PATENT DOCUMENT

Publication Number: US-8223077-B2
Application Number: US-40160109-A
Country: US
Kind Code: B2

Title: Multisector parallel plate antenna for electronic devices

Abstract:
Electronic device antennas with multiple parallel plate sectors are provided for handling multiple-input-multiple-output wireless communications. Each antenna sector in a multisector parallel plate antenna may have upper and lower parallel plates with curved outer edges and a straight inner edge. A vertical rear wall may be used to connect the upper and lower parallel plates in each antenna sector along the straight inner edge. Each antenna sector may have an antenna probe. The antenna probe may be formed from a monopole antenna loaded with a planar patch. The planar loading patch may be provided in the form of a conductive disk that is connected to the end of a conductive antenna feed member. The conductive member may be coupled to the center conductor of a transmission line that is used to convey radio-frequency signals between the antenna probe and radio-frequency transceiver circuitry. The antenna sectors may have interplate dielectric structures.

Claims:
1. A multisector parallel plate electronic device antenna, comprising:
 a plurality of parallel plate antenna sectors, each parallel plate antenna sector having a conductive upper plate, a conductive lower plate that is parallel to the upper plate, and a conductive rear wall structure that joins the upper and lower plates; 
 support posts that are connected between the upper and lower parallel plates in at least one of the parallel plate antenna sectors; and 
 interplate dielectric that surrounds the support posts, wherein the support posts comprise support posts in each of the parallel plate antenna sectors and wherein the support posts in each parallel plate antenna sector have a different pattern. 
 
     
     
       2. The multisector parallel plate electronic device antenna defined in  claim 1 , wherein each of the plurality of parallel plate antenna sectors comprises a respective antenna feed. 
     
     
       3. The multisector parallel plate electronic device antenna defined in  claim 2  wherein each of the antenna feeds comprises a monopole antenna probe. 
     
     
       4. The multisector parallel plate electronic device antenna defined in  claim 2  wherein each of the antenna feeds comprises a monopole antenna probe having a loading patch, wherein the loading patch of each monopole antenna probe is located between the upper and lower plates of a respective one of the parallel plate antenna sectors. 
     
     
       5. The multisector parallel plate electronic device antenna defined in  claim 4  wherein each loading patch comprises a loading disk. 
     
     
       6. The multisector parallel plate electronic device antenna defined in  claim 5  wherein the loading disk in each parallel plate antenna sectors comprises a planar surface that is parallel to the upper and lower plates in that parallel plate antenna sector. 
     
     
       7. The multisector parallel plate electronic device antenna defined in  claim 4  wherein the loading patch in the monopole antenna probe of each parallel plate antenna sectors comprises a planar surface that is parallel to the upper and lower plates in that parallel plate antenna sector. 
     
     
       8. The multisector parallel plate electronic device antenna defined in  claim 1  wherein the multisector parallel plate electronic device antenna comprises a dual sector antenna in which the plurality of parallel plate antenna sectors comprises first and second parallel plate antenna sectors whose respective conductive rear wall structures are parallel to each other and wherein the conductive upper and lower plates comprise curved outer edges. 
     
     
       9. The multisector parallel plate electronic device antenna defined in  claim 1  wherein the multisector parallel plate electronic device antenna comprises a four sector antenna in which the plurality of parallel plate antenna sectors comprises first, second, third, and fourth parallel plate antenna sectors and wherein the conductive upper and lower plates comprise curved outer edges. 
     
     
       10. The multisector parallel plate electronic device antenna defined in  claim 1  wherein the multisector parallel plate electronic device antenna comprises an eight sector antenna and wherein the conductive upper and lower plates comprise curved outer edges. 
     
     
       11. An electronic device, comprising:
 storage and processing circuitry that handles data signals for the electronic device; 
 wireless communications circuitry that transmits and receives the data signals, wherein the wireless communications circuitry comprises a multisector parallel plate antenna that has a plurality of parallel plate antenna sectors and wherein each parallel plate antenna sector has conductive first and second parallel plates; and 
 dielectric support posts between the first and second parallel plates of each of the parallel plate antenna sectors and wherein the dielectric support posts in each parallel plate antenna sector have a different pattern. 
 
