PATENT DOCUMENT

Publication Number: US-10484112-B2
Application Number: US-201715442463-A
Country: US
Kind Code: B2

Title: Dynamically adjustable antennas for wearable devices

Abstract:
An electronic device such as a wristwatch may include a housing with a dielectric rear wall. Wireless circuitry in the device may include an antenna formed on or over the rear wall. Matching circuitry may match the impedance of the antenna to the rest of the wireless circuitry. Processing circuitry may gather receive signal strength information and/or phase and magnitude information from radio-frequency signals received through the rear wall. The processing circuitry may track the position of the device and accumulate user statistics over time. The processing circuitry may determine whether changes in loading of the antenna through the dielectric rear housing wall have occurred based on the receive signal strength information, user statistics, and/or phase and magnitude information. If a change is detected, the processing circuitry may adjust the matching circuitry to mitigate any potential antenna detuning as a result of the change.

Claims:
What is claimed is: 
     
       1. A method of operating a wearable electronic device having a display formed at a front face of the electronic device, a dielectric rear housing wall formed at a rear face of the electronic device, an antenna, and processing circuitry, the method comprising:
 with the antenna, transmitting and receiving radio-frequency signals through the dielectric rear housing wall; 
 with the processing circuitry, gathering received signal strength indicator (RSSI) values associated with an amount of loading of the antenna by an external object through the dielectric rear housing wall; and 
 with the processing circuitry, adjusting the antenna to compensate for a change in the amount of loading of the antenna by the external object through the dielectric rear housing wall, wherein adjusting the antenna comprises:
 generating filtered RSSI values by filtering the gathered RSSI values, 
 detecting a trigger event based on the filtered RSSI values, and 
 adjusting the antenna based on the detected trigger event. 
 
 
     
     
       2. The method defined in  claim 1 , wherein the wearable electronic device comprises radio-frequency transceiver circuitry and impedance matching circuitry coupled between the radio-frequency transceiver circuitry and the antenna and adjusting the antenna to compensate for the change in the amount of loading of the antenna by the external object through the dielectric rear housing wall comprises adjusting an impedance of the impedance matching circuitry. 
     
     
       3. The method defined in  claim 1 , wherein the antenna comprises a tunable component and adjusting the antenna to compensate for a change in the amount of loading of the antenna by the external object through the dielectric rear housing wall comprises adjusting the tunable component. 
     
     
       4. The method defined in  claim 1 , wherein detecting the trigger event comprises comparing the filtered RSSI values to a plurality of predetermined sets of RSSI values stored at the wearable electronic device. 
     
     
       5. A method of operating a wearable electronic device having a display formed at a front face of the electronic device, a dielectric rear housing wall formed at a rear face of the electronic device, an antenna, and processing circuitry, the method comprising:
 with the antenna, receiving radio-frequency signals from external equipment through the dielectric rear housing wall; 
 with the processing circuitry, gathering information on an amount of loading of the antenna by an external object through the dielectric rear housing wall, wherein the information comprises Received Signal Strength Indicator (RSSI) values associated with the radio-frequency signals received from the external equipment through the dielectric rear housing wall; and 
 with the processing circuitry, adjusting the antenna to compensate for a change in the amount of loading of the antenna by the external object through the dielectric rear housing wall based on the gathered RSSI values, wherein gathering the information on the amount of loading of the antenna comprises storing acquisition times associated with each of the gathered RSSI values and storing wearable electronic device acquisition positions associated with each of the gathered RSSI values. 
 
     
     
       6. The method defined in  claim 5 , wherein adjusting the antenna to compensate for the change in the amount of loading of the antenna by the external object through the dielectric rear housing wall comprises adjusting the antenna based on the gathered RSSI values, the stored acquisition times, and the stored wearable electronic device acquisition positions. 
     
     
       7. A method of operating a wearable electronic device having a display formed at a front face of the electronic device, a dielectric rear housing wall formed at a rear face of the electronic device, an antenna, and processing circuitry, the method comprising:
 with the antenna, receiving radio-frequency signals from external equipment through the dielectric rear housing wall; 
 with the processing circuitry, gathering information on an amount of loading of the antenna by an external object through the dielectric rear housing wall; and 
 with the processing circuitry, adjusting the antenna to compensate for a change in the amount of loading of the antenna by the external object through the dielectric rear housing wall, wherein gathering the information on the amount of loading comprises gathering phase and magnitude measurements of an impedance of the antenna based on radio-frequency signals that are transmitted to the antenna by radio-frequency transmitter circuitry on the wearable electronic device, and adjusting the antenna to compensate for the change in the amount of loading of the antenna by the external object through the dielectric rear housing wall comprises adjusting the antenna based on the gathered phase and magnitude measurements of the impedance of the antenna. 
 
     
     
       8. A wearable electronic device having opposing front and rear faces, the wearable electronic device comprising:
 a dielectric rear housing wall that forms the rear face of the electronic device; 
 a display having a display cover layer that forms the front face of the electronic device; 
 an antenna resonating element formed from conductive traces overlapping the dielectric rear housing wall, wherein the antenna resonating element is subject to loading by external objects through the dielectric rear housing wall; 
 radio-frequency transceiver circuitry that is configured to transmit and receive radio-frequency signals through the dielectric rear housing wall using the antenna resonating element; 
 impedance matching circuitry coupled between the antenna resonating element and the radio-frequency transceiver circuitry; and 
 storage and processing circuitry that is configured to adjust the impedance matching circuitry in response to detecting a change in the loading of the antenna resonating element through the dielectric rear housing wall. 
 
     
     
       9. The wearable electronic device defined in  claim 8 , further comprising:
 a receive path coupled between the radio-frequency transceiver circuitry and the impedance matching circuitry; and 
 receive signal strength measurement circuitry coupled to the receive path, wherein the receive signal strength measurement circuitry is configured to generate receive signal strength information based on radio-frequency signals on the receive path, and the storage and processing circuitry is configured to detect the change in the loading of the antenna resonating element based on the generated receive signal strength information. 
 
     
     
       10. The wearable electronic device defined in  claim 9 , wherein the generated receive signal strength information comprises Received Signal Strength Indicator (RSSI) values, acquisition times associated with each of the RSSI values, and wearable electronic device acquisition positions associated with each of the RSSI values. 
     
     
       11. The wearable electronic device defined in  claim 10 , wherein the storage and processing circuitry is configured to detect the change in the loading of the antenna resonating element by determining whether the RSSI values match a predetermined pattern of RSSI values. 
     
     
       12. The wearable electronic device defined in  claim 11 , wherein the radio-frequency transceiver circuitry comprises:
 a cellular telephone transceiver that is configured to transmit and receive signals at frequencies between 700 MHz and 960 MHz through the dielectric rear housing wall using the antenna resonating element. 
 
     
     
       13. The wearable electronic device defined in  claim 11 , further comprising:
 metal housing sidewalls that extend from the dielectric rear housing wall to the display cover layer; 
 a first antenna feed terminal coupled to conductive traces, wherein the conductive traces are patterned onto the dielectric rear housing wall; 
 a second antenna feed terminal coupled to the metal housing sidewalls; and 
 a radio-frequency transmission line that couples the radio-frequency transceiver circuitry to the first and second antenna feed terminals. 
 
     
     
       14. The wearable electronic device defined in  claim 11 , wherein the antenna resonating element is configured to form a waveguide with a wrist of a user while the user wears the wearable electronic device. 
     
     
       15. The wearable electronic device defined in  claim 8 , further comprising:
 power amplifier circuitry coupled to the radio-frequency transceiver circuitry; 
 a radio-frequency coupler coupled between the power amplifier circuitry and the impedance matching circuitry; and 
 a feedback path coupled between the radio-frequency coupler and the radio-frequency transceiver circuitry, wherein the storage and processing circuitry is configured to gather phase and magnitude measurements of an impedance of the antenna resonating element based on feedback signals received by the radio-frequency transceiver circuitry from the radio-frequency coupler over the feedback path, and the storage and processing circuitry is further configured to detect the change in the loading of the antenna resonating element based on the gathered phase and magnitude measurements. 
 
     
     
       16. A method of operating a wearable electronic device having a display formed at a front face of the electronic device, a dielectric rear housing wall formed at a rear face of the electronic device, an antenna, impedance matching circuitry coupled to the antenna, and processing circuitry, the method comprising:
 with the antenna, receiving radio-frequency signals from external equipment through the dielectric rear housing wall; 
 with the processing circuitry, gathering and storing Received Signal Strength Indicator (RSSI) values and corresponding RSSI acquisition times based on the received radio-frequency signals; 
 with the processing circuitry, accumulating user statistics associated with operation of the wearable electronic device by a user over time; 
 with the processing circuitry, processing the accumulated user statistics, the stored RSSI values, and the stored RSSI acquisition times to detect a trigger event; and 
 with the processing circuitry, in response to detecting the trigger event, adjusting the impedance matching circuitry. 
 
     
     
       17. The method defined in  claim 16 , wherein the accumulated user statistics comprise a user RSSI pattern and processing the accumulated user statistics, the stored RSSI values, and the stored RSSI acquisition times comprises:
 filtering out the user RSSI pattern from the stored RSSI values to generate filtered RSSI values; and 
 detecting the trigger event based on the filtered RSSI values. 
 
     
     
       18. The method defined in  claim 17 , wherein the user statistics comprise an event RSSI pattern associated with a change in loading of the antenna through the dielectric rear housing wall and detecting the trigger event comprises:
 detecting a sequence of RSSI values in the filtered RSSI values that matches the event RSSI pattern. 
 
     
     
       19. The method defined in  claim 18 , wherein adjusting the impedance matching circuitry comprises:
 controlling the impedance matching circuitry to exhibit an adjusted impedance; 
 gathering an additional RSSI value from the received radio-frequency signals while the impedance matching circuitry exhibits the adjusted impedance; 
 determining whether radio-frequency performance of the antenna has improved based on the gathered additional RSSI value; 
 in response to determining that the radio-frequency performance of the antenna has not improved, controlling the impedance matching circuitry to exhibit an additional adjusted impedance; and 
 in response to determining that the radio-frequency performance of the antenna has improved, storing a matching setting associated with the adjusted impedance on storage circuitry. 
 
