PATENT DOCUMENT

Publication Number: US-9190712-B2
Application Number: US-201213366142-A
Country: US
Kind Code: B2

Title: Tunable antenna system

Abstract:
An electronic device antenna may be provided with an antenna ground. An antenna resonating element may have a first end that is coupled to the ground using an inductor and may have a second end that is coupled to a peripheral conductive housing member in an electronic device. The peripheral conductive housing member may have a portion that is connected to the ground and may have a portion that is separated from the ground by a gap. The gap may be bridged by an inductor that couples the second end of the antenna resonating element to the antenna ground. The inductor may be bridged by a switch. A tunable circuit such as a capacitor bridged by a switch may be interposed in the antenna resonating element. The switches that bridge the gap and the capacitor may be used in tuning the antenna.

Claims:
What is claimed is: 
     
       1. An antenna, comprising:
 a ground plane; 
 a first arm that has opposing first and second ends, that includes first and second segments, and that is electrically coupled to the ground plane; 
 an antenna feed coupled between the ground plane and the second end of the first arm; 
 a tunable circuit interposed in the first arm between the first and second segments; 
 a second arm having a first end that is directly connected to the first end of the first arm and having a second end that is coupled to the ground plane; and 
 an inductor that electrically couples the second end of the first arm to the ground plane. 
 
     
     
       2. The antenna defined in  claim 1  further comprising a switch that is coupled between the end of the first arm and the ground plane. 
     
     
       3. The antenna defined in  claim 1  wherein the tunable circuit comprises a variable capacitor. 
     
     
       4. The antenna defined in  claim 1  wherein the tunable circuit comprises a capacitor. 
     
     
       5. The antenna defined in  claim 1  wherein the tunable circuit comprises a switch and a capacitor in parallel with the switch. 
     
     
       6. The antenna defined in  claim 1  wherein the tunable circuit comprises a first switch and a capacitor in parallel with the first switch, the antenna further comprising a switch that is coupled between the end of the first arm and the ground plane. 
     
     
       7. The antenna defined in  claim 1  wherein the second arm comprises at least part of a peripheral conductive member that runs around at least some edges of a housing for an electronic device. 
     
     
       8. The antenna defined in  claim 7  further comprising a gap in the peripheral conductive member, wherein the antenna further comprises an inductor that bridges the gap. 
     
     
       9. The antenna defined in  claim 8  further comprising a switch that bridges the gap. 
     
     
       10. The antenna defined in  claim 8  further comprising a first switch that bridges the gap, wherein the tunable circuit comprises a second switch and a capacitor in parallel with the second switch. 
     
     
       11. An antenna, comprising:
 an antenna ground; 
 a resonating element arm having opposing first and second ends; 
 an antenna feed coupled between the antenna ground and the resonating element arm; 
 a first inductor that is coupled between the resonating element arm and the antenna ground at the first end; 
 a peripheral conductive member that runs around at least some edges of a conductive housing for an electronic device, wherein portions of the peripheral conductive member are separated from the antenna ground by first and second gaps that create respective parasitic capacitances between the peripheral conductive member and the antenna ground and that divide the peripheral conductive member into at least three segments; and 
 a second inductor that is coupled between the peripheral conductive member and the antenna ground and that bridges the second gap. 
 
     
     
       12. The antenna defined in  claim 11  further comprising a switch that is coupled in parallel with the second inductor. 
     
     
       13. The antenna defined in  claim 11  further comprising a switch that is coupled in parallel with the second inductor and the second gap. 
     
     
       14. The antenna defined in  claim 13  wherein the peripheral conductive member has a first portion that is electrically connected to the antenna ground and a second portion that is separated from the antenna ground by the second gap, and the second end of the antenna resonating element arm is coupled to the second portion of the peripheral conductive member. 
     
     
       15. The antenna defined in  claim 11  further comprising a tunable circuit that is interposed in the antenna resonating element arm. 
     
     
       16. The antenna defined in  claim 15  wherein the tunable circuit includes a capacitor. 
     
     
       17. An antenna, comprising:
 an antenna ground; 
 a peripheral conductive member that runs around at least two external edges of a housing for an electronic device; 
 a resonating element arm having a first end that is coupled to the antenna ground and a second end that is coupled to the peripheral conductive member; 
 an antenna feed coupled between the ground plane and the resonating element arm; and 
 a switch that is coupled between the peripheral conductive member and the antenna ground. 
 
