Patent Publication Number: US-10763578-B2

Title: Dual band multiple-input multiple-output antennas

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/698,575 filed Jul. 16, 2018. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure generally relates to dual-band multiple-input multiple-output antennas. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Multiple-input multiple-output (MIMO) radios typically require two or more separately mounted antennas for optimal MIMO performance. However, mounting two separate internal/embedded antennas in a single enclosure can create issues with correct isolation, polarization, and tuning. Also, many devices in which MIMO radios are desirable may not have the necessary footprint size to accept two separate internal/embedded antennas. 
     When designing MIMO antennas with smaller profiles, improved isolation (e.g., &gt;15 decibels (dB), etc.) and efficiency across all operating frequency bands, challenges arise for planar inverted-F antennas with quarter-wave designs. In some cases, ground proximity coupling has been applied to flexible planar inverted-F antennas (PIFAs) to achieve improved isolation for a dual band antenna while maintaining total efficiency and max gain. 
     Separately, a planar inverted-F antenna generally can include a planar radiator or upper radiating patch element having a slot. A lower surface of the PIFA is spaced apart from the upper radiating patch element. First and second shorting elements electrically connect the planar radiator to the lower surface. The PIFA also includes a feeding element electrically connected between the upper radiating patch element and the lower surface. The PIFA may be mounted on a ground plane that is larger than the lower surface of the PIFA. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a front view of a dual-band multiple-input multiple-output (MIMO) antenna according to an exemplary embodiment; 
         FIG. 2  is a side view of the MIMO antenna of  FIG. 1 ; 
         FIG. 3  illustrates exemplary line graphs of isolation and voltage standing wave ratio (VSWR) versus frequency in gigahertz (GHz) measured for each port of a prototype of the exemplary antenna of  FIG. 1 ; 
         FIG. 4  is an exemplary line graph illustrating 3D maximum gain in decibels relative to isotropic (dBi) versus frequency in megahertz (MHz) measured for a prototype of the exemplary antenna of  FIG. 1 ; 
         FIGS. 5-8  illustrate radiation patterns simulated for the exemplary antenna of  FIG. 1  at frequencies of 2400 MHz, 2440 MHz, 2480 MHz, 4900 MHz, 5150 MHz, 5500 MHz, 5800 MHz, and 5900 MHz; 
         FIG. 9A  is a top view of a flattened flexible PCB layout or pattern development of a dual-band multiple-input multiple-output (MIMO) antenna according to another exemplary embodiment; 
         FIG. 9B  is a bottom view of the flattened flexible PCB layout or pattern development of a view of the MIMO antenna of  FIG. 9A ; 
         FIG. 10  is a top view of a flattened flexible PCB layout or pattern development of a dual-band multiple-input multiple-output (MIMO) antenna according to yet another exemplary embodiment; 
         FIGS. 11A and 11B  are side views of a ground element and a radiating element of the MIMO antennas of  FIGS. 9A and 9B ; 
         FIG. 11C  is a side view of a ground element and radiating element of the MIMO antenna of  FIG. 10 ; 
         FIG. 12  is an exemplary line graph illustrating port to port isolation in decibels (dB) versus frequency in megahertz (MHz) measured for a prototype of the antenna of  FIG. 9A ; 
         FIGS. 13A-13C  illustrate performance summary data measured for a prototype of the antennas of  FIGS. 9A, 9B and 10  with different positions and types of ground elements; 
         FIG. 14  is an exemplary line graph illustrating VSWR versus frequency in megahertz (MHz) measured for a prototype of the antennas of  FIGS. 9A, 9B and 10  with different positions and types of ground elements; 
         FIG. 15  is an exemplary line graph illustrating port to port isolation in decibels versus frequency in megahertz (MHz) measured for a prototype of the antennas of  FIGS. 9A, 9B and 10  with different positions and types of ground elements; 
         FIG. 16  illustrates various polarizations of radiation patterns for the simulated design of the antenna of  FIG. 9A  at frequencies of 2440 MHz and 5400; and 
         FIG. 17-19  illustrate various radiation patterns for the simulated design of the antenna of  FIG. 9A  at frequencies of 2400 MHz, 2440 MHz, 2480 MHz, 4900 MHz, 5400 MHz, and 5900 MHz. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Disclosed herein are example embodiments of dual-band multiple-input multiple-output antennas. In some embodiments, a dual-band multiple-input multiple-output antenna includes two stacked antennas in a single package with two antenna leads coming off of the MIMO antenna. The antenna can be optimized and tuned for 2×2 MIMO operations in an embedded device. For example, tuning, isolation, polarization, etc. can be optimized for MIMO operations. 
     A dual-band multiple-input multiple-output antenna may include an adhesive (e.g., adhesive backing, liner, etc.) positioned on a side of the antenna, to simplify mounting of the MIMO antenna to a surface. This can greatly reduce complexity when integrating a MIMO device. 
     In some embodiments, a wireless local area network (WLAN) dual-band MIMO antenna can operate in a frequency range of about 2.4-2.48 GHz, and a frequency range of about 4.9-5.9 GHz. The antenna may include two radiating elements (e.g., planar inverted-F antenna (PIFA) elements, etc.) and a ground element (e.g., layer, isolator, plane, etc.). 
