PATENT DOCUMENT

Publication Number: US-9444130-B2
Application Number: US-201313860396-A
Country: US
Kind Code: B2

Title: Antenna system with return path tuning and loop element

Abstract:
Electronic devices may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may include a dual arm inverted-F antenna resonating element and an antenna ground. An antenna feed may be coupled between the inverted-F antenna resonating element and the antenna ground. An adjustable component such as an adjustable inductor may be coupled between the inverted-F antenna resonating element and the antenna ground in parallel with the antenna feed. The adjustable component may be operable in multiple states such as an open circuit state, a short circuit state, and a state in which the adjustable component exhibits a non-zero inductance. Antenna bandwidth can be broadened by coupling a loop antenna resonating element across the antenna feed. A portion of the antenna ground may overlap the loop antenna resonating element to further enhance antenna bandwidth.

Claims:
What is claimed is: 
     
       1. Electronic device antenna structures, comprising:
 an antenna ground; 
 a first antenna resonating element; 
 an antenna feed coupled between the antenna ground and the first antenna resonating element, wherein the antenna feed has a positive antenna feed terminal and a ground antenna feed terminal; and 
 a second antenna resonating element interposed between the first antenna resonating element and the antenna ground that has a first end coupled to the positive antenna feed terminal and a second end coupled to the ground antenna feed terminal, wherein the first antenna resonating element comprises an inverted-F antenna resonating element, the second antenna resonating element comprises a loop antenna resonating element, a portion of the loop antenna resonating element overlaps a portion of the antenna ground, the first antenna resonating element comprises a portion of a peripheral conductive electronic device housing member that is formed at an exterior of an electronic device, and the portion of the peripheral conductive electronic device housing member is separated from the antenna ground by a first dielectric gap having a first length and is separated from the portion of the antenna ground that overlaps the portion of the loop antenna resonating element by a second gap having a second length that is less than the first length. 
 
     
     
       2. The electronic device antenna structures defined in  claim 1  wherein the inverted-F antenna resonating element comprises a portion of a peripheral conductive electronic device housing member. 
     
     
       3. The electronic device antenna structures defined in  claim 2  further comprising a return path coupled between the first antenna resonating element and the antenna ground in parallel with the antenna feed. 
     
     
       4. The electronic device antenna structures defined in  claim 3  wherein the return path includes an adjustable electrical component. 
     
     
       5. The electronic device antenna structures defined in  claim 4  wherein the adjustable electrical component comprises an adjustable inductor. 
     
     
       6. The electronic device antenna structures defined in  claim 5  wherein the adjustable inductor includes switching circuitry, a short circuit path, and a fixed inductor and wherein the switching circuitry is configured to selectively switch the short circuit path and the fixed inductor into use in the return path. 
     
     
       7. The electronic device antenna structures defined in  claim 6  wherein the switching circuitry is further configured to simultaneously switch the short circuit path and the fixed inductor out of use to place the return path in an open circuit state. 
     
     
       8. The electronic device antenna structures defined in  claim 2 , wherein the portion of the peripheral conductive electronic device housing member comprises at least one external surface of an electronic device and the antenna ground is separated from the portion of the peripheral conductive electronic device housing member by a gap. 
     
     
       9. The electronic device antenna structures defined in  claim 8 , wherein the portion of the peripheral conductive electronic device housing member forms at three different external surfaces of the electronic device. 
     
     
       10. The electronic device antenna structures defined in  claim 1  further comprising a return path coupled between the first antenna resonating element and the antenna ground in parallel with the antenna feed, wherein the return path is selectively placed in at least two different states including a short circuit state and a non-zero inductance state. 
     
     
       11. The electronic device antenna structures defined in  claim 10  further comprising an adjustable circuit in the return path that places the return path in the short circuit state and the non-zero inductance state, wherein the adjustable circuit is operable to place the return path in an open circuit state. 
     
     
       12. The electronic device antenna structures defined in  claim 1 , wherein a first end of the loop antenna resonating element is electrically connected to the positive antenna feed terminal and a second end of the loop antenna resonating element is electrically connected to the negative antenna feed terminal. 
     
