Patent Publication Number: US-10320069-B2

Title: Electronic device antennas having distributed capacitances

Description:
BACKGROUND 
     This relates generally 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 circuitry for electronic devices. 
     SUMMARY 
     An electronic device may be provided with wireless circuitry and control circuitry. The wireless circuitry may include multiple antennas and transceiver circuitry. The antennas may include antenna structures at opposing first and second ends of the electronic device. The antenna structures at a given end of the device may include adjustable components that are adjusted by the control circuitry to place the antenna structures and the electronic device in one of a number of different operating modes or states. 
     An antenna in the electronic device may have an inverted-F antenna resonating element formed from portions of a peripheral conductive electronic device housing structure and may have an antenna ground that is separated from the antenna resonating element by a gap. A short circuit path may bridge the gap. An antenna feed may be coupled across the gap in parallel with the short circuit path. 
     The antenna ground for the antenna may include a first conductive structure that is separated from the inverted-F antenna resonating element by a first distance and a second conductive structure that is electrically connected to the first conductive structure and separated from the inverted-F antenna resonating element by a second distance that is less than the first distance. A distributed impedance matching capacitor for the antenna may be formed from the second conductive structure and the antenna resonating element arm. 
     The first conductive structure may be a planar conductive layer that extends between the first and second sidewalls of the electronic device housing. The second conductive structure may be a conductive frame for an electronic component such as a sensor. The electronic component may be interposed between lower and upper portions of the conductive frame. A conductive spring may electrically connect the lower portion of the conductive frame to the planar conductive layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of illustrative circuitry in an electronic device in accordance with an embodiment. 
         FIG. 3  is a diagram of illustrative wireless circuitry in accordance with an embodiment. 
         FIG. 4  is a diagram of an illustrative inverted-F antenna in accordance with an embodiment. 
         FIG. 5  is a top view of an illustrative electronic device having an inverted-F antenna with a distributed capacitance in accordance with an embodiment. 
         FIG. 6  is a top view of an illustrative electronic device showing how a distributed capacitance of the type shown in  FIG. 5  may be formed between an antenna ground and an antenna resonating element in accordance with an embodiment. 
         FIGS. 7 and 8  are cross-sectional side views of an illustrative electronic device showing how a distributed capacitance of the type shown in  FIG. 5  may be formed between an antenna ground and an antenna resonating element in accordance with an embodiment. 
         FIG. 9  is a graph of antenna performance (antenna efficiency) as a function of frequency for an antenna of the type shown in  FIGS. 5-8  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. 
     The wireless communications circuitry may include one more antennas. The antennas of the wireless communications circuitry can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures. 
     The conductive electronic device structures may include conductive housing structures. The housing structures may include peripheral structures such as peripheral conductive structures that run around the periphery of an electronic device. The peripheral conductive structures may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, may have portions that extend upwards from an integral planar rear housing (e.g., to form vertical planar sidewalls or curved sidewalls), and/or may form other housing structures. 
     Gaps may be formed in the peripheral conductive structures that divide the peripheral conductive structures into peripheral segments. One or more of the segments may be used in forming one or more antennas for electronic device  10 . Antennas may also be formed using an antenna ground plane and/or an antenna resonating element formed from conductive housing structures (e.g., internal and/or external structures, support plate structures, etc.). 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a handheld device such as a cellular telephone, a media player, or other small portable device. Device  10  may also be a set-top box, a desktop computer, a display into which a computer or other processing circuitry has been integrated, a display without an integrated computer, or other suitable electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material (e.g., glass, ceramic, plastic, sapphire, etc.). In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may be mounted on the front face of device  10 . Display  14  may be a touch screen that incorporates capacitive touch electrodes or may be insensitive to touch. The rear face of housing  12  (i.e., the face of device  10  opposing the front face of device  10 ) may have a planar housing wall. The rear housing wall may have slots that pass entirely through the rear housing wall and that therefore separate housing wall portions (and/or sidewall portions) of housing  12  from each other. The rear housing wall may include conductive portions and/or dielectric portions. If desired, the rear housing wall may include a planar metal layer covered by a thin layer or coating of dielectric such as glass, plastic, sapphire, or ceramic. Housing  12  (e.g., the rear housing wall, sidewalls, etc.) may also have shallow grooves that do not pass entirely through housing  12 . The slots and grooves may be filled with plastic or other dielectric. If desired, portions of housing  12  that have been separated from each other (e.g., by a through slot) may be joined by internal conductive structures (e.g., sheet metal or other metal members that bridge the slot). 
     Display  14  may include pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable pixel structures. A display cover layer such as a layer of clear glass or plastic may cover the surface of display  14  or the outermost layer of display  14  may be formed from a color filter layer, thin-film transistor layer, or other display layer. Buttons such as button  24  may pass through openings in the cover layer if desired. The cover layer may also have other openings such as an opening for speaker port  26 . 
     Housing  12  may include peripheral housing structures such as structures  16 . Structures  16  may run around the periphery of device  10  and display  14 . In configurations in which device  10  and display  14  have a rectangular shape with four edges, structures  16  may be implemented using peripheral housing structures that have a rectangular ring shape with four corresponding edges (as an example). Peripheral structures  16  or part of peripheral structures  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or that helps hold display  14  to device  10 ). Peripheral structures  16  may, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls, curved sidewalls, etc.). 
     Peripheral housing structures  16  may be formed of a conductive material such as metal and may therefore sometimes be referred to as peripheral conductive housing structures, conductive housing structures, peripheral metal structures, or a peripheral conductive housing member (as examples). Peripheral housing structures  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming peripheral housing structures  16 . 
     It is not necessary for peripheral housing structures  16  to have a uniform cross-section. For example, the top portion of peripheral housing structures  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. The bottom portion of peripheral housing structures  16  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). Peripheral housing structures  16  may have substantially straight vertical sidewalls, may have sidewalls that are curved, or may have other suitable shapes. In some configurations (e.g., when peripheral housing structures  16  serve as a bezel for display  14 ), peripheral housing structures  16  may run around the lip of housing  12  (i.e., peripheral housing structures  16  may cover only the edge of housing  12  that surrounds display  14  and not the rest of the sidewalls of housing  12 ). 
