PATENT DOCUMENT

Publication Number: US-10290946-B2
Application Number: US-201615274328-A
Country: US
Kind Code: B2

Title: Hybrid electronic device antennas having parasitic resonating elements

Abstract:
An electronic device may have a hybrid antenna that includes a slot resonating element formed from a slot in a ground plane and a planar resonating element formed over the slot. A parasitic element may be disposed over the planar element. A switch may couple the parasitic element to the ground. A tunable circuit may couple the planar element to the ground. The switch and tunable circuit may be placed in different tuning states. In a first state, the tunable circuit and switch form open circuits. In a second state, the tunable circuit may an open circuit and the switch is closed. In a third state, the tunable circuit forms a return path and the switch forms an open circuit. This may allow the antenna to operate with satisfactory efficiency in low, mid, and high bands despite volume constraints imposed on the antenna.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing having a metal housing wall that forms a ground plane; 
 a slot in the metal housing wall that forms a slot antenna resonating element for a hybrid antenna; 
 a planar antenna resonating element for the hybrid antenna, wherein the planar antenna resonating element is formed over the slot; 
 an antenna feed having a signal feed terminal coupled to the planar antenna resonating element and a ground feed terminal coupled to the ground plane, wherein the planar antenna resonating element is configured to indirectly feed the slot antenna resonating element; 
 a parasitic antenna resonating element for the hybrid antenna, wherein the planar antenna resonating element is interposed between the parasitic antenna resonating element and the slot; 
 a dielectric carrier, wherein the planar antenna resonating element and the parasitic antenna resonating element are supported by the dielectric carrier and the planar antenna resonating element is interposed between the parasitic antenna resonating element and a surface of the dielectric carrier; and 
 control circuitry, wherein the control circuitry is configured to control the hybrid antenna to operate in first and second tuning states, the parasitic antenna resonating element is decoupled from the ground plane and the hybrid antenna is configured to transmit radio-frequency signals in a frequency band in the first tuning state, and the parasitic antenna resonating element is coupled to the ground plane and the hybrid antenna is configured to transmit radio-frequency signals in the frequency band in the second tuning state. 
 
     
     
       2. The electronic device defined in  claim 1 , further comprising:
 a switch coupled between the parasitic antenna resonating element and the ground plane. 
 
     
     
       3. The electronic device defined in  claim 2 , further comprising:
 an adjustable inductor coupled between the planar antenna resonating element and the ground plane. 
 
     
     
       4. The electronic device defined in  claim 3 ,
 wherein the control circuitry is configured to place the electronic device in the first tuning state by controlling the adjustable inductor to form an open circuit between the planar antenna resonating element and the ground plane and by opening the switch coupled between the parasitic antenna resonating element and the ground plane. 
 
     
     
       5. The electronic device defined in  claim 4 , wherein the control circuitry is further configured to place the electronic device in the second tuning state by controlling the adjustable inductor to form the open circuit between the planar antenna resonating element and the ground plane and by closing the switch coupled between the parasitic antenna resonating element and the ground plane. 
     
     
       6. The electronic device defined in  claim 5 , wherein the slot antenna resonating element is configured to resonate in a low band frequency range while the electronic device is placed in the first and second tuning states and the planar antenna resonating element, the ground plane, and the parasitic antenna resonating element are configured to resonate in a midband frequency range while the electronic device is placed in the second tuning state. 
     
     
       7. The electronic device defined in  claim 6 , wherein the control circuitry is further configured to place the electronic device in a third tuning state by controlling the adjustable inductor to form a return path between the planar antenna resonating element and the ground plane and by opening the switch coupled between the parasitic antenna resonating element and the ground plane and, when the electronic device is placed in the third tuning state, the slot antenna resonating element is configured to resonate in the low band frequency range and a high band frequency range and the planar antenna resonating element and the ground plane are configured to resonate in the midband frequency range. 
     
     
       8. The electronic device defined in  claim 7 , wherein the slot antenna resonating element is configured to resonate at a low band frequency in the low band frequency range when the electronic device is placed in the first, second, and third tuning states, the electronic device further comprising:
 a switch; and 
 a capacitor coupled in series with the switch between opposing sides of the slot, wherein the control circuitry is configured to control the switch to adjust the low band frequency at which the slot antenna resonating element resonates. 
 
     
     
       9. The electronic device defined in  claim 1 , wherein the dielectric carrier is interposed between the antenna resonating element and the metal housing wall, the electronic device further comprising:
 a display having a display cover layer, wherein the parasitic antenna resonating element is interposed between the display cover layer and the planar antenna resonating element. 
 
     
     
       10. The electronic device defined in  claim 1 , wherein the slot defines first and second opposing sides of the metal housing wall, the dielectric carrier is disposed on the first side, and the ground feed terminal is coupled to the second side, the electronic device further comprising:
 a switch coupled between the parasitic antenna resonating element and the second side. 
 
     
     
       11. The electronic device defined in  claim 1 , further comprising:
 a dielectric layer interposed between the parasitic antenna resonating element and the planar antenna resonating element. 
 
     
     
       12. An electronic device, comprising:
 a metal housing that forms an antenna ground; 
 a hybrid antenna, comprising:
 a slot in the metal housing that forms a slot antenna resonating element; 
 a planar antenna resonating element; 
 an antenna feed having a positive feed terminal coupled to the planar antenna resonating element and a ground feed terminal coupled to the antenna ground, wherein the planar antenna resonating element is configured to indirectly feed the slot antenna resonating element; and 
 a parasitic element that is coupled to the antenna ground by a switch; and 
 
 control circuitry, wherein the control circuitry is configured to control the hybrid antenna to operate in first, second, and third tuning states, wherein the switch is closed in the first tuning state and open in the second and third tuning states, and the hybrid antenna is configured to resonate in a first frequency band and a third frequency band in the first tuning state, in the first frequency band and a second frequency band in the second tuning state, and in the third frequency band in the third tuning state. 
 
     
     
       13. The electronic device defined in  claim 12 , further comprising:
 an adjustable inductor coupled between the planar antenna resonating element and the antenna ground. 
 
     
     
       14. The electronic device defined in  claim 13 , wherein the adjustable inductor comprises switching circuitry and the control circuitry is configured to control the switching circuitry to form an open circuit between the planar antenna resonating element and the antenna ground in the first and third tuning states. 
     
     
       15. The electronic device defined in  claim 14 , wherein the hybrid antenna is configured to resonate in the first frequency band, the second frequency band, and the third frequency band in the second tuning state, and the switching circuitry in the adjustable inductor forms a return path between the planar antenna resonating element and the antenna ground in the second tuning state. 
     
     
       16. The electronic device defined in  claim 15 , wherein the first frequency band comprises a first range of frequencies, the second frequency band comprises a second range of frequencies that is greater than the first range of frequencies, and the third frequency band comprises a third range of frequencies that is less than the second range of frequencies. 
     
     
       17. The electronic device defined in  claim 13 , wherein the slot has opposing first and second sides that are defined by the metal housing, the electronic device further comprising:
 adjustable capacitor circuitry coupled between the first and second sides of the slot, wherein the switch is coupled to the antenna ground at the first side of the slot, the adjustable inductor is coupled to the antenna ground at the first side of the slot, and the ground feed terminal is coupled to the antenna ground at the first side of the slot. 
 
     
     
       18. The electronic device defined in  claim 12 , further comprising:
 an adjustable inductor coupled between the planar antenna resonating element and the antenna ground, wherein the control circuitry is configured to switch the adjustable inductor between at least first and second configurations in the first, second, and third tuning states. 
 
     
     
       19. An antenna, comprising:
 a metal electronic device housing wall that forms an antenna ground; 
 a slot in the metal electronic device housing wall that forms a slot antenna resonating element; 
 a parasitic antenna element; 
 a switching circuit coupled between the parasitic antenna element and the antenna ground; 
 a planar metal element formed between the parasitic antenna element and the metal electronic device housing wall, wherein the planar metal element forms a planar antenna resonating element, and the planar antenna resonating element is configured to indirectly feed the slot antenna resonating element via nearfield electromagnetic coupling; 
 a first antenna feed terminal coupled to the planar metal element; 
 a second antenna feed terminal coupled to the antenna ground; and 
 a tunable component coupled between the planar metal element and the antenna ground, wherein the tunable component forms a return path between the planar metal element and the antenna ground in a tuning setting, the switching circuit is open in the tuning setting, and the slot antenna resonating element, the planar antenna resonating element, and the antenna ground are configured to resonate in at least first and second frequency bands in the tuning setting. 
 
