PATENT DOCUMENT

Publication Number: US-8599089-B2
Application Number: US-75066110-A
Country: US
Kind Code: B2

Title: Cavity-backed slot antenna with near-field-coupled parasitic slot

Abstract:
Electronic devices may be provided with antennas. The antennas may include conductive antenna cavities. Antenna resonating elements may be mounted in the antenna cavities to form cavity antennas. An antenna cavity may be formed from metal structures with curved edges that define a curved cavity opening. A flexible printed circuit substrate may be coated with a layer of metal. Slot antenna structures such as a directly fed antenna slot and a parasitic antenna slot may be formed from openings in the metal layer. The flexible printed circuit substrate may be flexed so that the antenna resonating element forms a non-planar curved shape that mates with the opening of the antenna cavity. A ring of solder may be used to electrically seal the edges of the cavity opening to the metal layer in the antenna resonating element. The curved opening may be aligned with curved housing walls in an electronic device.

Claims:
What is claimed is: 
     
       1. A cavity-backed slot antenna, comprising:
 a conductive cavity; and 
 an antenna resonating element comprising a first slot that is directly fed using first and second antenna feed terminals and a second slot that is not directly feed by the first and second antenna feed terminals and that serves as a parasitic antenna slot, wherein the conductive cavity has cavity edges, wherein the antenna resonating element comprises a layer of metal in which the first and second slots are formed, wherein the layer of metal has peripheral edges, and wherein the cavity-backed slot antenna further comprises a conductive ring of solder along the peripheral edges that electrically connects the peripheral edges of the layer of metal in the antenna resonating element to the cavity edges. 
 
     
     
       2. The cavity-backed slot antenna defined in  claim 1  further comprising an electrical component on the antenna resonating element that tunes the antenna. 
     
     
       3. The cavity-backed slot antenna defined in  claim 1  further comprising a capacitor on the antenna resonating element that is electrically connected across the first slot. 
     
     
       4. The cavity-backed slot antenna defined in  claim 1  wherein the antenna resonating element comprises a flexible printed circuit board substrate. 
     
     
       5. The cavity-backed slot antenna defined in  claim 4  wherein the flexible printed circuit board substrate comprises epoxy. 
     
     
       6. The cavity-backed slot antenna defined in  claim 4  wherein the flexible printed circuit board substrate comprises fiberglass-filled epoxy having a thickness of less than 0.2 mm. 
     
     
       7. The cavity-backed slot antenna defined in  claim 1  wherein the ring of solder shorts the antenna resonating element to the conductive cavity. 
     
     
       8. The cavity-backed slot antenna defined in  claim 1  wherein the cavity edges include at least one curved cavity edge, wherein the layer of metal comprises a non-planar layer of metal in which the first and second slots are formed, and wherein the conductive ring of solder electrically connects the peripheral edges of the non-planar layer of metal in the antenna resonating element to the cavity edges including the curved cavity edge. 
     
     
       9. The cavity-backed slot antenna defined in  claim 1  wherein the conductive cavity has a curved non-planar opening and wherein the layer of metal is flexed about a flex axis to mate with the curved non-planar opening of the conductive cavity. 
     
     
       10. A cavity antenna, comprising:
 a conductive cavity having a curved non-planar opening; 
 an antenna resonating element having a non-planar layer of metal that forms a curved shape that mates with the curved non-planar opening, wherein the antenna resonating element comprises first and second antenna slots in the non-planar layer of metal; and 
 a first antenna feed terminal and a second antenna feed terminal, wherein the first antenna feed terminal and the second antenna feed terminal are located on opposing sides of the first antenna slot. 
 
     
     
       11. The cavity antenna defined in  claim 10  further comprising a capacitor that is connected across one of the two antenna slots. 
     
     
       12. The cavity antenna defined in  claim 10  wherein the antenna resonating element comprises a flexible printed circuit board substrate and wherein the conductive cavity is filled with air. 
     
     
       13. The cavity antenna defined in  claim 12  wherein the first antenna slot comprises a directly fed antenna slot and wherein the second antenna slot comprises a parasitic antenna slot. 
     
     
       14. The cavity antenna defined in  claim 10  wherein the non-planar metal layer has peripheral edges, wherein the conductive cavity comprises cavity edges, and wherein the antenna resonating element is sealed to the cavity with a ring of solder that shorts the peripheral edges of the antenna resonating element to the cavity edges. 
     
