Patent Publication Number: US-8970443-B2

Title: Compact balanced embedded antenna

Description:
BACKGROUND 
     Information can be wirelessly transferred using electromagnetic waves. Generally, such electromagnetic waves are either transmitted or received using a specified range of frequencies, such as established by a spectrum allocation authority for a particular location where a wireless device or assembly will be used or manufactured. Wireless devices or assemblies generally include one or more antennas, and each antenna can be configured for transfer of information at a particular range of frequencies. Such ranges of frequencies can include frequencies used by wireless digital data networking technologies. Digital data networking technologies can use, conform to, or otherwise incorporate aspects of one or more protocols or standards, such as for providing cellular telephone or data services, fixed or mobile terrestrial radio communications, satellite communications, or for other applications. 
     OVERVIEW 
     A wireless device can be configured to transfer information using different operating frequency ranges (e.g., bands). In generally-available devices, such information transfer can be performed using separate antennas designed to operate in respective frequency ranges. Such antennas can be assemblies separate from other communication circuitry, such as coupled to the communication circuitry using one or more cables or connectors. Manufacturing cost, complexity, or reliability can be negatively affected by use of such separate antennas. The present inventor has recognized, among other things, that a printed circuit board wide-band antenna can reduce or eliminate a need for separate antennas to provide coverage of different operating frequency ranges. 
     Also, antenna configurations can include balanced or unbalanced configurations. For example, a balanced antenna configuration can provide enhanced gain, substantially-omnidirectional response in at least one plane, and reduced radiation pattern sensitivity and reduced input impedance fluctuation in response to changing surroundings, as compared to single-ended antenna configurations, but at a cost of larger dimensions or additional interface circuitry as compared to various unbalanced antenna configurations. 
     For example, generally-available communication circuits generally provide an electrically unbalanced communication port for coupling communication signals between an antenna and the communication circuit. In applications where a balanced antenna is desired, a balun can be used to couple and match the balanced antenna to an unbalanced source. A discrete balun, such as included as a portion of a communication circuit, can increase cost and consume substantial volume. Such costs and complexity can increase further in multi-band applications where multiple antennas or baluns may be needed. 
     The present inventor has recognized, among other things, that a balanced antenna configuration can be formed as a portion of a printed circuit board (PCB) assembly (e.g., the planar antenna can be “embedded” in the PCB design rather than including a separate antenna assembly). The present inventor has also recognized that such a balanced antenna configuration can include a distributed balun as a portion of one or more conductive layers included in the PCB assembly. 
     A planar antenna, such as included as a portion of printed circuit board assembly, can include a balanced configuration comprising a first conductive layer. The first conductive layer can include a first arm having a footprint extending in a first direction and a second arm having a footprint extending in a direction opposite the first direction. The second arm can be sized and shaped to be similar to the footprint of the first arm. 
     This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
         FIG. 1A  illustrates generally an example of at least a portion of a planar antenna, such as can include first conductive layer, and  FIG. 1B  illustrates generally an example of at least a portion of a planar antenna, such as can include a second conductive layer. 
         FIG. 2  illustrates generally an illustrative example of a voltage standing wave ratio (VSWR), such as can be simulated for the antenna configuration of  FIGS. 1A through 1B . 
         FIG. 3  illustrates generally an illustrative example of an impedance Smith Chart that can be simulated for the antenna configuration of  FIGS. 1A and 1B . 
         FIG. 4  illustrates generally an illustrative example of a technique, such as a method that can include forming first and second arms of a conductive layer of planar antenna. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  illustrates generally an example of at least a portion of a planar antenna, such as can include first conductive layer  100 A comprising one or more conductive strips. The planar antenna can include one or more conductive layers, such as shown in the example of  FIGS. 1A and 1B . For example, the planar antenna can include a first conductive layer  100 A aligned with corresponding conductive strips on a second conductive layer  100 B, such as shown in the example of  FIG. 1B , or aligned with one or more other conductive layers. 
     The first conductive layer  100 A can include a reference conductor  102 A, such as ground plane or other structure that can be laterally offset from other portions of the planar antenna. The region of reference conductor  102 A can include other circuitry, such as a wireless communication circuit configured to transmit or receive information electromagnetically using the planar antenna. The first conductive layer  100 A can be formed, patterned, or otherwise fabricated such as coupled to a dielectric material  124  (e.g., one or more of the first conductive layer  100 A or the second conductive layer  100 B can include metallization layers on a printed circuit board assembly). 
