PATENT DOCUMENT

Publication Number: US-8798554-B2
Application Number: US-201213368855-A
Country: US
Kind Code: B2

Title: Tunable antenna system with multiple feeds

Abstract:
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 an antenna having first and second feeds at different locations. The transceiver circuit may have a first circuit that handles communications using the first feed and may have a second circuit that handles communications using the second feed. A first filter may be interposed between the first feed and the first circuit and a second filter may be interposed between the second feed and the second circuit. The first and second filters and the antenna may be configured so that the first circuit can use the first feed without being adversely affected by the presence of the second feed and so that the second circuit can use the second feed without being adversely affected by the presence of the first feed.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 an antenna; 
 a first antenna feed at a first location in the antenna; 
 a second antenna feed at a second location in the antenna; 
 a first radio-frequency receiver that is configured to receive radio-frequency signals from the antenna in a first communications band; 
 a second radio-frequency receiver that is configured to receive radio-frequency signals from the antenna in a second communications band; 
 a first filter coupled between the first radio-frequency receiver and the first antenna feed, wherein the first filter is configured to pass the radio-frequency signals in the first communications band and is configured to block the radio-frequency signals in the second communications band; and 
 a second filter coupled between the second radio-frequency receiver and the second antenna feed, wherein the second filter is configured to pass the radio-frequency signals in the second communications band and is configured to block the radio-frequency signals in the first communications band, wherein the second filter comprises a notch filter. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the first filter comprises a band-pass filter. 
     
     
       3. The electronic device defined in  claim 2  wherein the band-pass filter has a passband and wherein the notch filter has a stopband that overlaps the passband. 
     
     
       4. The electronic device defined in  claim 3  wherein the first radio-frequency receiver comprises a satellite navigation system receiver. 
     
     
       5. The electronic device defined in  claim 4  wherein the second radio-frequency receiver comprises a cellular telephone receiver. 
     
     
       6. The electronic device defined in  claim 5  wherein the cellular telephone receiver is configured to operate in a third communications band, wherein the second filter is configured to pass radio-frequency signals in the third communications band. 
     
     
       7. The electronic device defined in  claim 6  wherein the third communications band includes frequencies lower than the stopband and wherein the second communications band includes frequencies higher than the stop band. 
     
     
       8. The electronic device defined in  claim 7  further comprising a tunable circuit coupled to the notch filter that is configured to tune the antenna to cover the third communications band. 
     
     
       9. The electronic device defined in  claim 8  wherein the tunable circuit comprises a switch-based adjustable capacitor configured to exhibit at least first and second selectable capacitances. 
     
     
       10. The electronic device defined in  claim 1  further comprising a tunable circuit coupled to the second filter that is configured to tune the antenna. 
     
     
       11. The electronic device defined in  claim 10  wherein the tunable circuit comprises a switch-based adjustable capacitor having at least first and second selectable capacitances. 
     
     
       12. The electronic device defined in  claim 11  further comprising a signal path coupled between the second antenna feed and the second radio-frequency receiver, wherein the switch-based adjustable capacitor is interposed within the path between the second antenna feed and the second radio-frequency receiver, and wherein the second filter is interposed between the second antenna feed and the switch-based adjustable capacitor. 
     
     
       13. The electronic device defined in  claim 12  wherein the first radio-frequency receiver comprises a satellite navigation system receiver and wherein the second radio-frequency receiver comprises a cellular telephone receiver. 
     
     
       14. The electronic device defined in  claim 13  further comprising a cellular telephone transmitter that is coupled to the signal path. 
     
     
       15. The electronic device defined in  claim 1  further comprising:
 a housing containing conductive structures that form an antenna ground for the antenna and having a peripheral conductive member that runs around at least some edges of the housing, wherein at least part of the peripheral conductive member forms an antenna resonating element for the antenna. 
 
     
     
       16. An electronic device, comprising:
 an antenna having a first antenna feed at a first location and a second antenna feed at a second location; 
 a first radio-frequency receiver that is configured to receive radio-frequency signals from the antenna in a first communications band; 
 a second radio-frequency receiver that is configured to receive radio-frequency signals from the antenna in a second communications band; 
 a first filter coupled between the first radio-frequency receiver and the first antenna feed, wherein the first filter is configured to pass the radio-frequency signals in the first communications band and is configured to exhibit a first impedance in the second communications band; 
 a second filter coupled between the second radio-frequency transceiver and the second antenna feed, wherein the second filter is configured to pass the radio-frequency signals in the second communications band and is configured to exhibit a second impedance in the first communications band, wherein the second filter and the antenna are configured so that the antenna exhibits a first resonance in the first communications band while the second filter is exhibiting the second impedance in the first communications band and wherein the first filter and the antenna are configured so that the antenna exhibits a second resonance in the second communications band while the first filter is exhibiting the first impedance in the second communications band; and 
 a housing containing conductive structures that form an antenna ground for the antenna and having a peripheral conductive member that runs around at least some edges of the housing, wherein at least part of the peripheral conductive member forms an antenna resonating element for the antenna. 
 
     
     
       17. The electronic device defined in  claim 16  wherein the first filter is configured to exhibit a third impedance in the first communications band and wherein the third impedance is less than the second impedance. 
     
     
       18. The electronic device defined in  claim 16  further comprising a tunable circuit coupled to the second filter that is configured to tune the antenna. 
     
