PATENT DOCUMENT

Publication Number: US-9166279-B2
Application Number: US-201113041905-A
Country: US
Kind Code: B2

Title: Tunable antenna system with receiver diversity

Abstract:
A wireless electronic device may include antenna structures and antenna tuning circuitry. The device may include a display mounted within a housing. A peripheral conductive member may run around the edges of the display and housing. Dielectric-filled gaps may divide the peripheral conductive member into individual segments. A ground plane may be formed within the housing. The ground plane and the segments of the peripheral conductive member may form antennas in upper and lower portions of the housing. The antenna tuning circuitry may include switchable inductor circuits and variable capacitor circuits for the upper and lower antennas. The switchable inductor circuits associated with the upper antenna may be tuned to provide coverage in at least two high-band frequency ranges of interest, whereas the variable capacitor circuits associated with the upper antenna may be tuned to provide coverage in at least two low-band frequency ranges of interest.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a housing having a conductive member that runs around a periphery of the housing; 
 an inverted-F antenna that is formed from an antenna ground and a portion of the conductive member, wherein the inverted-F antenna is configured to operate in a low-band frequency range centered at a first frequency and a high-band frequency range centered at a second frequency that is greater than the first frequency; and 
 a switchable inductor coupled between the antenna ground and the portion of the peripheral conductive member, wherein the switchable inductor is configured to center the high-band frequency range at a third frequency that is greater than the first and second frequencies while the inverted-F antenna maintains operation in the low-band frequency range centered at the first frequency. 
 
     
     
       2. The electronic device defined in  claim 1 , wherein the conductive member comprises at least one gap that divides the conductive member into a plurality of segments and wherein the portion includes at least one of the plurality of segments. 
     
     
       3. The electronic device defined in  claim 2 , wherein the antenna ground includes conductive housing structures formed within the electronic device. 
     
     
       4. The electronic device defined in  claim 3 , wherein the conductive housing structures comprises a printed circuit board. 
     
     
       5. The electronic device defined in  claim 2 , wherein the inverted-F antenna comprises first and second antenna feed terminals and wherein the switchable inductor is coupled between the first and second antenna feed terminals. 
     
     
       6. The electronic device defined in  claim 5 , wherein the switchable inductor comprises an inductor and a switch that are connected in series between the first and second antenna feed terminals. 
     
     
       7. The electronic device defined in  claim 6 , further comprising:
 wireless transceiver circuitry, wherein the wireless transceiver circuitry is coupled to the first antenna feed terminal. 
 
     
     
       8. The electronic device defined in  claim 7 , further comprising:
 a conductive path coupled in parallel with the switchable inductor between the first and second antenna feed terminals. 
 
     
     
       9. The electronic device defined in  claim 8 , further comprising:
 a variable capacitor circuit that bridges the at least one gap in the conductive member. 
 
     
     
       10. A wireless electronic device comprising:
 a housing containing conductive structures that form an antenna ground and having a conductive member that runs around a periphery of the housing; 
 an antenna that is formed from the antenna ground and a portion of the conductive member; and 
 a switchable inductor circuit coupled between the antenna ground and the portion of the conductive member, wherein:
 when the switchable inductor circuit is switched out of use, the antenna is configured to operate in a low-band frequency range and in a first high-band frequency range; and 
 when the switchable inductor circuit is switched into use, the antenna is configured to operate in the low-band frequency range and is configured to maintain operation in a second high-band frequency range that is higher in frequency than the first high-band frequency range. 
 
 
     
     
       11. The wireless electronic device defined in  claim 10 , wherein the antenna comprises first and second antenna feed terminals and wherein the switchable inductor circuit is coupled between the first and second antenna feed terminals, further comprising:
 wireless transceiver circuitry coupled to the first antenna feed terminal. 
 
     
     
       12. The wireless electronic device defined in  claim 11 , wherein the antenna comprises an inverted-F antenna. 
     
     
       13. The wireless electronic device defined in  claim 12 , wherein the conductive member has at least two gaps, further comprising:
 a variable capacitor circuit that bridges one of the two gaps. 
 
     
     
       14. The wireless electronic device defined in  claim 12 , wherein the switchable inductor circuit comprises an inductor and a switch that are connected in series between the first and second antenna feed terminals. 
     
     
       15. The wireless electronic device defined in  claim 12 , wherein the switchable inductor circuit comprises:
 a switch; 
 a first inductor, wherein the first inductor and the switch are coupled in series between the first and second antenna feed terminals; and 
 a second inductor, wherein the second inductor and the switch are coupled in series between the first and second antenna feed terminals. 
 
     
     
       16. The wireless electronic device defined in  claim 12 , wherein the switchable inductor circuit comprises:
 first and second switches; 
 a first inductor, wherein the first inductor and the first switch are coupled in series between the first and second antenna feed terminals; and 
 a second inductor, wherein the second inductor and the second switch are coupled in series between the first and second antenna feed terminals. 
 
     
     
       17. A wireless electronic device comprising:
 a housing having a periphery; 
 a conductive structure that runs along the periphery and that has at least two gaps on the periphery; and 
 an inverted-F antenna formed at least partly from an antenna ground and a portion of the conductive structure; 
 a switchable inductor coupled between the antenna ground and the portion of the conductive structure; and 
 a variable capacitor that bridges at least one of the two gaps in the conductive structure that runs along the periphery, wherein: 
 when the variable capacitor is tuned to provide a first capacitance, the inverted-F antenna is configured to operate in a first low-band frequency range and in a first high-band frequency range; and 
 when the variable capacitor is tuned to provide a second capacitance that is different than the first capacitance and the switchable inductor is switched into use, the inverted-F antenna is configured to operate in a second low-band frequency range that is lower in frequency than the first low-band frequency range and is configured to operate in a second high-band frequency range that is higher than the first high-band frequency range. 
 