     If desired, housing  12  may have a conductive rear surface or wall. For example, housing  12  may be formed from a metal such as stainless steel or aluminum. The rear surface of housing  12  may lie in a plane that is parallel to display  14 . In configurations for device  10  in which the rear surface of housing  12  is formed from metal, it may be desirable to form parts of peripheral conductive housing structures  16  as integral portions of the housing structures forming the rear surface of housing  12 . For example, a rear housing wall of device  10  may be formed from a planar metal structure and portions of peripheral housing structures  16  on the sides of housing  12  may be formed as flat or curved vertically extending integral metal portions of the planar metal structure. Housing structures such as these may, if desired, be machined from a block of metal and/or may include multiple metal pieces that are assembled together to form housing  12 . The planar rear wall of housing  12  may have one or more, two or more, or three or more portions. Peripheral conductive housing structures  16  and/or the conductive rear wall of housing  12  may form one or more exterior surfaces of device  10  (e.g., surfaces that are visible to a user of device  10 ) and/or may be implemented using internal structures that do not form exterior surfaces of device  10  (e.g., conductive housing structures that are not visible to a user of device  10  such as conductive structures that are covered with layers such as thin cosmetic layers, protective coatings, and/or other coating layers that may include dielectric materials such as glass, ceramic, plastic, or other structures that form the exterior surfaces of device  10  and/or serve to hide structures  16  from view of the user). 
     Display  14  may have an array of pixels that form an active area AA that displays images for a user of device  10 . An inactive border region such as inactive area IA may run along one or more of the peripheral edges of active area AA. 
     Display  14  may include conductive structures such as an array of capacitive electrodes for a touch sensor, conductive lines for addressing pixels, driver circuits, etc. Housing  12  may include internal conductive structures such as metal frame members and a planar conductive housing member (sometimes referred to as a backplate) that spans the walls of housing  12  (i.e., a substantially rectangular sheet formed from one or more metal parts that is welded or otherwise connected between opposing sides of member  16 ). The backplate may form an exterior rear surface of device  10  or may be covered by layers such as thin cosmetic layers, protective coatings, and/or other coatings that may include dielectric materials such as glass, ceramic, plastic, or other structures that form the exterior surfaces of device  10  and/or serve to hide the backplate from view of the user. Device  10  may also include conductive structures such as printed circuit boards, components mounted on printed circuit boards, and other internal conductive structures. These conductive structures, which may be used in forming a ground plane in device  10 , may extend under active area AA of display  14 , for example. 
     In regions  22  and  20 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive housing structures  16  and opposing conductive ground structures such as conductive portions of housing  12 , conductive traces on a printed circuit board, conductive electrical components in display  14 , etc.). These openings, which may sometimes be referred to as gaps, may be filled with air, plastic, and/or other dielectrics and may be used in forming slot antenna resonating elements for one or more antennas in device  10 , if desired. 
     Conductive housing structures and other conductive structures in device  10  may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, may contribute to the performance of a parasitic antenna resonating element, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . If desired, the ground plane that is under active area AA of display  14  and/or other metal structures in device  10  may have portions that extend into parts of the ends of device  10  (e.g., the ground may extend towards the dielectric-filled openings in regions  20  and  22 ), thereby narrowing the slots in regions  20  and  22 . 
     In general, device  10  may include any suitable number of antennas (e.g., one or more, two or more, three or more, four or more, etc.). The antennas in device  10  may be located at opposing first and second ends of an elongated device housing (e.g., at ends  20  and  22  of device  10  of  FIG. 1 ), along one or more edges of a device housing, in the center of a device housing, in other suitable locations, or in one or more of these locations. The arrangement of  FIG. 1  is merely illustrative. 
     Portions of peripheral housing structures  16  may be provided with peripheral gap structures. For example, peripheral conductive housing structures  16  may be provided with one or more peripheral gaps such as gaps  18 , as shown in  FIG. 1 . The gaps in peripheral housing structures  16  may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  18  may divide peripheral housing structures  16  into one or more peripheral conductive segments. There may be, for example, two peripheral conductive segments in peripheral housing structures  16  (e.g., in an arrangement with two of gaps  18 ), three peripheral conductive segments (e.g., in an arrangement with three of gaps  18 ), four peripheral conductive segments (e.g., in an arrangement with four of gaps  18 , etc.). The segments of peripheral conductive housing structures  16  that are formed in this way may form parts of antennas in device  10 . 
     If desired, openings in housing  12  such as grooves that extend partway or completely through housing  12  may extend across the width of the rear wall of housing  12  and may penetrate through the rear wall of housing  12  to divide the rear wall into different portions. These grooves may also extend into peripheral housing structures  16  and may form antenna slots, gaps  18 , and other structures in device  10 . Polymer or other dielectric may fill these grooves and other housing openings. In some situations, housing openings that form antenna slots and other structure may be filled with a dielectric such as air. 
     In a typical scenario, device  10  may have one or more upper antennas and one or more lower antennas (as an example). An upper antenna may, for example, be formed at the upper end of device  10  in region  22 . A lower antenna may, for example, be formed at the lower end of device  10  in region  20 . The antennas may be used separately to cover identical communications bands, overlapping communications bands, or separate communications bands. The antennas may be used to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. 
     Antennas in device  10  may be used to support any communications bands of interest. For example, device  10  may include antenna structures for supporting local area network communications, voice and data cellular telephone communications, global positioning system (GPS) communications or other satellite navigation system communications, Bluetooth® communications, etc. 
     A schematic diagram showing illustrative components that may be used in device  10  of  FIG. 1  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, multiple-input and multiple-output (MIMO) protocols, antenna diversity protocols, etc. 
     Input-output circuitry  30  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, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, position and orientation sensors (e.g., sensors such as accelerometers, gyroscopes, and compasses), capacitance sensors, proximity sensors (e.g., capacitive proximity sensors, light-based proximity sensors, etc.), fingerprint sensors (e.g., a fingerprint sensor integrated with a button such as button  24  of  FIG. 1  or a fingerprint sensor that takes the place of button  24 ), etc. 
