PATENT DOCUMENT

Publication Number: US-10355344-B1
Application Number: US-201815903733-A
Country: US
Kind Code: B1

Title: Electronic devices having antenna diversity capabilities

Abstract:
An electronic device such as a wristwatch may be provided with a wireless local area network (WLAN) transceiver, satellite receiver, and cellular transceiver. A first antenna may include a radiating slot between a conductive housing wall and a display module. A second antenna may include conductive structures that radiate through a rear face of the device. The WLAN transceiver and the satellite receiver may be coupled to the first antenna. A switch may be coupled between the cellular transceiver and the first and second antennas. Control circuitry may adjust the switch to route signals between the cellular transceiver and a selected one of the first and second antennas based on wireless performance metric data so that the antenna exhibiting superior wireless performance at cellular telephone frequencies is used for cellular telephone communications regardless of environmental conditions.

Claims:
What is claimed is: 
     
       1. An electronic device having opposing front and rear faces, comprising:
 a display on the front face, wherein the display forms part of a first antenna resonating element for a first antenna; 
 a housing having a rear housing wall on the rear face; 
 conductive structures that form part of a second antenna resonating element for a second antenna; 
 radio-frequency transceiver circuitry mounted in the housing; and 
 switching circuitry having a first terminal coupled to the first antenna, a second terminal coupled to the second antenna, and a third terminal coupled to the radio-frequency transceiver circuitry, wherein the switching circuitry has a first state in which the first terminal is coupled to the third terminal and a second state in which the second terminal is coupled to the third terminal, the first antenna is configured to transmit and receive the radio-frequency signals while the switching circuitry is in the first state, and the second antenna is configured to transmit and receive the radio-frequency signals through the rear housing wall while the switching circuitry is in the second state. 
 
     
     
       2. The electronic device defined in  claim 1 , wherein the display comprises conductive display structures and a display cover layer that overlaps the conductive display structures, the housing comprises conductive housing walls that extend from the rear housing wall to the display cover layer, and the first antenna includes a first antenna feed having a first antenna feed terminal coupled to the conductive display structures and a second antenna feed terminal coupled to the conductive housing walls. 
     
     
       3. The electronic device defined in  claim 2 , wherein the first antenna comprises a radiating slot having edges defined by the conductive housing walls and the conductive display structures. 
     
     
       4. The electronic device defined in claim  3 , wherein the second antenna comprises a second antenna feed having a third antenna feed terminal coupled to the conductive structures and a fourth antenna feed terminal coupled to the conductive housing walls. 
     
     
       5. The electronic device defined in  claim 4 , wherein the conductive structures comprise conductive structures selected from the group consisting of: conductive traces patterned directly onto the rear housing wall and conductive traces on a substrate that overlaps the rear housing wall. 
     
     
       6. The electronic device defined in  claim 5 , further comprising:
 a wireless power receiving coil that is aligned with an opening in the conductive structures and that is configured to receive wireless power through the rear housing wall. 
 
     
     
       7. The electronic device defined in  claim 1 , wherein the housing comprises conductive housing walls that extend from the rear housing wall to the display, the second antenna comprises an antenna feed having a first antenna feed terminal coupled to the conductive structures and a second antenna feed terminal coupled to the conductive housing walls, and the conductive structures comprise conductive structures selected from the group consisting of: conductive traces patterned directly onto the rear housing wall and conductive traces on a substrate that overlaps the rear housing wall. 
     
     
       8. The electronic device defined in  claim 1 , wherein the radio-frequency transceiver circuitry comprises cellular telephone transceiver circuitry and the radio-frequency signals comprise radio-frequency signals in a cellular telephone communications band. 
     
     
       9. The electronic device defined in  claim 8 , further comprising:
 control circuitry coupled to the cellular telephone transceiver circuitry, wherein the control circuitry is configured to identify wireless performance metric data associated with wireless performance of the first and second antennas in the cellular telephone communications band. 
 
     
     
       10. The electronic device defined in  claim 9 , wherein the control circuitry comprises baseband processor circuitry coupled to the cellular telephone transceiver circuitry, and the baseband processor circuitry is configured to control the switching circuitry to place the switching circuitry into a selected one of the first and second states based on the wireless performance metric data. 
     
     
       11. The electronic device defined in  claim 10 , further comprising:
 wireless local area network transceiver circuitry coupled to the first antenna; and 
 satellite navigation receiver circuitry coupled to the first antenna, wherein the first antenna is configured to convey additional radio-frequency signals for the wireless local area network transceiver circuitry and the satellite navigation receiver circuitry while the switching circuitry is in the first state and while the switching circuitry is in the second state. 
 
     
     
       12. The electronic device defined in  claim 11 , wherein the cellular telephone communications band comprises a cellular telephone communications band at frequencies between 1700 MHz and 2200 MHz. 
     
     
       13. A wristwatch, comprising:
 a housing having opposing first and second sides; 
 a first antenna at the first side of the housing; 
 a second antenna at the second side of the housing; 
 a first radio-frequency transceiver configured to transmit first radio-frequency signals in a first communications band using the first antenna; 
 switching circuitry coupled to the first and second antennas; 
 a second radio-frequency transceiver coupled to the switching circuitry and configured to transmit second radio-frequency signals in a second communications band; and 
 control circuitry configured to control the switching circuitry to route the second radio-frequency signals to a selected one of the first and second antennas. 
 
     
     
       14. The wristwatch defined in  claim 13 , wherein the control circuitry is configured to identify wireless performance metric data associated with wireless performance of the second antenna in the second communications band and is configured to control the switching circuitry based on the wireless performance metric data. 
     
     
       15. The wristwatch defined in  claim 14 , wherein the wireless performance metric data comprises receive signal strength Received Signal Strength Indicator (RSSI) data gathered based at least on signals received by the second antenna. 
     
     
       16. The wristwatch defined in  claim 14 , further comprising:
 a radio-frequency coupler interposed between the switching circuitry and the second antenna, wherein the wireless performance metric data comprises impedance information associated with the second antenna gathered by the control circuitry using the radio-frequency coupler. 
 
     
     
       17. The wristwatch defined in  claim 13 , further comprising:
 a satellite navigation receiver configured to receive third radio-frequency signals in a satellite navigation communications band using the first antenna. 
 
     
     
       18. The wristwatch defined in  claim 17 , wherein the first radio-frequency transceiver comprises a wireless local area network transceiver, the first communications band comprises a wireless local area network communications band, the second radio-frequency transceiver comprises a cellular telephone transceiver, and the second communications band comprises a cellular telephone communications band. 
     
     
       19. The wristwatch defined in  claim 18 , further comprising:
 a display at the first side of the housing, wherein the housing comprises a rear housing wall and conductive housing sidewalls extending from the rear housing wall to the display; and 
 conductive structures that form at least part of an antenna resonating element for the second antenna and that transmit the second radio-frequency signals through the rear housing wall, wherein the first antenna comprises a first antenna feed terminal coupled to conductive display structures in the display, a second antenna feed terminal coupled to the conductive housing sidewalls, and a radiating slot defined by the conductive display structures and the conductive housing sidewalls, the second antenna further comprising a third antenna feed terminal coupled to the conductive structures and a fourth antenna feed terminal coupled to the conductive housing sidewalls. 
 
     
     
       20. A wristwatch having opposing first and second faces, comprising:
 a housing having a rear housing wall on the second face and having a conductive housing sidewall; 
 a display mounted to the housing on the first face; 
 a first antenna having a first antenna resonating element formed from conductive structures in the display and the conductive housing sidewall; 
 a second antenna having a second antenna resonating element configured to radiate through the rear housing wall; 
 wireless local area network transceiver circuitry configured to transmit and receive first wireless signals in a wireless local area network communications band using the first antenna; 
 satellite navigation receiver circuitry configured to receive second wireless signals in satellite navigation communications band using the first antenna; 
 cellular telephone transceiver circuitry configured to transmit and receive third wireless signals in a cellular telephone communications band; 
 switching circuitry coupled to the first and second antennas and configured to route the third wireless signals between the cellular telephone transceiver circuitry and a selected one of the first and second antennas; and 
 filter circuitry coupled to the first antenna and configured to isolate the wireless local area network transceiver circuitry and the satellite navigation receiver circuitry from the third wireless signals. 
 
     
     
       21. The electronic device defined in  claim 1 , wherein the display comprises conductive display structures and a display cover layer that overlaps the conductive display structures, the first antenna having an antenna feed terminal coupled to the conductive display structures.