     
     
       20. The antenna defined in  claim 19 , wherein the antenna is operable in the tuning setting and first and second additional tuning settings, the tunable component forms an open circuit between the planar metal element and the antenna ground in the first and second additional tuning settings, the switching circuit is open in the first additional tuning setting, the switching circuit is closed in the second additional tuning setting, the slot antenna resonating element is configured to resonate at the first frequency band in the tuning setting and the first and second additional tuning settings, the planar antenna resonating element and the antenna ground are configured to resonate at the second frequency band in the tuning setting, the planar antenna resonating element, the parasitic antenna element, and the antenna ground are configured to resonate at the second frequency band in the second additional tuning setting, and the second frequency band is at least partially higher than the first frequency band.

Description:
BACKGROUND 
     This relates 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. 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, there is a desire for wireless devices to cover a growing number of communications bands. 
     Because antennas have the potential to interfere with each other and with components in a wireless device, care must be taken when incorporating antennas into an electronic device. 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 
     An electronic device may have a metal housing that forms a ground plane. The ground plane may, for example, be formed from a rear housing wall and sidewalls. The ground plane and other structures in the electronic device may be used in forming antennas. 
     The electronic device may include one or more hybrid antennas. The hybrid antennas may each include a slot antenna resonating element formed from a slot in the ground plane and a planar antenna resonating element formed from a planar metal member disposed over the slot. The planar antenna resonating element may be coupled to a positive antenna feed terminal. The planar antenna resonating element may be directly fed and may serve as an indirect feed structure for the slot antenna resonating element. 
     A parasitic antenna resonating element may be disposed over the planar antenna resonating element. The parasitic antenna resonating element may be configured to constructively interfere with the electromagnetic field generated by the planar antenna resonating element. A switch may be coupled between the parasitic antenna resonating element and the ground plane. A tunable circuit such as an adjustable inductor may be coupled between the planar antenna resonating element and the ground plane. 
     The electronic device may include control circuitry. The control circuitry may control the switch and the tunable circuit to place the hybrid antenna in at least one of three different tuning states (settings) or modes. In the first tuning state, the tunable circuit may form an open circuit between the planar antenna resonating element and the ground plane and the switch may be opened to form an open circuit between the parasitic antenna resonating element and the ground plane. In the second tuning state, the tunable circuit may form an open circuit between the planar antenna resonating element and the ground plane and the switch may be closed to form a short circuit path between the parasitic antenna resonating element and the ground plane. In the third tuning state, the tunable circuit may form a closed return path between the planar metal element and the antenna ground and the switch may form an open circuit between the parasitic antenna resonating element and the antenna ground. 
     When controlled to operate in the first tuning state, the slot antenna resonating element may resonate at a first frequency in a low band (e.g., 700-960 MHz). When controlled to operate in the second tuning state, the slot antenna resonating element may resonate at the first frequency while the parasitic antenna resonating element, the antenna ground, and the planar antenna resonating element resonate at a second frequency in a midband (e.g., 1400-1900 MHz). When controlled to operate in the third tuning state, the slot antenna resonating element may resonate at the first frequency and at a third (harmonic) frequency in a high band (e.g., 1900-2700 MHz) while the planar antenna resonating element and the antenna ground resonate in the midband. Adjustable capacitor circuitry that bridges the slot may be controlled to tune the first frequency if desired. This may allow the antenna to operate with satisfactory antenna efficiency in the low band, midband, and high band (e.g., to allow the antenna to perform concurrent communications in cellular telephone and satellite navigation communications bands) despite volume constraints imposed on the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 2  is a rear perspective view of a portion of the illustrative electronic device of  FIG. 1  in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of a portion of an illustrative electronic device in accordance with an embodiment. 
         FIG. 4  is a schematic diagram of illustrative circuitry in an electronic device in accordance with an embodiment. 
         FIG. 5  is a diagram of illustrative wireless circuitry in an electronic device in accordance with an embodiment. 
         FIG. 6  is a perspective interior view of an illustrative electronic device with a metal housing having a dielectric-filled slot for hybrid antennas having parasitic antenna resonating elements in accordance with an embodiment. 
         FIG. 7  is a perspective view of an illustrative hybrid antenna having a switchable parasitic antenna resonating element and a return path that includes an adjustable circuit in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view showing how a hybrid antenna having a switchable parasitic antenna resonating element may be placed within an electronic device housing in accordance with an embodiment. 
         FIG. 9  is a chart showing how antennas of the type shown in  FIGS. 6-8  may be used in covering different communications bands of interest by adjusting associated tuning circuitry in accordance with an embodiment. 
         FIG. 10  is a graph of antenna performance (antenna efficiency) plotted as a function of operating frequency for an illustrative antenna of the type shown in  FIGS. 6-8  when operated using different tuning circuitry settings in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device such as electronic device  10  of  FIG. 1  may be provided with wireless circuitry that includes antenna structures. The antenna structures may include hybrid antennas. The hybrid antennas may be hybrid planar-inverted-F-slot antennas that include slot antenna resonating elements and planar inverted-F antenna resonating elements. The planar inverted-F antenna resonating elements may indirectly feed the slot antenna resonating elements and may contribute to the frequency responses of the antennas. Slots for the slot antenna resonating elements may be formed in ground structures such as conductive housing structures and may be filled with a dielectric such as plastic. The hybrid antennas may be provided with switchable parasitic antenna resonating elements that are not directly fed. The parasitic antenna resonating elements may optimize the efficiency of the antenna in certain communications bands, for example. 
     The wireless circuitry of device  10  may handle one or more communications bands. For example, the wireless circuitry of device  10  may include a Global Position System (GPS) receiver that handles GPS satellite navigation system signals at 1575 MHz or a GLONASS receiver that handles GLONASS signals at 1609 MHz. Device  10  may also contain wireless communications circuitry that operates in communications bands such as cellular telephone bands and wireless circuitry that operates in communications bands such as the 2.4 GHz Bluetooth® band and the 2.4 GHz and 5 GHz WiFi® wireless local area network bands (sometimes referred to as IEEE 802.11 bands or wireless local area network communications bands). Device  10  may also contain wireless communications circuitry for implementing near-field communications at 13.56 MHz or other near-field communications frequencies. If desired, device  10  may include wireless communications circuitry for communicating at 60 GHz, circuitry for supporting light-based wireless communications, or other wireless communications. 
     Electronic device  10  may be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     In the example of  FIG. 1 , device  10  includes a display such as display  14 . Display  14  may be mounted in a housing such as housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). In the example of  FIG. 1 , housing  12  includes a conductive peripheral sidewall structure  12 W that surrounds a periphery of device  10  (e.g., that surrounds the rectangular periphery of device  10  as shown in  FIG. 1 ). Housing  12  may, if desired, include a conductive rear wall structure  12 R that opposes display  14  (e.g., conductive rear wall structure  12 R may form the rear exterior face, side, or surface of device  10 ). If desired, rear wall  12 R and sidewalls  12 W may be formed from a continuous metal structure (e.g., in a unibody configuration) or from separate metal structures. Openings may be formed in housing  12  to form communications ports, holes for buttons, and other structures if desired. 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. 
