PATENT DOCUMENT

Publication Number: US-8102318-B2
Application Number: US-40159409-A
Country: US
Kind Code: B2

Title: Inverted-F antenna with bandwidth enhancement for electronic devices

Abstract:
An inverted-F antenna is provided that has a resonating element arm and a ground element. A shorting branch of the resonating element arm shorts the resonating element arm to the ground element. An antenna feed that receives a transmission line is coupled to the resonating element arm and the ground element. One or more impedance discontinuity structures are formed along the resonating element arm at locations that are between the shorting branch and the antenna feed. The impedance discontinuity structures may include shorting structures and capacitance discontinuity structures. The impedance discontinuity structures may be formed by off-axis vertical conductors such as vias that pass through a dielectric layer separating the antenna resonating element arm from the ground element. Capacitance discontinuity structures may be formed from hollowed portions of the dielectric or other dielectric portions with a dielectric constant that differs from that of the dielectric layer.

Claims:
1. An inverted-F antenna comprising:
 an antenna ground element; 
 a resonating element arm that is shorted to the antenna ground element at a shorting branch of the resonating element arm; 
 an antenna feed coupled to the resonating element arm and the antenna ground element; 
 a shorting structure that shorts the resonating element arm to the antenna ground element at a location between the shorting branch and the antenna feed; 
 a dielectric layer between the resonating element arm and the antenna ground element; and 
 a capacitance discontinuity structure in the dielectric layer. 
 
     
     
       2. The inverted-F antenna defined in  claim 1  wherein the resonating element arm comprises a planar resonating element arm conductor and wherein the antenna ground element comprises a planar antenna ground element. 
     
     
       3. The inverted-F antenna defined in  claim 2  wherein the dielectric layer comprises printed circuit board dielectric and wherein the resonating element arm conductor comprises a T-shaped trace on the dielectric. 
     
     
       4. The inverted-F antenna defined in  claim 1  wherein the resonating element arm comprises a planar resonating element arm conductor, wherein the antenna ground element comprises a planar antenna ground element, wherein the dielectric layer comprises a planar dielectric layer between the planar resonating element arm conductor and the planar antenna ground element, and wherein the capacitance discontinuity structure is in the planar dielectric layer adjacent to the resonating element arm conductor. 
     
     
       5. The inverted-F antenna defined in  claim 4  wherein the capacitance discontinuity structure comprises a hollow region adjacent to the planar resonating element arm conductor. 
     
     
       6. The inverted-F antenna defined in  claim 4  wherein the planar dielectric layer has a first dielectric constant and wherein a portion of the planar dielectric layer serves as the capacitance discontinuity structure and has a second dielectric constant that is different than the first dielectric constant. 
     
     
       7. The inverted-F antenna defined in  claim 4  wherein the planar dielectric layer has a first dielectric constant and wherein a portion of the planar dielectric layer serves as the capacitance discontinuity structure and has a second dielectric constant that is less than the first dielectric constant. 
     
     
       8. An inverted-F antenna comprising:
 an antenna ground element; 
 a resonating element arm that is shorted to the antenna ground element at a shorting branch of the resonating element arm; 
 an antenna feed coupled to the resonating element arm and the antenna ground element; 
 a capacitance discontinuity structure that introduces an altered capacitance to the resonating element arm at a location along the resonating element arm that is between the shorting branch and the antenna feed; and 
 a dielectric layer between the resonating element arm and the antenna ground element, wherein the dielectric layer comprises at least one portion that serves as the capacitance discontinuity structure. 
 
     
     
       9. The inverted-F antenna defined in  claim 8  wherein the resonating element arm comprises a planar resonating element arm conductor, wherein the antenna ground element comprises a planar antenna ground element, and wherein the dielectric layer comprises a planar epoxy dielectric layer between the planar resonating element arm conductor and the planar antenna ground element. 
     
     
       10. The inverted-F antenna defined in  claim 8  wherein the resonating element arm comprises a planar resonating element arm conductor, wherein the antenna ground element comprises a planar antenna ground element, and wherein the a dielectric layer is between the planar resonating element arm conductor and the planar antenna ground element. 
     
     
       11. The inverted-F antenna defined in  claim 10  wherein the at least one portion of the dielectric layer that serves as the capacitance discontinuity structure comprises portions that define at least one gas-filled hollow region adjacent to the planar resonating element arm conductor that serves as the capacitance discontinuity structure. 
     