     
       13. The electronic device antenna structures defined in  claim 12 , wherein the loop antenna resonating element comprises a strip of metal. 
     
     
       14. The electronic device antenna structures defined in  claim 1 , wherein the inverted-F antenna resonating element has a first arm that is configured to resonate in high band frequency range and a second arm that is configured to resonate in a low band frequency range, the first arm extends from a first side of the positive antenna feed terminal and in a given plane, the second arm extends from a second side of the positive antenna feed terminal and in the given plane, and the loop antenna resonating element extends from the first side of the positive antenna feed terminal. 
     
     
       15. Electronic device antenna structures, comprising:
 an antenna ground; 
 an inverted-F antenna resonating element having a first arm that is configured to resonate in high band frequency range and a second arm that is configured to resonate in a low band frequency range; 
 an antenna feed coupled between the antenna ground and the inverted-F antenna resonating element, wherein the antenna feed has a positive antenna feed terminal and a ground antenna feed terminal, the first arm extends from a first side of the positive antenna feed terminal and in a given plane, and the second arm extends from a second side of the positive antenna feed terminal and in the given plane; and 
 a loop antenna resonating element interposed between the inverted-F antenna resonating element and the antenna ground that has a first end coupled to the positive antenna feed terminal and a second end coupled to the ground antenna feed terminal, wherein the loop antenna resonating element extends from the first side of the positive antenna feed terminal, an entirety of the loop antenna resonating element extends along the first side of the positive antenna feed terminal, and the loop antenna resonating element is configured to broaden the high band frequency range in which the first arm resonates. 
 
     
     
       16. Electronic device antenna structures, comprising:
 an antenna ground; 
 a first antenna resonating element; 
 an antenna feed coupled between the antenna ground and the first antenna resonating element, wherein the antenna feed has a positive antenna feed terminal and a ground antenna feed terminal; and 
 a second antenna resonating element that has a first end coupled to the positive antenna feed terminal and a second end coupled to the ground antenna feed terminal, wherein the first antenna resonating element has a first arm configured to resonate in a low band frequency range and a second arm configured to resonate in a high band frequency range, and the second antenna resonating element is configured to broaden the high band frequency range in which the second arm of the first antenna resonating element resonates.

