PATENT DOCUMENT

Publication Number: US-8169373-B2
Application Number: US-20582908-A
Country: US
Kind Code: B2

Title: Antennas with tuning structure for handheld devices

Abstract:
Handheld electronic devices are provided that contain wireless communications circuitry. The wireless communications circuitry may include antenna structures. To accommodate manufacturing variations, the antenna structures and handheld electronic devices may be characterized by performing measurements such as antenna performance measurements. Appropriate antenna adjustments may be made during manufacturing of a handheld electronic device based on the characterizing measurements. An antenna may be formed using an inverted-F design in which an antenna flex circuit is mounted to a dielectric antenna support structure. Cavities in the support may be selectively filled with dielectric material and dielectric patches may be added to the antenna flex circuit to adjust the dielectric loading of the antenna. The length of a ground return path in the antenna may be adjusted by appropriate positioning of an electrical connector within the ground return path.

Claims:
1. An electronic device, comprising:
 an inverted-F antenna that comprises:
 a main conductive antenna resonating element; 
 first and second conductive branch paths that are connected to the main conductive antenna resonating element, wherein the second conductive branch path forms a ground return path of a given length for the inverted-F antenna; and 
 at least one adjustable electrical connector interposed in the ground return path that adjusts the length of the ground return path to tune the inverted-F antenna. 
 
 
     
     
       2. The electronic device defined in  claim 1  wherein the adjustable electrical connector comprises conductive foam. 
     
     
       3. The electronic device defined in  claim 1  wherein the main conductive antenna resonating element is formed from a trace in a flex circuit. 
     
     
       4. The electronic device defined in  claim 1  wherein the inverted-F antenna further comprises an antenna support structure, wherein the main conductive antenna resonating element and the first and second conductive branch paths are formed at least partly from traces on an antenna flex circuit and wherein the antenna flex circuit is attached to the antenna support structure. 
     
     
       5. The electronic device defined in  claim 4  wherein the antenna flex circuit comprises at least three right-angle bends and is wrapped around the antenna support structure to form a three-dimensional antenna structure. 
     
     
       6. The electronic device defined in  claim 5  wherein the antenna support structure comprises at least one alignment post and wherein the antenna flex circuit comprises at least one hole that engages the alignment post. 
     
     
       7. The electronic device defined in  claim 6  wherein the antenna flex circuit is formed as an integral portion of a larger flex circuit structure that connects to a main logic board in the electronic device. 
     
     
       8. The electronic device defined in  claim 6  wherein the antenna support structure comprises a hole through which the antenna flex circuit passes. 
     
     
       9. The electronic device defined in  claim 6  wherein the antenna flex circuit has pads to which a radio-frequency integrated circuit is mounted. 
     
     
       10. The electronic device defined in  claim 4  wherein the antenna support comprises portions that define cavities and wherein the antenna flex circuit is mounted on top of the cavities. 
     
     
       11. The electronic device defined in  claim 4  wherein the antenna support comprises portions that define cavities, wherein the antenna flex circuit is mounted on top of the cavities, and wherein at least one of the cavities is filled with air and at least one of the cavities is filled with a dielectric other than air. 
     
     
       12. The electronic device defined in  claim 11  wherein the inverted-F antenna further comprises a layer of dielectric that is attached on top of the antenna flex circuit and that dielectrically loads the antenna to tune the antenna. 
     
     
       13. The electronic device defined in  claim 4  wherein the antenna support comprises portions that define cavities, wherein the antenna flex circuit is mounted on top of the cavities, and wherein at least one of the cavities is filled with air and at least one of the cavities is filled with dielectric foam. 
     
     
       14. The electronic device defined in  claim 4  wherein the inverted-F antenna further comprises a layer of dielectric that is attached on top of the antenna flex circuit and that dielectrically loads the antenna to tune the antenna. 
     
     
       15. An electronic device, comprising:
 at least one conductive housing member; 
 a dielectric antenna support structure; 
 an antenna flex circuit that is mounted to the dielectric antenna support structure and that forms an inverted-F antenna for the electronic device, wherein the antenna flex circuit comprises a ground trace; and 
 an adjustable electrical connector that forms an electrical connection with the ground trace, wherein the inverted-F antenna has a ground return path of a given length that includes a portion of the conductive housing member and the adjustable electrical connector and wherein the electrical connection of the adjustable electrical connector to the ground trace is formed at a location that adjusts the given length of the ground return path and tunes the inverted-F antenna. 
 
     
     
       16. The electronic device defined in  claim 15  wherein the portion of the conductive housing member comprises a portion of a metal case and a portion of a metal midplate. 
     
     
       17. The electronic device defined in  claim 16  wherein the adjustable electrical connector comprises conductive foam. 
     
     
       18. The electronic device defined in  claim 15  wherein the dielectric antenna support structure comprises at least one cavity adjacent to the antenna flex circuit, wherein the cavity is filled with a dielectric material to adjust dielectric loading for the antenna flex circuit and to tune the inverted-F antenna. 
     
     
       19. The electronic device defined in  claim 18  further comprising a dielectric patch attached to the antenna flex circuit to adjust dielectric loading for the antenna. 
     
     
       20. An electronic device comprising:
 a flex circuit having conductive traces; 
 an integrated circuit that is mounted directly to the flex circuit, wherein the flex circuit comprises portions defining an antenna flex circuit that serves at least partly to form an antenna for the electronic device; wherein the antenna comprises an inverted-F antenna having a ground return path of a given length; and a conductive elastic connector that is inserted into the ground return path during manufacturing to adjust the given length and tune the antenna. 
 