     
       12. The inverted-F antenna defined in  claim 10  wherein the at least one portion of the dielectric layer that serves as the capacitance discontinuity structure is adjacent to the planar resonating element arm conductor. 
     
     
       13. The inverted-F antenna defined in  claim 12  wherein the dielectric layer has a first dielectric constant and wherein the portion of the dielectric layer that serves as the capacitance discontinuity structure has a second dielectric constant that is different than the first dielectric constant. 
     
     
       14. The inverted-F antenna defined in  claim 13  further comprising:
 a shorting structure that shorts the resonating element arm to the antenna ground element at a location along the resonating element arm that is between the shorting branch and the antenna feed. 
 
     
     
       15. The inverted-F antenna defined in  claim 14  wherein the shorting structure comprises at least one via that passes through the dielectric layer and electrically connects the resonating element arm to the antenna ground element. 
     
     
       16. The inverted-F antenna defined in  claim 15  wherein the resonating element arm comprises an elongated conductive member having a central longitudinal axis and wherein the via of the shorting structure is connected to the elongated conductive member at a location that is laterally offset from the central longitudinal axis in a lateral direction perpendicular to the central longitudinal axis. 
     
     
       17. The inverted-F antenna defined in  claim 16  wherein the elongated conductive member comprises a lateral protrusion and wherein the via of the shorting structure is connected to the elongated conductive member at the protrusion. 
     
     
       18. The inverted-F antenna defined in  claim 8  further comprising:
 a shorting structure that shorts the resonating element arm to the antenna ground element at a location along the resonating element arm that is between the shorting branch and the antenna feed. 
 
     
     
       19. An electronic device, comprising:
 a radio-frequency transceiver; 
 a transmission line coupled to the radio-frequency transceiver to receive and transmit radio-frequency signals; and 
 an antenna having:
 a dielectric layer; 
 an antenna ground element; 
 a resonating element arm that is separated from the antenna ground element by the dielectric layer and that is shorted to the antenna ground element by a shorting branch of the resonating element arm at an end of the resonating element arm; 
 an antenna feed that is coupled to the resonating element arm and the antenna ground element and that receives the transmission line; and 
 at least one via that passes from the resonating element arm to the antenna ground element through the dielectric layer and shorts the resonating element arm to the antenna ground element at a location along the resonating element arm that is located between the shorting branch and the antenna feed, wherein there is no flat plane that passes through substantially all of the shorting branch, the antenna feed, and the via. 
 
 
     
     
       20. The electronic device defined in  claim 19  wherein the dielectric layer comprises a portion of a printed circuit board and wherein the shorting branch comprises at least one shorting branch via through the dielectric layer. 
     
     
       21. The electronic device defined in  claim 19  wherein the at least one via comprises at least four vias. 
     
     
       22. The electronic device defined in  claim 19  wherein there is no straight line that passes through the shorting branch, the antenna feed, and the via.

