Patent Publication Number: US-10312593-B2

Title: Antennas for near-field and non-near-field communications

Description:
BACKGROUND 
     This relates to electronic devices, and more particularly, to antennas for electronic devices with wireless communications circuitry. 
     Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications circuitry such as wireless local area network communications circuitry to handle communications with nearby equipment. Electronic devices may also be provided with satellite navigation system receivers and other wireless circuitry such as near-field communications circuitry. Near-field communications schemes involve electromagnetically coupled communications over short distances, typically 20 cm or less. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna components using compact structures. At the same time, there is a desire for wireless devices to cover a growing number of communications bands. For example, it may be desirable for a wireless device to cover a near-field communications band while simultaneously covering additional non-near-field (far field) bands such cellular telephone bands, wireless local area network bands, and satellite navigation system bands. 
     Because antennas have the potential to interfere with each other and with components in a wireless device, care must be taken when incorporating antennas into an electronic device. Moreover, care must be taken to ensure that the antennas and wireless circuitry in a device are able to exhibit satisfactory performance over a range of operating frequencies. 
     It would therefore be desirable to be able to provide improved wireless communications circuitry for wireless electronic devices. 
     SUMMARY 
     An electronic device may be provided with wireless circuitry. The wireless circuitry may include antenna structures. 
     The antenna structures may be coupled to non-near-field communications circuitry such as cellular telephone transceiver circuitry and wireless local area network circuitry. When operated at non-near-field communication frequencies, the antenna structures may be configured to serve as one or more far-field antennas. As an example, the antenna structures may be configured to form one or more inverted-F antennas when operated at non-near-field communications frequencies such as frequencies above 700 MHz. 
     Proximity sensor circuitry and near-field communications circuitry may also be coupled to the antenna structures. When operated at proximity sensor frequencies such as frequencies of about 200 kHz, the antenna structures may be used in forming capacitive proximity sensor electrode structures. Low pass filter circuitry may be used to couple the proximity sensor circuitry to the antenna structures. 
     The antenna structures may include frequency-dependent antenna circuitry such as band pass filter circuitry, capacitors (high-pass filters), inductors (low pass filters), and other frequency-dependent circuits. The band pass filter circuitry may have a pass band that passes signals at near-field communications frequencies such as 13.56 MHz. At non-near-field communications frequencies, the antenna circuitry is configured to form the inverted-F antennas or other far-field antennas for supporting wireless local area network communications, cellular telephone communications, and other non-near-field wireless signals. 
     When operated at near-field communications frequencies, the band pass filters, low pass filters, capacitors, and other antenna circuitry may be configured to form open and closed circuits that cause the inverted-F antenna structures to form a near-field communications loop antenna while isolating the proximity sensor circuitry and non-near-field communications circuitry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a display for a computer or television in accordance with an embodiment. 
         FIG. 5  is a schematic diagram of illustrative circuitry in an electronic device in accordance with an embodiment. 
         FIG. 6  is a schematic diagram of illustrative wireless circuitry in accordance with an embodiment. 
         FIG. 7  is a diagram of an illustrative inverted-F antenna structure in accordance with an embodiment. 
         FIG. 8  is a top view of illustrative antenna structures in accordance with an embodiment. 
         FIG. 9  is a top view of substrates and other structures that may be used in forming the illustrative antenna structures of  FIG. 8  in accordance with an embodiment. 
         FIG. 10  is a top view of illustrative antenna structures that may be used to gather proximity sensor data in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with antenna structures. The antenna structures may include antennas for cellular telephone communications and/or other far-field (non-near-field) communications. Circuitry in the antenna structures may allow the antenna structures to form a near-field communications loop antenna to handle near-field communications. The antenna structures may also include structures that can be used to gather proximity sensor data. Illustrative electronic devices that may include antenna structures such as these are shown in  FIGS. 1, 2, 3, and 4 . 
     Electronic device  10  of  FIG. 1  has the shape of a laptop computer and has upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  has hinge structures  20  (sometimes referred to as a clutch barrel) to allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  is mounted in housing  12 A. Upper housing  12 A, which may sometimes be referred to as a display housing or lid, is placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows an illustrative configuration for electronic device  10  based on a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , device  10  has opposing front and rear surfaces. The rear surface of device  10  may be formed from a planar portion of housing  12 . Display  14  forms the front surface of device  10 . Display  14  may have an outermost layer that includes openings for components such as button  26  and speaker port  27 . 