     
     
       18. The wireless electronic device defined in  claim 17 , wherein the inverted-F antenna comprises first and second antenna feed terminals, further comprising:
 wireless transceiver circuitry coupled to the first antenna feed terminal. 
 
     
     
       19. The wireless electronic device defined in  claim 18 , further comprising:
 the switchable inductor coupled between the first and second antenna feed terminals. 
 
     
     
       20. The wireless electronic device defined in  claim 19 , wherein the switchable inductor comprises an inductor and a switch that are coupled in series between the first and second antenna feed terminals. 
     
     
       21. The wireless electronic device defined in  claim 20 , further comprising a conductive shorting path coupled in parallel with the switchable inductor between the first and second antenna feed terminals. 
     
     
       22. The wireless electronic device defined in  claim 17 , further comprising:
 processing circuitry, wherein the processing circuitry generates control signals that tunes the variable capacitor to provide the first and second capacitance.

Description:
BACKGROUND 
     This relates generally to wireless communications circuitry, and more particularly, to electronic devices that have 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 at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz. 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. However, it can be difficult to fit conventional antenna structures into small devices. For example, antennas that are confined to small volumes often exhibit narrower operating bandwidths than antennas that are implemented in larger volumes. If the bandwidth of an antenna becomes too small, the antenna will not be able to cover all communications bands of interest. 
     In view of these considerations, it would be desirable to provide improved wireless circuitry for 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. An electronic device may include a display mounted within a housing. A peripheral conductive member may run around the edges of the display and housing. 
     The peripheral conductive member may be divided into individual segments by forming gaps in the peripheral conductive member at various points along its length. The gaps may be filled with a dielectric such as plastic and may form an open circuit between opposing portions of the conductive member. With one illustrative configuration, three gaps may be formed in the peripheral conductive member to divide the peripheral conductive member into three respective segments. 
     A conductive housing member such as a conductive midplate member that spans the width of the housing may be connected to the peripheral conductive member at the left and right edges of the display. The conductive housing member and other conductive structures such as electrical components and printed circuits may form a ground plane. The ground plane and the peripheral conductive member segments may surround dielectric openings to form the antenna structures. For example, an upper cellular telephone antenna may be formed at an upper end of the housing and a lower cellular telephone antenna may be formed at a lower end of the housing. In the upper cellular telephone antenna, a first dielectric opening may be surrounded by at least some of a first peripheral conductive member segment and portions of the ground plane. In the lower cellular telephone antenna, a second dielectric opening may be surrounded by at least some of a second peripheral conductive member segment and portions of the ground plane. The upper cellular telephone antenna may be a two-branch inverted-F antenna. The lower cellular telephone antenna may be a loop antenna. 
     The upper and lower antennas may include associated antenna tuning circuitry. The antenna tuning circuitry may include switchable inductor circuits that bridge the first and second peripheral conductive member segments to the ground plate, tunable impedance matching circuitry, and variable capacitor circuitry bridging each of the gaps in the peripheral conductive member. The tunable matching circuitry may be used to couple the radio-frequency transceiver circuitry to the lower and upper antennas. 
     During operation of the electronic device, the lower antenna may serve as the primary cellular antenna for the device. Radio-frequency antenna signals may be transmitted and received by the lower antenna in cellular telephone bands such as the bands at 750 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz. The upper antenna may serve as a secondary antenna that allows the electronic device to implement receiver diversity. When the performance of the lower antenna drops during operation, the radio-frequency transceiver circuitry in the device can receive signals with the upper antenna rather than the lower antenna. 
     The upper antenna may support only a subset of the bands that are supported by the lower antenna. During a first antenna mode in which the switchable inductor associated with the upper antenna is turned off and the variable capacitors associated with the upper antenna is tuned to exhibit a low capacitance value, the upper antenna may support a first low-band frequency range (e.g., a low-band region that covers 850 MHz and 900 MHz) and a first high-band frequency range (e.g., a high-band region that covers 1800 MHz and 1900 MHz). The coverage of the upper antenna can be extended by tuning the antenna tuning circuitry associated with the upper antenna in real time. 
     For example, the upper antenna may be configured in a second antenna mode in which the variable capacitors are tuned to exhibit higher capacitance values so that the upper antenna may support a second low-band frequency range (e.g., a low-band region that covers 750 MHz) that is lower in frequency than the first low-band frequency range. The upper antenna may be configured in a third antenna mode in which the switchable inductor is turned on so that the upper antenna may support a second high-band frequency range (e.g., a high-band region that covers 2100 MHz) that is higher in frequency than the first high-band frequency range. 
     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 illustrative wireless circuitry including multiple antennas in accordance with an embodiment of the present invention. 
