Patent Publication Number: US-10763584-B2

Title: Conductive plane antenna

Description:
The present specification relates to systems, methods, apparatuses, devices, articles of manufacture and instructions for antenna radiation. 
     SUMMARY 
     According to an example embodiment, a conductive plane antenna, comprising: a non-conductive substrate; a conductive plane coupled to the non-conductive substrate; wherein the conductive plane includes an open cavity over the non-conductive substrate; wherein the cavity includes a closed end and an open end; a first feed point coupled to the conductive plane and configured to pass a first polarity of a set of electromagnetic signals; and a second feed point coupled to the conductive plane and configured to pass a second polarity of the set of electromagnetic signals; wherein the conductive plane is configured to generate a first antenna gain pattern in response to the first and second polarity signals; wherein the cavity is configured to generate a second antenna gain pattern in response to the first and second polarity signals; and wherein a magnitude of the first antenna gain pattern is greater than a magnitude of the second antenna gain pattern. 
     In another example embodiment, the cavity further includes a first edge and a second edge; and the cavity is positioned within the conductive plane such that a first current distribution on the first edge of the cavity is opposite to a second current distribution on the second edge of the cavity. 
     In another example embodiment, a polarity of the first current distribution at the first edge is opposite to a polarity of the second current distribution on the second edge of the cavity. 
     In another example embodiment, a magnitude of the first current distribution at the first edge is substantially equal to a magnitude of the second current distribution on the second edge of the cavity. 
     In another example embodiment, the cavity further includes a first edge and a second edge; and the cavity is positioned within the conductive plane such that a first current distribution on the first edge of the cavity substantially cancels out a second current distribution on the second edge of the cavity. 
     In another example embodiment, the first and second feed points are located closer to the closed end of the cavity than the open end. 
     In another example embodiment, the conductive plane is connected to at least one of: a ground potential, a power supply potential, or an intermediate circuit potential. 
     In another example embodiment, the conductive plane includes an outer edge having a physical or electrical length of at least one-half wavelength of a lowest in-band frequency in the set of electromagnetic signals. 
     In another example embodiment, the open cavity includes a depth having a physical or electrical length at least one-quarter wavelength of a lowest in-band frequency in the set of electromagnetic signals. 
     In another example embodiment, excluding the open cavity, the conductive plane includes an outer edge which is continuously curved. 
     In another example embodiment, the conductive plane includes an outer edge; and
         wherein the outer edge is defined by an envelope that is either circular or oval in shape.       

     In another example embodiment, the closed end of the open cavity is located proximate to a geometrical center of the conductive plane. 
     In another example embodiment, further comprising a conducting reflector on one side of the conductive plane. 
     In another example embodiment, the conducting reflector is a loudspeaker. 
     In another example embodiment, the reflector includes a non-conductive cavity aligned with the open cavity in the conductive plane. 
     In another example embodiment, further comprising a second conductive plane;
         wherein the first conductive plane is coupled to the second conductive plane with vias.       

     In another example embodiment, further comprising a set of electrical circuits or components on a same side of the substrate as the conductive plane; and wherein the conductive plane surrounds the electrical circuits or components. 
     According to an example embodiment, a wearable device, comprising: a conductive plane antenna, including: a non-conductive substrate; a conductive plane coupled to the non-conductive substrate; wherein the conductive plane includes an open cavity over the non-conductive substrate; wherein the cavity includes a closed end and an open end; a first feed point coupled to the conductive plane and configured to pass a first polarity of a set of electromagnetic signals; and a second feed point coupled to the conductive plane and configured to pass a second polarity of the set of electromagnetic signals; wherein the conductive plane is configured to generate a first antenna gain pattern in response to the first and second polarity signals; wherein the cavity is configured to generate a second antenna gain pattern in response to the first and second polarity signals; and wherein a magnitude of the first antenna gain pattern is greater than a magnitude of the second antenna gain pattern. 
     In another example embodiment, the wearable device is at least one of: a wireless gaming headphone, a wireless headset, a smart helmet, or smart/VR goggles. 