     
     
       18. The antenna defined in  claim 17  wherein the peripheral conductive member is separated from the antenna ground by at least one gap that creates a parasitic capacitance between the peripheral conductive member and the antenna ground and wherein the switch bridges the gap. 
     
     
       19. The antenna defined in  claim 18  further comprising a capacitor interposed in the antenna resonating element arm. 
     
     
       20. The antenna defined in  claim 19  further comprising an additional switch that bridges the capacitor. 
     
     
       21. The antenna defined in  claim 20  further comprising:
 an inductor coupled in parallel with the switch. 
 
     
     
       22. The antenna defined in  claim 1 , wherein the tunable circuit is interposed in the first arm at a location between the antenna feed and where the first end of the first arm and the first end of the second arm are directly connected. 
     
     
       23. The antenna defined in  claim 17 , wherein the peripheral conductive member has portions that are separated from the antenna ground by first and second gaps that create respective parasitic capacitances between the peripheral conductive member and the antenna ground and divide the peripheral conductive member into at least three segments.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to antennas for electronic devices with wireless communications circuitry. 
     Electronic devices such as portable computers and cellular telephones 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. Electronic devices may use short-range wireless communications circuitry such as wireless local area network communications circuitry to handle communications with nearby equipment. Electronic devices may also be provided with satellite navigation system receivers and other wireless circuitry. 
     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. Moreover, care must be taken to ensure that the antennas and wireless circuitry in a device are able to exhibit satisfactory performance over a range of operating frequencies. 
     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 contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may form one or more antennas. 
     An electronic device antenna may be provided with an antenna ground. An antenna resonating element may have an arm with a first end that is coupled to the ground using an inductor and a second end that is coupled to a peripheral conductive housing member in an electronic device. The peripheral conductive housing member may have a portion that is connected to the ground and may have a portion that is separated from the ground by a gap. The gap may be bridged by an inductor that couples the second end of the antenna resonating element to the antenna ground. The inductor may be bridged by a switch. A tunable circuit such as a capacitor bridged by a switch may be interposed in the antenna resonating element arm. The switches that bridge the gap and the capacitor may be used in tuning the antenna. 
     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 diagram of an illustrative electronic device of the type shown in  FIG. 1  showing how structures in the device may form a ground plane and other antenna structures in accordance with an embodiment of the present invention. 
         FIG. 4  is diagram of an illustrative tunable antenna in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative inverted-F antenna structure for an antenna in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph of antenna performance associated with use of the antenna structure of  FIG. 5  in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram of illustrative inverted-F antenna structures with an inductor path in parallel with an antenna feed for an antenna in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of illustrative antenna structures with an inductor path in parallel with an antenna feed and an L-shaped parasitic antenna resonating element for an antenna in accordance with an embodiment of the present invention. 
         FIG. 9  is a graph of antenna performance associated with use of the antenna structures of  FIG. 8  in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of illustrative antenna structures of the type shown in  FIG. 8  that have been provided with a bypassable capacitor circuit for performing antenna tuning functions in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph of antenna performance associated with use of the antenna structures of  FIG. 10  in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram of illustrative antenna structures of the type shown in  FIG. 10  that have been provided with a tuning circuit such as a switch-based tuning circuit to form an antenna of the type shown in  FIG. 4  in accordance with an embodiment of the present invention. 
         FIGS. 13 and 14  are graphs of antenna performance associated with use of the antenna of  FIG. 12  in accordance with an embodiment of the present invention. 