     
     
       21. The electronic device defined in  claim 20  wherein the integrated circuit comprises a radio-frequency transceiver. 
     
     
       22. The electronic device defined in  claim 20  wherein the antenna flex circuit comprises a ground trace to which the conductive elastic connector is attached at a desired location to adjust the given length. 
     
     
       23. The electronic device defined in  claim 22  wherein the conductive elastic connector comprises a connector selected from the group consisting of: a fastener, a spring, and a spring-loaded pin. 
     
     
       24. The electronic device defined in  claim 22  further comprising a dielectric support structure having at least one cavity that is filled with a dielectric material, wherein the antenna flex circuit is attached to the dielectric support structure on top of the cavity filled with dielectric material. 
     
     
       25. The electronic device defined in  claim 24  wherein the dielectric material comprises dielectric foam. 
     
     
       26. The electronic device defined in  claim 25  wherein the conductive elastic connector comprises a conductive foam member. 
     
     
       27. An electronic device comprising:
 a flex circuit having conductive traces; 
 an integrated circuit that is mounted directly to the flex circuit, wherein the flex circuit comprises portions defining an antenna flex circuit that serves at least partly to form an antenna for the electronic device; 
 a housing having an upper end and a lower end; 
 an antenna support structure to which the antenna flex circuit and the integrated circuit are mounted to form a radio-frequency assembly, wherein the radio-frequency assembly is mounted at the upper end of the housing; and 
 a logic board mounted at the lower end of the housing, wherein the flex circuit comprises meandering path portions that interconnect the antenna support structure and the logic board.