     
       15. An electronic device, comprising:
 a curved electronic device housing wall; and 
 a cavity antenna having a conductive antenna cavity with a curved cavity opening and having a non-planar antenna resonating element that is flexed to mate with the curved cavity opening, wherein the non-planar antenna resonating element lies flush with the curved electronic device housing wall. 
 
     
     
       16. The electronic device defined in  claim 15  wherein the antenna resonating element comprises a flexed printed circuit board having a non-planar layer of metal in which a directly fed antenna slot is formed and in which a parasitic antenna slot is formed and wherein the cavity antenna is filled with air. 
     
     
       17. The electronic device defined in  claim 16  further comprising a ring of solder that electrically connects the non-planar layer of metal to mating edges of the conductive antenna cavity. 
     
     
       18. The electronic device defined in  claim 15  further comprising:
 processing circuitry, wherein the curved electronic device housing wall comprises exterior surface portions of the electronic device.

Description:
BACKGROUND 
     This relates generally to antennas, and more particularly, to electronic devices with cavity antennas such as cavity-backed slot antennas. 
     Electronic devices often incorporate wireless communications circuitry. For example, computers may communicate using the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz. Communications are also possible in cellular telephone telecommunications bands and other wireless bands. 
     To satisfy consumer demand for compact and aesthetically pleasing wireless devices, manufacturers are continually striving to produce antennas with appropriate shapes and small sizes. At the same time, manufacturers are attempting to ensure that antennas operate efficiently and do not interfere with nearby circuitry. These concerns are sometimes at odds with one another. If care is not taken, a small antenna or an antenna with a shape that allows the antenna to fit within a confined device housing may tend to exhibit poor efficiency or generate radio-frequency interference. 
     It would therefore be desirable to be able to provide electronic devices with improved antennas. 
     SUMMARY 
     Electronic devices may be provided with antennas. The electronic devices may be computers or other electronic equipment. A housing with curved housing walls may be used to house antennas and other electrical components for an electronic device. 
     The antennas may include conductive antenna cavities. The conductive antenna cavities may be formed from metal. Laser welding techniques may be used to join metal cavity parts to form an antenna cavity. 
     Antenna resonating elements may be mounted in antenna cavities to form cavity antennas. An antenna cavity may have metal structures with curved edges that define a curved cavity opening. An antenna resonating element may have a flexible printed circuit substrate that is coated with a layer of metal. Slot antenna structures such as a directly fed antenna slot and a parasitic antenna slot may be formed from openings in the metal layer. 
     The flexible printed circuit substrate in an antenna resonating element may be flexed about a flex axis so that the antenna resonating element bends and forms the shape of a non-planar curved layer that that mates with the curved opening of the antenna cavity. By using a flexible substrate that is sufficiently rigid to support the traces of the antenna resonating element, the need for underlying dielectric support structures can be reduced or eliminated. 
     A ring of solder may be used to electrically seal the edges of the cavity opening to the metal layer in the antenna resonating element. The curved opening may be aligned with curved housing walls in an electronic device. 
     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 antennas in accordance with an embodiment of the present invention. 
         FIG. 2  is a circuit diagram of an illustrative electronic device with antennas in accordance with an embodiment of the present invention. 
         FIG. 3  is a bottom perspective view of an illustrative antenna in accordance with an embodiment of the present invention. 
         FIG. 4  is an exploded top perspective view of an illustrative antenna in accordance with an embodiment of the present invention. 
         FIG. 5  is a perspective view of a flexible printed circuit substrate on which an antenna resonating element such as a slot antenna resonating element for an electrical device antenna may be formed in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional view of an illustrative cavity antenna in accordance with an embodiment of the present invention. 
         FIG. 7  is a plan view of an illustrative rectangular flexible printed circuit on which a slot antenna resonating element with a directly fed slot and a near-field-coupled parasitic slot have been formed for use in a cavity-backed electronic device antenna in accordance with embodiments of the present invention. 
