PATENT DOCUMENT

Publication Number: US-8963794-B2
Application Number: US-201113216073-A
Country: US
Kind Code: B2

Title: Distributed loop antennas

Abstract:
Electronic devices may be provided with antenna structures such as distributed loop antenna resonating element structures. A distributed loop antenna may be formed on an elongated dielectric carrier and may have a longitudinal axis. The distributed loop antenna may include a loop antenna resonating element formed from a sheet of conductive material that extends around the longitudinal axis. A gap may be formed in the sheet of conductive material. The loop antenna resonating element may be directly fed or indirectly fed. In indirect feeding arrangements, an antenna feed structure for indirectly feeding the loop antenna resonating element may be formed from a directly fed loop antenna structure on the elongated dielectric carrier.

Claims:
What is claimed is: 
     
       1. A loop antenna, comprising:
 a loop antenna resonating element formed from a sheet of conductive material that is wrapped around an axis to form a conductive loop; and 
 an antenna feed structure that is directly fed and that is configured to indirectly feed the loop antenna resonating element. 
 
     
     
       2. The loop antenna defined in  claim 1  wherein the antenna feed structure comprises a loop-shaped structure. 
     
     
       3. The loop antenna defined in  claim 1  further comprising:
 a dielectric carrier on which the sheet of conductive material is formed. 
 
     
     
       4. The loop antenna defined in  claim 1  wherein the sheet of conductive material forms a loop with a gap. 
     
     
       5. A loop antenna, comprising:
 a loop antenna resonating element formed from a sheet of conductive material that is wrapped around an axis to form a conductive loop; 
 dielectric carrier on which the sheet of conductive material is formed; and 
 an antenna feed structure on the dielectric carrier. 
 
     
     
       6. The loop antenna defined in  claim 5  wherein the antenna feed structure is directly fed and is configured to indirectly feed the loop antenna resonating element. 
     
     
       7. The loop antenna defined in  claim 6  wherein the antenna feed structure comprises a loop-shaped structure. 
     
     
       8. The loop antenna defined in  claim 7  wherein the axis comprises a longitudinal axis associated with the loop antenna resonating element and wherein the loop-shaped structure comprise a loop of conductive material that lies in a plane perpendicular to the longitudinal axis. 
     
     
       9. A loop antenna, comprising:
 a loop antenna resonating element formed from a sheet of conductive material that is wrapped around an axis to form a conductive loop, wherein the sheet of conductive material forms a loop with a gap and wherein the gap is configured to form a meandering path across the sheet of conductive material. 
 
     
     
       10. An electronic device, comprising:
 a housing; and 
 at least first and second antennas mounted in the housing, wherein at least the first antenna comprises a loop antenna having a longitudinal axis, wherein the loop antenna comprises a sheet of conductive material that extends around the longitudinal axis, wherein the second antenna lies along the longitudinal axis, wherein the sheet of conductive material is spanned by a gap that extends along the longitudinal axis, wherein the first antenna comprises an antenna feed structure, wherein the antenna feed structure is directly fed by a transmission line, wherein the sheet of conductive material is configured to form a loop antenna resonating element for the first antenna, and wherein the antenna feed structure is configured to indirectly feed the loop antenna resonating element. 
 
     
     
       11. The electronic device defined in  claim 10  wherein the second antenna comprises an indirectly fed loop antenna. 
     
     
       12. An electronic device, comprising:
 a housing; and 
 at least first and second antennas mounted in the housing, wherein at least the first antenna comprises a loop antenna having a longitudinal axis, wherein the loop antenna comprises a sheet of conductive material that extends around the longitudinal axis, wherein the second antenna lies along the longitudinal axis, wherein the sheet of conductive material is spanned by a gap that extends along the longitudinal axis, wherein the housing includes conductive structures that at least partly define an interior region in the electronic device in which the first antenna is mounted, and wherein the gap lies along an exterior surface of the electronic device. 
 
     
     
       13. An antenna, comprising:
 a dielectric carrier; 
 a loop antenna resonating element having a longitudinal axis, wherein the loop antenna resonating element comprises a sheet of conductive material that surrounds the dielectric carrier and extends around the longitudinal axis; and 
 an antenna feed structure, wherein the loop antenna resonating element is indirectly fed by the antenna feed structure. 
 
     
     
       14. The antenna defined in  claim 13  wherein the antenna feed structure comprises a loop of conductive material on the dielectric carrier that forms a loop antenna feed structure. 
     
     
       15. The antenna defined in  claim 14  further comprising at least some metal on the dielectric carrier that is shorted between the loop antenna feed structure and the sheet of conductive material that forms the loop antenna resonating element. 
     
     
       16. The antenna defined in  claim 15  wherein the loop antenna resonating element is configured to resonate in a first band and a second band and wherein the antenna feed structure is configured to resonate in the second band. 
     
