PATENT DOCUMENT

Publication Number: US-8270914-B2
Application Number: US-63075609-A
Country: US
Kind Code: B2

Title: Bezel gap antennas

Abstract:
Electronic devices are provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and antenna structures. A parallel-fed loop antenna may be formed from portions of an electronic device bezel and a ground plane. The antenna may operate in multiple communications bands. An impedance matching circuit for the antenna may be formed from a parallel-connected inductive element and a series-connected capacitive element. The bezel may surround a peripheral portion of a display that is mounted to the front of an electronic device. The bezel may contain a gap. Antenna feed terminals for the antenna may be located on opposing sides of the gap. The inductive element may bridge the gap and the antenna feed terminals. The capacitive element may be connected in series between one of the antenna feed terminals and a conductor in a transmission line located between the transceiver circuitry and the antenna.

Claims:
1. A parallel-fed loop antenna in an electronic device having a periphery, comprising:
 a conductive loop path formed at least partly from conductive structures disposed along the periphery; 
 an inductor interposed in the conductive loop path; and 
 first and second antenna feed terminals that are bridged by the inductor, wherein the conductive structures of the conductive loop path are formed at least partly from a conductive bezel that surrounds the periphery of the electronic device. 
 
     
     
       2. The parallel-fed loop antenna defined in  claim 1  wherein the conductive bezel comprises a gap. 
     
     
       3. The parallel-fed loop antenna defined in  claim 2  wherein the first and second antenna feed terminals are located on opposing sides of the gap. 
     
     
       4. A parallel-fed loop antenna in an electronic device having a periphery, comprising:
 a conductive loop path formed at least partly from conductive structures disposed along the periphery; 
 an inductor interposed in the conductive loop path; 
 first and second antenna feed terminals that are bridged by the inductor; 
 an antenna feed line that carries antenna signals between a transmission line and the first antenna feed terminal; and 
 a capacitor interposed in the antenna feed line. 
 
     
     
       5. The parallel-fed loop antenna defined in  claim 1  wherein the inductor comprises inductive transmission line structures. 
     
     
       6. A parallel-fed loop antenna in an electronic device having a periphery, comprising:
 a conductive loop path formed at least partly from conductive structures disposed along the periphery; 
 an inductor interposed in the conductive loop path; and 
 first and second antenna feed terminals that are bridged by the inductor, wherein the inductor comprises inductive transmission line structures, wherein the inductive transmission line structures comprise a first conductive structure formed from a portion of a ground plane and a second conductive structure that runs parallel to the first conductive structure, and wherein the first and second conductive structures are separated by an opening. 
 
     
     
       7. An electronic device, comprising:
 a housing having a periphery; 
 a conductive structure that runs along the periphery and that has at least one gap on the periphery; 
 an antenna formed at least partly from the conductive structure; 
 a display, wherein the conductive structure comprises a bezel for the display; 
 first and second antenna feed terminals for the antenna, wherein the antenna comprises a parallel-fed loop antenna; 
 a substantially rectangular ground plane, wherein a portion of the loop antenna is formed from the substantially rectangular ground plane and wherein the second antenna feed terminal is connected to the substantially rectangular ground plane; 
 radio-frequency transceiver circuitry; 
 a transmission line having positive and ground conductors, wherein the transmission line is coupled between the radio-frequency transceiver circuitry and the first and second antenna feed terminals; and 
 a capacitor interposed in the positive conductor of the transmission line. 
 
     
     
       8. The electronic device defined in  claim 7  further comprising an inductor that bridges the first and second antenna feed terminals. 
     
     
       9. The electronic device defined in  claim 7  wherein the second antenna feed terminal is connected to the substantially rectangular ground plane and wherein the first antenna feed terminal is electrically connected to the bezel. 
     
     
       10. Wireless circuitry, comprising:
 a ground plane; 
 a conductive electronic device bezel having a gap; 
 a solid dielectric that fills the gap; 
 first and second antenna feed terminals, wherein the ground plane, bezel, and first and second antenna feed terminals form a parallel-fed loop antenna; and 
 an inductive element, wherein the inductive element bridges the first and second antenna feed terminals. 
 
     
     
       11. The wireless circuitry defined in  claim 10  further comprising:
 radio-frequency transceiver circuitry that is coupled to the parallel-fed loop antenna and that is configured to operate in at least first and second communications bands. 
 