     The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The Figures and Detailed Description that follow also exemplify various example embodiments. 
     Various example embodiments may be more completely understood in consideration of the following Detailed Description in connection with the accompanying Drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a first example conductive plane antenna. 
         FIG. 2  is an example current density distribution on the conductive plane antenna. 
         FIG. 3A  is a second example conductive plane antenna. 
         FIG. 3B  is a third example conductive plane antenna. 
         FIG. 3C  is a fourth example conductive plane antenna. 
         FIG. 4  is an example wearable device including a conductive plane antenna. 
         FIG. 5  is an example measured frequency vs. return-loss diagram of the conductive plane antenna of  FIG. 4 . 
         FIG. 6  is an example measured radiation pattern for the first example conductive plane antenna having a vertically oriented open cavity of  FIG. 1 . 
         FIG. 7  is an example measured radiation pattern for third example conductive plane antenna having a horizontally oriented open cavity of  FIG. 3B . 
         FIG. 8  is an example simulated radiation pattern for fourth example conductive plane antenna having a 45 degree oriented open cavity of  FIG. 3C ; 
         FIG. 9A  is a fifth example conductive plane antenna. 
         FIG. 9B  is an example simulated radiation pattern for the fifth example conductive plane antenna of  FIG. 9A . 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the spirit and scope of the appended claims are covered as well. 
     DETAILED DESCRIPTION 
     Headphone systems are used as wireless communication devices and high quality audio playback devices. High quality audio must be understood like CD like quality sound with larger audio bandwidth than voice audio. 
     A basic headphone comprises a wireless communication system, speaker and associated electronics. Some also may have one or more microphones. When a communication must be established across a larger range, like more than 1 meter, often solutions use a radio module that works with electromagnetic (EM) waves. 
     Electromagnetic waves can propagate over large distances and their power rolls off as the inverse of the square of the distance from the source. For example, Bluetooth or Bluetooth low energy (BLE) devices operate in the 2.5 GHz frequency band and have an operating range to 30 meters. 
     Such headphones are used for example in hands-free cellular operation or gaming where there is communication with a dongle attached to the gaming computer or network. Wireless antenna communications for such use-cases are designed for robustness. 
     One important parameter for a wireless antenna is a frequency range in which the antenna can be used with sufficient efficiency (i.e. the antenna&#39;s bandwidth). For example, the bandwidth required to operate in the world wide 2.4 GHz ISM band is 83 MHz. 
     One other challenge associated with the robust design of such wireless antennas is achieving a desired input impedance for reasonably matching the antenna to a front end RF integrated transceiver circuit. Without a proper impedance matching the available power from the RF integrated circuit is not accepted by the antenna and reflected to the source. This matching quality is characterized over the operating band as return-loss. 
     Furthermore, integrating such wireless antennas in space constrained headphones present various additional problems. For example a headphone usually has a dedicated design and not much volume left for the wireless antenna. This often results in wireless antenna gain patterns that are not sufficiently omnidirectional. 
       FIG. 1  is a first example conductive plane antenna  100 . The first example conductive plane antenna  100  includes a substrate  102 , a conductive plane  104 , an open cavity  106  (non-conductive), a first feed point (F 1 )  108 , a second feed point (F 2 )  110 , and electronic components/circuits  112 . 
     The substrate  102  includes a first side (i.e. front side, shown) and a second side (i.e. back side, not shown). The conductive plane  104  an outer edge  122  (circumference), a one-half (½) wavelength edge portion  124 , and a dotted line  126  (bisecting the conductive plane  104 ). 
     The substrate  102  may be a printed circuit board with conductive areas and electric connections between various electronic components and circuits. The substrate  102  material in one example is an FR4 material but can also be any other non-conductive material. 
     The open cavity  106  includes an open end  114  and a closed end  116  which together define a depth (i.e. physical distance from open to closed end) of the cavity  106 . The cavity  106  also includes a first edge  118  and a second edge  120 . 