     Display  14  may have an active area AA that includes an array of display pixels. The array of pixels may be formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of plasma display pixels, an array of organic light-emitting diode display pixels or other light-emitting diode pixels, an array of electrowetting display pixels, or display pixels based on other display technologies. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass, clear plastic, transparent ceramic, sapphire, or other transparent crystalline material, or other transparent layer(s). The display cover layer may have a planar shape, a convex curved profile, a shape with planar and curved portions, a layout that includes a planar main area surrounded on one or more edges with a portion that is bent out of the plane of the planar main area, or other suitable shapes. The display cover layer may cover the entire front face of device  10  (e.g., extending across an entirety of a length dimension of device  10  parallel to the y-axis and a width dimension of device  10  parallel to the x-axis of  FIG. 1 ). In another suitable arrangement, the display cover layer may cover substantially all of the front face of device  10  or only a portion of the front face of device  10 . Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button such as button  16 . An opening may also be formed in the display cover layer to accommodate ports such as a speaker port. Openings such as openings  8  may be formed in housing  12  to form communications ports (e.g., an audio jack port, a digital data port, etc.) and/or audio ports for audio components such as a speaker and/or a microphone. 
     Display  14  may have an inactive border region that runs along one or more of the edges of active area AA. Inactive area IA may be free of pixels for displaying images and may overlap circuitry and other internal device structures in housing  12 . To block these structures from view by a user of device  10 , the underside of the display cover layer or other layer in display  14  that overlaps inactive area IA may be coated with an opaque masking layer in inactive area IA. The opaque masking layer may have any suitable color. 
     Antennas may be mounted in housing  12 . For example, housing  12  may have four peripheral edges (e.g., conductive sidewalls  12 W) as shown in  FIG. 1  and one or more antennas may be located along one or more of these edges. As shown in the illustrative configuration of  FIG. 1 , antennas may, if desired, be mounted in regions  20  along opposing peripheral edges of housing  12  (as an example). The antennas may include antenna resonating elements that emit and receive signals through the front of device  10  (i.e., through inactive portions IA of display  14 ) and/or from the rear and sides of device  10 . In practice, active components within active display area AA may block or otherwise inhibit signal reception and transmission by the antennas. By placing the antennas within regions  20  of inactive area IA of display  14 , the antennas may freely pass signals through the display without the signals being blocked by active display circuitry. Antennas may also be mounted in other portions of device  10 , if desired. The configuration of  FIG. 1  is merely illustrative. 
     In order to provide an end user of device  10  with as large of a display as possible (e.g., to maximize an area of the device used for displaying media, running applications, etc.), it may be desirable to increase the amount of area at the front face of device  10  that is covered by active area AA of display  14 . Increasing the size of active area AA may reduce the size of inactive area IA within device  10 . This may reduce the space  20  that is available for forming antennas within device  10 . In general, antennas that are provided with larger operating volumes or spaces may have wider bandwidth efficiency than antennas that are provided with smaller operating volumes or spaces. If care is not taken, increasing the size of active area AA may reduce the operating space available to the antennas, which can undesirably inhibit the efficiency and bandwidth of the antennas (e.g., such that the antennas no longer exhibit satisfactory radio-frequency performance). Such inhibition of efficiency and bandwidth can become particularly pronounced at lower frequencies such as cellular telephone frequencies between 700 and 960 MHz. It would therefore be desirable to be able to provide antennas that occupy a small amount of space within device  10  (e.g., to allow for as large of a display active area AA as possible) while still allowing the antennas to operate with optimal efficiency and bandwidth at all frequencies of interest. 
       FIG. 2  is a rear perspective view of the upper end of housing  12  and device  10  of  FIG. 1 . As shown in  FIG. 2 , one or more slots such as slot  22  may be formed in housing  12 . Housing  12  may be formed from a conductive material such as metal. Slot  22  may be an elongated opening in the metal of housing  12  and may be filled with a dielectric material such as glass, ceramic, plastic, or other insulator (i.e., slot  22  may be a dielectric-filled slot). The width of slot  22  may be 0.1-1 mm, less than 1.3 mm, less than 1.1 mm, less than 0.9 mm, less than 0.7 mm, less than 0.5 mm, less than 0.3 mm, more than 0.2 mm, more than 0.5 mm, more than 0.1 mm, 0.2-0.9 mm, 0.2-0.7 mm, 0.3-0.7 mm, or other suitable width. The length of slot  22  may be more than 4 cm, more than 6 cm, more than 10 cm, 5-20 cm, 4-15 cm, less than 15 cm, less than 25 cm, or other suitable length. 
     Slot  22  may extend across rear housing wall  12 R and, if desired, an associated sidewall such as sidewall  12 W. Rear housing wall  12 R may be planar or may be curved. Sidewall  12 W may be an integral portion of rear wall  12 R or may be a separate structure. Housing wall  12 R (and, if desired, sidewalls such as sidewall  12 W) may be formed from aluminum, stainless steel, or other metals and may form a ground plane for device  10 . Slots in the ground plane such as slot  22  may be used in forming antenna resonating elements. 
     In the example of  FIG. 2 , slot  22  has a U-shaped footprint (i.e., the outline of slot  22  has a U shape when viewed along dimension Z). Other shapes for slot  22  may be used, if desired (e.g., straight shapes, shapes with curves, meandering shapes, circular shapes, shapes with curved and straight segments, etc.). Slot  22  may be partially formed within one sidewall  12 W or within two or more sidewalls  12 W. With a layout of the type shown in  FIG. 2 , the bends in slot  22  create space along the left and right edges of housing  12  for components  26 . Components  26  may be, for example, speakers, microphones, cameras, sensors, or other electrical components. 
     Slot  22  may be divided into two shorter slots using a conductive member such as conductive structure  24  or a set of one or more switches that can be controlled by a control circuit. Conductive structure  24  may be formed from metal traces on a printed circuit, metal foil, metal portions of a housing bracket, wire, a sheet metal structure, or other conductive structure in device  10 . Conductive structure  24  may be shorted to metal housing wall  12 R on opposing sides of slot  22 . If desired, conductive structures such as conductive structure  24  may be formed from integral portions of metal housing  12  (e.g., slot  22  may be discontinuous and housing  12  may be continuous at the location element  24 ) and/or adjustable circuitry that bridges slot  22 . 
     In the presence of conductive structure  24  (or when switches in structure  24  are closed), slot  22  may be divided into first and second slots  22 L and  22 R. Ends  22 - 1  of slots  22 L and  22 R are surrounded by air and dielectric structures such as glass or other dielectric associated with a display cover layer for display  14  and are therefore sometimes referred to as open slot ends. Ends  22 - 2  of slots  22 L and  22 R are terminated in conductive structure  24  and therefore are sometimes referred to as closed slot ends. In the example of  FIG. 2 , slot  22 L is an open slot having an open end  22 - 1  and an opposing closed end  22 - 2 . Slot  22 R is likewise an open slot. If desired, device  10  may include closed slots (e.g., slots in which both ends are terminated with conductive structures). The configuration of  FIG. 2  is merely illustrative. Slot  22  and the other structures of  FIG. 2  may be formed on the lower side of device  10  (e.g., the side of device  10  adjacent to button  16 ) or elsewhere on device  10  if desired. If desired, only one of slots  22 L and  22 R may be formed at any location along housing  12 . 
     Slot  22  may be fed using an indirect feeding arrangement. With indirect feeding, a structure such as a planar antenna resonating element may be near-field coupled to slot  22  and may serve as an indirect feed structure. The planar antenna resonating element may also exhibit resonances that contribute to the frequency response of the antenna formed from slot  22  (e.g., the antenna may be a hybrid planar-inverted-F-slot antenna). 
     A cross-sectional side view of device  10  in the vicinity of slot  22  is shown in  FIG. 3 . In the example of  FIG. 3 , conductive structures  28  may include display  14 , conductive housing structures such as metal rear housing wall  12 R, etc. Dielectric layer  30  may be a portion of a glass layer (e.g., a portion of a display cover layer for protecting display  14 ). The underside of layer  30  may, if desired, be covered with an opaque masking layer to block internal components in device  10  from view. Dielectric support  32  may be used to support conductive structures such as metal structure  34 . Metal structure  34  may be located under dielectric layer  30  and may, if desired, be used in forming an antenna feed structure (e.g., structure  34  may be a planar metal member that forms part of a planar inverted-F antenna resonating element structure or patch antenna resonating element structure that is near-field coupled to slot  22  in housing  12 ). During operation, antenna signals associated with an antenna formed from slot  22  and/or metal structure  34  may be transmitted and received through the front of device  10  (e.g., through dielectric layer  30 ) and/or the rear of device  10 . 