     
     
       12. The electronic device defined in  claim 11  wherein the storage and processing circuitry and wireless communications circuitry are configured to implement a multiple-input-multiple-output communications protocol in which data signals are transmitted and received with the plurality of parallel plate antenna sectors. 
     
     
       13. The electronic device defined in  claim 12  wherein the first and second parallel plates in each parallel plate antenna sector comprise at least one straight edge and wherein each of the parallel plate antenna sectors comprises a planar conductive rear wall structure connected between the first and second parallel plates along the straight edge of that parallel plate antenna sector. 
     
     
       14. The electronic device defined in  claim 13  further comprising an antenna probe in each parallel plate antenna sector, wherein the antenna probe comprises a monopole with a planar loading patch, wherein the loading patch of each antenna probe is parallel to the first and second parallel plates of the parallel plate antenna sector containing that antenna probe. 
     
     
       15. The electronic device defined in  claim 12  further comprising:
 switching circuitry that is coupled to each of the parallel plate antenna sectors. 
 
     
     
       16. An electronic device, comprising:
 storage and processing circuitry that handles data signals for the electronic device; and 
 wireless communications circuitry that transmits and receives the data signals, wherein the wireless communications circuitry comprises a multisector parallel plate antenna, wherein the multisector parallel plate antenna comprises a plurality of parallel plate antenna sectors, and wherein each parallel plate antenna sector has:
 a conductive upper plate having a curved outer edge and at least one straight edge; 
 a conductive lower plate having a curved outer edge and at least one straight edge; 
 a conductive planer rear wall that joins the conductive upper plate to the conductive lower plate along the straight edges of the conductive upper and lower plates; and 
 dielectric posts that are coupled between the conductive upper plate and the conductive lower plate, wherein the dielectric posts in a first one of the parallel plate antenna sectors are disposed in a first pattern relative to the first one of the parallel plate antenna sectors, wherein the dielectric posts in a second one of the parallel plate antenna sectors are disposed in a second pattern relative to the second one of the parallel plate antenna sectors, and wherein the first and second patterns are different. 
 
 
     
     
       17. The electronic device defined in  claim 16  further comprising:
 transceiver circuitry in the wireless communications circuitry; and 
 an antenna probe in each parallel plate antenna sector, wherein each antenna probe has a conductive member that is coupled to a transmission line center conductor that is coupled to the transceiver circuitry, wherein the conductive member in each antenna probe has an end, and wherein each antenna probe has a planar loading disk connected to the end of the conductive member of that antenna probe. 
 
     
     
       18. A multisector parallel plate electronic device antenna, comprising:
 a plurality of parallel plate antenna sectors, each parallel plate antenna sector having a conductive upper plate, a conductive lower plate that is parallel to the upper plate, and a conductive rear wall structure that joins the upper and lower plates; 
 support posts that are connected between the upper and lower parallel plates in at least one of the parallel plate antenna sectors; and 
 interplate dielectric that surrounds the support posts, wherein the interpolate dielectric has a first dielectric constant and wherein at least one of the support posts has a second dielectric constant that is different from the first dielectric constant.