     
     
       20. The method defined in  claim 18 , wherein adjusting the impedance matching circuitry comprises:
 retrieving a matching setting associated with the event RSSI pattern from storage circuitry on the wearable electronic device, wherein the matching setting identifies an adjusted impedance; 
 controlling the impedance matching circuitry to exhibit the adjusted impedance; 
 gathering an additional RSSI value from the received radio-frequency signals while the impedance matching circuitry exhibits the adjusted impedance; 
 determining whether the additional RSSI value exceeds a minimum RSSI threshold value; and 
 in response to determining that the additional RSSI value does not exceed the minimum RSSI threshold value, controlling the impedance matching circuitry to exhibit an additional adjusted impedance.

Description:
BACKGROUND 
     This relates to electronic devices, and more particularly, to electronic devices with wireless communications circuitry. 
     Electronic devices often include wireless communications circuitry. For example, cellular telephones, computers, and other devices often contain antennas and wireless transceivers for supporting wireless communications. 
     It can be challenging to form electronic device antenna structures with desired attributes. In some wireless devices, antennas are bulky. In other devices, antennas are compact, but are sensitive to the position of the antennas relative to external objects. If care is not taken, antennas may become detuned, may emit wireless signals with a power that is more or less than desired, or may otherwise not perform as expected. 
     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 have a housing with metal portions such as metal sidewalls. A display may be mounted on a front face of the device. A rear face of the electronic device may be formed using a dielectric rear housing wall. 
     The electronic device may include wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and an antenna. The antenna may include an antenna ground. The antenna ground may be formed using the metal housing sidewalls and/or a conductive layer on a printed circuit board within the electronic device. The antenna may include an antenna resonating element formed from conductive traces that are patterned onto or over an interior surface of the dielectric rear housing wall. The radio-frequency transceiver circuitry may transmit and receive radio-frequency signals through the dielectric rear housing wall using the antenna. Impedance matching circuitry may be used to match the impedance of the antenna to the rest of the wireless communications circuitry. 
     The antenna may be subject to over-the-air loading variations through the dielectric rear housing wall. For example, the particular manner in which the user wears the electronic device, the user&#39;s physiology, the amount of moisture adjacent to the dielectric rear housing wall, and other environmental factors may affect how the antenna is loaded through the dielectric rear housing wall. Additional loading variations may be caused due to the user&#39;s hand/wrist touching the metal enclosure that forms part of antenna structure. Furthermore, the material of the wristband may also contribute to the loading variations. Processing circuitry may gather receive signal strength information and/or phase and magnitude information from the received radio-frequency signals. The processing circuitry may track the position of the electronic device over time. The processing circuitry may accumulate user statistics associated with how the user operates the electronic device over time. 
     The receive signal strength information gathered by the processing circuitry may include Received Signal Strength Indicator (RSSI) values as a function of time and position of the electronic device, for example. The processing circuitry may determine whether a change in loading of the antenna through the dielectric rear housing wall has occurred based on the gathered receive signal strength information, the accumulated user statistics, and/or the gathered phase and magnitude information. If the processing circuitry determines that a change in the loading of the antenna has occurred, the processing circuitry may adjust the impedance matching circuitry to compensate for the change in loading of the antenna through the dielectric rear housing wall. In this way, the processing circuitry may ensure that the antenna is impedance matched to the rest of the wireless communications circuitry in real time regardless of any variable antenna loading conditions that may occur as a result the antenna being located on the dielectric rear housing wall of the electronic device. Ensuring satisfactory impedance matching for the antenna over time may mitigate any potential antenna detuning or degradation of antenna efficiency as a result of the variable antenna loading conditions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative electronic device 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 an antenna that conveys wireless signals through a rear side of the electronic device in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative electronic device showing how an antenna at the rear of the device and a user&#39;s wrist may guide electromagnetic energy away from the device in accordance with an embodiment. 
         FIG. 6  is a diagram of illustrative circuitry that may be used in gathering antenna performance information and adjusting an impedance matching circuit for an antenna in accordance with an embodiment. 
         FIG. 7  is a flow chart of illustrative steps involved in operating an electronic device having adjustable wireless circuitry to compensate for different antenna loading conditions in accordance with an embodiment. 
         FIG. 8  is a flow chart of illustrative steps that may be performed by an electronic device in determining whether to adjust an impedance matching circuit to compensate for different antenna loading conditions in accordance with an embodiment. 
         FIGS. 9 and 10  are flow charts of illustrative steps that may be performed by an electronic device in adjusting an impedance matching circuit to compensate for different antenna loading conditions in accordance with an embodiment. 
         FIG. 11  is an illustrative plot of receive signal strength information gathered by an electronic device that may be processed to determine whether to adjust an impedance matching circuit in accordance with an embodiment. 
         FIG. 12  is a diagram showing how receive signal strength information gathered by an illustrative electronic device may be filtered and compared to predetermined receive signal strength patterns to determine whether to adjust an impedance matching circuit in accordance with an embodiment. 
         FIG. 13  is a Smith chart showing illustrative impedances associated with operation of an antenna in an electronic device when operated under different antenna loading conditions in accordance with an embodiment. 
         FIG. 14  is a graph of illustrative antenna frequency responses that may be exhibited by an antenna when operating under different impedance matching circuit settings in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device such as electronic device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. 
     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 wearable device such as a wristwatch. 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, gold, silver, 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. 
     Display  14  may be formed at the front side (face) of device  10 . Housing  12  may have a rear housing wall such as rear wall  12 R that opposes front face of device  10 . Rear housing wall  12 R may form the rear side (face) of device  10 . Housing sidewalls  12 W may surround the periphery of device  10  (e.g., housing sidewalls  12 W may extend around peripheral edges of device  10 ). Rear housing wall  12 R may be formed from dielectric. 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 . Housing sidewall  12 W may extend across some or all of the height of device  10  (e.g., parallel to z-axis). 
     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 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., in side wall  12 W or rear 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, combinations of these, 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  16 . Strap  16  may be used to hold device  10  against a user&#39;s wrist (as an example). In the example of  FIG. 1 , strap  16  is connected to opposing sides  8  of device  10 . Housing walls  12 W on sides  8  of device  10  may include attachment structures for securing strap  16  to housing  12  (e.g., lugs or other attachment mechanisms). Strap  16  may be formed from any desired materials (e.g., metal materials, dielectric materials, or combinations of metal and dielectric materials). For example, metal materials in strap  16  may include stainless steel, aluminum, silver, gold, metal alloys, or any other desired conductive material. Dielectric materials in strap  16  may include plastic, polymer, ceramics, leather, rubber, cloth or other textiles, glass, or any other desired dielectric materials. 
     If desired, strap  16  may be removable. For example, a user may replace strap  16  with a different strap having similar or different materials. If desired, strap  16  may be adjustable. For example, strap  16  may include a clasp, buckle, or other adjustable structures that allow a user to adjust the length of strap  16  and/or to adjust how tight strap  16  is on the user&#39;s wrist while the user is wearing device  10 . 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 control circuitry such as storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, MIMO protocols, antenna diversity protocols, etc. 
     Input-output circuitry  44  may include input-output devices  32 . Input-output devices  32  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  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices  32  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, digital data port devices, light sensors, 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. 
     As shown in  FIG. 2 , electronic device  10  may communicate wirelessly with external equipment  52  over wireless links such as wireless link  54 . External equipment  52  may include cellular telephone network base stations, wireless local area network equipment (e.g., wireless routers and/or wireless access points), peer devices, other portable electronic devices such as a cellular telephone or wireless headset, and other external equipment. Link  54  may be a cellular telephone link, a wireless local area network link, or a communications link supported using other types of wireless communications. 
     Input-output circuitry  44  may include wireless circuitry  34 . Wireless circuitry  34  may include coil  50  and wireless power receiver  48  for receiving wirelessly transmitted power from a wireless power adapter. 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  56  for handling various radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  36 ,  38 ,  42 , and  46 . Transceiver circuitry  36  may be wireless local area network transceiver circuitry that may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and that may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in frequency ranges such as a low communications band from 700 to 960 MHz, a midband from 1400 MHz or 1500 MHz to 2170 MHz (e.g., a midband with a peak at 1700 MHz), and a high band from 2170 or 2300 to 2700 MHz (e.g., a high band with a peak at 2400 MHz) or other communications bands between 700 MHz and 2700 MHz or other suitable frequencies (as examples). Circuitry  38  may handle voice data and non-voice data. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include 60 GHz transceiver circuitry, circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) transceiver circuitry  46  (e.g., an NFC transceiver operating at 13.56 MHz or other suitable frequency), etc. Wireless circuitry  34  may include satellite navigation system circuitry such as global positioning system (GPS) receiver circuitry  42  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, monopole antenna structures, dipole antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands or 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, and/or cellular telephone communications bands such as one or more cellular telephone bands at 700-960 MHz, 1400-2170 MHz, and 2170-2700 MHz. 
     However, in practice, the general size required for the antenna increases as the desired frequency for operation decreases (i.e., as the corresponding wavelength increases). In addition, space is at a premium in compact electronic devices such as device  10  (e.g., especially as the demand for smaller and more aesthetically pleasing device form factors increases). If care is not taken, it can be difficult to be able to provide compact electronic devices with satisfactory antenna coverage in all communications bands of interest, particularly for relatively low frequencies (i.e., relatively long wavelengths) such as low band cellular telephone frequencies at 700-960 MHz. 
