PATENT DOCUMENT

Publication Number: US-9203139-B2
Application Number: US-201213464789-A
Country: US
Kind Code: B2

Title: Antenna structures having slot-based parasitic elements

Abstract:
Electronic devices may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may include antenna resonating elements and antenna ground plane structures. An electronic device may have antennas formed from the antenna resonating elements and an antenna ground plane. The antenna ground plane may have slot structures. The slot structures may be configured to form a slot-based parasitic antenna element to minimize coupling between the antennas in a device. The slot-based parasitic antenna element may be located between the antennas in a device. The slots structures from which a parasitic antenna element is formed may include open slots and closed slots. Slots may have one or more arms and one or more bends. Slots may be formed in internal housing members, traces on dielectric carriers, and other conductive structures.

Claims:
What is claimed is:  
     
       1. An electronic device having a length, a width that is less than the length, and a height that is less than the width, comprising:
 a conductive housing having first and second ends; 
 an antenna ground plane; 
 a first antenna resonating element that forms a first portion of the conductive housing at the first end and that extends across an entirety of the width of the electronic device; 
 a second antenna resonating element that forms a second portion of the conductive housing at the second end and that extends across the entirety of the width of the electronic device; and 
 a slot-based parasitic antenna element formed from slot structures in the antenna ground plane, wherein the first antenna resonating element and the antenna ground plane form a first antenna, the second antenna resonating element and the antenna ground plane form a second antenna, and the slot-based parasitic antenna element is configured to serve as an antenna isolation element to minimize coupling between the first and second antennas. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the slot structures comprise at least one closed slot in the antenna ground plane between the first and second ends. 
     
     
       3. The electronic device defined in  claim 2  further comprising an internal metal housing structure that forms at least part of the antenna ground plane, wherein the closed slot is formed in the internal metal housing structure. 
     
     
       4. The electronic device defined in  claim 3  wherein the internal metal housing structure comprises at least one planar metal layer in which the closed slot is formed and wherein the electronic device comprises cellular telephone transceiver circuitry coupled to the first and second antennas. 
     
     
       5. The electronic device defined in  claim 1 , wherein the first portion of the conductive housing formed from the first antenna resonating element comprises a first external surface of the electronic device and the second portion of the conductive housing formed from the second antenna resonating element comprises a second external surface of the electronic device that opposes the first external surface. 
     
     
       6. The electronic device defined in  claim 1 , wherein the first and second antenna resonating elements each extend across an entirety of the height of the electronic device. 
     
     
       7. The electronic device defined in  claim 1 , wherein the first portion of the conductive housing that is formed from the first antenna resonating element runs along at least first, second, and third external surfaces of the electronic device. 
     
     
       8. The electronic device defined in  claim 7 , wherein the second portion of the conductive housing that is formed from the second antenna resonating element runs along at least the first and second external surfaces and a fourth external surface of the electronic device. 
     
     
       9. The electronic device defined in  claim 7 , wherein the first external surface is substantially parallel to the second external surface and the third external surface is substantially perpendicular to the first and second external surfaces. 
     
     
       10. The electronic device defined in  claim 7 , wherein the slot structures comprises a first slot in the antenna ground plane between the first and second ends adjacent to the first external surface of the electronic device and a second slot in the antenna ground plane between the first and second ends adjacent to the second external surface of the electronic device. 
     