         FIG. 15  is a diagram of illustrative antenna structures of the type shown in  FIG. 12  in which the switch-based tuning circuitry of  FIG. 12  had been replaced with a passive resonant-circuit in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  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, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas 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 peripheral conductive member that runs around the periphery of an electronic device. The peripheral conductive member may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, and/or may form other housing structures. Gaps in the peripheral conductive member may be associated with the antennas. 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, or a media player. Device  10  may also be a television, a set-top box, a desktop computer, a computer monitor into which a computer has been integrated, or other suitable electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), 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. In other situations, housing  12  or at least some of the structures that make up 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 from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. A cover glass layer may cover the surface of display  14 . Buttons such as button  19  may pass through openings in the cover glass. The cover glass may also have other openings such as an opening for speaker port  26 . 
     Housing  12  may include a peripheral member such as member  16 . Member  16  may run around the periphery of device  10  and display  14 . In configurations in which device  10  and display  14  have a rectangular shape, member  16  may have a rectangular ring shape (as an example). Member  16  or part of member  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or helps hold display  14  to device  10 ). Member  16  may also, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls, etc.). 
     Member  16  may be formed of a conductive material and may therefore sometimes be referred to as a peripheral conductive member or conductive housing structures. Member  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, three, or more than three separate structures may be used in forming member  16 . 
     It is not necessary for member  16  to have a uniform cross-section. For example, the top portion of member  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. If desired, the bottom portion of member  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 , member  16  has substantially straight vertical sidewalls. This is merely illustrative. The sidewalls of member  16  may be curved or may have any other suitable shape. In some configurations (e.g., when member  16  serves as a bezel for display  14 ), member  16  may run around the lip of housing  12  (i.e., member  16  may cover only the edge of housing  12  that surrounds display  14  and not the rear edge of housing  12  of the sidewalls of housing  12 ). 
     Display  14  may include conductive structures such as an array of capacitive electrodes, conductive lines for addressing pixel elements, driver circuits, etc. Housing  12  may include internal structures such as metal frame members, a planar housing member (sometimes referred to as a midplate) that spans the walls of housing  12  (i.e., a substantially rectangular member that is welded or otherwise connected between opposing sides of member  16 ), printed circuit boards, and other internal conductive structures. These conductive structures may be located in the center of housing  12  under display  14  (as an example). 
     In regions  22  and  20 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive member  16  and opposing conductive structures such as conductive housing structures, a conductive ground plane associated with a printed circuit board, and conductive electrical components in device  10 ). These openings may be filled with air, plastic, and other dielectrics. Conductive housing structures and other conductive structures in device  10  may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . 
     In general, device  10  may include any suitable number of antennas (e.g., one or more, two or more, three or more, four or more, etc.). The antennas in device  10  may be located at opposing first and second ends of an elongated device housing, along one or more edges of a device housing, in the center of a device housing, in other suitable locations, or in one or more of such locations. The arrangement of  FIG. 1  is merely illustrative. 
     Portions of member  16  may be provided with gap structures. For example, member  16  may be provided with one or more gaps such as gaps  18 , as shown in  FIG. 1 . The gaps may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  18  may divide member  16  into one or more peripheral conductive member segments. There may be, for example, two segments of member  16  (e.g., in an arrangement with two gaps), three segments of member  16  (e.g., in an arrangement with three gaps), four segments of member  16  (e.g., in an arrangement with four gaps, etc.). The segments of peripheral conductive member  16  that are formed in this way may form parts of antennas in device  10 . 