     The depth in some example embodiments has a physical or electrical length at least one-quarter (¼) wavelength of a lowest in-band frequency in the set of electromagnetic signals. In some example embodiments, the closed end  116  of the open cavity  106  is located proximate to a geometrical center of the conductive plane  104 . 
     The cavity  106  can be of any shape, however, for discussion purposes a rectangular cavity  106  is shown in the Figures. 
     The cavity  106  is filled with a non-conductive material or substrate  102  material or a mixture of substrate  102  materials. In some example embodiments, the cavity  106  is filled with air. In other example embodiments, the cavity  106  is first filled with a layer of air and then with a second layer of FR4 material. The first layer of air can have a height of 35 μmeter while the second layer of FR4 material can have a height of 1 millimeter. 
     The cavity  106  in some examples can have a length of 18 mm on a FR4 printed circuit board of 1 mm thickness, and a width W that influences the operational bandwidth of the antenna (e.g. the width can be 1 mm). 
     The antenna&#39;s  100  polarization can be changed by reorienting the cavity  106  at a different angle (e.g. horizontal, 45 degree, etc. further discussed below). The antenna&#39;s  100  reactance can be partially set by the width of the cavity  106 . 
     The first feed point (F 1 ) is connected to the conductive plane  104  at position  108 . The first feed point  108  is configured to pass a first polarity of a set of electromagnetic signals. 
     The second feed point (F 2 )  110  is connected to the conductive plane  104  at position  110 . The second feed point  110  is configured to pass a second polarity of the set of electromagnetic signals. The first feed point (F 1 ) and the second feeding point (F 2 ) are connected to various electronic components/circuits  112 . 
     If the feeding points F 1   108  and F 2   110  were moved along the edges  118 ,  120  of the cavity  106 , an impedance seen at the feeding points would increase from zero at the closed end  116  to a greater impedance as the feeding points&#39; positions are moved toward the open end  114  of cavity  106 . In some example embodiments, the impedance at the feeding port should be 50 Ohms for maximum power transfer between antenna  100  and the electronic components/circuits  112  (e.g. a radio integrated circuit (RF-IC)). For further impedance optimization and frequency filtering, an additional matching network can be used. 
     The first F 1  and second F 2  feed points in some example embodiments are located closer to the closed end  116  of the cavity  106  than the open end  114 . 
     The electronic components/circuits  112  in various example embodiment may include an antenna impedance matching circuit, a radio circuit, an audio decoding circuit, an audio amplifier circuit, a controller circuit, a user interface circuit and/or a power supply circuit. The set of electrical circuits or components  112  can be located on a same side or opposite of the substrate  102  as the conductive plane  104 . 
     Once all electronic components are connected to the substrate  102  the remaining area is filled with the conductive plane  104 . Shown is an example embodiment where the conductive plane  104  surrounds the electrical circuits or components  112 . 
     The conductive plane  104  is configured to generate a first antenna gain pattern in response to the first and second polarity signals. The cavity  106  is configured to generate a second antenna gain pattern in response to the first and second polarity signals. With the structure discussed, the conductive plane  104  acts as a primary source of radiation (i.e. a magnitude of the first antenna gain pattern from the conductive plane  104  is greater than a magnitude of the second antenna gain pattern from the cavity  106 ). Thus current density/flow patterns in the conductive plane  104  results in radiation primarily, if not completely, from the conductive plane  104  and not the cavity  106 . 
     The conductive plane  104  is connected to at least one of: a ground potential, a power supply potential, or an intermediate circuit potential. 
     The conductive plane  104  includes an outer edge  122  having a physical or electrical length of at least one-half (½) wavelength of a lowest in-band frequency in the set of electromagnetic signals. 
     In some example embodiments, excluding the open cavity  106 , the outer edge  122  of the conductive plane  104  is continuously curved, and may be defined by an envelope that is either circular or oval in shape (e.g. a circular diameter of 50 mm). Curve is herein defined to include at least one of: a circular portion, a spherical portion, a conical portion, a parabola portion, or any topological space which is locally homeomorphic to a line. This curve may also be defined as a substantially curved envelope which may include locally sharp edges (e.g. due to the manufacturing process). 