     
       11. The electronic device defined in  claim 1 , where the slot structures comprise a C-shaped closed slot.

Description:
BACKGROUND 
     This relates to wireless electronic devices, and, more particularly, to antenna structures for wireless electronic devices. 
     Electronic devices such as computers and handheld electronic devices are often provided with wireless communications capabilities. For example, electronic devices may use cellular telephone circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications links to handle communications with nearby equipment. For example, electronic devices may communicate using the WiFi® (IEEE 802.11) bands at 2.4 GHz and 5 GHz and the Bluetooth® band at 2.4 GHz. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna components using compact structures. In such wireless devices, it may be desirable or necessary to locate antennas relatively close to one another. If care is not taken, however, there will be a potential for interference between the antennas. 
     It would therefore be desirable to be able to provide improved ways in which to provide electronic devices with antennas. 
     SUMMARY 
     Electronic devices may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may include antenna resonating elements and antenna ground plane structures. Antennas may be formed from the antenna resonating elements and the antenna ground plane. Antennas may be located along the edge of a computer or other device that includes a display, at opposing ends of a cellular telephone or other handheld device, or may be located elsewhere within the housing of an electronic device. 
     The antenna ground plane may have slot structures. The slot structures may be configured to form a slot-based parasitic antenna element that enhances isolation between the antennas in a device. The slot-based parasitic antenna element may be located between the antennas in a device. 
     The slots structures from which a parasitic antenna element is formed may include open slots and closed slots. Slots may have one or more arms and one or more bends. Slots with L-shapes, C-shapes, T-shapes, H-shapes, and other suitable shapes may be formed. 
     In a device such as a cellular telephone or other portable equipment, an antenna ground plane may include conductive structures that are part of internal housing member such as a metal midplate member. Slot structures may be formed in the midplate member or other conductive structures in a device. In some configurations, parts of an antenna ground plane may be configured to form antenna cavity structures for the antennas in a device. Antenna ground plane structures and antenna resonating element structures may be formed from patterned traces on a dielectric support structure. 
     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 perspective view of an illustrative electronic device such as a display with an integrated computer that may be provided with wireless circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a cellular telephone, tablet computer, or other portable device that may be provided with wireless circuitry in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a portable computer with wireless circuitry in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of illustrative wireless circuitry that may be used in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative antenna resonating element of the type that may be used in wireless circuitry in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram showing antennas may be isolated from each other using a slot-based parasitic antenna element in accordance with an embodiment of the present invention. 
         FIG. 7  is a graph in which antenna-to-antenna coupling has been plotted as a function of distance for antenna configurations with and without a slot-based parasitic antenna element in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram showing how a pair of antennas with a shared ground plane may be isolated using a parasitic antenna element formed from a C-shaped closed slot in the ground plane in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram showing how a pair of antennas with a shared ground plane may be isolated using a parasitic antenna element formed from a pair of slots in the ground plane that have different lengths in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram showing how a pair of antennas with a shared ground plane may be isolated using a parasitic antenna element formed from a T-shaped slot in the ground plane that has multiple branches of different lengths in accordance with an embodiment of the present invention. 
         FIG. 11  is a diagram of a pair of antennas backed by antenna cavity structures and an associated slot-based parasitic antenna element of the type that may be used to help isolate the antennas from each other in accordance with an embodiment of the present invention. 
         FIG. 12  is a side view of an illustrative electronic device showing how a ground plane structure of the type that may be formed on a dielectric support structure may have a slot-based parasitic antenna element in accordance with an embodiment of the present invention. 
         FIG. 13  is a perspective view of a portion of an electronic device showing how a pair of antennas may be isolated using a slot-based parasitic antenna element in accordance with an embodiment of the present invention. 
         FIG. 14  is a diagram of an illustrative L-shaped slot-based parasitic antenna element in accordance with an embodiment of the present invention. 
         FIG. 15  is a graph in which antenna coupling between a pair of antennas has been plotted as a function of frequency in both the presence and in the absence of a slot-based parasitic antenna element in accordance with an embodiment of the present invention. 
         FIG. 16  is a cross-sectional view of a portion of an electronic device having a conductive internal housing structure such as a midplate member that may serve as an antenna ground plane for forming a slot-based parasitic antenna element in accordance with an embodiment of the present invention. 
         FIG. 17  is a diagram showing how a midplate structure of the type shown in  FIG. 16  or other antenna ground plane structure may be used in forming slot-based parasitic antenna elements to help isolate antennas in a device in accordance with an embodiment of the present invention. 
         FIG. 18  is a graph in which antenna coupling between a pair of antennas has been plotted as a function of frequency in both the presence and in the absence of slot-based parasitic antenna element structures of the type shown in  FIG. 17  in accordance with an embodiment of the present invention. 