       FIG. 3  is a diagram showing how transceiver circuitry  56  in wireless circuitry  34  may be coupled to antenna structures  40  using paths such as path  60 . Wireless circuitry  34  may be coupled to control circuitry  28 . Control circuitry  28  may be coupled to input-output devices  32 . Input-output devices  32  may supply output from device  10  and may receive input from sources that are external to device  10 . 
     To provide antenna structures  40  with the ability to cover communications frequencies of interest, antenna structures  40  may be provided with circuitry such as filter circuitry (e.g., one or more passive filters and/or one or more tunable filter circuits). Discrete components such as capacitors, inductors, and resistors may be incorporated into the filter circuitry. Capacitive structures, inductive structures, and resistive structures may also be formed from patterned metal structures (e.g., part of an antenna). If desired, antenna structures  40  may be provided with adjustable circuits such as tunable components  62  to tune antennas over communications bands of interest. Tunable components  62  may include tunable inductors, tunable capacitors, or other tunable components. Tunable components such as these may be based on switches and networks of fixed components, distributed metal structures that produce associated distributed capacitances and inductances, variable solid state devices for producing variable capacitance and inductance values, tunable filters, or other suitable tunable structures. 
     During operation of device  10 , control circuitry  28  may issue control signals on one or more paths such as path  64  that adjust inductance values, capacitance values, or other parameters associated with tunable components  62 , thereby tuning antenna structures  40  to cover desired communications bands. 
     Path  60  may include one or more radio-frequency transmission lines. As an example, signal path  60  of  FIG. 3  may be a transmission line having first and second conductive paths such as paths  66  and  68 , respectively. Path  66  may be a positive signal line and path  68  may be a ground signal line. Lines  66  and  68  may form parts of a coaxial cable, a stripline transmission line, and/or a microstrip transmission line (as examples). A matching network formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna structures  40  to the impedance of transmission line  60 . Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. Matching network components may, for example, be interposed on line  60 . The matching network components may be adjusted using control signals received from control circuitry  28  if desired. Components such as these may also be used in forming filter circuitry in antenna structures  40 . 
     Transmission line  60  may be directly coupled to an antenna resonating element and ground for antenna  40  or may be coupled to near-field-coupled antenna feed structures that are used in indirectly feeding a resonating element for antenna  40 . As an example, antenna structures  40  may form an inverted-F antenna, a loop antenna, a patch antenna, a slot antenna, or other antenna having an antenna feed with a positive antenna feed terminal such as terminal  70  and a ground antenna feed terminal such as ground antenna feed terminal  72 . Positive transmission line conductor  66  may be coupled to positive antenna feed terminal  70  and ground transmission line conductor  68  may be coupled to ground antenna feed terminal  72 . 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  60  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. 
       FIG. 4  is a cross-sectional side view of illustrative device  10  showing how antenna  40  may be formed within device  10 . 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 have conductive housing sidewalls  12 W that extend from the rear face to the front face of device  10 . Display  14  may form the front face of device  10  whereas dielectric rear housing wall  12 R forms the rear face of device  10 . Metal housing sidewalls  12 W may be used in forming a portion of an antenna ground for antenna  40  if desired. 
     Display  14  may include a display cover layer  86  and a display module  84 . Display module  84  may include active display components such as touch sensors, pixels, or other light-emitting components that emit light through display cover layer  86 . Display cover layer  86  may extend across some or substantially all of the length and width of device  10 . Display cover layer  86  may include a transparent portion that passes the light emitted by display module  172  (e.g., so that the light may be seen by a user). If desired, an opaque masking layer such as an ink layer may be formed along the portion of display cover layer  86  that extends beyond display module  84  to hide the internal components of device  10  from view. 
     Strap  16  may be secured to housing sidewalls  12 W using corresponding attachment structures  88 . Attachment structures  88  may include lugs, spring structures, or any other desired attachment mechanisms. Strap  16  may be formed using any desired materials (e.g., metal materials, dielectric materials, or combinations of metal and dielectric materials). If desired, strap  16  may be removed from attachment structures  88  (e.g., so that a user of device  10  can swap in different straps having similar or different materials). 
     Device  10  may include printed circuit board structures such as printed circuit board  80 . Printed circuit board  80  may be a rigid printed circuit board, a flexible printed circuit board, or may include both flexible and rigid printed circuit board structures. Printed circuit board  80  may sometimes be referred to herein as main logic board  80 . Electrical components  82  may be mounted to main logic board  80 . Electrical components  82  may include, for example, transceiver circuitry  56 , one or more input-output devices  32 , some or all of control circuitry  28  ( FIG. 2 ), portions of housing  12 , or any other desired components. Main logic board  80  may include one or more conductive layers such as conductive layer  76 . Conductive layer  76  may, for example, form a portion of the antenna ground for antenna  40 . Conductive layer  76  may therefore sometimes be referred to herein as grounded layer  76 , ground layer  76 , ground conductor  76 , or grounded conductor  76 . 
     Conductive layer  76  may, if desired, be shorted (grounded) to metal housing sidewalls  12 W (e.g., the antenna ground for antenna  40  may include conductive layer  76  and metal housing sidewalls  12 W). Conductive layer  76  may be formed using metal foil, stamped sheet metal, conductive traces patterned onto a surface of main logic board  80 , a conductive trace on a flexible printed circuit mounted to main logic board  80 , metal housing portions, or from any other desired conductive structures. If desired, conductive layer  76  may be formed (embedded) within main logic board  80  (e.g., conductive layer  76  may be stacked between dielectric layers of logic board  80 ). In another suitable arrangement, conductive layer  76  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. 
     Antenna  40  may include antenna structures  74 . Antenna structures  74  may, for example, be some or all of an antenna resonating element for antenna  40  (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, etc.). In one suitable arrangement, antenna resonating element  74  may be formed from conductive traces that are patterned directly onto the interior surface of dielectric housing wall  12 R (e.g., the patterned conductive traces may be in direct contact with the inner surface of dielectric housing wall  12 R). If desired, antenna resonating element  74  may be formed using conductive foil or other conductive structures that are placed in direct contact with rear housing wall  12 R. In another suitable arrangement, antenna resonating element  74  may be formed from conductive traces on a flexible printed circuit substrate or other dielectric substrate that is located over (e.g., vertically separated from and overlapping) or in direct contact with rear housing wall  12 R. Antenna resonating element traces  74  may be formed using any desired conductive material (e.g., aluminum, copper, metal alloys, stainless steel, gold, etc.). 
     The example of  FIG. 4  in which rear housing wall  12 R is formed using dielectric materials is merely illustrative. If desired, the rear housing wall of device  10  may include a combination of conductive and dielectric materials. For example, a portion of the rear housing wall may be formed from metal whereas another portion of the rear housing wall is formed from dielectric (e.g., the portion of the rear housing wall formed from dielectric may extend across some but not all of the length and width of device  10 ). The dielectric portion of the rear housing wall may, for example, include a dielectric window within a conductive portion of the rear housing wall (e.g., the rear housing wall may include a metal frame for the dielectric portion of the rear housing wall or other structures that surround the dielectric portion of the rear housing wall). The rear housing wall may include multiple dielectric windows if desired. 
     Positive antenna feed terminal  70  of antenna  40  may be coupled to a portion of antenna resonating element traces  74  to feed radio-frequency antenna signals for antenna  40 . Ground antenna feed terminal  72  may be coupled to the antenna ground for antenna  40 . In the example of  FIG. 4 , ground antenna feed terminal  72  is coupled to metal housing sidewall  12 W. If desired, ground antenna feed terminal  72  may be coupled to conductive layer  76  or any other grounded structures. If desired, one or more additional portions of antenna resonating element traces  74  may be shorted to the antenna ground (e.g., housing wall  12 W, conductive layer  76 , and/or other grounded structures) using other conductive paths (not shown). Such conductive paths may, for example, form a return (short) path for antenna  40  (e.g., in scenarios where antenna  40  is an inverted-F antenna or planar inverted-F antenna). 
     In scenarios where antenna resonating element traces  74  are patterned directly onto rear housing wall  12 R, rear housing wall  12 R may serve as a mechanical support structure or carrier structure for antenna resonating element  74 . Antenna resonating element traces  74  may conform to the shape of the interior surface of dielectric rear housing wall  12 R. In the example of  FIG. 4 , the interior surface of dielectric rear housing wall  12 R has a slightly curved shape (e.g., to increase the total volume for components within device  10  relative to scenarios where the interior surface of wall  12 R is flat). Antenna resonating element traces  74  may therefore be formed within a curved surface that is in direct contact with rear housing wall  12 R. In another suitable arrangement, antenna resonating element traces  74  may be formed on a flexible printed circuit or other substrate that is placed in contact with or layered over rear housing wall  12 R. 
     Antenna  40  may receive and/or transmit radio-frequency signals through rear housing wall  12 R. Radio-frequency signals transmitted by antenna  40  may be shielded from electrical components  82  by conductive layer  76  and main logic board  80 , for example. Similarly, conductive layer  76  and main logic board  80  may shield antenna  40  from components  82 , thereby mitigating electromagnetic interference between antenna  40  and components  82 . 
     If desired, other components (e.g., one or more sensors  32  such as a light sensor, proximity sensor, touch sensor, etc.) may be mounted to rear housing wall  12 R. For example, antenna resonating element traces  74  may surround or be formed around the periphery of other components that are mounted to rear housing wall  12 R. In one suitable arrangement, coil  50  ( FIG. 2 ) is placed in contact with rear housing wall  12 R for receiving wireless power (e.g., wireless charging signals) through dielectric rear housing wall  12 R. In this scenario, antenna resonating element traces  74  may surround coil  50  at the interior surface of rear housing wall  12 R. 
     By forming antenna  40  adjacent to rear housing wall  12 R, the vertical height H of device  10  may be shorter than would otherwise be possible in scenarios where the antenna resonating element is located elsewhere on device  10  (while still allowing antenna  40  to exhibit satisfactory antenna efficiency). As an example, vertical height H 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 antenna  40  to operate with satisfactory antenna efficiency. Forming antenna  40  along the rear side of device  10  may also allow for reduction of the size of the inactive region of display  14  (as shown by arrow I), because antenna  40  can transmit radio-frequency signals through the rear side of device  10  without concern that the signals will be blocked by display module  84 . 