     A schematic diagram showing illustrative components that may be used in device  10  is shown in  FIG. 4 . As shown in  FIG. 4 , device  10  may include control circuitry such as storage and processing circuitry  42 . Storage and processing circuitry  42  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  42  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Storage and processing circuitry  42  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  42  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  42  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, MIMO protocols, antenna diversity protocols, etc. 
     Input-output circuitry  44  may include input-output devices  46 . Input-output devices  46  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  46  may include user interface devices, data port devices, and other input-output components. For example, input-output devices  46  may include touch screens, displays without touch sensor capabilities, buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, etc. 
     Input-output circuitry  44  may include wireless communications circuitry  48  for communicating wirelessly with external equipment. Wireless communications circuitry  48  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, transmission lines, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  48  may include radio-frequency transceiver circuitry  50  for handling various radio-frequency communications bands. For example, circuitry  48  may include transceiver circuitry  52 ,  54 , and  56 . Transceiver circuitry  52  may be wireless local area network transceiver circuitry that may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and that may handle the 2.4 GHz Bluetooth® communications band. Circuitry  48  may use cellular telephone transceiver circuitry  54  for handling wireless communications in frequency ranges such as a low communications band “LB” from 700 to 960 MHz, a midband “MB” from 1400 MHz or 1500 MHz to 2170 MHz (e.g., a midband with a peak at 1700 MHz), and a high band “HB” from 2170 or 2300 to 2700 MHz (e.g., a high band with a peak at 2400 MHz) or other communications bands between 700 MHz and 2700 MHz or other suitable frequencies (as examples). Circuitry  54  may handle voice data and non-voice data. Wireless communications circuitry  48  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  48  may include 60 GHz transceiver circuitry, circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) circuitry, etc. Wireless communications circuitry  48  may include satellite navigation system circuitry such as global positioning system (GPS) receiver circuitry  56  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. 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  48  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, monopole antenna structures, dipole antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     As shown in  FIG. 5 , transceiver circuitry  50  in wireless circuitry  48  may be coupled to antenna structures  40  using paths such as path  60 . Wireless circuitry  48  may be coupled to control circuitry  42 . Control circuitry  42  may be coupled to input-output devices  46 . Input-output devices  46  may supply output from device  10  and may receive input from sources that are external to device  10 . 
     To provide antenna structures  40  with the ability to cover communications frequencies of interest, antenna structures  40  may be provided with circuitry such as filter circuitry (e.g., one or more passive filters and/or one or more tunable filter circuits). Discrete components such as capacitors, inductors, and resistors may be incorporated into the filter circuitry. Capacitive structures, inductive structures, and resistive structures may also be formed from patterned metal structures (e.g., part of an antenna). If desired, antenna structures  40  may be provided with adjustable circuits such as tunable components  62  to tune antennas over communications bands of interest. Tunable components  62  may include tunable inductors, tunable capacitors, or other tunable components. Tunable components such as these may be based on switches and networks of fixed components, distributed metal structures that produce associated distributed capacitances and inductances, variable solid state devices for producing variable capacitance and inductance values, tunable filters, or other suitable tunable structures. 
     During operation of device  10 , control circuitry  42  may issue control signals on one or more paths such as path  64  that adjust inductance values, capacitance values, or other parameters associated with tunable components  62 , thereby tuning antenna structures  40  to cover desired communications bands. 
     Path  60  may include one or more transmission lines. As an example, signal path  60  of  FIG. 5  may be a transmission line having first and second conductive paths such as paths  66  and  68 , respectively. Path  66  may be a positive signal line and path  68  may be a ground signal line. Lines  66  and  68  may form parts of a coaxial cable, a stripline transmission line, and/or a microstrip transmission line (as examples). A matching network formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna structures  40  to the impedance of transmission line  60 . Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. Components such as these may also be used in forming filter circuitry in antenna structures  40 . 
     Transmission line  60  may be directly coupled to an antenna resonating element and ground for antenna  40  or may be coupled to near-field-coupled antenna feed structures that are used in indirectly feeding a resonating element for antenna  40 . As an example, antenna structures  40  may form an inverted-F antenna, a slot antenna, a hybrid inverted-F slot antenna or other antenna having an antenna feed with a positive antenna feed terminal such as terminal  70  and a ground antenna feed terminal such as ground antenna feed terminal  72 . Positive transmission line conductor  66  may be coupled to positive antenna feed terminal  70  and ground transmission line conductor  68  may be coupled to ground antenna feed terminal  72 . Antenna structures  40  may include an antenna resonating element such as a slot antenna resonating element or other element that is indirectly fed using near-field coupling. In a near-field coupling arrangement, transmission line  60  is coupled to a near-field-coupled antenna feed structure that is used to indirectly feed antenna structures such as an antenna slot or other element through near-field electromagnetic coupling. 
     Antennas  40  may include hybrid antennas formed both from planar antenna structures (e.g., planar inverted-F antenna structures) and slot antenna structures. An illustrative configuration in which device  10  has two hybrid antennas formed from the left and right portions of slot  22  in housing  12  is shown in  FIG. 6 .  FIG. 6  is an interior perspective view of device  10  at the upper end of housing  12 . 
     As shown in  FIG. 6 , slot  22  may be divided into left slot  22 L and right slot  22 R by conductive structures  24  (e.g., an integral and continuous portion of rear housing wall  12 R) that bridge the center of slot  22 . Rear housing wall  12 R (e.g., a metal housing wall in housing  12  that opposes the face of device  10  at which display  14  is formed) may have a first portion such as portion  12 R- 1  and a second portion such as portion  12 R- 2  that is separated from portion  12 R- 1  by slot  22 . Conductive structures  24  may be shorted to rear housing wall portion  12 R- 1  on one side of slot  22  and may be shorted to rear housing wall portion  12 R- 2  on the other side of slot  22  (or may extend continuously from portion  12 R- 1  to portion  12 R- 2  on both sides of slot  22  when structures  24  are an integral portion of housing  12 R). The presence of the short circuit formed by structures  24  across slot  22  creates closed ends  22 - 2  for left slot  22 L and right slot  22 R. 
     Antennas  40  of  FIG. 6  include left antenna  40 L and right antenna  40 R. Device  10  may switch between antennas  40 L and  40 R in real time to ensure that signal strength is maximized, may use antennas  40 L and  40 R simultaneously, or may otherwise use antennas  40 L and  40 R to enhance wireless performance for device  10  (e.g., using antenna diversity or multiple-input multiple-output (MIMO) schemes). 
     Left antenna  40 L and right antenna  40 R may be hybrid antennas each of which has a planar antenna resonating element (e.g., a planar patch or planar inverted-F antenna resonating element) and a slot antenna resonating element. 
     The slot antenna resonating element of antenna  40 L may be formed by slot  22 L. Planar antenna resonating element  80 L (e.g., planar inverted-F antenna or planar patch antenna resonating element  80 L) serves as an indirect feeding structure for antenna  40 L and is near-field coupled to the slot resonating element formed from slot  22 L. During operation, slot  22 L and element  80 L may each contribute to the overall frequency response of antenna  40 L. As shown in  FIG. 6 , antenna  40 L may have an antenna feed such as feed  82 L. Feed  82 L is coupled between planar antenna resonating element  80 L and ground (i.e., metal housing  12 R- 1 ). A radio-frequency transmission line (see, e.g., transmission line  60  of  FIG. 5 ) may be coupled between transceiver circuitry  50  and antenna feed  82 L. Feed  82 L has positive antenna feed terminal  70 L and ground antenna feed terminal  72 L. Ground antenna feed terminal  72 L may be shorted to ground (e.g., metal wall  12 R- 1 ). Positive antenna feed terminal  70 L may be coupled to planar metal element  78 L via a leg, arm, branch, or other conductive path that extends downwards from planar resonating element  80 L towards the ground formed from metal wall  12 R- 1 . Planar antenna resonating element  80 L may also have a return path such as return path  84 L that is coupled between planar element  78 L and antenna ground (metal housing  12 R- 1 ) in parallel with feed  82 L. 