         FIGS. 5A and 5B  are circuit diagrams showing illustrative tunable impedance matching circuitry of the type that may be used in connection with the wireless circuitry of  FIG. 4  in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an electronic device of the type shown in  FIG. 1  showing how antennas with antenna tuning circuitry may be formed within the device in accordance with an embodiment of the present invention. 
         FIGS. 7-9  are diagrams of an antenna of the type shown in the upper portion of the device of  FIG. 6  in accordance with an embodiment of the present invention. 
         FIG. 10  is a chart showing how antennas of the type shown in  FIG. 6  may be used in covering communications bands of interest by adjusting associated antenna tuning circuitry in accordance with an embodiment of the present invention. 
         FIG. 11  is a plot showing how the upper antenna of  FIG. 6  may be tuned to cover multiple low-band frequency ranges of interest in accordance with an embodiment of the present invention. 
         FIG. 12  is a plot showing how the upper antenna of  FIG. 6  may be tuned to cover multiple high-band frequency ranges of interest in accordance with an embodiment 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, 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, or may form other housing structures. Gaps in the peripheral conductive member may be associated with the antennas. 
     An illustrative electronic device of the type that may be provided with one or more antennas is shown in  FIG. 1 . 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, a media player, etc. 
     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, electronic ink elements, 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. 
     Housing  12  may include structures such as peripheral member  16 . Member  16  may run around the rectangular periphery of device  10  and display  14 . 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 . 
     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, or more than two separate structures may be used in forming member  16 . In a typical configuration, member  16  may have a thickness (dimension TT) of about 0.1 mm to 3 mm (as an example). The sidewall portions of member  16  may, as an example, be substantially vertical (parallel to vertical axis V). Parallel to axis V, member  16  may have a dimension TZ of about 1 mm to 2 cm (as an example). The aspect ratio R of member  16  (i.e., the ratio R 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 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  also 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 center CN of housing  12  (as an example). 
     In regions  22  and  20 , openings may be formed between the conductive housing structures and conductive electrical components that make up device  10 . These openings may be filled with air, plastic, or other dielectrics. Conductive housing structures and other conductive structures in region CN of 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 . 
     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 A,  18 B,  18 C, and  18 D, as shown in  FIG. 1 . The gaps may be filled with dielectric such as polymer, ceramic, glass, etc. Gaps  18 A,  18 B,  18 C, and  18 D 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 separate communications bands of interest or may be used together 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 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 . This 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, to support antenna diversity schemes and MIMO schemes or other multi-antenna schemes, circuitry  28  may perform signal quality monitoring operations, sensor monitoring operations, and other data gathering operations and may, in response to the gathered data, control which antenna structures within device  10  are being used to receive and process data. 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, 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), 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). 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 at 700 MHz, 710 MHz, 750 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz or other cellular telephone bands of interest. 
     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, 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 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 . Housing  12  may include sidewalls formed from member  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 glass, ceramic, or plastic, and/or metals or other suitable materials (e.g., fiber composites). Snaps, clips, screws, adhesive, and other structures may be used in assembling the parts of housing  12  together. 
     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 interconnect  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 . 
     Antennas in device  10  such as illustrative antenna  40  of  FIG. 3  may have antenna feed terminals. For example, each antenna in device  10  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 . As shown 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 for implementing wireless circuitry  34  of  FIG. 2  (e.g., receiver  35  and transceiver circuits  36  and  38 ). 
     Connectors such as connector  50  may be used in coupling transmission lines in device  10  to printed circuit boards such as board  46 . Connector  50  may be, for example, a coaxial cable connector that is connected to printed circuit board  46  using solder (as an example). Cable  52  may be a coaxial cable or other transmission line. Examples of transmission lines that may be used in device  10  include coaxial cables, microstrip and stripline transmission lines formed from a flex circuit or rigid printed circuit board, transmission lines that are formed from multiple transmission line structures such as these, etc. 
     When coupled to the feed of antenna  40 , transmission line  52  may be used to transmit and receive radio-frequency signals using antenna  40 . As shown in  FIG. 3 , 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. For example, impedance matching circuits may be used in coupling transceiver circuitry to antenna structures. The arrangement of  FIG. 3  is merely illustrative. 