Description:
BACKGROUND 
     This invention relates to electronic devices and, more particularly, to antennas for electronic devices. 
     Portable computers and other electronic devices often use wireless communications circuitry. For example, wireless communications circuitry may be used to communicate with local area networks and remote base stations. 
     Wireless computer communications systems use antennas. It can be difficult to design antennas that perform satisfactorily in electronic devices. For example, it can be difficult to produce an antenna that performs well in noisy environments. 
     To enhance reliability and performance in a variety of wireless environments, some electronic devices use antenna diversity schemes. In some diversity schemes, an electronic device is provided with multiple redundant antennas each of which is located in a different portion of the device. These antennas may operate in similar radio-frequency bands and may be coupled to radio-frequency transceiver circuitry that monitors the quality of the signals that are received from the antennas in real time. If an antenna&#39;s performance drops below a given threshold, another antenna may be used for wireless communications activities. Antenna schemes of this type may offer superior performance to arrangements that rely solely on a single antenna. However, it is not always desirable to provide an electronic device with multiple antennas located in different portions of the device, as this adds wiring layout complexity and consumes valuable space within the device. 
     It would be desirable to be able to provide improved antenna arrangements suitable for enhancing wireless performance for an electronic device. 
     SUMMARY 
     Electronic device antennas are provided that have multiple antenna sectors for supporting wireless communications protocols such as multiple-input-multiple-output protocols. 
     An electronic device may have storage and processing circuitry. The storage and processing circuitry may handle data signals. Wireless communications circuitry may be coupled to the storage and processing circuitry and may be used in transmitting and receiving the antenna signals. The wireless communications circuitry may include radio-frequency transceiver circuitry and a multisector antenna. The storage and processing circuitry and the wireless communications circuitry may be configured to implement wireless communications protocols that make use of multiple antennas such as multiple-input-multiple-output communications protocols. During operation of the electronic device, a multiple-input-multiple-output protocol can use each of multiple individual antenna sectors in the multisector antenna to improve wireless performance. Wireless throughput, range, and reliability can be enhanced in this way. 
     Each antenna sector in the multisector antenna may have a pair of parallel plates. The outer edges of the parallel plates may be curved and the inner edges of the parallel plates may be straight. For example, in a dual-sector antenna, each of the parallel plates may have a curved outer edge and a straight inner edge that forms a half circle. In a four-sector antenna, each of the parallel plates may have the shape of a quarter of a disk. The plates may be placed close to each other, so that the gain pattern of the antenna spreads significantly in the vertical dimension (perpendicular to the plates). For example, in a dual sector arrangement, each of the two antenna sectors may be configured to exhibit a complementary hemispherical gain pattern. 
     Each antenna sector may have an antenna probe that serves as an antenna feed. The antenna probe may have a radio-frequency connector that is connected to a transmission line such as a coaxial cable that has a center conductor. The transmission line may be coupled between the antenna probe and radio-frequency transceiver circuitry. The antenna probe may have a conductive monopole antenna member that protrudes into the cavity formed by the parallel plates in the antenna sector. One end of the conductive member may be connected to the center conductor in the coaxial cable. The other end of the conductive member in the antenna probe may be connected to a loading patch. The loading patch may be formed from a conductive planar member such as a conductive disk. The plane of the loading patch may be oriented parallel to the upper and lower plates. 
     Each antenna sector may have interplate structures such as dielectric support posts. Different antenna sectors may have different corresponding patterns of posts, which helps to reduce symmetry between the antenna sectors and thereby improve performance in reflective environments. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device in which an antenna may be implemented in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative two sector antenna in accordance with an embodiment of the present invention. 
         FIG. 3  is a side view of one of the two antenna sectors in the antenna of  FIG. 2  in accordance with an embodiment of the present invention. 