     
     
       12. The wireless circuitry defined in  claim 10  further comprising:
 radio-frequency transceiver circuitry that is coupled to the parallel-fed loop antenna and that is configured to operate in a first communications band that covers sub-bands at 850 MHz and 900 MHz and a second communications band that covers sub-bands at 1800 MHz, 1900 MHz, and 2100 MHz. 
 
     
     
       13. The wireless circuitry defined in  claim 12  further comprising a capacitive element coupled in series with the first antenna feed terminal, wherein the second antenna feed terminal is connected to the ground plane. 
     
     
       14. An electronic device, comprising:
 a display having a rectangular periphery; 
 radio-frequency transceiver circuitry; 
 a conductive structure that surrounds the rectangular periphery of the display and that has a gap along the periphery; 
 an antenna that includes a portion of the conductive structure that has the gap and that includes antenna feed terminals; and 
 a transmission line coupled between the radio-frequency transceiver circuitry and the antenna feed terminals. 
 
     
     
       15. The electronic device defined in  claim 14  further comprising a solid dielectric in the gap. 
     
     
       16. The electronic device defined in  claim 14  further comprising an inductive element that bridges the antenna feed terminals. 
     
     
       17. The electronic device defined in  claim 16  wherein the conductive structure comprises a bezel for the display. 
     
     
       18. The electronic device defined in  claim 16  wherein the inductive element comprises portions of a ground plane and a conductive member that are separated by an opening. 
     
     
       19. The electronic device defined in  claim 14  further comprising a capacitive element connected to a first antenna feed terminal of the antenna feed terminals. 
     
     
       20. The electronic device defined in  claim 19  wherein the transmission line comprises a positive conductor and wherein the capacitive element is connected in series between the positive conductor and the first antenna feed terminal. 
     
     
       21. The electronic device defined in  claim 20  wherein the conductive structure comprises a bezel for the display. 
     
     
       22. The electronic device defined in  claim 14  further comprising:
 a printed circuit board on which components are mounted, wherein the printed circuit board and components form at least part of a ground plane and wherein the antenna is formed at least partly from the ground plane. 
 
     
     
       23. The electronic device defined in  claim 22  wherein a second antenna feed terminal of the antenna feed terminals comprises a ground antenna feed terminal that is connected to the ground plane.