     In the illustrative example of  FIG. 3 , device  10  includes antenna  40 . To enhance signal quality and to cover multiple bands of interest, device  10  may contain multiple antennas. With one suitable arrangement, which is sometimes described herein as an example, a WiFi® antenna may be located in region  22 , a first (e.g., a primary) cellular telephone antenna may be located in region  20 , and a second (e.g., secondary) cellular telephone antenna may be located in region  22 . The second cellular telephone antenna may, if desired, be configured to receive GPS signals. Illustrative wireless circuitry  34  that includes an antenna arrangement of this type is shown in  FIG. 4 . 
     As shown in  FIG. 4 , wireless circuitry  34  may have input-output ports such as ports  100  and  130  for interfacing with digital data circuits in storage and processing circuitry  28 . Wireless circuitry  34  may include one or more integrated circuits for implementing transceiver circuits such as baseband processor  102  and cellular telephone transceiver circuitry  38 . Port  100  may receive digital data from storage and processing circuitry  28  for transmission over antenna  40 L. Incoming data that has been received by antennas  40 U and  40 L, cellular transceiver circuitry  38 , and baseband processor  102  may be supplied to storage and processing circuitry  28  via port  100 . Port  130  may be used to handle digital data associated with transmitted and received wireless local area network signals such as WiFi® signals (as an example). Outgoing digital data that is supplied to port  130  by storage and processing circuitry  28  may be transmitted using wireless local area network transceiver circuitry  36 , paths such as path  128 , and one or more antennas such as antenna  40 WF. During data reception operations, signals received by antenna  40 WF may be provided to transceiver  36  via path  128 . Transceiver  36  may convert the incoming signals to digital data. The digital data may be provided to storage and processing circuitry  28  via port  130 . If desired, local signals such as Bluetooth® signals may also be transmitted and received via antennas such as antenna  40 WF. 
     Transceiver circuitry  38  may include one or more transmitters and one or more receivers. In the example of  FIG. 4 , transceiver circuitry  38  includes radio-frequency transmitter  104  and radio-frequency receivers  110 . Transmitter  104  and receivers  110  (i.e., receiver RX 1  and receiver RX 2 ) may be used to handle cellular telephone communications. Signals that are received by transmitter  104  over path  118  may be supplied to power amplifier  106  by transmitter  104 . Power amplifier  106  may strengthen these outgoing signals for transmission over antenna  40 L. Incoming signals that are received by antenna  40 L may be amplified by low noise amplifier  112  and provided to receiver RX 1 . Receiver RX 1  may provide data received from antenna  40 U to processor  102  via path  118 . Incoming signals that are received by antenna  40 U may be amplified by low noise amplifier  124  and provided to receiver RX 2  (or to RX 1  using a switch). Receiver RX 2  may provide data received from antenna  40 L to processor  102  via path  118 . Circuits such as transmitter  104  and receivers  110  may each have multiple ports (e.g., for handling different respective communications bands) and may be implemented using one or more individual integrated circuits. 
     Antennas  40 U and  40 L may be coupled to transceiver circuitry  38  using circuitry such as impedance matching circuitry, filters, and switches. This circuitry, which is sometimes referred to as front-end module (FEM) circuitry, can be controlled by storage and processing circuitry in device  10  (e.g., control signals from a processor such as baseband processor  102 ). As shown in the example of  FIG. 4 , the front-end circuitry in wireless circuitry  34  may include impedance matching circuitry  108  such as tunable matching circuitry M 1  and tunable matching circuitry M 2 . Impedance matching circuitry M 1  and M 2  may be formed using conductive structures with associated capacitance, resistance, and inductance values, and/or discrete components such as inductors, capacitors, and resistors that form circuits to match the impedances of transceiver circuitry  38  and antennas  40 U and  40 L. Matching circuitry M 1  may be coupled between wireless transceiver circuitry  38  (including associated amplifier circuitry  106  and  112 ) and antenna  40 L. Matching circuitry M 2  may be coupled between transceiver circuitry  38  (and associated amplifier  124 ) and antenna  40 U using paths such as paths  132  and  122 . 
     Matching circuitry M 1  and M 2  may be fixed or adjustable. For example, matching circuitry M 1  may be fixed and matching circuitry M 2  may be adjustable. As another example, matching circuitry M 1  may be adjustable and matching circuitry M 2  may be fixed. As another example, matching circuitry M 1  and M 2  may both be adjustable. In this type of configuration, a control circuit such as baseband processor  102  may issue control signals such as signal SELECT 1  on path  117  to configure tunable matching circuitry M 1  and may issue control signals such as signal SELECT 2  on path  116  to configure tunable matching circuitry M 2 . 
     Matching circuitry M 1  may be placed in a first configuration when SELECT 1  has a first value and may be placed in a second configuration when SELECT 1  has a second value. The state of matching circuitry M 1  may serve to fine tune the coverage provided by antenna  40 L. Similarly, matching circuitry M 2  may be placed in a first configuration when SELECT 2  has a first value and may be placed in a second configuration when SELECT 2  has a second value. The state of matching circuitry M 2  may serve to fine tune the coverage provided by antenna  40 U. Matching circuitry M 1  and M 2  may or may not be used. By using an antenna tuning scheme of this type, antennas  40 L and  40 U may be able to cover a wider range of communications frequencies than would otherwise be possible. The use of tuning for antennas  40 L and  40 U may allow a relatively narrow bandwidth (and potentially compact) design to be used for antennas  40 L and  40 U, if desired. 