Description:
BACKGROUND 
     This invention relates to electronic devices and, more particularly, to antennas for electronic devices. 
     Portable computers and other electronic devices often use wireless communications circuitry. For example, wireless communications circuitry may be used to communicate with local area networks and remote base stations. 
     Wireless computer communications systems use antennas. It can be difficult to design antennas that perform satisfactorily in electronic devices. For example, it can be difficult to produce an antenna that is suitable for volume manufacturing and that performs efficiently over communications frequencies of interest. 
     It would therefore be desirable to be able to provide improved antenna arrangements for electronic devices such as portable computers. 
     SUMMARY 
     An antenna for an electronic device is provided. The antenna may have an inverted-F configuration based on an antenna ground element and a resonating element arm. A shorting branch of the resonating element arm may short the resonating element arm to the ground element. At another location along the longitudinal axis of the resonating element arm, an antenna feed may be provided that is coupled to a transmission line. 
     Antenna bandwidth may be enhanced by including one or more impedance discontinuity structures in the antenna at locations along the resonating element arm between the shorting branch and the antenna feed. The impedance discontinuity structures may be implemented using shorting structures and capacitance discontinuity structures. 
     The resonating element arm may be formed from traces on a printed circuit board dielectric layer. The ground element may be formed using a ground plane layer on the dielectric. The shorting structures may be formed by creating off-axis vias through the dielectric to connect the resonating element arm to the ground element. The capacitance discontinuity structures may be formed from regions in the dielectric layer under the antenna resonating element arm. The regions may have an increased or decreased dielectric constant relative to the dielectric constant of the dielectric layer. A capacitance discontinuity structure may, for example, be formed from a hollow portion of the dielectric under the resonating element arm. 
     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 schematic diagram of an illustrative electronic device in which an antenna may be implemented in accordance with an embodiment of the present invention. 
         FIG. 2A  is a diagram of a conventional inverted-F antenna. 
         FIG. 2B  is a diagram of a conventional inverted-F antenna such as the antenna of  FIG. 2A  that has been modified with an additional resonating element arm to enhance antenna bandwidth. 
         FIG. 3  is a diagram of an illustrative inverted-F antenna that has a short circuit structure that enhances antenna bandwidth in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of an illustrative inverted-F antenna having a short circuit structure of the type shown in  FIG. 3  that has been implemented using a conductive via in a printed circuit board substrate in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional view of an inverted-F antenna with a short circuit structure implemented using a conductive via in a printed circuit board substrate of the type shown in  FIG. 4  in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an illustrative inverted-F antenna that has a capacitance discontinuity structure that enhances antenna bandwidth in accordance with an embodiment of the present invention. 
         FIG. 7  is a perspective view of an illustrative inverted-F antenna having a capacitance discontinuity structure of the type shown in  FIG. 6  that has been implemented using holes in a printed circuit board dielectric layer under the inverted-F antenna resonating element conductive layer in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional view of an inverted-F antenna with capacitance discontinuity structures of the type shown in  FIG. 7  in accordance with an embodiment of the present invention. 
         FIG. 9  is a top view of an illustrative inverted-F antenna having a short circuit structure that has been formed using a via connected to a laterally protruding portion of an antenna resonating element in accordance with an embodiment of the present invention. 
         FIG. 10  is a top view of an illustrative inverted-F antenna having a first short circuit structure that has been formed using a via connected to a protruding portion of an antenna resonating element, having a second short circuit structure that has been formed using a via at a laterally offset location along the main branch of the antenna resonating element, and having capacitance discontinuity structures in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph showing how the bandwidth of an inverted-F antenna may be enhanced by incorporating shorting structures and capacitance discontinuity structures in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to antenna structures for electronic devices. Antennas may be used to convey wireless signals for suitable communications links. For example, an electronic device antenna may be used to handle communications for a short-range link such as an IEEE 802.11 link (sometimes referred to as WiFi®) or a Bluetooth® link. An electronic device antenna may also handle communications for long-range links such as cellular telephone voice and data links. 