     
       19. The electronic device defined in  claim 18  further comprising an adjustable capacitor in the tunable circuit. 
     
     
       20. The electronic device defined in  claim 16 , wherein the second filter comprises a notch filter. 
     
     
       21. An electronic device, comprising:
 an antenna having first and second antenna feeds at different locations; 
 radio-frequency transceiver circuitry having a first circuit that handles communications associated with the first antenna feed and a second circuit that handles communications associated with the second antenna feed; 
 a first filter coupled between the first antenna feed and the first circuit, wherein the first filter is configured to pass radio-frequency signals in a first communications band and is configured to block radio-frequency signals in a second communications band; 
 a second filter coupled between the second antenna feed and the second circuit, wherein the second filter is configured to block the radio-frequency signals in the first communications band and is configured to pass the radio-frequency signals in the second communications band; 
 a tunable circuit coupled to the second filter that is configured to tune the antenna; and 
 a tunable capacitor in the tunable circuit. 
 
     
     
       22. The electronic device defined in  claim 21  further comprising a housing containing conductive structures that form an antenna ground for the antenna and having a peripheral conductive member that runs around at least some edges of the housing, wherein at least part of the peripheral conductive member forms an antenna resonating element for the antenna. 
     
     
       23. The electronic device defined in  claim 22  further comprising a signal path between the second filter and the second circuit, the electronic device further comprising:
 an additional antenna; and 
 an antenna selection switch interposed in the signal path, wherein the antenna selection switch is coupled to the additional antenna. 
 
     
     
       24. The electronic device defined in  claim 21 , wherein the radio-frequency transceiver circuitry is configured to cover radio-frequency signals at low-band cellular telephone frequencies, at high-band cellular telephone frequencies, and at satellite navigation system frequencies that are less than the high-band cellular telephone frequencies and greater than the low-band cellular telephone frequencies. 
     
     
       25. The electronic device defined in  claim 24 , wherein the tunable capacitor comprises a switch-based adjustable capacitor that is configured to tune the antenna between first and second sub-bands of the low-band cellular telephone frequencies while the antenna covers the high-band cellular telephone frequencies. 
     