     To effect radiation primarily from the conductive plane  104 , the cavity  106  is positioned within the conductive plane  104  such that a first current distribution on the first edge  118  of the cavity  106  is opposite to a second current distribution on the second edge  120  of the cavity  106 . Thus currents on either side of the cavity tend to cancel each other, thereby minimizing radiation from the cavity  106 . 
     As will be further shown and discussed in  FIG. 2 , the polarity of the first current distribution at the first edge  118  is opposite to a polarity of the second current distribution on the second edge  120  of the cavity  106 . In some example embodiments, the magnitude of the first current distribution at the first edge  118  is substantially equal to the magnitude of the second current distribution on the second edge  120  of the cavity  106 . 
     Thus, the cavity  106  is positioned within the conductive plane  104  such that the first current distribution on the first edge  118  of the cavity  106  substantially cancels out the second current distribution on the second edge  120  of the cavity  106 . 
     In this example, the cavity  106  has a vertical geometric orientation and thereby is resonant with radiated energy having a horizontal polarization. 
     The dimensions of the conductive plane  104  are related to the wavelengths of electromagnetic signals to be received and/or transmitted. A circular shape has been found beneficial and fits very well in a headphone design form factor. 
     When an electrical length of a portion  124  of the edge  122  of the conductive plane  104  is a ½ wavelength of the transmit frequency, then the antenna reaches an optimal performance. However, portion  124  (e.g. “S”) might deviate somewhat from an ideal electrical length and still be efficient enough for some applications. 
     Unless otherwise specified, edge is herein defined as an edge of the conductive plane  104  and not the edge of the substrate  102 . The dotted line  126  denotes a ½ wavelength electrical length of a higher in-band frequency to be transmitted or received by the conductive plane  104  antenna  100 . 
     A size of the various dimensions of the antenna  100  structures can be scaled to obtain an application specific radiation performance over a wide variety of operating frequencies. 
     For comparison purposes, for an antenna operating at the world-wide ISM band, the 2.5 GHz carrier frequency wavelength is 12 cm. A prior art dipole antenna would require a total length of a half wavelength, which is 6 cm at 2.5 GHz. A prior art monopole antenna consists of a quarter wave radiator (3 cm) and a conductive plane  104  with a size of at least a half wavelength (6 cm). Such dipole and monopole antennas are quite large and unlikely or difficult to be integrated into an small wearable device. They both require additional height above their conductive planes to be efficient. However, the antenna  100  presented wherein the cavity  106  has a ¼ wavelength electrical/physical length is implemented in a same plane as the conductive plane  104 , and thus no extra space is required above the conductive plane  104  and/or the electronic circuits/components or substrate  102 . 
       FIG. 2  is an example current density distribution  200  on the conductive plane antenna  100  with a vertical cavity  106 . The example current density distribution  200  shows the conductive plane  104  covered in simulated current vectors (i.e. arrows). The arrow size represents a current magnitude and the arrow direction represents a current polarity. 
     Also shown is the open cavity  106  including the open end  114 , the closed end  116 , the first edge  118 , and the second edge  120 . The feeding points F 1  and F 2 , with feeding positions,  108 ,  110  are near the closed end  116  of the cavity  106 . 
     Note that the current arrows near the first edge  118 , have a first cavity edge current magnitude and polarity that is substantially opposite in polarity but equal in magnitude to a second cavity edge current magnitude and polarity near the second edge  120 . 
     Based on the geometry, the conductive plane  104  hosts a high frequency current path region  202 , having longer physical/electrical lengths), and a low frequency current path region  210 , having shorter physical/electrical lengths. An example high frequency electrical length  204  between locations  206  and  208  is shown in the high frequency current path region  202 , and an example low frequency electrical length  212  between locations  206  and  208  is shown in the low frequency current path region  210 . 
     In this example embodiment, the ½ wavelength edge portion  124  locations  206  and  208  on the outer edge  122  of the conductive plane  104  are perpendicular to the closed end  116  of the cavity  106 , thus a half wave resonance is formed between locations  206  and  208 . 