     Input-output circuitry  30  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 handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in frequency ranges such as a low communications band from 700 to 960 MHz, a low-midband from 960 to 1710 MHz, a midband from 1710 to 2170 MHz, a high band from 2300 to 2700 MHz, an ultra-high band from 3400 to 3700 MHz or other communications bands between 600 MHz and 4000 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) circuitry, etc. Wireless communications circuitry  34  may include global positioning system (GPS) receiver equipment such as 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 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, dipole antenna structures, monopole antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     As shown in  FIG. 3 , transceiver circuitry  90  in wireless circuitry  34  may be coupled to antenna structures  40  using paths such as path  92 . 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 such as antenna(s)  40  with the ability to cover communications frequencies of interest, antenna(s)  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(s)  40  may be provided with adjustable circuits such as tunable components  102  to tune antennas over communications bands of interest. Tunable components  102  may be part of a tunable filter or tunable impedance matching network, may be part of an antenna resonating element, may span a gap between an antenna resonating element and antenna ground, etc. 
     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. 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. 
     Path  92  may include one or more transmission lines. As an example, signal path  92  of  FIG. 3  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, a stripline transmission line, or a microstrip transmission line (as examples). A matching network (e.g., an adjustable matching network formed using tunable components  102 ) may include components such as inductors, resistors, and capacitors used in matching the impedance of antenna(s)  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 in antenna(s)  40  and may be tunable and/or fixed components. 
     Transmission line  92  may be coupled to antenna feed structures associated with antenna structures  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  112  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  100 . Other types of antenna feed arrangements may be used if desired. For example, antenna structures  40  may be fed using multiple feeds. The illustrative feeding configuration of  FIG. 3  is merely illustrative. 
     Control circuitry  28  may use information from a proximity sensor (see, e.g., sensors  32  of  FIG. 2 ), wireless performance metric data such as received signal strength information, device orientation information from an orientation sensor, device motion data from an accelerometer or other motion detecting sensor, information about a usage scenario of device  10 , information about whether audio is being played through speaker  26 , information from one or more antenna impedance sensors, and/or other information in determining when antenna(s)  40  is being affected by the presence of nearby external objects or is otherwise in need of tuning. In response, control circuitry  28  may adjust an adjustable inductor, adjustable capacitor, switch, or other tunable component  102  to ensure that antenna structures  40  operate as desired. Adjustments to component  102  may also be made to extend the coverage of antenna structures  40  (e.g., to cover desired communications bands that extend over a range of frequencies larger than antenna structures  40  would cover without tuning). 
     Antennas  40  may include slot antenna structures, inverted-F antenna structures (e.g., planar and non-planar inverted-F antenna structures), loop antenna structures, combinations of these, or other antenna structures. 
     An illustrative inverted-F antenna structure is shown in  FIG. 4 . As shown in  FIG. 4 , inverted-F antenna structure  40  (sometimes referred to herein as antenna  40  or inverted-F antenna  40 ) may include an inverted-F antenna resonating element such as antenna resonating element  106  and an antenna ground (ground plane) such as antenna ground  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  40  resonates at desired operating frequencies. For example, the length of arm  108  (or a branch of arm  108 ) may be a quarter of a wavelength at a desired operating frequency for antenna  40 . Antenna structure  40  may also exhibit resonances at harmonic frequencies. If desired, slot antenna structures or other antenna structures may be incorporated into an inverted-F antenna such as antenna  40  of  FIG. 4  (e.g., to enhance antenna response in one or more communications bands). As an example, a slot antenna structure may be formed between arm  108  or other portions of resonating element  106  and ground  104 . In these scenarios, antenna  40  may include both slot antenna and inverted-F antenna structures and may sometimes be referred to as a hybrid inverted-F and slot antenna. 
     Arm  108  may be separated from ground  104  by a dielectric-filled opening such as dielectric gap  101 . Antenna ground  104  may be formed from housing structures such as a conductive support plate, printed circuit traces, conductive portions of a display, metal portions of electronic components, or other conductive ground structures. Gap  101  may be formed by air, plastic, and/or other dielectric materials. 
     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 parallel to return path  110  between arm  108  and ground  104 . If desired, inverted-F antenna structures such as illustrative antenna structure  40  of  FIG. 4  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.). Arm  108  may have other shapes and may follow any desired path if desired (e.g., paths having curved and/or straight segments). 
     If desired, antenna  40  may include one or more adjustable circuits (e.g., tunable components  102  of  FIG. 3 ) that are coupled to antenna resonating element structures  106  such as arm  108 . As shown in  FIG. 4 , for example, tunable components  102  such as adjustable inductor  114  may be coupled between antenna resonating element arm structures in antenna  40  such as arm  108  and antenna ground  104  (e.g., adjustable inductor  114  may bridge gap  101 ). Adjustable inductor  114  may exhibit an inductance value that is adjusted in response to control signals  116  provided to adjustable inductor  114  from control circuitry  28 . 
     A top interior view of an illustrative portion of device  10  that contains antennas is shown in  FIG. 5 . As shown in  FIG. 5 , device  10  may have peripheral conductive housing structures such as peripheral conductive housing structures  16 . Peripheral conductive housing structures  16  may be divided by dielectric-filled peripheral gaps (e.g., plastic gaps)  18  such as gaps  18 - 1  and  18 - 2 . Antenna  40  may include a resonating element and ground  104 . In the example of  FIG. 5 , the resonating element may include an inverted-F antenna resonating element arm such as arm  108  that is formed from a segment of peripheral conductive housing structures  16  extending between gaps  18 - 1  and  18 - 2 . Air and/or other dielectric may fill slot  101  between arm  108  and ground structures  104 . If desired, opening  101  may be configured to form a slot antenna resonating element structure that contributes to the overall performance of the antenna. Antenna ground  104  may be formed from conductive housing structures, from electrical device components in device  10 , from printed circuit board traces, from strips of conductor such as strips of wire and metal foil, or other conductive structures. In one suitable arrangement ground  104  has portions formed from conductive portions of housing  12  (e.g., portions of a rear wall of housing  12  and portions of peripheral conductive housing structures  16  that are separated from arm  108  by peripheral gaps  18 - 1  and  18 - 2 ). Antenna ground  104  may also have portions formed by portions of display  14  (e.g., conductive portions of a display panel, a conductive plate for supporting the display panel, and/or a conductive frame for supporting the conductive plate and/or the display panel). 