Description:
BACKGROUND 
     This relates to electronic devices, and more particularly, to electronic devices with wireless communications circuitry. 
     Electronic devices 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 such as a wristwatch may be provided with wireless circuitry. The wireless circuitry may include transceiver circuitry such as a wireless local area network transceiver, a satellite navigation receiver, and a cellular telephone transceiver. The wireless circuitry may include antennas for conveying radio-frequency signals for the transceiver circuitry. 
     The electronic device may have front and rear faces and may include a display on the front face. The electronic device may include a housing having a rear housing wall on the rear face. The housing may include conductive housing sidewalls extending between the display and the rear housing wall. The display may include conductive display structures that are separated from the conductive housing walls by a slot. The slot may form an antenna resonating element for a first antenna at the front face of the device. The first antenna may include a first antenna feed coupled between the conductive display structures and the conductive housing walls across the slot. Conductive structures such as conductive traces may form an antenna resonating element for a second antenna at the rear face of the device. The second antenna may include a second antenna feed coupled between the conductive traces and the conductive housing walls. The second antenna may transmit and receive radio-frequency signals through the rear housing wall. 
     The wireless local area network transceiver may be coupled to the first antenna and may convey radio-frequency signals in wireless local area network communications bands using the first antenna. The satellite navigation receiver may be coupled to the first antenna and may receive radio-frequency signals in a satellite navigation communications band using the first antenna. The wireless circuitry may include switching circuitry having a first terminal coupled to the first antenna, a second terminal coupled to the second antenna, and a third terminal coupled to the cellular telephone transceiver circuitry. Control circuitry in the electronic device may control the switching circuitry to route radio-frequency signals in a cellular telephone communications band between the cellular telephone transceiver circuitry and a selected one of the first and second antennas at a given time. The wireless local area network transceiver and the satellite navigation receiver may perform wireless communications using the first antenna whereas the second antenna only handles cellular telephone communications, if desired. 
     The control circuitry may gather wireless performance metric data associated with wireless performance of the first and/or second antennas in the cellular telephone communications band. The control circuitry may control the switching circuitry based on the wireless performance metric data so that the antenna that exhibits optimal wireless performance in the cellular telephone communications band is used for conveying radio-frequency signals for the cellular telephone transceiver, regardless of any change in the environmental conditions of the device. The wireless performance metric data may include receive signal strength data such as Received Signal Strength Indicator (RSSI) data, impedance information measured using radio-frequency couplers coupled to the first and second antennas, and/or any other desired performance metric data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless circuitry in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless circuitry in accordance with an embodiment. 
         FIG. 3  is a diagram of illustrative wireless circuitry in an electronic device in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative electronic device having antennas formed at opposing front and rear sides of the electronic device in accordance with an embodiment. 
         FIG. 5  is a top-down view of an illustrative antenna formed at the front side of an electronic device of the type shown in  FIG. 4  in accordance with an embodiment. 
         FIG. 6  is a perspective view of an illustrative antenna formed at the rear side of an electronic device of the type shown in  FIG. 4  in accordance with an embodiment. 
         FIG. 7  is a diagram of illustrative wireless circuitry having multiple antennas that are controlled using an antenna diversity scheme in accordance with an embodiment. 
         FIG. 8  is a flow chart of illustrative steps involved in selecting an optimal one of the antennas shown in  FIGS. 4-7  for performing wireless communications in accordance with an embodiment. 
         FIG. 9  is a graph of antenna performance (antenna efficiency) for illustrative antennas of the types shown in  FIGS. 4-7  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device such as electronic device  10  of  FIG. 1  may be provided with wireless circuitry. The wireless circuitry may be used to support wireless communications in multiple wireless communications bands. The wireless circuitry may include antennas. Antennas may be formed from electrical components such as displays, touch sensors, near-field communications antennas, wireless power coils, peripheral antenna resonating elements, conductive traces, and device housing structures, as examples. 
     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 wristwatch 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 wristwatch (e.g., a smart watch). 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.). Housing  12  may have metal sidewalls such as sidewalls  12 W or sidewalls formed from other materials. Examples of metal materials that may be used for forming sidewalls  12 W include stainless steel, aluminum, silver, gold, metal alloys, or any other desired conductive material. Sidewalls  12 W may sometimes be referred to herein as housing sidewalls  12 W or conductive housing sidewalls  12 W. 
     Display  14  may be formed at (e.g., mounted on) the front side (face) of device  10 . Housing  12  may have a rear housing wall on the rear side (face) of device  10  such as rear housing wall  12 R that opposes the front face of device  10 . Conductive housing sidewalls  12 W may surround the periphery of device  10  (e.g., conductive housing sidewalls  12 W may extend around peripheral edges of device  10 ). Rear housing wall  12 R may be formed from conductive materials and/or dielectric materials. Examples of dielectric materials that may be used for forming rear housing wall  12 R include plastic, glass, sapphire, ceramic, wood, polymer, combinations of these materials, or any other desired dielectrics. 
     Rear housing wall  12 R and/or display  14  may extend across some or all of the length (e.g., parallel to the X-axis of  FIG. 1 ) and width (e.g., parallel to the Y-axis) of device  10 . Conductive housing sidewalls  12 W may extend across some or all of the height of device  10  (e.g., parallel to Z-axis). Conductive housing sidewalls  12 W and/or the rear housing wall  12 R may form one or more exterior surfaces of device  10  (e.g., surfaces that are visible to a user of device  10 ) and/or may be implemented using internal structures that do not form exterior surfaces of device  10  (e.g., conductive or dielectric housing structures that are not visible to a user of device  10  such as conductive structures that are covered with layers such as thin cosmetic layers, protective coatings, and/or other coating layers that may include dielectric materials such as glass, ceramic, plastic, or other structures that form the exterior surfaces of device  10  and/or serve to hide housing walls  12 R and/or  12 W from view of the user). 
     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 include an array of display pixels formed from liquid crystal display (LCD) components, an array of electrophoretic display pixels, an array of plasma display pixels, an array of organic light-emitting diode (OLED) display 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. The display cover layer may be formed from a transparent material such as glass, plastic, sapphire or other crystalline dielectric materials, ceramic, or other clear materials. The display cover layer may extend across substantially all of the length and width of device  10 , for example. 
     Device  10  may include buttons such as button  18 . There may be any suitable number of buttons in device  10  (e.g., a single button, more than one button, two or more buttons, five or more buttons, etc. Buttons may be located in openings in housing  12  (e.g., openings in conductive housing sidewall  12 W or rear housing wall  12 R) or in an opening in display  14  (as examples). Buttons may be rotary buttons, sliding buttons, buttons that are actuated by pressing on a movable button member, etc. Button members for buttons such as button  18  may be formed from metal, glass, plastic, or other materials. Button  18  may sometimes be referred to as a crown in scenarios where device  10  is a wristwatch device. 
     Device  10  may, if desired, be coupled to a strap such as strap  15 . Strap  15  may be used to hold device  10  against a user&#39;s wrist (as an example). Strap  15  may sometimes be referred to herein as wrist strap  15 . In the example of  FIG. 1 , wrist strap  15  is connected to opposing sides  8  of device  10 . Conductive housing sidewalls  12 W on sides  8  of device  10  may include attachment structures for securing wrist strap  15  to housing  12  (e.g., lugs or other attachment mechanisms that configure housing  12  to receive wrist strap  15 ). Configurations that do not include straps may also be used for device  10 . 
     A schematic diagram showing illustrative components that may be used in device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may include storage and processing circuitry such as control circuitry  20 . Control circuitry  20  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 control circuitry  20  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. 
     Control circuitry  20  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, control circuitry  20  may be used in implementing communications protocols. Communications protocols that may be implemented using control circuitry  20  include internet protocols, wireless local area network (WLAN) 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 or other wireless personal area network (WPAN) protocols, cellular telephone protocols, MIMO protocols, antenna diversity protocols, satellite navigation system protocols, etc. 
     Device  10  may include input-output circuitry  22 . Input-output circuitry  22  may include input-output devices  24 . Input-output devices  24  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  24  may include user interface devices, data port devices, and other input-output components. For example, input-output devices  24  may include touch screens, displays without touch sensor capabilities, buttons, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, vibrators or other haptic feedback engines, digital data port devices, light sensors (e.g., infrared light sensors, visible light sensors, etc.), light-emitting diodes, motion sensors (accelerometers), capacitance sensors, proximity sensors, magnetic sensors, force sensors (e.g., force sensors coupled to a display to detect pressure applied to the display), etc. 
     Input-output circuitry  22  may include wireless circuitry  34 . Wireless circuitry  34  may include coil  44  and wireless power receiver  28  for receiving wirelessly transmitted power from a wireless power adapter. Wireless power receiver  28  may include, for example, rectifier circuitry and other circuitry for powering or charging a battery on device  10  using wireless power received by coil  44 . To support wireless communications, wireless 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 such as antennas  40 , transmission lines, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless circuitry  34  may include radio-frequency transceiver circuitry  42  for handling various radio-frequency communications bands. For example, wireless circuitry  34  may include transceiver circuitry  38 ,  36 ,  32 , and  30 . Transceiver circuitry  36  may be wireless local area network transceiver circuitry. Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications or other WLAN bands and may handle the 2.4 GHz Bluetooth® communications band or other WPAN bands. Transceiver circuitry  36  may sometimes be referred to herein as WLAN transceiver circuitry  36 . 