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. 
     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 include radio-frequency transceiver circuitry and antenna structures. The radio-frequency transceiver circuitry may operate in multiple communications bands. The radio-frequency transceiver circuitry may, for example, operate in multiple cellular telephone bands. 
     The antenna structures may include a dual arm inverted-F antenna resonating element and an antenna ground. An antenna feed may be coupled between the inverted-F antenna resonating element and the antenna ground. An adjustable component such as an adjustable inductor may be coupled between the inverted-F antenna resonating element and the antenna ground to form an adjustable return path in parallel with the antenna feed. 
     The adjustable component may be operable in multiple states such as an open circuit state, a short circuit state, and a state in which the adjustable component exhibits a non-zero inductance. The adjustable component may also be operable in a pair of states such as a short circuit state and a non-zero inductance state. Control circuitry in the electronic device may be used to place the adjustable component in a suitable state for operating the antenna structures in a desired frequency range. 
     Antenna bandwidth can be broadened by coupling a loop antenna resonating element across the antenna feed. The loop antenna resonating element may contribute to the resonance of the antenna in a high frequency communications band. A portion of the antenna ground may overlap the loop antenna resonating element to further enhance antenna bandwidth. Adjustments to the adjustable component may be used to tune a low frequency band and may be used to ensure that the antenna operates efficiently in the high frequency band. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative electronic device with an adjustable antenna in accordance with an embodiment of the present invention. 
         FIG. 4  is a table showing illustrative settings for a tunable component such as an adjustable inductor that may be used when configuring an antenna in an electronic device to cover various different communications bands of interest in accordance with an embodiment of the present invention. 
         FIG. 5  is a graph in which antenna efficiency has been plotted as a function of operating frequency in a high frequency communications band for two different settings of an adjustable inductor in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph in which antenna efficiency has been plotted as a function of operating frequency in a low frequency communications band for two different settings of an adjustable inductor in accordance with an embodiment of the present invention. 
         FIG. 7  is a table showing illustrative settings for a tunable component such as an adjustable inductor that may be used when configuring an antenna in an electronic device to cover high and low communications bands in accordance with an embodiment of the present invention. 
         FIG. 8  is a graph in which antenna efficiency has been plotted as a function of operating frequency for antenna structures such as those using the settings of  FIG. 7  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 peripheral structures such as 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 display cover layer such as a layer of clear glass or plastic may cover the surface of display  14 . Buttons such as button  19  may pass through openings in the cover layer. The cover layer may also have other openings such as an opening for speaker port  26 . 
     Housing  12  may include peripheral housing structures such as structures  16 . Structures  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, structures  16  may be implemented using a peripheral housing member have a rectangular ring shape (as an example). Peripheral structures  16  or part of peripheral structures  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 ). Peripheral structures  16  may also, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls, etc.). 
     Peripheral housing structures  16  may be formed of a conductive material such as metal and may therefore sometimes be referred to as peripheral conductive housing structures, conductive housing structures, peripheral metal structures, or a peripheral conductive housing member (as examples). Peripheral housing structures  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming peripheral housing structures  16 . 
     It is not necessary for peripheral housing structures  16  to have a uniform cross-section. For example, the top portion of peripheral housing structures  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. If desired, the bottom portion of peripheral housing structures  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 , peripheral housing structures  16  have substantially straight vertical sidewalls. This is merely illustrative. The sidewalls formed by peripheral housing structures  16  may be curved or may have other suitable shapes. In some configurations (e.g., when peripheral housing structures  16  serve as a bezel for display  14 ), peripheral housing structures  16  may run around the lip of housing  12  (i.e., peripheral housing structures  16  may cover only the edge of housing  12  that surrounds display  14  and not the rest of the sidewalls of housing  12 ). 