     
       26. The electronic device defined in  claim 21 , wherein the second filter comprises a notch filter.

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 an antenna having first and second feeds at different locations. The transceiver circuit may have a first circuit that handles communications using the first feed and may have a second circuit that handles communications using the second feed. 
     A first filter may be interposed between the first feed and the first circuit and a second filter may be interposed between the second feed and the second circuit. The first and second filters and the antenna may be configured so that the first circuit can use the first feed without being adversely affected by the presence of the second feed and so that the second circuit can use the second feed without being adversely affected by the presence of the first feed. For example, the first filter may be configured to pass signals in a frequency band of interest to the first circuit while exhibiting an impedance that ensures satisfactory antenna performance in frequency bands of interest to the second circuit. The second filter may likewise be configured to pass signals in a frequency band of interest to the second circuit while exhibiting an impedance that ensures satisfactory antenna performance in frequency bands of interest to the first circuit. 
     The first circuit may be coupled to the first feed using a first signal path. The second circuit may be coupled to the second feed using a second signal path. One or more impedance matching circuits may be interposed within the first and second signal paths. For example, a tunable impedance matching circuit may be interposed within the second signal path. The tunable impedance matching circuit may be tuned to provide antenna coverage over a desired range of frequencies. 
     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 antenna having multiple feeds in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of an illustrative planar inverted-F antenna with multiple feeds in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative slot antenna with multiple feeds in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an illustrative inverted-F antenna with multiple feeds in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram of an illustrative loop antenna with multiple feeds in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of an inverted-F antenna with multiple feeds showing how radio-frequency transceiver circuitry may be coupled to the feeds using transmission lines in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram of an illustrative antenna with multiple feeds each of which has an associated radio-frequency filter circuit in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of an illustrative antenna with a feed in a first location in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph in which antenna performance for an antenna configuration of the type shown in  FIG. 10  has been plotted as a function of frequency in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram of an illustrative antenna of the type shown in  FIG. 10  with a feed in a second location in accordance with an embodiment of the present invention. 
         FIG. 13  is a graph in which antenna performance for an antenna configuration of the type shown in  FIG. 12  has been plotted as a function of frequency in accordance with an embodiment of the present invention. 
         FIG. 14  is a diagram in which an antenna has been provided with feeds and filters in the first and second locations of  FIGS. 10 and 12  in accordance with an embodiment of the present invention. 
         FIG. 15  is a graph in which antenna performance for an antenna configuration of the type shown in  FIG. 14  has been plotted as a function of frequency when using the first feed of the antenna in accordance with an embodiment of the present invention. 
         FIG. 16  is a graph in which antenna performance for an antenna configuration of the type shown in  FIG. 14  has been plotted as a function of frequency when using the second feed of the antenna in accordance with an embodiment of the present invention. 
         FIG. 17  is a diagram of an illustrative antenna with a feed in a first feed location and circuitry that provides an impedance in a second feed location during operation of the first feed in accordance with an embodiment of the present invention. 
         FIG. 18  is a graph in which antenna performance for an antenna configuration of the type shown in  FIG. 17  has been plotted as a function of frequency in accordance with an embodiment of the present invention. 
         FIG. 19  is a diagram of an illustrative antenna with a feed in a second feed location and circuitry that provides an impedance in the first feed location of  FIG. 18  during operation of the second feed in accordance with an embodiment of the present invention. 
         FIG. 20  is a graph in which antenna performance for an antenna configuration of the type shown in  FIG. 19  has been plotted as a function of frequency in accordance with an embodiment of the present invention. 
         FIG. 21  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 antenna resonating element structures in accordance with an embodiment of the present invention. 
         FIG. 22  is a diagram showing how device structures of the type shown in  FIG. 21  may be used in forming an antenna with multiple feeds in accordance with an embodiment of the present invention. 
         FIG. 23  is a diagram of an antenna of the type shown in  FIG. 22  with multiple feeds and associated wireless circuitry such as filters and matching circuits in accordance with an embodiment of the present invention. 
         FIG. 24  is a diagram showing how frequency responses of filter circuitry associated with the first and second antenna feeds of  FIG. 23  may be configured in accordance with an embodiment of the present invention. 
         FIG. 25  is a graph of antenna performance associated with use of the first antenna feed of  FIG. 23  in accordance with an embodiment of the present invention. 
         FIG. 26  is a graph of antenna performance associated with use of the second antenna feed of  FIG. 23  in accordance with an embodiment of the present invention. 
         FIG. 27  is a diagram of an illustrative antenna tuning element based on a variable capacitor in accordance with an embodiment of the present invention. 
         FIG. 28  is a diagram of an illustrative antenna tuning element based on a switch in accordance with an embodiment of the present invention. 
         FIG. 29  is a diagram of an illustrative antenna tuning element based on a variable inductor in accordance with an embodiment of the present invention. 
         FIG. 30  is a diagram of an illustrative antenna tuning element based on a switch-based adjustable capacitor in accordance with an embodiment of the present invention. 
         FIG. 31  is a diagram of an illustrative antenna tuning element based on a switch-based adjustable inductor in accordance with an embodiment of the present invention. 
         FIG. 32  is a diagram showing adjustable antenna circuitry that may be associated with the second antenna feed of  FIG. 23  in accordance with an embodiment of the present invention. 