     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 antennas may be used separately to cover identical communications bands, overlapping communications bands, or distinct non-overlapping communications bands. The antennas may be used to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. 
     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 or other satellite navigation system communications, Bluetooth® communications, etc. 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , electronic 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 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application 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. 
     Circuitry  28  may be configured to implement control algorithms that control the use of antennas in device  10 . For example, circuitry  28  may perform signal quality monitoring operations, sensor monitoring operations, and other data gathering operations and may, in response to the gathered data and/or information on which communications bands are to be used in device  10 , control which antenna structures within device  10  are being used to receive and process data and/or may adjust one or more switches, tunable elements, or other adjustable circuits in device  10  to adjust antenna performance. As an example, circuitry  28  may control which of two or more antennas is being used to receive incoming radio-frequency signals, may control which of two or more antennas is being used to transmit radio-frequency signals, may control the process of routing incoming data streams over two or more antennas in device  10  in parallel, may tune an antenna to cover desired communications bands, etc. In performing these control operations, circuitry  28  may open and close switches, may turn on and off receivers and transmitters, may adjust impedance matching circuits, may configure switches in front-end-module (FEM) radio-frequency circuits that are interposed between radio-frequency transceiver circuitry and antenna structures (e.g., filtering and switching circuits used for impedance matching and signal routing), may adjust switches, tunable circuits, and other adjustable circuit elements that are formed as part of an antenna or that are coupled to an antenna or a signal path associated with an antenna, and may otherwise control and adjust the components of device  10 . 
     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 circuitry  30  may include input-output devices  32 . Input-output devices  32  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  32  and may receive status information and other output from device  10  using the output resources of input-output devices  32 . 
     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 satellite navigation system receiver circuitry such as Global Positioning System (GPS) receiver circuitry  35  (e.g., for receiving satellite positioning signals at 1575 MHz) or satellite navigation system receiver circuitry associated with other satellite navigation systems. 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 bands in frequency ranges of about 700 MHz to about 2700 MHz or bands at higher or lower frequencies. 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 or other satellite navigation system 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 one or more 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, closed and open slot antenna structures, planar inverted-F antenna structures, helical antenna structures, strip antennas, monopoles, dipoles, 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. 
     A top interior view of device  10  in a configuration in which device  10  has a peripheral conductive housing member such as housing member  16  of  FIG. 1  with one or more gaps  18  is shown in  FIG. 3 . As shown in  FIG. 3 , device  10  may have an antenna ground plane such as antenna ground plane  52 . Ground plane  52  may be formed from traces on printed circuit boards (e.g., rigid printed circuit boards and flexible printed circuit boards), from conductive planar support structures in the interior of device  10 , from conductive structures that form exterior parts of housing  12 , from conductive structures that are part of one or more electrical components in device  10  (e.g., parts of connectors, switches, cameras, speakers, microphones, displays, buttons, etc.), or other conductive device structures. Gaps such as gaps  82  may be filled with air, plastic, or other dielectric. 
     One or more segments of peripheral conductive member  16  may serve as part of the conductive structures for an antenna in device  10 . For example, the lowermost segment of peripheral conductive member  16  in region  20  may serve as part of the conductive structures for an antenna in device  10 . These structures may be provided with switches and other adjustable components or may be provided with fixed components. In arrangements in which an antenna is provided with adjustable components, the antenna may be tuned during operation to cover communications bands of interest. Tunable antennas  40  in device  10  may be implemented using antenna structures in region  22  and/or region  20 . Illustrative tunable antenna structures of the type that may be used in region  20  are sometimes described herein as an example. 