     
       17. The antenna defined in  claim 16  wherein the first band comprises a 2.4 GHz band and wherein the second band comprises a 5 GHz band.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with antennas. 
     Electronic devices such as computers are often provided with antennas. For example, a computer monitor with an integrated computer may be provided with antennas that are located along an edge of the monitor and are backed by antenna cavities. 
     Challenges can arise in mounting antennas within an electronic device. For example, the relative position between an antenna and surrounding device structures can have an impact on antenna tuning and bandwidth. If care is not taken, an antenna may become detuned or may exhibit an undesirably small efficiency bandwidth. 
     It would therefore be desirable to be able to provide improved antennas for use in electronic devices. 
     SUMMARY 
     Electronic devices may be provided with antenna structures. The antenna structures may include distributed loop antennas. A distributed loop antenna may have a distributed loop antenna resonating element structure with a longitudinal axis. The distributed loop antenna resonating element may be formed from a strip of metal having a first dimension that is wrapped around the longitudinal axis and a second dimension that is distributed along the longitudinal axis. A gap may be formed across the second dimension of the strip of metal. The gap may follow a meandering path to increase its capacitance. Additional components such as capacitors may bridge the gap. If desired, tunable components may be used to bridge the gap. The tunable components may include adjustable capacitors or other circuitry that may be adjusted by control circuitry to control antenna frequency response. 
     A distributed loop antenna may be formed on an elongated dielectric carrier that is aligned with the longitudinal axis of the distributed loop antenna resonating element structure. Part or all of the volume of the loop antenna may be buried inside the housing of the electronic device, leaving only a portion of the gap on the loop antenna exposed. The loop antenna resonating element structure may be directly fed or indirectly fed. In indirect feeding arrangements, an antenna feed structure for indirectly feeding the loop antenna resonating element may be formed from a directly fed loop antenna structure on the elongated dielectric carrier. 
     In electronic devices with multiple antennas, one or more antennas may be mounted in a device housing so that they lie along the longitudinal axis of a distributed loop antenna. This type of arrangement may help maximize isolation between antennas. 
     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 antenna structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross-sectional side view of illustrative antenna structures mounted within an illustrative electronic device in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of illustrative wireless circuitry for an electronic device including a transceiver circuit and antenna coupled by a transmission line path in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of conductive structures forming an illustrative antenna resonating element for a distributed loop antenna in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional end view of an illustrative distributed loop antenna having an oval cross-sectional shape in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional end view of an illustrative distributed loop antenna having a rectangular cross-sectional shape in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional end view of an illustrative distributed loop antenna having a cross-sectional shape with an angled side in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional end view of an illustrative distributed loop antenna having a cross-sectional shape with a combination of straight and curved sides in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of conductive structures forming an illustrative antenna resonating element for a distributed loop antenna with at least one angled surface in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of illustrative distributed loop antenna structures showing illustrative locations that may be used for antenna feed terminals that directly feed a distributed loop antenna in accordance with an embodiment of the present invention. 
         FIG. 11  is a diagram showing how a first loop antenna structure that is directly fed may serve as an indirect feeding structure for indirectly feeding a second loop antenna structure through near field electromagnetic coupling in a configuration in which the first loop antenna structure is coplanar with the second loop antenna structure in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram showing how a first loop antenna structure that is directly fed may serve as an indirect feeding structure for indirectly feeding a second loop antenna structure through near field electromagnetic coupling in a configuration in which the first loop antenna structure lies in a plane that is perpendicular to the plane of the second loop antenna structure in accordance with an embodiment of the present invention. 
         FIG. 13  is a diagram showing how a first loop antenna structure that is directly fed may serve as an indirect feeding structure for indirectly feeding a second loop antenna structure through near field electromagnetic coupling in a configuration in which the first loop antenna structure and the second loop antenna structure lie in distinct parallel planes in accordance with an embodiment of the present invention. 
         FIG. 14  is a graph of antenna performance for an illustrative indirectly fed distributed loop antenna showing respective contributions to performance that may be made by a loop-shaped indirect feeding structure and a distributed loop antenna resonating element structure in accordance with the present invention. 
         FIG. 15  is a table of antenna performance data for an illustrative indirectly fed distributed loop antenna showing respective contributions to performance that may be made by a loop-shaped indirect feeding structure and a distributed loop antenna resonating element structure in first and second communications bands of interest in accordance with the present invention. 
         FIG. 16   a  is a perspective view of an illustrative indirectly fed distributed loop antenna in which a feeding loop structure and a distributed loop antenna structure are mounted parallel to each other without lying in a common plane in accordance with an embodiment of the present invention. 
         FIG. 16   b  is a perspective view of an illustrative indirectly fed distributed loop antenna in which a feeding loop structure and a distributed loop antenna structure are mounted parallel to one another within a common plane with the feeding loop nested within the distributed loop antenna structure in accordance with an embodiment of the present invention. 