     Control signals may be provided to receiver circuitry  110  over path  119  so that wireless circuitry  34  can selectively activate one or both of receivers RX 1  and RX 2  or can otherwise select which antenna signals are being received in real time (e.g., by controlling a multiplexer in circuitry  34  that routes signals from a selected one of the antennas to a shared receiver so that the receiver can be shared between antennas). For example, baseband processor  102  or other storage and processing circuitry in device  10  can monitor signal quality (bit error rate, signal-to-noise ratio, frame error rate, signal power, etc.) for signals being received by antennas  40 U and  40 L. Based on real-time signal quality information or other data (e.g., sensor data indicating that a particular antenna is blocked), signals on path  119  or other suitable control signals can be adjusted so that optimum receiver circuitry (e.g., receiver RX 1  or RX 2 ) is used to receive the incoming signals. Antenna diversity schemes such as this in which circuitry  34  selects an optimum antenna and receiver to use in real time based on signal quality measurements or other information while radio-frequency signals are transmitted by a fixed antenna and transmitter (i.e., antenna  40 L and transmitter  104 ) may sometimes be referred to as receiver diversity schemes. 
     In a receiver diversity configuration (i.e., in a device without transmitter diversity), the radio-frequency transmitter circuitry in a device is configured to receive signals through two or more different antennas, so that an optimum antenna can be chosen in real time to enhance signal reception, whereas the radio-frequency transceiver circuitry is configured to transmit signals through only a single one of the antennas and not others. If desired, wireless circuitry  34  may be configured to implement both receiver and transmitter diversity and/or may be configured to handle multiple simultaneous data streams (e.g., using a MIMO arrangement). The use of wireless circuitry  34  to implement a receiver diversity scheme while using a dedicated antenna for handling transmitted signals is merely illustrative. 
     As shown in  FIG. 4 , wireless circuitry  34  may be provided with filter circuitry such as filter circuitry  126 . Circuitry  126  may route signals by frequency, so that cellular telephone signals are conveyed between antenna  40 U and receiver RX 2 , whereas GPS signals that are received by antenna  40 U are routed to GPS receiver  35 . 
     Illustrative configurable circuitry that may be used for implementing matching circuitry M 1  is shown in  FIG. 5A . As shown in  FIG. 5A , matching circuitry M 1  may have switches such as switches  134  and  136 . Switches  134  and  136  may have multiple positions (shown by the illustrative A and B positions in  FIG. 5A ). When signal SELECT 1  has a first value, switches  134  and  136  may be placed in their A positions and matching circuit MA may be switched into use (as shown in  FIG. 5A ), so that matching circuit MA is electrically coupled between paths  120  and amplifiers  106  and  112 . When signal SELECT 1  has a second value, switches  134  and  136  may be placed in their B positions. 
     Illustrative configurable circuitry that may be used for implementing matching circuitry M 2  is shown in  FIG. 5B . As shown in  FIG. 5B , matching circuitry M 2  may have switches such as switches  134  and  136 . Switches  134  and  136  may have multiple positions (shown by the illustrative A and B positions in  FIG. 5B ). When signal SELECT 2  has a first value, switches  134  and  136  may be placed in their A positions and matching circuit MA may be switched into use. When signal SELECT 2  has a second value, switches  134  and  136  may be placed in their B positions (as shown in  FIG. 5B ), so that matching circuit MB is electrically coupled between paths  122  and  132 . 
       FIG. 6  is a top view of the interior of device  10  showing how antennas  40 L,  40 U, and  40 WF may be implemented within housing  12 . As shown in  FIG. 6 , ground plane G may be formed within housing  12 . Ground plane G may form antenna ground for antennas  40 L,  40 U, and  40 WF. Because ground plane G may serve as antenna ground, ground plane G may sometimes be referred to as antenna ground, ground, or a ground plane element (as examples). 
     In central portion C of device  10 , ground plane G may be formed by conductive structures such as a conductive housing midplate member that is connected between the left and right edges of member  16 , printed circuit boards with conductive ground traces, etc. At ends  22  and  20  of device  10 , the shape of ground plane G may be determined by the shapes and locations of conductive structures that are tied to ground. Examples of conductive structures that may overlap to form ground plane G include housing structures (e.g., a conductive housing midplate structure, which may have protruding portions), conductive components (e.g., switches, cameras, data connectors, printed circuits such as flex circuits and rigid printed circuit boards, radio-frequency shielding cans, buttons such as button  144  and conductive button mounting structure  146 ), and other conductive structures in device  10 . In the illustrative layout of  FIG. 6 , the portions of device  10  that are conductive and tied to ground to form part of ground plane G are shaded and are contiguous with central portion C. 
     Openings such as openings  72  and  140  may be formed between ground plane G and respective portions of peripheral conductive member  16 . Openings  72  and  140  may be filled with air, plastic, and other dielectrics. Opening  72  may be associated with antenna structure  40 L, whereas opening  140  may be associated with antenna structures  40 U and  40 WF. 
     Gaps such as gaps  18 B,  18 C, and  18 D may be present in peripheral conductive member  16  (gap  18 A of  FIG. 1  may be absent or may be implemented using a phantom gap structure that cosmetically looks like a gap from the exterior of device  10 , but that is electrically shorted within the interior of housing  12  so that no gap is electrically present in the location of gap  18 A). The presence of gaps  18 B,  18 C, and  18 D may divide peripheral conductive member  16  into segments. As shown in  FIG. 6 , peripheral conductive member  16  may include first segment  16 - 1 , second segment  16 - 2 , and third segment  16 - 3 . 