     The two radiating elements may be arranged, positioned, located, etc. at a top layer of the MIMO antenna. The ground element is optionally located at a top or bottom layer of the MIMO antenna. For example, a flexible printed circuit board (PCB) may include two radiating elements on a top layer (e.g., copper trace layer, etc.) of the PCB and a ground element on a bottom layer (e.g., copper trace layer, etc.) of the PCB. Alternatively, or in addition, the two radiating elements and the ground element may be located on the top layer of the PCB. 
     Each radiating element may include an upper planar radiator, and a lower surface electrically connected to the upper planar radiator. The ground element may optionally be positioned below the lower surface of each radiating element, above the lower surface of the radiating element, electrically connected to (e.g., integral with, etc.) the lower surface of the radiating element, etc. 
     The ground element may include a smaller arrow portion corresponding to a 5 GHz band, and a larger arrow portion corresponding to a 2.4 GHz band. For example, the two arrow portions may be located at opposite corners and connected to one another via a middle portion of the ground element. 
     The ground element may be configured (e.g., shaped, sized, etc.) to have a ¼ wavelength for the 2.4 GHz band and a ½ wavelength for the 5 GHz band, at the ground element. This ground element may substantially cancel current flow at 2.4 GHz and 5 GHz, and thus improve antenna isolation. 
     Two top radiating elements (e.g., PIFA elements) may be positioned at least partially over the larger arrow portion of the ground element, at an angle of about ninety degrees with respect to one another. This can improve antenna isolation and introduce different polarities for each antenna element at each frequency band. 
     Example embodiments may provide one or more (or none) of the following advantages: reduced complexity when mounting antennas, faster time to market for customers, a reduced footprint compared to using two separate PCB or similar antennas, improved tuning for a 2×2 MIMO antenna to reduce customer error when selecting antenna placement, improved isolation for MIMO WLAN dual-band antennas with same or separate ground elements, reduced size, improved isolation on plastic or metal surfaces, improved voltage standing wave ratios (VSWRs), etc. 
     Referring now to the Figures,  FIGS. 1 and 2  illustrate a dual-band multiple-input multiple-output (MIMO) antenna  100  according to one example embodiment of the present disclosure. The antenna  100  includes a circuit board  102 , a first antenna radiating element  104  positioned on the circuit board  102 , and a second antenna radiating element  106  positioned on the circuit board  102 . 
     Two antenna feeding elements  108  extend from the antenna radiating elements  104  and  106 , respectively. Each of the two antenna feeding elements  108  are electrically connected with different ones of each of the first and second antenna radiating elements  104  and  106 . 
     As shown in  FIG. 1 , the circuit board  102  has a rectangular shape, and the first and second antenna radiating elements  104  and  106  are positioned along different sides of the circuit board  102 . Specifically, the first and second antenna radiating elements  104  and  106  are positioned at opposite corners of the circuit board  102  from one another. 
     The first and second antenna radiating elements  104  and  106  are each oriented at a ninety degree angle with respect to one another. This can improve antenna isolation and introduce different polarities for each antenna radiating element  104  and  106  at each frequency band (e.g., a 2.4-2.48 GHz frequency band, a frequency 4.9-5.9 GHz frequency band, etc.). Similarly, the antenna feeding elements  108  are each oriented at a ninety degree angle with respect to one another. In other embodiments, the antenna feeding elements  108  may be oriented at other angles (e.g., parallel, etc.), which may depend on a device feeding requirement. 
     Each antenna radiating element  104  and  106  may include any suitable radiating portion arrangement, design, layout, etc., such as a planar inverted-F antenna (PIFA) element. For example, each antenna radiating element  104  and  106  may include a planar radiator or upper radiating patch element having a slot, a lower surface spaced apart from the planar radiator or upper radiating patch element, first and second shorting elements electrically connecting the planar radiator or upper radiating patch element to the lower surface, a feeding element electrically connected between the planar radiator or upper radiating patch element and the lower surface, etc. 
     The circuit board  102  may be a flexible printed circuit board (PCB), and each antenna radiating element  104  and  106  may include one or more copper traces, plates, etc. positioned on a surface of the flexible printed circuit board  102 . 
     As shown in  FIG. 2 , an adhesive layer  110  is positioned on a side of the circuit board  102 . The adhesive layer  110  can be used to mount the antenna  100  to a surface, which can reduce complexity when mounting the antenna  100 , etc. 
     Example dimensions in millimeters (mm) are provided in  FIGS. 1 and 2  for purposes of illustration only, and other embodiments may include components with smaller and/or larger dimensions. 
     Immediately below is Table 1 with performance summary data measured for the antenna  100  illustrated in  FIGS. 1 and 2 . As shown by Table 1, the antenna  100  has good isolation, peak gain, VSWR, etc. at desired operating frequencies. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Antenna Performance Characteristics 
               
