PATENT DOCUMENT

Publication Number: US-8368602-B2
Application Number: US-79364110-A
Country: US
Kind Code: B2

Title: Parallel-fed equal current density dipole antenna

Abstract:
Electronic devices such as handheld devices may have wireless communications circuitry. The wireless communications circuitry may include a broadband antenna and circuitry that covers multiple communications bands. The broadband antenna may be formed from a parallel-fed dipole. The antenna may have first and second antenna resonating element regions on opposing sides of a slot. The slot may be an open slot that has one open end and one closed end. The slot may be formed from an opening in conductive housing structures in a conductive housing for an electronic device. The conductive housing structures may include sidewall structures, rear housing wall structures, and other conductive structures. The antenna may have a feed with a feed line that crosses the slot. An interposed dielectric substrate member may separate the feed line from the conductive structures. The feed line may have sections with different widths to minimize feed line length.

Claims:
1. An electronic device, comprising:
 a housing having at least some conductive housing structures; 
 an open slot formed in the conductive structures, wherein the open slot has a closed end and an open end; and 
 an antenna formed from a first portion of the conductive housing structures located on one side of the slot and a second portion of the conductive housing structures located on an opposing side of the slot; and 
 an antenna feed for the antenna that has an antenna feed line that crosses the slot and that is not connected to the conductive housing structures. 
 
     
     
       2. The electronic device defined in  claim 1  further comprising a transmission line having a first signal conductor that is coupled to the antenna feed line and a second signal conductor that is connected to the housing structure. 
     
     
       3. The electronic device defined in  claim 2  further comprising a dielectric substrate, wherein the antenna feed line comprises a conductive trace on the substrate. 
     
     
       4. The electronic device defined in  claim 3  wherein the electronic device comprises a housing having four edges and wherein the slot has at least one portion that runs parallel to at one of the edges. 
     
     
       5. The electronic device defined in  claim 1  further comprising a coaxial cable, wherein the coaxial cable has a center conductor coupled to the antenna feed line. 
     
     
       6. The electronic device defined in  claim 1  wherein the antenna feed line has portions of different widths. 
     
     
       7. The electronic device defined in  claim 1 , wherein the antenna comprises a broadband antenna, the electronic device further comprising:
 wireless circuitry that operates in communications bands at 850 MHz, 900 MHz, 1575 MHz, 1800 MHz, 1900 MHz, 2.4 GHz, and 5.0 GHz; and 
 a transmission line path that couples the wireless circuitry to the antenna feed, wherein the wireless circuitry receives signals in all of the communications bands at 850 MHz, 900 MHz, 1575 MHz, 1800 MHz, 1900 MHz, 2.4 GHz, and 5.0 GHz using the broadband antenna. 
 
     
     
       8. The electronic device defined in  claim 7  wherein the electronic device comprises a cellular telephone, wherein the electronic device comprises a display having edges, and wherein at least some of the slot runs parallel to one of the edges of the display. 
     
     
       9. The electronic device defined in  claim 8  wherein the antenna feed line has a plurality of different widths. 
     
     
       10. The electronic device defined in  claim 9  wherein the slot has a length of less than two inches. 
     
     
       11. The electronic device defined in  claim 1  wherein the slot has a length of less than two inches. 
     
     
       12. An antenna, comprising:
 conductive structures having a slot, wherein the conductive structures are formed from conductive housing structures; 
 a dielectric member that covers at least part of the slot; and 
 an antenna feed having an antenna feed line on the dielectric member that crosses the slot, wherein the dielectric member is interposed between the antenna feed line and the conductive structures so that the antenna feed line is not connected to the conductive structures. 
 
     
     
       13. The antenna defined in  claim 12  wherein the slot comprises an open slot that has a closed end and an open end. 
     
     
       14. The antenna defined in  claim 13 , wherein the dielectric member comprises a layer of printed circuit board material. 
     
     
       15. The antenna defined in  claim 14  wherein the conductive structures comprise metal electronic device housing structures. 
     
     
       16. The antenna defined in  claim 14  wherein the conductive structures include at least some conductive electronic device housing sidewalls. 
     