     An illustrative antenna  40  that has been implemented in region  20  of device  10  is shown in  FIG. 4 . Antenna  40  of  FIG. 4  may have an antenna feed such as antenna feed  106 . Antenna feed  106  may have a positive antenna feed terminal such as positive antenna feed terminal  92  (+) and a ground antenna feed terminal such as ground antenna feed terminal  94  (−). Wireless circuitry such as radio-frequency transceiver circuitry  108  (e.g., transceiver circuitry such as circuitry  38  of  FIG. 2  or other suitable radio-frequency transceiver circuitry) may be coupled to antenna feed  106  using signal paths such as path  90 . Path  90  may include one or more transmission lines such as coaxial cable transmission lines, microstrip transmission lines, stripline transmission lines, or other transmission line structures. As shown in  FIG. 4 , path  90  may include a positive signal conductor such as conductor  90 P and a ground signal conductor such as conductor  90 N. Impedance matching circuits, filters, switches, and other circuits may be interposed within path  90 , if desired. 
     Conductive structures  52  may form part of antenna (e.g., an antenna ground plane). Antenna  40  may also include conductive structures such as conductive arm  96  and a conductive arm formed from peripheral conductive member  16 . Conductive arm  96  may be formed from a strip of metal or other conductive materials. Conductive arm  96  may, for example, be formed from a patterned metal trace on a flexible printed circuit, rigid printed circuit, plastic support structure, or other substrate. Arm  96  may have an L-shape, a shape with two or more straight segments, a shape with curved segments or a combination of curved and straight segments, or other suitable shape. Antenna feed  106  may be coupled between arm  96  and conductive ground plane structures  52 . Inductor L 2  (e.g., a discrete inductor component such as a surface mount technology component or other inductive element) may be coupled between arm  96  and ground plane structures  52  at a first end of arm  96 . Another inductor such as inductor L 1  may be coupled to an opposing second end of arm  96 . 
     A circuit such as tunable circuit  98  may be interposed in arm  96 . Circuit  98  may include one or more adjustable components that may be used in tuning antenna  40 . As shown in  FIG. 4 , for example, circuit  98  may include a capacitor such as capacitor C 2  (e.g., a tunable capacitor or a fixed capacitor) and a bypass switch such as switch SW 2 . Circuit  98  may have a first terminal such as terminal  100  and a second terminal such as terminal  102 . Capacitor C 2  and switch SW 2  may be coupled in parallel between terminals  100  and  102 . The state of switch SW 2  may be controlled by control signals from control circuitry in device  10  such as storage and processing circuitry  28  (e.g., a baseband processor). Switch control signals may be provided to switch SW 2  over a control signal path such as path  104 . When switch SW 2  is open, capacitance C 2  (e.g., a fixed or variable capacitance) may be interposed in arm  96 . When switch SW 2  is closed, capacitance C 2  may be bypassed. Other types of adjustable capacitance circuitry may be interposed in arm  96  if desired. The example of  FIG. 4  is merely illustrative. 
     Peripheral conductive member  16  may form a conductive path (arm) that is shorted to antenna ground  52  at one end (e.g., on the left-hand side of gap  82  at location  101 ) and that is separated from ground  52  (e.g., portions of member  16  that are shorted to ground  52 ) at another end (e.g., at gap  18 ). Gap  18  may give rise to a parasitic capacitance C 1  between the end of arm  96  and ground structure  52 . 
     An antenna tuning circuit such as a circuit formed from inductor L 1  and switch SW 1  may bridge gap  18 . The state of switch SW 1  may be controlled by control signals from control circuitry in device  10  such as storage and processing circuitry  28  (e.g., a baseband processor). Switch control signals may be provided to switch SW 1  over a control signal path such as path  106 . When switch SW 1  is open, inductor L 1  may be coupled across gap  18  in parallel with parasitic capacitance C 1 . When switch SW 1  is closed, inductor L 1  and capacitance C 1  may be bypassed by the short circuit formed by switch SW 1  (i.e., gap  18  may be temporarily bridged by the short circuit formed by switch SW 1 ). 
     Antenna tuning adjustments may be made to antenna  40  to configure antenna  40  to cover desired operating frequencies. The frequency response of antenna  40  may be tuned by adjusting adjustable components in antenna  40  such as capacitor C 2 , switch SW 2 , and switch SW 1 . If desired, additional adjustable circuitry may be used (e.g., adjustable matching circuits, additional switches in antenna  40 , etc.). 