Description:
BACKGROUND 
     This relates generally to wireless communications circuitry, and more particularly, to electronic devices that have wireless communications circuitry. 
     Electronic devices such as handheld electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. 
     Devices such as these are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry to communicate using cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz (e.g., the main Global System for Mobile Communications or GSM cellular telephone bands). Long-range wireless communications circuitry may also handle the 2100 MHz band. 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. At the same time, it may be desirable to include conductive structures in an electronic device such as metal device housing components. Because conductive components can affect radio-frequency performance, care must be taken when incorporating antennas into an electronic device that includes conductive structures. 
     It would therefore be desirable to be able to provide improved wireless communications circuitry for wireless electronic devices. 
     SUMMARY 
     Electronic devices may be provided that include antenna structures. An antenna may be configured to operate in first and second communications bands. An electronic device may contain radio-frequency transceiver circuitry that is coupled to the antenna using a transmission line. The transmission line may have a positive conductor and a ground conductor. The antenna may have a positive antenna feed terminal and a ground antenna feed terminal to which the positive and ground conductors of the transmission line are respectively coupled. 
     The electronic device may have a rectangular periphery. A rectangular display may be mounted on a front face of the electronic device. The electronic device may have a rear face that is formed form a plastic housing member. Conductive sidewall structures may run around the periphery of the electronic device housing and display. The conductive sidewall structures may serve as a bezel for the display. 
     The bezel may include at least one gap. The gap may be filled with a solid dielectric such as plastic. The antenna may be formed from the portion of the bezel that includes the gap and a portion of a ground plane. To avoid excessive sensitivity to touch events, the antenna may be fed using a feed arrangement that reduces electric field concentration in the vicinity of the gap. An impedance matching network may be formed that provides satisfactory operation in both the first and second bands. 
     The impedance matching network may include an inductive element that is formed in parallel with the antenna feed terminals and a capacitive element that is formed in series with one of the antenna feed terminals. The inductive element may be formed from a transmission line inductive structure that bridges the antenna feed terminals. The capacitive element may be formed from a capacitor that is interposed in the positive feed path for the antenna. The capacitor may, for example, be connected between the positive ground conductor of the transmission line and the positive antenna feed terminal. 
     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 with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional end view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of an illustrative antenna in accordance with an embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an illustrative series-fed loop antenna that may be used in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph showing how an electronic device antenna may be configured to exhibit coverage in multiple communications bands in accordance with an embodiment of the present invention. 
         FIG. 7  is a schematic diagram of an illustrative parallel-fed loop antenna that may be used in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of an illustrative parallel-feed loop antenna with an inductance interposed in the loop in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram of an illustrative parallel-fed loop antenna having an inductive transmission line structure in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of an illustrative parallel-fed loop antenna with an inductive transmission line structure and a series-connected capacitive element in accordance with an embodiment of the present invention. 
         FIG. 11  is a Smith chart illustrating the performance of various electronic device loop antennas in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. The wireless communications circuitry may include one or more antennas. 
     The antennas can include loop antennas. Conductive structures for a loop antenna may, if desired, be formed from conductive electronic device structures. The conductive electronic device structures may include conductive housing structures. The housing structures may include a conductive bezel. Gap structures may be formed in the conductive bezel. The antenna may be parallel-fed using a configuration that helps to minimize sensitivity of the antenna to contact with a user&#39;s hand or other external object. 
     Any suitable electronic devices may be provided with wireless circuitry that includes loop antenna structures. As an example, loop antenna structures may be used in electronic devices such as desktop computers, game consoles, routers, laptop computers, etc. With one suitable configuration, loop antenna structures are provided in relatively compact electronic devices in which interior space is relatively valuable such as portable electronic devices. 