     
       17. An electronic device, comprising:
 a display; 
 a conductive housing in which the display is mounted, wherein the conductive housing has conductive housing wall structures; 
 a slot formed in the conductive housing wall structures; 
 an antenna formed from a first portion of the conductive housing wall structures located on one side of the slot and a second portion of the conductive housing wall structures located on an opposing side of the slot; and 
 an antenna feed for the antenna that has an antenna feed line that crosses the slot; and 
 a dielectric substrate, wherein the antenna feed line is separated from the conductive housing wall structures by the dielectric substrate and is not connected to the conductive housing structures. 
 
     
     
       18. The electronic device defined in  claim 17  wherein the slot comprises an open slot that has a closed end and an open end. 
     
     
       19. The electronic device defined in  claim 18  wherein the antenna feed line has a first segment that has a first width and has a second segment that has a second width that is larger than the first width, wherein the first and second segments are both located on the opposing side of the slot.

Description:
BACKGROUND 
     This relates generally to antennas, and more particularly, to electronic device antennas and electronic device antenna feed arrangements. 
     Electronic devices such as handheld electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. 
     Devices such as these 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 at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz (e.g., the main Global System for Mobile Communications or GSM cellular telephone bands). Long-range wireless communications circuitry may also handle the 2100 MHz band. Electronic devices may use short-range wireless communications links to handle communications with nearby equipment. For example, electronic devices may communicate using the WiFi® (IEEE 802.11) bands at 2.4 GHz and 5 GHz and the Bluetooth® band at 2.4 GHz. It is sometimes desirable to receive satellite navigation system signals such as signals from the Global Positioning System (GPS). Electronic devices may therefore be provided with circuitry for receiving satellite navigation signals such as GPS signals at 1575 MHz. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna structures using compact structures. At the same time, it may be desirable to form an electronic device from conductive structures such as conductive housing structures. Because conductive materials can affect radio-frequency performance, challenges arise when incorporating antennas into electronic devices with conductive structures. Efficient antenna feed arrangements are also challenging to implement. If care is not taken, antenna performance can be degraded in an electronic device with a conductive structure such as a conductive housing. 
     It would therefore be desirable to be able to provide improved antenna structures for electronic devices. 
     SUMMARY 
     An electronic device may be provided that has wireless communications circuitry. The wireless communications circuitry may include one or more antennas. The antennas may be formed from conductive structures such as conductive housing structures. Feed structures may be provided for the antennas. 
     The electronic device may be a portable electronic device with a rectangular housing. A display may be provided on the front surface of the housing. Conductive housing sidewalls may surround the housing and a planar conductive rear housing wall may be used in forming the rear of the housing. 
     The conductive structures from which the antennas may be formed may include portions of the conductive housing walls. For example, an antenna may be formed from a slot in a housing sidewall that runs parallel to one of the edges of the rectangular housing and one of the edges of the display. 
     The antennas may be broadband antennas formed from using a parallel-fed dipole configuration. An antenna of this type may have first and second antenna resonating element regions on opposing sides of a slot. The slot may be an open slot that has one open end and one closed end. The slot may be formed from an opening in conductive structures such as conductive housing walls. 
     The antenna may have a feed with a feed line that crosses the slot. An interposed dielectric substrate member may separate the feed line from the conductive structures. The feed line may have sections with different widths to minimize feed line length. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional side view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of a dipole antenna architecture that may be used for an antenna in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of a broadband dipole antenna architecture that may be used for an antenna in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of a series fed dipole antenna arrangement that may be used for an antenna in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram of a parallel-fed dipole antenna architecture that may be used for an antenna in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of a broadband parallel-fed dipole antenna architecture that may be used for an antenna in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram of a conventional quarter wavelength slot antenna. 