         FIG. 33  is a graph in which antenna performance has been plotted as a function of frequency for an antenna of the type shown in  FIG. 23  using adjustable circuitry of the type shown in  FIG. 32  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, or more than two 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 separate 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 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 a desired communications band, 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 2200 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 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. 
     If desired, one or more of antennas  40  may be provided with multiple antenna feeds and/or adjustable components. Antennas such as these may be used to cover desired communications bands of interest. For example, a first antenna feed may be associated with a first set of communications frequencies and a second antenna feed may be associated with a second set of communications frequencies. The use of multiple feeds (and/or adjustable antenna components) may make it possible to reduce antenna size (volume) within device  10  while satisfactorily covering desired communications bands. 
     An illustrative configuration for an antenna with multiple feeds of the type that may be used in implementing one or more antennas for device  10  is shown in  FIG. 3 . As shown in  FIG. 3 , antenna  40  may have conductive antenna structures such as antenna resonating element  50  and antenna ground  52 . The conductive structures that form antenna resonating element  50  and antenna ground  52  may be formed from parts of conductive housing structures, from parts of electrical device components in device  10 , from printed circuit board traces, from strips of conductor such as strips of wire and metal foil, or other conductive materials. 
     Each antenna feed associated with antenna  40  may, if desired, have a distinct location. As shown in  FIG. 3 , antenna  40  may have a first feed such as feed FA at a first location in antenna  40 , a second feed such as feed FB at a second location in antenna  40 , and one or more additional antenna feeds at potentially different respective locations of antenna  40 . 
     Each feed may be coupled to an associated set of conductive signal paths using terminals such as positive antenna feed terminals (+) and ground antenna feed terminals (−). For example, path  54 A may have a positive conductor  58 A that is coupled to a positive antenna feed terminal in feed FA and a ground conductor  56 A that is coupled to a ground antenna feed terminal in feed FA, whereas path  54 B may have a positive conductor  58 B that is coupled to a positive antenna feed terminal in feed FB and a ground conductor  56 B that is coupled to a ground antenna feed terminal in feed FB. Paths such as paths  54 A and  54 B may be implemented using transmission line structures such as coaxial cables, microstrip transmission lines (e.g., microstrip transmission lines on printed circuits), stripline transmission lines (e.g., stripline transmission lines on printed circuits), or other transmission lines or signal paths. Circuits such as impedance matching and filter circuits and other circuitry may be interposed within paths  54 A and  54 B. 
     The conductive structures that form antenna resonating element  50  and antenna ground  52  may be used to form any suitable type of antenna. 
     In the example of  FIG. 4 , antenna  40  has been implemented using a planar inverted-F configuration having a first antenna feed (feed FA) and a second antenna feed (feed FB). 
       FIG. 5  is a top view of an illustrative slot antenna configuration that may be used for antenna  40 . In the  FIG. 5  example, antenna resonating element  50  is formed from a closed (enclosed) rectangular slot (e.g., a dielectric-filled opening) in ground plane  52 . Feeds FA and FB may each have a respective pair of antenna feed terminals (+/−) located at a respective position along the antenna slot. 
     In the illustrative configuration of  FIG. 6 , antenna  40  has been implemented using an inverted-F antenna design. Inverted-F antenna  40  of  FIG. 6  has a first antenna feed (feed FA with a corresponding positive terminal and ground terminal) and has a second antenna feed (feed FB with a corresponding positive terminal and ground terminal). Feeds FA and FB may be located at different respective locations along the length of the main resonating element arm that forms inverted-F antenna  40 . Inverted-F configurations with multiple arms or arms of different shapes may be used, if desired. 
       FIG. 7  is a diagram showing how antenna  40  may be implemented using a loop antenna configuration with multiple antenna feeds. As shown in  FIG. 7 , antenna  40  may have a loop of conductive material such as loop  60 . Loop  60  may be formed from conductive structures  50  and/or conductive structures  52  ( FIG. 3 ). A first antenna feed such as feed FA may have a positive antenna feed terminal (+) and a ground antenna feed terminal (−) and may be used to feed one portion of loop  60  and a second antenna feed such as feed FB may have a positive antenna feed terminal (+) and a ground antenna feed terminal (−) and may be used to feed antenna  40  at a different portion of loop  60 . 
     The illustrative examples of  FIGS. 4 ,  5 ,  6 , and  7  are merely illustrative. Antenna  40  may, in general, have any suitable number of antenna feeds and may be formed using any suitable type of antenna structures. 
       FIG. 8  shows how antenna  40  may be coupled to transceiver circuitry  62 . Antenna  40  of  FIG. 8  is an inverted-F antenna, but, in general, any suitable type of antenna may be used in implementing antenna  40 . Antenna  40  may have multiple feeds such as illustrative first antenna feed FA with a positive antenna feed terminal (+) and a ground antenna feed terminal (−) and illustrative second antenna feed FB with a positive antenna feed terminal (+) and ground antenna feed terminal (−). Path  54 A may include one or more transmission line segments and may include positive conductor  56 A and ground conductor  58 A. Path  54 B may include one or more transmission line segments and may include positive conductor  56 B and ground conductor  58 B. One or more circuits such as filter circuits and impedance matching circuits and other circuits (not shown in  FIG. 8 ) may be interposed within paths  54 A and  54 B. Transceiver circuitry  62  may include radio-frequency receivers and/or radio-frequency transmitters such as transceivers  62 A and  62 B. 
     Path  54 A may be coupled between a first radio-frequency transceiver circuit such as transceiver  62 A and first antenna feed FA. Path  54 B may be used to couple a second radio-frequency transceiver circuit such as transceiver  62 A to second antenna feed FA. Feeds FA and FB may be used in transmitting and/or receiving radio-frequency antenna signals. Transceiver  62 A may include a radio-frequency receiver and/or a radio-frequency transmitter. Transceiver  62 B may also include a radio-frequency receiver and/or a radio-frequency transmitter. 