     Wireless circuitry  34  may use cellular telephone transceiver circuitry  32  (sometimes referred to herein as cellular transceiver circuitry  32 ) for handling wireless communications in frequency ranges (communications bands) such as a low band (sometimes referred to herein as a cellular low band LB) from 600 to 960 MHz, a midband (sometimes referred to herein as a cellular midband MB) from 1400 MHz or 1700 MHz to 2170 or 2200 MHz, and a high band (sometimes referred to herein as a cellular high band HB) from 2200 or 2300 to 2700 MHz (e.g., a high band with a peak at 2400 MHz) or other communications bands between 600 MHz and 4000 MHz or other suitable frequencies (as examples). Cellular transceiver circuitry  32  may handle voice data and non-voice data. 
     Wireless circuitry  34  may include satellite navigation system circuitry such as Global Positioning System (GPS) receiver circuitry  38  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data (e.g., GLONASS signals at 1609 MHz). Satellite navigation system signals for receiver  38  are received from a constellation of satellites orbiting the earth. Wireless circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless circuitry  34  may include circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) transceiver circuitry  30  (e.g., an NFC transceiver operating at 13.56 MHz or another suitable frequency), etc. 
     In NFC links, wireless signals are typically conveyed over a few inches at most. In satellite navigation system links, cellular telephone links, and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. In WLAN and WPAN links at 2.4 and 5 GHz and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. Antenna diversity schemes may be used if desired to ensure that the antennas that have become blocked or that are otherwise degraded due to the operating environment of device  10  can be switched out of use and higher-performing antennas used in their place. 
     Wireless circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from slot antenna structures, loop antenna structures, patch antenna structures, stacked patch antenna structures, antenna structures having parasitic elements, inverted-F antenna structures, planar inverted-F antenna structures, helical antenna structures, monopole antennas, dipole antenna structures, Yagi (Yagi-Uda) antenna structures, surface integrated waveguide structures, hybrids of these designs, etc. If desired, one or more of antennas  40  may be cavity-backed antennas. 
     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 whereas another type of antenna is used in forming a remote wireless link antenna. If desired, space may be conserved within device  10  by using a single antenna to handle two or more different communications bands. For example, a single antenna  40  in device  10  may be used to handle communications in a WiFi® or Bluetooth® communication band at 2.4 GHz, a GPS communications band at 1575 MHz, a WiFi® or Bluetooth® communications band at 5.0 GHz, and one or more cellular telephone communications bands such as a cellular midband between about 1700 MHz and 2200 MHz. If desired, a combination of antennas for covering multiple frequency bands and dedicated antennas for covering a single frequency band may be used. 
     It may be desirable to implement at least some of the antennas in device  10  using portions of electrical components that would otherwise not be used as antennas and that support additional device functions. As an example, it may be desirable to induce antenna currents in components such as display  14  ( FIG. 1 ), so that display  14  and/or other electrical components (e.g., a touch sensor, near-field communications loop antenna, conductive display assembly or housing, conductive shielding structures, etc.) can serve as part of an antenna for Wi-Fi, Bluetooth, GPS, cellular frequencies, and/or other frequencies without the need to incorporate separate bulky antenna structures in device  10 . 
       FIG. 3  is a diagram showing how transceiver circuitry  42  in wireless circuitry  34  may be coupled to antenna structures of a corresponding antenna  40  using signal paths such as signal path  54 . Wireless circuitry  34  may be coupled to control circuitry  20 . Control circuitry  20  may be coupled to input-output devices  24 . Input-output devices  24  may supply output from device  10  and may receive input from sources that are external to device  10 . 
     To provide antenna  40  with the ability to cover communications bands (frequencies) of interest, antenna  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  40  may be provided with adjustable circuits such as tunable components  50  to tune the antenna over communications bands of interest. Tunable components  50  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  20  may issue control signals on one or more paths such as path  52  that adjust inductance values, capacitance values, or other parameters associated with tunable components  50 , thereby tuning antenna  40  to cover desired communications bands. 
     Signal path  54  may include one or more radio-frequency transmission lines. As an example, signal path  54  of  FIG. 3  may be a transmission line having first and second conductive paths such as paths  62  and  64 , respectively. Path  62  may be a positive signal line and path  64  may be a ground signal line. Lines  62  and  64  may form part of a coaxial cable, a stripline transmission line, a microstrip transmission line, an edge-coupled microstrip transmission line, an edge-coupled stripline transmission line, a waveguide structure, a transmission line formed from combinations of these structures, etc. Signal path  54  may sometimes be referred to herein as radio-frequency transmission line  54  or transmission line  54 . 
     Transmission lines in device  10  such as transmission line  54  may be integrated into rigid and/or flexible printed circuit boards. In one suitable arrangement, transmission lines such as transmission line  54  may also include transmission line conductors (e.g., positive signal line  62  and ground signal line  64 ) integrated within multilayer laminated structures (e.g., layers of a conductive material such as copper and a dielectric material such as a resin that are laminated together without intervening adhesive). The multilayer laminated structures may, if desired, be folded or bent in multiple dimensions (e.g., two or three dimensions) and may maintain a bent or folded shape after bending (e.g., the multilayer laminated structures may be folded into a particular three-dimensional shape to route around other device components and may be rigid enough to hold its shape after folding without being held in place by stiffeners or other structures). All of the multiple layers of the laminated structures may be batch laminated together (e.g., in a single pressing process) without adhesive (e.g., as opposed to performing multiple pressing processes to laminate multiple layers together with adhesive). 
     A matching network formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna  40  to the impedance of transmission line  54 . 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. Matching network components may, for example, be interposed on transmission line  54 . The matching network components may be adjusted using control signals received from control circuitry  20  if desired. Components such as these may also be used in forming filter circuitry in antenna  40  (e.g., tunable components  50 ). 
     Transmission line  54  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  40  may be a slot antenna, an inverted-F antenna, a loop antenna, a patch antenna, or other antenna having an antenna feed  60  with a positive antenna feed terminal such as terminal  56  and a ground antenna feed terminal such as terminal  58 . Positive signal line  62  may be coupled to positive antenna feed terminal  56  and ground signal line  64  may be coupled to ground antenna feed terminal  58 . 
     If desired, antenna  40  may include an antenna resonating element that is indirectly fed using near-field coupling. In a near-field coupling arrangement, transmission line  54  is coupled to a near-field-coupled antenna feed structure that is used to indirectly feed antenna structures such as the antenna resonating element. This example is merely illustrative and, in general, any desired antenna feeding arrangement may be used. 
     Electronic device  10  may include multiple antennas  40  for covering multiple different communications bands. As an example, each antenna  40  may cover different respective communications bands or two or more antennas  40  may cover one or more of the same communications bands. 
     If desired, multiple antennas  40  in device  10  may be controlled using an antenna diversity scheme. In the antenna diversity scheme, two or more antennas  40  may be capable of covering a given communications band (e.g., where antennas  40  are mounted at different locations within device  10  for spatial diversity, exhibit different radiation patterns for pattern diversity, and/or exhibit different polarizations for polarization diversity). Control circuitry  20  may determine which antenna  40  is to be used in performing wireless communications in the given communications band at any particular time. For example, the antenna  40  that exhibits optimal wireless performance in the given communications band at a particular time may be selected to perform wireless communications in the given communications band while the other antennas  40  are switched out of use for covering the given communications band. 
     In this way, even if external objects in the vicinity of device  10  or other environmental factors deteriorate wireless performance for one antenna in the given communications band, a different antenna that offers superior wireless performance in the given communications band may be switched into use to cover the given communications band. If desired, the antenna that is switched out of use for the given communications band may still perform wireless communications in other communications bands. The antenna that is switched into use for covering the given communications band may also concurrently perform wireless communications in other communications bands if desired. Combining antennas that are capable of covering multiple frequency bands with an antenna diversity scheme may allow device  10  to maintain optimal wireless performance across many different communications bands regardless of the environmental conditions for device  10  while also minimizing the amount of space consumed by antennas  40  in device  10 . 
       FIG. 4  is a cross-sectional side view of electronic device  10  showing how multiple antennas  40  may be integrated within device  10  for implementing an antenna diversity scheme while also covering multiple communications bands. The plane of the page of  FIG. 4  may be, for example, the X-Z plane of  FIG. 1 . 
     As shown in  FIG. 4 , device  10  may include at least two antennas  40  such as a first antenna  40 F mounted at the front (top) side of device  10  and a second antenna  40 B mounted at the rear (bottom) side of device  10 . Antenna  40 F may sometimes be referred to herein as front antenna  40 F, front side antenna  40 F, display antenna  40 F, or front side module antenna  40 F. Antenna  40 B may sometimes be referred to herein as rear antenna  40 B, rear side antenna  40 B, back antenna  40 B, back side antenna  40 B, or back side module antenna  40 B. 
     Display  14  may form the front face of device  10  whereas rear housing wall  12 R forms the rear face of device  10 . In the example of  FIG. 4 , rear housing wall  12 R is formed from a dielectric material such as glass, sapphire, ceramic, or plastic. Conductive housing sidewalls  12 W may extend from the rear face to the front face of device  10  (e.g., from rear housing wall  12 R to display  14 ). 
     Strap  15  may be secured to conductive housing sidewalls  12 W using corresponding attachment structures  90 . Attachment structures  90  may include lugs, spring structures, clasp structures, adhesive structures, or any other desired attachment mechanisms. Strap  15  may be formed using any desired materials (e.g., metal materials, dielectric materials, or combinations of metal and dielectric materials). If desired, strap  15  may be removed from attachment structures  90  (e.g., so that a user of device  10  can swap in different straps having similar or different materials). 