         FIG. 10  is an equivalent circuit diagram of the conventional quarter wavelength slot antenna of  FIG. 9 . 
         FIG. 11  is a graph of antenna efficiency plotted as a function of operating frequency for an illustrative broadband antenna in accordance with an embodiment of the present invention. 
         FIG. 12  is a top view of an illustrative broadband antenna with a slot opening having bends in accordance with an embodiment of the present invention. 
         FIG. 13  is a perspective view of an electronic device having an antenna formed from a conductive housing structure in accordance with an embodiment of the present invention. 
         FIG. 14  is a diagram of a conventional balanced feed arrangement for a dipole antenna. 
         FIG. 15  is a diagram of a balanced feed arrangement that may be used in feeding an antenna in accordance with an embodiment of the present invention. 
         FIG. 16  is a diagram of a balanced feed arrangement that may be used in feeding an antenna in accordance with an embodiment of the present invention. 
         FIG. 17  is a Smith chart demonstrating how short circuit and open circuit points on an antenna element are separated by a quarter wavelength in antenna feed arrangements of the type shown in  FIG. 16  in accordance with an embodiment of the present invention. 
         FIG. 18  is a top view of an illustrative antenna that may use a feed arrangement in accordance with an embodiment of the present invention. 
         FIG. 19  is a perspective view of an illustrative antenna feed being used in conjunction with a slot antenna of the type shown in  FIG. 18  in accordance with an embodiment of the present invention. 
         FIG. 20  is a diagram of a transmission line structure with a single impedance that may form part of an antenna feed for an antenna in accordance with an embodiment of the present invention. 
         FIG. 21  is a diagram of a transmission line structure with multiple impedances that may form part of an antenna feed for an antenna in accordance with an embodiment of the present invention. 
         FIG. 22  is a diagram of an antenna feed line with multiple widths that may be used as part of a transmission line structure when implementing an antenna feed in an antenna in accordance with an embodiment of the present invention. 
         FIG. 23  is a perspective view of an illustrative antenna feed configuration that has unequal feed conductor widths and is being used in conjunction with a slot antenna of the type shown in  FIG. 18  in accordance with an embodiment of the present invention. 
         FIG. 24  is a top view of an illustrative antenna in which a feed conductor traverses an open slot in a ground plane in accordance with an embodiment of the present invention. 
         FIG. 25  is a top view of an illustrative antenna of the type shown in  FIG. 21  that has a feed conductor with unequal widths along its length in accordance with an embodiment of the present invention. 
         FIG. 26  is a top view of an illustrative antenna having a feed of the type shown in  FIG. 22  that is coupled to a radio-frequency transceiver circuit in accordance with an embodiment of the present invention. 
         FIG. 27  is an interior view of a portion of an electronic device showing how a conductive housing may be provided with an antenna in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices 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 or more antennas. 
     Antenna structures may be provided in electronic devices such as desktop computers, game consoles, routers, laptop computers, tablet computers, etc. With one suitable configuration, antenna structures may be provided in relatively compact electronic devices such as portable electronic devices. 
     An illustrative portable electronic device that may include antennas is shown in  FIG. 1 . Portable electronic devices such as illustrative portable electronic device  10  of  FIG. 1  may be laptop computers or small portable computers such as ultraportable computers, netbook computers, and tablet computers. Portable electronic devices such as device  10  may also be somewhat smaller devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, portable electronic device  10  may be a handheld electronic device such as a cellular telephone or music player. 