Description:
BACKGROUND 
     This invention relates generally to wireless communications circuitry, and more particularly, to antenna circuitry for electronic devices such as handheld electronic devices. 
     Handheld electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. 
     Due in part to their mobile nature, handheld electronic devices are often provided with wireless communications capabilities. Handheld electronic devices may use long-range wireless communications to communicate with wireless base stations. Handheld electronic devices may also use short-range wireless communications links. For example, handheld electronic devices may communicate using the WiFi® (IEEE 802.11) bands at 2.4 GHz and 5 GHz and the Bluetooth® band at 2.4 GHz. Communications are also possible in other bands. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to reduce the size of components that are used in these devices. For example, manufacturers have made attempts to miniaturize the antennas used in handheld electronic devices. 
     A typical antenna may be fabricated by patterning a metal layer on a circuit board substrate or by patterning a sheet of thin metal using a foil stamping process. Antennas such as planar inverted-F antennas (PIFAs) and antennas based on L-shaped resonating elements can be fabricated in this way. Antennas may also be formed using flexible printed circuit substrates. 
     Although modern handheld electronic devices often need antennas with precisely defined radio-frequency responses, manufacturing variations and unexpected design changes can lead to situations in which an antenna is detuned somewhat from its optimal frequency response. These manufacturing variations may arise due to variations in the flexible printed circuit substrates that are used in forming the antennas. For example, antenna performance variations can arise when flex circuit substrates are produced by different manufacturers and are therefore not all identical. 
     It would therefore be desirable to be able to provide improved antennas and wireless handheld electronic devices. 
     SUMMARY 
     Handheld electronic devices and antennas for handheld electronic devices are provided. Antenna performance may be adjusted during manufacturing based on the results of characterizing measurements. The characterizing measurements may reveal, for example, that an antenna is not tuned properly due to manufacturing variations in the parts that are being used to assembly a handheld electronic device. To accommodate these manufacturing variations, compensating adjustments may be made to the antenna that correct the antenna&#39;s performance. 
     An antenna may be provided for the handheld electronic device using an antenna flex circuit. The antenna flex circuit may be wrapped around a dielectric antenna support structure in three dimensions by forming multiple right-angle bends in the antenna flex circuit. The antenna flex circuit may be used in forming an antenna such as an inverted-F antenna. The inverted-F antenna may have a main conductive arm and branch arms. One of the branch arms may be used in forming a ground return path for the inverted-F antenna. 
     The antenna may be formed in a handheld electronic device that has a conductive housing. The conductive housing may include a metal case and metal structural members such as a metal midplate member. These conductive housing portions may form part of the ground return path. 
     An electrical connector may be interposed in the ground return path. Based on the characterizing measurements that are made as part of the manufacturing process, an optimal location for the electrical conductor may be determined. During assembly, the electrical connector may be placed at this location, thereby establishing an appropriate length for the ground return path. By ensuring that the ground return path in the inverted-F antenna has a desired length, the performance of the inverted-F antenna may be tuned. 
     Antenna adjustments may also be made by selectively loading the antenna during the manufacturing process. With one suitable arrangement, the amount of dielectric loading on the antenna flex circuit is adjusted by selectively placing an appropriate dielectric layer on top of the antenna flex circuit. Dielectric loading adjustments may also be made by selectively filling cavities in the dielectric antenna support structure with a dielectric material. For example, one or more cavities may be selectively filled with a dielectric foam. The number of cavities that are filled in this way affects the amount of dielectric loading that is experienced by the antenna flex circuit and thereby adjusts the frequency resonances for the antenna. Dielectric loading adjustments such as these and path length adjustments such as adjustments to the length of the ground return path may be made to ensure that the frequency response of the antenna is properly tuned for optimal antenna performance. 
     The antenna flex circuit may be formed as an integral part of a larger flex circuit. The antenna flex circuit and the larger flex circuit of which it is a part may be used for mounting integrated circuits and for forming a path that connects to a main logic board. 
     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 front perspective view of an illustrative handheld electronic device with an antenna in accordance with an embodiment of the present invention. 
         FIG. 2  is a rear perspective view of an illustrative handheld electronic device with an antenna in accordance with an embodiment of the present invention. 
         FIG. 3  is a graph showing how antennas may be tuned in accordance with an embodiment of the present invention. 
         FIG. 4  is a schematic diagram of an adjustable antenna for a handheld device that is based on an inverted-F antenna design in accordance with an embodiment of the present invention. 
         FIG. 5  is a top view of an illustrative handheld device showing how an antenna may be tuned by adjusting the position of a conductive elastic structure such as a conductive elastomer in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of an illustrative antenna formed from a flex circuit in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of an illustrative antenna of the type shown in  FIG. 6  to which dielectric loading has been added to adjust the antenna&#39;s performance in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of an illustrative antenna formed from a flex circuit mounted on an antenna support with empty cavities in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional side view of an illustrative antenna formed from a flex circuit mounted on an antenna support with cavities that have been filled with a non-air dielectric to tune the antenna in accordance with an embodiment of the present invention. 
         FIG. 10  is a front perspective view of an antenna assembly in accordance with an embodiment of the present invention. 
         FIG. 11  is a top view of an antenna assembly in accordance with an embodiment of the present invention. 
         FIG. 12  is a rear perspective view of an antenna assembly in accordance with an embodiment of the present invention. 
         FIG. 13  is a front perspective view of an antenna assembly showing how a portion of an antenna flex circuit may be provided with a conductive trace that mates with an elastic connector in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional perspective view of an antenna assembly in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional perspective view of a portion of an antenna assembly showing how the antenna may be grounded to a conductive device housing in accordance with an embodiment of the present invention. 