         FIG. 17   a  is a perspective view of an illustrative indirectly fed distributed loop antenna in which a feeding loop structure and a distributed loop antenna structure are oriented perpendicular to each other in accordance with an embodiment of the present invention. 
         FIG. 17   b  is a perspective view of an illustrative indirectly fed distributed loop antenna of the type shown in  FIG. 17   a  in which the feed for the feeding loop structure is not immediately adjacent to the distributed loop antenna structure in accordance with an embodiment of the present invention. 
         FIG. 18  is a perspective view of an illustrative indirectly fed distributed loop antenna in which the feeding structure includes a strip of conductor that overlaps part of a distributed loop antenna resonating element surface in accordance with an embodiment of the present invention. 
         FIG. 19  is a top view of an illustrative indirectly fed distributed loop antenna of the type shown in  FIG. 18  showing how the strip of conductor for forming an indirect feed may be an extension from part of a transmission line structure in accordance with an embodiment of the present invention. 
         FIG. 20  is a perspective view of an illustrative distributed loop antenna resonating element having a meandering gap that increases gap capacitance in a sheet of conductor wrapped around a longitudinal axis of the distributed loop antenna resonating element in accordance with an embodiment of the present invention. 
         FIG. 21  is a perspective view of an illustrative distributed loop antenna resonating element having electrical components that bridge a gap in the distributed loop resonating element in accordance with an embodiment of the present invention. 
         FIG. 22  is a diagram showing how a distributed loop antenna such as an indirectly fed distributed loop antenna may be provided with tunable circuitry such as a tunable capacitor to tune the distributed loop antenna in accordance with an embodiment of the present invention. 
         FIG. 23  is a diagram showing how a distributed loop antenna may be provided with tunable circuitry such as a tunable circuit with a parallel capacitor to tune the distributed loop antenna in accordance with an embodiment of the present invention. 
         FIG. 24  is a diagram showing how a loop structure for a distributed loop antenna resonating element may be oriented with respect to an X-Y-Z coordinate system in accordance with an embodiment of the present invention. 
         FIG. 25  is a graph of an illustrative radiation pattern that may be associated with a loop antenna of the type shown in  FIG. 24  in accordance with an embodiment of the present invention. 
         FIG. 26  is a perspective view of an illustrative indirectly fed distributed loop antenna formed from metal traces on a dielectric carrier showing how the loop structure of the antenna may be oriented with respect to an X-Y-Z coordinate system in accordance with an embodiment of the present invention. 
         FIG. 27  is a diagram showing how an antenna such as an inverted-F antenna or other antenna may be isolated from a distributed loop antenna by locating the antenna along the longitudinal axis of the distributed loop antenna in accordance with an embodiment of the present invention. 
         FIG. 28  is a diagram showing how a pair of distributed loop antennas can be isolated from each other by locating each distributed loop antenna along the longitudinal axis of the other distributed loop antenna in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with antennas and other wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. One or more antennas may be provided in an electronic device. For example, antennas may be used to form an antenna array to support communications with a communications protocol such as the IEEE 802.11(n) protocol that uses multiple antennas. 
     An illustrative electronic device of the type that may be provided with one or more antennas is shown in  FIG. 1 . Electronic device  10  may be a computer such as a computer that is integrated into a display such as a computer monitor. Electronic device  10  may also be a laptop computer, a tablet computer, a somewhat smaller portable device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, a media player, or other electronic equipment. Illustrative configurations in which electronic device  10  is a computer formed from a computer monitor are sometimes described herein as an example. In general, electronic device  10  may be any suitable electronic equipment. 
     Antennas may be formed in device  10  in any suitable location such as location  26 . The antennas in device  10  may include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, cavity antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. The antennas may cover cellular network communications bands, wireless local area network communications bands (e.g., the 2.4 and 5 GHz bands associated with protocols such as the Bluetooth® and IEEE 802.11 protocols), and other communications bands. The antennas may support single band and/or multiband operation. For example, the antennas may be dual band antennas that cover the 2.4 and 5 GHz bands. The antennas may also cover more than two bands (e.g., by covering three or more bands or by covering four or more bands). 
     Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures such as conductive housing structures, from conductive structures such as metal traces on plastic carriers, from metal traces in flexible printed circuits and rigid printed circuits, from metal foil supported by dielectric carrier structures, from wires, and from other conductive materials. 
     Device  10  may include a display such as display  18 . Display  18  may be mounted in a housing such as electronic device housing  12 . Housing  12  may be supported using a stand such as stand  14  or other support structure. 
     Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Display  18  may be a touch screen that incorporates capacitive touch electrodes or other touch sensor components or may be a display that is not touch sensitive. Display  18  may include image pixels formed from 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 layer may cover the surface of display  18 . Rectangular active region  22  of display  18  may lie within rectangular boundary  24 . Active region  22  may contain an array of image pixels that display images for a user. Active region  22  may be surrounded by an inactive peripheral region such as rectangular ring-shaped inactive region  20 . The inactive portions of display  18  such as inactive region  20  are devoid of active image pixels. Display driver circuits, antennas (e.g., antennas in regions such as region  26 ), and other components that do not generate images may be located under inactive region  20 . 
     The cover glass for display  18  may cover both active region  22  and inactive region  20 . The inner surface of the cover glass in inactive region  20  may be coated with a layer of an opaque masking material such as opaque plastic (e.g., a dark polyester film) or black ink. The opaque masking layer may help hide internal components in device  10  such as antennas, driver circuits, housing structures, mounting structures, and other structures from view. 