     Device  10  includes housing  12  and includes at least one antenna for handling wireless communications. Housing  12 , which is sometimes referred to as a case, may be formed of any suitable materials including, plastic, glass, ceramics, composites, metal, 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, so that the operation of conductive antenna elements that are located within housing  12  is not disrupted. In other situations, housing  12  may be formed from conductive elements. Housing  12  may be formed using a unibody construction technique in which most or all of housing  12  is formed from a single piece of material. Housing  12  may, for example, be formed from a piece of machined or cast aluminum or stainless steel. Housing  12  may also be formed from multiple smaller housing structures (i.e., frame structures, sidewalls, peripheral bands, bezels, etc.). Unibody housing structures and housing structures formed from multiple pieces may be formed from metal, plastic, composites, or other suitable materials. 
     Device  10  may have a display such as display  14 . Display  14  may be a touch screen that incorporates capacitive touch electrodes or other touch sensitive elements. Display  14  may include image pixels formed form light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electronic ink elements, liquid crystal display (LCD) components, or other suitable image pixel structures. A cover glass member may cover the surface of display  14 . Buttons such as button  19  and speaker ports such as speaker port  15  may be formed in openings in the cover glass. Buttons and ports may also be formed in housing  12 . 
     Housing  12  may include housing sidewall structures such as sidewall structures  16 . Some or all of structures  16  may be formed using conductive materials. For example, structures  16  may be implemented using a conductive ring-shaped band member that substantially surrounds the rectangular periphery of display  14 . Structures  16  may form straight or curved sidewalls for housing  12 . If desired, structures  16  may be formed from a unitary body structure that includes housing sidewalls and an associated rear planar portion (i.e., a planar portion that forms the rear of device  10 . Structures  16  and other structures in housing  12  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. Structures  16  or a separate member may serve as a bezel that holds display  14  to the front (top) face of device  10  and/or that serves as a cosmetic trim piece for display  14 . 
     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, Bluetooth® communications, etc. If desired, a broadband antenna may be used that covers multiple communications bands. 
     A schematic diagram of illustrative electronic components that may be used within device  10  of  FIG. 1  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may include 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, applications 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, etc. 
     Input-output circuitry  30  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  such as touch screens and other user input interface are examples of input-output circuitry  32 . Input-output devices  32  may also include user input-output devices such as buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, etc. A user can control the operation of device  10  by supplying commands through such user input devices. Display and audio devices such as display  14  ( FIG. 1 ) and other components that present visual information and status data may be included in devices  32 . Display and audio components in input-output devices  32  may also include audio equipment such as speakers and other devices for creating sound. If desired, input-output devices  32  may contain audio-video interface equipment such as jacks and other connectors for external headphones and monitors. 
     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, 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 circuits for handling multiple radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  36  and  38  and satellite navigation system receiver  39 . 
     Satellite navigation system receiver circuitry  39  may be used to receive satellite positioning system signals such as GPS signals at 1575 MHz from satellites associated with the Global Positioning System. 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 cellular telephone bands such as the bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz data band (as examples). 
     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 wireless circuitry for receiving radio and television signals, paging circuits, 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 communications circuitry  34  may include one or more antennas  40 . With one suitable arrangement, which is sometimes described herein as an example, at least one antenna  40  in device  10  may be formed using a dipole structure. 
     A cross-sectional side view of device  10  of  FIG. 1  taken is shown in  FIG. 3 . Display  14  may be mounted to the front surface of device  10 . Rear wall  42  and sidewalls  16  of housing  12  may be formed from separate housing structures or may be formed as integral portions of the same structure as shown in  FIG. 3 . 