     Lower antenna  40 L may be formed using a parallel-fed loop antenna structure having a shape that is determined at least partly by the shape of the lower portions of ground plane G and conductive housing segment  16 - 3 . As shown in  FIG. 6 , antenna  40 L may be formed in lower region  20  of device  10 . The portion of conductive segment  16 - 3  that surrounds opening  72  and the portions of ground plane G that lie along edge GE of ground plane G form a conductive loop around opening  72 . The shape of opening  72  may be dictated by the placement of conductive structures in region  20  such as a microphone, flex circuit traces, a data port connector, buttons, a speaker, etc. 
     Conductive structure  202  may bridge dielectric opening  72  and may be used to electrically short ground plane G to peripheral housing segment  16 - 3 . Conductive structure  202  may be formed using strips of conductive material, flex circuit traces, conductive housing structures, or other conductive structures. If desired, conductive structure  202  may be formed using discrete components such as surface mount technology (SMT) inductors. Transmission line  52 - 1  (e.g., a coaxial cable) may be used to feed antenna  40 L at positive and negative antenna feed terminals  58 - 1  and  54 - 1 , respectively. 
     Antenna  40 L may include associated tunable (configurable) antenna circuitry such as switchable inductor circuit  210 , tunable impedance matching circuitry M 1 , variable capacitor circuit  212 , and other suitable tunable circuits. The tunable antenna circuitry associated with antenna  40 L may, for example, allow antenna  40 L to operate in at least six wireless communications bands (e.g., to transmit and receive radio-frequency signals at 750 MHz, 800 MHz, 900 MHz, 1800 MHz, 1900 MHz, 2100 MHz, etc.). 
     Conductive structure  202  may have a first conductive segment SG and a second inductive segment SG′ formed in series between peripheral segment  16 - 3  and ground G. Segment SG may exhibit a first inductance, segment SG′ may exhibit a second inductance, and circuit  202  may exhibit a third inductance. Switchable inductor circuit (also referred to as tunable inductor circuit, configurable inductor circuit, or adjustable inductor circuit)  210  may be coupled between a point at which segments SG and SG′ are joined and a corresponding point  101  on ground plane edge GE. 
     When circuit  210  is switched into use (e.g., when circuit  210  is turned on), segment SG and circuit  210  collectively form a first transmission line path that bridges the antenna feeds of antenna  40 L. The first transmission line path may have an inductance that is equal to the series inductance of the first and third inductance. When circuit  210  is switched out of use (e.g., when circuit  210  is turned off), segments SG and SG′ may collectively form a second transmission line path that bridges the antenna feeds of antenna  40 L. The second transmission line path may have an inductance that is equal to the series inductance of the first and second inductance. Switchable inductor  210  serves to shunt a portion of the second transmission line path so that the inductance associated with the first transmission line path when circuit  210  is turned on is less than the inductance associated with the second transmission line path when circuit  210  is turned off. 
     The first transmission line inductance (i.e., the inductance of the first transmission line path) may be different than the second transmission line inductance (i.e., the inductance of the second transmission line path). The first transmission line inductance may be equal to 18 nH, whereas the second transmission line inductance may be equal to 20 nH (as an example). The first transmission line path (if circuit  210  is enabled) and the second transmission line path (if circuit  210  is disabled) are connected in parallel between feed terminals  54 - 1  and  58 - 1  and serve as parallel inductive tuning elements for antenna  40 L. The first and second transmission line paths may therefore sometimes be referred to as a variable inductor. The inductance of segments SG and SG′ are carefully chosen to provide desired band coverage. 
     Tunable impedance matching circuitry M 1  may be coupled between coaxial cable  52 - 1  and positive feed terminal  58 - 1 . Impedance matching circuitry M 1  may be formed using switching circuitry of the type described in connection with  FIG. 5A , conductive structures with associated capacitance, resistance, and inductance values, and/or discrete components such as inductors, capacitors, and resistors that form circuits to match the impedances of transceiver circuitry  38  and antenna  40 L. 
     Variable capacitor circuit (sometimes referred to as a varactor circuit, a tunable capacitor circuit, an adjustable capacitor circuit, etc.)  212  may be coupled between opposing ends of bezel gap  18 B. Baseband processor  102  may issue control voltage VtuneB to fine tune varactor  212  so that antenna  40 L operates at desired frequencies. 
     Bezel gap  18 B may, for example, have an intrinsic capacitance of 1 pF (e.g., an inherent capacitance value formed by the parallel conductive surfaces at gap  18 B). Component  212  may be, for example, a continuously variable capacitor, a semi-continuously adjustable capacitor that has two to four or more different capacitance values that can be coupled in parallel to the intrinsic capacitance. If desired, component  212  may be a continuously variable inductor or a semi-continuously adjustable inductor that has two or more different inductance values. 
     Antenna  40 WF may have an antenna resonating element formed from a strip of conductor such as strip  142 . Strip  142  may be formed from a trace on a flex circuit, from a trace on a rigid printed circuit board, from a strip of metal foil, or from other conductive structures. Antenna  40 WF may be fed by transmission line  52 - 2  (see, e.g., path  128  of  FIG. 4 ) using antenna feed terminals  58 - 2  and  54 - 2 . 
     Antenna  40 U may include associated tunable (configurable) antenna circuitry such as switchable inductor circuit  210 ′, tunable impedance matching circuitry M 2 , variable capacitor circuits  212 - 1  and  212 - 2 , and other suitable tunable circuits. The tunable antenna circuitry associated with antenna  40 U may allow antenna  40 U to have a wider coverage than otherwise possible. 