     Forming antenna  40  along rear housing wall  12 R may also allow the perimeter of antenna resonating element  74  to be sufficiently large so as to allow for coverage of relatively low frequencies such as frequencies in a cellular telephone band between 700 and 960 MHz. In general, antenna  40  may handle radio-frequency signals above 700 MHz, such as signals at 2.4 GHz and/or 5 GHz for IEEE 802.11 communications, Bluetooth®, and/or other wireless local area network communications may be handled by peripheral antenna  40 P (as an example), low band cellular telephone signals (e.g., cellular telephone communications at frequencies between 700 MHz and 960 MHz), cellular telephone signals and GPS signals in a mid-band, a high band, and other bands that are above 960 MHz such as cellular telephone and GPS signals at 960-2700 MHz, radio-frequency signals at 2.4 GHz and/or 5 GHz for IEEE 802.11 communications, Bluetooth®, and/or other wireless local area network communications, and any other desired bands. By covering all of these bands using a single antenna  40 , the space that would have otherwise been occupied by additional antennas within device  10  may be used for other electronic device components or to further reduce the size (e.g., dimension H and/or I of  FIG. 4 ) of device  10  without sacrificing antenna efficiency. 
     In practice, the performance of antenna  40  may be optimized by the presence of an external object adjacent to rear housing wall  12 R. For example, the presence of a user&#39;s wrist  90  adjacent to rear housing wall  12 R when the user is wearing device  10  may enhance the performance of antenna  40 . During operation, antenna resonating element  74  may transmit and/or receive radio-frequency signals having electric fields (E) that are oriented normal to the surfaces of rear face  12 R and wrist  90 . These signals may sometimes be referred to as surface waves, which are then propagated along the surface of wrist  90  and outwards (e.g., antenna resonating element traces  74  and wrist  90  may serve as a waveguide that directs the surface waves outwards). 
       FIG. 5  is a cross-sectional side view showing how the electromagnetic signals transmitted by antenna  40  may be propagated outwards due to the presence of the user&#39;s wrist. As shown in  FIG. 5 , contour lines  92  indicate contours of constant electric field magnitude. The magnitude of the electric field generated by antenna  40  is highest in the space between device  10  and wrist  90 . The signals may propagate along resonating element trace  74  and the surface of wrist  90  in an outward direction away from device  10 , as shown by paths  98 . This may allow the signals to be properly received by external communications equipment (e.g., equipment  52  of  FIG. 2 ) even though antenna  40  is located close to wrist  90  and typically pointed away from the external communications equipment. In practice, the presence of wrist  90  may serve to enhance the propagation of the electromagnetic waves relative to situations when wrist  90  is not present. For example, the radio-frequency signals emitted by antenna  40  may not be properly directed in the absence of wrist  90 , resulting in poor or unsatisfactory wireless link quality with the external equipment. However, in the presence of wrist  90 , the signals may be properly directed as shown by arrows  98 , thereby allowing for a satisfactory link quality to be obtained. The example of  FIG. 5  is merely illustrative. In general, the electric field patterns may have any desired shape or configuration. 
     When performing wireless communications operations, antenna  40  may be loaded through rear housing wall  12 R by external objects in the vicinity of rear housing wall  12 R. If care is not taken, antenna  40  may exhibit an altered frequency response relative to a free space environment when an external object such wrist  90  is brought into the vicinity of antenna  40  (e.g., antenna  40  may be detuned because the impedance of the antenna has been changed due to loading from object  90  through rear wall  12 R). In addition, different types of objects or materials may load antenna  40  by differing amounts. Similarly, adjustments to the orientation or distance of the external object with respect to rear housing wall  12 R may load antenna  40  by different amounts. During normal operation of device  10  by an end 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 antenna  40  (e.g., by tightening or loosening strap  16 ), when the user swaps out strap  16  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 antenna  40  differently), when strap  16  or wrist  90  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  90 , as examples. These examples are merely illustrative. In general, any environmental factors may load antenna  40  by different amounts through housing wall  12 R. 
     Such environmental loading variations may alter the impedance of antenna  40  relative to transmission line  60 . If care is not taken, these variations may generate an impedance discontinuity between antenna  40  and the rest of wireless communications circuitry  34 . The impedance discontinuity may cause some radio-frequency energy to be reflected at the boundary between antenna  40  and the rest of wireless communications circuitry  34  instead of being used to convey signals with external equipment  52  ( FIG. 2 ). If these environmental loading variations are not compensated for, antenna  40  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, storage and processing circuitry  28  may control adjustable matching circuitry coupled to antenna  40  to ensure that antenna  40  is suitably matched to the rest of wireless circuitry  34  regardless of how antenna  40  is loaded through wall  12 R. If desired, storage and processing circuitry  28  may adjust tunable components  62  ( FIG. 3 ) in addition to adjustable matching circuitry to cover the desired frequency bands of interest and to compensate for any detuning of antenna  40  due to loading of the antenna by external objects. 
     Storage and processing circuitry  28  may use any desired information for determining when and how to adjust the adjustable matching circuitry to compensate for variations in antenna loading. For example, control circuitry  28  may adjust the matching circuitry based on instructions received from external equipment such as a wireless base station or access point. If desired, control circuitry  28  may adjust the matching circuitry based on the current operating state of device  10 . For example, control circuitry  28  may identify a usage scenario (e.g., whether device  10  is being used to browse the internet, conduct a phone call, send an email, access GPS, etc.) to determine how to adjust the matching circuitry. As another example, control circuitry  28  may identify sensor data that is used to identify how to adjust the matching circuitry (e.g., optical sensor data, proximity sensor data, touch sensor data, data indicative of how close a user&#39;s body is to rear housing wall  12 R, etc.). As yet another example, control circuitry  28  may gather antenna performance information (e.g., performance metric data gathered using antenna  40  that can be used to characterize the performance of antenna  40 ) that can be used to identify how to adjust the matching circuitry. If desired, information on the habits of the user of device  10  (sometimes referred to herein as user statistics) may also be processed for determining how to adjust the matching circuitry. In general, control circuitry  28  may process any desired combination of this information or other information to identify when to adjust the matching circuitry (e.g., when antenna loading variations occur) and to identify how to adjust the matching circuitry (e.g., in such a way so as to mitigate the potential detuning defects of the antenna loading variations). 
     Illustrative circuitry for gathering and processing antenna performance information to determine how to adjust antenna  40  to compensate for antenna loading variations is shown in  FIG. 6 . As shown in  FIG. 6 , wireless communications circuitry  34  may include one or more antennas  40 , front end circuitry  112 , radio-frequency coupler circuitry  110 , power amplifier circuitry  108 , low noise amplifier circuitry  114 , transceiver circuitry  56 , and receive signal strength measurement circuitry  122 . 
     Storage and processing circuitry  28  may include baseband processor circuitry, storage such as non-volatile or volatile memory, and control circuitry for controlling wireless communications circuitry  34  to transmit and/or receive radio-frequency signals. Digital data signals that are to be transmitted by device  10  may be generated by one or more baseband processors in circuitry  28 . Circuitry  28  may modulate the digital data signals in accordance with a desired communications protocol (e.g., a desired cellular telephone standard and modulation scheme, a wireless local area network protocol, etc.) and may provide corresponding output signals for transmission to transceiver circuitry  56  (e.g., to one or more transmitters  102  in transceiver circuitry  56 ). Transceiver circuitry  56  may include mixer circuitry that up-converts the output signals to a radio-frequency and that transmits the radio-frequency signals to radio-frequency power amplifier (PA) circuitry  108 . If desired, transceiver circuitry  56  may include digital-to-analog converter circuitry that converts the output signals to corresponding analog signals. 
     Control circuitry in storage and processing circuitry  28  may adjust the level of voltage Vcc (e.g., sometimes referred to herein as power supply voltage Vcc or power amplifier bias voltage Vcc) provided to power amplifier circuitry  108  over control path  118 . Bias voltage Vcc may be used as a power supply voltage for one or more active power amplifier stages in power amplifier circuitry  108 . During data transmission, power amplifier circuitry  108  may amplify the output power of transmitted signals TX to a sufficiently high level to ensure adequate signal transmission. 
     The output of power amplifier circuitry  108  may be coupled to radio-frequency front end circuitry  112  through radio-frequency coupler  110 . Front end circuitry  112  may include adjustable impedance matching circuitry such as adjustable matching network  111 . Adjustable impedance matching circuitry  111  may include networks of passive and/or active (adjustable) components such as resistors, inductors, and capacitors that are adjusted to ensure that antenna  40  is impedance matched to the rest of circuitry  34 . Storage and processing circuitry  28  may provide control signals CTRL to adjustable matching circuitry  111  in front end  112  over control path  116 . 
     In some scenarios, processing circuitry  28  controls matching circuitry  111  to exhibit a particular predetermined impedance that is selected based only on the frequency of the signals that are to be conveyed over antenna  40 . For example, processing circuitry  28  may store factory-calibrated data for matching circuitry  111  that identifies a particular setting for matching circuitry  111  corresponding to each possible frequency of operation. When processing circuitry  28  determines the frequency to be used for wireless communications, matching circuitry  111  is placed into the corresponding setting identified by the factory-calibrated data. However, performing such a priori adjustments based solely on the frequency to be used does not account for any potential antenna loading variations through rear housing wall  12 R that occur during normal operation. Processing circuitry  28  may therefore perform dynamic adjustment of matching circuitry  111  based on how antenna  40  is being loaded through rear housing wall  12 R in real time (e.g., so that circuitry  28  alters the impedance of antenna  40  to match the impedance of the rest of wireless circuitry  34  in real time regardless of the loading conditions of antenna  40 ). 
     As an example, when an external object such as wrist  90  ( FIG. 5 ) is brought into proximity of antenna  40 , antenna  40  may be loaded such that the impedance of antenna  40  is no longer matched to the rest of circuitry  34 . Storage and processing circuitry  28  may control the impedance of adjustable impedance matching network  111  to match the antenna  40  loaded by wrist  90 . When matching network  111  is matched to antenna  40 , the potential detuning as a result of the change in antenna loading may be mitigated and antenna efficiency may be maximized. As another example, antenna  40  may be loaded by a first amount when device  10  is oriented at position  94  with respect to the user&#39;s wrist  90  ( FIG. 5 ) and may be loaded by a second amount when device  10  is oriented at position  96 . Control circuitry  28  may place matching circuitry  111  in a first setting that mitigates the first amount of antenna loading when device  10  is at position  94  and may place circuitry  111  in a second setting that mitigates the second amount of antenna loading when device  10  is at position  96 . Storage and processing circuitry  28  may additionally or alternatively provide control signals to antenna  40  over path  124  to compensate for different antenna loading conditions, if desired (e.g., to adjust tunable components  62  of  FIG. 2 ). 