     The cover layer for display  18 , which is sometimes referred to as a cover glass, may be formed from a dielectric such as glass or plastic. Antennas mounted in region  26  under an inactive portion of the cover glass may transmit and receive signals through the cover glass. This allows the antennas to operate, even when some or all of the structures in housing  12  are formed from conductive materials. For example, mounting the antenna structures of device  10  in region  26  under part of inactive region  20  may allow the antennas to operate even in arrangements in which some or all of the walls of housing  12  are formed from a metal such as aluminum or stainless steel (as examples). 
     A cross-sectional side view of an illustrative antenna mounted in an electronic device such as device  10  of  FIG. 1  is shown in  FIG. 2 . As shown in  FIG. 2 , display  18  may be mounted within housing  12 . Housing  12  may have peripheral sidewalls that are perpendicular to the planar rear surface of housing  12  or may have sidewalls that are curved, as shown by dashed line  12 ′. Electrical components  32  may be mounted on one or more substrates such as substrate  30  within the interior of housing  12 . Electrical components  32  may include integrated circuits, discrete components such as resistors, capacitors, and inductors, connectors, sensors, audio components such as microphones and speakers, and other electronic equipment. Substrate  30  may be a plastic substrate, a rigid printed circuit board (e.g., a circuit board formed from fiberglass-filled epoxy such as an FR4 printed circuit board), a flexible printed circuit board (“flex circuit”) formed from a flexible sheet of polyimide or other flexible polymer, or other suitable support structure. 
     One or more antennas such as antenna  28  may be mounted within housing  12 . As shown in  FIG. 2 , antenna  28  may have a shape that allows antenna  28  to fit within the confines of housing  12  under regions such as region  26  (e.g., under an exterior surface of device  10  and housing  12  that is associated with inactive peripheral region  20  of display  18 ). In this type of configuration, housing  12  may have conductive walls or other conductive structures that at least partly define an interior region in which antenna  28  is mounted. A top surface of antenna  28  may lie within the exterior surface of housing  12  and device  10  while the remainder of antenna  28  is buried within the interior region of housing  12  and device  10  that is defined by housing walls  12  or  12 ′. 
     Other suitable mounting locations in device  10  include positions behind dielectric antenna windows, etc. In configurations in which device  10  uses a curved housing sidewall shape such as sidewall shape  12 ′, the shape of antenna  28  may be adjusted accordingly (e.g., so that the antenna has a cross-sectional outline that lies within line  28 ′). In general, antenna  28  may have any suitable cross-sectional shape. The illustrative shapes of outlines  28  and  28 ′ in  FIG. 2  are merely illustrative. 
     As shown in  FIG. 3 , wireless circuitry  38  for electronic device  10  may include radio-frequency transceiver circuitry  36  (e.g., one or more receivers, one or more transmitters, etc.). One or more antennas such as antenna  28  may be used in device  10 . Each antenna  28  may be coupled to transceiver circuitry  36  using a radio-frequency communications path such as transmission line  34 . Transmission line  34  may include one or more portions of transmission lines such as coaxial cable transmission lines, microstrip transmission lines, stripline transmission lines, edge coupled microstrip transmission lines, edge coupled stripline transmission lines, or other suitable transmission line structures. Transmission line  34  may include one or more portions of different types of transmission line structures (e.g., a segment of coaxial cable, a segment of a microstrip transmission line formed on a printed circuit board, etc.). Transmission line  34  may contain a positive conductor (+) and a ground conductor (−). The conductors in transmission line may be formed from wires, braided wires, strips of metal, conductive traces on substrates, planar metal structures, housing structures, or other conductive structures. 
     Loop antenna  28  may be formed using conductive antenna resonating element structures such as metal traces on a dielectric carrier such as a plastic support structure. If desired, the conductive structures that form loop antenna  28  may include wires, metal foil, conductive traces on printed circuit boards, portions of conductive housing structures such as conductive housing walls and conductive internal frame structures, and other conductive structures. 
     Loop antenna  28  may have conductive structures that are spread out (“distributed”) along the longitudinal axis of the loop. Loop antenna  28  may therefore sometimes be referred to as a distributed loop antenna. As shown in  FIG. 4 , loop antenna  38  may have a longitudinal axis such as axis  40 . Antenna  28  may be formed from an antenna resonating element structure that contains conductive structures  52 . Conductive structures  52  may include a sheet of conductor that has a first dimension that is wrapped around longitudinal axis  40  and a second dimension ZD that extends along the length of longitudinal axis  40 . 
     Conductive structures  50  may wrap around axis  40  following rotational directions  46 . During operation, antenna currents can flow within sheet  52  around axis  40 . In effect, sheet  52  forms a wide strip of conductor in the shape of a loop that is characterized by a perimeter P. The antenna currents flowing in sheet  52  tend to lie in planes parallel to the X-Y plane of  FIG. 4 , as indicated by arrows  44 . As a result, the “loop” of loop antenna  28  effectively lies in the X-Y plane, whereas the longitudinal axis  40  that runs along the center of the wrapped conductive sheet (sheet  52 ) lies parallel to the Z-axis (and perpendicular to the X-Y plane of the antenna loop). 
     It may be desirable to form antenna  28  from conductive structures that exhibit a relatively small dimension P. In a loop without any break along periphery P, the antenna may resonate at signal frequencies where the signal has a wavelength approximately equal to P. In compact structures with unbroken loop shapes, the frequency of the communications band covered by antenna  28  may therefore tend to be high. By incorporating a gap or other structure into the loop, a capacitance can be introduced into antenna  28 . With the presence of a capacitance within the loop antenna, the resonant frequency of the antenna may be reduced to a desired frequency of operation. 