     The slot antenna resonating element of antenna  40 R is formed by slot  22 R. Planar antenna resonating element  80 R (e.g., a planar inverted-F antenna resonating element or planar patch antenna resonating element) serves as an indirect feeding structure for antenna  40 R and is near-field coupled to the slot resonating element formed from slot  22 R. Slot  22 R and element  80 R both contribute to the overall frequency response of hybrid planar-inverted-F-slot antenna  40 R. Antenna  40 R may have an antenna feed such as feed  82 R. Feed  82 R is coupled between planar antenna resonating element  80 R and ground (metal housing  12 R- 1 ). A transmission line such as transmission line  60  may be coupled between transceiver circuitry  50  and antenna feed  82 R. Feed  82 R may have positive antenna feed terminal  70 R and ground antenna feed terminal  72 R. Ground antenna feed terminal  72 R may be shorted to ground (e.g., metal wall  12 R- 1 ). Positive antenna feed terminal  70 R may be coupled to planar metal structure  78 R of planar resonating element  80 R. Planar resonating element  80 R may have a return path such as return path  84 R that is coupled between planar element  78 R and antenna ground (metal housing  12 R- 1 ). 
     Return paths  84 L and  84 R may be formed from strips of metal without any tunable components or may include tunable inductors or other adjustable circuits for tuning antennas  40 . Additional tunable components may also be incorporated into antennas  40 , if desired. For example, tunable (adjustable) components  86 L may bridge slot  22 L in antenna  40 L and tunable (adjustable) components  86 R may bridge slot  22 R in antenna  40 R. 
     In the example of  FIG. 6 , tunable components  86 L are interposed between feed  82 L and open slot end  22 - 1  of left slot  22 L and tunable components  86 R are interposed between feed  82 R and open slot end  22 - 1  of right slot  22 R. This is merely illustrative. If desired, components  86 L may be interposed between feed  82 L and closed end  22 - 2  of slot  22 L and/or components  86 R may be interposed between feed  82 R and closed end  22 - 2  of slot  22 L. Components  86 L may bridge slot  22 L on both sides of feed  82 L and/or components  86 R may bridge slot  22 R on both sides of feed  82 R. If desired, components  86 L and/or  86 R may be omitted. 
     Antennas  40  may support any suitable frequencies of operation. As an example, antennas  40  may operate in a low band LB, midband MB, and high band HB. Slots  22 L and  22 R may have lengths (quarter wavelength lengths) that support resonances in the low communications band LB (e.g., a low band at frequencies between 700 and 960 MHz). Midband coverage (e.g., for a midband MB from 1400 or 1500 MHz to 1.9 GHz or other suitable midband range) may be provided by the resonance exhibited by planar antenna resonating elements  80 L and  80 R. High band coverage (e.g., for a high band centered at 2400 MHz and extending to 2700 MHz or another suitable frequency) may be supported using harmonics of the slot antenna resonating element resonance (e.g., a third order harmonic, etc.). 
     In order to provide as large an active area AA for display  14  as possible (e.g., to maximize an area of the device used for displaying media, running applications, etc.) it may be desirable to increase the amount of area at the front face of device  10  that is covered by active area AA of display  14 . Increasing the size of active area AA may reduce the size of inactive area IA within device  10  (see, e.g.,  FIG. 1 ). This reduces the amount of space available for forming antennas  40  within device  10 . 
     In general, antennas that are provided with larger operating volumes or spaces may have higher efficiency and bandwidth than antennas that are provided with smaller operating volumes or spaces. Increasing the size of active area AA may reduce the operating space available to the antennas and may undesirably inhibit the efficiency and bandwidth of the antennas (e.g., such that the antennas no longer exhibit satisfactory radio-frequency performance). This inhibition of efficiency and bandwidth may be particularly pronounced at lower frequencies (higher wavelengths) such as within low band LB (e.g., at frequencies between 700 and 960 MHz). Tuning circuitry such as tuning circuits  86  and  84  may be adjusted to help provide satisfactory efficiency and bandwidth within the low band LB. However, if care is not taken, it can be difficult for antennas  40  to exhibit satisfactory antenna performance (e.g., efficiency and bandwidth) in each of low band LB, mid band MB, and high band HB as the size of area IA is reduced (e.g., as the size of area IA is reduced so that the distance between active area AA and housing sidewall  12 W is 5 mm, less than 5 mm, 9 mm, less than 9 mm, between 9 and 15 mm, or another distance). 
     In order to enhance antenna efficiency and bandwidth as the size of area IA is reduced, antennas  40  may each be provided with a corresponding parasitic antenna resonating element  90  (sometimes referred to herein as parasitic resonating element  90 , parasitic antenna element  90 , parasitic element  90 , parasitic patch  90 , parasitic conductor  90 , parasitic structure  90 , or parasitic  90 ). For example, antenna  40 L may be provided with a corresponding parasitic antenna element  90 L and antenna  40 R may be provided with a corresponding parasitic antenna element  90 R. Parasitic element  90 L may be formed from a planar metal structure placed above (e.g., separated from) planar metal structure  78 L of planar antenna resonating element  80 L. Parasitic element  90 R may be formed from a planar metal structure placed above planar metal structure  78 R of planar antenna resonating element  80 R. Parasitic elements  90  may create a constructive perturbation of the electromagnetic field generated by antenna resonating elements  80 , creating a new resonance in a desired frequency band such as midband MB. Parasitic elements  90  are not directly fed, whereas resonating elements  80  are directly fed over feed terminals  70  and  72 . 
     Parasitic elements  90  may be coupled to ground (e.g., housing  12 R- 1 ) by a corresponding short (ground) path  92 . For example, parasitic element  90 L may be coupled to ground by short circuit path  92 L whereas parasitic element  90 R is coupled to ground by short circuit path  92 R. Short circuit paths  92  may include switching circuitry for selectively coupling and decoupling parasitic elements  90  to ground. When switching circuitry on path  92  couples parasitic element  90  to ground, parasitic element  90  may constructively interfere with the electromagnetic field generated by the corresponding resonating element  80 . When switching circuitry on path  92  decouples parasitic element  90  from ground, parasitic element  90  may become a floating element that has negligible effect on the electromagnetic field generated by antenna resonating elements  80  (e.g., the parasitic element may create no new resonances for the corresponding antenna  40 ). 
     Control circuitry  42  ( FIG. 1 ) may actively adjust switching circuitry on tunable paths  86 ,  84 , and  92  to ensure that antennas  40  provide satisfactory coverage (e.g., satisfactory efficiency and bandwidth) in low band LB, mid band MB, and/or high band HB during communications. For example, control circuitry  42  may adjust tunable components in paths  86  to adjust the performance of antenna  40  in low band LB (e.g., to tune the antenna to a desired frequency in the low band LB). Control circuitry  42  may adjust tunable components in paths  84  to adjust the performance of antenna  40  in mid band MB (e.g., to tune the antenna to a desired frequency in the mid band MB) or to decouple planar element  78  from ground  12 R. Control circuitry  42  may adjust tunable components in paths  82  to enhance the resonance of antenna  40  in mid band MB while antenna  40  also covers frequencies in low band LB, for example. 
     Antennas  40 L and  40 R may cover identical sets of frequencies or may cover overlapping or mutually exclusive sets of frequencies. As an example, antenna  40 R may serve as a primary antenna for device  10  and may cover frequencies of 700-960 MHz and 1700-2700 MHz, whereas antenna  40 L may serve as a secondary antenna that covers frequencies of 700-960 MHz and 1575-2700 MHz (or 1500-2700 MHz or 1400-2700 MHz, etc.). 
     The presence of the body of a user (e.g., a user&#39;s hand) or other external objects in the vicinity of antennas  40  may change the operating environment and tuning of antennas  40 . For example, the presence of an external object may shift the low band resonance of antennas  40  to lower frequencies. If desired, real time antenna tuning using the adjustable components of  FIG. 6  and/or other adjustable components may be used to ensure that antennas  40  operate satisfactorily regardless of whether external objects adjacent to antennas  40  are loading antennas  40 . 
       FIG. 7  is a perspective view of an illustrative antenna configuration for device  10 . Antenna  40 ′ of  FIG. 7  may be used in implementing an antenna such as antenna  40 R and/or  40 L of  FIG. 6 . In the arrangement of  FIG. 7 , planar antenna resonating element  80  is formed from planar metal structure  78 . Structure  78  may overlap slot  22 . Antenna  40 ′ may be a hybrid antenna that includes a planar antenna (e.g., a planar inverted-F or patch antenna) formed from resonating element  80  and ground (e.g., metal housing  12 R- 1  and  12 R- 2 ) and that includes the slot antenna formed from slot  22 . 
     Planar antenna  80  may serve as an indirect feed for the slot antenna formed from slot  22 . Transmission line  82  may be coupled to terminals  70  and  72  of feed  82  for antenna  80 . Return path  84  may be coupled between planar element  78  and the antenna ground formed from metal housing  12 R- 1  in parallel with feed  82 . Return path  84  may include adjustable circuitry such as an adjustable inductor. The adjustable inductor may include switching circuitry such as switches  120  and respective inductors  122  coupled in parallel between terminal  124  on the ground formed from metal  12 R- 1  and terminal  126  on element  78 . Control circuitry  42  may adjust adjustable circuits in device  10  such as adjustable return path  84  of  FIG. 7  to tune antenna  40 ′. For example, switches  180  may be selectively opened and/or closed to switch desired inductors  122  into or out of use, thereby adjusting the inductance of the adjustable circuitry of return path  134 . Adjusting the inductance of return path  134  may adjust the performance of antenna  40 ′ at frequencies within the mid band MB, for example. 