         FIG. 19  is a diagram showing how an antenna ground structure such as a midplate structure of the type shown in  FIG. 16  may be used to form a slot-based parasitic antenna element with an H-shaped closed slot that enhances isolation between antennas in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 20  is a graph in which antenna coupling between a pair of antennas has been plotted as a function of frequency with in the presence of different types of slot-based parasitic antenna elements in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic devices  10  of  FIGS. 1 ,  2 , and  3  may contain wireless circuitry. For example, an electronic device may contain wireless communications circuitry that operates in long-range communications bands such as cellular telephone bands and wireless circuitry that operates in short-range communications bands such as the 2.4 GHz Bluetooth® band and the 2.4 GHz and 5 GHz WiFi® wireless local area network bands (sometimes referred to as IEEE 802.11 bands). Devices such as device  10  of  FIGS. 1 ,  2 , and  3  may contain multiple antennas. The antennas may share a common antenna ground plane. Slot-based parasitic antenna element structures may be used to enhance isolation between the antennas. 
     In the illustrative configuration of  FIG. 1 , electronic device  10  has a display such as display  14  mounted in housing  12  on a stand such as stand  16 . Electronic device  10  of  FIG. 1  may be, for example, a computer monitor such as a computer monitor with an integrated computer or a television. In configurations such as the illustrative configuration of  FIG. 2 , electronic device  10  may be a handheld electronic device such as a mobile telephone, may be a portable media player, may be a tablet computer, or may be other portable electronic equipment. In the configuration of  FIG. 3 , electronic device  10  has a housing with multiple parts. Housing  12  of electronic device  10  of  FIG. 3  may, for example, have upper housing  12 A and lower housing  12 B. Housing portions  12 A and  12 B may be coupled using a hinge. Device  10  of  FIG. 3  may be a portable computer or other equipment with a multi-part housing. 
     In general, electronic devices such as devices  10  of  FIGS. 1 ,  2 , and  3  may be any suitable type of electronic device. Device  10  may be, for example, a handheld electronic device such as a cellular telephone, media player, gaming device, or other device, may be a laptop computer, tablet computer, or other portable computer, may be a desktop computer, may be a television or set top box, or may be other electronic equipment. The examples of  FIGS. 1 ,  2 , and  3  are merely illustrative. 
     Device  10  may have a housing such as housing  12 . Housing  12  may be formed from plastic, metal (e.g., aluminum or stainless steel), fiber composites such as carbon fiber, glass, ceramic, other materials, and combinations of these materials. Housing  12  or parts of housing  12  may be formed using a unibody construction in which housing structures are formed from an integrated piece of material. Multipart housing constructions may also be used in which housing  12  or parts of housing  12  are formed from frame structures, housing walls, sheet metal structures and other planar structures, and other components that are attached to each other using fasteners, adhesive, and other attachment mechanisms. 
     Some of the structures in housing  12  may be conductive. For example, metal parts of housing  12  such as metal housing walls may be conductive. Other parts of housing  12  may be formed from dielectric material such as plastic, glass, ceramic, non-conducting composites, etc. To ensure that antenna structures in device  10  function properly, care should be taken when placing the antenna structures relative to the conductive portions of housing  12 . If desired, portions of housing  12  may form part of the antenna structures for device  10 . For example, conductive housing sidewalls, metal structures that are shorted to conductive housing sidewalls, or other internal metal housing structures may be used in forming an antenna ground plane element. 
     Device  10  may include a display such a display  14 . Display  14  may be a liquid crystal display (LCD), a plasma display, an organic light-emitting diode (OLED) display, an electrophoretic display, an electrowetting display, or a display implemented using other display technologies. A touch sensor may be incorporated into display  14  (i.e., display  14  may be a touch screen display) or display  14  may be insensitive to touch. Touch sensors for display  14  may be resistive touch sensors, capacitive touch sensors, acoustic touch sensors, light-based touch sensors, force sensors, or touch sensors implemented using other touch technologies. 
     Antennas for devices such as device  10  of  FIG. 1  may be located in peripheral edge portions of device  10  such as edge regions  42  or may be located in other portions of device  10  (e.g., in the center of the rear of housing  12 , etc.). As an example, an array of two or more antennas may be located along the top edge or the right or left edge of device  10  of  FIG. 1 . 
     As shown in  FIG. 2 , housing  12  may include a peripheral conductive housing member separated into segments by optional dielectric gaps  18 . The peripheral conductive housing member may be formed, for example, from a metal member such as a peripheral conductive housing band or a display bezel that runs around the four edges of rectangular housing  12 . If desired, sidewall portions of housing  12  (e.g., left and right edge portions of a peripheral conductive housing structure or other sidewall structures) may be formed as integral portions of a rear housing structure in housing  12  (e.g., sidewalls that project vertically upwards along the edges of housing  12  from a rear planar portion) or may be formed as parts of other housing structures. Portions of housing  12  that are conductive may be formed from metals such as stainless steel or aluminum (as examples). Portions of housing  12  that are formed from dielectric may be formed from plastic, glass, ceramic, or other dielectric materials. 
     Device  10  may have a display cover layer such as a layer of glass or transparent plastic that covers display  14  and the front face of housing  12 . Openings may be formed in the display cover layer such as an opening for buttons such as button  20  and openings for ports such as speaker port  22 . Openings may be formed in housing  12  to accommodate connectors for digital and audio plugs and other components. 