     If desired, housing  12  may have a conductive rear surface. For example, housing  12  may be formed from a metal such as stainless steel or aluminum. The rear surface of housing  12  may lie in a plane that is parallel to display  14 . In configurations for device  10  in which the rear surface of housing  12  is formed from metal, it may be desirable to form parts of peripheral conductive housing structures  16  as integral portions of the housing structures forming the rear surface of housing  12 . For example, a rear housing wall of device  10  may be formed from a planar metal structure and portions of peripheral housing structures  16  on the left and right sides of housing  12  may be formed as vertically extending integral metal portions of the planar metal structure. Housing structures such as these may, if desired, be machined from a block of metal. 
     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 sheet formed from one or more parts 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 housing structures  16  and opposing conductive structures such as conductive housing midplate or rear housing wall structures, a conductive ground plane associated with a printed circuit board, and conductive electrical components in device  10 ). These openings, which may sometimes be referred to as gaps, 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, may contribute to the performance of a parasitic antenna resonating element, 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 peripheral housing structures  16  may be provided with gap structures. For example, peripheral housing structures  16  may be provided with one or more gaps such as gaps  18 , as shown in  FIG. 1 . The gaps in peripheral housing structures  16  may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  18  may divide peripheral housing structures  16  into one or more peripheral conductive segments. There may be, for example, two peripheral conductive segments in peripheral housing structures  16  (e.g., in an arrangement with two gaps), three peripheral conductive segments (e.g., in an arrangement with three gaps), four peripheral conductive segments (e.g., in an arrangement with four gaps, etc.). The segments of peripheral conductive housing structures  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 control circuitry such as 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, filters, duplexers, 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. Wireless local area network transceiver circuitry such as transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in cellular telephone bands such as bands in frequency ranges of about 700 MHz to about 2700 MHz or bands at higher or lower frequencies. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include wireless circuitry for receiving radio and television signals, paging circuits, etc. Near field communications may also be supported (e.g., at 13.56 MHz). 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 have antenna structures such as one or more antennas  40 . Antenna structures  40  may be formed using any suitable antenna types. For example, antenna structures  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, dual arm 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. Antenna structures in device  10  such as one or more of antennas  40  may be provided with one or more antenna feeds, fixed and/or adjustable components, and optional parasitic antenna resonating elements so that the antenna structures cover desired communications bands. 
     Illustrative antenna structures of the type that may be used in device  10  (e.g., in region  20  and/or region  22 ) are shown in  FIG. 3 . Antenna structures  40  of  FIG. 3  may be located at lower end  20  of device  10  or other suitable portions of device  10  (e.g., upper end  22 ). Antenna structures  40  may include antenna ground  52  and may include antenna resonating element structures  50 . Antenna resonating element structures  50  may include an antenna resonating element such as antenna resonating element  50 A. Antenna resonating element  50 A may be a dual arm inverted-F antenna resonating element (sometimes referred to as a T antenna resonating element). Antenna resonating element structures  50  may also include an antenna resonating element such as loop antenna resonating element  50 B. Antenna resonating element structures  50  may use structures such as inverted-F antenna resonating element  50 A and loop antenna resonating element  50 B to form an antenna that covers communications bands of interest. 
     The conductive structures that form antenna resonating element structures  50 A and  50 B 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 may be formed using other conductive structures. 
     Both resonating element  50 A and resonating element  50 B may contribute to the overall response of antenna  40 . Antenna  40  may therefore sometimes be referred to as being a hybrid antenna that includes both loop antenna and inverted-F antenna structures. If desired, antenna  40  can be based on other types of antenna (e.g., a monopole antenna, a patch antenna, a slot antenna, or other suitable antenna structures). The configuration of  FIG. 3  in which antenna  40  has an inverted-F resonating element and a loop resonating element is merely illustrative. 