     If desired, front circuitry  112  may include other circuitry such as radio-frequency switching circuitry (e.g., multiplexing circuits), filtering circuitry (e.g., duplexers and diplexers), or any other desired radio-frequency front end circuitry. If desired, filtering circuitry in front end  112  may be used to route input (receive) and output (transmit) signals based on their frequency. For example, filtering circuitry in front end  112  may transmit (uplink) signals TX received from coupler  110  to antenna  40  and may route receive (downlink) signals RX that have been received by antenna  40  onto receive path  113 . If desired, low noise amplifier (LNA) circuitry  114  may be interposed on receive path  113 . Low noise amplifier circuitry  114  may amplify receive signals RX on path  113 . The amplified receive signals RX may be routed to transceiver circuitry  56  (e.g., to one or more receiver circuits  106  in transceiver circuitry  56 ). Transceiver circuitry  56  may provide signals received over path  113  to baseband circuitry in storage and processing circuitry  18  (e.g., after down-converting the signals to a baseband frequency using mixer circuitry). 
     Coupler  110  may be used to tap antenna signals flowing to and from antenna  40 . Tapped antenna signals from coupler  110  may be processed using a receiver in transceiver circuitry  56  or a separate receiver. As shown in  FIG. 6 , coupler  110  may provide tapped antenna signals TX′ to feedback receiver  104  over feedback path  120 . Storage and processing circuitry  28  may use control path  119  to control coupler  110 . For example, storage and processing circuitry  28  may direct coupler  110  to provide receiver  104  with a tapped version of the signals TX being transmitted by power amplifier  108  (sometimes referred to as forward signals) or to provide receiver  104  with a corresponding tapped version of the transmitted signals TX that have been reflected from antenna  40  (sometimes referred to as reverse signals). 
     The tapped signals may be down-converted and provided to storage and processing circuitry  28 . Storage and processing circuitry  28  may process the tapped signals to generate antenna performance metric information such as phase and magnitude measurements of the impedance of antenna  40 . For example, by processing the forward and reverse signals for antenna  40 , storage and processing circuitry  28  may gather information on the phase and magnitude of the impedance of antenna  40  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 antenna  40 . 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  110  from antenna  40  during signal transmission. 
     The phase and magnitude of the impedance of antenna  40  may be used to determine whether the operation of antenna  40  has 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 antenna  40 ). For example, storage and processing circuitry  28  may detect variations in the gathered phase and magnitude information (e.g., excessively high magnitude S11 measurements, etc.) to identify when antenna  40  has been detuned/loaded by the presence of an external object. If storage and processing circuitry  28  detects that antenna  40  has been detuned due to the loading of antenna  40  (e.g., due to the user adjusting strap  16 , changing strap  16 , adjusting an orientation of device  10  relative to wrist  90 , strap  16  becoming wet, a different user wearing device  10 , etc.), circuitry  28  may issue control signals CTRL over path  116  to adjust impedance matching network  111  to compensate for the detuning. After impedance matching network  111  has been adjusted, antenna  40  is impedance matched with the rest of wireless communications circuitry  34  and the antenna efficiency is maximized. 
     If desired, other performance metric information such as receive signal strength information may be used to determine how to adjust circuitry  111  in response to variations in antenna loading. Receive signal strength measurement circuitry  122  in wireless communications circuitry  34  may receive signals RX from low noise amplifier circuitry  114 . Measurement circuitry  122  may gather information indicative of the receive signal strength of signals RX. For example, measurement circuitry  122  may gather Received Signal Strength Indicator (RSSI) values from receive signals RX. In one suitable arrangement, circuitry  122  may include diode detector circuitry that converts the received radio-frequency signal to a known voltage level for extracting the RSSI values. The RSSI values may be transmitted to storage and processing circuitry  28 . RSSI values gathered by measurement circuitry  122  may be accumulated and stored on circuitry  28  as gathered RSSI data  126 . Gathered RSSI data  126  may be stored on circuitry  28  in a data structure such as a database file, as one example. 
     Storage and processing circuitry  28  may track the physical location of device  10  over time. For example, GPS receiver circuitry  42  ( FIG. 2 ) may receive satellite navigation signals for identifying the location of device  10  over time. As another example, short range transceiver  36  may be used to determine the location of device  10  relative to a wireless base station having a known position. The position of device  10  relative to the wireless base station may be compared to the known position of the wireless base station to identify the spatial location of device  10 . In general, any desired methods may be used for identifying the location of device  10 . The location of device  10  may be identified using spatial coordinates such as latitude, longitude, and/or elevation coordinates, or any other desired spatial coordinates. 
     When accumulating and storing RSSI data  126 , storage and processing circuitry  28  may also identify the time at which each RSSI measurement was made (sometimes referred to herein as an acquisition time or RSSI acquisition time) and/or the geographical location of device  10  at the time each RSSI measurement was made (sometimes referred to herein as an acquisition position or wearable electronic device acquisition position). For example, gathered RSSI data  126  may include entries (e.g., rows in a data structure or database) that each identify a particular RSSI value measured by circuitry  122 , a corresponding acquisition time at which that RSSI value was measured, and/or a corresponding wearable electronic device acquisition position identifying the location of device  10  when that RSSI value was measured. In this way, gathered RSSI data  126  may be stored as a function of time and space (i.e., device position) on storage and processing circuitry  28 . 
     If desired, storage and processing circuitry  28  may accumulate and store information about the habits of one or more users of device  10  as user statistics  128 . User statistics  128  may be maintained in one or more data structures stored in memory on circuitry  28  (e.g., the same data structure as RSSI data  126  or a different data structure). User statistics  128  may include location data (e.g., information identifying where device  10  is typically located at different times of day), information about how the user typically wears device  10 , information about the typical configuration of strap  16  when device  10  is worn by the user, information about the typical performance of antenna  40  or other components in wireless circuitry (e.g., performance metric data), or any other information about the routine or habits of the user of device  10 . 
     If desired, user statistics  128  may include information identifying predetermined patterns of RSSI data as a function of time and/or space. For example, user RSSI patterns  132  may be stored on circuitry  28 . User RSSI patterns  132  may be predetermined patterns of RSSI values as a function of time and/or space that are associated with typical operation of device  10  by a user. For example, as the user goes about their day (e.g., wakes up, drives to work, drives home from work, goes to sleep, etc.), the gathered RSSI values may exhibit predetermined patterns associated with the performance of antenna  40  as the user goes about their day. User RSSI patterns  132  may, for example, serve as a background or baseline measurement that is used by circuitry  28  to determine when unusual events requiring antenna matching adjustment have occurred. RSSI patterns  132  may, if desired, be loaded onto device  10  during manufacture of device  10  (e.g., using factory-calibrated patterns or settings). If desired, storage and processing circuitry  28  may continually update (train) user RSSI patterns  132  based on real time RSSI measurements performed by circuitry  122 . For example, circuitry  28  may update RSSI patterns  132  as it learns the behavior of the user or to account for any changes in the behavior of the user over time. In this way, RSSI patterns  132  may be reflective of typical operation of device  10  by a corresponding user. If desired, user RSSI patterns  132  may include patterns associated with the typical behavior of multiple users. 
     If desired, user statistics  128  may include event RSSI patterns stored on circuitry  28 . Event RSSI patterns  134  may be predetermined patterns of RSSI values as a function of time and/or space that correspond to particular events associated with the operation of device  10  or actions performed by the user of device  10 . For example, a given event RSSI pattern  134  may be a sequence of RSSI values as a function of time at a fixed location that is expected or predetermined to be associated with the user removing band  16  (e.g., a so-called band replacement event). As another example, a given event RSSI pattern may be a sequence of RSSI values as a function of time at a fixed location that is expected or predetermined to be associated with a user taking device  10  off of their wrist. As yet another example, a given event RSSI pattern may be a sequence of RSSI values as a function of time and location that is expected or predetermined to be associated with a user tightening or loosening strap  16  (e.g., a so-called strap adjustment event). As still another example, a given event RSSI pattern may be a sequence of RSSI values as a function of time that is expected or predetermined to be associated with the user&#39;s wrist  90  becoming wet. 
     Event RSSI patterns  134  may, if desired, be loaded onto device  10  during manufacture of device  10  (e.g., calibration data). If desired, storage and processing circuitry  28  may continually update (train) event RSSI patterns  134  based on real time RSSI measurements performed by circuitry  122 . For example, circuitry  28  may update RSSI patterns  134  as it learns how antenna  40  performs as various events or actions are performed. Each RSSI pattern  134  may include identifier information identifying the type of event that it represents (e.g., a particular RSSI pattern  134  may be labeled as corresponding to a strap replacement event performed by a first user, whereas another RSSI pattern may be labeled as corresponding to a strap adjustment event performed by a second user, etc.). In this way, RSSI patterns  134  may be reflective of events that may occur during operation of device  10  by a corresponding user. If desired, user RSSI patterns  132  and/or event RSSI patterns  134  may be omitted. 
     Storage and processing circuitry  28  may process gathered RSSI data  126 , user RSSI patterns  132 , event RSSI patterns  134 , other user statistics  128 , and/or other information in determining when to adjust matching circuitry  111  and/or how to adjust matching circuitry  111  to compensate for different loading conditions of antenna  40 . Matching settings  130  for matching circuitry  111  may be stored on storage and processing circuitry  28 . Matching settings  130  may identify particular impedance matching settings for matching circuitry  111  to be used during communications operations. Matching settings  130  may be stored on one or more data structures on circuitry  28 . 