     As an example, transceiver  62 A may include a satellite navigation system receiver and transceiver  62 B may include a cellular telephone transceiver (having a cellular telephone transmitter and a cellular telephone receiver). As another example, transceiver  62 A may have a transmitter and/or a receiver that operate at frequencies associated with a first communications band (e.g., a first cellular or wireless local area network band) and transceiver  62   b  may have a transmitter and/or a receiver that operate at frequencies associated with a second communications band (e.g., a second cellular or wireless local area network band). Other types of configurations may be used, if desired. Transceivers  62 A and  62 B may be implemented using separate integrated circuits or may be integrated into a common integrated circuit (as examples). One or more associated additional integrated circuits (e.g., one or more baseband processor integrated circuits) may be used to provide transceiver circuitry  62  with data to be transmitted by antenna  40  and may be used to receive and process data that has been received by antenna  40 . 
     Filter circuitry and impedance matching circuitry may be interposed in paths such as paths  54 A and  54 B. As shown in  FIG. 9 , for example, filter  64 A may be interposed in path  54 A between feed FA and transceiver  62 A, so that signals that are transmitted and/or received using antenna feed FA are filtered by filter  64 A. Filter  64 B may likewise be interposed in path  54 B, so that signals that are transmitted and/or received using antenna feed FB are filtered by filter  64 B. Filters  64 A and  64 B may be adjustable or fixed. In fixed filter configurations, the transmittance of the filters as a function of signal frequency is fixed. In adjustable filter configurations, adjustable components may be placed in different states to adjust the transmittance characteristics of the filters. If desired, fixed and/or adjustable impedance matching circuits (e.g., circuitry for impedance matching a transmission line to antenna  40  or other wireless circuitry) may be included in paths  54 A and  54 B (e.g., as part of filters  64 A and  64 B or as separate circuits). 
     Filters  64 A and  64 B may be configured so that the antenna feeds in antenna  40  may operate satisfactorily, even in a configuration in which multiple feeds are coupled to antenna  40  simultaneously. The way in which filters  64 A and  64 B may be configured to support the simultaneous presence of multiple feeds is set forth in connection with  FIGS. 10 ,  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 ,  18 ,  19 , and  20 . 
       FIG. 10  is a diagram of antenna  40  in a configuration in which antenna  40  has only a single feed (feed FA). In the illustrative arrangement of  FIG. 10 , the conductive material that makes up antenna resonating element  50  and antenna ground  52  has been configured so that antenna  40  exhibits a resonance in a desired communications band when operated using feed FA.  FIG. 11  is a graph in which antenna performance (standing wave ratio) for antenna  40  of  FIG. 10  has been plotted as a function of operating frequency f. The illustrative communications band of interest in the example of  FIGS. 10 and 11  is centered at frequency f 1 , as indicated by the resonance peak at frequency f 1  in curve  66  of the graph of  FIG. 11 . 
     When the antenna structures of  FIG. 10  are fed using a different antenna feed such as antenna feed FB of  FIG. 12  instead of antenna feed FA, the frequency response of antenna  40  will be different. In particular, antenna  40  may be configured to exhibit a resonance in a different desired communications band when operated using feed FB. As shown by curve  68  of  FIG. 13 , for example, antenna  40  with feed FB of  FIG. 12  may exhibit an antenna resonance covering a communications band centered at frequency f 2 . 
     To allow wireless communications circuitry  34  ( FIG. 2 ) of device  10  to operate in both the communications band at f 1  and the communications band at f 2 , feeds FA and FB may be coupled to antenna  40  using respective filters  64 A and  64 B, as shown in  FIG. 14 . Filters  64 A and  64 B may be configured so that antenna  40  of  FIG. 14  continues to exhibit the frequency response of curve  66  of  FIG. 11  when using feed FA and continues to exhibit the frequency response of curve  68  of  FIG. 13  when using feed FB, even though feeds FA and FB are both present in antenna  40 . 
     In particular, filter  64 A may be configured to form an impedance at frequencies near f 1  (e.g., in the communications band centered at frequency f 1 ) that allows signals at frequencies near frequency f 1  to pass through the filter. Filter  64 A may also be configured to form an impedance (e.g., an open circuit or a short circuit) at frequencies near f 2 , (e.g., in the communications band centered at frequency f 2 ) that effectively decouples the circuitry associated with feed FA from antenna  40  at frequencies near f 2 . Filter  64 B may be configured to form an impedance at frequencies near f 2  (e.g., in the communications band centered at frequency f 2 ) that allows signals at frequencies near frequency f 2  to pass through filter  64 B. Filter  64 B may also be configured to form an impedance (e.g., an open circuit or a short circuit) at frequencies near f 1 , (e.g., in the communications band centered at frequency f 1 ) that effectively decouples the circuitry associated with feed FB from antenna  40  at frequencies near f 1 . 
     Using this type of filter configuration, antenna  40  may exhibit a response of the type shown by curve  70  of  FIG. 15  when using feed FA and a response of the type shown by curve  72  when using feed FB. At frequencies near frequency f 1 , filter  64 A will pass signals to be transmitted and/or received by antenna  40  using feed FA, whereas filter  64 B will form an open circuit (or other impedance) that effectively disconnects feed FB from antenna  40  at frequencies near frequency f 1 . When operating antenna  40  using feed FA at frequencies near f 1 , antenna  40  of  FIG. 14  will therefore be able to exhibit a frequency response similar to that of curve  66  of  FIG. 11  (i.e., curve  70  of  FIG. 15  will match curve  66  of  FIG. 11 ). If filter  64 B were instead configured to have an impedance that does not decouple feed FB from antenna  40  at frequencies near frequency f 1 , feed FB would effectively be present during operation of feed FA. This could adversely affect the performance of antenna  40  (e.g., by producing a response curve such as response curve  74  of  FIG. 15 ). 
     The frequency responses of filters  64 A and  64 B may likewise be used to isolate feed FB from feed FA when operating antenna  40  of  FIG. 14  at frequencies near frequency f 2 . In particular, antenna  40  may exhibit a response of the type shown by curve  72  of  FIG. 16  when using feed FB because the impedance that is formed by filter  64 B at frequencies near frequency f 2  will allow signals to be transmitted and/or received by antenna  40  through filter  64 B using feed FB, while filter  64 A forms an open circuit (i.e., a high impedance or other suitable impedance) that effectively disconnects feed FA from antenna  40  at frequencies near frequency f 2 . As a result, antenna  40  of  FIG. 14  will be able to exhibit a frequency response similar to that of curve  68  of  FIG. 113  (i.e., curve  72  of  FIG. 16  will match curve  68  of  FIG. 13 ) using feed FB. If filter  64 A were instead configured to have an impedance that does not decouple feed FA from antenna  40  at frequencies near frequency f 2 , feed FA would effectively be present during operation of feed FB. This could adversely affect the performance of antenna  40  (e.g., by producing a response curve such as response curve  76  of  FIG. 16 ). 