     Antennas such as these may be used in various electronic devices. For example, an antenna may be used in an electronic device such as a handheld computer, a miniature or wearable device, a portable computer, a desktop computer, a router, an access point, a backup storage device with wireless communications capabilities, a mobile telephone, a music player, a remote control, a global positioning system device, devices that combine the functions of one or more of these devices and other suitable devices, or any other electronic device. 
     A schematic circuit diagram of an illustrative electronic device  10  that may include one or more antennas is shown in  FIG. 1 . As shown in  FIG. 1 , device  10  may include storage and processing circuitry  12  and input-output circuitry  14 . Storage and processing circuitry  12  may include hard disk drives, solid state drives, optical drives, random-access memory, nonvolatile memory and other suitable storage. Storage may be implemented using separate integrated circuits and/or using memory blocks that are provided as part of processors or other integrated circuits. 
     Storage and processing circuitry  12  may include processing circuitry that is used to control the operation of device  10 . The processing circuitry may be based on one or more circuits such as a microprocessor, a microcontroller, a digital signal processor, an application-specific integrated circuit, and other suitable integrated circuits. Storage and processing circuitry  12  may be used to run software on device  10  such as operating system software, code for applications, or other suitable software. To support wireless operations, storage and processing circuitry  12  may include software for implementing wireless communications protocols such as wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, protocols for handling 3G communications services (e.g., using wide band code division multiple access techniques), 2G cellular telephone communications protocols, WiMAX® communications protocols, communications protocols for other bands, etc. 
     Input-output devices  14  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  14  may include user input-output devices such as buttons, display screens, touch screens, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, cameras, etc. A user can control the operation of device  10  by supplying commands through the user input devices. This may allow the user to adjust device settings, etc. Input-output devices  14  may also include data ports, circuitry for interfacing with audio and video signal connectors, and other input-output circuitry. 
     As shown in  FIG. 1 , input-output devices  14  may include wireless communications circuitry  16 . Wireless communications circuitry  16  may include communications circuitry such as radio-frequency (RF) transceiver circuitry  18  formed from one or more integrated circuits such as a baseband processor integrated circuit and other radio-frequency transmitter and receiver circuits. Circuitry  18  may include power amplifier circuitry, transmission lines such as transmission line(s)  20 , passive RF components, antennas  22 , and other circuitry for handling RF wireless signals. 
     Electronic device  10  may include one or more antennas such as antenna  22 . The antenna structures in device  10  may be used to handle any suitable communications bands of interest. For example, antennas and wireless communications circuitry in device  10  may be used to handle cellular telephone communications in one or more frequency bands and data communications in one or more communications bands. Typical data communications bands that may be handled by wireless communications circuitry  16  include the 2.4 GHz band that is sometimes used for Wi-Fi® (IEEE 802.11) and Bluetooth® communications, the 5 GHz band that is sometimes used for Wi-Fi® communications, the 1575 MHz Global Positioning System band, and 2G and 3G cellular telephone bands. These bands may be covered using single-band and multiband antennas. For example, cellular telephone communications can be handled using a multiband cellular telephone antenna. A single band antenna may be provided to handle Bluetooth® communications. Device  10  may, as an example, include a multiband antenna that handles local area network data communications at 2.4 GHz and 5 GHz (e.g., for IEEE 802.11 communications), a single band antenna that handles 2.4 GHz IEEE 802.11 communications and/or 2.4 GHz Bluetooth® communications, or a single band or multiband antenna that handles other communications frequencies of interest. These are merely examples. Any suitable antenna structures may be used by device  10  to cover communications bands of interest. 
     With one suitable arrangement, which is sometimes described herein as an example, antennas such as antenna  22  are formed using an inverted-F antenna design. If desired, this type of configuration may be implemented using planar structures to form a planar inverted-F antenna (PIFA). An inverted-F antenna arrangement may be used to cover one or more communications bands of interest. Bandwidth can be enhanced by including perturbing structures such as short circuit structures and capacitance discontinuity structures in the inverted-F structure. 
     A schematic diagram of a conventional inverted-F antenna is shown in  FIG. 2A . As shown in  FIG. 2A , antenna  24  has a ground  26  and a main resonating element  28 . Arm  28  has branches  30  and  32 . Branch  30  connects resonating element arm  28  to ground  26  and thereby forms a short circuit. Radio-frequency circuit  34  is associated with branch  32  and feeds antenna  24 . The separation L 2  between arm  32  and arm  30  influences the impedance of antenna  24 . If the size of L 2  is reduced, feed  34  is moved closer to short circuit branch  30 , so the input impedance tends to decrease. 