         FIG. 8  is a plan view of an illustrative flexible printed circuit structure having a footprint with an angled section on which a slot antenna resonating element with a directly fed slot and a near-field-coupled parasitic slot have been formed for use in a cavity-backed electronic device antenna in accordance with embodiments of the present invention. 
         FIG. 9  is a graph showing how a cavity-backed slot antenna design may be used to implement a dual-band antenna in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Antennas are used in wireless electronic devices to support wireless communications. The wireless electronic devices may be desktop computers, computer monitors, computer monitors containing embedded computers, wireless computer cards, wireless adapters, televisions, set-top boxes, gaming consoles, routers, or other electronic equipment. If desired, portable electronic devices such as laptop computers, tablet computers, or small portable computers of the type that are sometimes referred to as handheld computers may be provided with antennas. Antennas may be used in wireless electronic devices such as cellular telephones or media players. The wireless electronic devices in which the antennas are used may also be somewhat smaller devices. Examples of smaller wireless electronic devices include wrist-watch devices, pendant devices, handheld devices, headphone and earpiece devices, and other wearable and miniature devices. 
     An illustrative electronic device that includes antennas is shown in  FIG. 1 . Electronic device  10  of  FIG. 1  may have a housing such as housing  12 . Housing  12  may include plastic walls, metal housing structures, structures formed from carbon-fiber materials or other composites, glass, ceramics, or other suitable materials. Housing  12  may be formed using a single piece of material (e.g., using a unibody configuration) or may be formed from a frame, housing walls, and other individual parts that are assembled to form a completed housing structure. 
     Antennas such as antennas  14  may be mounted within housing  12  (as an example). In general, there may be one antenna, two antennas, or three or more antennas in housing  12 . In the example of  FIG. 1 , there are two antennas in device  10  formed flush with curved walls in housing  12 . This is merely illustrative. 
     Antennas  14  may include an antenna resonating element and, if desired, a cavity structure. In a cavity-type antenna, a resonating element structure is placed adjacent to an opening in a conductive antenna cavity. The presence of the cavity can help prevent radio-frequency interference between the antenna and surrounding electrical components in device  10  and can help direct radio-frequency antenna signals in desired directions. A cavity structure may be used in connection with a patch antenna, a strip antenna, antenna resonating element traces with multiple arms, bends, and other features, or other suitable antenna resonating element structures. With one suitable configuration, which is sometimes described herein as an example, cavity-backed slot antennas are formed in which a slot antenna resonating element is backed by an antenna cavity. This is merely illustrative. In general, any suitable cavity antenna structures may be used in device  10  if desired. 
     As shown in  FIG. 2 , device  10  may include storage and processing circuitry  16 . Storage and processing circuitry  16  may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., static or dynamic random-access-memory), etc. Storage and processing circuitry  16  may be used in controlling the operation of device  10 . Processing circuitry in circuitry  16  may be based on processors such as microprocessors, microcontrollers, digital signal processors, dedicated processing circuits, power management circuits, audio and video chips, and other suitable integrated circuits. 
     With one suitable arrangement, storage and processing circuitry  16  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, antenna and wireless circuit control functions, etc. Storage and processing circuitry  16  may be used in implementing suitable communications protocols. Communications protocols that may be implemented using storage and processing circuitry  16  include internet protocols, 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 cellular telephone communications services, etc. 
     Input-output devices  18  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. Examples of input-output devices  18  that may be used in device  10  include display screens such as touch screens (e.g., liquid crystal displays or organic light-emitting diode displays), buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers and other devices for creating sound, cameras, sensors, etc. A user can control the operation of device  10  by supplying commands through devices  18  or by supplying commands to device  10  through an accessory that communicates with device  10  through a wireless or wired communications link. Devices  18  or accessories that are in communication with device  10  through a wired or wireless connection may be used to convey visual or sonic information to the user of device  10 . Device  10  may include connectors for forming data ports (e.g., for attaching external equipment such as computers, accessories, etc.). 