     In general, filters  64 A and  64 B may be configured to have any suitable impedance versus frequency characteristics. Consider, as an example, a scenario of the type shown in  FIGS. 17 ,  18 ,  19 , and  20 . As shown in  FIG. 17 , antenna  40  may be configured so that a desired frequency response such as the frequency response of curve  78  of  FIG. 18  (i.e., a frequency resonance that peaks for a communications band centered at frequency f 1 ) is obtained when a given impedance value ZB is present in the location associated with feed FB during use of antenna feed FA (at least at frequencies in the vicinity of resonant frequency f 1 ). Antenna  40  may, at the same time, be configured so that a desired frequency response such as the frequency response of curve  80  of  FIG. 20  (i.e., a frequency resonance that peaks for a communications band centered at frequency f 2 ) is obtained when an impedance ZA is present in the location associated with feed FA during use of antenna feed FB (at least at frequencies in the vicinity of resonant frequency f 2 ). 
     Antenna  40  of  FIG. 14  may be provided with the same antenna resonating element  50  and ground plane  52  as the illustrative antenna structures of  FIGS. 17 and 19 . To ensure that the desired frequency response for antenna  40  is obtained when both feeds FA and FB are present, filter  64 A may be configured to form an impedance at frequencies near frequency f 1  that allows signals to pass through filter  64 A to antenna  40  at feed FA during operation at frequencies near f 1  and may be configured to form an impedance of ZA of  FIG. 19  during operation at frequencies near frequency f 2 . Filter  64 B may be configured to form an impedance at frequencies near frequency f 2  that allows signals to pass through filter  64 B to antenna  40  at feed FB during operation at frequencies near f 2  and may be configured to form a circuit with an impedance of ZB of  FIG. 17  during operation at frequencies near frequency f 1 . 
     With this arrangement, use of feed FA will result in a frequency response (for antenna  40  of  FIG. 14 ) such as curve  78  of  FIG. 18  (because filter  64 B will have impedance ZB as desired during operation in the communications band at frequency f 1 ). Use of feed FB will result in a frequency response (for antenna  40  of  FIG. 14 ) such as curve  80  of  FIG. 20  (because filter  64 A will have impedance ZA as desired during operation in the communications band at frequency f 2 ). 
     Impedances ZA and ZB may, in general, have any complex values (e.g., with zero or non-zero real and imaginary parts). For example, Z 1  may be associated with a particular value of capacitance between resonating element  50  and ground  52 , may be associated with a particular inductance between resonating element  50  and ground  52 , may be associated with parallel inductive and capacitive components, may exhibit a short circuit behavior at particular frequencies, may produce an open circuit at particular frequencies, etc. 
     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. 21 . As shown in  FIG. 21 , 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 antenna resonating elements such as antenna resonating element  50  of  FIG. 3 . For example, the uppermost segment of peripheral conductive member  16  in region  22  may serve as an antenna resonating element for an antenna in device  10 . The conductive materials of peripheral conductive member  16 , the conductive materials of ground plane  52 , and dielectric openings  82  (and gaps  18 ) may be used in forming one or more antennas in device  10  such as an upper antenna in region  22  and a lower antenna in region  20 . Configurations in which an antenna in upper region  22  is implemented using a dual feed arrangement of the type described in connection with  FIG. 14  are sometimes described herein as an example. 
     Using a device configuration of the type shown in  FIG. 22 , a dual-feed antenna such as antenna  40  of  FIG. 22  may be implemented (e.g., a dual-feed inverted-F antenna). Segment  16 ′ of the peripheral conductive member (see, e.g., peripheral conductive member  16  of  FIG. 21 ) may form antenna resonating element  50 . Ground plane  52  may be separated from antenna resonating element  50  by gap  82 . Gaps  18  may be formed at either end of segment  16 ′ and may have associated parasitic capacitances. Conductive path  84  may form a short circuit path between antenna resonating element (i.e., segment  16 ′) and ground  52 . First antenna feed FA and second antenna feed FB may be located at different locations along the length of antenna resonating element  50 , as described in connection with the example of  FIG. 14 . 
     As shown in  FIG. 23 , it may be desirable to provide each of the feeds of antenna  40  with filter circuitry and impedance matching circuitry. In a configuration of the type shown in  FIG. 23 , antenna resonating element  50  may be formed from a segment of peripheral conductive member  16  (e.g., segment  16 ′ of  FIG. 22 ). Antenna ground  52  may be formed from ground plane structures such as ground plane structure  52  of  FIG. 21 . Antenna  40  of  FIG. 23  may be, for example, an upper antenna in region  22  of device  10  (e.g., an inverted-F antenna). Device  10  may also have additional antennas such as antenna  40 ′ (e.g., an antenna formed in lower portion  20  of device  10 , as shown in  FIG. 21 ). 
     In the illustrative example of  FIG. 23 , satellite navigation receiver  35  (e.g., a Global Positioning System receiver or a receiver associated with another satellite navigation system) may serve as a first transceiver for device  10  such as transceiver  62 A of  FIG. 9 , whereas cellular telephone transceiver circuitry  38  (e.g., a cellular telephone transmitter and a cellular telephone receiver) may serve as a second transceiver for device  10  such as transceiver  62 B of  FIG. 9 . If desired, other types of transceiver circuitry may be used in device  10 . The example of  FIG. 23  is merely illustrative. 
     As shown in  FIG. 23 , receiver  35  may be coupled to antenna  40  at first antenna feed FA and transceiver  38  may be coupled to antenna  40  at second antenna feed FB. 
     Incoming signals for receiver  35  may be received through band-pass filter  64 A, optional impedance matching circuits such as matching circuits M 1  and M 4 , and low noise amplifier  86 . The signals received from feed FA may be conveyed through components such as matching filter M 1 , band-pass filter  64 A, matching circuit M 4 , and low noise amplifier  86  using transmission lines paths such as transmission line path  54 A (see, e.g.,  FIGS. 3 and 9 ). Additional components may be interposed in transmission line path  54 A, if desired. 
     Signals associated with transmit and receive operations for cellular transceiver circuitry  38  may be handled using notch filter  64 B, optional impedance matching circuits such as matching circuits M 2  and M 3 , antenna selection switch  88 , and circuitry  90 . Antenna selection switch  88  may have a first state in which antenna  40  is coupled to transceiver  38  and a second state in which antenna  40 ′ is coupled to transceiver  38  (as an example). If desired, switch  88  may be a cross-bar switch that couples either antenna  40  or antenna  40 ′ to transceiver  38  while coupling the remaining antenna to another transceiver. 