     Display  14  may include a display module  70  (sometimes referred to herein as display stack  70 , display assembly  70 , or active area  70  of display  14 ) and a display cover layer  82 . Display module  70  may, for example, form an active area or portion of display  14  that displays images and/or receives touch sensor input. The lateral portion of display  14  that does not include display module  70  (e.g., portions of display  14  formed from display cover layer  82  but without an underlying portion of display module  70 ) may sometimes be referred to herein as the inactive area or portion of display  14  because this portion of display  14  does not display images or gather touch sensor input. 
     Display module  70  may include conductive components (sometimes referred to herein as conductive display structures) that are used in forming portions of front antenna  40 F. Other conductive structures in device  10  such as conductive housing sidewalls  12 W may also form portions of front antenna  40 F. 
     The conductive display structures in display module  70  may, for example, have planar shapes (e.g., planar rectangular shapes, planar circular shapes, etc.) and may be formed from metal and/or other conductive material that carries antenna currents for front antenna  40 F. The thin planar shapes of these components and the stacked configuration of  FIG. 4  may, for example, capacitively couple these components to each other so that they may operate together at radio frequencies to effectively/electrically form a single conductor. 
     Conductive display structures in display module  70  may include, for example, planar components on one or more display layers in display module  70  such as a first display layer  76 , a second display layer  74 , a third display layer  72 , or other desired layers. As one example, display layer  72  may form a touch sensor for display  14 , display layer  74  may form a display panel (sometimes referred to as a display, display layer, or pixel array) for display  14 , and display layer  76  may form a near-field communications antenna for device  10  and/or other circuitry for supporting near-field communications (e.g., at 13.56 MHz). 
     The touch sensor formed from display layer  72  may be a capacitive touch sensor and may be formed from a polyimide substrate or other flexible polymer layer with transparent capacitive touch sensor electrodes (e.g., indium tin oxide electrodes), for example. The display panel formed from display layer  74  may be an organic light-emitting diode display layer or other suitable display layer (e.g., display pixel circuitry may be formed in display layer  74 ). The near-field communications antenna formed from display layer  76  may be formed from a flexible layer that includes a magnetic shielding material (e.g., a ferrite layer or other magnetic shielding layer) and that includes loops of metal traces. If desired, a conductive back plate, metal shielding cans or layers, and/or a conductive display frame may be formed under and/or around display layer  76  and may provide structural support and/or a grounding reference for the components of display module  70 . 
     Conductive material in display layers  72 ,  74 , and  76 , a conductive back plate for display  14 , conductive shielding layers, conductive shielding cans, and/or a conductive frame for display  14  may be used in forming conductive display structures that form a part of front antenna  40 F (e.g., a part of the antenna resonating element and/or ground plane for front antenna  40 F). Conductive display structures from different display layers in display module  70  may be coupled together using conductive traces, vertical conductive interconnects or other conductive interconnects, and/or via capacitive coupling, for example. 
     Display cover layer  82  may be formed from an optically transparent dielectric such as glass, sapphire, ceramic, or plastic. Display module  70  may display images (e.g., emit image light) through display cover layer  82  for view by a user and/or may gather touch or force sensor inputs through display cover layer  82 . If desired, portions of display cover layer  82  may be provided with opaque masking layers (e.g., ink masking layers) and/or pigment to obscure interior  80  of device  10  from view of the user. 
     Substrates such as substrate  102  (e.g., a rigid or flexible printed circuit board, integrated circuit or chip, integrated circuit package, etc.) may be located within interior  80  of device  10 . Substrate  102  may be, for example, a main logic board (MLB) for device  10 . Other components such as components  104  (e.g., components used in forming control circuitry  20  and/or input-output circuitry  22  of  FIG. 2 ) may be mounted to substrate  102  and/or elsewhere within interior  80  of device  10 . 
     Display module  70  may be laterally separated from conductive housing sidewalls  12 W by a dielectric-filled slot such as slot  100  (sometimes referred to herein as gap or opening  100 ). Slot  100  may be filled with air and/or solid dielectric materials such as plastic, dielectric portions of display  14 , glass, ceramic, etc. Slot  100  may extend around some or all of the lateral sides of display module  70  (e.g., in the X-Y plane of  FIG. 4 ). If desired, the conductive display structures in display module  70  may be shorted to conductive housing sidewalls  12 W at one or more locations over optional conductive path  78  across slot  100 . 
     Front antenna  40 F may be fed using an antenna feed  60 F having a positive antenna feed terminal  56 F and a ground antenna feed terminal  58 F coupled across slot  100 . For example, positive antenna feed terminal  56 F may be coupled to conductive display structures in display module  70  whereas ground antenna feed terminal  58 F is coupled to a given conductive housing sidewall  12 W. This is merely illustrative and, if desired, positive antenna feed terminal  56 F may be coupled to conductive housing sidewalls  12 W and ground antenna feed terminal  58 F may be coupled to display module  70 . Antenna feed  60 F may be coupled to transceiver circuitry in device  10  using a corresponding transmission line (e.g., to transceiver circuitry  42  over a corresponding transmission line  54  as shown in  FIG. 3 ). Antenna currents for front antenna  40 F may be conveyed by antenna feed  60 F and may flow over the conductive display structures in display module  70  and conductive housing sidewalls  12 W. In this way, front antenna  40 F may be formed at or adjacent to the front face or side of device  10 . 
     When configured in this way, slot  100  may form a radiating slot (e.g., a slot antenna resonating element) for front antenna  40 F. Slot  100  (i.e., front antenna  40 F) may be used to transmit and receive radio-frequency signals  84  in WLAN and/or WPAN bands at 2.4 GHz and 5.0 GHz, in a cellular midband between 1.7 GHz and 2.2 GHz, and in a satellite navigation bands at 1575 MHz through display cover layer  82 , as one example. 
     Rear antenna  40 B may also be used to cover one or more of these communications bands (e.g., for performing wireless communications using an antenna diversity scheme with front antenna  40 F). As shown in  FIG. 4 , substrate  102  may include one or more conductive layers such as conductive layer  112 . Conductive layer  112  may, for example, form a portion of the antenna ground for rear antenna  40 B. Conductive layer  112  may therefore sometimes be referred to herein as grounded layer  112 , ground layer  112 , ground plane  112 , ground conductor  112 , or grounded conductor  112 . 
     If desired, conductive layer  112  may be shorted (grounded) to conductive housing sidewalls  12 W (e.g., the antenna ground for rear antenna  40 B may include conductive layer  112  and conductive housing sidewalls  12 W). Conductive layer  112  may be formed using metal foil, stamped sheet metal, conductive traces patterned onto a surface of substrate  102 , a conductive trace on a flexible printed circuit mounted to substrate  102 , metal housing portions, and/or from any other desired conductive structures. If desired, conductive layer  112  may be formed (embedded) within substrate  102  (e.g., conductive layer  112  may be stacked between dielectric layers of substrate  102 ). In another suitable arrangement, conductive layer  112  may be omitted. 
     As shown in  FIG. 4 , rear housing wall  12 R may extend across substantially all of the length and width of device  10 . Rear housing wall  12 R may be formed from any desired dielectric material. For example, rear housing wall  12 R may be formed from plastic, glass, sapphire, ceramic, wood, polymer, combinations of these materials, or any other desired dielectrics. Rear housing wall  12 R may be optically opaque or optically transparent or may include both optically opaque and optically transparent portions (e.g., rear housing wall  12 R may include optically transparent windows in an otherwise optically opaque member). 
     Rear antenna  40 B may include conductive structures  110 . Conductive structures  110  may, for example, form some or all of an antenna resonating element for rear antenna  40 B (e.g., an inverted-F antenna resonating element arm, a planar inverted-F antenna resonating element, a patch antenna resonating element, a dipole antenna resonating element, a monopole antenna resonating element, the edges of a slot antenna resonating element, etc.). 
     In one suitable arrangement, conductive structures  110  may be formed from conductive traces that are patterned directly onto the interior surface of rear housing wall  12 R (e.g., the patterned conductive traces may be in direct contact with the inner surface of rear housing wall  12 R). In another suitable arrangement, conductive structures  110  may be formed using conductive foil, stamped sheet metal, or other conductive structures that are placed over and in direct contact with rear housing wall  12 R. In yet another suitable arrangement, conductive structures  110  may be formed from conductive traces on a flexible or rigid printed circuit substrate or other dielectric substrate that is located over (e.g., vertically separated from and overlapping) or that is in direct contact with rear housing wall  12 R. If desired, springs, clips, or other biasing structures may be used to exert a downward force on conductive structures  110  that serves to press conductive structures  110  towards, into, or onto rear housing wall  12 R. If desired, adhesive may be used to adhere conductive structures  110  onto rear housing wall  12 R. Ink or other opaque masking layers may be interposed between conductive structures  110  and rear housing wall  12 R or rear housing wall  12 R may be opaque or provided with pigment that obscures conductive structures  110  from view through the rear of device  10 , if desired. Conductive structures  110  may be formed using any desired conductive materials (e.g., aluminum, copper, metal alloys, stainless steel, gold, etc.). In this way, conductive structures  110  used in forming the antenna resonating element for rear antenna  40 B and thus rear antenna  40 B itself may be formed at or adjacent to the rear face or side of device  10  (e.g., at or adjacent to rear housing wall  12 R). 
     If desired, conductive structures  110  may conform to the shape of the interior surface of rear housing wall  12 R. In the example of  FIG. 4 , the interior surface of rear housing wall  12 R and thus conductive structures  110  have a slightly curved or concave shape (e.g., to increase the total volume for components within device  10  relative to scenarios where the interior surface of rear housing wall  12 R is flat). 
     The example of  FIG. 4  in which rear housing wall  12 R is formed using dielectric materials is merely illustrative. If desired, rear housing wall  12 R of device  10  may include a combination of conductive and dielectric materials. For example, a portion of rear housing wall  12 R may be formed from metal whereas another portion of rear housing wall  12 R is formed from dielectric (e.g., the portion of rear housing wall  12 R formed from dielectric may extend across some but not all of the length and width of device  10 ). The dielectric portion of rear housing wall  12 R may, for example, include a dielectric window within a conductive portion of rear housing wall  12 R (e.g., rear housing wall  12 R may include a metal frame for the dielectric portion of rear housing wall  12 R or other structures that surround the dielectric portion of rear housing wall  12 R). Rear housing wall  12 R may include multiple dielectric windows if desired. 