     An illustrative portable electronic device in accordance with an embodiment of the present invention is shown in  FIG. 1 . Portable electronic devices such as illustrative portable electronic device  10  may be laptop computers or small portable computers such as ultraportable computers, netbook computers, and tablet computers. Portable electronic devices may also be somewhat smaller devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, the portable electronic devices are handheld electronic devices such as cellular telephones. 
     Space is at a premium in portable electronic devices. Conductive structures are also typically present, which can make efficient antenna operation challenging. For example, conductive housing structures may be present around some or all of the periphery of a portable electronic device housing. 
     In portable electronic device housing arrangements such as these, it may be particularly advantageous to use loop-type antenna designs that cover communications bands of interest. The use of portable devices such as handheld devices is therefore sometimes described herein as an example, although any suitable electronic device may be provided with loop antenna structures, if desired. 
     Handheld devices may be, for example, cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, and handheld gaming devices. Handheld devices and other portable devices may, if desired, include the functionality of multiple conventional devices. Examples of multi-functional devices include cellular telephones that include media player functionality, gaming devices that include wireless communications capabilities, cellular telephones that include game and email functions, and handheld devices that receive email, support mobile telephone calls, and support web browsing. These are merely illustrative examples. Device  10  of  FIG. 1  may be any suitable portable or handheld electronic device. 
     Device  10  includes housing  12  and includes at least one antenna for handling wireless communications. Housing  12 , which is sometimes referred to as a case, may be formed of any suitable materials including, plastic, glass, ceramics, composites, metal, or other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material, so that the operation of conductive antenna elements that are located within housing  12  is not disrupted. In other situations, housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may, for example, be a touch screen that incorporates capacitive touch electrodes. Display  14  may include image pixels formed form light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electronic ink elements, liquid crystal display (LCD) components, or other suitable image pixel structures. A cover glass member may cover the surface of display  14 . Buttons such as button  19  may pass through openings in the cover glass. 
     Housing  12  may include sidewall structures such as sidewall structures  16 . Structures  16  may be implemented using conductive materials. For example, structures  16  may be implemented using a conductive ring member that substantially surrounds the rectangular periphery of display  14 . Structures  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming structures  16 . Structures  16  may serve as a bezel that holds display  14  to the front (top) face of device  10 . Structures  16  are therefore sometimes referred to herein as bezel structures  16  or bezel  16 . Bezel  16  runs around the rectangular periphery of device  10  and display  14 . 
     Bezel  16  may have a thickness (dimension TT) of about 0.1 mm to 3 mm (as an example). The sidewall portions of bezel  16  may be substantially vertical (parallel to vertical axis V). Parallel to axis V, bezel  16  may have a dimension TZ of about 1 mm to 2 cm (as an example). The aspect ratio R of bezel  16  (i.e., the of TZ to TT) is typically more than 1 (i.e., R may be greater than or equal to 1, greater than or equal to 2, greater than or equal to 4, greater than or equal to 10, etc.). 
     It is not necessary for bezel  16  to have a uniform cross-section. For example, the top portion of bezel  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. If desired, the bottom portion of bezel  16  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). In the example of  FIG. 1 , bezel  16  has substantially straight vertical sidewalls. This is merely illustrative. The sidewalls of bezel  16  may be curved or may have any other suitable shape. 
     Display  14  includes conductive structures such as an array of capacitive electrodes, conductive lines for addressing pixel elements, driver circuits, etc. These conductive structures tend to block radio-frequency signals. It may therefore be desirable to form some or all of the rear planar surface of device from a dielectric material such as plastic. 
     Portions of bezel  16  may be provided with gap structures. For example, bezel  16  may be provided with one or more gaps such as gap  18 , as shown in  FIG. 1 . Gap  18  lies along the periphery of the housing of device  10  and display  12  and is therefore sometimes referred to as a peripheral gap. Gap  18  divides bezel  16  (i.e., there is generally no conductive portion of bezel  16  in gap  18 ). 
     As shown in  FIG. 1 , gap  18  may be filled with dielectric. For example, gap  18  may be filled with air. To help provide device  10  with a smooth uninterrupted appearance and to ensure that bezel  16  is aesthetically appealing, gap  18  may be filled with a solid (non-air) dielectric such as plastic. Bezel  16  and gaps such as gap (and its associated plastic filler structure) may form part of one or more antennas in device  10 . For example, portions of bezel  16  and gaps such as gap  18  may, in conjunction with internal conductive structures, form one or more loop antennas. The internal conductive structures may include printed circuit board structures, frame members or other support structures, or other suitable conductive structures. 