     The way in which antenna  40  of  FIG. 4  operates may be understood with reference to  FIGS. 5-14 , which show how antenna  40  of  FIG. 4  may be constructed by adding progressively more components to an inverted-F antenna (i.e., antenna  40 ′ of  FIG. 5 ). 
     As shown in  FIG. 5 , antenna  40 ′ may have an antenna resonating element such as antenna resonating element  118  and a ground structure such as ground  52 . Antenna resonating element  118  may have a main resonating element arm such as arm  96 . Short circuit branch  114  may couple arm  96  to ground  52 . Antenna feed  106  may contain positive antenna feed terminal  92  (+) and ground antenna feed terminal  94  (−). Antenna feed  106  may be formed using a branch of antenna resonating element  118  that couples arm  96  to ground  52 . 
       FIG. 6  is a graph of antenna performance (standing wave ratio) as a function of operating frequency for an antenna such as inverted-F antenna  40 ′ of  FIG. 5 . As shown by curve  120  of  FIG. 6 , antenna  40 ′ of  FIG. 5  may exhibit a resonance in a communications band centered on frequency fc. During operation, signals in this communications band may be transmitted and received using antenna  40 ′. 
     If desired, short circuit branch  114  of antenna resonating element  118  in antenna  40 ′ may be implemented using a discrete component such as a surface mount technology (SMT) inductor or other inductor. This type of configuration for antenna  40 ′ is shown in  FIG. 7 . As shown in  FIG. 7 , inductor L 2  may be coupled between arm  96  and ground  52  in place of short circuit branch  114  of  FIG. 5  (e.g., at the leftmost end of arm  96  in the orientation of  FIG. 7 ). Branch  114  of  FIG. 5  may be characterized by a finite inductance. The resulting frequency response of antenna  40 ′ when inductor L 2  of  FIG. 7  is used in place of short circuit branch  114  of  FIG. 5  may therefore still be characterized by a curve such as curve  120  of  FIG. 6 . 
     If desired, antenna  40 ′ may be provided with a parasitic antenna resonating element such as L-shaped parasitic antenna resonating element  16  of  FIG. 8  (e.g., a portion of peripheral conductive member  16  of  FIG. 4 ). Parasitic antenna resonating element  16  may, for example, have an arm that runs parallel to arm  96 . The lengths of the L-shaped parasitic antenna resonating element arm and the inverted-F antenna resonating element arm in antenna  40 ′ may be different. For example, parasitic antenna resonating element arm  16  may be longer than arm  96 . This may help to broaden the frequency response of antenna  40 ′. 
       FIG. 9  is a graph of antenna performance (standing wave ratio) as a function of operating frequency for an antenna such as inverted-F antenna  40 ′ of  FIG. 8 . Parasitic antenna resonating element  16  may be characterized by a resonance such as the resonance of curve  124 , centered at frequency fb. In the absence of parasitic antenna resonating element  16 , antenna  40 ′ (i.e., antenna resonating element arm  96 ) may be characterized by curve  126 , which exhibits a resonance centered at frequency fc. When inverted-F antenna resonating element arm  96  and parasitic antenna resonating element  16  are both present, as in  FIG. 8 , antenna  40 ′ may exhibit a response of the type shown by curve  128 . Because curve  128  is influenced by both the shorter antenna arm (resonating element arm  96 ) and the longer antenna arm (parasitic antenna resonating element arm  16 ), the resonance of curve  128  may be broader than the resonance of curve  120  of  FIG. 6 . 
     As shown in  FIG. 10 , antenna  40 ′ may be provided with a tunable circuit such as tunable circuit  98  in arm  96  and may have conductive structures such as conductive path  130  that couples antenna resonating element arm  96  to arm  16 . Circuit  98  may include a capacitor such as capacitor C 2 . Capacitor C 2  may be a fixed capacitor or may be a variable capacitor. Switch SW 2  may be used to selectively bypass capacitor C 2 . Circuit  98  may be formed using one or more components. For example, capacitor C 2  and switch SW 2  may be formed using individual components or may be formed using a single unitary part. 
       FIG. 11  is a graph of antenna performance (standing wave ratio) as a function of operating frequency for an antenna such as antenna  40 ′ of  FIG. 10 . In the absence of capacitor C 2 , antenna  40 ′ may be characterized by curve  128  (i.e., curve  128  of  FIG. 9 ). When capacitance C 2  is present, however, antenna  40 ′ may be characterized by narrower curve  132 . If, for example, curve  128  is characterized by frequency resonance peaks fb (from element  16 ) and fc (from element  96 ), curve  132  may be characterized by frequency response peaks at frequency fb′ (i.e., a frequency greater than fb) and at frequency fc′ (i.e., a frequency less than fc). Capacitance C 2  may be switched into use (e.g., by opening switch SW 2 ) to ensure that the response of antenna  40 ′ matches a desired communications band of interest (e.g., so that antenna  40 ′ exhibits the narrower resonance of curve  132  of  FIG. 11 ). In configurations in which capacitance C 2  is variable, the magnitude of capacitance C 2  may be adjusted to adjust the width of curve  132 . 