     Rear antenna  40 B may be fed using an antenna feed  60 B having a positive antenna feed terminal  56 B and a ground antenna feed terminal  58 B coupled between conductive structures  110  and conductive housing sidewalls  12 W. Positive antenna feed terminal  56 B may be coupled to conductive structures  110  whereas ground antenna feed terminal  58 B is coupled to conductive housing sidewalls  12 W. This example is merely illustrative. If desired, ground antenna feed terminal  58 B may be coupled to conductive layer  112  or any other grounded structures within device  10 . In another suitable arrangement, positive antenna feed terminal  56 B may be coupled to conductive housing sidewalls  12 W or conductive layer  112  whereas ground antenna feed terminal  58 B is coupled to conductive structures  110 . 
     Antenna feed  60 B may be coupled to transceiver circuitry in device  10  using a corresponding transmission line (e.g., to transceiver circuitry  42  over a corresponding transmission line  54  as shown in  FIG. 3 ). If desired, conductive structures  110  may be shorted to the antenna ground for rear antenna  40 B (e.g., to conductive housing sidewalls  12 W, conductive layer  112 , and/or other grounded structures) using conductive paths (not shown in  FIG. 4  for the sake of clarity). Such conductive paths may, for example, form a return (short) path for rear antenna  40 B (e.g., in scenarios where rear antenna  40 B is an inverted-F antenna or planar inverted-F antenna). Antenna currents for rear antenna  40 B may be conveyed by antenna feed terminals  56 B and  58 B and may flow over conductive structures  110 , conductive housing sidewalls  12 W, and/or conductive layer  112 , for example. 
     Rear antenna  40 B may transmit and receive radio-frequency signals through rear housing wall  12 R in one or more of the communications bands that are also covered by front antenna  40 F. In one suitable arrangement, rear antenna  40 B may transmit and receive radio-frequency signals in the same cellular telephone communications band as front antenna  40 F (e.g., in a cellular midband between approximately 1700 MHz and 2200 MHz). Control circuitry  20  ( FIGS. 2 and 3 ) in device  10  may control front antenna  40 F and rear antenna  40 B using an antenna diversity scheme. Under the antenna diversity scheme, control circuitry  20  may select a given one of front antenna  40 F and rear antenna  40 B to convey radio-frequency signals in the cellular telephone communications band at a given time (e.g., a given one of antennas  40 F and  45 B having optimal wireless performance in the cellular telephone communications band). 
     Radio-frequency signals transmitted by rear antenna  40 B may be shielded from electrical components  104  and front antenna  40 F by conductive layer  112  and substrate  102 , for example. Similarly, conductive layer  112  and substrate  102  may shield rear antenna  40 B from components  104  and front antenna  40 F, thereby mitigating electromagnetic interference between rear antenna  40 B, components  104 , and front antenna  40 F. 
     If desired, other components such as components  108  may be mounted at or adjacent to rear housing wall  12 R. Components  108  may include one or more sensors such as a light sensor, proximity sensor, or touch sensor, and/or may include coil  44  ( FIG. 2 ), as an example. Components  108  may be mounted to substrate  106  or to substrate  102 . Components  108  may be vertically separated from rear housing wall  12 R, may be pressed against (e.g., in direct contact with) rear housing wall  12 R, or may be mounted to rear housing wall  12 R. In scenarios where components  108  are present, conductive structures  110  for rear antenna  40 B may laterally surround or be distributed around the periphery of components  108  at rear housing wall  12 R (e.g., conductive structures  110  may include a hole or opening that is aligned with components  108 ). If desired, optically transparent windows in rear housing wall  12 R may be aligned with components  108  to allow light (e.g., visible light, infrared light, etc.) to pass to and/or from components  108  through rear housing wall  12 R. 
     As one example, components  108  may include at least one infrared light emitter, at least one infrared light sensor, and coil  44  ( FIG. 2 ). In this example, coil  44  may laterally surround the infrared light sensor and emitter. The infrared light emitter may emit infrared light through rear housing wall  12 R (e.g., through a transparent window in rear housing wall  12 R). The infrared light sensor may receive a reflected version of the emitted infrared light that has been reflected off of an external object in the vicinity of device  10  such as wrist  114  of a user (e.g., a user who is wearing device  10  on their wrist in scenarios where device  10  is a wristwatch). Coil  44  in components  108  may receive wireless power from a wireless power adapter (e.g., a wireless charging device) through rear housing wall  12 R. This example is merely illustrative and, if desired, components  108  may include any other desired components or may be omitted. 
     By forming rear antenna  40 B at rear housing wall  12 R, the vertical height of device  10  (e.g., parallel to the Z-axis of  FIG. 4 ) may be shorter than would otherwise be possible in scenarios where the corresponding antenna resonating element is located elsewhere on device  10  (while still allowing rear antenna  40 B to exhibit satisfactory antenna efficiency). As an example, the vertical height of device  10  may be less than or equal to 11.4 mm, less than 15 mm, between 8 and 11.4 mm, or any other desired height while still allowing rear antenna  40 B to operate with satisfactory antenna efficiency. Maximizing the vertical separation between front antenna  40 F and rear antenna  40 B by forming front antenna  40 F from display  14  and forming rear antenna  40 B at rear housing wall  12 R and shielding antennas  40 F and  40 B using conductive structures such as conductive layer  112  may also allow for such a reduction in the vertical height of device  10  while still allowing front antenna  40 F to operate with satisfactory antenna efficiency. 
     In practice, the wireless performance of rear antenna  40 B may be optimized by the presence of an external object adjacent to rear housing wall  12 R. For example, the presence of the user&#39;s wrist  114  adjacent to rear housing wall  12 R when the user is wearing device  10  may enhance the wireless performance of rear antenna  40 B. During operation, the antenna resonating element for rear antenna  40 B (e.g., conductive structures  110 ) may transmit and/or receive radio-frequency signals having electric fields (E) that are oriented normal to the surfaces of rear housing wall  12 R and wrist  114 . These signals may sometimes be referred to as surface waves, which are then propagated along the surface of wrist  114  and outwards, as shown by paths  115  (e.g., conductive structures  110  and wrist  114  may serve as a waveguide that directs the surface waves outwards). This may allow the radio-frequency signals conveyed by rear antenna  40 B to be properly received by external communications equipment (e.g., a wireless base station) even though rear antenna  40 B is located close to wrist  114  and typically pointed away from the external communications equipment. 
     In practice, the wireless performance of rear antenna  40 B within cellular telephone communications bands may be particularly sensitive to variations in impedance loading through rear housing wall  12 R. When performing wireless communications operations, rear antenna  40 B may be loaded through rear housing wall  12 R by external objects such as wrist  114  in the vicinity of rear housing wall  12 R. If care is not taken, rear antenna  40 B may exhibit an altered frequency response relative to a free space environment when an external object such wrist  114  is brought into the vicinity of rear antenna  40 B (e.g., rear antenna  40 B may be detuned because the impedance of the antenna has been changed due to loading from wrist  114  through rear housing wall  12 R). In addition, different types of objects or materials may load rear antenna  40 B by differing amounts. Similarly, adjustments to the orientation or distance of the external object with respect to rear housing wall  12 R may load rear antenna  40 B by different amounts. During normal operation of device  10  by a user, these loading variations may occur when the user adjusts the location or orientation of device  10  on their wrist, when the user adjusts the distance between their wrist and rear antenna  40 B (e.g., by tightening or loosening strap  15 ), when the user swaps out strap  15  for a different strap, when a different user wears device  10  (e.g., because different users may have different wrist physiologies that affect the loading of rear antenna  40 B differently), when strap  15  or wrist  114  becomes wet (e.g., with sweat or water such as when the user is swimming while wearing device  10 ), or when a part of the user&#39;s clothing such as a shirt sleeve is placed between or removed from between device  10  and wrist  114 , as examples. These examples are merely illustrative. In general, any environmental factors may load rear antenna  40 B by different amounts through rear housing wall  12 R. 
     Such environmental loading variations may alter the impedance of rear antenna  40 B relative to its corresponding transmission line  54  ( FIG. 3 ). If care is not taken, these variations may generate an impedance discontinuity between rear antenna  40 B and the rest of wireless circuitry  34 . The impedance discontinuity may cause some radio-frequency energy to be reflected at the boundary between rear antenna  40 B and the rest of wireless communications circuitry  34  instead of being used to convey signals with external communications equipment. If these environmental loading variations are not compensated for, rear antenna  40 B may become detuned as the environmental loading variations change over time, thereby reducing the overall antenna efficiency and communications link quality during normal operation of device  10 . 
     In order to compensate for these antenna impedance changes, control circuitry  20  ( FIG. 3 ) may control adjustable matching circuitry coupled to rear antenna  40 B to ensure that rear antenna  40 B is suitably matched to the rest of wireless circuitry  34  regardless of how rear antenna  40 B is loaded through rear housing wall  12 R. If desired, control circuitry  20  may adjust tunable components  50  ( FIG. 3 ) in addition to adjustable matching circuitry to cover the desired frequency bands of interest and to compensate for any detuning of rear antenna  40 B due to loading of the antenna by external objects. 
     However, in practice, adjusting impedance matching circuitry and tunable components  50  may not be sufficient to compensate for changes in loading within some cellular telephone communications bands such as the cellular midband. In these scenarios, control circuitry  20  may control front antenna  40 F to handle the cellular telephone communications band instead of rear antenna  40 B (e.g., using an antenna diversity scheme). Front antenna  40 F may, for example, be more immune to changes in loading through rear housing wall  12 R than rear antenna  40 B. By switching front antenna  40 F into use for handling the cellular telephone communications band, satisfactory communications in the cellular telephone communications band may be maintained even if rear antenna  40 B has become unsatisfactorily detuned. In free space, rear antenna  40 B may exhibit greater efficiency and bandwidth in the cellular telephone communications band than front antenna  40 F (e.g., because rear antenna  40 B need only cover the cellular telephone communications band and not the wireless local area network and satellite navigation bands that are also covered by front antenna  40 F). Rear antenna  40 B may therefore be switched back into use once its wireless performance in the cellular telephone communications band returns to a satisfactory level, if desired. 
       FIG. 5  is a top-down of device  10  view showing how front  40 F be integrated within device  10  (e.g., as taken in the direction of arrow  116  of  FIG. 4 ). The plane of the page of  FIG. 5  may, for example, lie within the X-Y plane of  FIG. 4 . In the example of  FIG. 5 , display cover layer  82  of  FIG. 4  is not shown for the sake of clarity. 