     The planar antenna can include a first arm  116 , such as having a footprint (e.g., pattern or plan view such as shown in  FIG. 1A ) extending in a first direction. For example, the first direction can be an axial direction extending away from a central line of symmetry  142 . The first arm  116  can include a first conductive strip  108 , such as having a first lateral width. The planar antenna can include a second arm  118  having a footprint sized and shaped to be similar to the footprint of the first arm  116 . The second arm  118  need not be identical to the first arm  116 . For example, the second arm  118  can include a second conductive strip  104  that can be narrower in lateral width than the first conductive strip  108  of the first arm, such as shown in  FIG. 1A . The phrase “footprint” can refer to an extent of outer or inner boundaries of conductive portions of one of the first or second arms  116  or  118 , or can refer to a path traced out by an antenna conductor, for example. 
     The second arm  118  can be coupled (e.g., conductively coupled) to the first arm  116  at a distal location  112 , such as a location distal with respect to a feed location  110 . The second arm  118  can include one or more conductive strips coplanar with the second conductive strip  104 , such as located laterally nearby the second conductive strip  104 . For example, the one or more conductive strips can include an outside-facing conductive strip  106 A or an inside-facing conductive strip  106 B. The outside-facing or inside-facing conductive strips  106 A or  106 B can be terminated as stubs at or nearby the distal location  112 . In this manner, the outside-facing or inside-facing conductive strips  106 A or  106 B can provide at least a portion of a balun structure, such as configured to transition from a single-ended antenna port at the feed location  110 , to a balanced configuration for operation of the planar antenna. 
     The planar antenna of the example of  FIGS. 1A and 1B  need not provide uniform separation between portions of the respective conductive strips closer to the feed location  110 , such as an inboard portion  136  of the first conductive strip  108 , and an outboard portion  138  of the first conductive strip  108 . For example, the planar antenna can include one or more pinched regions, such as a first pinched region  132  about halfway along a long axis of the first arm  116 . The present inventor has recognized, among other things, that in this manner, the non-pinched regions, such as a first non-pinched region  130 , or a second non-pinched region  134 , can be used to tune the antenna for wideband operation in a specified range of frequencies while consuming less total area than a corresponding folded-dipole configuration. 
     A width of one or more conductive strips need not be uniform in the planar antenna. For example, the planar antenna may include a second conductive strip  104  that can vary along the footprint of the second arm  118 , such as including a wider portion  114  in a first region, and a narrower portion elsewhere. One or more discrete or distributed matching components can be used to establish a specified input impedance for the planar antenna, such as including one or more conductive pads in the region  126 . For example, one or more “L” or “it” matching networks can be used, such as including one or more series inductors and one or more shunt capacitors. 
     A feed location  110  of the planar antenna can be coupled to a coplanar waveguide or transmission line structure in the region  128  near the feed location  110 . For example, the wider portion  114  of a conductive strip included in the second arm  118  can sized to establish a specified impedance, such as a real impedance of about 50 ohms, and can transition to the narrow portion at a location in the region  126 . The location of the transition can be specified at least in part to establish a specified impedance-matched bandwidth of the planar antenna, such as to provide the voltage standing wave ratio (VSWR) as shown in the illustrative example of  FIG. 3 . An input impedance of the planar antenna can be controlled, such as to present a specified input impedance (e.g., a specified real impedance or a specified conjugate match to an output impedance of the communication circuit). 
       FIG. 1B  illustrates generally an example of at least a portion of a planar antenna, such as located vertically offset (e.g., above or below) from a plane of the first conductive layer  100 A of the example of  FIG. 1A . The example of  FIG. 1B  can include a second conductive layer  100 B, such as having a similar footprint to the conductive layer  100 A. For example, as shown in  FIG. 1B , the second conductive layer  100 B can include a first arm  216 , such as located vertically offset from the first arm  116  of the first conductive layer  100 A. The second conductive layer  100 B can include a second arm  218  having a footprint similar to the first arm  216  of the second conductive layer  218  (e.g., such as including an outline representing a mirror image of the first arm  216 ). The two arms  216  and  218  need not be identical. For example, one or more vias such as a via  240  may be used to connect portions of one or more of the conductive layers  100 A or  100 B together in specified locations. 
     The first arm  216  of the second conductive layer  100 B can include a first conductive strip  208 , such as having a similar footprint to the first conductive strip  108  of the first conductive layer  100 A. Similarly, the second arm  218  of the second conductive layer  100 B can include a second conductive strip  204 , such as having an outline similar to the outline defined by one or more portions of the second arm  118  of the first conductive layer  100 A. 
     Similar to the first conductive layer  100 A, the second conductive layer  100 B can include a first unpinched region  230 , such as coupled to a feed location  210  using a conductive strip in the region  228  between the unpinched region  230  and the feed location  210 . The second conductive layer  100 B can include a pinched region  232 , and a second unpinched region  234 , to provide a footprint similar to the footprint of the first arm  116  of the first conductive layer. 