     If desired, opening  101  may contribute slot antenna resonances in one or more frequency bands for antenna  40 . Antenna  40  may sometimes be referred to herein as an inverted-F antenna or a hybrid inverted-F slot antenna (e.g., because slot  101  may contribute to the frequency response of antenna  40 ). 
     Ground  104  may serve as antenna ground for one or more antennas. For example, inverted-F antenna  40  may include resonating element arm  108  and ground  104 , whereas another antenna (e.g., a wireless local area network and/or ultra-high band antenna) may be formed from a separate resonating element in region  206  and ground  104 . Inverted-F antenna  40  may be fed using an antenna feed such as feed  112  having positive feed terminal  98  coupled to peripheral conductive housing structures  16  and ground feed terminal  100  coupled to antenna ground  104 . Positive transmission line conductor  94  and ground transmission line conductor  96  may form transmission line  92  coupled between transceiver circuitry  90  and antenna feed  112 . 
     Antenna feed  112  may be coupled across slot  101  at a location along antenna ground  104  that is within a distributed capacitance region  230 . In the distributed capacitance region, antenna ground  104  may be separated from peripheral conductive structures  16  by distances  238  and  240 . Distances  238  and  240  may, for example, be selected so that a desired distributed capacitance is formed between ground  104  and peripheral conductive housing structures  16  around feed  112 . The distributed capacitance may be selected to ensure that antenna  40  is impedance matched to transmission line  92 , for example. The distributed capacitance region  230  may be surrounded by two regions where ground plane  104  is separated from peripheral conductive housing structures  16  by distance  232  (that is greater than distances  238  and  240 ), if desired. Antenna ground  104  and peripheral conductive housing structures  16  may form a distributed impedance matching capacitor in region  230 . In some situations, regions  234  and  236  of antenna ground  104  may referred to as forming independent distributed inductance matching capacitors. 
     Distributed capacitance region  230  may include regions  234  and  236  where ground  104  is separated from peripheral conductive housing structures  16  by distance  238 . In the region interposed between regions  234  and  236 , ground  104  is separated from peripheral conductive housing structures  16  by distance  240 . In the example of  FIG. 5 , antenna feed  112  is coupled across slot  101  at a location along antenna ground  104  where antenna ground  104  is separated from peripheral conductive housing structures  16  by distance  240 . These examples are merely illustrative. In general, antenna ground  104  may be separated from peripheral conductive housing structures  16  by any desired distance in region  230  to form a desired distributed capacitance between ground  104  and peripheral conductive housing structures  16  around feed  112 . Antenna ground  104  may be separated from peripheral conductive housing structures  16  by a uniform distance in distributed capacitance region  230  or by two or more different distances in distributed capacitance region  230 . Additionally, antenna feed  112  may be coupled across slot  101  at any desired location (e.g., at a location in the distributed capacitance region where ground  104  and peripheral conductive structures  16  are separated by distance  240 , at a location in the distributed capacitance region where ground  104  and peripheral conductive structures  16  are separated by distance  238 , at a location outside of the distributed capacitance region where ground  104  and peripheral conductive structures  16  are separated by distance  232 , etc.). The distance between ground  104  and peripheral conductive structures  16  is inversely proportional to the distributed capacitance of region  230 . The location of the antenna feed and the separation between the antenna ground  104  and the peripheral conductive housing structures  16  in distributed capacitance region  230  may be chosen to exhibit one or more desired capacitances to ensure that antenna  40  is impedance matched to transmission line  92 . 
     Including the distributed capacitance in region  230  may allow an additional component such as a surface mount technology capacitor to be omitted, thereby conserving space within the electronic device. Additionally, forming the distributed impedance matching capacitor between peripheral conductive structures  16  and antenna ground  104  may improve antenna efficiency over a wider range of frequencies than if a surface mount technology capacitor is coupled between peripheral conductive structures  16  and antenna ground  104 . 
     Distances  232 ,  238 , and  240  in  FIG. 5  may be any desired distances. For example, distance  232  may be about 2 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, more than 0.5 mm, more than 1.5 mm, more than 2.5 mm, 1-3 mm, or another desired distance. Distance  238  may be about 1 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, less than 0.5 mm, between 0.5 and 2 mm, between 0.5 and 1.5 mm, more than 0.5 mm, more than 1.5 mm, more than 2.5 mm, 1-3 mm, or another desired distance. Distance  240  may be about 1 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, less than 0.5 mm, between 0.5 and 2 mm, between 0.5 and 1.5 mm, more than 0.5 mm, more than 1.5 mm, more than 2.5 mm, 1-3 mm, or another desired distance. 
     Transceiver circuitry  90  may include cellular telephone transceiver circuitry (e.g., remote wireless transceiver circuitry  38  as shown in  FIG. 2 ) that handles wireless communications in frequency ranges such as a low communications band from 700 to 960 MHz, a low-midband from 960 to 1710 MHz, a midband from 1710 to 2170 MHz, a high band from 2300 to 2700 MHz, and/or an ultra-high band from 3400 to 3700 MHz, for example. Transceiver circuitry  90  may use transmission line  92  and feed  112  to handle low band, low-midband, midband, high band, and/or ultra-high band communications (e.g., radio-frequency signals in the low band, low-midband, midband, high band, and/or ultra-high band may be conveyed by antenna  40  over feed  112 ). 