     Wireless communications devices  20  may include communications circuitry such as radio-frequency (RF) transceiver circuitry  22 . Circuitry  22  may include one or more integrated circuits such as baseband processors, radio-frequency transceivers, power amplifiers, matching circuits, filters, and switching circuitry. One or more transmission lines such as transmission lines  24  may be used to route radio-frequency antenna signals between antennas  14  and transceiver circuitry  22 . Transmission lines  24  may include microstrip transmission lines, coaxial cable transmission lines, etc. 
     As shown in  FIG. 1 , device  10  may have a housing with curved sidewalls. To accommodate curved sidewalls or to satisfy other design constraints, it may be desirable to form a cavity-backed antenna with a curved antenna resonating element and a corresponding curved cavity opening.  FIG. 3  shows an illustrative cavity antenna having a curved surface that may be used in a device such as device  10  of  FIG. 1 .  FIG. 3  is a bottom perspective view of cavity antenna  14 . As shown in  FIG. 3 , cavity antenna  14  may have a cavity structure such as cavity  26  and an antenna resonating element such as antenna resonating element  30 . Cavity structure  26  may be formed from metal or other conductive materials, plastic or other dielectric support structures that have been coated with metal or other conductive materials, or other suitable conductive structures. If desired, cavity structure  26  may be formed from first and second pieces. For example, cavity structure  26  may be formed from first and second metal structures that are joined and laser welded at seam  28 . 
     Antenna resonating element  30  may be formed on a substrate such as a printed circuit board that is mounted in an opening in cavity  26 . In  FIG. 3 , cavity  26  is oriented so that its opening faces downward. As shown, cavity  26  may include planar vertical sidewall structures such as sidewalls  26 A,  26 B, and  26 C and planar rear wall  26 D. If desired, cavity  26  may be formed in other shapes (e.g., shapes with horizontally and vertically curved walls, shapes with bends, etc.). The example of  FIG. 3  is merely illustrative. 
       FIG. 4  is an exploded perspective view of antenna  14  of  FIG. 3  in an orientation in which cavity  26  is facing upwards. In this orientation, cavity opening  32  is visible at the top of cavity  26 . Cavity opening  32  has four edges (in the  FIG. 4  example), including curved edges  34  and straight edges  36 . Because edges  34  are curved, opening  32  and other openings of this type are sometimes referred to as curved antenna cavity openings. Antenna resonating element  30  may have a curved shape such as a non-planar curved layer that is formed by flexing element  30  about flex axis  33 . As a result, element  30  mates with the curved shape of opening  32 . This provides antenna  14  with a curved shape that may fit against curved housing walls  12  of device  10 , as shown in  FIG. 1 . 
     Antenna resonating element  30  may be formed from stamped metal foil, wires, traces of copper or other conductive materials that are formed on a dielectric substrate, combinations of these conductive structures, or other suitable conductive structures. The resonating elements may be based on patch antenna designs, inverted-F antenna designs, monopoles, dipoles, slots, antenna coils, planar inverted-F antennas, or other types of antenna. With one suitable arrangement, which is sometimes described herein as an example, antenna resonating element  30  is formed from a layer of metal or other conductive material (sometimes referred to as a ground plane element or ground plane) in which one or more slot antenna structures have been formed. The slot structures may, for example, be defined by rectangular or angled-rectangular openings in the conductive layer. The conductive layer may be formed from one or more copper layers (e.g., patterned copper traces) or other metals (as examples). 
     The conductive portions of antenna resonating element  30  may be formed on a dielectric substrate such as an injection-molded or compression-molded plastic part, on a rigid printed circuit board, or on a substrate formed from rigid and flexible portions (“rigid flex”). Antenna resonating element  30  may also be formed on a flexible printed circuit board that is based on a thin flexible layer of polymer such as a thin flexible sheet of polyimide. If desired, a support structure (e.g., a rigid support or a flexible layer of plastic) may be used to support the thin flexible polyimide sheet. 
     Antenna resonating element  30  may also be formed from rigid printed circuit board materials that have been formed in sufficiently thin layers to render them flexible. For example, antenna resonating element  30  may be formed from a layer of FR-4 (a flame retardant fiberglass-filled epoxy printed circuit board substrate material) that is about 0.09 to 0.2 mm thick, is about 0.05 to 0.3 mm thick, is less than 0.25 mm thick, is less than 0.2 mm thick, is about 0.14 mm thick, or is another suitable thickness that allows antenna resonating element  30  to be flexed to accommodate the shape of opening  32 . 