     The frequency response of antenna  24  is influenced by the length L 1  of arm  28 . Maximum antenna performance is generally obtained at radio-frequency signal frequencies at which L 1  is equal to about a quarter of a wavelength. 
     Conventional inverted-F antennas of the type shown in  FIG. 2A  often have insufficient bandwidth to cover a communications band of interest. To address this issue, the resonating element arm  28  may be provided with two portions each having a different associated arm length. This type of conventional inverted-F antenna is shown in  FIG. 2B . In the arrangement of  FIG. 2B , antenna resonating element arm  28  has a first arm portion  28 A with a length of L 1  and a second arm portion  28 B with a length of L 3 . Because lengths L 1  and L 3  are different, each arm portion will contribute a different resonance peak to the frequency response of antenna  24 , thereby broadening its radio-frequency performance. However, it is not always desirable to broaden an antenna&#39;s bandwidth by adding additional segments to the resonating element arm, as this may not be permitted due to layout constraints and may involve rerouting the antenna layout. 
     An arrangement for providing enhanced antenna bandwidth in accordance with an embodiment of the present invention is shown in  FIG. 3 . As shown in  FIG. 3 , antenna  22  may have a ground  50  and a main resonating element arm  34 . Arm  34  has branches  36  and  38 . Branch  36  connects arm  34  to ground  50  and forms a short circuit. Radio-frequency circuit  44  and associated antenna feed terminals  40  and  42  schematically represent a location at which transmission line  20  ( FIG. 1 ) may be coupled to antenna  22  for feeding antenna  22 . Terminal  40  may be a positive antenna feed terminal and terminal  42  may be a ground antenna feed terminal. Positive antenna feed terminal  40  may be electrically connected to resonating element arm  34 , whereas ground antenna feed terminal  42  may be grounded to ground  50 . Branch  38  and its associated antenna terminals may therefore serve as an antenna feed for antenna  22 . 
     In addition to shorting branch  36 , antenna  22  may be provided with one or more additional shorting structures. These structures are illustrated schematically by line  46  in  FIG. 3 . As shown in  FIG. 3 , shorting structures  46  provide a shorting path between resonating element arm  34  and ground  50  that is parallel to shorting path  36 . 
     Shorting structures  46  are located at a different longitudinal location along resonating element longitudinal axis  52  than shorting path  36 . For example, shorting structures  46  may be located a longitudinal distance LB from feed path  38 , whereas shorting branch path  36  is located further along arm  34  at a distance LC from shorting structures  46 . To ensure that shorting structures  46  do not overwhelm shorting path  36 , shorting structures  46  may also be laterally offset from main resonating element longitudinal axis  52 , as shown schematically in the diagram of  FIG. 3 . 
     With the arrangement of  FIG. 3 , length LA of resonating element arm  34  may be configured to be about a quarter of a wavelength at the antenna operating frequency of interest. When length LA is selected in this way, antenna  22  will cover this desired operating frequency. Bandwidth broadening may be provided by the impedance perturbations introduced by the impedance discontinuity associated with shorting structure  46 . In the absence of shorting structures  46 , antenna  22  would exhibit a gain peak at a given frequency. In the presence of shorting structures  46 , the radio-frequency properties of antenna  22  are perturbed and a second, shifted gain peak may arise due to the presence of structures  46 . When the contributions of the unperturbed and perturbed gain peaks are combined, the resulting overall bandwidth performance of antenna  22  tends to increase. The perturbation arises because in the presence of shorting structure  46  there are two possible contributors to signal reflections at the short circuit end of resonating element  34 —the first being associated with short circuit branch  36  at a distance of LB+LC from feed branch  38  and the second being associated with short circuit structure  46  at a distance of LB from feed branch  38 . 
     Antennas such as antenna  22  of  FIG. 3  may be implemented as planar inverted-F structures or other suitable inverted-F structures using conductive components such as wires, conductive circuit board traces and vias, stamped metal foil, portions of a conductive housing or support for electronic device  10 , etc. 
     With one suitable arrangement, antenna  22  may be implemented using a printed circuit board structure. In this type of configuration, resonating element arm  34  may be formed from circuit board trace and ground  50  may be formed from a planar ground plane structure on the circuit board (e.g., a backside conductive layer). Conductive materials in this type of antenna  22  may include copper, gold, tungsten, aluminum, etc. Branch conductors for forming shorting path  36 , shorting structures  46 , and conductive paths in branch  38  may be implemented using conductive vias. Vias may be formed, for example, by plating copper or otherwise forming suitable conductive materials within one or more openings in a printed circuit board substrate. The openings may be, for example, cylindrical holes that run vertically so that their longitudinal axes are perpendicular to longitudinal axis  52  of resonating element arm  34  and perpendicular to ground plane  50 . 