         FIG. 16  is a perspective view of an antenna support that may be used in an antenna assembly in accordance with an embodiment of the present invention. 
         FIG. 17  is a perspective view of an antenna assembly in accordance with an embodiment of the present invention from which the antenna support of  FIG. 16  has been omitted. 
         FIG. 18  is a perspective view of an antenna assembly that includes an antenna support of the type shown in  FIG. 16  and an antenna flex circuit of the type shown in  FIG. 17  in accordance with an embodiment of the present invention. 
         FIG. 19  is a perspective view of an antenna flex circuit that is formed as an integral portion of a larger flex circuit structure and which is shown in its unassembled state unattached to an antenna support in accordance with an embodiment of the present invention. 
         FIG. 20  is a flow chart of illustrative steps involved in testing electronic device antennas and making corresponding antenna tuning adjustments during manufacturing in accordance with an embodiment of the present invention. 
         FIG. 21  is a cross-sectional side view showing how an inverted-F antenna in an electronic device may be tuned by adjusting the position of a conductive elastomeric member such as a piece of conductive foam in accordance with an embodiment of the present invention. 
         FIG. 22  is a cross-sectional side view showing how an inverted-F antenna in an electronic device may be tuned by adjusting the position of a conductive member such as a metal spring member in accordance with an embodiment of the present invention. 
         FIG. 23  is a cross-sectional side view showing how an inverted-F antenna in an electronic device may be tuned by adjusting the position of a conductive connector such as a solder connection in accordance with an embodiment of the present invention. 
         FIG. 24  is a cross-sectional side view showing how an inverted-F antenna in an electronic device may be tuned by adjusting the position of a conductive connector such as a screw or other mechanical fastener in accordance with an embodiment of the present invention. 
         FIG. 25  is a cross-sectional side view showing how an inverted-F antenna in an electronic device may be tuned by adjusting the position of a conductive connector such as a spring-loaded pin in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to wireless communications, and more particularly, to wireless electronic devices and antennas for wireless electronic devices. 
     The wireless electronic devices may be portable electronic devices such as laptop computers or small portable computers of the type that are sometimes referred to as ultraportables. Portable electronic devices may also be somewhat smaller devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, which is sometimes described herein as an example, the portable electronic devices are handheld electronic devices. 
     The handheld devices may be, for example, cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, and handheld gaming devices. The handheld devices may also be hybrid devices that combine the functionality of multiple conventional devices. Examples of hybrid handheld devices include a cellular telephone that includes media player functionality, a gaming device that includes a wireless communications capability, a cellular telephone that includes game and email functions, and a handheld device that receives email, supports mobile telephone calls, has music player functionality and supports web browsing. These are merely illustrative examples. 
     An illustrative handheld electronic device in accordance with an embodiment of the present invention is shown in  FIG. 1 . As shown in  FIG. 1 , device  10  may have a housing  12 . Device  10  may include user input interface devices such as button  14 . Other input-output devices that may be provided in device  10  include display  16 , additional buttons (e.g., for placing device  10  in standby mode), data ports, audio jacks, speakers, etc. Display  16  may, for example, be a touch screen display. 
     Device  10  may include one or more antennas for handling wireless communications. Embodiments of device  10  that contain a single antenna are sometimes described herein as an example. The antenna in device  10  may be located, for example, where indicated by dashed lines  18 . Antenna  18  may be used to cover WiFi® (IEEE 802.11) bands at 2.4 GHz and/or 5 GHz and/or the Bluetooth® communications band at 2.4 GHz. These are merely illustrative examples. Antenna  18  may be configured to handle any suitable communications band or bands of interest. 
     Housing  12 , which is sometimes referred to as a case, may be formed of any suitable materials such as plastic, glass, ceramics, metal, other conductive or insulating materials, or a combination of these materials. As an example, housing  12  or portions of housing  12  may be formed from conductive materials such as stainless steel, or aluminum. In configurations in which housing  12  is mainly formed from a conductive material such as metal, one or more portions of housing  12  may be formed from a dielectric or other low-conductivity material to form an antenna “window.” This type of arrangement is shown in the rear view of device  10  of  FIG. 2 . As shown in  FIG. 2 , housing  12  may have a dielectric antenna window such as window  20 , so that antenna  18  is not blocked by housing  12 . During operation, radio-frequency signals may be conveyed between antenna  18  and external equipment through window  20 . Window  20  may be formed of plastic or other suitable dielectrics. 
     An example of a plastic that may be used in forming window  20  and other dielectric structures in device  10  is PC-ABS (a blend of polycarbonate and acrylonitrile butadiene styrene). This type of plastic may be used, for example, to form a support for a flex circuit antenna structure. 
     Additional dielectrics that may be used in device  10  include materials such as glass, polyimide (e.g., in the form of flexible printed circuit board substrates called flex circuits), epoxy (e.g., in rigid circuit boards), flexible plastic films covered with pressure sensitive adhesive (i.e., double-sided tape), Kapton® (a brand of polyimide available from Dupont Electronics), dielectric foam, gel, dielectrics filled with hollow or solid dielectric microspheres, etc. 
     Due to manufacturing variations, parts of device  10  may be manufactured with shapes and sizes that do not exactly match ideal specifications. In some situations, sufficient tolerance may be built into the design for device  10  to accommodate these manufacturing variations. As an example, if it is intended that two plastic parts fit together, these parts may be manufactured so that there is sufficient clearance between the parts to accommodate variations in size due to manufacturing variations. 
     Other types of manufacturing variations may be more difficult to accommodate. For example, changes in the shape and size of antenna parts in device  10  may affect the performance of antenna  18 . If care is not taken, antenna  18  will not be tuned properly and will therefore not be able to satisfactorily cover a communications band of interest. 
     Antenna  18  may be designed with sufficient tolerance to accommodate manufacturing variations. Adjustable features may also be incorporated into antenna  18 . These features may allow the performance of the antenna to be tuned during the manufacturing process. For example, the adjustable features of antenna  18  may allow the frequency of the communications band (or bands) that are covered by antenna  18  to be adjusted. 