            
           
           
               
               
            
               
                 SPECIFICATION 
                 PERFORMANCE 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Frequency Bands, MHz 
                 2400-2480 
                 4900-5900 
               
               
                 Peak Gain, dBi (Typ) 
                 1.7 
                 2.5 
               
               
                 Peak Gain, dBi (Max) 
                 2.0 
                 3.5 
               
               
                 VSWR Port1: (Typ) 
                 &lt;2.3:1 
                 &lt;2.3:1 
               
               
                 VSWR Port2: (Typ) 
                 &lt;2.3:1 
                 &lt;2.3:1 
               
               
                 Isolation, dB (Typ) 
                 &gt;19        
                 &gt;19        
               
               
                 Max Gain +/− 30 above Horizon, dBi 
                 NA 
                 2.2 
               
               
                 Maximum VSWR 
                 &lt;2.5:1 
                 &lt;3.0:1 
               
            
           
           
               
               
            
               
                 Nominal Impedance 
                 50 Ω 
               
               
                 Max Power (Ambient temp of 25° C.) 
                 10 Watts 
               
               
                 Polarization 
                 Linear H/V for each radiator 
               
               
                 Azimuth Beam Width 
                 Omnidirectional 
               
               
                 Dimensions (L × W × H) 
                 33.25 × 33.25 × 4.44 mm 
               
               
                 Weight 
                 2.5 g 
               
               
                 Storage Temperature (° C.) 
                 −40° C. to +85° C. 
               
               
                 Operational Temperature (° C.) 
                 −30° C. to +70° C. 
               