     An illustrative antenna  22  that has been formed using a printed circuit board is shown in  FIG. 4 . As shown in  FIG. 4 , antenna  22  may have ground plane element  50  and resonating element  34 . Ground plane element  50  may be formed from a planar conductive layer such as the underside of a two-sided printed circuit board. Resonating element  34  may be formed from a planar conductive layer such as the upper side of a two-sided printed circuit board. Dielectric layer  60  may be formed from rigid printed circuit board dielectric (e.g., fiberglass-filled epoxy) or other suitable dielectric materials. Layer  60  generally covers all of ground plane layer  50  (e.g., in the shape of a rectangle or other convenient printed circuit board shape), but only the portion of dielectric  60  that lies directly beneath conductive layer  34  in  FIG. 4  is shown in  FIG. 4 ). 
     As shown in  FIG. 4 , resonating element layer  34  may have a shape such as a T-shape with an elongated portion  62  and a base portion  64 . Elongated portion  62  may be, for example, a rectangular region having a length that is substantially longer than its width. In the  FIG. 4  example, the length of region  62  runs parallel to longitudinal axis  52  of element  34  and antenna  22 . Portion  62  may, in general, have any suitable shape. For example, portion  62  may have one or more arms, may have one or more bent portions (e.g., to form a meandering path), may have protrusions, etc. The arrangement of  FIG. 4  in which elongated portion  62  is formed from an elongated planar rectangular conductive member is merely illustrative. 
     In base region  64  of resonating element  34 , one or more vertical conductive structures may be provided that connect resonating element  34  to ground  50 . These vertical conductive structures may run parallel to vertical dimension  66  and form shorting branch  36  of antenna  22  ( FIG. 3 ). Any suitable conductive materials may be used to form shorting branch  36 . In the example of  FIG. 4 , shorting branch  36  has been formed by conductive vias  68 . Vias  68  are short columns of metal or other conductive materials that short resonating element  34  to ground plane  50 . There are six vias  68  in the example of  FIG. 4 . In general, any suitable number of vias  68  or other vertical shorting structures may be used to electrically connect upper planar resonating element portion  64  with lower ground plane layer  50  and thereby from shorting branch  36 . 
     Shorting structures  46  of  FIG. 3  may be formed from metal members or other conductive structures that run parallel to vertical axis  66 . In the  FIG. 4  example, shorting structure  46  has been formed by a via  82  having a center  70  that is laterally offset from longitudinal axis  52  by distance D. Use of smaller distances D may increase the magnitude of the impact of via  82  on antenna performance, whereas use of relatively larger distances D (e.g., large lateral offsets from the longitudinal axis of arm  34  so that via  82  is formed under a lateral protrusion from the main conductive portion of arm  32  as shown in  FIG. 3 ) may help prevent shorting structure  46  from exhibiting too much impact on antenna performance. This is merely illustrative. Shorting structure  46  may be formed by one or more vias, by bent metal tabs, by wires, etc. 
     Antenna  22  may be fed by coupling a transmission line such as coaxial cable  54  to antenna  22  at an antenna feed (feed  72 ) formed from antenna feed terminals such as feed terminal  40  and  42 . Coaxial cable  54  may have a positive conductor and a ground conductor. The ground conductor may be provided by an outer conductive layer such as layer  56 . The positive conductor may be provided by a center conductor such as center conductor  58 . Center conductor  58  may be coupled to positive antenna feed terminal  40  using a vertical conductor  38 . Vertical conductor  38  may be formed from an extending portion of center conductor  58 , a via, or other suitable conductive structure. Ground conductor  56  may be connected to ground antenna feed terminal  42  (e.g., at ground plane  50 ). To improve impedance matching, a matching network may be connected to the antenna feed (e.g., using shunt-connected and series-connected components such as inductors, capacitors, resistors, conductive and dielectric structures that contribute inductance, capacitance, and resistance, etc.). Although the transmission line in the  FIG. 4  example is formed from a coaxial cable, this is merely illustrative. The transmission line that connects radio-frequency transceiver  18  to antenna  22  (i.e., transmission line  20  in  FIG. 1 ) may be implemented using a microstrip transmission line, a stripline transmission line, a coaxial cable transmission line, etc. 
     A broadened bandwidth is obtained for antenna  22 , when antenna signals can propagate past shorting structure  46  from antenna feed  72  to reach shorting structure  36 . If the effect of shorting structure  46  is too prominent, signals will be prevented from reaching shorting structures  36 , so antenna  22  will function as a conventional inverted-F antenna in which shorting structures  46  form shorting branch  36  and in which there are no additional shorting structure. To ensure that shorting structures  46  do not behave in this way, the size and location of shorting structures  46  may be selected to properly scale the impact of shorting structures  46  on the operation of antenna  22 . 
     One way in which the impact of shorting structures  46  can be adjusted relates to the location of the shorting path. As shown in  FIG. 4 , for example, the via that makes up shorting path  46  may be offset somewhat (e.g., by lateral distance D) relative to central longitudinal axis  46 . 