     In the example of  FIG. 3 , electronic device  10  is a tablet computer. In electronic device  10  of  FIG. 3 , device  10  has opposing planar front and rear surfaces. The rear surface of device  10  is formed from a planar rear wall portion of housing  12 . Curved or planar sidewalls may run around the periphery of the planar rear wall and may extend vertically upwards. Display  14  is mounted on the front surface of device  10  in housing  12 . As shown in  FIG. 3 , display  14  has an outermost layer with an opening to accommodate button  26 . 
       FIG. 4  shows an illustrative configuration for electronic device  10  in which device  10  is a computer display, a computer that has an integrated computer display, or a television. Display  14  is mounted on a front face of device  10  in housing  12 . With this type of arrangement, housing  12  for device  10  may be mounted on a wall or may have an optional structure such as support stand  30  to support device  10  on a flat surface such as a tabletop or desk. 
     An electronic device such as electronic device  10  of  FIGS. 1, 2, 3, and 4 , may, in general, be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, 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. The examples of  FIGS. 1, 2, 3, and 4  are merely illustrative. 
     Device  10  may include a display such as display  14 . Display  14  may be mounted in housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     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 such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button, an opening may be formed in the display cover layer to accommodate a speaker port, etc. Display  14  may have an active area and an inactive area. For example, display  14  may have a rectangular central region that contains an array of display pixels that display images for a user. The active region may be surrounded by a peripheral border region that is inactive. The inactive border of the display does not contain display pixels and does not display images for a user. The display cover layer may cover the inactive border. To block interior components of device  10  from view, the inner surface of the display cover layer may be coated with an opaque masking material such as a layer of black ink in the inactive area. Antenna structures may be formed in portions of device  10  that lie beneath the inactive regions of display  14  to minimize interference between the antenna structures and conductive display structures. 
     Housing  12  may be formed from conductive materials and/or insulating materials. In configurations in which housing  12  is formed from plastic or other dielectric materials, antenna signals can pass through housing  12 . Antennas in this type of configuration can be mounted behind a portion of housing  12 . In configurations in which housing  12  is formed from a conductive material (e.g., metal), it may be desirable to provide one or more radio-transparent antenna windows in openings in the housing. As an example, a metal housing may have openings that are filled with plastic antenna windows. Antennas may be mounted behind the antenna windows and may transmit and/or receive antenna signals through the antenna windows. 
     A schematic diagram showing illustrative components that may be used in device  10  is shown in  FIG. 5 . As shown in  FIG. 5 , 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 may include touch screens, displays without touch sensor capabilities, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, etc. 
     Input-output circuitry  44  may include wireless communications circuitry  34  for communicating wirelessly with external equipment. Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, transmission lines, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include radio-frequency transceiver circuitry  90  for handling various radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  36 ,  38 , and  42 . 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 1710 to 2170 MHz, and a high band from 2300 to 2700 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  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. 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, etc. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless circuitry  34  may include near-field communications circuitry  120 . Near-field communications circuitry  120  may produce and receive near-field communications signals to support communications between device  10  and a near-field communications reader or other external near-field communications equipment. Near-field communications may be supported using loop antennas (e.g., to support inductive near-field communications in which a loop antenna in device  10  is electromagnetically near-field coupled to a corresponding loop antenna in a near-field communications reader). Near-field communications links typically are generally formed over distances of 20 cm or less (i.e., device  10  must be placed in the vicinity of the near-field communications reader for effective communications). 
     Wireless communications 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, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. In addition to supporting cellular telephone communications, wireless local area network communications, and other far-field wireless communications, the structures of antennas  40  may be used in supporting near-field communications. The structures of antennas  40  may also be used in gathering proximity sensor signals (e.g., capacitive proximity sensor signals). 
     Radio-frequency transceiver circuitry  90  does not handle near-field communications signals and is therefore sometimes referred to as far field communications circuitry or non-near-field communications circuitry. Near-field communications transceiver circuitry  120  may be used in handling near-field communications. With one suitable arrangement, near-field communications can be supported using signals at a frequency of 13.56 MHz. Other near-field communications bands may be supported using the structures of antennas  40  if desired. Transceiver circuitry  90  may handle non-near-field communications frequencies (e.g., frequencies above 700 MHz or other suitable frequency). 