     Antenna  40 U may be a two-branch inverted-F antenna. Transmission line  52 - 3  (see, e.g., path  120  of  FIG. 4 ) may be used to feed antenna  40 U at antenna feed terminals  58 - 3  and  54 - 3 . Conductive structure  150  may be bridge dielectric opening  140  and may be used to electrically short ground plane G to peripheral housing member  16 . Conductive structure  148  and matching circuitry M 2  may be used to connect antenna feed terminal  58 - 3  to peripheral conductive member  16  at point  152 . Conductive structures such as structures  148  and  150  may be formed by flex circuit traces, conductive housing structures, springs, screws, or other conductive structures. 
     Peripheral conductive segment  16 - 1  may form antenna resonating element arms for antenna  40 U. In particular, a first portion of segment  16 - 1  (having arm length LBA) may extend from point  152  (where segment  16 - 1  is fed) to the end of segment  16 - 1  that is defined by gap  18 C and a second portion of segment  16 - 1  (having arm length HBA) may extend from point  152  to the opposing end of segment  16 - 1  that is defined by gap  18 D. The first and second portions of segment  16 - 1  may form respective branches of an inverted F antenna and may be associated with respective low band (LB) and high band (HB) antenna resonances for antenna  40 U. 
     Switchable inductor circuit  210 ′ may be coupled in parallel with structures  148  and  150  between segment  16 - 1  and ground plane G. Circuit  210 ′ may be coupled to the right of structure  150  (as shown in  FIG. 6  when device  10  is viewed from the top) or may be coupled to the left of structure  150 . Circuit  210 ′ may serve to provide wider high band coverage for antenna  40 U. Antenna  40 U may operate in a first high-band region when circuit  210 ′ is switched out of use, whereas antenna  40 U may operate in a second high-band region that is higher in frequency than the first high-band region when circuit  210 ′ is switched into use. For example, antenna  40 U may be used to receive signals in the 1900 MHz band when circuit  210 ′ is turned off and in the 2100 MHz band when circuit  210 ′ is turned on. 
     Variable capacitor circuit  212 - 1  may be coupled between opposing ends of conductive bezel gap  18 C, whereas variable capacitor circuit  212 - 2  may be coupled between opposing ends of bezel gap  18 D. Circuit  212 - 2  need not be formed, if desired. Varactors  212 - 1  and  212 - 2  may be formed from using integrated circuits, one or more discrete components (e.g., SMT components), etc. 
     Variable capacitor  212 - 1  may serve to provide wider low-band coverage for antenna  40 U. Baseband processor  102  may issue control voltage VtuneC to tune varactor  212 - 1  to configure antenna  40 U to operate in first and second low-band regions. For example, antenna  40 U may be used to receive signals in the 850 MHz band when varactor  212 - 1  is tuned to exhibit a low capacitance value (e.g., less than 0.1 pF) and to receive signals in the 750 MHz band when varactor  212 - 1  is tuned to exhibit a high capacitance value (e.g., greater than 0.2 pF). 
     For example, bezel gaps  18 C and  18 D may each have an intrinsic capacitance of 1.0 pF (e.g., an inherent capacitance value formed by the parallel conductive surfaces at gaps  18 C and  18 D). Varactors  212 - 1  and  212 - 2  may be, for example, continuously variable capacitors, semi-continuously adjustable capacitors that have two to four or more different capacitance values that can be coupled in parallel to the intrinsic capacitance. 
       FIG. 7  is a circuit diagram of antenna  40 U. As shown in  FIG. 7 , capacitances C C  and C D  may respectively be associated with gaps  18 C and  18 D. Capacitance C C  may represent a lumped capacitance that includes the parasitic capacitance of gap  18 C and varactor  212 - 1 , whereas capacitance C D  may represent a lumped capacitance that includes the parasitic capacitance of gap  18 D and varactor  212 - 2 . Ground plane G may form antenna ground. Short circuit branch  150  may form a stub that connects peripheral conductive member segment  16 - 1  to ground G to facilitate impedance matching between the antenna feed (formed from feed terminals  58 - 3  and  54 - 3 ) and antenna  40 U. Short circuit branch  150  may have an associated inductance Ls. 
     Antenna  40 U may be operable in a first high-band mode (e.g., a mode that covers band  1900  MHz) when circuit  210 ′ is switched out of use and a second high-band mode (e.g., a mode that covers band  2100  MHz) when circuit  210 ′ is switched into use.  FIG. 7  shows one suitable circuit implementation of switchable inductor circuit  210 ′. As shown in  FIG. 7 , circuit  210  includes a switch SW and inductive element  214  coupled in series. Switch SW may be implemented using a p-i-n diode, a gallium arsenide field-effect transistor (FET), a microelectromechanical systems (MEMs) switch, a metal-oxide-semiconductor field-effect transistor (MOSFET), a high-electron mobility transistor (HEMI), a pseudomorphic HEMI (PHEMT), a transistor formed on a silicon-on-insulator (SOI) substrate, etc. 
     Inductive element  214  may be formed from one or more electrical components. Components that may be used as all or part of element  214  include inductors and capacitors. Desired inductances and capacitances for element  214  may be formed using integrated circuits, using discrete components (e.g., a surface mount technology inductor) and/or using dielectric and conductive structures that are not part of a discrete component or an integrated circuit. For example, 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 (e.g., a transmission line) on a printed circuit board. 
     In another suitable arrangement, configurable inductor circuit  209  may be used to form a shorting path for antenna  40 U (i.e., shorting structure  150  and circuit  210 ′ of  FIG. 7  are not formed). As shown in  FIG. 8 , circuit  209  may include inductors  214  and  216  coupled between conductive segment  16 - 1  and switch  218 . Switch  218  may have multiple positions (shown by the illustrative A and B positions). Switch  218  may be placed in it&#39;s A position to couple inductor  214  between the antenna feeds (e.g., between positive and negative terminals  58 - 3  and  54 - 3 ) during the second high-band mode and may be placed in its B position to coupled inductor  216  between the antenna feeds during the first high-band mode. Inductor  216  may have an inductance value that is approximately equal to Ls ( FIG. 8 ), as an example. 