     If desired, all of switches  120  may be open (e.g., in an “off” state or deactivated) to form an open circuit between metal structure  78  and ground  12 R- 1 . When an open circuit is formed between structure  78  and ground  12 R- 1 , planar resonating element  80  may operate as a patch antenna resonating element, for example. The patch antenna resonating element may contribute to the overall resonance of antenna  40 ′ and/or may indirectly feed slot  22 . When a conductive path is formed between structure  78  and ground  12 R- 1  (e.g., when one or more of switches  120  is closed), planar resonating element  80  may operate as a planar inverted-F antenna (e.g., where the return path of the planar inverted-F antenna is formed by path  84 ). The planar inverted-F antenna may contribute to the overall resonance of antenna  40 ′ and/or may indirectly feed slot  22 . Antenna  40 ′ may therefore sometimes be referred to herein as a hybrid planar inverted-F slot antenna, a hybrid patch slot antenna, or simply as a hybrid antenna. 
     The example of  FIG. 7  is merely illustrative. In general, any desired inductive and/or capacitive components may be coupled in path  84  between structure  78  and ground  12 R- 1  in any desired manner (e.g., in series and/or in parallel). Any desired number of switches  120  may be used. For example, a single switch or more than one switch may couple each inductor  122  to terminal  124 . If desired, switches  120  or other switching circuits may be interposed between inductors  122  and terminal  126 . 
     Antenna  40 ′ of  FIG. 7  may also have adjustable circuitry such as adjustable circuitry  86  that bridges slot  22 . Circuitry  86  may have capacitors  130  or other circuit components that can be selectively switched into or out of use with switching circuitry such as switches  132 . If desired, inductors may be coupled in parallel with or instead of capacitors  130 . Any desired number of switches  132  may be used. For example, a single switch or more than one switch may couple each capacitor  130  to ground plane  12 R- 1 . If desired, switches  132  or other switching circuits may be interposed between capacitors  130  and ground plane  12 R- 2 . 
     Parasitic antenna resonating element  90  may be formed over metal structure  78  of planar antenna resonating element  80  (e.g., at a predetermined distance above and not in contact with structure  78 ). Parasitic antenna resonating element  90  may be coupled to ground  12 R- 1  via switchable short circuit path  92 . A switchable component such as switch  144  may be interposed in path  92  between a first terminal  142  located on parasitic element  90  and a second terminal  140  coupled to ground plane  12 R- 1 . Switch  144  may be selectively switched into or out of use to couple or decouple parasitic element  90  from ground  12 R- 1 . When switch  144  is activated, parasitic element  90  may constructively interfere with the electromagnetic field produced by resonating element  80  to contributed to the overall performance of antenna  40 ′. When switch  144  is deactivated, parasitic element  90  may have negligible effect on the overall performance of antenna  40 ′. 
     Terminal  142  may be located at an edge of parasitic element  90  or elsewhere on element  90 . In the example of  FIG. 7 , terminal  142  of path  92  is located at a corner of element  90 . If desired, terminal  140  may be connected to ground portion  12 R- 2  instead of ground portion  12 R- 1 . 
     Structure  78  may lie in a plane that is parallel to the plane of ground  12 R. Parasitic metal structure  90  may lie in a plane that is parallel to the plane of structure  78 . In the example of  FIG. 7 , planar resonating element structure  78  has a rectangular shape (outline) with lateral dimensions D 1  and D 2 . Dimension D 1  may be greater than dimension D 2  or dimension D 2  may be greater than or equal to dimension D 1 . Configurations in which structure  78  has a meandering arm shape, shapes with multiple branches, shapes with one or more curved edges, or other shapes may also be used for planar antenna resonating element  80 . If desired, parasitic resonating element structure  90  has a rectangular shape with lateral dimensions D 3  and D 4  (as an example). Dimension D 3  may be greater than dimension D 4  or dimension D 4  may be greater than or equal to dimension D 3 . Dimension D 3  may be less than or equal to dimension D 1  whereas dimension D 4  is less than or equal to dimension D 2 . In general, the total area of parasitic element  90  may be less than the total area of element  78 . Configurations in which structure  78  has a meandering arm shape, shapes with multiple branches, shapes with one or more curved edges, or other shapes may also be used for planar parasitic element  90 . Structures  90  and  78  may have the same outline shape or may have different outline shapes. 
     In the example of  FIG. 7 , the entirety of element  90  is located above the projected outline of planar element  78 . If desired, some or all of element  90  may be located outside of the projected outline of planar element  78 . If desired, parasitic element  90  may lie within a plane that is not parallel to the plane of element  78  and/or element  78  may lie within a plane that is not parallel to the plane of housing surface  12 R. The edges of parasitic element  90  may be parallel to the edges of element  78  or may be oriented at angles that are not parallel to the edges of element  78 . The edges of elements  90  and  78  may be parallel to the sidewalls  12 W of housing  12  or may be oriented at angles that are not parallel to sidewalls  12 W. 
     Although not shown in  FIG. 7  for the sake of clarity, planar antenna resonating element  80  may be formed on a dielectric support structure within device  10 .  FIG. 8  is a cross-sectional side view of a portion of electronic device  10  showing how antenna  40 ′ may include metal structures formed on a dielectric support structure. 
     As shown in  FIG. 8 , electronic device  10  may have a display such as display  14  that has an associated display module  152  and display cover layer  150 . Display module  152  may be a liquid crystal display module, an organic light-emitting diode display, or other display for producing images for a user. Display module  152  may include touch sensitive components in scenarios where display  14  is a touch-sensitive display, for example. Display cover layer  150  may be a clear sheet of glass, a transparent layer of plastic, or other transparent member. If desired, display cover layer  150  may form a portion of display module  152 . Display cover layer  150  may extend across the entire front face of device  10  if desired. 
     In active area AA, an array of display pixels associated with display structures such as display module  152  may present images to a user of device  10 . In inactive display border region IA, the inner surface of display cover layer  150  may be coated with a layer of black ink or other opaque masking layer  156  to hide internal device structures from view by a user. Antenna  40 ′ may be mounted within housing  12  under opaque masking layer  156 . During operation, antenna signals may be transmitted and received through a portion display cover layer  150  and/or through the rear or side of device  10 . Forming antenna  40 ′ under inactive region IA of display  14  may allow antenna  40 ′ to transmit and receive radio-frequency signals through display cover layer  150  without the signals being blocked or otherwise impeded by active circuitry in display module  152 . 
     As shown in  FIG. 7 , planar antenna resonating element structures  78  may be formed on a top surface of a dielectric support structure such as dielectric carrier  154  (e.g., a carrier such as carrier  32  of  FIG. 3 ). Dielectric carrier  154  may be a plastic substrate, foam substrate, ceramic substrate, glass substrate, polymer substrate, or any other desired dielectric substrate. Dielectric carrier  154  may be solid or may enclose a hollow cavity. Planar antenna resonating element structures  78  may be formed from conductive traces patterned directly onto the top surface of dielectric carrier  154 , may be formed from sheet metal, conductive foil, or other planar conductors that are placed over or adhered to the top surface of dielectric carrier  154 , or may be formed from conductive traces on a rigid or flexible printed circuit board placed on top of dielectric carrier  154 . 
     Dielectric structure  154  may have a height H and may separate resonating element  78  from ground plane  12 R- 2  by height H. Planar structures  78  may overlap some or all of slot  22  in rear housing wall  12 R. Dielectric substrate  154  and planar structures  78  may extend over ground plane portion  12 R- 2  to sidewall  12 W. In another suitable arrangement, other structures may be interposed between substrate  154  and sidewall  12 W. Planar structures  78  may be coupled to ground plane  12 R- 1  on the opposing side of slot  22  via return path  84 . 