     As shown in  FIG. 6 , non-near-field transceiver circuitry  90  in wireless circuitry  34  may be coupled to antenna structures  40  using paths such as path  92 . Near-field communications transceiver circuitry  120  may be coupled to antenna structures  40  using paths such as path  132 . Paths such as path  134  may be used to allow control circuitry  28  to transmit near-field communications data and to receive near-field communications data using a near-field communications antenna formed from structures  40 . Proximity sensor circuitry  122  may use antenna structures  40  as capacitive proximity sensor electrodes to gather proximity sensor data (i.e., capacitive proximity sensor data indicating whether or not external objects are in the vicinity of device  10 ). Proximity sensor data may be conveyed from proximity sensor circuitry  122  to control circuitry  28  using paths such as path  136 . Proximity sensor data may be used to adjust wireless transmit powers (e.g., to reduce transmit powers for wireless signals being transmitted by transceiver circuitry  90 ) when external objects are detected in the vicinity of device  10  or to make other wireless circuitry adjustments. 
     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 impedance matching circuitry, filters, and other antenna circuitry. This circuitry may include fixed and tunable circuits. Discrete components such as capacitors, inductors, and resistors may be incorporated into the antenna 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  102  to tune antennas over communications bands of interest. Tunable components  102  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. For example, tunable components  102  may include one or more adjustable capacitors (e.g., a programmable capacitor that can produce one of multiple different capacitance values by adjusting switching circuitry), one or more adjustable inductors (e.g., an adjustable inductor circuit having a multiplexer or other adjustable switching circuitry that allows a desired inductor value to be selected from multiple different available inductor values), or other adjustable components. 
     During operation of device  10 , control circuitry  28  may issue control signals on one or more paths such as path  103  that adjust inductance values, capacitance values, or other parameters associated with tunable components  102 , thereby tuning antenna structures  40  to cover desired communications bands. Active and/or passive components may also be used to allow antenna structures  40  to be shared between non-near-field-communications transceiver circuitry  90 , near-field communications transceiver circuitry  120 , and proximity sensor circuitry  122 . 
     Path  92  may include one or more transmission lines. As an example, signal path  92  of  FIG. 6  may be a transmission line having a positive signal conductor such as line  94  and a ground signal conductor such as line  96 . Lines  94  and  96  may form parts of a coaxial cable 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  92 . Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. Components such as these may also be used in forming filter circuitry and other antenna circuitry in antenna structures  40 . 
     Transmission line  92  may be directly coupled to an antenna resonating element and ground for antenna  40  or may be coupled to indirect-feed antenna feed structures that are used in indirectly feeding a resonating element for antenna  40 . As an example, antenna structures  40  may form an inverted-F antenna, a slot antenna, a hybrid inverted-F slot antenna or other antenna having an antenna feed with a positive antenna feed terminal such as terminal  98  and a ground antenna feed terminal such as ground antenna feed terminal  100 . Positive transmission line conductor  94  may be coupled to positive antenna feed terminal  98  and ground transmission line conductor  96  may be coupled to ground antenna feed terminal  92 . As another example, antenna structures  40  may include an antenna resonating element such as a slot antenna resonating element or other element that is indirectly fed. In a indirect feeding arrangements, transmission line  92  is coupled to an antenna feed structure that is used to indirectly feed antenna structures such as an antenna slot or other element through electromagnetic near-field coupling. 
     Antennas  40  may include slot antenna structures, inverted-F antenna structures (e.g., planar and non-planar inverted-F antenna structures), loop antenna structures, or other antenna structures. 
     An illustrative inverted-F antenna structure is shown in  FIG. 7 . Inverted-F antenna structure  140  of  FIG. 7  has antenna resonating element  106  and antenna ground (ground plane)  104 . Antenna resonating element  106  may have a main resonating element arm such as arm  108 . The length of arm  108  may be selected so that antenna structure  140  resonates at desired operating frequencies. For example, the length of arm  108  may be a quarter of a wavelength at a desired operating frequency for antenna  40 . Antenna structure  140  may also exhibit resonances at harmonic frequencies. 