     As shown in  FIG. 5 , slot  100  of front antenna  40 F may follow a meandering path and may have edges defined by different conductive electronic device structures. Slot  100  may have a first set of edges (e.g., outer edges) defined by conductive housing sidewalls  12 W and a second set of edges (e.g., inner edges) defined by conductive structures such as conductive display structures  120 . Conductive display structures  120  may, for example, include conductive portions of display module  70  ( FIG. 4 ) such as metal portions of a frame or assembly of display  14 , touch sensor electrodes within display layer  72 , pixel circuitry within display layer  74 , portions of a near field communications antenna embedded within display layer  76 , ground plane structures within display  14 , a metal back plate for display  14 , or other conductive structures on or in display  14 . 
     In the example of  FIG. 5 , slot  100  follows a meandering path and has a first segment  124  between edge the left conductive housing sidewall  12 W and conductive display structures  120 , a second segment  122  between the top conductive housing sidewall  12 W and conductive display structures  120 , a third segment  128  between the right conductive housing sidewall  12 W and conductive display structures  120 , and a fourth segment  126  between the bottom conductive housing sidewall  12 W and conductive display structures  120 . Segments  124  and  128  may extend along parallel longitudinal axes. Segments  122  and  126  may extend between ends of segments  124  and  128  (e.g., along parallel longitudinal axes perpendicular to the longitudinal axes of segments  124  and  128 ). In this way, slot  100  may be an elongated slot that extends between conductive display structures  120  and multiple conductive housing sidewalls  12 W (e.g., to maximize the length of slot  100  for covering relatively low frequency bands such as satellite navigation communications bands and low band cellular telephone communications bands). 
     Front antenna  40 F may be fed using antenna feed  60 F coupled across width W of slot  100  (e.g., a width W extending perpendicular to the elongated length of slot  100 ). In the example of  FIG. 5 , antenna feed  60 F is coupled across segment  122  of slot  100 . This is merely illustrative and, if desired, antenna feed  60 F may be coupled across any portion of slot  100 . Ground antenna feed terminal  58 F of antenna feed  60 F may be coupled to a given conductive housing sidewall  12 W and positive antenna feed terminal  56 F of antenna feed  60 F may be coupled to conductive display structures  120 . This is merely illustrative and, if desired, ground antenna feed terminal  58 F of antenna feed  60 F may be coupled to conductive display structures  120  and positive antenna feed terminal  56 F of antenna feed  60 F may be coupled to a given conductive housing sidewall  12 W. 
     When configured in this way, front antenna  40 F may form a slot antenna, as an example. Slot  100  may form the radiating element for front antenna  40 F and may sometimes be referred to herein as slot antenna resonating element  100 , slot antenna radiating element  100 , slot radiating element  100 , or slot element  100 . Front antenna  40 F may, for example, exhibit response peaks when the perimeter of slot  100  (e.g., as given by the length of the edges of slot  100  defined by conductive housing sidewalls  12 W and conductive display structures  120 ) is approximately equal to the effective wavelength of operation of the antenna (e.g., the wavelength after accounting for dielectric effects associated with the materials in device  10 ). If desired, conductive paths  78  may short conductive display structures  120  to conductive housing sidewalls  12 W at one or more locations to adjust the electrical length and thus the perimeter and frequency response of slot  100 . Harmonic modes of slot  100 , adjustable matching circuitry, optional conductive paths  78 , and/or tunable components  50  of  FIG. 3  coupled to antenna feed  60 F or elsewhere on front antenna  40 F may configure front antenna  40 F to perform wireless communications in multiple communications (frequency) bands such as a satellite navigation band, a 2.4 GHz WLAN and WPAN band, a cellular telephone midband, and 5.0 GHz WLAN band. Front antenna  40 F may perform wireless communications in the cellular telephone midband together with rear antenna  40 B of  FIG. 4  using an antenna diversity scheme if desired. 
     The example of  FIG. 5  is merely illustrative. Slot  100  may have a uniform width W along its length or may have different widths along its length. If desired, width W may be adjusted to tweak the bandwidth of front antenna  40 F. As an example, width W may be between 0.5 mm and 1.0 mm. Slot  100  may have other shapes if desired (e.g., shapes with more than three segments extending along respective longitudinal axes, fewer than three segments, curved edges, etc.). Device  10  may have any desired shape or profile. 
       FIG. 6  is a perspective view of rear antenna  40 B (e.g., as taken in the direction of arrow  117  of  FIG. 4 ) in scenarios where conductive structures  110  of rear antenna  40 B are implemented using a planar metal structure such as a metal patch (e.g., in a scenario where rear antenna  40 B is implemented using a planar inverted-F or patch antenna structure). In the example of  FIG. 6 , rear housing wall  12 R and substrate  106  of  FIG. 4  are not shown for the sake of clarity. 
     As shown in  FIG. 6 , rear antenna  40 B may include conductive structures  110  and antenna ground  153 . Antenna ground  153  may, for example, include portions of conductive housing sidewalls  12 W, conductive layer  112 , and/or other grounded conductive structures within device  10  ( FIG. 4 ). Conductive structures  110  may be substantially planar and may, if desired, conform to the shape of rear housing wall  12 R of  FIG. 4 . 
     As shown in  FIG. 6 , conductive structures  110  may be separated from antenna ground  153  by at least distance  155 . Antenna feed  60 B of rear antenna  40 B may be coupled across distance  155 . Positive antenna feed terminal  56 B may be coupled to conductive structures  110  whereas ground antenna feed terminal  58 B is coupled to antenna ground  153 . This is merely illustrative and, if desired, the locations of antenna feed terminals  56 B and  58 B shown in  FIG. 6  may be reversed. If desired, positive antenna feed terminal  56 B may be coupled to a feed leg of conductive structures  110  that protrudes downward towards antenna ground  153 . When fed in this way, rear antenna  40 B may form a patch antenna. If desired, an optional return path such as return path  151  may short conductive structures  110  to antenna ground  153  at one or more locations. In these scenarios, rear antenna  40 B may form a planar inverted-F antenna, for example. Conductive structures  110  may form an antenna resonating element for rear antenna  40 B and may sometimes be referred to herein as antenna resonating element  110 , antenna radiating element  110 , or patch  110 . 
     In the example of  FIG. 6 , conductive structures  110  have a rectangular plate shape. Configurations in which conductive structures  110  have a meandering arm shape, shapes with multiple branches, one or more curved edges, one or more straight edges, or other shapes may also be used for forming the antenna resonating element of rear antenna  40 B. Conductive structures  110  may be fed using other feeding schemes if desired (e.g., the antenna resonating element formed by conductive structures  110  may be a resonating element in a patch antenna, monopole antenna, dipole antenna, slot antenna, loop antenna, etc.). 
     As shown in the example of  FIG. 6 , a slot  150  may be formed in conductive structures  110  (sometimes referred to herein as notch  150  or hole  150 ). Slot  150  may be defined by edges of conductive structures  110 . Slot  150  may be a closed slot that is completely surrounded by (e.g., enclosed by) conductive material in conductive structures  110  or may be an open slot that extends to an outer edge of conductive structures  110  (e.g., slot  150  may be formed by a cut or notch extending from one side of the outer edge of conductive structures  110  towards the interior of conductive structures  110 ). 
     Slot  150  may have any desired perimeter or shape. In the example of  FIG. 6 , slot  150  has a curved (e.g., circular or oval) shape. The shape of slot  150  may accommodate other components such as components  108  that are aligned with or placed within slot  150 . If desired, the shape of slot  150  may be configured to conform to the shape of components  108 . Components  108  may lie in a common plane with conductive structures  110  and/or may lie below the plane of conductive structures  110 . 
     The example of  FIG. 6  is merely illustrative. In general, positive antenna feed terminal  56 B and optional return path  151  may be coupled to conductive structures  110  at any desired locations. Conductive structures  110  and slot  150  may have any desired shapes (e.g., shapes having one or more curved sides, one or more straight sides, etc.). When configured in this way, rear antenna  40 B may convey radio-frequency signals in a desired communications band such as the cellular midband using an antenna diversity scheme with front antenna  40 F of  FIGS. 4 and 5 . Slot  150  in rear antenna  40 B may allow components  108  to transmit and/or receive wireless signals through rear housing wall  12 R of  FIG. 4  (e.g., without blocking the wireless signals with conductive structures  110 ). 
       FIG. 7  is a circuit diagram of wireless circuitry  34  showing how rear antenna  40 B and front antenna  40 F of  FIGS. 4-6  may be controlled to perform wireless communications over a set of communications bands while performing wireless communications using an antenna diversity scheme over a subset of those communications bands. 
     As shown in  FIG. 7 , wireless circuitry  34  may include WLAN transceiver (TX/RX) circuitry  36 , GPS receiver circuitry  38 , and cellular transceiver circuitry  32 . WLAN transceiver circuitry  36  may also cover WPAN communications bands if desired. WLAN transceiver circuitry  36  may be coupled to applications processor (AP)  202  over data path  204 . GPS receiver circuitry  38  may be coupled to applications processor  202  over data path  208 . Cellular transceiver circuitry  32  may be coupled to cellular baseband (BB) processor circuitry  200  over data path  212 . Baseband processor circuitry  200  (sometimes referred to herein as baseband processor  200 ) may be coupled to applications processor  202  over path  206 . Applications processor  202  may run operating system software or other software associated with the control and operation of device  10 . 
     If desired, applications processor  202 , baseband processor circuitry  200 , cellular transceiver circuitry  32 , GPS receiver circuitry  38 , and WLAN transceiver circuitry  36  may each be formed on separate substrates such as separate integrated circuits, integrated circuit packages, chips, or printed circuit boards. In another suitable arrangement, two or more of applications processor  202 , baseband processor circuitry  200 , cellular transceiver circuitry  32 , GPS receiver circuitry  38 , and WLAN transceiver circuitry  36  may be formed on the same substrate such as a shared integrated circuit, integrated circuit package, chip, or printed circuit board (e.g., substrate  102  of  FIG. 4 ). 
     WLAN transceiver circuitry  36  may include digital-to-analog converter circuitry, analog-to-digital converter circuitry, power amplifier circuitry, low noise amplifier circuitry, mixer circuitry (e.g., up-converter and down-converter circuitry), or other circuitry for generating radio-frequency signals in WLAN or WPAN communications bands and for receiving radio-frequency signals in WLAN or WPAN communications bands. GPS receiver circuitry  38  may include analog-to-digital converter circuitry, low noise amplifier circuitry, mixer circuitry (e.g., down-converter circuitry) or other circuitry for receiving radio-frequency signals in a satellite navigation communications band. 