     As shown in  FIG. 3 , antenna structures  40  may be coupled to wireless circuitry  90  such as transceiver circuitry, filters, switches, duplexers, impedance matching circuitry, and other circuitry using transmission line structures such as transmission line  92 . Transmission line  92  may have positive signal path  92 A and ground signal path  92 B. Paths  92 A and  92 B may be formed from metal traces on rigid printed circuit boards, may be formed from metal traces on flexible printed circuits, may be formed on dielectric support structures such as plastic, glass, and ceramic members, may be formed as part of a cable, or may be formed from other conductive signal lines. Transmission line  92  may be formed using one or more microstrip transmission lines, stripline transmission lines, edge coupled microstrip transmission lines, edge coupled stripline transmission lines, coaxial cables, or other suitable transmission line structures. Circuits such as impedance mating circuits, filters, switches, duplexers, diplexers, and other circuitry may, if desired, be interposed in transmission line  92 . 
     Transmission line  92  may be coupled to an antenna port for antenna  40 . Antenna port  106 , which may sometimes be referred to as an antenna feed or antenna feed path, may include positive antenna feed terminal  94  and ground antenna feed terminal  96 . If desired, antenna  40  may have multiple feeds. The configuration of  FIG. 3  in which antenna  40  has a single feed is merely illustrative. 
     If desired, tunable components such as adjustable capacitors, adjustable inductors, filter circuitry, switches, impedance matching circuitry, duplexers, and other circuitry may be interposed within transmission line paths (i.e., between wireless circuitry  90  and feed  106 ). Tunable components may also be formed within the structures of antenna  40 . For example, antenna resonating element structures  50  may include a tunable component such as tunable component LT in a return path (sometimes referred to as a short circuit branch or path) such as return path SC. Return path SC couples resonating element arm structures such as arms  100  and  102  of inverted-F antenna resonating element  50 A to antenna ground  52 . Tunable component LT may be an adjustable circuit such as a circuit including switching circuitry, inductor circuitry, and/or capacitor circuitry (as examples). 
     In the example of  FIG. 3 , tunable electrical component LT is an adjustable inductor that has a pair of terminals (terminals  110  and  112 ) that are coupled to the main arm of resonating element  50 A and to antenna ground  52 , respectively. Switch SW can be used to selectively switch short circuit path  114  or inductor  116  into use. Inductor  116  may have a fixed non-zero value (e.g., 24 mH as an example). When short circuit path  114  is switched into use (and inductor  116  is switched out of use), the impedance between terminals  110  and  112  will be 0 ohms (i.e., return path SC will form a short circuit. When short circuit path  114  is switched out of use and inductor  116  is switched into use, the impedance between terminals  110  and  112  will be 24 nH (in this example). Switch SW may also be placed in an open state in which both short circuit path  114  and inductor  116  are switched out of use (i.e., to cause return path SC to be an open circuit and thereby create an effectively infinite impedance between terminals  110  and  112 ). Depending on the type of impedance changes that are desired for a given antenna design, tunable element LT may alternate between a 0 ohm impedance state (short circuit operating mode) and a 24 nH impedance state (non-zero impedance operating mode) or may alternate between 0 ohms (short circuit state), 24 nH (non-zero impedance state), and infinite impedance (open circuit state). Other types of tunable inductor (e.g., with different numbers of operating modes) may be used, if desired. 
     Dielectric gap  101  separates arms  100  and  102  from antenna ground  52 . Antenna ground  52  may be formed from housing structures such as a metal midplate member, printed circuit traces, metal portions of electronic components, or other conductive ground structures. Gap  101  may be formed by air, plastic, and other dielectric materials. Return path SC may be implemented using a strip of metal, a metal trace on a dielectric support structure such as a printed circuit or plastic carrier, or other conductive path that bridges gap  101  between resonating element arm structures (e.g., arms  102  and/or  100 ) and antenna ground  52 . Tunable component LT may be implemented by a surface mount technology (SMT) device with terminals that are soldered within the metal of path SC, may be formed from multiple parts such as a packaged switch, a length of metal (for forming short circuit path  114 ), and an inductor (for forming inductor  116 ), or may be formed from other tunable circuitry imposed in return path SC. 
     Antenna feed  106  and its associated terminals  94  and  96  may be coupled in a path that bridges gap  101 . The antenna feed formed from terminals  94  and  96  may, for example, be coupled in a path that bridges gap  101  in parallel with return path SC. 
     Resonating element arms  100  and  102  may form respective arms in a dual arm inverted-F antenna resonating element. Arms  100  and  102  may have one or more bends. The illustrative arrangement of  FIG. 3  in which arms  100  and  102  run parallel to ground  52  is merely illustrative. 
     Arm  100  may be a (longer) low-band arm that handles lower frequencies, whereas arm  102  may be a (shorter) high-band arm that handles higher frequencies. Low-band arm  100  may allow antenna  40  to exhibit an antenna resonance at low band (LB) frequencies such as frequencies from 700 MHz to 960 MHz or other suitable frequencies. High-band arm  102  may allow antenna  40  to exhibit one or more antenna resonances at high band (HB) frequencies such as resonances at one or more ranges of frequencies between 960 MHz to 2700 MHz or other suitable frequencies. 