     Another way in which the impact of shorting structures  46  can be adjusted is by ensuring that the size of vias such as via  82  is not too large. If there are too many vias or the vias have lateral dimensions that are too large, shorting structures  46  may exhibit an undesirably large amount of shorting. In the  FIG. 4  example, there is only one via  46  and its diameter is significantly less than the lateral dimension (width W) of elongated portion  62 . 
       FIG. 5  shows a cross-sectional view of an illustrative printed circuit board antenna  22  of the type shown in  FIG. 4  taken along line  74  in  FIG. 4  and viewed in direction  76 . As shown in  FIG. 5 , antenna resonating element structure  34  may be formed from a planar conductive layer that is separated from an associated planar ground layer  50  by a layer of dielectric  60  (e.g., a layer of rigid or flexible printed circuit board material). Conductive structures such as structures  68 ,  46 , and  38  may be formed from one or more vias or other structures that run parallel to vertical dimension  66 . Resonating element arm  34  has a longitudinal axis that runs parallel to longitudinal axis  52  of antenna  22 . Coaxial cable  54  may be coupled to antenna feed  72  by connecting outer conductive layer  56  to ground plane conductive layer  50  at terminal  42  (e.g., using a solder connection, a weld, a coaxial connector, or other suitable electrical connector) and by electrically coupling center conductor  58  to vertical conductive member  38 . Vertical member  38  may be formed from one or more vias, a wire, an extended portion of center conductor  58 , or any other suitable vertically extending conductor. Vertical member  38  may be coupled to antenna resonating element arm  34  at point  40  (e.g., using solder, a weld, an electroplated via connection, etc.). 
     If desired, an electrical (impedance) discontinuity along the length of the resonating element arm  34  may be generated using a capacitance discontinuity structure. The capacitance discontinuity structure may, for example, be located between feed  72  and shorting branch  36  of antenna  22 , as shown schematically by capacitance discontinuity  78  of  FIG. 6 . 
     Capacitance discontinuity  78  can be implemented by structures that locally increase or decrease the capacitance of antenna resonating element  34 . Capacitance discontinuity  78  may, for example, be located at a distance LB from feed  74  and a distance LC from shorting branch  36 . Capacitance discontinuity  78  may be offset laterally from longitudinal axis  52  of resonating element  34  as shown schematically in  FIG. 6 . In arrangements such as these, the vias or other structures used to form capacitance impedance discontinuity  78  are offset sufficiently so as not to lie directly beneath the conductive portions of antenna resonating element arm  34 , thereby preventing the impact of discontinuity  78  from becoming too large and overwhelming the performance characteristics of antenna  22 . 
     As with the electrical discontinuity produced with shorting structure  46  of  FIG. 3 , capacitance discontinuity structure  78  may create two impedance contributions for antenna  22 —a first impedance characteristic that is associated with the signal path between feed  74  and shorting structure  36  (corresponding to path length LB+LC) and a second impedance characteristic associated with the signal path between feed  74  and capacitance discontinuity  78  (of path length LB). 
     Capacitance discontinuity  78  may be generated using a structure that adds a local capacitance to arm  34  such as an added metal patch or locally increased dielectric constant region in dielectric  60  or may be generated using as structure that removes a local capacitance from arm  34 . 
     An illustrative arrangement in which capacitance discontinuity  78  is generated by hollowing out portions of dielectric  66  or otherwise locally increasing or decreasing the dielectric constant of the dielectric at a location adjacent to antenna resonating element  34  is shown in  FIG. 7 . As shown in the example of  FIG. 7 , antenna  22  may have a conductive member such as antenna resonating element arm  34  that is separated from conductive ground plane member  50  by a dielectric layer  60 . Dielectric layer  60  may be formed from a dielectric such a printed circuit board dielectric (e.g., fiberglass-filled epoxy, flex circuit dielectrics such as polyimide, etc.). Capacitance discontinuity structure  78  may be formed by creating one or more altered-dielectric-constant regions  80  in dielectric layer  60 . Regions  80  may be filled with dielectric that has a lower dielectric constant than dielectric  60 . For example, regions  80  may be created by hollowing out portions of dielectric  60  so that they become filled with a gas such as air. Regions  80  may also be filled with a dielectric that has a greater dielectric constant than dielectric  60  (e.g., by locally treating dielectric  60  or by hollowing out regions  80  and filling the hollowed regions with a dielectric with a greater dielectric constant than dielectric  60 . Combinations of these techniques may also be used. Regions  80  may be laterally offset from longitudinal axis  52  by a distance D to avoid overwhelming antenna  22  with the presence of capacitance discontinuity  78 . 