     A dielectric layer  152  may be placed on top of planar antenna resonating element structure  78 . Layer  152  may be a dielectric such as plastic, ceramic, foam, or other dielectric material. If desired, layer  152  may be formed from adhesive (e.g., pressure sensitive adhesive, thermal adhesive, light cured adhesive, etc.), formed from a rigid or flexible printed circuit, or formed from any other desired structures. If desired, layer  152  may be omitted. Parasitic antenna resonating element  90  may be placed on dielectric layer  152 . Parasitic antenna element  90  may be formed from conductive traces patterned directly onto the top surface of dielectric layer  152 , may be formed from sheet metal, conductive foil, or other planar conductors that are placed over or adhered to the top surface of dielectric carrier  152  or element  78 , or may be formed from conductive traces on a rigid or flexible printed circuit board placed on top of dielectric layer  152  or structure  78 . Parasitic antenna element  90  may extend across the entire length of element  78  or may extend across only some of the length of element  78 . If desired, parasitic antenna element  90  may extend past the outline of layers  152  and/or  78 . Parasitic antenna element  90  may overlap some, all, or none of slot  22  in rear housing wall  12 R. Parasitic antenna element  90  may extend over ground plane portion  12 R- 2  to sidewall  12 W or may be separated from sidewall  12 W by a gap. Parasitic antenna element  90  may be coupled to ground plane  12 R- 1  on the opposing side of slot  22  via shorting path  92 . 
     In the example of  FIG. 8 , carrier  154  has a polygonal cross-sectional shape (e.g., the sides of carrier  154  are substantially planar). This is merely illustrative. If desired, some or all of the sides of carrier  154  may be curved. In general, one or more sides of carrier  154  may conform to (e.g., accommodate, extend parallel to, or abut) the shape of housing sidewall  12 W and housing rear wall  12 R. The cross section of carrier  154  may have more than four sides if desired. In general, carrier  154 , conductors  78  and  90 , housing sidewall  12 W, and housing rear wall  12 R may have any desired shapes or relative orientations. 
     During operation, antenna  40 ′ may operate in different frequency bands such as a low band LB, midband MB, and high band HB. Antenna  40 ′ may operate in one or more of bands LB, MB, and HB concurrently if desired. Switches  132  ( FIG. 7 ) may be selectively closed or opened to tune antenna  40 ′ in the low band LB. For example, the low band resonance of antenna  40 ′ may be centered on a first frequency in band LB when switch a first switch  132  (e.g., the switch  132  that is farthest from feed  84 ) is on and the other switches  132  are off, may be centered on a second frequency in band LB that is greater than the first frequency when a second switch  132  (e.g., the second-farthest switch  132  from feed  84 ) is on and the other switches  132  are off, may be centered on a third frequency in band LB that is greater than the second frequency when a third switch  132  is on and the other switches  132  are off, etc. The adjustable inductor of return path  84  may be used to provide multiple tuning settings for the midband MB if desired. 
     However, as the area IA available for forming antenna  40 ′ decreases (e.g., to increase the size of active area AA of display  14 ), the performance (e.g., efficiency and bandwidth) of antenna  40 ′ is typically reduced, particularly in the low band LB. In addition, coupling planar element  78  to ground (e.g., by closing at least one of switches  120 ) in order to cover frequencies in the midband MB can also limit the efficiency of antenna  40 ′ in the low band LB. If desired, control circuitry  42  may actively control switches  132 ,  120 , and  144  to operate antenna  40 ′ in different tuning or switching modes to improve performance of antenna  40 ′ in the low band LB while also allowing for coverage of frequencies in the midband MB and for further reduction to the size of inactive area IA of display  14 . 
     A table showing how control circuitry  42  may control antenna  40 ′ to operate in different tuning modes is shown in  FIG. 9 . As shown in  FIG. 9 , control circuitry  42  may control antenna  40 ′ to operate in first, second, and third tuning modes M 1 , M 2 , and M 3 , respectively. Tuning modes M 1 , M 2 , and M 3  may sometimes be referred to herein as switching modes, switching states, switching settings, tuning states, or tuning settings. 
     When controlling antenna  40 ′ to operate in first tuning mode M 1 , control circuitry  42  may provide control signals that open parasitic switch  144  (e.g., to deactivate or turn off switch  144 ). Control circuitry  42  may provide control signals that open all of switches  120 . This may decouple parasitic antenna element  90  from ground plane  12 R- 1  so that parasitic element  90  does not significantly perturb (e.g., constructively interfere with) the electromagnetic field generated by planar structure  78  and slot  22 . Opening all of switches  120  in tuning mode M 1  may decouple planar element  78  from ground plane  12 R- 1  (e.g., so that element  78  operates as a patch element). 
     When controlled in this way, patch structure  78  may be directly fed with radio-frequency signals over feed  82 . Patch structure  78  may indirectly feed the radio-frequency signals to slot  22 . In indirectly feeding slot  22 , patch  78  may excite the fundamental frequency (resonance) of slot  22 . This fundamental frequency may be a frequency in the low band LB. The low band performance of antenna  40 ′ (e.g., the antenna efficiency and bandwidth in low band LB) may thereby be relatively high when operating in tuning mode M 1 . Because planar element  82  is decoupled from ground  12 R- 1 , antenna  40 ′ may not exhibit any resonance (or may exhibit negligible or relatively low antenna efficiency) at frequencies outside of the low band LB (e.g., at frequencies in the mid band MB and high band HB). However, decoupling element  78  from ground  12 R- 1  may allow the efficiency of slot element  22  in low band LB to be greater than would otherwise be possible when element  78  is coupled to ground  12 R- 1  for relatively small sizes of inactive display area IA. 
     Control circuitry  42  may, for example, control antenna  40 ′ to operate in first tuning state M 1  when it is desired to only cover frequencies in low band LB (e.g., cellular telephone frequencies between 700 and 960 MHz) or when a high efficiency in low band LB is required. If desired, one or more capacitors  130  may be switched into use (e.g., by closing one or more corresponding switches  132 ) to adjust (shift) the particular frequency within the low band LB that is used. First tuning mode M 1  may therefore sometimes be referred to herein as a low-band-only mode or a high performance low band mode. 
     While operating at frequencies in low band LB, it may be desirable to also cover frequencies in midband MB. For example, it may be desirable to be able to convey signals such as GPS signals at a midband frequency of 1575 MHz or GLONASS signals at a frequency of 1609 MHz while also performing cellular telephone communications at a low band frequency between 760 and 900 MHz. Slot  22  may not exhibit a resonance at frequencies in the midband MB, so indirectly feeding slot  22  using element  78  may be insufficient for covering frequencies in the midband MB. If desired, planar element  78  may be shorted to ground (e.g., by closing one or more of switches  120 ) to allow planar resonating element structure  78  to resonate at frequencies in the midband MB. However, shorting planar element  78  to ground may degrade or reduce the efficiency of antenna  40 ′ in low band LB, particularly when the distance between active display area AA and sidewall  12 W (e.g., the width of inactive area IA) is sufficiently small (e.g., less than 15 mm). 
     In order to operate at frequencies in low band LB and midband MB, control circuitry  42  may control antenna  40 ′ to operate in second tuning mode M 2 . In second tuning mode M 2 , control circuitry  42  may provide control signals that close parasitic switch  144  (e.g., to activate or turn on switch  144 ). Control circuitry  42  may provide control signals that open all of switches  120 . This may couple parasitic antenna element  90  to ground plane  12 R- 1  so that parasitic element  90  perturbs (e.g., constructively interfere with) the electromagnetic field generated by planar structure  78 . Opening all of switches  120  in tuning mode M 2  decouples planar element  78  from ground plane  12 R- 1  (e.g., so that element  78  operates as a patch element without degrading performance in low band LB). 
     In second tuning mode M 2 , patch structure  78  may be directly fed with radio-frequency signals over feed  82 . Patch structure  78  may indirectly feed the radio-frequency signals to slot  22  to excite the fundamental frequency (resonance) of slot  22  in low band LB. Parasitic element  90  may perturb (e.g., constructively interfere with) the electromagnetic field generated by element  78  in response to being directly fed the radio-frequency signals over feed  82 . The constructive electromagnetic field interference generated by parasitic element  90  may establish a resonance for antenna  40 ′ at a frequency in the midband MB (e.g., at a GPS frequency at 1575 MHz). 
     Because the directly fed patch element  78  remains decoupled from ground in second tuning state M 2 , the low band performance of antenna  40 ′ (e.g., the antenna efficiency and bandwidth in low band LB) may be relatively high when operating in second tuning mode M 2 . Coupling parasitic element  90  to ground (e.g., using switch  144 ) may allow antenna  40 ′ to concurrently exhibit relatively high midband performance (e.g., the antenna efficiency or efficiency bandwidth in midband MB may be relatively high). Antenna  40 ′ may not exhibit any resonance (or may exhibit negligible or relatively low antenna efficiency) at frequencies outside of the low band LB and midband MB (e.g., at frequencies in the high band HB). Control circuitry  42  may, for example, control antenna  40 ′ to operate in second tuning state M 2  when it is desired to only cover frequencies in low band LB (e.g., cellular telephone frequencies between 700 and 960 MHz) and midband MB (e.g., GPS frequencies at 1575, cellular frequencies at 1900 MHz, etc.). If desired, one or more of capacitors  130  may be switched into use to adjust the particular frequency within the low band LB that is used. Second tuning mode M 2  may sometimes be referred to herein as a GPS mode, a GPS/cellular mode, a low band and midband-only mode, or a high performance low band and midband mode. 