     Any suitable structure may be used to interpose a capacitance within the loop of conductor formed by conductive sheet  52 . For example, one or more gaps such as gap  50  may be formed. Gap  50  may be filled with dielectric (e.g., a solid dielectric such as plastic, etc. or a dielectric such as air). The gap width GW of gap  50  may affect the value of the capacitance formed by gap  50  (e.g., the capacitance of the gap may tend to increase as gap width GW is decreased). 
     Conductive sheet  52  may be formed by metal traces on a dielectric carrier, metal on a wrapped flex circuit, metal foil that has been bent into a desired shape, and other suitable conductive structures. In the example of  FIG. 4 , metal sheet  52  has a constant dimension ZD as sheet  52  wraps around axis  40 . If desired, metal layer  52  may have a dimension ZD parallel to longitudinal antenna axis  40  that varies as a function of position around axis  40  (i.e., ZD need not be constant at all portions of the loop antenna). The  FIG. 4  arrangement is merely illustrative. 
     Distributed loop antenna  28  may have any suitable cross-sectional shape that forms a loop of antenna currents around axis  40 . As shown in  FIG. 5 , for example, conductive layer  52  may have an oval cross-sectional shape when viewed along longitudinal axis  40 . In the  FIG. 6  example, conductive layer  52  of distributed loop antenna  28  has a rectangular cross-sectional shape. In the example of  FIG. 7 , conductive layer  52  forms a rectangular cross-sectional shape for antenna  28  with an angled sidewall. In particular, the upper and lower surfaces of antenna  28  of  FIG. 7  are parallel to each other and are perpendicular to the right surface of antenna  28 . The left surface of antenna  28  is angled at a non-orthogonal angle with respect to the upper and lower surfaces and does not lie parallel to the right surface of antenna  28 . If desired, some of the surfaces of antenna  28  may be planar and other surfaces of antenna  28  may be non-planar, so that the cross-sectional shape of antenna  28  when viewed along longitudinal axis  40  has a combination of straight and curved sides, as shown in  FIG. 8 . Part or all of antenna&#39;s volume may be buried inside the housing of the electronic device, as shown in  FIG. 2 , leaving only gap  50  exposed. For example, structures of the type shown in  FIGS. 5 ,  6 ,  7 , and  8  may be located where shown by structures  28  of  FIG. 2 , with gap  50  (i.e., a gap on top surface TS of  FIG. 17   a ) located in the opening under region  26  that is formed between display  18  and housing wall  12  or other openings within device  10 . The examples of  FIGS. 5 ,  6 ,  7 , and  8  are merely illustrative. In general, conductive structures  52  may have any suitable shape that causes antenna currents to flow around axis  40 . 
       FIG. 9  is a perspective view of an illustrative shape that may be used for conductive structures  52  of distributed loop antenna  28 . As shown in  FIG. 9 , conductive structures  52  may have a planar upper portion such as planar upper portion  52 A. Longitudinal gap  50  may run across dimension ZD, parallel to longitudinal distributed loop antenna axis  40  (i.e., gap  50  may span the strip of conductor forming conductive structures  52 ). Conductive structure  52  may also have a planar lower portion such as planar lower portion  52 B. Planar side portion  52 C may lie in a plane that is perpendicular to the planes of upper planar member  52 A and lower planar member  52 B. Planar side portion  52 D may lie in a plane that is oriented with a non-zero angle with respect to the plane of planar side portion  52 C and may lie in a plane that is not orthogonal to the planes containing upper layer  52 A and lower layer  52 B. Although shown as being planar in the example of  FIG. 9 , structures  52 A,  52 B,  52 C, and  52 D may, if desired, contain curves or bends. Different number of surfaces and surfaces with different orientations may also be used in forming conductive structures  52 . The  FIG. 9  configuration is merely illustrative. 
     If desired, antenna  28  may be directly fed. For example, the positive and ground conductors of transmission line  34  ( FIG. 3 ) may be coupled respectively to a positive antenna feed terminal and a ground antenna feed terminal on distributed loop antenna  28 . Illustrative feed terminal locations for the antenna feed on distributed loop antenna  28  are shown in  FIG. 10 . A shown in  FIG. 10 , antenna  28  may be fed using an antenna feed that includes positive antenna feed terminal P 1  on upper antenna surface  52 A and ground antenna feed terminal P 2  on lower antenna surface  52 C (which is not parallel to upper surface  52 A in the  FIG. 10  example). Distributed loop antenna  28  of  FIG. 10  may also be fed using an antenna feed formed from positive antenna feed terminal P 2  and ground antenna feed terminal G 2 . Another possible feed location is associated with positive antenna feed terminal P 3  and ground antenna feed terminal P 4 . Positive antenna feed terminal P 5  and corresponding ground antenna feed terminal G 5  may also be used in forming an antenna feed for distributed loop antenna  28 . If desired, matching network elements formed from discrete electrical components and/or conductive structures such as metal structures may be used in forming an antenna feed arrangement for distributed loop antenna  28 . The illustrative antenna feed locations of  FIG. 10  are merely illustrative. 
     Another way in which to feed distributed loop antenna  28  involves near field electromagnetic coupling. This type of arrangement, which may be referred to as an indirect feed arrangement involves the use of first antenna structure to indirectly feed a second antenna structure. Transmission line  34  may be used to directly feed the first structure (sometimes referred to as an antenna feed structure). Near-field electromagnetic coupling may be used to transfer radio-frequency signals from the antenna feed structure to a second antenna structure (sometimes referred to as an antenna resonating element structure). 
     During signal transmission, radio-frequency signals from a transmitter circuit are directly feed to the feed structure and are electromagnetically coupled to the antenna resonating element structure. The antenna resonating element structure radiates the coupled signals. During signal reception, radio-frequency signals that are received by the antenna resonating element structure are coupled to the nearby antenna feed structure and, using the transmission line, are routed to a receiver circuit. In some configurations, the antenna feed structure may contribute to antenna performance (e.g., the antenna feed structure may form part of the radiating/receiving structures at certain frequencies of operation). 