     In the illustrative arrangement shown in  FIG. 3 , antenna  40  for device  10  has been formed from part of housing  12  (e.g., in an arrangement in which housing  12  is formed from a conductive material such as metal). Antenna  40  may, for example, be formed from part of housing  12  at the lower end of device  10  when viewed in the orientation shown in  FIG. 1 . Antenna  40  may also be formed on a sidewall of housing  12 , along a top edge of housing  12 , on a rear wall portion of housing  12 , or elsewhere in device  10 . Antenna  40  may be fed using an antenna feed having terminals such as positive antenna feed terminal  54  and ground (negative) antenna feed terminal  56 . 
     Antenna signals may be conveyed to and from antenna  40  using transmission line  58 . Transmission line  58  may be, for example, a coaxial cable or a microstrip transmission line having an impedance of 50 ohms (as an example). A matching network formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna  40  to the impedance of transmission line  58 . 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. 
     Device  10  may contain printed circuit boards such as printed circuit board  46 . Printed circuit board  46  and the other printed circuit boards in device  10  may be formed from rigid printed circuit board material (e.g., fiberglass-filled epoxy) or flexible sheets of material such as polymers. Flexible printed circuit boards (“flex circuits”) may, for example, be formed from flexible sheets of polyimide. 
     Printed circuit board  46  may contain interconnects such as interconnects  48 . Interconnects  48  may be formed from conductive traces (e.g., traces of gold-plated copper or other metals). Connectors such as connector  50  may be connected to interconnects  48  using solder or conductive adhesive (as examples). Integrated circuits, discrete components such as resistors, capacitors, and inductors, and other electronic components may be mounted to printed circuit board  46 . These components are shown as components  44  in  FIG. 3 . 
     Components  44  may include one or more integrated circuits that implement transceiver circuits  36  and  38  and receiver circuit  39  of  FIG. 2 . Connector  50  may be, for example, a coaxial cable connector that is connected between printed circuit board  46  and coaxial cable  58 . Terminal  54  may be connected to coaxial cable center connector  60 . Terminal  56  may be connected to a ground conductor in cable  58  (e.g., a conductive outer braid conductor). If desired, transmission line  58  may be coupled to feed terminals  54  and  56  using a connector in the vicinity of terminals  54  and  56 . Feed conductors (e.g., transmission line conductors, conductive strips on printed circuit boards, vias, feed lines formed from other conductive structures, etc.) may be used in coupling transmission line  58  to antenna  40 . 
     Antenna  40  may use a dipole configuration of the type shown in  FIG. 4 . As shown in  FIG. 4 , positive antenna feed terminal  54  may be connected to first conductor  62  and ground antenna feed terminal  56  may be connected to second conductor  64 . Conductors  62  and  64  serve as antenna resonating elements (antenna radiating elements) and may be formed from wires, strips of metal, or other conductive elements. 
       FIG. 5  shows how antenna resonating elements  62  and  64  may be formed from conductive structures with larger surface areas than the wires of  FIG. 4 . Conductive structures  62  and  64  of  FIG. 5  may be formed from metal traces on printed circuit boards, metal housing structures, or other conductive structures. Use of antenna resonating elements  62  and  64  that are formed from structures with substantial areas may help antenna  40  to exhibit a larger bandwidth than a dipole antenna based on antenna resonating elements formed from wires or narrow metal strips. This may allow antenna  40  to serve as a broadband antenna that covers multiple communications bands of interest. 
     Antenna  40  may be fed using a series feed or a parallel feed arrangement.  FIG. 6  shows how antenna  40  may be series fed from transmission line  58 . In  FIG. 7 , antenna  40  is being fed by transmission line  58  using a parallel feed arrangement. When parallel fed, antenna  40  has a section of antenna resonating element conductor (i.e., section Q) that joins antenna resonating elements  62  and  64 . 
     As shown in  FIG. 8 , antenna  40  may be formed from conductive regions such as rectangular conductive regions or other two-dimensional resonating elements  62  and  64  to form a broadband antenna. Resonating elements  62  and  64  may be separated by a slot such as slot  66 . Slot  66  may be filled with a dielectric such as air, plastic, or other dielectric materials. The conductive structures on opposing sides of antenna slot  66  at end  61  are not electrically connected to each other in the vicinity of end  61  (i.e., end  61  of slot  66  is open), whereas the conductive structures on opposing sides of antenna slot  66  at end  63  are connected through portion Q of conductive structures  68  (i.e., end  63  of slot  66  is closed). Slots such as slot  66  in which one end is open are sometimes referred to as open slots. Slots in which both ends are closed are sometimes referred to as closed slots. 