     In a typical scenario, device  10  may have upper and lower antennas (as an example). An upper antenna may, for example, be formed at the upper end of device  10  in region  22 . A lower antenna may, for example, be formed at the lower end of device  10  in region  20 . 
     The lower antenna may, for example, be formed partly from the portions of bezel  16  in the vicinity of gap  18 . 
     Antennas in device  10  may be used to support any communications bands of interest. For example, device  10  may include antenna structures for supporting local area network communications, voice and data cellular telephone communications, global positioning system (GPS) communications, Bluetooth® communications, etc. As an example, the lower antenna in region  20  of device  10  may be used in handling voice and data communications in one or more cellular telephone bands. 
     A schematic diagram of an illustrative electronic device is shown in  FIG. 2 . Device  10  of  FIG. 2  may be a portable computer such as a portable tablet computer, a mobile telephone, a mobile telephone with media player capabilities, a handheld computer, a remote control, a game player, a global positioning system (GPS) device, a combination of such devices, or any other suitable portable electronic device. 
     As shown in  FIG. 2 , handheld device  10  may include storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, applications specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, etc. 
     Input-output circuitry  30  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  32  such as touch screens and other user input interface are examples of input-output circuitry  32 . Input-output devices  32  may also include user input-output devices such as buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, etc. A user can control the operation of device  10  by supplying commands through such user input devices. Display and audio devices such as display  14  ( FIG. 1 ) and other components that present visual information and status data may be included in devices  32 . Display and audio components in input-output devices  32  may also include audio equipment such as speakers and other devices for creating sound. If desired, input-output devices  32  may contain audio-video interface equipment such as jacks and other connectors for external headphones and monitors. 
     Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). Wireless communications circuitry  34  may include radio-frequency transceiver circuits for handling multiple radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  36  and  38 . Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in cellular telephone bands such as the GSM bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, and the 2100 MHz data band (as examples). Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include global positioning system (GPS) receiver equipment, wireless circuitry for receiving radio and television signals, paging circuits, etc. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structure, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link. 
     With one suitable arrangement, which is sometimes described herein as an example, the lower antenna in device  10  (i.e., an antenna  40  located in region  20  of device  10  of  FIG. 1 ) may be formed using a loop-type antenna design. When a user holds device  10 , the user&#39;s fingers may contact the exterior of device  10 . For example, the user may touch device  10  in region  20 . To ensure that antenna performance is not overly sensitive to the presence or absence of a user&#39;s touch or contact by other external objects, the loop-type antenna may be fed using an arrangement that does not overly concentrate electric fields in the vicinity of gap  18 . 
     A cross-sectional side view of device  10  of  FIG. 1  taken along line  24 - 24  in  FIG. 1  and viewed in direction  26  is shown in  FIG. 3 . As shown in  FIG. 3 , display  14  may be mounted to the front surface of device  10  using bezel  16 . Housing  12  may include sidewalls formed from bezel  16  and one or more rear walls formed from structures such as planar rear housing structure  42 . Structure  42  may be formed from a dielectric such as plastic or other suitable materials. Snaps, clips, screws, adhesive, and other structures may be used in attaching bezel  16  to display  14  and rear housing wall structure  42 . 
     Device  10  may contain printed circuit boards such as printed circuit board  46 . Printed circuit board  46  and the other printed circuit boards in device  10  may be formed from rigid printed circuit board material (e.g., fiberglass-filled epoxy) or flexible sheets of material such as polymers. Flexible printed circuit boards (“flex circuits”) may, for example, be formed from flexible sheets of polyimide. 
     Printed circuit board  46  may contain interconnects such as interconnects  48 . Interconnects  48  may be formed from conductive traces (e.g., traces of gold-plated copper or other metals). Connectors such as connector  50  may be connected to interconnects  48  using solder or conductive adhesive (as examples). Integrated circuits, discrete components such as resistors, capacitors, and inductors, and other electronic components may be mounted to printed circuit board  46 . 