     Antennas (e.g., antennas  60 A and  60 B) may be formed in regions  24  and  26  at the opposing top and bottom ends of device  10  or elsewhere in device  10 . As an example, one or more cellular telephone antennas may be formed in region  24  and one or more wireless local area network antennas may be formed in region  26 . As another example, cellular telephone antennas may be formed in both regions  24  and  26 . Wireless local area network antennas may also be formed in region  24  and region  26 . Other types of antennas may be formed in regions  24  and  26 , if desired. 
     As shown in the illustrative configuration for electronic device  10  of  FIG. 3 , device  10  may have input-output devices such as track pad  28  and keyboard  30 . Camera  32  may be used to gather image data. Device  10  may also have components such as microphones, speakers, buttons, removable storage drives, status indicator lights, buzzers, sensors, and other input-output devices. These devices may be used to gather input for device  10  and may be used to supply a user of device  10  with output. Ports in device  10  such as ports  34  may receive mating connectors (e.g., an audio plug, a connector associated with a data cable such as a Universal Serial Bus cable, a data cable that handles video and audio data such as a cable that connects device  10  to a computer display, television, or other monitor, etc.). 
     Device  10  may have a one-piece housing or a multi-piece housing. As shown in  FIG. 3 , for example, electronic device  10  may be a device such as a portable computer or other device that has a two-part housing formed from upper housing  12 A and lower housing  12 B. Upper housing  12 A may include display  14  and may sometimes be referred to as a display housing or lid. Lower housing  12 B may sometimes be referred to as a base or main housing. Housings  12 A and  12 B may be connected to each other using a hinge (e.g., a hinge located in region  36  along the upper edge of lower housing  12 B and the lower edge of upper housing  12 A). The hinge may allow upper housing  12 A to rotate about axis  38  in directions  40  relative to lower housing  12 B. The plane of lid (upper housing)  12 A and the plane of lower housing  12 B may be separated by an angle that varies between 0° when the lid is closed to 90° or more when the lid is fully opened. 
     Antennas for devices such as device  10  of  FIG. 3  may be located in hinge region  44 , along the upper edge of housing  12 A in peripheral regions such as region  46 , along the right-hand edge of housing  12 A in peripheral regions such as region  48 , on the left-hand edge of housing  12 A, in a peripheral portion of housing  12 B, in part of the planar center portion of housing  12 A or  12 B (e.g., under a dielectric antenna window formed within a planar metal housing member), or elsewhere in device  10 . 
     As shown in  FIG. 4 , device  10  may include control circuitry  50 . Control circuitry  50  may include storage such as flash memory, hard disk drive memory, solid state storage devices, other nonvolatile memory, random-access memory and other volatile memory, etc. Control circuitry  50  may also include processing circuitry. The processing circuitry of control circuitry  50  may include digital signal processors, microcontrollers, application specific integrated circuits, microprocessors, power management unit (PMU) circuits, and processing circuitry that is part of other types of integrated circuits. 
     Wireless circuitry  52  may be used to transmit and receive radio-frequency signals in devices such as the electronic devices of  FIGS. 1 ,  2 , and  3 . Wireless circuitry  52  may include wireless radio-frequency transceiver  54  and one or more antennas  56  (sometimes referred to herein as antenna structures). Wireless transceiver  54  may transmit and receive radio-frequency signals from device  10  using antenna structures  56 . Circuitry  52  may be used to support communications in one or more communications bands. Examples of communications bands that may be handled by circuitry  52  include cellular telephone bands, satellite navigation bands (e.g., the Global Positioning System band at 1575 MHz), bands for short range links such as the Bluetooth® band at 2.4 GHz and wireless local area network (WLAN) bands such as the IEEE 802.11 band at 2.4 GHz and the IEEE 802.11 band at 5 GHz, etc. 
     When more than one antenna is used in device  10 , radio-frequency transceiver circuitry  54  can use the antennas to implement multiple-input and multiple-output (MIMO) protocols (e.g., protocols associated with IEEE 802.11(n) networks) and antenna diversity schemes. Multiplexing arrangements can be used to allow different types of traffic to be transmitted and received over a common antenna structure. For example, transceiver  54  may transmit and receive both 2.4 GHz Bluetooth® signals and 802.11 signals over a shared antenna. 
     Transmission line paths such as paths  58  may be used to couple antenna structures  56  to transceiver  54 . Transmission lines  58  may include coaxial cable paths, microstrip transmission lines, stripline transmission lines, edge-coupled microstrip transmission lines, edge-coupled stripline transmission lines, transmission lines formed from combinations of transmission lines of these types, etc. During operation, antennas  56  may receive incoming radio-frequency signals. The received incoming radio-frequency signals may be routed to radio-frequency transceiver circuitry  54  by paths  58 . During signal transmission operations, radio-frequency transceiver circuitry  54  may transmit radio-frequency signals. The transmitted signals may be conveyed by paths  58  to antenna structures  56  and transmitted to remote receivers. 
     One or more antenna components may be mounted within device  10 . These antenna components may include active antenna components such as directly fed antenna resonating elements (sometimes referred to herein as “antenna resonating elements” or “resonating elements”). Antenna components in device  10  may also include passive (unfed) antenna components such as parasitic antenna resonating elements (sometimes referred to herein as parasitic elements, parasitic antenna element structure, or parasitic antenna elements). Parasitic antenna element structures may, if desired, be configured to serve as isolation structures that improve the isolation between antennas in device  10  and thereby improve wireless performance. 