         FIG. 4  is a graph of measured antenna efficiency as a function of operating frequency for a dual sector parallel plate antenna in accordance with an embodiment of the present invention. 
         FIG. 5  is a graph of measured antenna throughput as a function of operating range at an operating frequency of 2.45 GHz for a dual sector parallel plate antenna in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph of measured antenna throughput as a function of operating range at an operating frequency of 5.5 GHz for a dual sector parallel plate antenna in accordance with an embodiment of the present invention. 
         FIG. 7  is a perspective view of a parallel plate antenna structure with a relatively narrow plate separation in accordance with an embodiment of the present invention. 
         FIG. 8  is a perspective view of a parallel plate antenna structure with a relatively wide plate separation in accordance with an embodiment of the present invention. 
         FIG. 9  is a top view of a four-sector parallel plate antenna in accordance with an embodiment of the present invention. 
         FIG. 10  is a top view of an eight sector parallel plate antenna in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph showing how an antenna sector in the eight sector parallel plate antenna of the type shown in  FIG. 10  may exhibit a radiation pattern associated with a one-eighth section of a sphere in accordance with an embodiment of the present invention. 
         FIG. 12  is a top view of a two-sector parallel plate antenna showing gain as a function of direction and showing illustrative locations for plate support posts in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to antenna structures for electronic devices. Antennas may be used to convey wireless signals for suitable communications links. For example, an electronic device antenna may be used to handle communications for a short-range link such as an IEEE 802.11 link (sometimes referred to as WiFi®) or a Bluetooth® link. An electronic device antenna may also handle communications for long-range links such as cellular telephone voice and data links. 
     Antennas such as these may be used in various electronic devices. For example, an antenna may be used in an electronic device such as a handheld computer, a miniature or wearable device, a portable computer or other portable device, a desktop computer, a router, an access point, a backup storage device with wireless communications capabilities, a mobile telephone, a music player, a remote control, a global positioning system device, devices that combine the functions of one or more of these devices and other suitable devices, or any other electronic device. 
     A schematic circuit diagram of an illustrative electronic device  10  that may include one or more antennas is shown in  FIG. 1 . As shown in  FIG. 1 , device  10  may include storage and processing circuitry  12  and input-output circuitry  14 . Storage and processing circuitry  12  may include hard disk drives, solid state drives, optical drives, random-access memory, nonvolatile memory and other suitable storage. Storage may be implemented using separate integrated circuits and/or using memory blocks that are provided as part of processors or other integrated circuits. 
     Storage and processing circuitry  12  may include processing circuitry that is used to control the operation of device  10 . The processing circuitry may be based on one or more circuits such as a microprocessor, a microcontroller, a digital signal processor, an application-specific integrated circuit, and other suitable integrated circuits. Storage and processing circuitry  12  may be used to run software on device  10  such as operating system software, code for applications, or other suitable software. To support wireless operations, storage and processing circuitry  12  may include software for implementing wireless communications protocols such as wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, protocols for handling 3 G communications services (e.g., using wide band code division multiple access techniques), 2G cellular telephone communications protocols, WiMAX® communications protocols, communications protocols for other bands, etc. These protocols may include protocols such as multiple-input-multiple-output (MIMO) protocols that employ multiple antennas (multiple antenna sectors in a multisector antenna) to increase data throughput, wireless range, and link reliability. 
     Input-output devices  14  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  14  may include user input-output devices such as buttons, display screens, touch screens, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, cameras, etc. A user can control the operation of device  10  by supplying commands through the user input devices. This may allow the user to adjust device settings, etc. Input-output devices  14  may also include data ports, circuitry for interfacing with audio and video signal connectors, and other input-output circuitry. 