     In another suitable arrangement, configurable inductor circuit  211  may be used to form a shorting path for antenna  40 U (i.e., shorting structure  150  and circuit  210 ′ of  FIG. 7  are not formed). As shown in  FIG. 9 , circuit  211  may include inductor  214  and first switch SW coupled in series between segment  16 - 1  and ground G and may include inductor  216  and second switch SW coupled in series between segment  16 - 1  and ground G. During the first high-band mode, first switch SW may be open and second switch SW may be closed to electrically connect inductor  216  between the antenna feed terminals. During the second high-band mode, second switch SW may be disabled and first switch may be enabled to electrically connect inductor  214  between the antenna feed terminals. 
       FIGS. 7-9  are merely illustrative. If desired, antenna  40 U may include more than two inductive branches to support wireless coverage in more than two low-band regions. 
     Antenna  40 L may cover at least six transmit and receive communications bands (e.g., 700 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz), as shown in the table of  FIG. 10 . Antenna  40 U may be configured to cover a subset of these six illustrative communications bands. For example, antenna  40 U may be configured to cover three receive bands of interest and, with tuning, six receive bands of interest. 
     Antenna  40 U may be configured in a first operating mode in which capacitor  212 - 1  is tuned to provide a first capacitance value and in which inductor circuit  210 ′ is turned off. In the first operating mode (see, e.g., row  250  in  FIG. 10 ), antenna  40 U may be capable of covering receive bands 850 RX (the 850 MHz receive band), 900 RX (the 900 MHz receive band), 1800 RX (the 1800 MHz receive band), 1900 RX (the 1900 MHz receive band), and any other communications bands of interest. 
     Antenna  40 U may be configured in a second operating mode in which capacitor  212 - 1  is tuned to provide a second capacitance value that is higher than the first capacitance value and in which inductor circuit  210 ′ is off. In the second operating mode (see, e.g., row  252  in  FIG. 10 ), antenna  40 U may be capable of covering receive bands 750 RX (the 750 MHz receive band), 1800 RX, 1900 RX, and other communications bands of interest. 
     Antenna  40 U may be configured in a third operating mode in which capacitor  212 - 1  is tuned to provide the first capacitance value and in which inductor circuit  210 ′ is turned on. In the third operating mode (see, e.g., row  254  in  FIG. 10 ), antenna  40 U may be capable of covering receive bands 850 RX, 900 RX, 2100 RX (the 2100 MHz receive band), and other communications bands of interest. 
     The modes described in connection with  FIG. 10  are merely illustrative. If desired, circuit  210 ′ may be turned on/off and capacitor  212 - 1  may be tuned to provide suitable capacitance to cover desired high-band and low-band frequency ranges of interest. If desired, antenna  40 U may also be used to transmit radio-frequency signals in the indicated bands. 
     By using antenna tuning schemes of the type described in connection with  FIGS. 4-10 , antenna  40 L and  40 U may be able to cover a wider range of communications frequencies than would otherwise be possible. A standing-wave-ratio (SWR) versus frequency plot such as SWR plot of  FIG. 11  illustrates low-band tuning capability for antenna  40 U. As shown in  FIG. 11 , solid SWR frequency characteristic curve  300  corresponds to a first antenna tuning mode in which antenna  40 U of device  10  exhibits satisfactory resonant peaks at low-band frequency f 1  (to cover the 850 MHz band) and high-band frequency f 2  (e.g., to cover the 1900 MHz band). In the first antenna tuning mode, variable capacitor circuit  212 - 1  may be tuned to a first capacitance, whereas switchable inductor circuit  210 ′ is turned off. 
     Dotted SWR frequency characteristic curve  302  corresponds to a second antenna tuning mode in which the antennas of device  10  exhibits satisfactory resonant peaks at low-band frequency f 1 ′ (to cover the 750 MHz band) and high-band frequency f 2 . In the second antenna tuning mode, variable capacitor circuit  212 - 1  may be tuned to a second capacitance that is greater than the first capacitance to shift the wireless coverage from frequency f 1  to f 1 ′. 
       FIG. 12  illustrates antenna  40 U operating in a third antenna tuning mode. As shown in  FIG. 12 , dotted SWR frequency characteristic curve  304  corresponds to the third antenna tuning mode in which antenna  40 U exhibits satisfactory resonant peaks at low-band frequency f 1  and high-band frequency f 2 ′ (to cover the 2100 MHz band). In the third antenna tuning mode, circuit  210 ′ is switched into use to shift the wireless coverage from frequency f 2  to f 2 ′. 
     In general, the switchable inductor circuits described in connection with  FIGS. 7-9  can be used to tune the high-band coverage for antenna  40 U (e.g., the switchable inductor circuits may be configured in at least two states to provide wireless coverage in at least two high-band frequency ranges), whereas variable capacitor  212 - 2  may be tuned to adjust the low-band coverage for antenna  40 U (e.g., the variable capacitor associated with low-band gap  18 C may be tuned to provide wireless coverage in at least two low-band frequency ranges).  FIGS. 11 and 12  are merely illustrative. If desired, antennas  40 L,  40 U, and  40 WF may include antenna tuning circuitry that enables device  10  to transmit and receive wireless signals at any suitable number of radio-frequency communications bands. 
     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: 20110307
Publication Date: 20151020
Grant Date: 20151020
Priority Date: 20110307
Inventors: JIN NANBO
PASCOLINI MATTIA
MOW MATT A.
SCHLUB ROBERT W.
CABALLERO RUBEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/307", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/307", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/307", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/06", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/48", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/19107", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 45774096