     An illustrative antenna for use in device  10  is shown in  FIG. 5 . Antenna  56  of  FIG. 5  has antenna resonating element  60  and antenna ground plane  62 . Antenna ground  62  and the conductive structures of antenna resonating element  60  may be formed from conductive housing structures such as portions of housing  12 , from internal conductive housing structures such as metal frame members, metal midplate members, or other metal housing structures. Antenna ground  62  and antenna resonating element  60  may also be formed from metal traces on printed circuits (e.g., rigid printed circuit boards such as fiberglass-filled epoxy boards and/or flexible printed circuits formed from flexible sheets of polyimide or other polymer layers), metal traces on plastic carriers, glass carriers, ceramic carriers, or dielectric support structures formed from other dielectric materials or combinations of these materials, metal wires, metal foil, stamped sheet metal parts, and other conductive materials. 
     Antenna resonating element  60  may include a main resonating element arm such as arm  72 . Antenna resonating element arm  72  may also include a short circuit branch such as short circuit branch  64  that couples main resonating element arm  72  to antenna ground  62 . Antenna feed  66  may be coupled between main resonating element arm  72  and ground  62  in parallel with short circuit branch  64 . Main resonating element arm  72  may, if desired, include one or more branches such as additional branch  72 ′ (e.g., to form a T-shaped antenna). Branches of different lengths may be used, for example, to enhance the bandwidth of antenna  56 . The main resonating element arm of antenna  56  may include straight lengths of conductor, conductive structures with curves, conductive structures with combinations of straight and curved edges, conductive structures that follow meandering paths, conductive structures that have bends, and other suitable antenna resonating element structures. 
     Antenna feed  66  may include a positive antenna feed terminal such as positive antenna feed terminal  68  and a ground antenna feed terminal such as ground antenna feed terminal  70 . Transmission line conductors (e.g., a positive signal conductor and an associated ground signal conductor) may be coupled to terminals  68  and  70 , respectively. The positive and ground transmission line conductors may be associated with a transmission line such as transmission line  58  of  FIG. 4  and may be used to couple antenna  56  of  FIG. 5  to radio-frequency transceiver circuitry. If desired, filters, switches, impedance matching circuits, connectors, and other components may be interposed in the transmission line path coupling radio-frequency transceiver circuitry  54  to antenna  56 . 
     The illustrative antenna configuration of  FIG. 5  forms an inverted-F antenna. If desired, other types of antennas may be used in device  10  such as patch antennas, planar inverted-F antennas, monopole antennas, dipole antennas, loop antennas, closed slot antennas, and open slot antennas, other suitable antennas, and hybrid antennas that include antenna resonating elements formed from two or more of these antenna structures. The illustrative inverted-F antenna configuration of antenna  56  of  FIG. 5  is merely an example. 
     In device  10 , multiple antennas  56  may be used to cover communications bands of interest. For example, multiple antennas may be used to cover the same communications band or multiple antennas may cover overlapping communications bands (as examples). To prevent antennas in device  10  from interfering with each other and thereby adversely affecting wireless performance, one or more isolation structures may be incorporated into device  10 . As an example, one or more slot-based parasitic antenna elements that serve as antenna isolation structures may be incorporated into device  10 . 
     An illustrative antenna system for device  10  that includes a slot-based antenna isolation structure is shown in  FIG. 6 . As shown in  FIG. 6 , device  10  may include a first antenna such as antenna  56 A and a second antenna such as antenna  56 B. Antenna  56 A and antenna  56 B may be, for example, wireless local area network antennas, may be a wireless local area network antenna and a cellular telephone antenna, respectively, or may be a pair of cellular telephone antennas (as examples). 
     Antenna ground plane  62  may be shared by antennas  56 A and  56 B. Antenna ground plane  62  may, for example, include conductive housing structures, traces on a printed circuit, traces on a dielectric carrier, or combinations of conductive structures such as these that extend continuously past antenna resonating element  60 A in antenna  56 A and antenna resonating element  60 B in antenna  56 B. 
     Antenna  56 A may include antenna resonating element  60  and a portion of antenna ground plane  62 . Antenna  56 B may be formed from antenna resonating element  60  and a portion of antenna ground plane  62 . Slot-based parasitic antenna element  74  may be formed using one or more openings in ground plane  62  such as L-shaped slot  76 . Slots such as slot  76  may sometimes be referred to open slots because one end of the slot (end  78 ) is open and is not surrounded and enclosed by ground plane  62 . 
     Slot  76  may be characterized by a length L. The location of slot  76  along dimension X between antennas  56 A and  56 B and the magnitude of length L may be selected to reduce interference between antennas  56 A and  56 B. With one suitable arrangement, the length L of slot  76  may be about a quarter of a wavelength at an operating frequency of interest (e.g., at or near a communications band for which it is desired to minimize interference). 
     Interference between antennas  56 A and  56 B may result from ground plane coupling (i.e., currents coupled between antenna  56 A and antenna  56 B through ground plane  62 ) and from free space near-field electromagnetic coupling (i.e., radio-frequency electromagnetic fields coupled through the air and other dielectric materials between antennas  56 A and  56 B).  FIG. 7  is a graph in which coupling between a first antenna (i.e., antenna  56 A) and a second antenna (i.e., antenna  56 B) has been plotted as a function of separation dimension X. Curve  80  corresponds to coupling (i.e., coupling parameter S 12  between first antenna  56 A and second antenna  56 B) in the absence of parasitic antenna element  74 . Curve  86  corresponds to coupling (S 12 ) between the first antenna  56 A and second antenna  56 B in the presence of parasitic antenna element  74 . 
     As shown in the graph of  FIG. 7 , the coupling characteristic of curve  80  may exhibit peaks and valleys as a function of increasing separation (dimension X) between antennas  56 A and  56 B. These peaks and valleys can be shifted (i.e., the coupling characteristic of curve  80  can change to the coupling characteristic of curve  86 ) due to the presence of parasitic antenna element  74  (e.g., due to current phase shifts within ground plane  62  due to the presence of slot  76 ). 