     As shown in  FIG. 1 , input-output devices  14  may include wireless communications circuitry  16 . Wireless communications circuitry  16  may include communications circuitry such as radio-frequency (RF) transceiver circuitry  18  formed from one or more integrated circuits such as a baseband processor integrated circuit and other radio-frequency transmitter and receiver circuits. Circuitry  18  may include power amplifier circuitry, transmission lines such as transmission line(s)  20 , passive RF components, antennas  22 , and other circuitry for handling RF wireless signals. 
     Electronic device  10  may include one or more antennas such as antenna  22 . The antenna structures in device  10  may be used to handle any suitable communications bands of interest. For example, antennas and wireless communications circuitry in device  10  may be used to handle cellular telephone communications in one or more frequency bands and data communications in one or more communications bands. Typical data communications bands that may be handled by wireless communications circuitry  16  include the 2.4 GHz band that is sometimes used for Wi-Fi® (IEEE 802.11) and Bluetooth® communications, the 5 GHz band that is sometimes used for Wi-Fi® communications, the 1575 MHz Global Positioning System band, and 2G and 3G cellular telephone bands. These bands may be covered using single-band and multiband antennas. For example, cellular telephone communications can be handled using a multiband cellular telephone antenna. A single band antenna may be provided to handle Bluetooth® communications. Device  10  may, as an example, include a multiband antenna that handles local area network data communications at 2.4 GHz and 5 GHz (e.g., for IEEE 802.11 communications), a single band antenna that handles 2.4 GHz IEEE 802.11 communications and/or 2.4 GHz Bluetooth® communications, or a single band or multiband antenna that handles other communications frequencies of interest. These are merely examples. Any suitable antenna structures may be used by device  10  to cover communications bands of interest. 
     It can be challenging to reliably implement high-throughput wireless links in an electronic device. Accordingly, device  10  may use a multisector antenna design for one or more of its antennas. Arrangements in which device  10  uses a single antenna  22  having multiple antenna sectors is sometimes described herein as an example. In general, however, device  10  may have one or more antennas  22  and one or more of the antennas may have multiple parts (i.e., multiple sectors). The use of a single multisector antenna  22  in device  10  is merely illustrative. 
     Each sector in multisector antenna  22  may exhibit a different wireless performance characteristic (e.g., a different directionality to its gain). This allows the antenna sectors to be used to implement MIMO protocols or other communications schemes that employ multiple antennas to enhance performance. When a wireless communications technique that exploits multiple antenna sectors is used, wireless performance can be enhanced (e.g., data capacity can be increased, wireless range can be increased, and/or immunity to dropped wireless links can be improved). 
     To implement wireless communications using a multisector antenna, radio-frequency transceiver circuitry  18  is provided with transceiver and switching circuitry that is coupled to each of the multiple sectors in multisector antenna  22 . Each antenna sector may have its own antenna feed with positive and ground antenna feed terminals and may therefore operate as a separate antenna. Coaxial cables or other transmission lines (path  20  of  FIG. 1 ) may be used to connect circuitry  18  to each of the feeds for the different antenna sectors. Circuitry  18  may include a circuit network that performs operations such as impedance matching, signal distribution, and signal switching for the antenna. Circuitry in device  10  such as circuitry  12  and  14  may also include radio circuits and general purpose processing circuitry that is configured to process the signals from multiple antenna sectors for implementing communications protocols such as MIMO protocols. The communications scheme that is used may comply with standard protocols. For example, device  10  may use multisector antenna  22  and circuitry  12  and  14  in implementing IEEE 802.11 protocols such as the IEEE 802.11n multiple-input multiple-output (MIMO) protocols. Circuitry  12  and  14  may therefore be configured to implement a multiple-input-multiple-output protocol that transmits and receives wireless data using the multiple sectors in multisector antenna  22 . 