     The current density is at a relative maximum in the ½ wavelength edge portion  124  between locations  206  and  208 . The current density is at a relative minimum near locations  206  and  208 . Currents are induced throughout the lower half of the conductive plane  104  resulting in the wide bandwidth of frequencies that can be transmitted and/or received. 
     In some example embodiments, this mode of operation is achieved by locating the closed end  116  of the cavity  106  roughly at the geometric center of conductive plane  104  and minimizing the area of the cavity  106  region. 
     The cavity  106  itself generates minimal radiation since the first and second edge  118 ,  120  currents are flowing in opposite directions and thus substantially cancel out. 
     Currents in the conductive plane  104  that are further from the closed end of the cavity  106  are not canceled out and radiate RF energy from the conductive plane  104  itself. 
     Moving from the high frequency region  202  to the low frequency region  210 , differing physical/electrical lengths radiating enable a wide-band of RF frequencies. 
     The current vectors responsible for the far field radiation create arcs that follow the circular shape of the conductive plane  104  as shown by the example high frequency electrical length  204  and the example low frequency electrical length  212 . 
       FIG. 3A  is a second example conductive plane antenna  300 . The second example conductive plane antenna  300  includes a first conductive plane  302 , an open cavity  304 , and a set of vias  306  (i.e. each of the small circles is a via). 
     This second antenna  300  in some examples is coupled using the vias  306  to a second conductive plane  303  (not shown) substantially parallel with the first conductive plane  302 . Both conductive planes  302 ,  303  have similar cavities that are substantially aligned (e.g. you can “look through it”). Thus in some example embodiments, there are two stacked conductive planes  302 ,  303  separated by the substrate  102 . 
     In some example embodiments, a distance between the vias are less than 1/10 th  of the wavelength of the electromagnetic signals to be transmitted and/or received by the antenna  300  so as not to substantially attenuate antenna gain within the operating bandwidth. 
     If a more complex conductive plane stack-up is used, for example 4 or 6 layer printed circuit board, one of the layers may be the conductive plane  302 . 
       FIG. 3B  is a third example conductive plane antenna  308 . The third example conductive plane antenna  308  includes a conductive plane  310  and an open cavity  312 . Because the cavity  312  has a horizontal orientation, the antenna  308  resonates with vertically polarized electromagnetic signals. This is because the current direction in the conductive plane  310  that is responsible for the far field radiation is mainly perpendicular to the cavity  312  direction. 
       FIG. 3C  is a fourth example conductive plane antenna  314 . The fourth example conductive plane antenna  314  includes a conductive plane  316  and an open cavity  318 . The 45 degree orientation of the cavity  318  results in electromagnetic signal resonance in both horizontal and vertical polarizations. 
       FIG. 4  is an example wearable device  400  including a conductive plane antenna  402 . The example wearable device  400  includes a conductive plane antenna  402 , such as those examples discussed above. More than one conductive plane may be included in the wearable device  400 . 
     In various example embodiments, the wearable device  400  can be either a wireless headphone (e.g. a gaming headphone), a headset, a smart helmet, or smart/VR goggles. 
     In these examples, the conductive plane  402  is mounted in parallel with a user&#39;s ear. A user wearing the wearable device  400  further shapes the antenna gain pattern. 
       FIG. 5  is an example frequency vs. return-loss diagram of the conductive plane antenna of  FIG. 4 . The example frequency vs. return-loss diagram  500  includes a frequency axis  502 , a return-loss axis  504 , and a return-loss  506  plot. The return loss is a measurement that shows an impedance matching performance. The return-loss  506  plot is based on one of the set of example embodiment dimension presented above. 
     Usually a −10 dB return loss indicates a very good matching situation. As can be seen in the return-loss  506  plot the −10 dB range is more than 180 MHz wide and twice a required bandwidth in the 2.4 GHz BLE band. Two markers (M 1  and M 2 ) are at the 2.5 and 2.68 GHz. The BLE (Bluetooth Low Energy) band ranges from 2.4 GHz to 2.4835 GHz and 83 MHz wide also benefits from at least −10 dB return loss. 