     An illustrative situation is shown in  FIG. 3 . As shown in  FIG. 3 , antenna  18  may nominally have a frequency response peak at frequency f b . This is the desired operating frequency for the antenna and is characterized by curve  24  in  FIG. 3 . Due to manufacturing variations (e.g., variations during the manufacturing process used to create a flex circuit for antenna  18 ), the actual performance of antenna  18  may initially be detuned. For example, when first measured as part of a test characterization operation, antenna  18  may be characterized by a frequency response of the type shown by curve  22 . As shown in  FIG. 3 , curve  22  has a frequency response peak of f a , not f b  as desired. 
     If frequencies f a  and f b  are sufficiently close, antenna  18  will operate satisfactorily. However, if frequencies f a  and f b  are too dissimilar, it may be advantageous to adjust antenna  18  as part of the manufacturing process. If appropriate adjustments are made, the frequency peak of antenna  18  will be tuned from f a  to f b , thereby ensuring that antenna  18  will operate properly during normal use by a customer. 
     Antenna  18  may be formed from any suitable antenna structures. For example, antenna  18  may be implemented using a planar inverted-F (PIFA) structure, an L-shaped antenna resonating element, a slot antenna structure, etc. With one suitable arrangement, which is described herein as an example, antenna  18  may be formed using an inverted-F design, as shown in  FIG. 4 . 
     As shown in the schematic diagram of  FIG. 4 , inverted-F antenna  18  may have main antenna resonating element  36 . The F-shaped structure of antenna  18  is formed by two shorter arms—arm  34  and arm  28 . Arms  34  and  28  form conductive branch paths for antenna  18 . Arm  34  may extend between ground  32  and main arm  36 . Similarly, arm  28  may extend between ground  30  and antenna resonating element arm  36 . As indicated by signal source  26  in  FIG. 4 , antenna  18  may be fed between ground  30  and arm  28 . Ground  30  and ground  32  may be shorted together and may therefore be considered to form part of the same ground plane. 
     The frequency response of antenna  18  may be adjusted by altering the shapes and sizes of the structure of  FIG. 1 . For example, adjustments to the length L 1  of the ground return path in antenna  4  (i.e., the conductive path between points P 1  and P 2  in  FIG. 4 ) may be used to tune the frequency response of antenna  18 . Tuning may also be accomplished by altering the amount of dielectric loading on the elements of antenna  18 . As an example, dielectric  38  may be added or taken away in the vicinity of the conductive traces of antenna  18 , thereby altering the effective length of the traces and tuning the frequency response of antenna  18 . 
     Dielectric loading may be implemented using any suitable scheme. For example, one or more lengths of polyimide (e.g., Kapton® polyimide from DuPont Electronics) may be added to or removed from antenna  18 . As another example, dielectric such as non-conductive foam may be inserted into a cavity adjacent to the conductive lines in antenna  18 . When more dielectric foam is added, dielectric loading is increased, thereby effectively altering the path length of one or more of the portions of antenna  18  (e.g., arm  36  and/or arms such as arms  34  and  28 ). 
     Once a manufacturer has determined that antenna  18  is working properly with a given amount of dielectric loading and/or a given length L 1  for the ground return path in antenna  18 , it is generally not necessary to make additional adjustments on a device-by-device bases. Rather, all devices  10  that are formed from identical parts can be manufactured using the same amount of adjustable dielectric loading and using an adjustable ground return path of the same length. Nevertheless, should testing reveal that there are significant device-to-device variations, a manufacturer may, if desired, make more frequent adjustments (e.g., on a per-device or per-batch basis). In a typical scenario, tuning is used to accommodate variations in the sizes and shapes of subsystems that are acquired from various vendors whose manufacturing processes may or may not be directly under the control of the device manufacturer. 
       FIG. 5  shows a top view of an illustrative electronic device  10  showing how antenna  18  may be tuned by adjusting the position of a conductive component that is interposed in the ground return path of antenna  18 . As shown in  FIG. 5 , device  10  may have components such as main logic board  44 , midplate assembly  42  (which may be attached to housing  12  or may be considered to form part of conductive housing  12  for device  10 ), and radio-frequency antenna assembly  40 . Antenna assembly  40  may have a main structural member formed from plastic. This structure, which may be formed from one or more subparts, is sometimes referred to herein as an antenna support. 
     Conductive paths that make up antenna  18  may be formed from any suitable conductive structures in device  10 . With one suitable arrangement, conductive paths for antenna  18  are partly formed from conductive traces on a flexible printed circuit substrate. Flexible printed circuit substrates, which are sometimes referred to as flex circuits, may be formed from flexible dielectrics such as polyimide. Conductive flex circuit traces may be formed, for example, from gold, copper, or other suitable materials. As with rigid printed circuit boards, flex circuits may contain multiple layers, so that conductive traces may cross one another without becoming shorted to each other. Transmission line structures such as microstrip transmission lines structures may be formed in flex circuits by running positive and ground conductors in parallel (e.g., on the same layer of the flex circuit, on different layers of the flex circuit, or both on the same and different layers). 
     If desired, the same flex circuit that is used in forming part of antenna  18  may be used to interconnect antenna assembly  40  with main logic board  44 . This portion of the flex circuit may have a meandering path to provide flexibility to the flex circuit structure during assembly. Dashed lines  46  show an illustrative meandering path that the flex circuit may take when connecting antenna assembly  40  and main logic board  44 . 
     In the example of  FIG. 5 , some of the conductive portions of antenna  18  are formed by non-flex structures such as portions of conductive housing  12  and conductive elastic connector  62 . 
     The portion of antenna  18  that is shown in the schematic representation of  FIG. 5  receives outgoing radio-frequency signals at point  60  (e.g., from an output associated with an output amplifier on assembly  40 ). When receiving over-the air signals, signals are provided from antenna  18  to circuitry on board  44  via point  60 . 
     Between point  60  and point  52  along path  48 , the antenna traces in the flex circuit structure that makes up the antenna form a transmission line (e.g., a microstrip transmission line). At point  52 , the positive and ground conductive paths of the antenna diverge. The ground path continues by itself to point  58 . At point  58 , a screw and other conductive structures may be used to ground antenna  18  to case  12 . Between points  52  and  54 , along segment  50  of antenna  18 , the positive conductive path is unaccompanied by the ground path. There is also no accompanying ground path along segment  56  between point  70  and point  58 . Segment  56  of antenna  18  in the diagram of  FIG. 5  corresponds to arm  36  in the schematic of  FIG. 4 . Although illustrated as a straight line, this portion of antenna  18  may, if desired, contain one or more bends to make antenna  18  more compact and to ensure that the distal end of segment  56  is not immediately adjacent to conductive housing portions in device  10 . 