     Storage and processing circuitry  28  may identify the particular loading condition for antenna  40  at any given time (e.g., based on RSSI data  126  gathered by circuitry  122 , user RSSI patterns  132 , event RSSI patterns  134 , and/or other information). Processing circuitry  28  may retrieve an appropriate matching setting  130  corresponding to the identified loading condition and may control matching circuitry  111  to implement that setting. For example, processing circuitry  28  may place matching circuitry  111  in a first setting  130  when processing circuitry  28  identifies that antenna  40  is in the presence a dry wrist  90  whereas processing circuitry  28  places matching circuitry  111  in a second setting  130  when processing circuitry  28  identifies that antenna  40  is in the presence of a wet wrist  90 . 
     Matching settings  130  may, if desired, be loaded onto device  10  during manufacture of device  10  (e.g., using factory-calibrated settings). If desired, storage and processing circuitry  28  may continually update or overwrite matching settings  130  based on real time RSSI measurements performed by circuitry  122 . For example, circuitry  28  may update matching settings  130  as it learns what particular settings best match antenna  40  under a variety of loading conditions. In another suitable arrangement, circuitry  28  may sweep through different possible matching settings until a satisfactory matching setting is found. 
     In this way, storage and processing circuitry  28  may continue to monitor the performance of antenna  40  for changes in antenna loading and may actively adjust matching circuitry  111  to compensate for such changes in real time. These adjustments may thereby dynamically and adaptively compensate for any potential deteriorations in antenna performance that arise as a result of different users operating device  10 , different orientations of device  10  on the user&#39;s wrist  90 , different strap tightness, different strap materials, presence of water or moisture adjacent to or on device  10 , or any other environmental variations affecting the loading of antenna  40  that may arise during normal use of device  10 . 
     The example of  FIG. 6  is merely illustrative. If desired, storage and processing circuitry  28  may use gathered RSSI data in combination with phase and magnitude measurements gathered using coupler  110  in determining how to adjust matching circuitry  111 . Coupler  110  and feedback receiver circuitry  104  may be omitted in scenarios where phase and magnitude measurements are not used in adjusting matching circuitry  111 . Similarly, measurement circuitry  122  may be omitted in scenarios where RSSI measurements are not used in adjusting matching circuitry  111 . If desired, antenna  40  may include a single antenna that transmits signals TX and that conveys receive signals RX to measurement circuitry  122 . In another suitable arrangement, a first antenna  40  may be used to transmit signals TX from coupler  110  whereas a second antenna  40  is used to receive signals RX for gathering RSSI data. In general, wireless communications circuitry  34  may include any desired circuitry arranged in any desired manner. Circuitry  102 ,  104 , and  106  in transceiver circuitry  56  may each be implemented using respective integrated circuits or may be formed on together on one or more shared integrated circuits. 
       FIG. 7  is a flow chart of illustrative steps that may be performed by device  10  in gathering and processing RSSI data for adjusting matching circuitry  111 . The steps of  FIG. 7  may, for example, be performed by device  10  to compensate for variations in antenna loading in real time (e.g., so that an optimal antenna efficiency is maintained regardless of how device  10  is being worn, who is wearing device  10 , etc.). 
     At step  140 , wireless communications circuitry  34  may begin wireless communications using factory calibrated settings. For example, storage and processing circuitry  28  may identify a factory calibrated matching setting  130  that corresponds to the particular frequency to be used for communications. The factory calibrated settings may be loaded onto circuitry  28  during manufacture of device  10 . The factory calibrated settings may not provide sufficient impedance matching for antenna  40  under all real world antenna loading conditions, for example. Wireless communications circuitry  34  may transmit signals TX to external devices such as external devices  52  ( FIG. 2 ) and may receive signals RX from external devices  52  (e.g., using the factory calibrated settings). 
     At step  142 , storage and processing circuitry  28  may gather RSSI values  126  from wireless signals that are received from external devices  52  (e.g., as measured by receive signal strength measurement circuitry  122  of  FIG. 6 ). Storage and processing circuitry  28  may track the location of device  10  while the RSSI values are gathered. As device  10  performs wireless communications, circuitry  28  may continue to gather and store RSSI values from the received signals as a function of the position of device  10  and/or as a function of time (step  144 ). 
     Device  10  may also gather user statistics  128  based on the transmitted and received signals. For example, storage and processing circuitry  28  may store information about the behavior of the user as user statistics  128  (step  146 ). The behavioral information may include information on where the user is typically located at different times of day, activities that are preformed typically by the user, or other information associated with user behavior. If desired, one or more sensors in input-output devices  32  ( FIG. 2 ) may be used to help track the user&#39;s behavior. For example, ambient light sensors and/or motion sensors on device  10  may be used to identify times or device locations when the user is typically stationary, asleep, moving, etc. As another example, strap sensors, proximity sensors, touch sensors, or other sensors may be used to identify when the user removes or adjusts strap  16 . 
     If desired, storage and processing circuitry  28  may update stored RSSI patterns  132  and  134  based on the gathered RSSI data and on the gathered information about user behavior (step  148 ). Storage and processing circuitry  28  may identify and store user RSSI patterns  132  that are associated with typical use of device  10  by one or more users. Storage and processing circuitry  28  may identify and store event RSSI patterns  134  that are associated with various events or activities that may affect the loading of antenna  40 . For example, storage and processing circuitry  28  may compare user statistics  128  to gathered RSSI data  126  to identify a pattern in the gathered RSSI data that typically occurs when the user is removes or adjusts strap  16 . The identified pattern may be stored as a given one of event RSSI patterns  134 . Similarly, storage and processing circuitry  28  may identify patterns in gathered RSSI data  126  that are typical of normal wear by the user (e.g., patterns associated with normal motion of the user&#39;s arms or other typical user activities that do not necessarily detune antenna  40 ). These identified patterns may be stored as user RSSI patterns  132 . Throughout the lifetime of device  10 , storage and processing circuitry  28  may continue to update and refine (e.g., train) user RSSI patterns  132 , event RSSI patterns  134 , and/or other user statistics  128  based on the behavior of the user of device  10  and gathered RSSI data. The example of  FIG. 7  is merely illustrative. If desired, steps  144 ,  146 , and/or  148  may be omitted. Steps  144 ,  146 , and/or  148  may be performed concurrently or at different times. 
     At step  150 , storage and processing circuitry  28  may process gathered user statistics  128  and gathered RSSI data  126  to determine whether an adjustment to matching circuitry  111  is needed. The adjustment to the matching circuitry may be needed when a change in the loading conditions of antenna  40  or detuning of antenna  40  due to the presence external objects are detected in the gathered RSSI data. User statistics  128  may be used to filter and/or identify patterns in gathered RSSI data  126  that are indicative of such changes, for example. If desired, step  150  may be performed concurrently with some or all of step  142  (e.g., storage and processing circuitry  28  may continue to gather and store data while also performing data processing). 
     If processing circuitry  28  determines that no adjustment is needed (e.g., if no changes in antenna loading or antenna detuning are detected), processing may loop back to step  142  as shown by path  152  to continue to gather and store RSSI data and user statistics. If processing circuitry  28  determines that an adjustment is needed (e.g., if a change in antenna loading or antenna detuning is detected), processing may proceed to step  160  as shown by path  154 . 
     At step  160 , storage and processing circuitry  28  may adjust matching circuitry  111  to compensate for the detected change in antenna loading/detuning. For example, storage and processing circuitry  28  may provide control signals CTRL over path  116  ( FIG. 6 ) to control circuitry  111  to implement a desired matching setting. Wireless communications circuitry  34  may continue to perform wireless communications operations using the adjusted matching setting. Processing may subsequently loop back to step  142  as shown by path  162  to continue to gather and store RSSI data and user statistics. 
       FIG. 8  is a flow chart of illustrative steps that may be performed by storage and processing circuitry  28  to determine when to perform an adjustment to matching circuitry  111 . The steps of  FIG. 8  may, for example, be performed while processing step  150  of  FIG. 7 . 
     At step  170 , processing circuitry  28  may identify a sequence of RSSI values as a function of time and/or device position in gathered RSSI data  126 . For example, processing circuitry  28  may identify a set of the most recently gathered RSSI values from gathered RSSI data  126 . 
     At step  172 , processing circuitry  28  may perform filtering operations on the identified RSSI values. For example, processing circuitry  28  may filter out a user RSSI pattern  132  as a function of time from the identified RSSI values as a function of time. User RSSI pattern  132  may be a factory-calibrated pattern that is stored on device  10  during manufacture and/or may be a pattern that is stored and updated on device  10  during normal operation (e.g., while processing step  148  of  FIG. 7 ). In this way, processing circuitry  28  may filter out a baseline from the gathered RSSI data that is otherwise associated with normal operation of device  10  by the user. As another example, processing circuitry  28  may filter out a constant baseline RSSI value from the identified RSSI values. 
     At step  174 , processing circuitry may determine whether a trigger event is present in the filtered RSSI values. As one example, the trigger event may be a glitch in the filtered RSSI values. Processing circuitry  28  may determine that a glitch is present if a portion of the filtered RSSI values as a function of time has a slope that exceeds a positive slope threshold value or a slope that is less than a negative slope threshold value. As another example, the trigger event may be an excessive deviation in the filtered RSSI values. Processing circuitry  28  may determine that an excessive deviation is present if the filtered RSSI values include values that are less than a predetermined minimum threshold RSSI value or greater than a predetermined maximum threshold RSSI value. As yet another example, processing circuitry  28  may compare the filtered RSSI values to one or more predetermined event RSSI patterns  134  to determine whether one of the event RSSI patterns is present in the filtered RSSI values. Predetermined event RSSI patterns  134  may be factory-calibrated patterns that are stored on device  10  during manufacture and/or may be patterns that are stored and updated on device  10  during normal operation (e.g., while processing step  148  of  FIG. 7 ). Processing circuitry  28  may identify that a trigger event is present when a particular sequence of the filtered RSSI values sufficiently matches a stored event RSSI pattern  134  such as an RSSI pattern associated with a user removing or adjusting strap  16 . In this scenario, the trigger event may be the event RSSI pattern that was detected in the filtered data. Stored event RSSI patterns  134  may include, as examples, sequences of RSSI values corresponding to different users wearing device  10 , the tightening or loosening of strap  16 , the presence or absence of water or moisture on strap  16 , device  10 , and/or wrist  90 , a change in position or orientation of device  10  on wrist  90 , etc. 