     When it is desired to operate at frequencies in high band HB (e.g., at cellular telephone frequencies between 2100 MHz and 2700 MHz or at other frequencies that are greater than frequencies in midband MB), control circuitry  42  may control antenna  40 ′ to operate in third tuning mode M 3 . In third tuning mode M 3 , control circuitry  42  may provide control signals that open parasitic switch  144 . Control circuitry  42  may provide control signals that close at least one of switches  120 . This may decouple parasitic antenna element  90  from ground plane  12 R- 1  so that parasitic element  90  does not affect or constructively interfere with the electromagnetic field generated by planar structure  78 . Closing at least one of switches  120  in tuning mode M 3  couples (shorts) planar element  78  to ground plane  12 R- 1  over return path  84  (e.g., so that element  78  operates as a planar inverted-F element). 
     In third tuning mode M 3 , planar inverted-F structure  78  may be directly fed with radio-frequency signals over feed  82 . Planar structure  78  may indirectly feed the radio-frequency signals to slot  22  to excite the fundamental frequency (resonance) of slot  22  in low band LB. The low band performance of antenna  40 ′ (e.g., the antenna efficiency or efficiency bandwidth in low band LB) may be degraded due to at least one of switches  120  being turned on. The low band performance of antenna  40 ′ may therefore be relatively low when operating in third tuning mode M 3 . Planar inverted-F structure  78  may exhibit a resonance in the midband MB in response to being directly fed the radio-frequency signals over feed  82 . The midband performance of antenna  40 ′ may therefore be relatively high when operating in third tuning mode M 3 . Control circuitry  18  may selectively close one or more of switches  120  to adjust the particular midband frequency that is used if desired. Planar inverted-F structure  78  may also excite a harmonic frequency (resonance) of slot  22  in third tuning mode M 3 . This harmonic frequency may be a frequency in the high band HB. The high band performance of antenna  40 ′ (e.g., the antenna efficiency or efficiency bandwidth in high band HB) may thereby be relatively high when operating in tuning mode M 3 . 
     Control circuitry  42  may, for example, control antenna  40 ′ to operate in third tuning state M 3  when it is desired to only cover frequencies in high band HB (e.g., cellular telephone frequencies between 2100 and 2700 MHz), when it is desired to cover frequencies in midband MB and high band HB, or whenever a relatively high efficiency in the low band LB is not needed. Third tuning mode M 3  may sometimes be referred to herein as a multi-band mode, a low band midband high band mode, or a high band mode. 
     Control circuitry  42  may determine which mode of modes M 1 , M 2 , and M 3  to use for communications based on any desired criteria. For example, control circuitry  42  may receive instructions from a wireless base station or access point that identify one or more frequencies of operation for device  10 . If desired, the current operating state of device  10  may be used to identify frequencies for communications. For example, control circuitry  42  may identify a usage scenario (e.g., whether device  10  is being used to browse the internet, conduct a phone call, send an email, access GPS, etc.) to determine the frequencies for communications. As another example, control circuitry  42  may identify sensor data that is used to identify the frequencies for communications. In general, control circuitry  42  may process any desired combination of this information (e.g., information about a usage scenario of device  10 , sensor data, information from a wireless base station, user input, etc.) to identify the desired frequencies for operation. 
     As an example, if control circuitry  42  determines that device  10  is to convey radio-frequency signals at a frequency in the low band LB only, control circuitry  42  may control antenna  40 ′ to operate in first tuning state M 1  or second tuning state M 2 . If control circuitry  42  identifies that device  10  is to convey radio-frequency signals at a frequency in midband MB only, control circuitry  42  may control antenna  40 ′ to operate in second tuning state M 2  or third tuning state M 3 . If control circuitry  42  identifies that device  10  is to convey radio-frequency signals at a frequency in high band HB (e.g., at a frequency in high band HB only, at a frequency in high band HB and low band LB, at a frequency in high band HB and midband MB, or at a frequency in high band HB, midband MB, and low band LB), control circuitry  42  may control antenna  40 ′ to operate in third tuning state M 3 . If control circuitry  42  identifies that antenna  40 ′ is to operate in low band LB and midband MB, control circuitry  42  may control antenna  40 ′ to operate in second tuning state M 2 . Control circuitry  42  may adjust antenna  40 ′ to the desired tuning state prior to beginning communications or may actively update the tuning state of antenna  40 ′ in real time. By switching between tuning states M 1 , M 2 , and M 3 , control circuitry  42  may allow antenna  40 ′ to maintain high efficiency coverage in multiple different communications bands of interest even in scenarios where antenna  40  occupies a relatively small volume (e.g., in scenarios where the width of inactive area IA between active area AA and sidewall  12 W is 15 mm or less). 
     The example of  FIG. 9  is merely illustrative. In general, control circuitry  42  may control antenna  40 ′ to exhibit any desired number of tuning states. Each tuning state may alter the performance of antenna  40 ′ in any desired frequency bands of interest. 
       FIG. 10  is a graph in which antenna performance (antenna efficiency) has been plotted as a function of operating frequency f. Dashed-dotted curve  204  illustrates the performance of antenna  40 ′ when set to first tuning mode M 1  of  FIG. 9 . Dashed curve  202  illustrates the performance of antenna  40 ′ when set to second tuning mode M 2 . Solid curve  200  illustrates the performance of antenna  40 ′ when set to third tuning mode M 3 . 
     Slot  22  may have a length (e.g., a quarter wavelength) that supports resonances in low communications band LB (e.g., a low band at frequencies between 700 and 760 MHz). When set to first tuning mode M 1  or second tuning mode M 2 , antenna  40 ′ exhibits a relatively high efficiency at a frequency within low band LB. However, due to the active return path between planar metal element  78  and ground  12 R- 1 , antenna  40 ′ may exhibit a relatively low efficiency within low band LB when set to third tuning mode M 3  (curve  200 ). If desired, the particular frequency of operation within low band LB may be tuned by adjusting tunable circuit  86  across slot  22 , as shown by arrow  208  (e.g., by selectively enabling at least one of switches  132  in  FIG. 7 ). 
     Midband coverage (e.g., for midband MB from 1400 or 1500 MHz to 1.9 GHz or another suitable midband range that is greater than low band LB and less than high band HB) may be supported by the resonance exhibited by planar element  78  when operated in tuning state M 3  (curve  200 ) or by the resonance of planar element  78  combined with the field perturbation provided by parasitic element  90  when operated in tuning mode M 2  (curve  202 ). The efficiency of antenna  40 ′ may thereby be relatively high at frequencies in midband MB when operating in second tuning mode M 2  or third tuning mode M 3 . The efficiency of antenna  40 ′ may be relatively low at frequencies in midband MB when operating in first tuning mode M 1 . 
     High band coverage (e.g., for a high band centered at 2400 MHz and extending from 1.9 GHz or 2.1 GHz to 2700 MHz or another suitable frequency) may be supported using harmonics of the slot antenna resonating element resonance (e.g., a third order harmonic, etc.) that are excited by planar element  78  when operated in third tuning mode M 3 . The efficiency of antenna  40 ′ may thereby be relatively high at frequencies in high band HB when operating in third tuning mode M 3 . The efficiency of antenna  40 ′ may be relatively low at frequencies in high band HB when operating in second tuning mode M 2  or first tuning mode M 1 . If desired, the particular midband frequency and/or the band width of resonance  200  may be tuned by adjusting tunable circuit  84  coupled between planar element  78  and ground  12 R- 1 , as shown by arrows  210  (e.g., by selectively enabling at least one of switches  120  of  FIG. 7 ). 
     Control circuitry  42  may switch between tuning modes M 1 , M 2 , and M 3  to provide satisfactory efficiency for antenna  40 ′ in the desired bands of interest (e.g., as is required by the current operating state of device  10 , by a corresponding wireless base station, etc.). The example of  FIG. 10  is merely illustrative. In general, any desired low band, midband, and high band may be used (e.g., where the midband includes only frequencies greater than the low band and the high band includes only frequencies greater than the midband). 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20160923
Publication Date: 20190514
Grant Date: 20190514
Priority Date: 20160923
Inventors: ROMANO, Pietro
RAJAGOPALAN, HARISH
AZAD, Umar
ZHANG, LU
GOMEZ ANGULO, RODNEY A.
PASCOLINI, MATTIA
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/385", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/285", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0414", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/241", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/48", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/241", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/48", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/385", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/285", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0414", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 61688011