     Main resonating element arm  108  may be coupled to ground  104  by return path  110 . Antenna feed  112  may include positive antenna feed terminal  98  and ground antenna feed terminal  100  and may run in parallel to return path  110  between arm  108  and ground  104 . If desired, inverted-F antenna structures such as illustrative antenna structure  140  of  FIG. 7  may have more than one resonating arm branch (e.g., to create multiple frequency resonances to support operations in multiple communications bands) or may have other antenna structures (e.g., parasitic antenna resonating elements, tunable components to support antenna tuning, etc.). A planar inverted-F antenna (PIFA) may be formed by implementing arm  108  using planar structures (e.g., a planar metal structure such as a metal patch or strip of metal that extends into the page of  FIG. 7 ). Antennas such as inverted-F antenna  40  of  FIG. 7  may have adjustable circuits such as circuit  126  (sometimes referred to as matching circuits). Circuit  126  may be coupled in path  124  between resonating element arm  108  and ground  104 . Adjustments to circuit  126  may be used to adjust the performance of antenna  40  (e.g., the frequency response of antenna  40 ). Antenna circuitry such as illustrative circuit  126  of  FIG. 7  may include tunable components such as components  102  of  FIG. 6 . 
     Device  10  may include one or more antennas. A top view of an illustrative portion of device  10  that contains two antennas is shown in  FIG. 8 . Antennas  40 A and  40 B may be located in an inactive portion of the display in device  10  such as inactive area IA. A display module or other active display portion for the display may be located in region  14 ′. Ground plane  104  may be formed from peripheral conductive structures on housing  12 , housing walls, a midplate internal housing member, and/or other conductive structures in device  10 . Ground plane  104  may serve as an antenna ground for multiple antennas such as antennas  40 A and  40 B. 
     Antenna  40 A has feed  112 A with positive feed terminal  98 A and ground feed terminal  100 A, resonating element arm  108 A, return path  110 A, and matching circuit path  124 A coupled between arm  108 A and ground  104 . Capacitor C 1  may be interposed in path  112 A. Capacitor C 2  and matching circuit M 1  or other antenna circuitry may be interposed in path  124 A. Circuit M 1  may be adjustable (e.g., circuit M 1  may include tunable components  102  of  FIG. 6 ). 
     A filter circuit such as a circuit based on inductor L 1  (e.g., an inductor having a value of about 80 nH to 200 nH) or other suitable circuit may couple arm  108 A of antenna  40 A and arm  108 B of antenna  40 B. This circuit may serve as a low-pass circuit. If desired, other types of filter circuitry may be incorporated into the antenna structures in the position occupied by inductor L 1 . 
     Antenna  40 B may include antenna feed path  112 B with positive feed terminal  98 B and ground feed terminal  100 B, return path  110 B, and matching circuit path  124 B. Capacitor C 5  may be interposed in path  112 B. Capacitor C 4  may be interposed in path  110 B. Matching circuit M 2  or other antenna circuitry and capacitor C 3  may be interposed in path  124 B. Circuit M 2  may include tunable circuitry such as components  102  of  FIG. 6 . A filter such as a frequency-dependent circuit based on inductor L 2  (e.g., an inductor having a value of 80 nH to 200 nH) or other suitable frequency-dependent circuit may couple arm  108 B of antenna  40 B to near-field communications circuitry  140 . 
     Near-field communications circuitry  140  may include near-field communications transceiver  120 , a matching circuit such as matching circuit  130 , and a balun such as balun  128 . Balun  128  may be used to convert differential near-field communications signals on path  142  to single-ended near-field communications signals on path  144 . Other types of near-field communications circuits may be used in handling near-field communications signals for device  10  if desired. 