     If desired, processing circuitry  28  may compute a probability that a trigger event is present based on a combination of the filtered RSSI values, user statistics  128 , and/or other information. If the computed probability exceeds a minimum probability threshold then processing circuitry  28  may determine that the trigger event is present. If the computed probability is less than or equal to the minimum probability threshold, then processing circuitry  28  may determine that no trigger event is detected. As an example, processing circuitry  28  may identify a relatively large degradation in the filtered RSSI values (e.g., an excessive deviation of RSSI values as a function of time that is below a predetermined minimum threshold RSSI value). Processing circuitry  28  may combine this information with information identifying that the filtered RSSI values were gathered during the afternoon while the device was located at the user&#39;s work location to determine that there is a relatively high probability that a trigger event such as a strap change trigger event associated with the user changing strap  16  is present in the gathered RSSI values. 
     If no trigger event is detected (e.g., if no glitch, excessive deviation, or predetermined RSSI pattern is present) in the filtered RSSI values, processing may loop back to step  170  as shown by path  176 . Processing circuitry  28  may then continue to search for the presence of trigger events in subsequently gathered RSSI values as a function of time and/or device position (e.g., as updated RSSI values and user statistics are gathered during device operation). If a trigger event is detected, processing may proceed to optional step  180  as shown by path  178 . 
     At optional step  180 , processing circuitry  28  may update stored event RSSI patterns  134  based on the filtered RSSI values. For example, sensor data, user input, or other information may be used to identify that a particular user action or environmental event occurred when the trigger event was detected. The pattern (sequence) of gathered RSSI data as a function of time and/or device position associated with that user action or environmental event may be stored as an event RSSI pattern  134  on circuitry  28  for future processing. For example, that pattern may be used to identify similar trigger events in the future if desired. Processing may subsequently proceed to step  160  of  FIG. 7  to adjust matching network  111 . 
       FIG. 9  is a flow chart of illustrative steps that may be performed by processing circuitry  28  for dynamically adjusting matching network  111  in response to detecting a trigger event. The steps of  FIG. 9  may, for example, be performed while processing step  160  of  FIG. 7 . 
     At step  190 , processing circuitry  28  may perform an adjustment to matching circuitry  111 . For example, processing circuitry  28  may control one or more components within circuitry  111  to adjust the impedance of circuitry  111 . 
     At step  192 , processing circuitry  28  may gather additional RSSI values using the adjusted matching circuitry (e.g., while the matching circuitry exhibits the adjusted impedance). 
     At step  194 , processing circuitry  28  may determine whether performance of antenna  40  has improved by comparing the gathered additional RSSI values to RSSI values that were gathered before the adjustment was made. For example, processing circuitry  28  may determine that the antenna performance has improved if the additional RSSI values are greater than the RSSI values that were gathered prior to the adjustment. If the antenna performance has not improved (e.g., if the additional RSSI values gathered at step  192  are less than or equal to the RSSI values gathered prior to the adjustment), processing may loop back to step  190  as shown by path  196  and the matching circuitry may be further adjusted. In another suitable arrangement, the adjustment performed at step  190  may be reverted and processing may proceed to step  142  of  FIG. 7 . If the antenna performance has improved, processing may proceed to optional step  200  as shown by path  198 . 
     The example of  FIG. 9  in which the gathered RSSI values are compared to previously-gathered RSSI values is merely illustrative. If desired, processing circuitry  28  may compare the additional RSSI values gathered at step  192  to a predetermined threshold value. The predetermined threshold value may be determined by industry standards, design standards, regulatory standards, manufacturing standards, or by any other means. The predetermined threshold value may be, for example, a minimum RSSI value for which satisfactory link quality between device  10  and external equipment  52  may be maintained. If the additional RSSI values are greater than the predetermined threshold value, processing may proceed to step optional step  200  as shown by path  198 . If the additional RSSI values are less than or equal to the predetermined threshold value, processing may loop back to step  190  as shown by path  196 . 
     At optional step  200 , processing circuitry  28  may store the adjusted matching network setting as an entry in matching settings  130  ( FIG. 6 ). Processing circuitry  28  may use the stored matching network setting for performing future adjustments to circuitry  111 . For example, processing circuitry  28  may use a particular matching network setting  130  whenever the corresponding trigger event that led to the matching circuit adjustment is detected in the future. Processing may subsequently proceed to step  202 . 
     At step  202 , wireless communications circuitry  34  may continue communications using the adjusted matching network setting (e.g., processing may proceed to step  142  of  FIG. 7 ). In this way, processing circuitry  28  may sweep through a number of possible settings for matching network  111  while continuing to gather RSSI data until a setting is found that improves or optimizes antenna performance. This example is merely illustrative. In another suitable arrangement, predetermined matching settings  130  may be used in adjusting matching network  111 . 
       FIG. 10  is a flow chart of illustrative steps that may be performed by processing circuitry  28  for adjusting matching network  111  based on predetermined matching settings  130  in response to detecting a trigger event. The steps of  FIG. 10  may, for example, be performed while processing step  160  of  FIG. 7 . 
     Each trigger event may have a type corresponding to the environmental/antenna loading factors that caused it to be present in the gathered RSSI data. At step  210 , processing circuitry  28  may identify the type of trigger event that was detected based on the filtered RSSI values as a function of time and/or device position, user statistics  128 , user input, sensor data, and/or event RSSI patterns  134 . The types of trigger events may include trigger events associated with the user adjusting the location or orientation of device  10  on their wrist, the user adjusting the distance between their wrist and antenna  40  (e.g., by tightening or loosening strap  16 ), the user swapping out strap  16  for a different strap, a different user wearing device  10 , strap  16 , device  10 , or wrist  90  becoming wet or dry, 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  90 , or any other environmental factors that may affect loading of antenna  40 . 
     As an example, processing circuitry  28  may identify that a trigger event associated with a strap replacement (e.g., a strap replacement type trigger event or strap replacement trigger event) has occurred if the filtered RSSI values match an event RSSI pattern  134  associated with replacing strap  16 , if a strap sensor in device  10  detects that strap  16  has been replaced, or based on any other desired information. For example, processing circuitry  28  may identify the trigger event as a strap replacement trigger event if a relatively large degradation in the filtered RSSI values is measured during the afternoon while the device was located at the user&#39;s work location. As another example, processing circuitry  28  may identify the user removing device  10  from their wrist as the type of trigger event in response to identifying that the gathered RSSI data included a rapid increase in measured RSSI values over time and that the increase occurred during the evening after the user&#39;s location has changed from a work location to a home location (e.g., user statistics  128  may identify that this set of conditions has a high probability of being associated with the user removing device  10  from their wrist). As yet another example, processing circuitry  28  may identify the user tightening strap  16  as the type of trigger event in response to identifying that the gathered RSSI values have decreased over a relatively short amount of time while also identifying that the device location did not change during that amount of time. These examples are merely illustrative and, in general, processing circuitry  23  may process any desired combination of the gathered RSSI information as a function of device position and/or time, user input, sensor data, event patterns  134 , and other user statistics  128  in identifying the type of trigger event. 
     At step  212 , processing circuitry  28  may obtain a particular matching setting  130  corresponding to the identified type of trigger event (e.g., a first matching setting if the trigger event is identified as being associated with the user changing strap  16 , a second matching setting if the trigger event is identified as being associated with the user&#39;s skin becoming wet, a third matching setting if the trigger event is identified as being associated with a different user wearing device  10 , a fourth matching setting if the trigger event is identified as being associated with device  10  being positioned at orientation  94  of  FIG. 5 , a fifth matching setting if device  10  is positioned at orientation  96  of  FIG. 5 , etc.). The obtained matching setting  130  may be loaded onto device  10  during manufacture of device  10  for use whenever the corresponding type of trigger event is detected or the obtained matching setting may be stored on processing circuitry  28  while processing step  148  of  FIG. 7 . 
     At step  214 , processing circuitry  28  may apply the obtained matching setting  130  to matching network  111  (e.g., circuitry  28  may configure matching network  111  to exhibit an impedance associated with the obtained matching setting). Processing may subsequently proceed to optional step  216 . 
     At optional step  216 , processing circuitry  28  may gather additional RSSI values while the adjusted matching circuitry is configured using the obtained matching network setting. Processing circuitry  28  may determine whether performance of antenna  40  has improved by comparing the gathered additional RSSI values to RSSI values that were gathered before the adjustment was made. If the antenna performance has not improved (e.g., if the additional RSSI values gathered at step  216  are less than or equal to the RSSI values gathered prior to the adjustment), processing may proceed to step  220 . 
     At step  220 , processing circuitry  28  may take appropriate action. For example, processing circuitry  28  may proceed to step  190  of  FIG. 9  to begin sweeping through additional matching network settings until a satisfactory setting has been found. As another example, processing circuitry  28  may control matching circuitry  111  to revert to the previous matching setting and processing may proceed to step  142  of  FIG. 7  to continue to gather and process user statistics and RSSI values. If the antenna performance has improved (e.g., if the additional RSSI values gathered at step  216  are greater than the RSSI values gathered prior to the adjustment), processing may proceed to step  222 . In scenarios where optional step  216  is not performed, processing may proceed directly from step  214  to step  224 . 
     The example of  FIG. 10  in which the gathered RSSI values are compared to previously-gathered RSSI values is merely illustrative. If desired, processing circuitry  28  may compare the additional RSSI values gathered at step  216  to a predetermined threshold value. If the additional RSSI values are greater than the predetermined threshold value, processing may proceed to step  224  as shown by path  222 . If the additional RSSI values are less than or equal to the predetermined threshold value, processing may proceed to step  220  as shown by path  218 . 
     At step  224 , wireless communications circuitry  34  may continue communications using the adjusted matching network setting (e.g., processing may proceed to step  142  of  FIG. 7 ). In this way, processing circuitry  28  may select and use predetermined matching settings  130  based on the gathered RSSI data. This may allow for faster antenna adjustment than in scenarios where processing circuitry  28  sweeps through different settings (e.g., as in  FIG. 9 ), but may be less adaptable to changing or unpredictable environmental conditions (e.g., conditions for which there may not already be optimized matching settings stored on circuitry  28 ). 