     Antenna  40  of  FIG. 8  may be fed at antenna feed terminals  54  and  56 . Resonating elements  62  and  64  (and therefore terminals  54  and  56 ) may be electrically shorted to each other at the end of slot  66  using conductive portion Q (i.e., antenna  40  of  FIG. 8  uses a parallel-fed arrangement as described in connection with  FIG. 7 ). Because resonating elements  62  and  64  are electrically shorted to each other through portion Q, elements  62  and  64  may be maintained at the same direct-current (DC) voltage level. For example, resonating elements  62  and  64  may be maintained at a common DC ground voltage (at DC frequencies). 
     Antenna  40  of  FIG. 8  may be formed from conductive structure  68 . Conductive structure  68  may be formed from an electronic device housing (e.g., housing  12  of device  10 ) or other conductive structures. When using a parallel-fed arrangement for antenna  40  such as the arrangement of  FIG. 8 , slot  66  does not completely bisect conductive structure  68 . This may help housing  12  maintain structural integrity in configurations in which structure  68  is formed from housing  12 . 
     Slot  66  of antenna  40  of  FIG. 8  may have a length LG that is less than the length of a conventional quarter wavelength open slot antenna. A conventional quarter-wavelength open slot antenna is shown in  FIG. 9 . As shown in  FIG. 9 , antenna  70  may have a conductive structure  72  having open slot  74 . Slot  74  has a length equal to a quarter of a wavelength at signal frequencies of interest. An equivalent circuit for slot antenna  70  of  FIG. 9  is shown in  FIG. 10 . As shown in  FIG. 10 , antenna  70  of  FIG. 9  is electrically equivalent to an inverted-F antenna. In contrast to quarter-wavelength antenna  70  of  FIGS. 9 and 10 , the length LG of slot  66  in parallel-fed broadband dipole antenna  40  of  FIG. 8  need not be equal to a quarter-wavelength in length at all operating frequencies. For example, a quarter of a wavelength at a given operating frequency might be 3 inches, while length LG might be only 2.5 inches or less, only 2 inches or less, or only 1.5 inches or less. 
     Antennas such as parallel-fed broadband dipole antenna  40  of  FIG. 8  may exhibit bandwidths that are sufficiently large to cover multiple communications bands of interest. A graph showing the efficiency of an antenna such as antenna  40  of  FIG. 8  as a function of operating frequency is shown in  FIG. 11 . As shown in  FIG. 11 , antennas of this type (e.g., an antenna with a slot length of 2 inches or less implemented in housing  12 ) may exhibit satisfactory efficiency in cellular communications bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz, while simultaneously exhibiting satisfactory efficiency in the GPS band at 1575 MHz and the wireless bands at 2.4 GHz (Bluetooth® and WiFi®) and 5.0 GHz (WiFi®). 
     As shown in  FIG. 12 , slot  66  need not be straight, but may have one or more bends. Slots with curved sections may also be used in antenna  40 . 
     Slot  66  may be located in any suitable portion of housing  12 . For example, slot  66  may be formed in the rear surface of hosing  12 , in a sidewall of housing  12 , on portions of both a sidewall and a rear planar section of housing  12 , etc.  FIG. 13  shows an illustrative example in which slot  66  of antenna  40  has been formed from a slot that runs along one of the sidewalls of housing  12 . The illustrative slot of  FIG. 13  has one bend. If desired, slot  66  may have no bends or may have more than one bend. 
     A balanced feed arrangement may be used to feed antenna  40 .  FIG. 14  shows a conventional balanced feed for dipole antenna  76 . Dipole antenna  76  is coupled to coaxial cable  82 . Coaxial cable  82  has an outer braid conductor and a center conductor. To couple coaxial cable  82  to dipole antenna  76 , balun  88  is formed from coaxial cable sections  84  and  86 . In coaxial cable section  84 , both the outer braid conductor and the center conductor of the cable are present. The outer braid conductor is shorted to antenna arm  78  at point  92 . Arm lengths L 1  and L 4  may be equal. Section  90  of the center conductor is connected to arm  80  at point  94 . In coaxial cable section  84 , only the outer braid conductor is present. This conductor is shorted to the outer braid conductor of section  84  at points  96 . The size and shape of section  86  is the same as the size and shape of the outer braid conductor of section  84 . Lengths L 2  and L 3  are also equal. In this arrangement, sections  86  and  84  exhibit equalized current densities and serve as a transmission line that feeds antenna  76 . 