     Antenna  40  may have antenna feed terminals. For example, antenna  40  may have a positive antenna feed terminal such as positive antenna feed terminal  58  and a ground antenna feed terminal such as ground antenna feed terminal  54 . In the illustrative arrangement of  FIG. 3 , a transmission line path such as coaxial cable  52  may be coupled between the antenna feed formed from terminals  58  and  54  and transceiver circuitry in components  44  via connector  50  and interconnects  48 . Components  44  may include one or more integrated circuits that implement the transceiver circuits  36  and  38  of  FIG. 2 . Connector  50  may be, for example, a coaxial cable connector that is connected to printed circuit board  46 . Cable  52  may be a coaxial cable or other transmission line. Terminal  58  may be coupled to coaxial cable center connector  56 . Terminal  54  may be connected to a ground conductor in cable  52  (e.g., a conductive outer braid conductor). Other arrangements may be used for coupling transceivers in device  10  to antenna  40  if desired. The arrangement of  FIG. 3  is merely illustrative. 
     As the cross-sectional view of  FIG. 3  makes clear, the sidewalls of housing  12  that are formed by bezel  16  may be relatively tall. At the same time, the amount of area that is available to form an antenna in region  20  at the lower end of device  10  may be limited, particularly in a compact device. The compact size that is desired form forming the antenna may make it difficult to form a slot-type antenna shape of sufficient size to resonant in desired communications bands. The shape of bezel  16  may tend to reduce the efficiency of conventional planar inverted-F antennas. Challenges such as these may, if desired, be addressed using a loop-type design for antenna  40 . 
     Consider, as an example, the antenna arrangement of  FIG. 4 . As shown in  FIG. 4 , antenna  40  may be formed in region  20  of device  10 . Region  20  may be located at the lower end of device  10 , as described in connection with  FIG. 1 . Conductive region  68 , which may sometimes be referred to as a ground plane or ground plane element, may be formed from one or more conductive structures (e.g., planar conductive traces on printed circuit board  46 , internal structural members in device  10 , electrical components  44  on board  46 , radio-frequency shielding cans mounted on board  46 , etc.). Conductive region  68  in region  66  is sometimes referred to as forming a “ground region” for antenna  40 . Conductive structures  70  of  FIG. 4  may be formed by bezel  16 . Regions  70  are sometimes referred to as ground plane extensions. Gap  18  may be formed in this conductive bezel portion (as shown in  FIG. 1 ). 
     Ground plane extensions  70  (i.e., portions of bezel  16 ) and the portions of region  68  that lie along edge  76  of ground region  68  form a conductive loop around opening  72 . Opening  72  may be formed from air, plastics and other solid dielectrics. If desired, the outline of opening  72  may be curved, may have more than four straight segments, and/or may be defined by the outlines of conductive components. The rectangular shape of dielectric region  72  in  FIG. 4  is merely illustrative. 
     The conductive structures of  FIG. 4  may, if desired, be fed by coupling radio-frequency transceiver  60  across ground antenna feed terminal  62  and positive antenna feed terminal  64 . As shown in  FIG. 4 , in this type of arrangement, the feed for antenna  40  is not located in the vicinity of gap  18  (i.e., feed terminals  62  and  64  are located to the left of laterally centered dividing line  74  of opening  72 , whereas gap  18  is located to the right of dividing line  74  along the right-hand side of device  10 ). While this type of arrangement may be satisfactory in some situations, antenna feed arrangements that locate the antenna feed terminals at the locations of terminals  62  and  64  of  FIG. 4  tend to accentuate the electric field strength of the radio-frequency antenna signals in the vicinity of gap  18 . If a user happens to place an external object such as finger  80  into the vicinity of gap  18  by moving finger  80  in direction  78  (e.g., when grasping device  10  in the user&#39;s hand), the presence of the user&#39;s finger may disrupt the operation of antenna  40 . 
     To ensure that antenna  40  is not overly sensitive to touch (i.e., to desensitize antenna  40  to touch events involving the hand of the user of device  10  and other external objects), antenna  40  may be fed using antenna feed terminals located in the vicinity of gap  18  (e.g., where shown by positive antenna feed terminal  58  and ground antenna feed terminal  54  in the  FIG. 4  example). When the antenna feed is located to the right of line  74  and, more particularly, when the antenna feed is located close to gap  18 , the electric fields that are produced at gap  18  tend to be reduced. This helps minimize the sensitivity of antenna  40  to the presence of the user&#39;s hand, ensuring satisfactory operation regardless of whether or not an external object is in contact with device  10  in the vicinity of gap  18 . 
     In the arrangement of  FIG. 4 , antenna  40  is being series fed. A schematic diagram of a series-fed loop antenna of the type shown in  FIG. 4  is shown in  FIG. 5 . As shown in  FIG. 5 , series-fed loop antenna  82  may have a loop-shaped conductive path such as loop  84 . A transmission line composed of positive transmission line conductor  86  and ground transmission line conductor  88  may be coupled to antenna feed terminals  58  and  54 , respectively. 
     It may be challenging to effectively use a series-fed feed arrangement of the type shown in  FIG. 5  to feed a multi-band loop antenna. For example, it may be desired to operate a loop antenna in a lower frequency band that covers the GSM sub-bands at 850 MHz and 900 MHz and a higher frequency band that covers the GSM sub-bands at 1800 MH and 1900 MHz and the data sub-band at 2100 MHz. This type of arrangement may be considered to be a dual band arrangement (e.g., 850/900 for the first band and 1800/1900/2100 for the second band) or may be considered to have five bands (850, 900, 1800, 1900, and 2100). In multi-band arrangements such as these, series-fed antennas such as loop antenna  82  of  FIG. 5  may exhibit substantially better impedance matching in the high-frequency communications band than in the low-frequency communications band. 