     The antenna feed structure and antenna resonating element structure may have any suitable orientation with respect to each other. With one suitable arrangement, which is described in connection with the examples of  FIGS. 11 ,  12 , and  13 , the antenna feed structure is formed from a directly fed loop antenna structure (antenna structure L 1 ) and the antenna resonating element structure is formed from a distributed loop antenna structure (antenna structure L 2 ). Directly fed loop antenna structure L 1  may include a loop of conductive material  56  that is directly fed by transmission line  34 . The positive conductor in transmission line  34  may be connected to positive antenna feed terminal (+) and the ground conductor in transmission line  34  may be connected to ground antenna feed terminal (−). Distributed loop antenna L 2  may be formed using conductive structures such as conductive structures  52  that are distributed along the length of longitudinal axis  40 . To avoid over-complicating the drawings, the “distributed” shape of conductive structures  52  in antenna resonating element L 2  is not depicted in  FIGS. 11 ,  12 , and  13 . Electromagnetic fields that may be coupled between structures L 1  and L 2  during operation are represented by lines  54 . 
     In configurations of the type shown in  FIG. 11 , directly fed antenna structure L 1  and indirectly feed antenna structure L 2  lie within a common plane. In configurations of the type shown in  FIG. 12 , the plane that contains antenna feed structure L 1  lies perpendicular to the plane that contains antenna resonating element structure L 2 .  FIG. 13  shows another illustrative configuration that may be used for antenna  28 . In the  FIG. 13  arrangement, antenna feed structure L 1  and antenna resonating element structure L 2  are formed from loops that lie in distinct parallel planes. 
     The relative contribution of directly fed antenna structure L 1  and indirectly fed antenna resonating element structure to the overall performance of distributed loop antenna  28  depends on the frequency of operation of antenna  28 , the relative positions of structures L 1  and L 2 , and the shape of structures L 1  and L 2 . 
     A graph corresponding to an illustrative antenna  28  in which both structures L 1  and L 2  contribute to antenna performance (for at least some frequencies of operation) is shown in  FIG. 14 . In  FIG. 14 , standing wave ratio (SWR) for a distributed loop antenna that includes both antenna structure L 1  and antenna structure L 2  (e.g., in an arrangement of the type shown in  FIG. 12 ) is plotted as a function of operating frequency f. Frequency f 1  may correspond to the center frequency of a first band of interest such as an IEEE 802.11 band of 2.4 GHz (as an example). Frequency f 2  may correspond to the center frequency of a second band of interest such as an IEEE 802.11 band of 5 GHz (as an example). Antennas that cover more than two bands, fewer than two bands, and/or other bands of interest may use a distributed loop configuration. The example of  FIG. 14  is merely illustrative. 
     Curve L 2  of  FIG. 14  corresponds to the contribution to antenna  28  from antenna resonating element L 2 . As shown in  FIG. 14 , there are performance contributions from L 2  at frequency f 1  and a frequency that is equal to about 2 times f 1  (i.e., at 2f 1 , which is the second harmonic of frequency f 1 ). The antenna performance contribution from antenna structure L 2  at the second harmonic of frequency f 1  may lie close to upper band center frequency f 2 . 
     Curve L 1  corresponds to the contribution to antenna  28  from antenna resonating element L 1 . There may be relatively little contribution to antenna performance from L 1  at frequencies in the vicinity of low band frequency f 1 . However, at frequencies in the vicinity of f 2 , L 1  may exhibit a resonance that broadens the bandwidth of antenna  28  from L 2  and helps antenna  28  adequately cover the upper band at f 2 . 
     A table illustrating directly fed structure L 1  and indirectly fed structure L 2  may contribute to the performance of distributed loop antenna  28  that incorporates structures L 1  and L 2 . At a first frequency (e.g., frequency f 1  of  FIG. 14  such as 2.4 GHz), directly fed structure L 1  may not contribute significantly to the resonant behavior of antenna  28 , as indicated by the entry “weak radiation” in the table of  FIG. 15 . As indicated by the entry “strong radiation,” however, structure L 1  may contribute significantly to antenna performance at a second frequency (e.g., frequency f 2  of  FIG. 14  such as 5 GHz). The performance of structure L 2  due to coupling from structure L 1  may be strong at 2.4 GHz and at 5 GHz, as indicated by the entries in the right-hand row of the table of  FIG. 15 . 
       FIG. 16   a  is a perspective view of an illustrative configuration that may be used for distributed loop antenna  28 . Distributed loop antenna  28  has a first portion formed from antenna resonating element structure L 2  and a second portion formed from antenna feed structure L 1 . Feed structure L 1  may be a loop antenna structure that is directly fed by transmission line  34  at a positive antenna feed terminal (+) and ground antenna feed terminal (−). Antenna resonating element structure L 2  may be a distributed loop antenna structure having a dimension ZD along longitudinal axis  40  (i.e., the conductor of the loop in antenna resonating element structure L 2  may be axially distributed). Conductive loop structure  56  of antenna feed structure L 1  may be located in a longitudinally offset plane that lies parallel to the plane containing the loop of structure L 2 , as described in connection with  FIG. 13 . 
     If desired, the structures of antenna  28  may be configured so that the loops of structures L 1  and L 2  are coplanar. As shown in  FIG. 16   b , for example, indirectly fed distributed loop antenna  28  may have a feeding loop structure L 1  and a distributed loop antenna structure L 2  that are mounted parallel to one another within a common plane. In a configuration of the type shown in  FIG. 16   b , the feeding loop L 1  may be nested within the distributed loop antenna structure L 2 . 
     Conductive structures  52  and  56  may be formed from metal, conductive materials that contain metal, or other conductive substances. One or more support structures such as support structures  58  may be used to support conductive structures  52  and  56  of antenna structures L 1  and L 2  in distributed loop antenna  28 . Support structures  58  may be formed from a dielectric such as plastic. Conductive structures  52  may be, for example, metal traces formed on a plastic carrier or metal traces formed on a flex circuit substrate or other substrate that is attached to support structures  58  (as examples). 
     In the illustrative configuration for distributed loop antenna  28  that is shown in  FIG. 17   a , support structures  58  have parallel left and right surfaces LS and RS and have a bottom surface BS that is angled with respect to top surface TS. Directly fed antenna feed structure L 1  may be directly fed by transmission line  34  using an antenna feed formed a positive antenna feed terminal (+) and a ground antenna feed terminal (−). During operation, currents in structure L 1  may circulate within structure L 1  as indicated by loop  60 . 