     Antennas  40 A and  40 B are inverted-F antennas. Radio-frequency transceiver circuitry  90  is coupled to antennas  40 A and  40 B at feeds  112 A and  112 B (e.g., using respective transmission lines). During operation of circuitry  90 , antennas  40 A and  40 B may serve as a primary and secondary antenna in a two-antenna system. Switching circuitry in device  10  can switch between antennas  40 A and  40 B to switch an optimum antenna into use in real time (e.g., based on receive signal strength information, based on proximity sensor data, etc.). The frequencies of the signals associated with transceiver circuitry  90  are typically 700 MHz or greater. At these frequencies, inductor L 1  forms an open circuit that electrically isolates arm  108 A from arm  108 B and inductor L 2  forms an open circuit to isolate antenna  40 B from near-field communications circuitry  140 . Capacitors C 1 , C 2 , C 3 , C 4 , and C 5  (e.g., capacitors with values of about 20-30 pF) form short circuits at these frequencies, so that antennas  40 A and  40 B serve as inverted-F antennas for transceiver circuitry  90 . Near-field communications circuitry  140  may operate at lower frequencies (e.g., at 13.56 MHz). At near-field communications frequencies, capacitors C 1 , C 2 , C 3 , C 4 , and C 5  form open circuits, isolating the paths containing these capacitors from near-field communications signal currents. Inductors L 1  and L 2  form short circuits at near-field communications frequencies, so near-field communications signal currents such as illustrative near-field communications current I can flow through a loop antenna formed from portions of antennas  40 A and  40 B. Current I may, for example, flow in a loop through arm  108 B of antenna  40 B, arm  108 A of antenna  40 A, return path  110 A of antenna  40 A, and ground  104 . 
     As this example demonstrates, antenna structures  40  of  FIG. 8  can serve both as a non-near-field communications antenna structures (i.e., inverted-F antenna  40 A and inverted-F antenna  40 B) and as near-field communications antenna structures (i.e., a loop antenna formed from portions of antennas  40 A and  40 B). The ability to share antenna structures  40  between both near-field and non-near-field functions allows the size of antenna structures  40  to be minimized and avoids duplication of antenna parts. 
       FIG. 9  is a top view of a portion of device  10  showing illustrative components that may be used in implementing antenna structures such as antenna structures  40  of  FIG. 8 . As shown in the example of  FIG. 9 , device  10  may have a first antenna substrate such as substrate  170  for forming portions of antenna  40 A (e.g., resonating element arm  108 A, etc.) and may have a second antenna substrate such as substrate  172  for forming portions of antenna  40 B (e.g., resonating element arm  108 B). Substrates  170  and  172  may be printed circuits, plastic carriers, or other antenna support structures carrying patterned metal traces or other conductive antenna structures. Components such as components  162  and  166  (e.g., strips of flexible printed circuit material populated with electrical devices such as capacitor C 2 , matching circuit M 1 , capacitor C 3 , and matching circuit M 2 ) may be used to couple traces on substrates  170  and  172  (e.g., arms  108 A and  108 B) to ground  104 . Substrate  164  may carry an inductor such as inductor L 1  or other filter circuit and may be used to couple substrate  170  to substrate  172 . Component  168  may be an inductor other filter circuit that couples substrate  172  to path  144 . If desired, fewer substrates or more substrates may be used in implementing antennas  40 A and  40 B. For example, a single substrate may carry metal traces and components for both antennas  40 A and  40 B, one or more additional substrates may be used in forming antenna structures  40 , etc. The example of  FIG. 9  is merely illustrative. 
     Antennas  40 A and  40 B may be separated by region  150 . Components may be formed in region  150  such as component  152  (e.g., a camera on a flexible printed circuit), component  154  (e.g., a microphone on a flexible printed circuit), and component  156  (e.g., a monopole satellite navigation system antenna that is fed using antenna feed terminals  158  and  160 ). Flexible printed circuits can be coupled using hot-barred solder connections or other suitable conductive attachment mechanisms. If desired, the portions of device  10  above and below antenna structures  40  may be dielectric structures so that antenna structures  40  can be used for near-field communications (and non-near-field communications) through both the front and rear of device  10  (as an example). 
     The diagram of  FIG. 10  shows how proximity sensor circuitry may be incorporated into antenna structures  40 . As shown in  FIG. 10 , a proximity sensor for device  10  may be formed from a structure such as proximity sensor flex  174  and metal arm  108 B in antenna  40 B. Proximity sensor flex  174  may be a flexible printed circuit or other printed circuit that contains metal traces for forming proximity sensor electrode structures. Arm  108 B may serve as a portion of antenna  40 B and may also form a proximity sensor structure (e.g., a capacitive proximity sensor electrode, a shield layer, etc.). Proximity sensor structure  174  may be coupled to proximity sensor circuitry  122  by low-pass filter  176  and path  180 . The proximity sensor structure formed from antenna resonating element arm  108 B of antenna  40 B may be coupled to proximity sensor circuitry  122  by low pass filter  178  and path  182 . Proximity sensor circuitry  122  may operate at a proximity sensor frequency below that used for near-field communications circuitry  140 . As an example, proximity sensor circuitry  122  may operate at a frequency of about 200 kHz. 