     The ground return path of antenna  18  includes point  58 , the conductive case  12 , the upper right corner of midplate  42 , and conductive foam  62 . The ground return path terminates on a ground trace in portion  48  of antenna  18 . With this arrangement, the performance of antenna  18  can be tuned, because the position of conductive foam  62  along lateral dimension  64  controls the length L 1  of the ground return path. If conductive foam  62  is positioned in the location shown in  FIG. 5 , the ground return path terminates at point  66 , as shown by path  74 . If conductive foam  62  is moved slightly in direction  64 , the ground return path for antenna  18  will terminate at point  68 , as shown by path  72 . Because path  72  and path  74  have different lengths, the position of conductive foam  62  can be used as an adjustable parameter that controls the length L 1  of the ground return path in inverted-F antenna  18 . 
     The use of conductive foam  62  to complete the ground return path in the  FIG. 5  example is merely illustrative. Any suitable adjustable conductive structures may be used in adjusting the ground return path length. For example, the length of the ground return path may be adjusted by making selective connections using springs, spring-loaded pins, or other elastic connectors. Path length adjustments may also be made by making selective solder connections, by adjusting the position of a screw or other mechanical fastener, by plugging a connector into an appropriate socket, by inserting a bridging wire at a particular location, or by making any other suitable adjustable electrical connection. The use of an elastic connection such as elastomeric foam is merely illustrative. 
     If desired, adjustable dielectric loading schemes may be used to adjust the performance of antenna  18 . Dielectric loading changes the effective length of antenna elements. The resonating properties of antennas can be strongly affected by the lengths of the resonating elements in the antennas. If, for example, an element has a length that matches a fraction of a wavelength (e.g., a half of a wavelength or a quarter of a wavelength), the antenna may exhibit a resonant peak. The “wavelength” in consideration when determining whether or not an antenna has a resonance is the effective wavelength of the radio-frequency signal being transmitted or received taking into account the dielectric constant of adjacent dielectrics. By adjusting the amount of dielectric loading on portions of antenna  18 , the effective wavelength associated with a resonant peak may be adjusted, thereby tuning the antenna, as described in connection with  FIG. 3 . 
     An example is illustrated in  FIGS. 6 and 7 . In  FIG. 6 , an illustrative cross-sectional diagram of a portion of a flex circuit antenna is shown. Antenna portion  76  has a flex circuit dielectric  80  (e.g., polyimide) containing a conductive antenna trace  78 . Trace  78  may be, for example, a portion of an inverted-F antenna such as portion  56  of antenna  18  in  FIG. 5 . In the  FIG. 6  example, air surrounds flex circuit  80 , so there is minimal dielectric loading on antenna portion  56 . In the  FIG. 7  example, dielectric loading structure  82  has been placed adjacent to a length of antenna portion  76 . Dielectric loading structure  82  may be, for example, a patch of polyimide film. Dielectric loading structure  82  may be attached to antenna portion  76  by adhesive or any other suitable arrangement. The presence of dielectric loading structure  82  changes the effective wavelength of the radio-frequency signals in antenna portion  76  and thereby adjusts the frequency at which antenna  18  exhibits its resonant peak. Antenna  18  may be adjusted in this way by attaching and removing dielectric loading structures of various sizes from the surface of the antenna flex circuit. 
     Another dielectric loading scheme that may be used involves selectively filling cavities in the antenna support structure for antenna  18 . This type of arrangement is illustrated in connection with  FIGS. 8 and 9 , which show cross-sections of an antenna having an antenna flex circuit portion  76  that is mounted on antenna support  84 . Antenna support  84  may have cavities  86  adjacent to flex circuit portion  76 . In the illustrative arrangement shown in  FIG. 8 , cavities  86  are empty prism-shaped regions (i.e., prism-shaped polyhedrons filled with air). In the illustrative arrangement shown in  FIG. 9 , cavities  86  have been filled with a dielectric such as foam. If desired, other dielectrics may be used to fill cavities  86  (e.g., solid plastic plugs, epoxy, gels, microsphere-filled substances, etc.). Any suitable number of cavities  86  may be provided on a given antenna support  84  and any suitable number of cavities may be filled (e.g., none, one, two, three, more than three, etc.). When none of the cavities are filled, dielectric loading will be minimized. When all of the cavities are filled, dielectric loading will be maximized. Intermediate antenna tuning configurations may be obtained by selectively filling a desired number of the cavities with dielectric (i.e., dielectric materials other than air). 
     Cavities  86  may, in general, have any suitable shape. For example, cavities  86  may have rectangular surface cross-sections and may be cubic in shape (in three dimensions). Such cubic cavities may have sides of equal length or may have sides of different lengths (e.g., to form rectangular cross-sections with dissimilar sides). The shape of the surface opening of cavities  86  may also have other any other suitable shape such as a triangular shape, a trapezoidal shape, a circular shape, an oval shape, the shape of a polygon with four or more than four sides, a shape with both straight and curved sides, a shape with irregular curved sides, etc. These surface shapes may be form part of three-dimensional cavities of various shapes such as conical shapes, hemispherical shapes, prisms and other polyhedrons, pyramids, cylinders, cones, combinations of these forms, etc. The use of polyhedral shapes is sometimes described herein as an example. Each cavity  86  may have substantially the same size or a nonunitary weighting scheme may be used for the sizes of cavities  86 . 
     Illustrative structures that may be used to implement antenna  18  in device  10  in accordance with embodiments of the present invention are shown in  FIGS. 10-19 . 
     As shown in  FIG. 10 , antenna assembly  40  may be formed by mounting antenna flex circuit  80  to antenna support  84 . Antenna flex circuit  80  may contain conductive antenna traces for forming an inverted-F antenna, as described in connection with  FIG. 5 . Antenna support  84  may be, for example, a dielectric support formed from plastic. Integrated circuits such as integrated circuit  90  may be mounted on flex circuit  80 . Integrated circuit  90  may be, for example, an integrated circuit for processing touch screen signals in device  10 . Flex circuit  80  may include interconnects that interconnect integrated circuits such as circuit  90  with circuitry on main logic board  44  ( FIG. 5 ). For example, meandering connector portion  46  of flex circuit  80  may contain digital and analog signals paths (buses) for conveying signals between antenna assembly  40  and main logic board  44 . 