     An illustrative feed arrangement that may be used for antenna  40  is shown in  FIG. 15 . In the example of  FIG. 15 , coaxial cable  58  is coupled to antenna  40  using a transmission line structure TL. Antenna  40  has a dipole-type antenna resonating element formed from first arm  62  and second arm  64 . First arm  62  and second arm  64  may be formed from conductive structures on carrier  110  (e.g., a dielectric substrate such as a plastic member, rigid printed circuit board, flexible printed circuit board, etc.) or as parts of housing structures, etc. 
     Transmission line section TL has first and second parallel segments S 1  and S 2 . Segment S 1  has conductor  100  and conductor  102 . Conductor  100  may be formed from a trace of metal on the upper surface of carrier  110 . Conductor  100  may be shorted to the outer braid conductor of coaxial cable  58  at point  98  and may be formed as an integral portion of arm  62 . Conductor  102  may be formed on the backside of carrier  110  to form a transmission line segment. One end of conductor  102  may be connected to the center conductor of coaxial cable  58 . The other end of conductor  102  may be connected to conductive segment  106 . Segment  106 , which may also be formed on the backside of carrier  110 , may be shorted to arm  64  through via  108 . 
     The feed arrangement of  FIG. 15  help match coaxial cable  58  to dipole antenna  40 , thereby reducing signal losses and ensuring satisfactory antenna performance. 
     If desired, the short circuit connection provided by via  108  of  FIG. 15  may be implemented at radio-frequencies without using a via (i.e., without forming an actual direct-current electrical connection between the front and back sides of carrier  110 ). For example, antenna  40  may be fed using an arrangement of the type shown in  FIG. 16 . In the arrangement of  FIG. 16 , segment S 2  has an underlying (backside) conductor  112  that extends from point X (where via  108  of  FIG. 15  was formed) to point Y, parallel to upper conductive trace  104 . The length of segment S 2  is about a quarter of a wavelength at operating frequencies of interest. At point Y, conductor  112  forms an open circuit (i.e., conductor  112  is not electrically connected to trace  104 ). As shown in the Smith chart of  FIG. 17 , a quarter of a wavelength away (i.e., at point X of  FIG. 16 ), conductor  112  is electrically “shorted” at RF frequencies to conductors  104  even though an actual conductive connection has not been formed. The feed arrangement of  FIG. 16  may therefore operate in substantially the same way as the feed arrangement of  FIG. 15  without involving the use of a physical via such as via  108  of  FIG. 15 . 
     As shown in  FIG. 18 , antenna  40  may be implemented using a closed slot in conductive structure  68 . At operating frequencies of interest, the perimeter of slot  66  should be equal to one wavelength (i.e., the length of slot  66  should be about one half of a wavelength). At the ends of slot  66  (i.e., ends E 1  and E 2 ), a short circuit condition exists, as denoted by the label “SC” in  FIG. 18 . In the middle of slot  66 , an open circuit condition exists (“OC”). At an intermediate position between the middle of slot  66  and the end of slot  66  (i.e., partway between the middle of slot  66  and end E 1 ), antenna  40  will exhibit an intermediate impedance (e.g., 50 ohms) that is matched to the impedance of transmission line  58  ( FIG. 3 ). 
       FIG. 19  shows how an antenna such as antenna  40  of  FIG. 18  may be fed. Antenna  40  may have a conductive structure  68  in which slot  66  is formed. Structure  68  may be, for example, a backside metal layer on a printed circuit board or other substrate  110 . Feed line  124  may be formed on the front side of substrate  110  and may form a transmission line in conjunction with backside metal layer  68  (in the regions where backside metal  68  is present under line  124 ). Feed line  124  may include feed line segment  114  and feed line segment  122 . Coaxial cable  58  ( FIG. 3 ) may have its positive and ground conductors connected to terminals  116  and  118 , respectively. The length of segment  122  (i.e., the distance between end  126  and point  120 ) may be about a quarter of a wavelength at operating frequencies of interest. This forms an RF short from line  124  to backside conductive layer  68  at point  120 , as described in connection with  FIGS. 16 and 17 . If desired, a via may be formed a point  120  to connect feed line  124  to backside conductor  68 . Point  120  may form the positive feed for antenna slot  66  (e.g., feed terminal  54 ). The ground feed (feed  56 ) may be formed on the opposing side of slot  66  by the portion of metal  68  under segment  124 . 
     It may be desirable to reduce the length of feed line  124 . For example, it may be desirable to reduce the length of feed line segment  122  of  FIG. 19 . This may be accomplished by providing segment  122  with multiple impedances. 
       FIG. 20  is a model of a feed line segment  122  having a single impedance per unit length (Zo) of the type shown in  FIG. 19 . At point  120 , segment  122  forms a short circuit. At point  126 , segment forms an open circuit. 