     Antenna resonating element arm  108 A of antenna  40 A may be coupled to an end of antenna resonating element arm  108 B of antenna  40 B by band pass filter BPF 1 . Band pass filter BPF 2  may be used to couple an opposing end of antenna resonating element arm  108 B to near-field communications signal path  144 . Band pass filters BPF 1  and BPF 2  may each have a pass band that is centered on near-field communications frequencies (e.g., these filters may be short circuits at 13.56 MHz) and may be configured to form open circuits and thereby block signals below or above this frequency range. This allows band pass filters BPF 1  and BPF 2  to form closed circuits for forming an NFC antenna at NFC frequencies, while forming open circuits at proximity sensor frequencies associated with proximity sensor circuitry  122  and at non-near-field communications frequencies associated with transceiver circuitry  90 . 
     Non-near-field communications circuitry  90  may have a first transmission line coupled to feed  112 A and a second transmission line coupled to feed  112 B. When operating at non-near-field communications frequencies (i.e., frequencies above 700 MHz), band pass filter BPF 2  will be an open circuit and will isolate arm  108 B from path  144 . Band pass filter BPF 1  will be an open circuit and will isolate arm  108 A from arm  108 B, thereby isolating antennas  40 A and  40 B from each other. Capacitors C 1 , C 2 , C 3 , C 4 , and C 5  form short circuits that configure antenna structures  40  into inverted-F antenna  40 A and inverted-F antenna  40 B. Low pass filters  176  and  178  are open circuits at frequencies above 700 MHz, so proximity sensor circuitry  122  is isolated from antennas  40 A and  40 B. The use of filters BPF 1 , BPF 2 , LPF  176 , and LPF  178 , and the filter circuitry formed from capacitors C 1 , C 2 , C 3 , C 4 , and C 5  therefore allows antennas  40 A and  40 B to be used to handle cellular telephone communications, wireless local area network communications, optional satellite navigation system communications, etc. 
     At low frequencies associated with proximity sensor circuitry  122  (e.g., at 200 kHz or other frequency below the near-field communications frequency of 13.56 MHz), low pass filters  176  and  178  form short circuits. This electrically couples proximity sensor circuitry  122  to capacitive proximity sensor electrodes  174  and  108 B. Band pass filters BPF 1  and BPF 2  and capacitors C 1 , C 2 , C 3 , C 4 , and C 5  are open circuits at proximity sensor signal frequencies, so when proximity sensor circuitry  122  is being used to gather capacitive proximity sensor signals, only structures  174  and  108 B are being used by proximity sensor circuitry  122 . The other portions of antenna structures  40  are electrically isolated from structures  174  and  108 B. Structures  174  and  108 B may be located near the periphery of device  10  and are preferably configured to serve as proximity sensor electrodes when electrically disconnected from near-field communications circuitry  140  and the portions of antenna structures  40  other than structure  108 B. 
     At near-field communications frequencies, low pass filters  176  and  178  are open circuits, which isolates proximity sensor circuitry  122  from antenna structures  40 . Capacitors C 1 , C 2 , C 3 , C 4 , and C 5  are open circuits and band pass filters BPF 1  and BPF 2  are short circuits. This configures antenna structures  40  to serve as a near-field communications loop antenna. As described in connection with  FIG. 8 , near-field communications antenna loop currents flow from near-field communications path  144  through band-pass filter BPF 2 , through antenna resonating element arm  108 B, through band pass filter BPF 1 , through arm  108 A, through return path  110 A, and through ground  104 . At near-field communications frequencies, structures  40  therefore serve as a near-field communications loop antenna for handling signals transmitted and received by near-field communications transceiver  120 , rather than serving as inverted-F antennas  40 A and  40 B for handling non-near-field communications signals. 
     The example of  FIG. 10  shows how antenna structures  40  can form proximity sensor electrodes at low frequencies, a near-field communications antenna at medium frequencies, and non-near-field communications antenna(s) at high frequencies. Other types of shared antenna structures and associated filter circuits may be used in supporting proximity sensing, NFC communications, and non-NFC communications if desired. The example of  FIG. 10  is merely illustrative. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.