     Circuitry  90  may include filters (e.g., duplexers, diplexers, etc.), power amplifier circuitry, band selection switches, and other components. The components used in transmitting and receiving signals with feed FB may be conveyed through components such as matching filter M 2 , notch filter  64 B, matching circuit M 3 , and circuitry  90  using transmission lines paths such as transmission line path  54 B (see, e.g.,  FIGS. 3 and 9 ). Additional components may be interposed in transmission line path  54 B, if desired. 
     The transmission T that may be exhibited by notch filter  64 B and band-pass filter  64 A as a function of frequency f is shown in  FIG. 24 . In the graph of  FIG. 24 , the transmission of notch filter  64 B is represented by the transmission characteristic of line  92 , whereas the transmission of band-pass filter  64 A is represented by the transmission characteristic of line  94 . As indicated by line  94 , band-pass filter  64 A may pass signals with frequencies in a passband centered at frequency f C  and may block lower and higher frequencies such as frequencies f L  and f H . As indicated by line  92 , notch filter  64 B may have a transmission characteristic that is complementary to that of band-pass filter  64 A. In particular, notch filter  64 B may block signals in a frequency band centered around frequency f C  while passing lower frequency signals in the vicinity of frequency f L  and while passing higher frequency signals in the vicinity of frequency f H  (i.e., notch filter  64 B may have a stopband that overlaps the passband of band-pass filter  64 A). 
       FIGS. 25 and 26  are graphs in which antenna performance (i.e., standing wave ratio) has been plotted as a function of frequency for antenna  40  using antenna feeds FA and FB, respectively. Three performance curves are shown in  FIG. 25 . Curve  96  corresponds to the performance of antenna  40  of  FIG. 23  when feed FA is in the position shown in  FIG. 23 . The location of feed FA (in this example) has been chosen to maximize antenna performance at frequencies surrounding frequency f C  (e.g., at frequencies surrounding 1575 MHz in a configuration in which receiver  35  is a Global Positioning System receiver). Alteration of the position of feed FA to position FA′ or FA″ of  FIG. 23  may result in detuning and reduced antenna performance, as indicated by lines  98  and  100 , respectively, in  FIG. 25 . Signals at frequencies surrounding frequency f C  (i.e., signals with frequencies between frequency f 1  and f 2 ) may be passed to receiver  35  via the passband of band-pass filter  64 A. Out-of-band signals at frequencies (i.e., signals below f 1  and above f 2 ) will be attenuated by band-pass filter  64 A. The ability to position feed FA in an portion of antenna  40  in which antenna performance at frequency f C  has been maximized may help device  10  receive and process satellite navigation system signals (or other suitable signals) using a receiver such as receiver  35 . 
     The illustrative antenna performance curve of  FIG. 26  (curve  102 ) corresponds to the performance of antenna  40  when feed FB and cellular telephone transceiver circuitry  38  are being used to transmit and receive radio-frequency signals (e.g., using feed FB in the position shown in  FIG. 23 ). The location of feed FB (in this example) has been chosen to maximize antenna performance for transceiver circuitry  38  at frequencies surrounding frequency f L  (e.g., at cellular telephone low-band frequencies from f 3  to f 4 ) and at frequencies surrounding frequency f H  (e.g., at high-band cellular telephone frequencies from f 5  to f 6 ). Frequencies f 3 , f 4 , f 5 , and f 6  may be, as examples, 700 MHz, 960 MHz, 1700 MHz, and 2200 MHz. Antenna  40  may be configured to cover other frequencies if desired (e.g., by shifting the position of feed FB, by changing the size and shape of resonating element  50 , etc.). 
     Notch filter  64 B is configured to pass signals below frequency f 1  (i.e., signals in the communications band extending from frequency f 3  to f 4 ) and is configured to pass signals above frequency f 2  (i.e., signals in the communications band extending from frequency f 5  to f 6 ). The stopband portion of notch filter  64 B may block signals with frequencies between f 1  and f 2  (i.e., the Global Positioning System signals that are handled by receiver  35 ), as indicated by blocked portion  101  of curve  102  of the graph of  FIG. 26 . 
     Filters  64 A and  64 B of antenna  40  of  FIG. 23  operate as described in connection with  FIG. 14 . During use of receiver  35  and feed FA to receive signals in the band at f C , filter  64 A may have an impedance that couples feed FA to antenna resonating element  50  of  FIG. 23  and allows the signals in the band at f C  to reach receiver  35 . Filter  64 B may have an impedance at frequency f C  that effectively disconnects the circuitry that is coupled to feed FB from antenna  40  (i.e., transceiver  38  may effectively be decoupled from antenna  40  at frequency f C ). During use of transceiver  38  and feed FB to transmit and receive signals in the bands at f L  and f H , filter  64 B may have an impedance that couples feed FB to antenna resonating element  50  of  FIG. 23  and allows the signals in the bands at f L  and f H  to reach transceiver  38 . Filter  64 A may have an impedance at frequencies in the bands at f L  and f H  that effectively disconnects the circuitry that is coupled to feed FA from antenna  40  (i.e., receiver  35  may be effectively decoupled from antenna  40  at frequencies in the bands at f L  and f H ). 
     With one suitable arrangement, filter  64 A may have a high impedance in the bands at f L  and f H  to effectively disconnect the circuitry that is coupled to feed FA from antenna  40 . Low impedances (short circuits) may also be used in decoupling receiver  35  and the other circuitry of feed FA from antenna  40  during operation in the frequencies associated with feed FB. For example, filter  64 A may be configured to exhibit a short circuit (low impedance) condition at frequencies above f 2  (e.g., at frequencies from f 5  to f 6 ), rather than an open circuit condition. When exposed to this short circuit, signals at frequencies from f 5  to f 6  may be reflected from filter  64 A with a phase shift of 180°. The short circuit may thereby effectively disconnect the circuitry that is coupled to feed FA from antenna  40 . Regardless of whether filter  64 A forms an open circuit at frequencies of f 3  to f 4  and at frequencies of f 5  to f 6 , whether filter forms an open circuit at frequencies of f 3  to f 4  while forming a short circuit at frequencies of f 5  to f 6 , or whether other suitable configurations are used, filters  64 A and  64 B may be configured to allow feed FA to be optimized to support operation of receiver  35  without being adversely affected by the presence of the circuitry coupled to feed FB, while allowing feed FB to be optimized to support operation of transceiver  38  without being adversely affected by feed FA. 
     If desired, device  10  may be provided with tunable components that can be used in tuning antenna  40 . For example, filters such as filters  64 A and  64 B and matching circuits such as optional matching circuits M 1 , M 2 , M 3 , and M 4  may be implemented using tunable components (or, if desired, fixed components). With one suitable arrangement, matching circuits such as matching circuits M 2  and M 4  of  FIG. 23  may be omitted, matching circuit M 1  of  FIG. 23  may be implemented using a fixed matching circuit, and matching circuit M 3  of  FIG. 23  may be implemented using a tunable matching circuit. 