     Loop antenna element  50 B may be formed from a loop of metal such as a strip of metal (e.g., stamped metal foil), metal traces on a flexible printed circuit (e.g., a printed circuit formed from a flexible substrate such as a layer of polyimide or a sheet of other polymer material), metal traces on a rigid printed circuit board substrate (e.g., a substrate formed from a layer of fiberglass-filled epoxy), metal traces on a plastic carrier, patterned metal on glass or ceramic support structures, wires, electronic device housing structures, metal parts of electrical components in device  10 , or other conductive structures. The metal of loop antenna element  50 B may, for example, form a metal strip with a circular shape or other elongated conductive line. One end of the metal strip or other elongated conductive member forming loop  50 B may be connected to positive antenna feed terminal  94  and the opposing end of this conductive loop path may be connected to ground antenna feed terminal  96 . 
     The presence of loop antenna resonating element  50 B in antenna  40  may help expand the range of frequencies covered by a high-band resonance for antenna  40  or may otherwise enhance antenna performance. If desired, loop element  50 B may be omitted and/or other types of antenna resonating elements for broadening the response of antenna resonances in antenna  40  may be used. The illustrative configuration of  FIG. 3  in which antenna  40  includes inverted-F antenna resonating element  50 A and loop antenna resonating element  50 B is merely illustrative. 
     To provide antenna  40  with tuning capabilities, antenna  40  may include adjustable circuitry (e.g., tunable electrical component LT). The adjustable circuitry may be coupled between different locations on antenna resonating element  50 , may be coupled between different locations on resonating element  50 A, may be coupled between different locations on resonating element  50 B, may form part of paths such as feed path  106  and return path SC that bridge gap  101 , may form part of transmission line structures  92  (e.g., circuitry interposed within one or more of the conductive lines in path  92 ), or may be incorporated elsewhere in antenna structures  40 , transmission line paths  92 , and wireless circuitry  90 . 
     The adjustable circuitry (e.g., tunable component LT) may be tuned using control signals from control circuitry  28  of  FIG. 2  (e.g., a control signal applied to switch SW). Control signals from control circuitry  28  may, for example, be provided to an adjustable capacitor, adjustable inductor, or other adjustable circuit using a control signal path that is coupled between control circuitry  28  and the adjustable circuit (e.g., a path coupled to switch SW). Control circuitry  28  may provide control signals to adjust a capacitance exhibited by an adjustable capacitor, may provide control signals to adjust the inductance exhibited by an adjustable inductor, may provide control signals that adjust the impedance of a circuit that includes one or more components such fixed and variable capacitors, fixed and variable inductors, switching circuitry for switching electrical components such as capacitors and inductors, resistors, and other adjustable circuitry into and out of use, or may provide control signals to other adjustable circuitry for tuning the frequency response of antenna structures  40 . As an example, antenna structures  40  may be provided with an adjustable inductor such as adjustable inductor LT of  FIG. 3 . By selecting a desired inductance value for adjustable inductor LT using control signals from control circuitry  28 , antenna structures  40  can be tuned to cover operating frequencies of interest with desired antenna efficiencies. 
       FIG. 4  is a table showing illustrative inductance values that can be produced by adjustable inductor LT in response to control signals that are provided to switching circuitry SW of adjustable inductor LT to support operation in various communications bands. In the example of  FIG. 4 , an antenna of the type shown in  FIG. 3  is being configured in three different ways to cover three different communications bands. When it is desired to use antenna  40  to cover high frequency communications band HB at frequencies of 1710-2170 MHz, inductor LT may be placed in a state in which short circuit line  114  is switched into use between terminals  110  and  112  (i.e., a 0 ohm operating mode for return path SC in which inductor LT forms a short circuit). When it is desired to use antenna  40  to cover a lower portion of low band LB from 700-790 MHz, inductor LT may be placed in a state in which short circuit path  114  and inductor  116  are both switched out of use (i.e., LT forms an open circuit for return path SC, so that the impedance of LT is effectively infinite). When it is desired to use antenna  40  to cover an upper portion of low band LB from 790-960 MHz, inductor LT may be placed in a state in which inductor  116  is switched into use. If, for example, inductor  116  has an inductance value of 24 nH, the inductance of inductor LT will be 24 nH. In this operating mode, return path SC will exhibit a non-zero inductance (e.g., 24 nH or other suitable value). 