     Indirectly fed antenna resonating element structure L 2 , which is indirectly fed by structure L 1 , may be formed from conductive structures  52  that are wrapped around longitudinal axis  40  of antenna  28 . Gap  50  or other suitable structures or components that are interposed in the loop of structure L 2  may be used to create a capacitance within the loop of structure L 2  (as an example). 
     As shown in  FIG. 17   a , some of the conductive structures of antenna structures L 1  and L 2  may be electrically coupled to each other. For example, some of the metal structures on surfaces LS, RS, and BS (sometimes referred to as ground plane structures) may extend into parts of structure L 1  and parts of structure L 2 . 
     In the example of  FIG. 17   a , the feed for structure L 1  that is formed from terminals (+) and (−) is located adjacent to structure L 2 . In the illustrative configuration for distributed loop antenna  28  that is shown in  FIG. 17   b , the feed for the feeding loop structure is not immediately adjacent to the distributed loop antenna structure in accordance with an embodiment of the present invention. These are merely illustrative feed locations for structure L 1 . Any suitable feeding arrangement may be used if desired. 
     The coupling between structures L 1  and L 2  is affected both by electromagnetic near field coupling and by electrical coupling through shared conductive structures. Electromagnetic coupling occurs when electromagnetic fields such as fields  54  of  FIGS. 11 ,  12 , and  13  that are generated by one loop pass through the other loop. Electric coupling occurs when current is generated in a shared conductor such as a portion of a shared ground plane structure. Consider, as an example, current flowing in portion  68  of loop L 1  in direction  64 . This current may electromagnetically induce a current in direction  66  in structures  62 . Because structure  62  is electrically connected to structures  52  (because structure  62  is a longitudinal extension of structures  52 ), the flow of induced current  66  tends to result in currents in structures  52 . The presence of portion  62  in antenna  28  may therefore enhance coupling between antenna structures L 1  and L 2 . 
     Another illustrative indirect feeding arrangement that may be used for antenna  28  is shown in  FIG. 18 . Conductive structures  52  may be distributed along longitudinal axis  40  in distributed loop antenna resonating element structure L 2 . In the example of  FIG. 18 , conductive strip  70  may have a portion such as portion  70  that overlaps with portion  52 ′ of conductive structures  52 . Portion  70 ′ may be a portion of a metal strip that is separated by air, plastic, or other dielectric from the metal of structures  52 ′. Through near-field electromagnetic coupling, radio-frequency signals on portion  70 ′ and radio-frequency signals in portion  52 ′ may be coupled to each other. 
     A top view of the antenna structures  28  taken in direction  72  of  FIG. 18  is shown in  FIG. 19 . As shown in  FIG. 19 , transmission line  34  may have a positive conductor formed from metal strip  70  and a ground structure formed from metal strip  74 . Metal strip  74  and metal strip  70  may be separated by a dielectric layer (e.g., in a printed circuit substrate or other suitable substrate) and may form a microstrip transmission line (as an example). Extension  70 ′ of strip  70  may protrude under structures  52  in distributed loop antenna resonating element L 2 , to create an arrangement that allows for near field coupling. 
     If desired, gap  50  may be provided with a meandering path shape, as shown in  FIG. 20 . The use of a meandering path may increase the total length of the gap and thereby increase the capacitance associated with the gap. For example, if the use of a meandering path shape of the type shown in  FIG. 20  or other suitable meandering path shape doubles the total length of the gap (without changing the gap width GW), the capacitance can be doubled without increasing dimension ZD. Reductions in gap width GW may also be used to obtain desired increases in gap capacitance. 
       FIG. 21  shows how gap capacitance can be configured using electrical components  76 . Gap  50  may have a built-in capacitance due to its shape (i.e., whether meandering or straight) and size (e.g., gap width GW). In addition to the capacitance due to the layout of gap  50 , the capacitance that is interposed within the loop formed by structures  52  may be affected by the capacitance of electrical components  76  that bridge gap  50 . Electrical components  76  may be capacitors or components that exhibit a capacitance. Electrical components  76  may be, for example, surface mount technology (SMT) components that are attached to the conductive material of conductive structures  52  using solder. Electronic components  76  may include integrated circuits, one or more components such as capacitors, resistors, inductors, etc. that are packaged within a common SMT package, radio-frequency filter components, or other suitable circuit components. 
     If desired, components such as one or more of electronic components  76  or other components associated with distributed loop antenna  28  may be implemented using tunable components. Tunable components may be controlled in real time using control circuitry in device  10  (e.g., to produce desired amounts of capacitance). This allows device  10  to tune the frequency response of distributed loop antenna  28 . Device  10  may, for example, tune antenna  28  when it is desired to cover additional frequency bands of interest (e.g., when switching from one type of wireless communications mode to another, when device  10  is moved into a new geographical region that uses a different set of wireless communications bands, etc.). 
       FIG. 22  shows how distributed loop antenna  28  may have a tunable component such a tunable capacitor  76  (e.g., a varactor). Tunable capacitor  76  may be implemented using an SMT component (e.g., an SMT varactor) that is controlled by control signal on path  80  from control circuitry  78 . Control circuitry  78  may include one or more processors such as microprocessors, microcontrollers, controllers in baseband processor integrated circuits, controllers that are part of digital signal processors, control circuitry that is part of application-specific integrated circuits, or other suitable storage and processing circuitry. The control circuitry in device  10  may adjust tunable capacitor  76  to adjust the frequency response of distributed loop antenna  28 . Feed antenna structure  56  in antenna  28  may also contain tunable components that are tuned by control signals from control circuitry  78 , as illustrated by control signal path  82  in  FIG. 22 . 