     With this type of configuration, element  30  can be both sufficiently flexible to conform to curved opening  32  and sufficiently rigid to hold a desired shape without resting on an additional dielectric support structure (e.g., without using a plastic support in cavity  26 ). Because dielectric support structures can (if desired) be omitted from cavity  26 , cavity  26  can be filled exclusively with air. As a result, there will be no dielectric support under antenna resonating element  30  in the interior of cavity  26 . This may help reduce performance variations that might otherwise arise when placing element  30  adjacent to a dielectric support (e.g., performance variations that might arise from uncertainty in the small separation between the antenna element and the underlying dielectric support). 
       FIG. 5  is a perspective view of an illustrative antenna resonating element. As shown in  FIG. 5 , antenna resonating element  30  may be formed from a substrate such as a rigid or flexible printed circuit board substrate (substrate  38 ). Substrate  38  may contain layers of dielectric and patterned metal (shown schematically as layers  40  in  FIG. 5 ). Components such as component  50  may be formed on the underside of substrate  38  (in the orientation of  FIG. 5 ) and components such as component  44  may be formed on the top side substrate  38  (in the orientation of  FIG. 5 ). Configurations in which components are mounted on only a single side of substrate  38  may also be used. 
     Components  44  and  50  may include electrical components such as surface mount technology (SMT) capacitors, resistors, inductors, switches, filters, radio-frequency connectors (e.g., miniature coaxial cable connectors), cables, clips, or other suitable components. Conductive traces in element  30  (e.g., patterned or blanket metal films on the surfaces of substrate  38  or in layers  40  of substrate  38 ) may be used to interconnect electrical components and to form antenna resonating element structures. Surface traces may be formed on upper surface  42  of antenna resonating element  30  (i.e., the interior surface of antenna resonating element  30  in the orientation of  FIG. 4 ) or may be formed on the lower surface of antenna resonating element  30  (i.e., the exterior surface of antenna resonating element  30  in the orientation of  FIG. 4 ). 
     One or more slots for antenna resonating element  30  such as antenna slot  48  may be formed within the layer of metal or other conductive material on surface  42  (or in layers  40 ). In the example of  FIG. 5 , slot  48  is formed in within metal layer  42  (e.g., a copper layer). Component  44  may be, for example, an SMT capacitor that bridges slot  48 . 
     During assembly, a ring of conductive material such as a ring of solder formed on a ring of gold or other ring of material at the periphery of surface  42  that accepts solder (i.e., ring  46 ) may be used to electrically short and thereby seal the edges of antenna resonating element  30  to edges  34  and  36  of antenna cavity  26  ( FIG. 4 ). Solder ring  46 , which is sometimes referred to as a sealing ring or conductive sealing ring, may surround the periphery of layer  38  and may have a rectangular shape, a shape with curved edges, a shape with angled edges, a shape with combinations of straight and curved edges, etc. 
     A cross-sectional end view of cavity antenna  14  of  FIG. 3  is shown in  FIG. 6 . As shown in  FIG. 6 , a transmission line such as coaxial cable  24  may be used to feed antenna  14 . Transmitted radio-frequency antenna signals may be routed from transceiver circuitry  22  to antenna  14  using cable  24 . During signal reception, received radio-frequency antenna signals may be routed from antenna  14  to transceiver circuitry  22  using cable  24 . Cable  24  (or other transmission line structures in device  10 ) may be coupled to antenna  14  using antenna feed terminals such as positive antenna feed terminal  58  and ground antenna feed terminal  56 . Ground feed  56  may be electrically connected to a conductive outer braid in cable (e.g., a ground path in cable  24 ) using solder or a connector. Positive feed  58  may be connected to positive center wire  54  (e.g., a positive signal path in cable  24 ) using solder or a connector. Antenna feed terminals  56  and  58  may bridge one or more slots such a slot  48  of  FIG. 5 . 
     Alignment brackets (spring clips) such as brackets  52  or other suitable alignment structures (e.g., plastic alignment structures) may be mounted to substrate  38  in antenna resonating element  30  (e.g., using solder, fasteners such as screws, clips, springs, welds, adhesive, etc.). Alignment structures such as brackets  52  may help to align resonating element  38  with respect to cavity  26  during assembly. If desired, mounting structures such as mounting brackets  60  may be connected to cavity structure  26  (e.g., using welds or other suitable attachment mechanisms). Brackets  60  may be provided with openings such as holes  62 . Screws, heat stakes, alignment posts, or other structures may pass through holes  62  when antenna  14  is mounted within housing  12  of device  10 . 