     A standing-wave-ratio (SWR) versus frequency plot that illustrates this effect is shown in  FIG. 6 . As shown in  FIG. 6 , SWR plot  90  may exhibit a satisfactory resonant peak (peak  94 ) at high-band frequency f 2  (e.g., to cover the sub-bands at 1800 MHz, 1900 MHz, and 2100 MHz). SWR plot  90  may, however, exhibit a relatively poor performance in the low-frequency band centered at frequency f 1  when antenna  40  is series fed. For example, SWR plot  90  for a series-fed loop antenna  82  of  FIG. 5  may be characterized by weak resonant peak  96 . As this example demonstrates, series-fed loop antennas may provide satisfactory impedance matching to transmission line  52  ( FIG. 3 ) in a higher frequency band at f 2 , but may not provide satisfactory impedance matching to transmission line  52  ( FIG. 3 ) in lower frequency band f 1 . 
     A more satisfactory level of performance (illustrated by low-band resonant peak  92 ) may be obtained using a parallel-fed arrangement with appropriate impedance matching features. 
     An illustrative parallel-fed loop antenna is shown schematically in  FIG. 7 . As shown in  FIG. 7 , parallel-fed loop antenna  90  may have a loop of conductor such as loop  92 . Loop  92  in the  FIG. 7  example is shown as being circular. This is merely illustrative. Loop  92  may have other shapes if desired (e.g., rectangular shapes, shapes with both curved and straight sides, shapes with irregular borders, etc.). Transmission line TL may include positive signal conductor  94  and ground signal conductor  96 . Paths  94  and  96  may be contained in coaxial cables, micro-strip transmission lines on flex circuits and rigid printed circuit boards, etc. Transmission line TL may be coupled to the feed of antenna  90  using positive antenna feed terminal  58  and ground antenna feed terminal  54 . Electrical element  98  may bridge terminals  58  and  54 , thereby “closing” the loop formed by path  92 . When the loop is closed in this way, element  98  is interposed in the conductive path that forms loop  92 . The impedance of parallel-fed loop antennas such as loop antenna  90  of  FIG. 7  may be adjusted by proper selection of the element  98  and, if desired, other circuits (e.g., capacitors or other elements interposed in one of the feed lines such as line  94  or line  96 ). 
     Element  98  may be formed from one or more electrical components. Components that may be used as all or part of element  98  include resistors, inductors, and capacitors. Desired resistances, inductances, and capacitances for element  98  may be formed using integrated circuits, using discrete components and/or using dielectric and conductive structures that are not part of a discrete component or an integrated circuit. For example, a resistance can be formed using thin lines of a resistive metal alloy, capacitance can be formed by spacing two conductive pads close to each other that are separated by a dielectric, and an inductance can be formed by creating a conductive path on a printed circuit board. These types of structures may be referred to as resistors, capacitors, and/or inductors or may be referred to as capacitive antenna feed structures, resistive antenna feed structures and/or inductive antenna feed structures. 
     An illustrative configuration for antenna  40  in which component  98  of the schematic diagram of  FIG. 7  has been implemented using an inductor is shown in  FIG. 8 . As shown in  FIG. 8 , loop  92  ( FIG. 7 ) may be implemented using conductive regions  70  and the conductive portions of region  68  that run along edge  76  of opening  72 . Antenna  40  of  FIG. 8  may be fed using positive antenna feed terminal  58  and ground antenna feed terminal  54 . Terminals  54  and  58  may be located in the vicinity of gap  18  to reduce electric field concentrations in gap  18  and thereby reduce the sensitivity of antenna  40  to touch events. 
     The presence of inductor  98  may at least partly help match the impedance of transmission line  52  to antenna  40 . If desired, inductor  98  may be formed using a discrete component such as a surface mount technology (SMT) inductor. The inductance of inductor  98  may also be implemented using an arrangement of the type shown in  FIG. 9 . With the configuration of  FIG. 9 , the loop conductor of parallel-fed loop antenna  40  may have an inductive segment SG that runs parallel to ground plane edge GE. Segment SG may be, for example, a conductive trace on a printed circuit board or other conductive member. A dielectric opening DL (e.g., an air-filled or plastic-filled opening) may separate edge portion GE of ground  68  from segment SG of conductive loop portion  70 . Segment SG may have a length L. Segment SG and associated ground GE form a transmission line with an associated inductance (i.e., segment SG and ground GE form inductor  98 ). The inductance of inductor  98  is connected in parallel with feed terminals  54  and  58  and therefore forms a parallel inductive tuning element of the type shown in  FIG. 8 . Because inductive element  98  of  FIG. 9  is formed using a transmission line structure, inductive element  98  of  FIG. 9  may introduce fewer losses into antenna  40  than arrangements in which a discrete inductor is used to bridge the feed terminals. For example, transmission-line inductive element  98  may preserve high-band performance (illustrated as satisfactory resonant peak  94  of  FIG. 6 ), whereas a discrete inductor might reduce high-band performance. 
