantially L-shaped radiating bodies electrically coupled to each other at a first terminal of the second antenna; and the second radiating element comprises a second pair of substantially L-shaped radiating bodies electrically coupled to each other at a second terminal of the second antenna.
In the foregoing specification, the present embodiments have been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader scope of the disclosure as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. For example, for other embodiments, parasitic elements 211 and/or 231 may be omitted, or additional parasitic elements may be added.
This application claims the benefit under 35 USC 119(e) of the co-pending and commonly owned U.S. Provisional Application No. 61/883,709 entitled “COLLOCATED OMNIDIRECTIONAL DUAL-POLARIZED ANTENNA” filed on Sep. 27, 2013, the entirety of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61883709 | Sep 2013 | US |