       FIG. 11  is an illustrative plot of gathered RSSI values as a function of time that shows how gathered RSSI data  126  may be compared to a predetermined threshold for detecting the presence of a trigger event. As shown in  FIG. 11 , curve  230  plots gathered RSSI values as a function of time and at a fixed position (e.g., as gathered while processing step  144  of  FIG. 7 ). Gathered RSSI values  230  may vary over time as the user wears device  10 . Relatively small variations in values  230  may have little effect on the overall performance of antenna  40 . However, relatively large variations may result in unsatisfactory antenna performance. 
     Processing circuitry  28  may process RSSI values  230  to identify a trigger event (e.g., while processing step  174  of  FIG. 8 ). In the example of  FIG. 11 , processing circuitry  28  may compare RSSI values  230  to predetermined threshold value RTH. Processing circuitry  28  may determine that a trigger event is present because RSSI values  230  fall below threshold value RTH. This example is merely illustrative. If desired, processing circuitry  28  may identify the slope of RSSI values  230  and may compare the slope to a predetermined slope threshold for identifying the presence of the trigger event. In another suitable arrangement, processing circuitry  28  may identify the presence and type of trigger event when RSSI values  230  match a predetermined event RSSI pattern  134 . The example of  FIG. 11  in which RSSI values as a function of time for a set location are processed is merely illustrative. In general, processing circuitry  28  may process RSSI values as a function of position at a fixed time or as a function of both position and time (e.g., a multi-dimensional surface of gathered RSSI values) for identifying the presence and type of trigger event. 
       FIG. 12  is an illustrative diagram showing how processing circuitry  28  may process gathered RSSI values using predetermined user and event RSSI patterns to identify the presence of a trigger event. 
     As shown in  FIG. 12 , curve  240  plots gathered RSSI values as a function of time (e.g., at a fixed device location). Curve  242  plots a particular user RSSI pattern  132  (e.g., RSSI values as a function of time as accumulated while processing step  148  of  FIG. 7 ). User RSSI pattern  242  may be indicative of typical RSSI data as a function of the same position and time values represented by curve  240 . User RSSI pattern  242  may be trained and updated over time as processing circuitry  28  continues to gather information about the behavior of the user (e.g., as user statistics  128  are updated). 
     User RSSI pattern  242  may be used to filter gathered RSSI values  240  (e.g., while processing step  172  of  FIG. 8 ). In the example of  FIG. 12 , user RSSI pattern  242  is filtered (subtracted) from gathered RSSI values  240  as shown by arrow  243  to generate filtered RSSI values  246  (e.g., portion  244  of curve  240  matching user pattern  242  may be removed from filtered curve  246 ). In this way, user RSSI pattern  242  may serve as a baseline measurement from which to process the gathered RSSI values for identifying trigger events. 
     Processing circuitry  28  may process filtered RSSI values  246  to determine whether a predetermined event RSSI pattern is present in the filtered data (e.g., while processing step  174  of  FIG. 8 ). In the example of  FIG. 12 , processing circuitry  28  may identify that portion  250  of filtered RSSI values  246  matches a given event RSSI pattern  248 . Event RSSI pattern  248  may, for example, be stored on processing circuitry  28  while processing step  180  of  FIG. 8 , while processing step  148  of  FIG. 7 , or during factory calibration. As one example, event RSSI pattern  248  may be an RSSI pattern associated with a strap tightening trigger event. The presence of event RSSI pattern  248  within filtered RSSI data  246  may be indicative of the user tightening strap  16 . Processing circuitry  28  may subsequently identify a matching setting  130  corresponding to the strap tightening trigger event (e.g., while processing step  210  of  FIG. 10 ) for use during subsequent communication (e.g., at least until another trigger event is detected). In another suitable arrangement, processing circuitry may sweep through different matching network settings (e.g., while processing the steps of  FIG. 9 ) until an optimal matching setting is found. Performing the matching network adjustment may allow matching network  111  to match antenna  40  even after the environment around antenna  40  has changed the antenna loading (e.g., after the loading of the antenna has changed as a result of the tightening of strap  16 ). By providing suitable matching for antenna  40 , antenna efficiency may be maximized regardless of how the user is wearing device  10  or regardless of who is wearing device  10 . 
     The example of  FIG. 12  is merely illustrative. In general, the gathered RSSI values may have any desired shape as a function of time and/or space. Similarly, user RSSI pattern  242  and event RSSI pattern  248  may have any desired shape. 
       FIG. 13  is a Smith chart showing how adjusting matching circuitry  111  may affect antenna performance differently under a particular antenna loading condition. In the Smith chart of  FIG. 13 , antenna impedances for antenna  40  are measured as a function of different operating conditions. A fifty ohm antenna impedance is characterized by impedance point  260  in the chart of  FIG. 13 . An antenna with an impedance close to point  260  may be considered well matched to a fifty ohm transmission line in device  10  (e.g., transmission line  60 ). 
     Antenna  40  may exhibit an impedance within region  264  of  FIG. 13  when tuned to a first matching network setting while device  10  is operated under a first antenna loading condition (e.g., when device  10  is oriented at position  94  of  FIG. 5 ). Region  264  is relatively far from point  260 , indicating a relatively high level of antenna detuning. Processing circuitry  28  may identify this detuning by gathering phase and magnitude information using coupler  110  ( FIG. 6 ) and/or by identifying a trigger event in the gathered RSSI data. In order to compensate for this detuning, control circuitry  28  may adjust matching circuitry  111  to tune antenna  40  to a second matching network setting as shown by arrow  268  (e.g., while processing step  160  of  FIG. 7 ). After being tuned to the second matching network setting, antenna  40  may exhibit an impedance within region  262 . Region  262  is closer to point  260  than region  264 , indicating a lower level of antenna detuning than when operated under the second matching network setting associated with region  262 . In this way, control circuitry  28  may compensate for the detuning of antenna  40  caused by the variable amount of antenna loading associated with the user wearing device  10  at different orientations. 
     However, antenna  40  may exhibit a different impedance when device  10  is oriented at position  96  of  FIG. 5 . If the user changes the orientation of device  10  from orientation  94  to orientation  96 , the impedance of antenna  40  may shift to a region that is farther from point  260  such as region  264  as shown by path  266 , indicating a relatively high level of antenna detuning. Processing circuitry  28  may subsequently identify this detuning and may adjust matching circuitry  111  to the first matching network setting. This may shift the impedance of antenna  40  closer to point  260  to reduce the detuning of antenna  40 . In this way, processing circuitry  28  may actively adjust matching circuitry  111  to compensate for loading variations of antenna  40  during normal operation. This example is merely illustrative. In general, processing circuitry  28  may adjust matching circuitry  111  to compensate for any changes in antenna loading due to any suitable event (e.g., the user changing straps, the user tightening strap  16 , a different user with a different wrist physiology wearing device  10 , water coming into contact with wrist  90  or device  10 , or any other variation in the operating environment of antenna  40 ). 
       FIG. 14  is a graph of illustrative antenna frequency responses that may be exhibited by an antenna when operating under different impedance matching circuit settings in accordance with an embodiment. In particular,  FIG. 14  plots antenna response (voltage standing wave ratio (VSWR)) as a function of operating frequency. As shown in  FIG. 14 , solid curve  270  represents the response of antenna  40  when operating under a first matching network setting and a first antenna loading condition. For example, curve  270  may be associated with a first user wearing device  10  while matching network  111  is set to the first setting. Antenna  40  may have a relatively high response for midband (MB) and high band (HB) frequencies but a relatively low and detuned response at low band (LB) frequencies. 
     Dashed curve  272  may represent the response of antenna  40  when operating under the first matching network setting and a second antenna loading condition. For example, curve  272  may be associated with a second user wearing device  10  while matching network  111  is set to the first setting. In this scenario, antenna  40  may have a relatively high response at low band frequencies (e.g., due to differing physiology between the first and second users loading antenna  40  differently). When the first user is wearing device  10 , processing circuitry  28  may detect the relatively low response of antenna  40  at the low band frequencies (e.g., using phase and magnitude measurements and/or RSSI values as in connection with step  150  of  FIG. 7 ). Processing circuitry  28  may subsequently adjust matching network  111  to a second setting that compensates for the difference in antenna loading resulting from the first user wearing device  10 . After adjusting matching network  111  to the second setting, antenna  40  may exhibit a similar response to curve  272  when device  10  is worn by the first user. If the first user were to give device  10  to the second user to wear, the response of antenna  40  may shift to the response illustrated by curve  270 . Processing circuitry  28  may detect this change and may subsequently adjust matching network  111  back to the first setting. After adjusting network  111  to the first setting, antenna  40  may exhibit a response as shown by curve  272 . In this way, processing circuitry  28  may actively adjust circuitry  111  to compensate for changes in antenna loading and detuning in real time. 
     The example of  FIG. 14  is merely illustrative. In general, antenna  40  may be operated in any desired number of different frequency bands and may have any desired response as a function of operating frequency. Antenna  40  may be detuned as a result of any change in environmental conditions. While the examples of  FIGS. 1-14  are described in connection with a wristwatch device, similar operations may be performed by any desired electronic device. 
     The operations of device  10  (e.g., the operations of  FIGS. 7-10 ) may be performed by control circuitry  28 . During operation, this control circuitry (which may sometimes be referred to as processing circuitry, processing and storage, computing equipment, a computer, etc.) may be configured to perform the methods of  FIGS. 7-10  and/or other operations (e.g., using dedicated hardware and/or using software code running on hardware such as control circuitry  28 ). Software code for performing these operations may be stored on non-transitory (tangible) computer readable storage media. The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, other computer readable media, or combinations of these computer readable media. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  28 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry. 
     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: 20170224
Publication Date: 20191119
Grant Date: 20191119
Priority Date: 20170224
Inventors: PASCOLINI, MATTIA
DA COSTA BRAS LIMA, EDUARDO JORGE
DI NALLO, CARLO
Ruaro, Andrea
Martinis, Mario
WANG, ZHEYU
NATH, JAYESH
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B17/318", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/385", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/273", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04G17/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/38", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q23/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/318", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/385", "inventive": false, "first": false, "tree": "[]"}, {"code": "G04G9/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/273", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/273", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/318", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/385", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/273", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 63112481