     Capacitive tuning may also be used to improve impedance matching for antenna  40 . For example, capacitor  100  of  FIG. 10  may be connected in series with center conductor  56  of coaxial cable  52  or other suitable arrangements can be used to introduce a series capacitance into the antenna feed. As shown in  FIG. 10 , capacitor  100  may be interposed in coaxial cable center conductor  56  or other conductive structures that are interposed between the end of transmission line  52  and positive antenna feed terminal  58 . Capacitor  100  may be formed by one or more discrete components (e.g., SMT components), by one or more capacitive structures (e.g., overlapping printed circuit board traces that are separated by a dielectric, etc.), lateral gaps between conductive traces on printed circuit boards or other substrates, etc. 
     The conductive loop for loop antenna  40  of  FIG. 10  is formed by conductive structures  70  and the conductive portions of ground conductive structures  66  along edge  76 . Loop currents can also pass through other portions of ground plane  68 , as illustrated by current paths  102 . Positive antenna feed terminal  58  is connected to one end of the loop path and ground antenna feed terminal  54  is connected to the other end of the loop path. Inductor  98  bridges terminals  54  and  58  of antenna  40  of  FIG. 10 , so antenna  40  forms a parallel-fed loop antenna with a bridging inductance (and a series capacitance from capacitor  100 ). 
     During operation of antenna  40 , a variety of current paths  102  of different lengths may be formed through ground plane  68 . This may help to broaden the frequency response of antenna  40  in bands of interest. The presence of tuning elements such as parallel inductance  98  and series capacitance  100  may help to form an efficient impedance matching circuit for antenna  40  that allows antenna  40  to operate efficiently at both high and low bands (e.g., so that antenna  40  exhibits high-band resonance peak  94  of  FIG. 6  and low-band resonance peak  92  of  FIG. 6 ). 
     A simplified Smith chart showing the possible impact of tuning elements such as inductor  98  and capacitor  100  of  FIG. 10  on parallel-fed loop antenna  40  is shown in  FIG. 11 . Point Y in the center of chart  104  represents the impedance of transmission line  52  (e.g., a 50 ohm coaxial cable impedance to which antenna  40  is to be matched). Configurations in which the impedance of antenna  40  is close to point Y in both the low and high bands will exhibit satisfactory operation. 
     With parallel-fed antenna  40  of  FIG. 10 , high-band matching is relatively insensitive to the presence or absence of inductive element  98  and capacitor  100 . However, these components may significantly affect low band impedance. Consider, as an example, an antenna configuration without either inductor  98  or capacitor  100  (i.e., a parallel-fed loop antenna of the type shown in  FIG. 4 ). In this type of configuration, the low band (e.g., the band at frequency f 1  of  FIG. 6 ) may be characterized by an impedance represented by point X 1  on chart  104 . When an inductor such as parallel inductance  98  of  FIG. 9  is added to the antenna, the impedance of the antenna in the low band may be characterized by point X 2  of chart  104 . When a capacitor such as capacitor  100  is added to the antenna, the antenna may be configured as shown in  FIG. 10 . In this type of configuration, the impedance of the antenna  40  may be characterized by point X 3  of chart  104 . 
     At point X 3 , antenna  40  is well matched to the impedance of cable  50  in both the high band (frequencies centered about frequency f 2  in  FIG. 6 ) and the low band (frequencies centered about frequency f 1  in  FIG. 6 ). This may allow antenna  40  to support desired communications bands of interest. For example, this matching arrangement may allow antennas such as antenna  40  of  FIG. 10  to operate in bands such as the communications bands at 850 MHz and 900 MHz (collectively forming the low band region at frequency f 1 ) and the communications bands at 1800 MHz, 1900 MHz, and 2100 MHz (collectively forming the high band region at frequency f 2 ). 
     Moreover, the placement of point X 3  helps ensure that detuning due to touch events is minimized. When a user touches housing  12  of device  10  in the vicinity of antenna  40  or when other external objects are brought into close proximity with antenna  40 , these external objects affect the impedance of the antenna. In particular, these external objects may tend to introduce a capacitive impedance contribution to the antenna impedance. The impact of this type of contribution to the antenna impedance tends to move the impedance of the antenna from point X 3  to point X 4 , as illustrated by line  106  of chart  104  in  FIG. 11 . Because of the original location of point X 3 , point X 4  is not too far from optimum point Y. As a result, antenna  40  may exhibit satisfactory operation under a variety of conditions (e.g., when device  10  is being touched, when device  10  is not being touched, etc.). 
     Although the diagram of  FIG. 11  represents impedances as points for various antenna configurations, the antenna impedances are typically represented by a collection of points (e.g., a curved line segment on chart  104 ) due to the frequency dependence of antenna impedance. The overall behavior of chart  104  is, however, representative of the behavior of the antenna at the frequencies of interest. The use of curved line segments to represent frequency-dependent antenna impedances has been omitted from  FIG. 11  to avoid over-complicating the drawing. 
     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: 20091203
Publication Date: 20120918
Grant Date: 20120918
Priority Date: 20091203
Inventors: PASCOLINI MATTIA
HILL ROBERT J.
ZAVALA JUAN
JIN NANBO
LI QINGXIANG
SCHLUB ROBERT W.
CABALLERO RUBEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 43828008