     If desired, an antenna such as a wireless local area network and ultra-high band antenna may be formed within region  206 . To help optimize performance (antenna efficiency) of antenna  40  and the antenna formed within region  206 , at least a portion of ground plane  104  may be removed underneath region  206  (e.g., cutout region  206 ). Ground plane  104  may have any desired shape within device  10 . For example, ground plane  104  may align with gap  18 - 1  in peripheral conductive hosing structures  16  (e.g., the lower edge of gap  18 - 1  may be aligned with the edge of ground plane  104  defining slot  101  adjacent to gap  18 - 1  such that the lower edge of gap  18 - 1  is approximately collinear with the edge of ground plane  104  at the interface between ground plane  104  and the portion of peripheral conductive structures  16  adjacent to gap  18 - 1 ). This example is merely illustrative and, in another suitable arrangement, ground plane  104  may have an additional vertical slot adjacent to gap  18 - 1  that extends below gap  18 - 1  (e.g., along the Y-axis of  FIG. 5 ). 
     If desired, ground plane  104  may include a vertical slot  162  adjacent to gap  18 - 2  that extends beyond the lower edge (e.g., lower edge  216 ) of gap  18 - 2  (e.g., in the direction of the Y-axis of  FIG. 5 ). Slot  162  may, for example, have two edges that are defined by ground  104  and one edge that is defined by peripheral conductive structures  16 . Slot  162  may have an open end defined by an open end of slot  101  at gap  18 - 2 . Slot  162  may have a width  172  that separates ground  104  from the portion of peripheral conductive structures  16  below slot  18 - 2  (e.g., in the direction of the X-axis of  FIG. 5 ). Because the portion of peripheral conductive structures  16  below gap  18 - 2  is shorted to ground  104  (and thus forms part of the antenna ground for antenna structures  40 ), slot  162  may effectively form an open slot having three sides defined by the antenna ground for antenna structures  40 . Slot  162  may have any desired width (e.g., about 2 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, more than 0.5 mm, more than 1.5 mm, more than 2.5 mm, 1-3 mm, etc.). Slot  162  may have an elongated length  178  (e.g., perpendicular to width  172 ). Slot  162  may have any desired length (e.g., 10-15 mm, more than 5 mm, more than 10 mm, more than 15 mm, more than 30 mm, less than 30 mm, less than 20 mm, less than 15 mm, less than 10 mm, between 5 and 20 mm, etc.). Electronic device  10  may be characterized by longitudinal axis  282 . Length  178  may extend parallel to longitudinal axis  282  (and the Y-axis). Portions of slot  162  may contribute slot antenna resonances to antenna  40  in one or more frequency bands if desired. For example, the length and width of slot  162  may be selected so that antenna  40  resonates at desired operating frequencies. If desired, the overall length of slots  101  and  162  may be selected so that antenna  40  resonates at desired operating frequencies. 
     Adjustable component  114  may bridge slot  101  at a first location along slot  101  (e.g., component  114  may be coupled between terminal  126  on ground plane  104  and terminal  128  on peripheral conductive structures  16 ). Component  114  may include switches coupled to fixed components such as inductors for providing adjustable amounts of inductance or an open circuit between ground  104  and peripheral conductive structures  16 . Component  114  may also include fixed components that are not coupled to switches or a combination of components that are coupled to switches and components that are not coupled to switches. These examples are merely illustrative and, in general, component  114  may include other components such as adjustable return path switches, switches coupled to capacitors, or any other desired components. Adjustable component  114  may include one or more inductors coupled to a radio-frequency switching circuit. In one illustrative example, adjustable component  114  may include two inductors coupled in parallel between terminals  126  and  128 . A radio-frequency switching circuit may selectively couple the inductors between terminals  126  and  128  to tune the antenna. Additional adjustable components may be included at any desired location within electronic device  10  (i.e., between resonating element arm  108  and ground  104 , between different portions of element  108 , across gap  18 - 1  or gap  18 - 2 , etc.). 
     The resonance of antenna  40  within low band LB (e.g., 700 MHz to 960 MHz or other suitable frequency range) may be associated with the distance along peripheral conductive structures  16  between feed  112  and gap  18 - 2 , for example.  FIG. 5  is a view from the front of device  10 , so gap  18 - 2  of  FIG. 5  lies on the right edge of device  10  when device  10  is viewed from the front (e.g., the side of device  10  on which display  14  is formed) and lies on the left edge of device  10  when device  10  is viewed from behind. Tunable components such as component  114  may be used to tune the response of antenna  40  in low band LB. The resonance of antenna  40  in midband MB (e.g., 1710 MHz to 2170 MHz) may be associated with the distance along peripheral conductive structures  16  between feed  112  and gap  18 - 1 , for example. Tunable components such as component  114  may be used to tune the response of antenna  40  in midband MB, if desired. Antenna performance in high band HB (e.g., 2300 MHz to 2700 MHz) may be supported by slot  162  in ground plane  104  and/or by a harmonic mode of the resonance associated with arm  108 . Tunable components such as component  114  may be used to tune the response of antenna  40  in high band HB, if desired. 
     Antenna structures  40  may have a return path such as return path  110  coupled between arm  108  (at terminal  202 ) and ground  104  (at terminals  204 - 1  and  204 - 2 ). Return path  110  may include one or more inductors such as inductors  212  and  214 . If desired, inductors  212  and  214  may be coupled in parallel between terminal  202  on peripheral conductive housing structure  16  and different locations on ground  104 . For example, inductor  212  may be coupled between terminal  202  and ground terminal  204 - 1 , whereas inductor  214  is coupled between terminal  202  and ground terminal  204 - 2 . Inductor  212  may therefore form a first conductive path (branch) of split return path  110  between terminal  202  and terminal  204 - 1  whereas inductor  214  forms a second conductive path (branch) of split return path  110  between terminal  202  and terminal  204 - 2 . Inductors  212  and  214  may be fixed inductors or may be adjustable inductors. For example, each inductor may be coupled to a switch that selectively opens to disconnect the inductor between terminal  202  and ground  104 . Inductors  212  and  214  may be adjusted (e.g., corresponding switches may be opened or closed) to tune the resonance of antenna structures  40  in the low band, midband, high band, and/or other bands. 