       FIG. 21  shows how segment  122  may be provided with two sub-segments  122 A and  122 B, each with a respective impedance (large impedance Zl and small impedance Zs, respectively). By configuring the lengths of sub-segments  122 A and  122 B, the impedance of segment  122  of  FIG. 21  can match the impedance of segment  122  of  FIG. 20 , but with a reduced total length (i.e., with LG of segment  122  of FIG.  21  being less than the length of segment  122  of  FIG. 20 ). 
       FIG. 22  shows how feed line segment  122  of  FIG. 21  may be implemented using a metal trace of varying width (measured perpendicular to the longitudinal axis of feed line segment  122 ). The width W 1  of segment  122 A is less than the width W 2  of segment  122 B, creating desired impedances Zl and Zs, respectively. In this example, the impedances of segments  122 A and  122 B were adjusted using a feed line conductor in which different segments of the conductor were provided with different widths. This is merely one illustrative way in which to adjust the impedances of antenna feed line segments  122 A and  122 B. In general, a microstrip transmission line such as segment  122  has an impedance that is proportional to width, the dielectric constant of substrate  110  ( FIG. 19 ), and the thickness T of substrate  110 . If desired, a multi-impedance structure of the type shown in  FIG. 21  can be implemented by changing any one or more of these parameters (e.g., by forming segment  122  from structures with underlying substrate materials with different dielectric constants, by varying the thickness of the substrate under different portions of segment  122 , by changing the width of conductor  122 , or by using combinations of these approaches). 
       FIG. 23  shows how an antenna of the type shown in  FIG. 19  may be implemented using a transmission line feed segment such as segment  122  of  FIG. 22 . As shown in  FIG. 23 , segment  122  may include sub-segments  122 A and  122 B of differing impedances. Using this approach, the length LG of segment  122  may be shorter than the quarter wavelength length of segment  122  of  FIG. 19 . If desired, feed path  124  may be formed without the bend at point  120 . For example, feed path  124  may be formed from a line in which segment  122  runs parallel to segment  114 , or in which path  124  has one or more, two or more, or three or more bends, curves, etc. 
     Feed arrangements such as these may be used with equal current density dipoles such as broadband dipole antenna  40  of  FIG. 8  or other antennas.  FIG. 24  is a top view of an illustrative feed arrangement of the type shown in  FIG. 19  being used to feed a broadband dipole antenna of the type shown in  FIG. 8 . As shown in  FIG. 24 , segment  122  may have a length of about a quarter of a wavelength at an operating frequency of interest to ensure that segment  122  of front-side trace  1224  is “shorted” at radio frequencies to backside conductor  68 .  FIG. 25  shows how segment  122  may be provided with widened portion  122 B to reduce its overall length, as described in connection with  FIG. 22 . 
     In the illustrative arrangement of  FIG. 26 , transceiver circuitry  34  (e.g., cellular transceiver circuitry  38  of  FIG. 2 , local area network circuitry  36  of  FIG. 2 , and satellite positioning system receiver circuitry  39  of  FIG. 2 ) may be coupled to transmission line  124  to feed antenna  40 . 
     As shown in  FIG. 27 , conductive structure  68  may be formed from housing  12 . Conductive structures  68  may, for example, be formed from housing sidewalls, a rear planar housing wall, parts of sidewalls and part of a rear wall, or other suitable conductive housing structures. Slot  66  may be formed in housing  12  (e.g., in metal housing walls). A portion of slot  66  may run parallel to the edges of display  14  and housing  12 . If desired, slot  66  may have a bend and may be formed in housing  12  so that slot  66  appears as shown in  FIG. 13 . Feed trace  124  and segment  122  may be located on substrate  110  (e.g., a rigid or flexible printed circuit board). The positive and ground conductors of coaxial cable  58  may be coupled to front-side trace  124  and conductive structure  68 , respectively. As with the illustrative feed arrangements of  FIG. 23 , antenna feed line  124  runs perpendicular to slot  66  as feed line  124  crosses slot  66  and bends to form section  122 . If desired, section  122  may be provided with a widened segment such as segment  122 B of  FIG. 23 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20100603
Publication Date: 20130205
Grant Date: 20130205
Priority Date: 20100603
Inventors: HILL ROBERT J.
SCHLUB ROBERT W.
CABALLERO RUBEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/285", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/364", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/285", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/364", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 45064855