       FIG. 5  is a graph in which antenna efficiency for antenna  40  of  FIG. 3  has been plotted as a function of frequency f in high band HB. Dashed line  120  corresponds to the performance of antenna  40  when inductor LT has been configured to exhibit an inductance of 24 nH. Solid line  122  corresponds to the performance of antenna  40  when inductor LT has been configured to exhibit a short circuit impedance (i.e., when short circuit path  114  has been switched into use between terminals  110  and  112  while inductor  116  has been switched out of use). By shorting the main resonating element arm of inverted-F antenna resonating element  50 A to antenna ground  52  via path  114  by configuring inductor LT in return path SC to exhibit a short circuit between terminals  110  and  112 , antenna efficiency for antenna  40  in high band HB can be enhanced, as illustrated by comparing efficiency curve  122  to efficiency curve  120  in  FIG. 5 . 
       FIG. 6  is a graph in which antenna performance in low band LB has been plotted as a function of operating frequency for two different settings of adjustable inductor LT. Solid line curve  124  corresponds to the performance of antenna  40  when inductor LT has been configured to form an open circuit between antenna resonating element  50 A and antenna ground  52  (i.e., when switching circuitry SW is off, thereby switching both short circuit path  114  and inductor  116  out of use to place return path SC in an open circuit mode). By placing return path SC in an open circuit state in this way, antenna efficiency at the lower portion of low band LB (e.g., frequencies from 700 to 790 MHz) can be enhanced. When it is desired to operate antenna  40  in a higher portion of low band LB (e.g., frequencies from 790 MHz to 960 MHz), adjustable inductor LT in return path SC may be placed in a state in which short circuit path  114  is switched out of use and inductor  116  is switched into use. In this configuration, return path SC will exhibit a non-zero impedance of 24 nH due to the presence of inductor  116 , and antenna efficiency will be enhanced at frequencies from 790 to 960 MHz, as illustrated by dashed line  126  of  FIG. 6 . 
     If desired, device  10  may be operated using two states for adjustable inductor LT. As shown in the table of  FIG. 7 , for example, inductor LT may be placed in a 0 ohms (short circuit) mode when it is desired for return path SC to form a short circuit. In this situation, antenna  40  may be used to handle high band (HB) signal frequencies from 1710 to 2690 MHz (as an example). When it is desired to operate antenna  40  from 790 to 960 MHz in low band LB, adjustable inductor LT may be placed in its 24 nH state by switching inductor  116  into use. 
       FIG. 8  is a graph in which antenna performance (standing wave ratio SWR) for an antenna such as antenna  40  of  FIG. 3  has been plotted as a function of operating frequency. In the illustrative configuration of  FIG. 8 , antenna  40  has an adjustable inductor LT that is adjusted between the two states of  FIG. 7 . When it is desired to operate antenna  40  in low band LB, inductor LT is configured to exhibit a non-zero inductance of 24 nH (i.e., return path SC is configured to exhibit a non-zero inductance value). The antenna resonance that is exhibited by antenna  40  (e.g., low band arm  100  of resonating element  50 A) is given by curve  128 . When it is desired to operate antenna  40  in high band HB, inductor LT is configured to form a short circuit path (i.e., return path SC is configured as a short circuit). 
     The bandwidth of the high band antenna resonance for antenna  40  at band HB can be broadened by incorporating loop antenna structures into antenna  40 . In the absence of loop antenna resonating element  50 B, for example, antenna  40  may exhibit a relatively narrow high band resonance, of the type shown by dashed-and-dotted curve  130  of  FIG. 8 . By incorporating loop antenna resonating element  50 B into antenna  40 , the bandwidth of the high band resonance may be expanded (i.e., loop antenna resonating element  50 B may contribute an additional response to the high band resonance). The resulting widened high band antenna resonance for antenna  40  in the presence of loop element  50 B is given by dashed line  132  in the example of  FIG. 8 . 
     Further broadening of the bandwidth of the high band antenna resonance for antenna  40  may be achieved by incorporating an additional ground plane structure such as ground plane portion  52 ′ of ground plane  52  of  FIG. 3  into antenna  40 . Portion  52 ′ of the antenna ground of  FIG. 3  may overlap some or all of loop antenna resonating element  50 B, as shown in  FIG. 3 . There is preferably a non-zero separation LZ in dimension Z (into the page in the orientation of  FIG. 3 ) between antenna ground  52 ′ and loop antenna resonating element  50 B. Air, plastic, or other dielectric can be formed in the gap between ground  52 ′ and overlapping loop antenna resonating element  50 B. The additional broadening of the high band antenna resonance that is achieved by incorporating antenna ground portion  52 ′ into antenna  40  of  FIG. 3  is illustrated by curve  134  of  FIG. 8 . This type of high band bandwidth broadening scheme may be used in antenna  40  in a configuration in which element LT is switched between two states, in a configuration in which element LT is switched between three states, or another antenna configurations. 
     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: 20130410
Publication Date: 20160913
Grant Date: 20160913
Priority Date: 20130410
Inventors: BEVELACQUA PETER
XU HAO
NATH JAYESH
EDWARDS JENNIFER M.
PASCOLINI MATTIA
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q7/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0442", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/0442", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 51686428