     If desired, more than one slot may be included in antenna resonating element  30 .  FIG. 7  shows an illustrative configuration that may be used for antenna resonating element  30  that is based on two slots. Each slot in antenna resonating element  30  of  FIG. 7  may be formed from a respective opening in conductive layer  42  (e.g., a copper layer that extends across the entire surface of the substrate for antenna resonating element). Conductive solder ring  46  may surround the periphery of layer  42 . Ring  46  may be formed before or after element  30  is mounted to cavity  26 . Components such as component  44  (e.g., an SMT capacitor) may be mounted to element  30  (e.g., with a pair of terminals that bridge one or more of slots  48 ). 
     One or both of the slots may be fed using the antenna feed formed from feed terminals  56  and  58 . In the example of  FIG. 7 , upper slot  48 A is directly fed using feed terminals  56  and  58  that are located on opposing sides (i.e., the longer sides) of slot  48 A and this slot is bridged by capacitor  44 , whereas lower slot  48 B serves as a parasitic antenna element that is not directly feed by transmission line  24 . In this type of configuration, the lower slot is near-field coupled to the upper slot through near-field electromagnetic coupling. Parasitic slot  48 B, in conjunction with tuning elements such a capacitor  44 , tunes antenna  14 . This allows attributes of the performance of antenna  14  such as the bandwidth of antenna  14  and the location of resonant peaks in the performance of antenna  14  to be optimized. 
       FIG. 8  shows how slots  48  may have other shapes (e.g., rectangles with bends). In general, there may be any number of directly fed slots and parasitic slots and these slots may be rectangular, rectangular with multiple arms or bends, curved shapes, etc. In a typical dual band arrangement, the size of the directly fed slot has a perimeter equal to one wavelength at the fundamental frequency of interest (i.e., at the center frequency of the lower band). Response in the upper band can be obtained by exploiting harmonic resonances (i.e., the center frequency of the upper band may coincide with a harmonic of the fundamental frequency). 
     The impact of tuning on the performance of a cavity-backed slot antenna with an antenna resonating element of the type shown in  FIG. 7  is shown in  FIG. 9 .  FIG. 9  is a graph of antenna performance (standing wave ratio SWR) versus operating frequency f. Dashed curve  66  corresponds to antenna performance when antenna slot  48 A is fed in the absence of parasitic slot  48 B and in the absence of tuning capacitor  44 . Solid curve  64  corresponds to antenna performance when antenna slot  48 A is fed directly, parasitic slot  48 B is present, and tuning capacitor  44  is present. 
     In the example of  FIG. 9 , frequencies fa and fb are center frequencies for a dual band antenna such as a dual band antenna for supporting IEEE 802.11 communications. In this type of scenario, frequency fa may be, for example, 2.4 GHz and frequency fb may be, for example, 5 GHz. Other types of antenna arrangements (e.g., using fewer than two bands or more than two bands in antenna  14  or using different band frequencies) may also be used. The use of a dual band IEEE 802.11 configuration is merely illustrative. 
     When slot  48 B and capacitor  44  are not present, the antenna may exhibit resonant peaks  72  and  74  that are not both aligned with desired communications bands (i.e., peaks  72  and  74  may not both be aligned with band center frequencies fa and fb). The bandwidths of the antenna in the upper and lower bands may also be narrower than desired. For example, the bandwidth BW 1  of the band associated with resonant peak  74  (i.e., the upper band) may be undesirably narrow. 
     When slot  48 B and capacitor  44  are present, antenna  44  may operate as desired. In particular, resonant peak  74  may be moved lower in frequency by the presence of capacitor  44  (larger values of which may be used to produce correspondingly larger downward frequency shifts in peak  74 ). In this position, frequency peak  70  may be properly aligned with upper band center frequency fb. The position of peak  72  may also shift (e.g., to the position shown by frequency peak  68 , which is properly aligned with lower band frequency fa). The presence of parasitic slot  48 B may help broaden the bandwidth of the antenna. For example, the bandwidth of antenna  14  at upper frequency fb may be broadened from BW 1  (when no parasitic slot is present) to BW 2  (in the presence of parasitic slot  48 B). 
     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: 20100330
Publication Date: 20131203
Grant Date: 20131203
Priority Date: 20100330
Inventors: BEVELACQUA PETER
HILL ROBERT J.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/18", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/18", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 44080286