     Due to layout constraints, it may be desirable to locate antennas  56 A and  56 B within a device so that they are separated by a distance such as distance X 1  (see, e.g.,  FIG. 6 ). In this type of scenario, the amount of coupling between antennas  56 A and  56 B in the absence of parasitic element  74  may be represented by point  82  on curve  80  of  FIG. 7 . When parasitic antenna element  74  is incorporated into device  10  as shown in  FIG. 6 , however, the amount of coupling between antennas  56 A and  56 B (in this example) may be reduced from the amount represented by point  82  on curve  80  to the amount represented by point  84  on curve  86 . When configured to exhibit the relatively small amount of coupling of point  84  due to the presence of parasitic element  74 , antennas  56 A and  56 B may exhibit minimal interference, thereby enhancing wireless performance for device  10 . 
     The amount of isolation that is produced by incorporating slot-based parasitic antenna element  74  into device  10  may be adjusted by making adjustments to the location and shape of slot  76 . For example, it may be desirable to slightly lengthen or shorten slot  76  or it may be desirable to move slot  76  so that opening  78  is closer to antenna resonating element  60 A or is closer to antenna resonating element  60 B. Adjustments may also be made to the shape of slot  76  (e.g., to add or remove slot branches, to use open and/or closed slot configurations, etc.) By optimizing the configuration of slot-based parasitic antenna element  74  in this way, antenna isolation and therefore wireless performance in device  10  may be maximized. 
     As shown in  FIG. 8 , parasitic antenna element  74  may, if desired, be formed from a closed slot such as closed slot  76 . Slot  76  is entirely surrounded and enclosed by portions of ground plane  62 , so no slot openings such as slot opening  78  of  FIG. 6  are present in slot  76  of  FIG. 8 . In an open slot such as slot  76  of  FIG. 6 , it may be desirable to configure slot  76  to have a slot length of about one quarter of a wavelength at an operating frequency of interest (i.e., a frequency in a communications band of operation for antennas  56 A and  56 B). In a closed slot such as slot  76  of  FIG. 8 , it may be desirable to configure slot  76  to have a slot length of about one half of a wavelength at the operating frequency of interest. Closed slot  76  may have a C-shape as shown in  FIG. 9 , may have an L-shape, may be straight, may have curved portions, may have an H-shape, or may have other suitable shapes. If desired, parasitic antenna element  74  may include both closed and open slots, closed open slots with multiple branches, etc. The configuration of  FIG. 8  is merely illustrative. 
     In the illustrative configuration for parasitic antenna element  74  of  FIG. 9 , parasitic antenna element  74  includes multiple slots such as slot  76 A and slot  76 B. Each slot (in this example) may have a different length and therefore a different frequency response. For example, slot  76 A may have a first length L 1  and slot  76 B may have a second length L 2 . Length L 1  may be less than length L 2 , so that slot  76 A is associated with providing enhanced antenna isolation at a higher operating frequency than slot  76 B. By incorporating two slots with different frequency tunings, the overall bandwidth of the isolation provided by parasitic antenna element  74  may be enhanced. In the example of  FIG. 9 , slots  76 A and  76 B are open slots having respective ground plane openings  78 A and  78 B. This is merely illustrative. Slots  76 A and/or  76 B may be open and/or closed slots, if desired. 
     An illustrative configuration for a slot-based parasitic antenna element in which the parasitic element has a slot with multiple branches (arms) is shown in  FIG. 10 . As shown in  FIG. 10 , parasitic antenna element  74  may have a T-shaped slot such as slot  76  that includes first branch  76 - 1  and second branch  76 - 2 . The lengths of branches  76 - 1  and  76 - 2  may be different, so as to give rise to different frequency response contributions for parasitic antenna element  74 , thereby enhancing isolation bandwidth. 
     If desired, antennas  56 A and  56 B may be formed using ground plane that is shaped in the form of a cavity (i.e., antennas  56 A and  56 B may be implemented using cavity-backed antenna designs). This type of configuration is shown in  FIG. 11 . As shown in  FIG. 11 , antenna  56 A may have antenna resonating element  60 A and antenna  56 B may have antenna resonating element  60 B. Ground plane  62  may be formed from structures that form a hollow triangular prism having base portion  62 - 1 , vertical portion  62 - 2 , and side portion  62 - 3 , and end portions  62 - 4  and  62 - 5 . Structures  62  may form an antenna cavity for antennas  56 A and  56 B. Parasitic antenna element  74  may have one or more slots such as slot  76 . Slot  76  may be formed in the conductive structures that form antenna ground plane  62 . For example, slot  76  may be formed in base portion  62 - 1 . 
     Antenna resonating elements  60 A and  60 B and ground plane  62  may be formed from patterned metal traces on a support structure (e.g., a plastic carrier, a glass carrier, a ceramic carrier, a rigid printed circuit board, a flexible printed circuit, or other dielectric support structure). Antenna resonating elements  60 A and  60 B may, if desired, be planar elements that are oriented perpendicular to slot  76  (i.e., elements  60 A and  60 B may lie in a plane having a surface normal that is perpendicular to the surface normal for a plane that contains slot  76 ). Other configurations for antenna resonating elements  60 A and  60 B may be used, if desired. For example, an antenna cavity for antennas  56 A and  56 B may be formed using more planar ground plane elements (e.g., to form a rectangular prism), using curved cavity walls, using a combination of curved and flat cavity walls, etc.). The example of  FIG. 11  is merely illustrative. 