     As shown in  FIG. 12 , when capacitor C 1  (e.g., a parasitic capacitance associated with gap  18  of  FIG. 4 ), inductor L 1 , and switch SW 1  are coupled between tip  132  of arm  96  (and/or an associated portion of arm  16 ) and ground (e.g., across gap  18  of  FIG. 4 ), antenna  40 ′ of  FIG. 10  may have the configuration of antenna  40  of  FIG. 4  (i.e., antenna  40  of  FIG. 12  may be implemented using structures of the type shown in  FIG. 4 ). If desired, antenna  40  of  FIG. 12  may be implemented using other structures. The antenna structures and circuitry of  FIG. 4  are merely an illustrative example of structures and circuits that can be used in implementing antenna  40  of  FIG. 12 . 
       FIGS. 13 and 14  are graphs showing how antenna  40  of  FIG. 12  may perform as a function of operating frequency and how antenna  40  may be tuned by controlling the states of switches SW 1  and SW 2 .  FIG. 13  is a graph of antenna performance (standing wave ratio) as a function of operating frequency for an antenna such as antenna  40  of  FIG. 12  in a configuration in which switches SW 1  and SW 2  are both open. Operating frequencies from about 700-960 MHz may correspond to a “low” communications band for antenna  40  (as an example). In this low band, inductor L 1  and capacitance C 1  may form a resonant circuit with a relatively large impedance (i.e., inductor L 1  and C 1  may form an open circuit at frequencies in the range of 700-960 MHz). Because the circuit formed by L 1  and C 1  is effectively open and because switch SW 1  is open, the shape of low band curve portion  136  of  FIG. 13  may match that of curve  132  in  FIG. 11  (the shape of which may be tuned by adjusting capacitance C 2  in configurations for antenna  40  in which capacitor C 2  is a variable capacitor). At higher frequencies (e.g., frequencies in the vicinity of 2300 MHz to 2700 MHz or other suitable frequency range), antenna  40  of  FIG. 12  may exhibit a resonant peak such as resonant peak  138  (i.e., antenna  40  may exhibit performance satisfactory for handling communications at frequencies from 2300 MHz to 2700 MHz while switches SW 1  and SW 2  are open). 
     When it is desired to cover lower high-band frequencies such as frequencies from 1710 MHz to 2170 MHz (or other suitable frequency range), control circuitry in device  10  may be used to close switches SW 1  and SW 2 . In this configuration, antenna  40  of  FIG. 12  may exhibit a response of the type shown by curve  140  of  FIG. 14 . The response of curve  140  may be influenced by contributions from two different loop antenna modes in antenna  40  of  FIG. 12 . As shown in  FIG. 12 , antenna  40  may, have a first (longer) loop antenna mode associated with loop-shaped signal path  148  and may have a second (shorter) loop antenna mode associated with loop-shaped signal path  150  of  FIG. 12 . The shorter loop antenna mode may give rise to resonant contribution  144  of curve  140  of  FIG. 14 . The longer loop antenna mode may give rise to resonant contribution  142  of curve  140  of  FIG. 14 . 
     In the illustrative configuration of  FIG. 12 , antenna  40  has actively adjusted components such as switches SW 1  and SW 2  for ensuring that antenna  40  exhibits a desired response as a function of frequency. If desired, passive switching techniques may be used to perform switching in antenna  40 . For example, an arrangement of the type shown in  FIG. 15  may be used for antenna  40  in which switch SW 1  is replaced by resonant circuit  146 . Resonant circuit  146  and capacitor C 1  may be configured to form a resonant circuit with an impedance that changes as a function of frequency. Circuit  146  may be configured so that a short circuit is formed across gap  18  at frequencies from 1710 MHz to 2170 MHz (or other suitable frequency range) and to form a high impedance (e.g., an open circuit) at other frequencies (e.g., the low band and/or the high band of  FIG. 13 ). When configured in this way, circuit  146  can form a short circuit of the type formed by closed switch SW 2  of  FIG. 12  during operation at 1710 MHz to 2170 MHz (e.g., to produce curve  140  of  FIG. 14 ) and can form an open circuit at other frequencies such as the frequencies associated with the low band (700-960 MHz) and high band (2300-2700 MHz) (e.g., to produce curves  136  and  138  of  FIG. 13 ). 
     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: 20120203
Publication Date: 20151117
Grant Date: 20151117
Priority Date: 20120203
Inventors: HU HONGFEI
PASCOLINI MATTIA
SCHLUB ROBERT W.
MOW MATTHEW A.
JIN NANBO
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 47604181