     In this way, return path  110  may be split between a single point  202  on peripheral conductive housing structures  16  and multiple points on ground  104 . Because return path  110  is split between two branches that are coupled in parallel between terminal  202  and ground  104 , return path  110  may sometimes be referred to herein as a split short path or a split return path. The split short path may, for example, improve antenna efficiency for the non-near-field communications antenna formed from structures  40  relative to scenarios where the return path is implemented using a single conductive path between terminal  202  and ground  104 . 
     Terminals  202 ,  204 - 1 , and  204 - 2  may include any desired conductive structures. For example, terminal  202  may include a conductive screw that is attached to peripheral conductive housing structures  16 . Terminal  204 - 1  may include a conductive screw that is attached to a portion of ground  104  such as a conductive layer of housing  12  (e.g., a backplate of housing  12 ). If desired, at terminal  204 - 1 , another conductive structure such as a spring or pin may electrically connect the conductive support plate to a conductive portion of display  14  (e.g., a grounded portion of display  14  that forms a part of ground  104  for antenna  40 ). Terminal  204 - 2  may have the same structure as terminal  204 - 1  or may have a different structure than terminal  204 - 1 . The position of terminals  204 - 1  and  204 - 2  may be adjusted to tweak the antenna efficiency and frequency response of antenna  40  (e.g., to tune antenna  40  to resonate at desired frequencies). Terminals  204 - 1  and  204 - 2  may be separated by any desired distance (e.g., between 2 and 15 millimeters, between 8 and 20 millimeters, between 5 and 15 millimeters, between 10 and 25 millimeters, between 5 and 30 millimeters, greater than 2 millimeters, greater than 5 millimeters, greater than 8 millimeters, greater than 10 millimeters, greater than 15 millimeters, less than 10 millimeters, less than 15 millimeters, less than 20 millimeters, less than 30 millimeters, etc.). 
     As previously discussed, a portion of ground plane  104  may be removed adjacent to gap  18 - 1  (e.g., to help improve performance of the wireless local area network and ultra-high band antenna in region  206 ). The removed portion of ground plane  104  may sometimes be referred to as a cutout. The cutout may have a width  247 . Width  247  may be between 2 and 15 millimeters, between 8 and 12 millimeters, between 5 and 15 millimeters, between 10 and 20 millimeters, between 5 and 30 millimeters, greater than 2 millimeters, greater than 5 millimeters, greater than 8 millimeters, greater than 10 millimeters, greater than 15 millimeters, less than 10 millimeters, less than 15 millimeters, less than 20 millimeters, less than 30 millimeters, or any other desired distance. Distance  247  may be adjusted to improve the antenna efficiency and ensure the antenna resonates in desired frequency bands. In embodiments where antenna ground  104  includes multiple layers (e.g., both a conductive layer of housing  12  and a conductive portion of display  14 ), the cutout may only be formed in a subset of the layers. For example, the cutout may only be formed in the conductive layer of housing  12  and not in the conductive portion of display  14 . 
       FIG. 6  is a top view of an illustrative electronic device showing how a distributed capacitance of the type shown in  FIG. 5  may be formed between an antenna ground and an antenna resonating element. As shown in  FIG. 6 , antenna ground  104  may include a conductive portion of housing  12  such as conductive housing layer  320 . To decrease the distance between ground  104  and peripheral conductive housing structures  16  (e.g., within distributed capacitance region  230 ), additional components within electronic device  10  may be electrically connected to conductive housing layer  320  and form portions of the antenna ground  104 . 
     In the example of  FIG. 6 , electronic device  10  includes electronic components  244 ,  246 , and  248 . Electronic components  244 ,  246 , and  248  may be any desired type of components. In some embodiments, components  244 ,  246 , and/or  248  may be input-output components or form portions of input-output components (e.g., input-output devices  32  in  FIG. 2 ) such as a button, camera, speaker, status indicator, light source, light sensor, position and orientation sensor (e.g., an accelerometer, gyroscope, compass, etc.), capacitance sensor, proximity sensor (e.g., capacitive proximity sensor, light-based proximity sensors, etc.), fingerprint sensor, etc. In one suitable arrangement, electronic components  244  and  246  may be sensors such as light-based sensors (e.g., camera modules) and electronic component  248  may be an emitter that emits light. 
     Electronic components  244 ,  246 , and  248  may be supported by a conductive frame  242  that is electrically connected to conductive housing layer  320 . Conductive frame  242  may extend closer to peripheral conductive housing structures  16  than conductive housing layer  320 . In this way, the distance between antenna ground  104  and peripheral conductive housing structures  16  is decreased in region  230  to form a desired distributed capacitance between antenna ground  104  and peripheral conductive housing structures  16 . If desired, conductive frame  242  may provide radio-frequency shielding for electronic components  244 ,  246 , and  248  in addition to mechanically supporting the electronic components (e.g., conductive frame  242  may shield the components from radio-frequency signals conveyed using antenna  40 ). 
     A substrate such as printed circuit  250  may pass underneath conductive frame  242  between components  246  and  248 . Printed circuit  250  may be a rigid printed circuit board (e.g., a printed circuit board formed from fiberglass-filled epoxy or other rigid printed circuit board material) or may be a flexible printed circuit (e.g., a flexible printed circuit formed from a sheet of polyimide or other flexible polymer layer). Printed circuit  250  may include antenna traces such as an antenna resonating element, (e.g., for a wireless local area network and ultra-high band antenna in region  206  of  FIG. 5 ), transmission line structures (e.g., transmission line structures for transmission line  92  of  FIG. 5 ) surface mount technology components, terminals for an antenna feed (e.g., positive feed terminal  98  or ground feed terminal  100  of  FIG. 5 ), or any other desired traces or components. A conductive fastener such as a screw or another desired conductive structure (e.g., a bracket, clip, spring, pin, screw, solder, weld, conductive adhesive, wire, metal strip, or a combination of these) may electrically connect flexible printed circuit board  250  to peripheral conductive housing structures  16  at positive antenna feed terminal  98 . Printed circuit board  250  may be coupled to an additional printed circuit that includes transceiver circuitry (e.g., transceiver circuitry  90  in  FIG. 5 ), if desired. 