     In region  92 , antenna flex circuit  80  may bend upward as shown in  FIG. 10 . This portion of antenna flex circuit  80  may contain a transmission line such as a microstrip transmission line, as described in connection with segment  48  of  FIG. 5 . Conductive elastic connector  62  (e.g., conductive foam such as foam that is wrapped on its surface with a conductive material or that is impregnated with conductive particles, etc.), may be mounted on exposed conductive ground trace  88  on flex circuit  80 . After bending several additional times, flex circuit  80  may protrude downward into hole  98  of support  84  and may wrap around the underside of support  84 . In this configuration, the tip of arm  36  in flex circuit  80  is not located immediately adjacent to conductive portions of case  12 , which helps to ensure satisfactory antenna performance. 
     If desired, alignment features may be provided on antenna support  84  to help guide antenna flex circuit  80 . For example, antenna flex circuit  80  may have alignment holes that mate with alignment posts such as alignment post  94  in  FIG. 10 . Shorting region  58 , which may be associated with a screw that is electrically connected to case  12 , may have ground conductive trace  100  surrounding screw hole  102 . A screw such as screw  142  ( FIG. 15 ) may be used to ground the antenna to housing  12  at point  58 . 
     Dielectric loading structure  82  of  FIG. 5  is an example of a dielectric structure that may be selectively added to antenna  18  during the manufacturing process to tune the antenna. As described in connection with  FIGS. 6 and 7 , when the amount of dielectric loading material that is mounted on antenna flex  80  in the vicinity of the antenna resonating element traces is adjusted, the frequency resonances of the antenna are shifted. Changes in dielectric loading structures such as loading structure  82  of  FIG. 10  may therefore be used to tune the antenna. With one suitable arrangement, structure  82  may be mounted on flex circuit  80  using adhesive (e.g., adhesive on structure  82  or double-sided tape). Structure  82  may be, for example, a patch of polyimide. Additional loading structures (e.g., pieces of plastic, etc.) may also be mounted on flex circuit  80  if desired. The arrangement of  FIG. 10  is merely illustrative. 
       FIG. 11  shows a top view of the antenna assembly of  FIG. 10 . As described in connection with  FIGS. 4 and 5 , the position at which the end of conductive structure  62  is attached to the conductive ground trace on antenna flex circuit  80  (i.e., position  66  or position  68  along lateral dimension  64 ) affects the length of ground return path L 1  ( FIG. 4 ) and thereby tunes the antenna. 
     As shown in  FIG. 12 , a radio-frequency connector such as connector  106  may be interposed in the transmission line portion of the radio-frequency signal path in antenna flex  80 . A test probe may be connected to connector  106  during calibration and testing operations.  FIG. 12  also shows how an alignment feature such as alignment post  108  may be provided at the distal tip of antenna flex  80 , after antenna flex  80  has passed through hole  98 . Grounding structure  110  may receive a screw that helps to ground antenna assembly  40  to housing  12 . 
     Integrated circuit  104  may be, for example, a radio-frequency transceiver module. As with integrated circuit  90  of  FIG. 10 , module  104  of  FIG. 12  may be connected to flex circuit  80 . In a typical arrangement, the surface of flex circuit  80  under circuits  90  and  104  is provided with pads to which the pins of circuits  90  and  104  may be attached with solder. Circuitry  90  and  104  may include integrated circuits, radio-frequency shielding structures (cans), discrete components (e.g., surface mount components), or any other suitable circuitry. 
       FIG. 13  shows ground trace  88  on antenna flex circuit  80  in a configuration where trace  88  is not visually obscured by conductive foam  62 . As shown in  FIG. 13 , conductive trace  88  may extend from location  112  to location  114  along the surface of flex circuit  80 . This provides an extensive grounding pad to which conductive foam  62  may be attached to complete the antenna&#39;s ground return path. The relatively large size of trace  88  may also provide sufficient margin to allow the lateral position of conductive foam  62  to be adjusted, without significantly overhanging the ends of trace  88 . 
     As shown in  FIG. 14 , the antenna formed by flex circuit  80  may be mounted over a dielectric window (window  20  of  FIG. 2 ) that is formed from a plastic insert such as insert  146 .  FIG. 15  shows another cross-sectional view of plastic insert  146 .  FIG. 15  also shows how ground trace  100  on antenna flex  80  may be grounded to conductive housing  12  at ground point  58  using conductive metal screw  142  and conductive structure  144  (e.g., a metal prong). 
     A perspective view of antenna support  84  without any attached structures is shown in  FIG. 16 . As shown in  FIG. 16 , antenna support  84  may have cavities  86  of the type described in connection with  FIGS. 8 and 9 . A selectable number of cavities  86  may be filled with a dielectric such as foam to add dielectric loading to antenna  18  and thereby tune the antenna&#39;s frequency response during the manufacturing process, if warranted by testing. In the example of  FIG. 16 , cavities  86  are shown as having the shape of prisms (i.e., polyhedrons with rectangular surface cross sections). This is merely illustrative. The volumes occupied by cavities  86  may have any suitable shapes such as conical shapes, hemispherical shapes, prisms and other polyhedrons, pyramids, cylinders, cones, combinations of these forms, etc. The use of polyhedral shapes is merely illustrative. Moreover, it is not necessary for cavities  86  to be deep (i.e., having depths that are comparable to or greater than their lateral dimensions). An advantage of such cavities is, however, that the weight of antenna support structure  84  can be reduced relative to antenna support structures  84  that use shallower cavity shapes (e.g., volumes in which the wall heights are less than the lengths and widths of the cavity at the surface). 
     A perspective view of antenna flex  80  without antenna support structure  84  is shown in  FIG. 17 . As shown in  FIG. 17 , antenna flex circuit  80  forms a substantially three-dimensional, non-planar structure. Initially, flex  80  is coplanar with meandering flex circuit portion  46 . At bend  118 , flex circuit  80  bends 180° around axis  116  (effectively making two adjacent 90° bends). At bend  124 , flex circuit  80  makes a right-angle band upward around horizontal axis  120 . At bend  126 , flex circuit  80  makes a right-angle band around vertical axis  122 . Another right-angle bend (bend  130 ) is formed around horizontal axis  128 . Two additional bends (bends  134  and  138 ) are formed by bending flex circuit  80  around axis  132  and axis  136 . 
     Any suitable techniques may be used to mount antenna flex circuit  80  to antenna support structure  84 . For example, adhesive or double-sided adhesive film  140  (i.e., tape) may be used to attach flex circuit  80  to support  84  and to make other attachments in device  10 . 
       FIG. 18  shows antenna flex circuit  80  as it is typically attached to antenna support structure  84 . Before assembly, antenna flex circuit  80  is unbent, as shown in the unassembled view of  FIG. 19 . 
     A flow chart of illustrative steps involved in characterizing and adjusting antennas and handheld electronic devices in accordance with embodiments of the present invention is shown in  FIG. 20 . 
     At step  148 , during the manufacturing process or as part of a pre-qualification process, some or all of the parts that are to be used to form device  10  may be characterized. Characterization measurements may be performed by measuring components individually (e.g., to gather data on mechanical and electrical component properties) or may be performed by performing tests on complete test devices or complete subassemblies. As an example, an antenna may be fabricated and its performance may be measured. Test equipment can be used, for example to make voltage standing wave ratio (VSWR) measurements to plot the frequency peaks for the antenna. 