     With one suitable multisector arrangement, which is sometimes described herein as an example, antennas such as antenna  22  are formed using parallel plate antenna designs. Each set of parallel plates may form a separate parallel plate antenna sector. These sectors may each have a corresponding antenna feed and may operate as individual antennas. When mounted together in a single antenna arrangement, each individual parallel plate antenna is sometimes referred to herein as forming an independent antenna sector for a multisector antenna. The antenna sectors preferably have substantially different operating characteristics. In particular, each sector preferably has a substantially different directionality to its gain pattern. If desired, some or all of the sectors may also be configured to exhibit different polarization characteristics (e.g., to implement a polarization diversity scheme). 
     Because the directionality of each antenna sector is different (i.e., each sector points in a different direction), the antenna sectors each pick up a different wireless signals and noise patterns. In accordance with the MIMO protocol implemented on device  10  (e.g., the IEEE 802.11n protocol), the signals from the antenna sectors can be processed together to support improved wireless link performance. 
     An illustrative parallel plate antenna  22  with two sectors (sectors  22 A and  22 B) is shown in  FIG. 2 . Antenna sector  22 A has an upper plate  24 A and a lower plate  26 A, and rear wall  28 A. Plates  24 A and  24 B and wall  28 A may be formed from conductive structures such as metal. Rear wall  28 A extends vertically parallel to vertical dimension  36 . As shown in  FIG. 2 , the parallel plates in each of the sectors of antenna  22  may have curved outer edges  21  and straight edges  23 . 
     Antenna sector  22 A may be fed using an antenna probe. The probe may be, for example, a top-loaded monopole probe. Other probe configurations may be used if desired. In operation, the probe excites radio-frequency signals in parallel plate antenna sector  22 A and thereby serves as an antenna feed for antenna sector  22 A. The probe may be coupled to a transmission line such as transmission line  20  ( FIG. 1 ) using feed path  30 A. Feed path  30 A may contain a transmission line path  32 A having a ground conductor coupled to ground (e.g., upper plate  24 A) and having a positive signal conductor coupled to a conductive disk or other planar loading structure associated with the monopole feed (not visible in the perspective view of  FIG. 2 ). The positive signal conductor may be, for example, a center conductor that passes through an opening in upper plate  24 A without electrically contacting upper plate  24 A. A connector such as coaxial cable connector  34 A may be used to facilitate electrical coupling of transmission line path  32 A to a coaxial cable or other transmission line such as transmission line  20  of  FIG. 1 . The transmission line that is connected to path  32 A by connector  34 A may, in turn, be connected to radio-frequency transceiver circuitry  18  ( FIG. 1 ). 
     Antenna sector  22 A may have a gain pattern that is directed in the general direction of arrows  38 . Antenna sector  22 B, in contrast, may operate primarily in directions  40 . The gain pattern of each sector may be substantially hemispherical in shape, thereby ensuring complete coverage in all possible signal transmission and reception directions. As shown in  FIG. 2 , antenna sector  22 B, like sector  22 A, may have two parallel plates (upper plate  24 B and lower plate  26 B), and rear wall  28 B. Feed path  30 B may include feed path transmission line portion  32 B and connector  34 B. 
     Upper plate  24 B in antenna sector  22 B may be separated from lower plate  26 B by a vertical distance D (sometimes referred to as the parallel plate height or thickness of antenna sector  22 B). Upper plate  24 A and lower plate  26 A of antenna sector  22 A may also be separated by a vertical distance (e.g., vertical distance D). Distance D may be, for example, a quarter of a wavelength at the operating frequency of interest. The rear walls  28 A and  28 B of antenna sectors  22 A and  22 B may be separated by a horizontal distance SD (as shown in  FIG. 2 ) or may be formed from a common conductive member. Curved plate edges  21  may be spaced at a radial distance R from feeds  30 A and  30 B. Radius R may be, for example, three quarters of a wavelength at the operating frequency of interest for antenna  22 . Feeds  30 A and  30 B may be spaced apart from their respective rear walls  28   a  and  28 B by a distance equal to about a quarter of a wavelength (as an example). The antenna feeds in antenna  20  may be tuned to resonate at a desired frequency of interest (e.g., 2.45 GHz). Resonance effects may allow antenna  22  to operate in multiple bands (e.g., at both 2.45 GHz and 5.5 GHz). 