       FIG. 7  is a cross-sectional side view of electronic device  10  taken along line  260  in  FIG. 6 . As shown in  FIG. 7 , display  14  for electronic device  10  may include a display cover layer such as display cover layer  302  that covers display panel  304 . Display panel  304  (sometimes referred to as a display module) may be any desired type of display panel and may include pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable pixel structures. The lateral area of display panel  304  may, for example, determine the size of active area AA of display  14  ( FIG. 1 ). Display panel  304  may include active light emitting components, touch sensor components (e.g., touch sensor electrodes), force sensor components, and/or other active components. Display cover layer  302  may be a layer of clear glass, plastic, or other dielectric that covers the light-emitting surface of the underlying display panel. In another suitable arrangement, display cover layer  302  may be the outermost layer of display panel  304  (e.g., layer  302  may be a color filter layer, thin-film transistor layer, or other display layer). Buttons may pass through openings in cover layer  302  (see button  24  in  FIG. 1 ). The cover layer may also have other openings such as an opening for a speaker port (see speaker port  26  in  FIG. 1 ), openings for a sensor (e.g., sensor  248 ), or openings for any other desired electronic component. 
     Display panel  304  may be supported within electronic device  10  by a conductive display support plate (sometimes referred to as a midplate or display plate) such as display plate  306 . Conductive display frame  308  may hold display plate  306  and/or display panel  304  in place on housing  12 . For example, display frame  308  may be ring-shaped and may include a portion that runs around the periphery of the display panel  304  and surrounds a central opening. Display plate  306  and display frame  308  may both be formed from conductive material (e.g., metal). Display plate  306  and display frame  308  may be in direct contact such that the display plate  306  and the display frame  308  are electrically connected. If desired, display plate  306  and display frame  308  may be formed integrally (e.g., from the same piece of metal). 
     A plastic frame  310  may be molded around display frame  308 . Plastic frame  310  may also be ring-shaped (similar to display frame  308 ). Electronic device  10  may have a rectangular periphery with upper and lower edges coupled together by left and right edges. Plastic frame  310  may run around the rectangular periphery of electronic device  10 . Plastic frame  310  may be formed from molded plastic or any other desired dielectric material and may serve to mount frame  308  and thus plate  306  and panel  304  to peripheral conductive housing structures  16 . Conductive frame  308 , conductive plate  306 , and conductive portions of panel  304  (e.g., conductive electrodes, pixel circuitry, ground layers, ferrite layers, shielding layers, etc.) may form a portion of antenna ground  104  for antenna  40  ( FIG. 5 ). 
     Peripheral conductive housing structure  16  may have integral ledge portions  326 . Integral ledge portions  326  may extend away from peripheral conductive housing structure  16  towards the interior of electronic device  10 . Integral ledge portions  326  may be used to mount various components within electronic device  10  if desired. For example, in one illustrative embodiment plastic frame  310  may be supported by a ledge portion  326  of peripheral conductive housing structure  16 . 
     As shown in  FIG. 7 , housing  12  ( FIG. 1 ) may include dielectric housing portions such as dielectric layer  324  and conductive housing portions such as conductive layer  320  (sometimes referred to herein as conductive housing wall  320 ). If desired, dielectric layer  324  may by formed under layer  320  such that layer  324  forms an exterior surface of device  10  (e.g., thereby protecting layer  320  from wear and/or hiding layer  320  from view of a user). Conductive housing portion  320  may form a portion of ground  104 . As examples, conductive housing portion  320  may be a conductive support plate or wall (e.g., a conductive back plate or rear housing wall) for device  10 . Conductive housing portion  320  may, if desired, extend across the width of device  10  (e.g., between two opposing sidewalls formed by peripheral housing structures  16 ). If desired, conductive housing portion  320  and the opposing sidewalls of device  10  may be formed from a single integral piece of metal or portion  320  may otherwise be shorted to the opposing sidewalls of device  10 . Dielectric layer  324  may be a thin glass, sapphire, ceramic, or sapphire layer or other dielectric coating, as examples. In another suitable arrangement, layer  324  may be omitted if desired. 
     At each ground terminal within the device (e.g., terminals  204 - 1 ,  204 - 2 ,  100 ,  126 ), different components of the device ground (e.g., ground  104  in  FIG. 5 ) may be electrically connected so that the conductive structures that are located closest to resonating element arm  108  are held at a ground potential and form a part of antenna ground  104 . In one suitable arrangement, ground  104  includes both conductive portions of housing  12  (e.g., portions of a rear wall of housing  12  such as a conductive backplate  320  and portions of peripheral conductive housing structures  16  that are separated from arm  108  by peripheral gaps  18 ) as well as conductive portions of display  14  (e.g., conductive portions of display panel  304 , conductive plate  306 , and/or conductive frame  308 ). Vertical conductive structures (e.g., a bracket, clip, spring, pin, screw, solder, weld, conductive adhesive, wire, metal strip, or a combination of these) may couple conductive portions of housing  12  (e.g., a conductive backplate) to conductive portions of display  14  at terminals  204 - 1 ,  204 - 2 , and/or  100 . Ensuring that the conductive structures close to resonating element arm  108  such as conductive portions of display  14  are held at a ground potential may, for example, serve to optimize the antenna efficiency of antenna structures  40 . In one suitable arrangement, ground terminals  204 - 1 ,  204 - 2 ,  126  and/or  100  may include a conductive structure such as a spring that electrically connects the conductive backplate to the conductive display portion that forms an additional portion of the device ground. 