     After characterizing the parts that will be assembled to form device  10  during manufacturing, adjustments to be made may be computed at step  150 . Available adjustments may include position adjustments to the conductive elastic connection  62  (e.g., the conductive foam lateral position along antenna ground trace  88 ), dielectric loading adjustments (e.g., using dielectric layers such as layer  82  of  FIG. 10 ), and dielectric cavity filling adjustments (e.g., to fill cavities  86  of  FIG. 16 ). Computations may be performed using analytical techniques, numeric techniques (e.g., computer-implemented computational techniques), and/or by using empirical methods (e.g., trial and error followed by recharacterizing measurements by repeating step  148 ). 
     After it has been determined which of the antenna tuning adjustments are to be made, the manufacturer may issue instructions to the robotic assembly equipment and/or assembly personnel at the manufacturing facility to assemble device  10  according to the desired adjustment settings. At step  152 , devices  10  may be assembled that include appropriate amounts of dielectric film loading, dielectric cavity filling, and ground return path length adjustments to ensure that the antennas in devices  10  perform optimally and in accordance with the desired parameters computed at step  150 . The process of  FIG. 20  may therefore ensure that devices  10  are produced with appropriately tuned antenna performance. 
     As these examples demonstrate, the flex circuit architecture that is used for antenna  18  in device  10  allows the performance of antenna  18  to be adjusted using several different performance-adjusting features. Moreover, the use of a single flex circuit such as flex circuit  80  for mounting multiple integrated circuits, for forming the entire antenna, and for forming signal paths to remote portions of device  10  helps to reduce assembly cost and complexity. Reliability may also be improved, because connectors for interconnecting the antenna with other portions of device  10  may be eliminated. The three-dimensional shape that is formed for antenna  18  by bending flex circuit  80  repeatedly around antenna support structure  84  has been demonstrated to exhibit satisfactory antenna efficiency and allows the antenna to be formed in the compact confines of a handheld electronic device such as a device with a conductive housing. 
     Antenna path length adjustments may be made by tuning the lengths of any suitable conductive paths associated with antenna  18 . The use of tuning arrangements based on conductive members such as conductive foam members that are placed at an adjustable position within the ground return path is merely illustrative. Moreover, as described in connection with  FIG. 5 , any suitable adjustable conductive element may be used in forming an adjustable path length in the antenna. 
       FIG. 21  is a cross-sectional side view showing how an inverted-F antenna such as antenna  18  may be tuned by making lateral position adjustments to conductive foam member  62 , ad described in connection with  FIGS. 5 and 10 . As shown in  FIG. 21 , conductive foam member  62  may form a conductive elastomeric structure that is compressed between conductive antenna ground trace  88  on flex circuit  80  and a conductive portion of device  10  such as a conductive midplate or other internal metal support structure  42 . As shown in  FIG. 5 , structure  42  may, in turn, be shorted to other conductive structures such as conductive housing  12 , thereby forming the rest of the ground return path for the inverted-F antenna by electrically shorting ground point  58  ( FIG. 5 ) to ground trace  88 . 
     An advantage of conductive elastomeric members and other members that can flex during assembly is that these members are compressible and can therefore accommodate variations in the sizes of the parts of device  10  that arise as part of a normal manufacturing process. It is not necessary, however, to use conductive foam to form the adjustable connector for the antenna. 
     As shown in  FIG. 22 , for example, a spring such as spring  620  may be placed at a suitable lateral position along the length of trace  88 . Spring  620  may be a metal spring that is formed as part of a tang on midplate  42 . During assembly, the manufacturer can bend spring  620  into place and can bend away or break off similar springs that are unused. Alternatively, a separate spring such as spring  620  can be attached at an appropriate location on trace  88  or midplate  42  using welds, conductive adhesive, or other suitable fasteners. 
     In the example of  FIG. 23 , a cross-sectional view is presented that shows how an inverted-F antenna in a handheld device may be tuned by adjusting the position of a conductive connector such as a solder connection. Solder bump  622  may be formed on trace  88  (e.g., on a predefined pad such as one of pads  623  that branch off from the rest of trace  88 ), may be formed on midplate  42 , or may otherwise be interposed in the ground return path. 
       FIG. 24  is a cross-sectional view showing how an inverted-F antenna such as antenna  18  may be tuned by adjusting the position of a conductive connector such as a screw or other mechanical fastener (fastener  624 ). To allow the lateral position of fastener  624  to be adjusted, midplate  42  may be provided with a series of threaded holes  625  into which the fastener may be inserted during assembly. Fastener  624  may be any suitable fastener such as a nut, rivet, bolt, etc. 
     Another illustrative arrangement is shown in  FIG. 25 . In the example of  FIG. 25 , the adjustable connection for antenna  18  is formed using spring-loaded pin  626 . As shown in the cross-section of  FIG. 25 , spring loaded pin  626  (which may be, for example, a Pogo® pin) may contain an internal biasing member such as spring  628 . Pins such as pin  626  are compressible. As with other elastic connector arrangements, pins  626  may therefore help accommodate variations in the sizes of the structures in device  10  that arise during manufacturing. With one suitable arrangement, a pin such as pin  626  may be welded to midplate  42  at a desired location along midplate. When device  10  is assembled, the welded location will cause the exposed end of pin  626  to bear against ground trace  88  at a location along its length that tunes antenna  18  as desired. 
     Although shown separately in the examples of  FIGS. 21 ,  22 ,  23 ,  24 , and  25 , the structures of these examples may be used in any suitable combination. Antenna  18  may include none, one, two, three, or more than three structures in its conductive paths. Moreover, dielectric loading schemes using additional layers of dielectric and selectively filled antenna support cavities may be used to provide additional or alternative tuning options if desired. 
     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: 20080905
Publication Date: 20120501
Grant Date: 20120501
Priority Date: 20080905
Inventors: SCHLUB ROBERT W.
DARNELL DEAN F.
HILL ROBERT J.
DABOV TEODOR
LIM HUI LENG
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T29/49016", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q9/0442", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/0442", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T29/49016", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/48", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/48", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 41798805