       FIG. 6  is an example measured radiation pattern  600  for first example conductive plane antenna  100  having a vertically oriented open cavity  106  of  FIG. 1 . The measured radiation pattern  600  in the horizontal plane is shown in a polar coordinate graph format centered about a user  602  wearing a headphone  604  containing the conductive plane antenna  100  of  FIG. 1 . 
     A vertical polarization antenna gain  606  plot and a horizontal polarization antenna gain  608  plot are as shown. As can be seen the horizontal polarization antenna gain  608  is dominant and has maximum gain on a side of the user&#39;s  602  head where the conductive plane antenna  100  is mounted. There is reduction of gain on the other side of the user&#39;s  602  head due to tissue absorption. 
       FIG. 7  is an example measured radiation pattern for third example conductive plane antenna  308  having a horizontally oriented open cavity  312  of  FIG. 3B . The measured radiation pattern  700  in the horizontal plane is shown in a polar coordinate graph format centered about a user  702  wearing a headphone  704  containing the antenna  308 . 
     A vertical polarization antenna gain  706  plot and a horizontal polarization antenna gain  708  plot are as shown. As can be seen the vertical polarization antenna gain  706  is dominant and has maximum gain on the side of the user&#39;s  702  head where the conductive plane antenna  308  is mounted. There is reduction of gain on the other side of the user&#39;s  702  head due to tissue absorption. 
     Mounting a second antenna with a second conductive plane antenna at the other ear side of the headphone will result in an overall omnidirectional radiation pattern. Different polarizations can also be used to make the communication link more robust in multipath environments. 
       FIG. 8  is an example simulated 3 dimensional radiation pattern for fourth example conductive plane antenna  314  having a 45 degree oriented open cavity  318  of  FIG. 3C . The simulated radiation pattern  800  is shown in a planar format centered about a user  802  wearing a headphone  804  containing the antenna  314 . 
     An antenna gain  806  for this configuration is also shown. There are no substantial gain attenuations at the side of the user&#39;s  802  head were the antenna  314  is mounted. At the other side of the user&#39;s  802  head gain is attenuated due to the absorption properties of a human head. For comparison purposes, dipole antennas would result in at least 2 strong directions where antenna gain is reduced (e.g. toroidal antenna gain shape of a dipole). 
       FIG. 9A  is a fifth example conductive plane antenna  900 . The fifth example conductive plane antenna  900  shows a user  902  wearing a headphone  904 . The headphone  904  includes a conductive plane  906  having an open cavity  908 , and a conducting (e.g. metal) reflector  910  (e.g. a conductive ring). In this example embodiment, the reflector  910  is part of (e.g. an outer rim of) a loudspeaker structure having a center electromagnetic coil  912 . 
     The reflector  910  is on one side of the conductive plane  906 . The reflector  910  is configured to redirects any energy radiated from the conductive plane  906  toward the user  902  back away from the user  902  so as to enhance radiation away from the user&#39;s  902  head and toward any other wireless device with which communication is desired. 
     In one example embodiment, the resultant increase in antenna  900  gain can be roughly 6 dB, which about doubles the antenna&#39;s  900  communication range. 
     In some example embodiments, the reflector  910  also includes a non-conductive cavity, which is aligned with the open cavity  908  in the conductive plane  906 . For example, if the spacing between the reflector  910  and the conductive plane  906  with slot  908  is sufficiently large, there does not need to be a non-conductive cavity in  910 . However, if  910  and  906  are close to each other, a  910  reflector with a cavity can yield a better antenna gain pattern. 
     Antenna  900  input impedance minimally affected so that impedance matching with various electronic components/circuits is still excellent. 
       FIG. 9B  is an example simulated 3 dimensional radiation pattern  914  for the fifth example conductive plane antenna  900  of  FIG. 9A . Shown is the user  902 , the headphone  904 , and an example antenna gain  916 . 
     It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended Figures could be arranged and designed in a wide variety of different configurations. Thus, the detailed description of various embodiments, as represented in the Figures, is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 
     Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. 
     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.