     A cross-sectional view of a portion of device  10  in the vicinity of an antenna cavity formed from an antenna ground plane that includes slot  76  is shown in  FIG. 12 . As shown in  FIG. 12 , display  14  may have display structures  86  and display cover layer  80 . Display structures  86  may include an array of display pixels formed from liquid crystal display (LCD) components, electrowetting display components, electrophoretic display components, organic light-emitting diode components, or other display circuitry. Display structures  86  may be covered by display cover layer  80 . Display cover layer  80  may be formed from a planar member such as a sheet of clear glass, a transparent layer of plastic, or other cover structures. If desired, a peripheral edge portion of display cover layer  80  may be covered with opaque masking layer  88  to prevent interior portions of device  10  from being visible from the exterior of device  10 . Opaque masking layer  88  may be formed from a layer of black ink or plastic other opaque material. Opaque masking material  88  may be radio-transparent for radio-frequency signals being handled by antenna structures  56 . 
     Components  84  may be interposed between display structures  86  and housing  12 . Components  84  may include batteries, integrated circuits, printed circuit boards, and other electrical components that include metal. To avoid blocking slot  76 , slot  76  may be formed at a location that provides clearance (e.g., a millimeter or more, several millimeters or more, or several centimeters or more) between slot  76  and conductive structures in device  10  such as components  84 , housing  12 , and display structures  86 . 
     Antenna structures  56  may be formed along the edge of device  10  (e.g., an edge such as edge  42  of  FIG. 1  or the edge of a portable device such as a portable computer, tablet computer, etc.) from conductive structures on dielectric carrier  82  (as an example). Carrier  82  may be formed from one or more dielectric members. For example, carrier (support structures)  82  may be formed from a hollow plastic carrier structure, a hollow glass carrier structure, a hollow ceramic carrier structure, structures formed from one or more layers of plastic, glass, or ceramic, structures formed from injection molding, structures formed from printed circuit board material, other dielectric structures, and support structures formed from combinations of such structures. Conductive traces structure on support structures  82  may be used in forming antenna resonating elements  60 A and  60 B (see, e.g.,  FIG. 6 ) and in forming an antenna ground plane. In the example of  FIG. 12 , antenna structures  56  may include ground plane conductive structures  62 A and  62 B. Structures  62 A and  62 B may be used in forming an antenna cavity structure for antennas  56 A and  56 B. Parasitic antenna element  74  may be formed from slots in conductive structures  62 A and/or  62 B. For example, parasitic element  74  may be formed from slot  76  in ground plane structure  62 B. Antennas  56 A and  56 B (located out of the plane of the page of  FIG. 12 ) may share ground plane structures  62 A and  62 B with parasitic element  74 . 
       FIG. 13  is a perspective view of illustrative antennas  56 A and  56 B that are separated by parasitic antenna element  74 . Antenna  56 A may be formed from antenna resonating element  60 A and a portion of conductive antenna ground plane structures  62 . Antenna  56 B may be formed from antenna resonating element  60 B and a portion of conductive antenna ground plane structures  62 . Conductive antenna ground plane structures  62  may be formed from structures such as structures  62 A and  62 B of  FIG. 12  or other conductive structures in device  10 . For example, antenna ground plane  62  of  FIG. 13  may be formed from metal that is part of housing structure  12  in an electronic device such as electronic device  10  of  FIG. 1 , from traces on dielectric carriers, from traces on printed circuits, from traces on a glass carrier, from traces on a plastic carrier, from traces on a ceramic carrier, or other conductive structures in device  10 . Structures  62  of  FIG. 13  may, if desired, be located along the edge of device  10  (e.g., in regions such as regions  42  of  FIG. 1 ) or may be located in other portions of device  10 . 
     As shown in  FIG. 14 , slot  76  of parasitic antenna element  74  of  FIG. 13  may be characterized by a length L. The value of length L may be selected so that it is about a quarter of a wavelength at an operating frequency of interest. Slot  76  may be an open slot having an opening in ground plane  62  such as opening  78 . There may be one or more bends such as right-angle bend  90  along the length of slot  76 . With one suitable arrangement, slot  76  may have an L-shape with one bend (bend  90 ), a width of less than 2 mm (e.g., 0.1 to 2 mm), a dimension D 1  that is about 2 mm (e.g., about 1-5 mm), and a dimension D 2  that is about 24 mm (e.g., about 12-28 mm). This size and shape for slot  76  may help provide antenna isolation at frequencies of about 2.4 GHz to 2.5 GHz. Other shapes and sizes may be used for slot  76 , if desired (e.g., to cover other operating frequencies). 
       FIG. 15  is a graph in which measured antenna coupling between antenna  56 A and antenna  56 B of  FIG. 13  has been plotted as a function of operating frequency. Band  92  corresponds to a communications band of interest (e.g., a wireless local area network band or other band). When antennas  56 A and  56 B are operated in a system of the type shown in  FIG. 13  in which parasitic antenna element  74  is present, the coupling between antennas  56 A and  56 B may be characterized by a curve such as curve  196 . In this situation, antennas  56 A and  56 B may be well isolated from each other and exhibit satisfactory wireless performance. In a configuration in which antenna resonating element  74  of  FIG. 13  is not present, antennas  56 A and  56 B are not well isolated (in this example) and exhibit significantly more coupling, as shown by curve  194 . 
     A cross-sectional view of electronic device  10  showing how device  10  may include internal conductive housing structures is shown in  FIG. 16 . As shown in  FIG. 16 , device  10  may include antenna structures such as antenna structures  56 . Display  14  may include display structures  86  and display cover layer  80 . Components  84  may include integrated circuits, printed circuit boards, batteries, and other components. Conductive structures such as conductive structures  94  may be interposed between display structures  86  and components  84 . Conductive structures  94  may, as an example, include one or more sheet metal structures or machined metal structures. These structures, which may sometimes be referred to as a midplate or midplate structures may span some or all of the width of device  10  of  FIG. 2 . For example, structures  94  of  FIG. 16  may be welded or otherwise coupled between the left edge of housing  12  of  FIG. 2  and the right edge of housing  12  of  FIG. 2  without significantly blocking regions  24  and  26 . 