     WLAN transceiver circuitry  36  and GPS receiver circuitry  38  may be coupled to front antenna  40 F over a corresponding radio-frequency transmission line  54 F. Filter (F) circuitry such as filter circuitry  214  may be coupled between WLAN transceiver circuitry  36 , GPS receiver circuitry  38 , and front antenna  40 F. Filter circuitry  214  may serve to isolate radio-frequency signals handled by WLAN transceiver circuitry  36  from GPS signals handled by GPS receiver circuitry  38 . In addition, filter circuitry  214  may block radio-frequency signals in cellular telephone communications bands from passing from front antenna  40 F to WLAN transceiver circuitry  36  and GPS receiver circuitry  38 . Filter circuitry  214  may include passive filtering circuitry such as duplexer circuitry, diplexer circuitry, low pass filter circuitry, high pass filter circuitry, bandpass filter circuitry, notch filter circuitry, impedance matching circuitry, etc. If desired, filter circuitry  214  may include active circuitry such as one or more switches. Front antenna  40 F may transmit radio-frequency signals generated by WLAN transceiver circuitry  36  in WLAN/WPAN communications bands and may receive radio-frequency signals in WLAN/WPAN communications bands for WLAN transceiver circuitry  36 . Similarly, front antenna  40 F may receive radio-frequency signals in satellite navigation communications bands for GPS receiver circuitry  38 . 
     Applications processor  202  may provide digital data to WLAN transceiver circuitry  36  over data path  204  that is used by WLAN transceiver circuitry  36  for generating radio-frequency signals in WLAN/WPAN communications bands. Applications processor  202  may receive incoming digital data from WLAN transceiver circuitry  36  over data path  204  corresponding to radio-frequency data that was received by front antenna  40 F in WLAN/WPAN communications bands. Similarly, applications processor  202  may receive incoming digital data from GPS receiver circuitry  38  over data path  208  corresponding to radio-frequency data that was received by front antenna  40 F in a satellite navigation communications band. 
     Applications processor  202  may control baseband processor circuitry  200  to generate baseband data for transmission in cellular telephone communications bands. Baseband processor circuitry  200  may pass the baseband data to cellular transceiver circuitry  32  over data path  212 . Cellular transceiver circuitry  32  may include digital-to-analog converter circuitry, analog-to-digital converter circuitry, power amplifier circuitry, low noise amplifier circuitry, mixer circuitry (e.g., up-converter and down-converter circuitry), or other circuitry for generating radio-frequency signals in cellular telephone communications bands and for receiving radio-frequency signals in cellular telephone communications bands. Cellular transceiver circuitry  32  may generate radio-frequency signals in cellular telephone communications bands corresponding to the baseband data received from baseband processor circuitry  200 . 
     Similarly, cellular transceiver circuitry  32  may receive radio-frequency signals in cellular telephone communications bands (e.g., from one of antennas  40 F and  40 B at a given time) and may down-convert the radio-frequency signals to generate corresponding baseband data. Cellular transceiver circuitry  32  may pass the baseband data to baseband processor circuitry  200 . Incoming data that has been received by baseband processor  200  may be passed to applications processor  202  over path  206  if desired. 
     Cellular transceiver circuitry  32  may be coupled to antennas  40 F and  40 B using switching circuitry such as switch SW. The configuration of switch SW may be controlled by control signal CTRL′ on switch control path  242 . Control circuitry in device  10  such as baseband processor circuitry  200  may control the state of control signal CTRL′ to optimize antenna performance in real time. For example, baseband processor circuitry  200  may be coupled to switch controller  216  over control path  210 . Baseband processor circuitry  200  may provide a switch control signal CTRL to switch controller  216  over control path  210  that identifies the desired state for switch SW. Switch controller  216  may convert control signal CTRL into control signal CTRL′ provided to switch SW over path  242 . As an example, switch controller  216  may assert control signal CTRL′ at a predetermined voltage level based on control signal CTRL to set switch SW to a desired state. 
     Switch SW may have a first terminal  222  coupled to cellular transceiver circuitry  32 , a second terminal  226  coupled to front antenna  40 F over transmission line  54 F, and a third terminal  224  coupled to rear antenna  40 B over transmission line  54 B. Transmission line  54 F may, for example, be coupled to antenna feed  60 F of front antenna  40 F ( FIG. 5 ). Transmission line  54 B may, for example, be coupled to antenna feed  60 B of rear antenna  40 B ( FIG. 6 ). 
     Switch SW may have a first state at which terminal  226  is coupled to terminal  222  and terminal  224  is decoupled from terminal  222 . In the first state, switch SW may couple cellular transceiver circuitry  32  to front antenna  40 F and may decouple cellular transceiver circuitry  32  from rear antenna  40 B. Switch SW may have a second state at which terminal  224  is coupled to terminal  222  and terminal  226  is decoupled from terminal  222 . In the second state, switch SW may couple cellular transceiver circuitry  32  to rear antenna  40 B and may decouple cellular transceiver circuitry  32  from front antenna  40 F. Control signal CTRL′ may control switch SW to place switch SW in a selected one of the first and second states. In this scenario, switch SW is implemented as a single-pole double-throw (SPDT) switch. This is merely illustrative. If desired, switch SW may have a third state at which terminal  222  is decoupled from both terminals  226  and  224 . Switch SW may, in general, be implemented using any desired switching circuits (e.g., networks of switches, a switch matrix, etc.). 
     If desired, filter circuitry such as filter circuitry  247  may be coupled between switch SW and cellular transceiver circuitry  32 . Filter circuitry  247  may include passive filtering circuitry such as duplexer circuitry, diplexer circuitry, low pass filter circuitry, high pass filter circuitry, bandpass filter circuitry, notch filter circuitry, impedance matching circuitry, etc. Filter circuitry  247  may serve to isolate transmit ports of cellular transceiver circuitry  32  from receive ports of cellular transceiver circuitry  32 , for example. Receive ports of cellular transceiver circuitry  32  may be coupled to low noise amplifiers such as low noise amplifier  245 . Transmit ports of cellular transceiver circuitry  32  may be coupled to power amplifiers such as power amplifier  244 . This example is merely illustrative and, in general, cellular transceiver circuitry  32  may include any desired number of transmit and receive ports and any desired filtering circuitry arranged in any desired manner. Low noise amplifier  245  and/or power amplifier  244  may be formed as a part of cellular transceiver circuitry  32  if desired. 
     If desired, additional radio-frequency front end circuitry may be coupled to transmission lines  54 F and  54 B (not shown in  FIG. 7  for the sake of clarity). This radio-frequency front end circuitry may include impedance matching circuitry, switching circuitry, filter circuitry, or any other desired radio-frequency front end components (e.g., networks of passive and/or active (adjustable) components such as resistors, inductors, and capacitors). As an example, additional filter circuitry may be coupled to transmission line  54 F to isolate cellular transceiver circuitry  32  from radio-frequency signals in WLAN, WPAN, and satellite navigation communications bands. 
     Baseband processor circuitry  200  may control switch SW (e.g., through switch controller  216 ) to couple an optimal one of front antenna  40 F and rear antenna  40 B to cellular transceiver circuitry  32  at a given time. For example, in scenarios where rear antenna  40 B is capable of satisfactory wireless performance in cellular telephone communications bands (e.g., in the cellular telephone midband), baseband processor circuitry  200  may control switch SW to couple cellular transceiver circuitry  32  to rear antenna  40 B and rear antenna  40 B may transmit and receive radio-frequency signals in the cellular telephone communications bands through rear housing wall  12 R ( FIG. 4 ). 
     However, if rear antenna  40 B exhibits unsatisfactory wireless performance in the cellular telephone communications band (e.g., in the cellular telephone midband), baseband processor circuitry  200  may toggle switch SW to couple cellular transceiver circuitry  32  to front antenna  40 F and front antenna  40 F may transmit and receive radio-frequency signals in the cellular telephone communications band through display cover layer  82  ( FIG. 4 ). 
     As shown in  FIG. 7 , a first radio-frequency coupler  218  may be coupled to transmission line  54 F and a second radio-frequency coupler  220  may be coupled to transmission line  54 B. Coupler  218  may be coupled to baseband processor circuitry  200  over feedback path  228 . Coupler  220  may be coupled to baseband processor circuitry  200  over feedback path  230 . This is merely illustrative and, in another suitable arrangement, feedback paths  228  and  230  may be provided to a feedback receiver interposed between the couplers and baseband processor circuitry  200 . 
     Coupler  218  may be used to tap radio-frequency signals in cellular telephone communications bands flowing to and from front antenna  40 F. Tapped radio-frequency signals from coupler  218  may be processed using baseband processor circuitry  200  and/or a feedback receiver to generate wireless performance metric data associated with the wireless performance of front antenna  40 F in the cellular telephone communications bands. Coupler  220  may be used to tap radio-frequency signals in cellular telephone communications bands flowing to and from rear antenna  40 B. Tapped antenna signals from coupler  220  may be processed using baseband processor circuitry  200  and/or a feedback receiver to generate wireless performance metric data associated with the wireless performance of rear antenna  40 B in the cellular telephone communications bands. The tapped radio-frequency signals may include a tapped version of the signals being transmitted by power amplifier  244  (sometimes referred to as forward signals) and a tapped version of the transmitted signals that have been reflected from antennas  40 F or  40 B (sometimes referred to as reverse signals). If desired, control circuitry such as baseband processor circuitry  200  may control switching circuitry in couplers  218  and  220  to provide a selected one of the forward and reverse signals to baseband processor circuitry  200  at a given time. 
     The wireless performance metric data generated using the tapped signals may include phase and magnitude measurements of the impedance of antennas  40 F and  40 B. For example, by processing the forward and reverse signals for front antenna  40 F, baseband processor circuitry  200  may gather information on the phase and magnitude of the impedance of front antenna  40 F in real time. The phase and magnitude measurements may include complex impedance data such as scattering parameter (so-called “S-parameter”) values that are indicative of the complex impedance of front antenna  40 F. Measurements of the S-parameters may include, for example, measured reflection coefficient parameter values (so-called S11 values) that are indicative of the amount of radio-frequency signals that is reflected back towards coupler  218  from front antenna  40 F during signal transmission. Similarly, baseband processor circuitry  200  may gather phase and magnitude measurements such as S-parameters for rear antenna  40 B. 