     Interplate structures such as posts  42 ,  44 ,  46 , and  48  may be connected between the parallel plates in each sector and may used to provide structural support for the parallel plates in antenna  22 . Structures such as posts  42 ,  44 ,  46 , and  48  may be formed from materials such as low-loss dielectrics. When these structures are formed from dielectrics that have dielectric constants different from the air or other surrounding interplate dielectric (such as dielectric  41 , shown in  FIG. 3 ), the locations of the posts or other such structures within the gap between opposing plates tends to affect antenna performance. To break the symmetry of antenna  22  with respect to bisecting axis  50  and thereby improve diversity performance in environments in which antenna  22  is arranged with axis  50  parallel to a conductive plane that creates reflections, the positions of posts  42 ,  44 ,  46 , and  48  can be arranged to break the symmetry of antenna  22  with respect to axis  50 . For example, support posts  42  and  44  can be arranged in sector  22 A using a different pattern than is used in locating support posts  46  and  48  within antenna sector  22 B. 
       FIG. 3  is a cross-sectional side view of antenna sector  22 A. As shown in  FIG. 3 , antenna probe  56 A may have a conductive member such as member  52 A that forms a positive antenna feed line. The top end of path  52 A (i.e., the bottom of path  52 A in the orientation of  FIG. 3 ) may be loaded with a planar conductive patch such as conductive patch  54 A to improve the bandwidth of antenna sector  22 A. Patch  54 A may be a substantially planar conductive structure such as a sheet of metal and may be arranged so that patch  54 A is parallel to planer inner surface  58 A of lower plate  36 A and corresponding planer upper plate  24 A. Loading patch  54 A of probe  56 A may be coupled to the center connector in path  32 A via path  52 A (i.e., so that patch  54 A is coupled to the center conductor of the coaxial path connected to connector  34 A). The shape of patch  54 A may be circular, oval, square, etc. 
     A graph showing measured antenna efficiency for an antenna such as antenna  44  of  FIG. 2  as a function of operating frequency is shown in  FIG. 4 . As shown in  FIG. 4 , parallel plate antennas that are fed with top-loaded monopole probes such as antenna probe  56 A may exhibit a satisfactory frequency response over signal frequencies of interest for 2.4 GHz and 5 GHz IEEE 802.11 operations (as an example). The 5 GHz band may be covered by a resonance of the 2.4 GHz band. If desired, multisector parallel plate antennas such as antenna  22  of  FIG. 2  may be used in other frequency ranges. The use of a parallel plate antenna to cover the wireless local area network bands of 2.4 GHz and 5 GHz in the measurements of  FIG. 4  is merely illustrative. 
     Additional performance graphs for a parallel plate antenna such as antenna  22  of  FIG. 2  are shown in  FIGS. 5 and 6 . 
     In the graph of  FIG. 5 , measured antenna throughput is plotted versus operating range for several channels in the 2.4 GHz communications band. Average throughput in the 2.4 GHz band is also plotted. 
     In the graph of  FIG. 6 , antenna throughput is plotted versus operating range for several channels in the 5 GHz communications band. The graph of  FIG. 6  also includes a trace corresponding to average measured throughput in the 5 GHz band for various operating range values. 
     The plate separation in a parallel plate antenna can be adjusted to tailor the spatial distribution of the gain pattern for the antenna. The effect of adjustments to the magnitude of the plate separation in antenna sector  22 A are illustrated in  FIGS. 7 and 8 . In the example of  FIG. 7 , the plate-to-plate spacing between plates  24 A and  26 A is equal to a relatively small thickness D 1 . In the example of  FIG. 8 , in contrast, the plate-to-plate spacing is equal to a relatively large thickness D 2 . Because the spacing D 1  is small in the  FIG. 7  example, the radiation pattern for antenna  22 A of  FIG. 7  is relatively wide, as indicated schematically by the relatively large angle A that is associated with beam  60 . In the configuration of  FIG. 8 , separation D 2  is greater than separation D 1  of  FIG. 7 , so beam  60  is characterized by a narrower beam  60  (i.e., a beam having an angle B that is less than angle A of  FIG. 7 ). 
     If the plate separation in antenna sector  22 A is made small enough and if the plate separation in antenna sector  22 B is made small enough, the angle of beam  60  in each sector will be large (e.g., near 180°). In this situation, a dual-sector antenna that is formed from antenna sectors  22 A and  22 B will be able to collectively cover all possible directions of radiation. Sector  22 A will cover a first half of the possible directions (i.e., a first hemisphere) and sector  22 B will cover the second half of the possible directions (i.e., a second hemisphere that complements the first hemisphere without excessive overlap). 