     Structures such as structures  94  of  FIG. 16  and/or other conductive structures associated with device  10  (e.g., conductive housing structures  12 , metal traces on dielectric structures, etc.) may be used in forming antenna ground plane  62 . As an example, structures  94  may be used in forming ground plane  62  of  FIG. 17 . As shown in  FIG. 17 , device  10  of  FIG. 17  may include antenna structures such as antenna structures  56 A and antenna structures  56 B. Antenna structures  56 A may be formed from antenna resonating element  60 A in region  24  and an associated portion of ground plane  62 . Antenna structures  56 B may be formed from antenna resonating element  60 B in region  26  and an associated portion of ground plane  62 . Regions  24  and  26  and respective antennas  56 A and  56 B may be located at opposing ends of device  10 . 
     To enhance isolation between antennas  56 A and  56 B, device  10  of  FIG. 17  may be provided with parasitic antenna element  74 . Parasitic antenna element  74  may be formed from one or more slots in ground plane  62 . As shown in  FIG. 17 , for example, parasitic antenna element  74  may include a first slot such as slot  76 L and a second slot such as slot  76 R. Slot  76 L may be located along the left-hand edge of ground plane  62  and may have an associated opening such as opening  78 L. Slot  76 R may be located along the right-hand edge of ground plane  62  and may have an associated opening such as opening  78 R. Slots  76 L and  76 R may have the same length or may have different lengths to broaden isolation bandwidth. To ensure that slots  76 L and  76 R operate effectively, conductive structures such as display structures  86  and components  84  may be confined to regions outside of keep-out regions  96 . 
       FIG. 18  is a graph in which coupling between a first antenna (i.e., antenna  56 A) and a second antenna (i.e., antenna  56 B) in a configuration of the type shown in  FIG. 17  has been plotted as a function of operating frequency. Antennas  56 A and  56 B may be, for example, cellular telephone antennas operating at frequencies from 1750 MHz to 2250 MHz (as an example). Curve  100  represents the coupling between antenna structures  56 A and  56 B in the absence of slot-based parasitic antenna element  74 . Curve  98  represents the minimized coupling between antenna structures  56 A and  56 B that may be obtained when ground plane  62  has been configured to form slots such as slots  76 A and  76 B for parasitic antenna isolation element  74 . 
     In configurations for device  10  where it may be difficult to form unobstructed slot openings such as openings  78 L and  78 R of  FIG. 17 , it may be desirable to form slot structures for parasitic antenna element  74  using closed slot arrangements.  FIG. 19  is a diagram showing how parasitic antenna element  74  may be formed using an H-shaped closed slot. As shown in  FIG. 19 , slot  76  in ground plane  62  of device  10  in  FIG. 19  may have a horizontal main arm such as arm  76 M of length LD 3 . Arm  76 M may extend horizontally between opposing vertical segments. The left-hand vertical segment of slot  76  may include first arm  76 L 1  and second arm  76 L 2 . Arm  76 L 1  may extend upwards from the left-hand end of main arm  76 M. Arm  76 L 2  may extend downwards from the left-hand end of arm  76 M. The right-hand vertical segment of slot  76  may include first arm  76 R 1  and second arm  76 R 2 . Arm  76 R 1  may extend upwards from the right-hand end of main arm  76 M. Arm  76 R 2  may extend downwards from the right-hand end of arm  76 M. 
     Arms  76 L 1 ,  76 L 2 ,  76 R 1 , and  76 R 2  may have four different lengths, three different lengths, two different lengths, or may all be of equal size. As an example, arms  76 L 1  and  76 R 1  may be of equal size (length LD 1 ) and arms  76 L 2  and  76 R 2  may be of equal size (length LD 2 , which may be smaller or larger than length LD 1 ). The H-shape of slot  76  may form upper and lower C-shaped slots that overlap along common main arm  76 M. In a configuration in which the upper arms of the H have equal lengths LD 1  and the lower arms of the H have equal lengths LD 2 , the length LH of the upper C-shaped slot may be equal to 2LD 1 +LD 3  and the length of the lower C-shaped slot may be equal to 2LD 2 +LD 3 . Length LD 1  may be equal to length LD 2  or different lengths may be used to broaden isolation bandwidth. To ensure satisfactory antenna isolation, the lengths of the upper and lower C-shaped portions of slot  76  may be configured to be about one half of a wavelength at an operating frequency of interest. In configurations for closed multi-arm slot  76  of  FIG. 19  with other arm lengths, isolation may be provided at different operating frequencies. The H-shaped slot of  FIG. 19  is merely illustrative. In general, parasitic element  74  may be formed by a single closed slot, two closed slots, three or more closed slots, one open slot, two open slots, three or more open slots, one or more slots with a single arm, one or more slots with multiple arms to enhance isolation bandwidth, and/or combinations of slots such as these. 
       FIG. 20  is a graph in which coupling between a first antenna (i.e., antenna  56 A) and a second antenna (i.e., antenna  56 B) in a configuration of the type shown in  FIG. 19  has been plotted as a function of operating frequency. Antennas  56 A and  56 B may be, for example, cellular telephone antennas operating at frequencies from 1750 MHz to 2250 MHz (as an example). Curve  106  represents the coupling between antenna structures  56 A and  56 B in the absence of slot-based parasitic antenna element  74 . Curves  104  and  102  represent the coupling between antenna structures  56 A and  56 B in configurations for slot  76  of  FIG. 19  in which LD 1  and LD 2  are equal. Curve  104  corresponds to a configuration in which LD 1  and LD 2  are each equal to 10 mm. Curve  102  corresponds to a configuration in which LD 1  and LD 2  are each equal to 25 mm. As curves  104  and  102  demonstrate, the use of slot-based parasitic antenna element  74  may enhance isolation between antennas  56 A and  56 B. 
     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: 20120504
Publication Date: 20151201
Grant Date: 20151201
Priority Date: 20120504
Inventors: ZHU JIANG
GUTERMAN JERZY
PASCOLINI MATTIA
HU HONGFEI
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/521", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/521", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 48227590