     Any suitable dielectric materials can be used to form dielectric layer  60  and regions  80 . For example, layer  60  and/or region  80  may be formed from a completely solid dielectric, a porous dielectric, a foam dielectric, a gelatinous dielectric (e.g., a coagulated or viscous liquid), a dielectric with grooves or pores, a dielectric having a honeycombed or lattice structure, a dielectric having spherical voids or other voids, a combination of such non-gaseous dielectrics, etc. Hollow features in solid dielectrics may be filled with air or other gases or lower dielectric constant materials. Examples of dielectric materials that may be used in antenna  22  and that contain voids include epoxy with gas bubbles, epoxy with hollow or low-dielectric-constant microspheres or other void-forming structures, polyimide with gas bubbles or microspheres, etc. Porous dielectric materials used in antenna  22  can be formed with a closed cell structure (e.g., with isolated voids) or with an open cell structure (e.g., a fibrous structure with interconnected voids). Foams such as foaming glues (e.g., polyurethane adhesive), pieces of expanded polystyrene foam, extruded polystyrene foam, foam rubber, or other manufactured foams can also be used in antenna  22 . If desired, the dielectric antenna materials for layer  60  and/or regions  80  can include layers or mixtures of different substances such as mixtures including small bodies of lower density material. 
       FIG. 8  is a cross-sectional side view of antenna  22  of  FIG. 7 . As shown in  FIG. 8 , antenna  22  may have an antenna resonating element arm layer  34  formed from a thin layer of metal (e.g., copper traces) on a layer of dielectric  60 . Dielectric layer  60 , in turn, may be formed on ground layer  50  (e.g., a planar conductive layer on the underside of a printed circuit board). Shorting branch  36  may be formed with one or more vias  68  or other vertical conducting structures. Feed  74  may be formed by coupling a transmission line such as coaxial cable  54  to antenna  22  using positive and ground antenna feed terminals. Capacitance discontinuity structure  78  may be located between feed  74  and shorting branch  36  (not shown to scale in  FIG. 8 ). Capacitance discontinuity structure  78  may be formed from regions  80  that are hollow or are otherwise filled with a dielectric substance that has a different dielectric constant than surrounding portions of dielectric layer  60 . 
       FIG. 9  is a top view of an illustrative antenna  22  showing how a given antenna may contain both an impedance discontinuity structure such as capacitance discontinuity structure  78  and an impedance discontinuity structure such as shorting structure  46  that are located along the length of elongated portion  62  of antenna resonating element arm  34  between feed  74  and shorting branch  36 . As shown in  FIG. 9 , shorting structure  46  may be formed from via  82 , which is electrically connected to protrusion  84  in the conductive trace that makes up resonating element arm  34 . Forming shorting structure  46  at least partly using a protrusion that extends laterally from the side arm  34  helps ensure that shorting structure  46  is not too powerful and does not create a short that completely blocks signals from feed  74  before they reach shorting branch  36 . Hole  80  for capacitance discontinuity structure  78  may also be laterally offset from the longitudinal axis of resonating element arm  34 . 
     As shown in  FIG. 10 , protrusions such a protrusion  84  may be used in forming shorting structures  46  in antenna configurations having other shorting structures. In the  FIG. 10  example, protrusion  84  and associated via  82  form a first shorting structure and via  86  forms a second shorting structure.  FIG. 10  shows how a shorting structure  46  with multiple vias such as vias  86  and  82  may be formed on the same elongated resonating element arm portion  62  as a capacitance discontinuity structure that contains multiple regions  80 . Different longitudinal and/or lateral locations may be used for shorting vias in structure  46  if desired to tune antenna performance (e.g., to adjust bandwidth and/or to reduce or increase the magnitude of the impact of shorting structure  46  on antenna performance). 
     The type of gain broadening effect that may be exhibited by antennas  22  with shorting structures  46  and/or capacitance discontinuity structures is shown in  FIG. 11 . In the graph of  FIG. 11 , antenna gain for antenna  22  is plotted as a function of operating frequency. In the absence of impedance discontinuity structures such as shorting structures  46  and capacitance discontinuity structures  78 , an antenna with a given resonating element arm  34 , dielectric layer  60 , and ground  50  may exhibit a first (unperturbed) gain curve such as curve  88  centered at frequency F 1 . The presence of a shorting structure such as shorting structure  46  and/or the presence of a capacitance discontinuity structure such as capacitance discontinuity structure  78  perturbs the impedance of antenna  22  and thereby contributes to the generation of a shifted gain curve such as gain curve  90  centered at frequency F 2 . In operation, when transmitting and receiving radio-frequency signals (e.g., using radio-frequency transceiver circuitry  18  of  FIG. 1 ), antenna  22  may exhibit an overall gain curve such as gain curve  92  that has a relatively broad bandwidth (e.g., covering subbands at both frequency F 1  and frequency F 2 ). 
     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.

Metadata:
Filing Date: 20090310
Publication Date: 20120124
Grant Date: 20120124
Priority Date: 20090310
Inventors: CHIANG BING
VAZQUEZ ENRIQUE AYALA
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/2258", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/2258", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 42730258