     If desired, antenna  22  may have more than two antenna sectors. An illustrative parallel plate antenna  22  having four parallel plate antenna sectors  22 A,  22 B,  22 C, and  22 D is shown in  FIG. 9 . Each antenna sector in the arrangement of  FIG. 9  has a top plate, a bottom plate, and a vertical rear wall. Each rear wall is connected to the top and bottom plates along the straight rear edges of the plates and has a bend. For example, antenna sector  22 A has top plate  24 A, a corresponding bottom plate (not shown in  FIG. 9 ), and a rear wall  28 A having 90° bend  62 A. Similarly, antenna sector  22 B has top plate  24 B, a corresponding bottom plate, and rear wall  28 B with 90° bend  62 B, antenna sector  22 C has top plate  24 C, a corresponding bottom plate, and rear wall  28 C with 90° bend  62 C, and antenna sector  22 D has top plate  24 D, a corresponding bottom plate, and rear wall  28 D with 90° bend  62 D. Rear walls  62 A,  62 B,  62 C, and  62 D may, if desired, be formed from opposing sides of one or more shared vertical planar conductive members. Antenna feeds such as feeds  30 A,  30 B,  30 C, and  30 D (each corresponding to a separate antenna probe structure such as probe  56 A of  FIG. 3 ) may be used to couple transmission lines  20  ( FIG. 1 ) to each of the antenna sectors from radio-frequency transceiver circuitry  18 . In a four-sector antenna of the type shown in  FIG. 9 , each sector may have a gain pattern shape of a quarter of a sphere (i.e., a gain distribution covering 90° azimuthally around the Z axis and 180° elevationally). 
     Antenna  22  may also be formed using other numbers of sectors. For example, parallel plate antenna  22  may be formed from eight sectors, as shown in  FIG. 10 . In antenna  22  of  FIG. 10 , each sector such as sector  22 A may have a top plate such as plate  24 A, a corresponding lower plate, an angled planar vertical rear wall such as rear wall  28 A, and an antenna feed such as feed  30 A. There are eight sectors in antenna  22  of  FIG. 10 , each of which may have a radiation pattern of the general shape shown by pattern  64 A of  FIG. 11  (i.e., one eighth of a sphere). When viewed from the Z direction, each of the eight sectors in the eight-sector antenna of  FIG. 10  will have an associated gain pattern that is directed outward over approximately one eighth of a 360° circle (i.e., over 45° azimuthally). As shown in  FIG. 11 , this one-eighth of a sphere gain pattern may cover 180° in elevation (i.e., completely from the +Z axis to the −Z axis). 
     A four-sector antenna will have a gain pattern where each antenna sector covers 90° in the X-Y plane. When viewed along the Z-axis, each antenna sector in a dual-sector parallel plate antenna may have a radiation gain pattern such as the gain pattern illustrated by dashed line  66  of  FIG. 12  that covers approximately 180° in the X-Y plane (i.e., 180° azimuthally) and that covers 180° elevationally. Antennas with other numbers of parallel plate sectors will have correspondingly proportioned radiation patterns. 
     In some situations, antenna  22  may operate near a conductive surface. The conductive surface can give rise to reflections that serve as a source of interference and reduce the amount of independence that is being sought by using individual antenna sectors. An illustrative system environment that contains a conductive planar surface is shown in  FIG. 12 . As illustrated in  FIG. 12 , system  502  may have an antenna  22  that operates in the vicinity of conductive object  500 . Conductor  500  may have a substantially planar face  503  that is perpendicular to the page in the orientation of  FIG. 12 . 
     Due to reflections from surface  503 , antenna sectors  22 A and  22 B may tend to receive identical signals along paths  505 . To reduce the amount of symmetry exhibited by sectors  22 A and  22 B with respect to bisecting axis  50  and thereby enhance the difference between sectors  22 A and  22 B in the way in which they respond to the reflected signals along paths  505 , sectors  22 A and  22 B may be provided with symmetry-disrupting structures such as support posts  420 ,  460 ,  480 , and  470 . These posts may be oriented at different lateral spacings from axis  50  in each sector or may otherwise be arranged so that the support structure pattern of one sector differs from the other. As an example, sector  22 B may be provided with more posts in the upper half of the antenna than sector  22 A (i.e., sector  22 B may have two posts such as posts  460  and  480  that lie above axis  50  in the orientation of  FIG. 12 , whereas sector  22 A may have no posts above axis  50 ). As another example, lateral spacing X 2  of post  420  of sector  22 A may, if desired, be different than lateral spacing X 1  of post  470  in sector  22 B. Symmetry may, in general, be reduced using any suitable interplate structures that change the radio-frequency properties of each sector with respect to the other, without preventing the sectors from collectively creating a gain pattern that covers all antenna directions of interest. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20090310
Publication Date: 20120717
Grant Date: 20120717
Priority Date: 20090310
Inventors: CHIANG BING
SPRINGER GREGORY A.
KOUGH DOUGLAS B.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q21/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 42730260