       FIG. 23  is a diagram showing how antenna  28  may have tunable components  76  that are incorporated into distributed loop antenna structure  52  in parallel with the capacitance formed by gap  50  (as an example). Tunable components  76  may include tunable capacitors, tunable resistors, tunable inductors, tunable filters, tunable integrated circuits, tunable filters, circuits that are tuned by adjusting switches, circuits that are tuned by adjusting multiple tunable components, or other tuning circuitry. Tunable components  76  may be incorporated into antenna feed structures L 1  and/or antenna resonating element structures L 2  in distributed loop antenna  28  and may be used in tuning impedance matching between radio-frequency structures. 
     Electronic device  10  may contain one distributed loop antenna  28 , two or more distributed loop antennas  28 , or one or more distributed loop antennas  28  in an array with one or more antennas of other types, or other suitable antennas. The conductive antenna structures of distributed loop antenna  28  may be oriented with respect to other antennas in device  10  so that isolation between antenna  28  and the other antennas in device  10  is maximized (i.e., so that coupling between antenna  28  and one or more additional antennas in device  10  is minimized). 
       FIG. 24  is a schematic diagram of an illustrative loop antenna resonating element L 2  showing how the loop antenna resonating element may be oriented with respect to an X-Y-Z coordinate system. 
       FIG. 25  is a graph showing an illustrative radiation pattern (curve  82 ) for the loop antenna resonating element L 2  of  FIG. 24 . Curve  82  corresponds to a typical far field radiation pattern and is also indicative of near field performance. The points on curve  82  are associated with antenna performance as a function of angular orientation and can therefore be used to determine where antenna coupling with nearby antennas is minimized. As an example, the loop antenna has a radiation strength given by point  86  in direction  84 , whereas antenna resonating element structure L 2  exhibits a minimum (null) in direction  90 . By locating additional antennas in device  10  so that they lie along null (longitudinal) axis Z of loop antenna resonating element structure L 2 , coupling between the additional antennas and loop antenna resonating element structure  28  may be minimized. 
       FIG. 26  is a perspective view of an illustrative distributed loop antenna showing how loop antenna resonating element L 2  may be oriented relative to an X-Y-Z coordinate system of the type shown in  FIGS. 24 and 25 . As shown in  FIG. 26 , longitudinal axis  40  of distributed loop antenna resonating element L 2  may be oriented along the “Z” axis (i.e., the Z axis may serve as the longitudinal axis of the distributed loop antenna). The longitudinal Z axis of distributed loop antenna  28  of  FIG. 26  represents a null position along which additional antennas may be located to minimize antenna-to-antenna coupling. In the configuration of  FIG. 26 , antenna feed structure L 1  is formed from a loop that lies in a plane that is perpendicular to the plane containing the “loop” of antenna resonating element L 2 . If desired, other types of feed configurations may be used (e.g., arrangements in which resonating element L 2  is directly fed, arrangements in which element L 1  is oriented at different angles with respect to element L 2 , etc.). The feeding configuration of  FIG. 26  is merely illustrative. 
       FIG. 27  is a top view of a portion of housing  12  of device  10  in which two antennas have been mounted. In the example of  FIG. 27 , first antenna ANT  1  is shown as having an inverted-F antenna resonating element RE, but may, in general, be formed using any suitable type of antenna structure). Second antenna ANT 2  is shown as being formed from a distributed loop antenna (antenna  28 ) having a loop antenna resonating element L 2  and an antenna feed structure L 1 . 
       FIG. 28  is a top view of a portion of housing  12  in a device (device  10 ) in which both antennas (ANT 1  and ANT 2 ) have been implemented using a distributed loop antenna design. 
     Loop antenna element L 2  of antenna ANT 1  in the configuration of  FIG. 27  and loop antenna elements L 2  of antennas ANT 1  and ANT 2  in the configuration of  FIG. 28  may be may be oriented so that their longitudinal axes (along axis Z) are pointed towards the other antenna in the array. In this way, ANT 1  of  FIG. 27  lies along the null axis of antenna ANT 2 . In  FIG. 28 , ANT 1  lies along the null axis of antenna ANT 2  and antenna ANT 2  lies along the null axis of antenna ANT 1 . Configurations such as these may help to minimize near field electromagnetic coupling between antennas. 
     Antennas that are mounted along a common axis in edge portion  26  of housing  12  such as common longitudinal axis  40  in  FIGS. 27 and 28  also have the potential to experience coupling through common ground plane currents. Common ground plane structures such as conductive portions of housing  12  or other conductive structures may form common ground paths such as ground paths  41  of  FIGS. 27 and 28 . When conductive housing structures that serve as antenna ground or other ground plane structures are shared by the antennas in the array, a first antenna in the array may induce current (e.g., current in a common ground path  41 ) that has the potential to couple into a second antenna in the array. 
     Due to presence of common ground path  41  in the examples of  FIGS. 27 and 28 , there is therefore the potential for induced ground current to lead to radio-frequency signal coupling between antennas ANT 1  and ANT 2 . 
     As shown in  FIGS. 27 and 28 , ground path  41  extends parallel to shared axis  40  and dimension Z (i.e., the axis along which each of the antennas in the array is located). Loop currents in each distributed loop antenna tend to circulate in the X-Y plane, perpendicular to shared axis  40  and dimension Z. Because the currents in the loop antenna resonating elements do not tend to run parallel to common ground path  41 , antenna-to-antenna coupling in the array via shared ground currents tends to be minimized. The use of one distributed loop antenna (e.g., antenna ANT 2  of the antenna array of  FIG. 27 ) or two or more distributed loop antennas (e.g., antennas ANT 1  and ANT 2  in the antenna array of  FIG. 28 ) in an antenna array in device  10  may therefore help reduce common ground plane coupling and therefore may help each antenna operate relatively independently. For example, antennas ANT 1  and ANT 2  may be used in a multiple antenna setup such as an IEEE 802.11(n) setup to receive independent streams of wireless data. In this type of multiple-antenna arrangement, enhancing isolation between antennas ANT 1  and ANT 2  may improve overall data throughput. 
     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: 20110823
Publication Date: 20150224
Grant Date: 20150224
Priority Date: 20110823
Inventors: ZHU JIANG
GUTERMAN JERZY
PASCOLINI MATTIA
NATH JAYESH
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/2283", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/2291", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2283", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2291", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 46750444