     The circuitry of tunable matching circuit M 3  (or other tunable antenna circuits) may be implemented using one or more adjustable components. Examples of adjustable components are shown in  FIGS. 27 ,  28 ,  29 ,  30 , and  31 . If desired, antenna  40  may be tuned using a tunable capacitor (variable capacitor) such as variable capacitor  104  of  FIG. 27 , may be tuned using a radio-frequency switch such as switch  106  of  FIG. 28 , may be tuned using a variable inductor such as variable inductor  108  of  FIG. 29 , may be tuned using an adjustable capacitor such as adjustable capacitor  110  of  FIG. 30 , may be tuned using an adjustable inductor such as adjustable inductor  112  of  FIG. 31 , and may be tuned using other adjustable components and combinations of two or more of such components (e.g., combinations of tunable and/or fixed components). 
     Adjustable capacitor  110  of  FIG. 30  may include an array of capacitors  114  and associated switches  116  for selectively switching one or more of capacitors  114  into place between adjustable capacitor terminals  118  and  120 . The states of switches  116  may be controlled by control signals from control circuitry in device  10  (e.g., a baseband processor in storage and processing circuitry  28  of  FIG. 2 ). Capacitors  114  may be selectively coupled in parallel between terminals  118  and  120  as shown in  FIG. 30 . Other configurations for adjustable capacitor  110  may be used, if desired. For example, configurations in which capacitors are connected in series and are provide with switch-based selective bypass paths may be used, configurations with combinations of parallel and series-connected capacitors may be used, etc. 
     Adjustable inductor  112  of  FIG. 31  may include an array of inductors  122  and associated switches  124  for selectively switching one or more of inductors  122  into place between adjustable inductor terminals  126  and  128 . Inductors  122  may, for example, be selectively coupled in parallel between terminals  126  and  128 . The states of switches  124  may be controlled by control signals from control circuitry in device  10  (e.g., a baseband processor in storage and processing circuitry  28  of  FIG. 2 ). Other configurations for adjustable inductor  112  may be used, if desired (e.g., configurations in which inductors are connected in series and are provide with switch-based selective bypass paths, configurations with combinations of parallel and series-connected inductors, etc.). 
       FIG. 32  is a diagram of a portion of the circuitry of  FIG. 23  that is associated with feed FB showing how impedance matching circuitry M 3  may be implemented using tunable circuitry. Tunable matching circuit M 3  may, for example, be provided with a tunable capacitor such as switched-based adjustable capacitor  110 . Tunable matching circuit M 3  and other circuitry in antenna  40  (e.g., matching circuits such as matching circuits M 1 , M 2 , M 4 , filters  64 A and  64 B, etc.) may, in general, include inductors, capacitors, resistors, continuously variable inductors, continuously variable resistors, continuously variable capacitors, switch-based adjustable capacitors such as switch-based adjustable capacitor  114  of  FIG. 30 , switch-based adjustable inductors such as switch-based adjustable inductor  112  of  FIG. 31 , switches, conductive lines, and additional fixed and/or adjustable components. 
     As shown in  FIG. 32 , adjustable components such as adjustable capacitor  110  of matching circuit M 3  may be controlled by control signals provided over signal path  130 . Path  130  may include one or more conductive lines (e.g., two or more lines, three lines or more than three lines, etc.) that carry control signals to respective switches  116  in adjustable capacitor  114  from control circuitry such as baseband processor  132  (e.g., control circuitry such as storage and processing circuitry  28  of  FIG. 2 ). During operation, baseband processor  132  may receive digital data that is to be transmitted from storage and processing circuitry  28  at path  134  and may use radio-frequency transceiver circuitry  38  to transmit corresponding radio-frequency signals over antenna  40  through matching circuit M 3  and notch filter  64 B at feed FB. During data reception operations, baseband processor  132  may receive signals using transceiver  38  and may provide corresponding data to path  134 . 
       FIG. 33  is a graph in which antenna performance (standing wave ratio) has been plotted as a function of operating frequency for antenna  40  using feed FB and the circuitry of  FIG. 32 . In the illustrative configuration of antenna  40  of  FIG. 23  in which matching circuits M 2  and M 4  have been omitted, in which matching circuit M 1  has been implemented using fixed impedance matching circuitry, and in which impedance matching circuit M 3  has been implemented using one or more tunable components such as switch-based adjustable capacitor  110  of  FIG. 32 , the performance of antenna  40  at high-band frequencies is relatively unaffected by the state of adjustable capacitor  110 . As a result, portion  134  of the antenna performance curve of  FIG. 33  is relatively constant regardless of the state of capacitor  110 . Portion  134  may, for example, cover a frequency range of about 1700 MHz (e.g., frequency f 5  of  FIG. 26 ) to a frequency of about 2200 MHz (e.g., frequency f 6  of  FIG. 26 ). 
     At lower frequencies such as frequencies from 700 MHz (e.g., frequency f 3  of  FIG. 26 ) to 960 MHz (e.g., frequency f 4  of  FIG. 26 ), a single antenna resonance peak can be tuned to cover a lower sub-band centered at frequency f 7  (as shown by curve  136 ), a middle sub-band centered at frequency f 8  (as shown by curve  138 ), and an upper sub-band centered at frequency f 9  (as shown by curve  140 ). 
     Adjustable capacitor  110  may have three states exhibiting respectively distinct capacitance values C 1 , C 2 , and C 3  (e.g., capacitances in the range of about 0.5 pF to about 10 pF). When capacitor  110  is placed in its C 1  state, antenna  40  may exhibit a response corresponding to curves  136  and  134 . When capacitor  110  is placed in its C 2  state, antenna  40  may exhibit a response corresponding to curves  138  and  134 . Antenna  40  may exhibit a response corresponding to curves  140  and  134  when capacitor  110  is placed in its C 3  state. Configurations for tunable matching circuit M 3  that exhibit more than three states or fewer than three states may also be used. The use of an adjustable capacitor and matching circuit such as matching circuit M 3  of  FIG. 32  that may be adjusted between three different tuning states is merely illustrative. 
     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: 20120208
Publication Date: 20140805
Grant Date: 20140805
Priority Date: 20120208
Inventors: DARNELL DEAN F.
OUYANG YUEHUI
XU HAO
AYALA VAZQUEZ ENRIQUE
ZHOU YIJUN
BEVELACQUA PETER
NICKEL JOSHUA G.
JIN NANBO
MOW MATTHEW A.
SCHLUB ROBERT W.
PASCOLINI MATTIA
HU HONGFEI
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/35", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 47710299