     Electronic component  248  may be contained within conductive frame portion  242 - 1  (sometimes referred to as lower conductive frame portion  242 - 1 ) and conductive frame portion  242 - 2  (sometimes referred to as upper conductive frame portion  242 - 2 ). Lower conductive frame portion  242 - 1  may be electrically connected to conductive housing layer  320  by conductive structure  254 . Conductive structure  254  may be any desired conductive structure (e.g., a bracket, clip, spring, pin, screw, solder, weld, conductive adhesive, wire, metal strip, or a combination of these). Because conductive frame portion  242 - 1  is electrically connected to conductive housing layer  320  by conductive structure  254 , conductive frame portion  242 - 1  may form a portion of the antenna ground (e.g., antenna ground  104 ). Conductive frame portion  242 - 1  may be electrically connected to conductive frame portion  242 - 2  such that conductive frame portion  242 - 2  also forms a portion of the antenna ground. Similarly, if desired, conductive portions of electronic component  248  may be electrically connected to conductive frame portion  242 - 1  using conductive adhesive  252 . In this arrangement, conductive portions of electronic component  248  also form a portion of the antenna ground. The example of conductive adhesive being used to electrically connect component  248  to frame  242 - 1  is merely illustrative. Any desired conductive structure (e.g., a bracket, clip, spring, pin, screw, solder, weld, conductive adhesive, wire, metal strip, or a combination of these) may electrically connect component  248  to frame  242 - 1 . The aforementioned examples of various components being included in antenna ground  104  are merely illustrative. In general, any desired components may be included in the antenna ground. 
     As shown in  FIG. 7 , peripheral conductive housing structures  16  may be separated from lower frame portion  242 - 1  by a smaller distance (distance  238 ) than the conductive housing portion (distance  320 ). Because lower frame portion  242 - 1  is shorted to conductive housing portion  320 , lower frame portion  242 - 1  forms a portion of antenna ground  104 . Therefore, peripheral conductive housing structures  16  are only separated from the antenna ground by distance  238 . If lower frame portion  242 - 1  was omitted or did not form a portion of the antenna ground, the peripheral conductive housing structures  16  would be separated from the antenna ground by the increased distance  232 . Decreasing the distance between peripheral conductive housing structures  16  and the antenna ground in these types of arrangements forms a selected distributed capacitance in the distributed capacitance region ( FIG. 5 ). The distributed capacitance between the peripheral conductive housing structures  16  and the antenna ground may, for example, improve the efficiency of antenna structures  40  by ensuring that feed  112  is impedance matched to transmission line  92 . 
       FIG. 8  is a cross-sectional side view of electronic device  10  taken along line  262  in  FIG. 6 . As shown in  FIG. 8 , electronic components  244 ,  246 , and  248  may be interposed between conductive frame portions  242 - 1  and  242 - 2 . Conductive frame portions  242 - 1  and  242 - 2  may be electrically connected using welds  256  or other desired conductive structures (e.g., a bracket, clip, spring, pin, screw, solder, conductive adhesive, wire, metal strip, or a combination of these). Conductive structures  254  such as springs may be placed on either side of flexible printed circuit board  250 . Each spring may electrically connect conductive housing layer  320  to lower conductive frame portion  242 - 1 . Other arrangements may be used to electrically connect conductive housing layer  320  to conductive frame portion  242 - 1 , if desired. Each electronic component may be electrically connected and mechanically secured to conductive frame portion  242 - 1  using conductive adhesive  252  or other desired conductive structures (e.g., a bracket, clip, spring, pin, screw, solder, conductive adhesive, wire, metal strip, or a combination of these). Therefore, conductive portions of each electronic component may form portions of the antenna ground (e.g., antenna ground  104  in  FIG. 5 ). 
     The upper conductive frame portion  242 - 2  may have openings such as openings  258 . Openings  258  may accommodate portions of the electronic components (e.g., portions of electronic components  246  and  248  may extend through respective openings). Openings  258  may allow light to reach or be transmitted from the electronic components (e.g., electrical component  244  may emit light through a respective opening). 
     A conductive fastener such as a screw  264  or another desired conductive structure (e.g., a bracket, clip, spring, pin, screw, solder, weld, conductive adhesive, wire, metal strip, or a combination of these) may electrically connect and/or mechanically secure flexible printed circuit board  250  to conductive housing layer  320 . A screw boss or threaded opening in conductive housing layer  320  may receive screw  264 . 
     Flexible printed circuit board  250  may include transmission line structures such as transmission line structures  266  (e.g., ground signal conductor  96  and/or positive signal conductor  94  in  FIG. 5 ). Additional components for antenna  40  in  FIG. 5  may be mounted on flexible printed circuit  250 . For example, a tunable component  268  that is used to tune the frequency response of antenna  40  may be mounted on flexible printed circuit  250 . If desired, conductive housing layer  320  may include an opening  270  underneath tunable component  268  to mitigate radio-frequency interference. 
       FIG. 9  is a graph of antenna efficiency as a function of frequency for an illustrative antenna of the type shown in  FIGS. 5-8 . As shown in  FIG. 9 , antenna  40  may exhibit resonances in midband MB and high band HB. The midband MB may extend from 1710 MHz to 2170 MHz or other suitable frequency range. The high band MB may extend from 2300 MHz to 2700 MHz or other suitable frequency range. As shown in  FIG. 9 , antenna  40  may have an antenna efficiency characterized by curve  402  in midband MB and high band HB when there is a distributed capacitance (e.g., in region  230  of  FIG. 5 ) formed between antenna ground  104  and peripheral conductive housing structures  16 . Antenna  40  may have an antenna efficiency characterized by curve  404  in midband MB and high band HB when the distributed capacitance is omitted (and the antenna ground is separated from the peripheral conductive housing structures by distance  232 ). When the distributed capacitance is omitted, antenna feed  112  may be poorly matched to transmission line  92 , thereby leading to a reduction in overall antenna efficiency for antenna  40 . Forming the distributed capacitance using peripheral conductive structures  16  and components of antenna ground  104  such as the lower frame portion  242 - 1  may ensure that antenna feed  112  is well matched to transmission line  92  and may therefore serve to improve the overall antenna efficiency for antenna  40 , as shown by curve  402 . This example is merely illustrative and, if desired, the curves may have any shapes in any bands. If desired, antenna  40  may exhibit resonances in a subset of these bands and/or in additional bands. 
     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.