     The second conductive layer  100 B of  FIG. 2  can include a reference conductor  102 B (e.g., a reference plane). The first and second arms  216  and  218  can be coupled to the reference conductor  102 B such as using a conductive strip in the region  228 . The conductive strip in the region  228  can include or can be a portion of a transmission line structure feeding the planar antenna, such as to establish a specified input impedance, at least in part. The second conductive layer  100 B can include a gap  212 , such as to establish a portion of a balun structure using the second arm  218  and the corresponding portion of the first conductive layer  100 A, such as the second  118  of the first conductive layer  100 A. For example, the conductive layers of  FIGS. 1A and 1B  can be at least approximately symmetric about an axis of symmetry  142  as shown in  FIG. 1A . A first current distribution can be established such as in the first conductive strip  108  of the first arm  116  in the first conductive layer  100 A. A complementary current distribution can be established in the second conductive strip  104  of the second arm  118  in the first conductive layer  100 A. Similarly, respective image currents can be established in the first and second arms  216  and  218  of the second conductive layer  100 B. 
     The planar antenna need not rely on image currents induced or established in the reference conductor  102 A or  102 B plane regions. In this manner, some degree of self-shielding is provided by the planar antenna, such as providing a more omni-directional and consistent radiation pattern in the presence of discontinuities in the plane geometry (e.g., due to traces, vias, or other circuitry in the region  120  laterally offset from the planar antenna). Such an antenna configuration can also be more immune to geometric variation in conductor geometry due to manufacturing process variations. Simulation of the illustrative example of  FIGS. 1A and 1B  indicates a radiation efficiency generally better than 50%. 
     The dielectric material  124  region of the example of  FIG. 1A  can include a dielectric substrate of a printed circuit board assembly (PCBA). Such a dielectric substrate can include a glass-epoxy laminate such as FR-4, FR-406, or one or more other materials, such as generally used for printed circuit board (PCB) fabrication. Such materials can include a bismaleimide-triazine (BT) material, a cyanate ester, a polyimide material, or a polytetrafluoroethylene material, or one or more other materials. One or more of the conductive portions of  FIG. 1A  or  1 B can include electrodeposited or rolled-annealed copper, such as patterned using a photolithographic process, or formed using one or more other techniques (e.g., a deposition, a stamping, etc.) 
       FIG. 2  illustrates generally an illustrative example  200  of a voltage standing wave ratio (VSWR)  220 , such as can be simulated for the antenna configuration of  FIGS. 1A through 1B . A usable range of operating frequencies can be specified in terms of VSWR, or in terms of a corresponding return loss, or using one or more other criteria. For example, a specified S 11  parameter of about −10 dB or lower (e.g., a return loss of 10 dB), can be considered generally acceptable for a variety of applications. Such a return loss corresponds to a VSWR of about 2:1 or less. In the illustrative example of  FIG. 2 , the VSWR  220  is less than 2:1 in a range from less than 0.87 gigahertz (GHz) to more than 0.95 GHz, indicating a usable bandwidth of over 0.8 GHz (80 megahertz (MHz)) according to a 2:1 VSWR criterion. Other criteria can be used to establish, determine, or estimate a usable bandwidth (e.g., a 3:1 VSWR criterion). 
       FIG. 3  illustrates generally an illustrative example of an impedance Smith Chart  300  that can be simulated for the antenna configuration of  FIGS. 1A and 1B . Loops in the impedance response indicate coupling behavior from the multiple elements. One or more geometric or material parameters of the planar antenna can be varied, such as to shift the locus of loops in the impedance closer to the center or unit impedance (e.g., corresponding to 50 ohms real impedance), or to some other desired input impedance to provide a conjugate impedance match to an output of a wireless communication circuit. 
       FIG. 4  illustrates generally an illustrative example of a technique  400 , such as a method, which can include forming first and second arms of a conductive layer of planar antenna, such as a planar antenna as discussed in the examples above. For example, at  402 , a reference conductor can be formed (e.g., such as using a lithographic technique or other technique, such as reference conductor  102 A or  102 B as shown in the example of  FIG. 1A  or  1 B.) At  404 , the technique  400  can include forming a first conductive layer comprising a first arm having a footprint extending in a first direction, such as shown in the example of  FIG. 1A  or  1 B. 
     At  406 , a second arm can be formed, such as having a footprint extending in a direction opposite the first direction. The second arm can be sized and shaped to be about the same as a footprint defined by the first arm (e.g., a mirror image of the footprint of the first arm). Other techniques, such as fabrication techniques discussed in the examples of  FIG. 1A  or  1 B, can be included as a portion of the technique  400 . 
     VARIOUS NOTES 
     The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventor also contemplates examples in which only those elements shown or described are provided. Moreover, the present inventor also contemplates examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein. 
     In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls. 
     In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. 
     Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, in an example, the code can be tangibly stored on one or more volatile, non-transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like. 
     The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.