     The phase and magnitude of the impedance of antennas  40 F and  40 B may be used to determine whether the operation of antennas  40 F or  40 B have been affected by the operating environment of device  10  (e.g., whether the presence of an external object has detuned or changed the loading of antennas  40 F or  40 B). For example, baseband processor circuitry  200  may detect variations in the gathered phase and magnitude information (e.g., excessively high magnitude S11 measurements, etc.) to identify when rear antenna  40 B has been detuned/loaded by the presence of an external object. If baseband processor circuitry  200  detects that rear antenna  40 B has been detuned due to the loading of rear antenna  40 B (e.g., due to the user adjusting strap  15  of  FIG. 4 , changing strap  15 , adjusting an orientation of device  10  relative to wrist  114 , strap  15  becoming wet, a different user wearing device  10 , etc.), baseband processor circuitry  200  may issue control signal CTRL over control path  210  to adjust switch SW to switch front antenna  40 F into use for handling cellular telephone communications (e.g., in the cellular telephone midband) instead of the detuned rear antenna  40 B. After front antenna  40 F has been switched into use, wireless circuitry  34  may continue to perform cellular telephone communications (using front antenna  40 F) even though rear antenna  40 B has become detuned. 
     If desired, other performance metric data such as receive signal strength data may be used to determine which of antennas  40 F and  40 B to couple to cellular transceiver circuitry  32  at a given time. If desired, baseband processor circuitry  200 , cellular transceiver circuitry  32 , and/or separate receive signal strength measurement circuitry may receive signals from antennas  40 F and  40 B (e.g., via low noise amplifier circuitry  245 ). These components may gather information indicative of the receive signal strength of radio-frequency signals received in cellular telephone communications bands using antennas  40 F and  40 B. For example, these components may gather Received Signal Strength Indicator (RSSI) values from the receive signals. In one suitable arrangement, diode detector circuitry may be used to convert the received radio-frequency signals to a known voltage level for extracting the RSSI values. The RSSI values may be transmitted to baseband processor circuitry  200  or applications processor  202 . The gathered RSSI values may be accumulated and stored for each antenna (e.g., in a data structure such as a database file). 
     Baseband processor circuitry  200  may process the gathered performance metric information (e.g., the gathered RSSI values) to determine whether the current antenna needs to be switched out of use for cellular telephone communications. For example, when the gathered RSSI values gathered by a given antenna drops below a predetermined threshold value, baseband processor circuitry  200  may control switch SW to switch the other antenna into use for performing cellular telephone communications. In general, any desired wireless performance metric values may be used in determining which antenna to use for cellular telephone communications (e.g., receiver sensitivity values, signal-to-noise ratio values, noise floor values, error rate values, RSSI values, etc.). 
     If desired, switch controller  216 , switch SW, coupler  218 , coupler  220 , filter circuitry  247 , power amplifier  244 , and/or low noise amplifier  245  may be formed on a common substrate  240  such as a shared integrated circuit, integrated circuit package, chip, flexible printed circuit, rigid printed circuit board, etc. The example of  FIG. 7  is merely illustrative and, in general, any desired circuitry may be used to control front antenna  40 F to perform wireless communications in WLAN, WPAN, GPS, and cellular telephone communications bands while also controlling rear antenna  40 B to perform wireless communications in cellular telephone communications bands with front antenna  40 F using an antenna diversity scheme. 
       FIG. 8  is a flow chart of illustrative steps that may be performed by wireless circuitry  34  and control circuitry  20  for operating front antenna  40 F and rear antenna  40 B in cellular telephone communications bands using an antenna diversity scheme. The steps of  FIG. 8  may, for example, be performed while front antenna  40 F concurrently transmits and/or receives radio-frequency signals in WLAN, WPAN, and/or satellite navigation communications bands using circuitry  36  and  38  of  FIG. 7 . 
     At step  300 , wireless circuitry  34  may begin performing cellular telephone communications. Cellular transceiver circuitry  32  of  FIG. 7  may transmit and/or receive radio-frequency signals in a cellular telephone communications band (e.g., the cellular midband) using antennas  40 F and/or  40 B. For example, baseband processor circuitry  200  may toggle switch SW to alternate between using antennas  40 F and  40 B to convey radio-frequency signals in the cellular telephone communications band or may convey radio-frequency signals in the cellular telephone communications band using only one of antennas  40 F and  40 B. 
     At step  302 , wireless circuitry  34  may gather wireless performance metric data associated with wireless performance of antennas  40 F and/or  40 B in the cellular telephone communications band. For example, wireless circuitry  34  may gather wireless performance metric data using both antennas  40 F and  40 B. In this scenario, baseband processor circuitry  200  may control switch SW to toggle between antennas  40 F and  40 B and baseband processor circuitry  200  may gather radio-frequency performance metric data for each antenna while that antenna is coupled to cellular transceiver circuitry  32 . In another suitable scenario, baseband processor circuitry  200  may gather radio-frequency performance metric data using only one of antennas  40 F and  40 B. The wireless performance metric data may include RSSI values, impedance data such as phase and magnitude values (e.g., gathered using couplers  218  and  220 ), and/or any other desired radio-frequency performance metric data. 
     At step  304 , baseband processor circuitry  200  and/or applications processor  202  may process the gathered wireless performance metric data to generate processed data. Baseband processor circuitry  200  may generate the processed data by, for example, generating averages of multiple individual wireless performance metric data values gathered by antennas  40 F and/or  40 B over time, generating linear combinations of multiple individual wireless performance metric data values gathered by antennas  40 F and/or  40 B over time, and/or by filtering the gathered wireless performance metric data. 
     Filtering the wireless performance metric data may, for example, allow baseband circuitry  200  to distinguish an actual deterioration in wireless antenna performance from noise or false positives. As an example, baseband processor circuitry  200  may compare the gathered wireless performance metric data to user statistics associated with the orientation/position of device  10 , the geographic location of device  10 , predetermined patterns of wireless performance metric data associated with known events, etc. 
     At step  306 , baseband processor circuitry  200  may select an optimal one of antennas  40 F and  40 B to use for cellular telephone communications based on the processed data generated at step  304 . For example, baseband processor circuitry  200  may determine which of antennas  40 F and  40 B exhibits superior wireless performance (e.g., greater RSSI values) in the cellular telephone communications band and may select that antenna to use for subsequent cellular telephone communications. In scenarios where wireless performance metric data was only gathered for a single antenna such as rear antenna  40 B during step  302 , baseband processor circuitry  200  may compare the processed data to a range of acceptable values (e.g., a range of acceptable wireless performance metric values such as a range of acceptable RSSI values defined by a minimum acceptable RSSI threshold value) to determine whether front antenna  40 F should be switched into use. In this scenario, if the processed data gathered for rear antenna  40 B falls outside of the range of acceptable values (e.g., if the processed data is less than the minimum acceptable RSSI threshold value), baseband processor circuitry  200  may select front antenna  40 F for use in performing subsequent cellular telephone communications. 
     At step  308 , baseband processor circuitry  200  may control switch SW to couple the selected antenna (e.g., as determined while processing step  306 ) to cellular transceiver circuitry  32  use for subsequent cellular telephone communications. The selected antenna may continue to convey radio-frequency signals in the cellular telephone communications band (e.g., the cellular telephone midband). Processing may loop back to step  302  as shown by path  310  to continue to monitor the wireless performance of antennas  40 F and/or  40 B. In this way, an optimal one of antennas  40 F and  40 B may be switched into use for performing cellular telephone communications at a given time regardless of any changing environmental conditions around device  10 . If desired, tunable components  50  of  FIG. 3  may also be adjusted to adjust the frequency response, polarization, or radiation pattern shape for the selected antennas to further optimize wireless performance. 
     The example of  FIG. 8  is merely illustrative. If desired, baseband processor circuitry  200  may continuously or periodically gather wireless performance metric data or may gather wireless performance metric data in response to a software trigger for one or both of antennas  40 F and  40 B in the cellular telephone communications band. Wireless performance metric data may be gathered in response to transmitted or received communications data or in response to transmitted or received test signals (e.g., signals that do not include communications data). 
       FIG. 9  is a graph in which the collective antenna performance (antenna efficiency) of antennas  40 F and  40 B of  FIGS. 4-7  has been plotted as a function of operating frequency. As shown in  FIG. 9 , front antenna  40 F may contribute coverage for wireless circuitry  34  in multiple communications bands such as the GPS band centered at 1575 MHz, a 2.4 GHz WLAN band WL (e.g., extending between about 2400 MHz and 2500 MHz), a 5.0 GHz WLAN band WH (e.g., extending between about 5150 MHz and 5850 MHz), and cellular midband MB (e.g., a band extending between approximately 1700 MHz and 2200 MHz). Rear antenna  40 B may also contribute coverage in cellular telephone midband MB. 
     When the wireless performance of the antenna coupled to cellular transceiver circuitry  32  is deteriorated (e.g., due to loading by environmental factors), wireless circuitry  34  may exhibit a reduced efficiency in cellular telephone midband MB as shown by curve  326 . Baseband processor circuitry  200  may identify this deterioration (e.g., using wireless performance metric data gathered at step  304  and processed at step  306  of  FIG. 8 ) and may subsequently toggle switch SW to switch the other antenna into use for performing wireless communications in cellular midband MB. After switching the other antenna into use, wireless circuitry  34  may exhibit a satisfactory efficiency in cellular midband MB as shown by curve  324 . By switching an optimal one of antennas  40 F and  40 B into use at a given time, wireless circuitry  34  may continue to exhibit satisfactory efficiency in cellular telephone midband MB regardless of external environmental factors, while also covering the GPS band and WLAN bands WL and WH. 
     The example of  FIG. 9  is merely illustrative. While the response of front antenna  40 F in bands GPS, MB, WL, and WH are shown as individual peaks, the bandwidth of front antenna  40 F may in practice be sufficiently wide to extend from at least the lower limit of band GPS to at least the upper limit of band WH, for example. If desired, front antenna  40 F may also cover the cellular telephone low band extending down to approximately 600 MHz and/or the cellular telephone high band extending between bands WL and WH. In general, antennas  40 F and  40 B may cover one or more of any desired communications bands and may perform antenna diversity operations in one or more of any desired communications bands. The antenna structures used to form antennas  40 F and  40 B of  FIGS. 4-7  are merely illustrative and, in general, any desired antenna structures may be used. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20180223
Publication Date: 20190716
Grant Date: 20190716
Priority Date: 20180223
Inventors: Ruaro, Andrea
DI NALLO, CARLO
PAPANTONIS, DIMITRIOS
DA COSTA BRAS LIMA, EDUARDO JORGE
NATH, JAYESH
NIU, Jiaxiao
Martinis, Mario
PASCOLINI, MATTIA
WANG, ZHEYU
Assignee: APPLE INC
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Family ID: 67220320