               
                 Material Substance Compliance 
                 RoHS Compliant 
               
               
                   
               
            
           
         
       
     
       FIGS. 3-8  provide analysis results for the antenna  100  illustrated in  FIGS. 1 and 2 . These analysis results shown in  FIGS. 3-8  are provided only for purposes of illustration and not for purposes of limitation. 
     More specifically,  FIG. 3  includes three exemplary line graphs illustrating isolation in decibels (dB), and VSWR, versus frequency in gigahertz (GHz) measured for each Port  1  and Port  2  of a prototype of the antenna  100  of  FIGS. 1 and 2 . Generally,  FIG. 3  shows that the antenna  100  is operable with a good standing wave ratio for each port, and good isolation, in frequency bands from about 2.4 GHz to about 2.48 GHz and about 4.9 GHz to about 5.9 GHz. 
       FIG. 4  is an exemplary line graph illustrating 3D maximum gain in decibels relative to isotropic (dBi) versus frequency in megahertz (MHz) measured for the prototype of the antenna  100 . Generally,  FIG. 4  shows that the antenna  100  is operable with good maximum gain in frequency bands from about 2400 MHz to about 2480 MHz and about 4900 MHz to about 5900 MHz. 
       FIGS. 5-8  illustrate various radiation patterns for the simulated design of the antenna  100 . More specifically,  FIGS. 5-8  illustrate far-field realized gain at Azimuth Plane (left), Phi=0° Plane (center), and Phi=90° Plane (right) at frequencies of 2400 MHz, 2440 MHz, 2480 MHz, 4900 MHz, 5150 MHz, 5500 MHz, 5800 MHz and 5900 MHz. 
       FIGS. 9A and 9B  illustrate a flattened flexible PCB layout or pattern development of a dual-band multiple-input multiple-output (MIMO) antenna  200  according to another example embodiment of the present disclosure. The antenna  200  includes a circuit board  202 , a first planar inverted-F antenna element  204  positioned on the circuit board  202 , and a second planar inverted-F antenna element  206  positioned on the circuit board  202 . 
     A ground element (e.g., layer, isolator, plane, etc.)  208  is also positioned on the circuit board  202 . The ground element  208  includes a first arrow portion  212  and a second arrow portion  214 . As shown in  FIG. 9B , the second arrow portion  214  is larger than the first arrow portion  212 . 
     The first arrow portion  212  is connected with the second arrow portion  214  via a middle portion  216  (e.g., linear connecting portion, etc.). In some cases, the first arrow portion  212  may correspond to a 5 GHz band, and the second arrow portion  214  may correspond to a 2.4 GHz band. For example, the ground element  208  may have a ¼ wavelength for 2.4 GHz and a ½ wavelength for 5 GHz. Although  FIG. 9B  illustrates a specific arrangement of the ground element  208 , other embodiments may include ground elements with different shapes, arrangements, orientations, etc. 
     The circuit board  202  includes a top or upper layer ( FIG. 9A ) and a bottom or lower layer ( FIG. 9B ). As shown in  FIG. 9A , the first planar inverted-F antenna element  204  and the second planar inverted-F antenna element  206  are located on the top layer of the circuit board  202 . The ground element  208  is located on the bottom layer of the circuit board  202 . 
     A portion of the first planar inverted-F antenna element  204  overlaps part of the second arrow portion  214  of the ground element  208  in a direction perpendicular to planes of the first planar inverted-F antenna element  204  and the ground element  208 . Similarly, a portion of the second planar inverted-F antenna element  206  overlaps another part of the second arrow portion  214  of the ground element  208  in a direction perpendicular to planes of the second planar inverted-F antenna element  206  and the ground element  208 . 
     Although  FIGS. 9A and 9B  illustrate a specific arrangement of the first and second planar inverted-F antenna elements  204  and  206  with respect to the position of the ground element  208 , other embodiments may include antenna elements that overlap more or less (or none) of the ground element, antenna elements with a different position and/or orientation with respect to the ground element, etc. 
     As shown in  FIG. 9A , the first planar inverted-F antenna element  204  element and the second planar inverted-F antenna element  206  are oriented at a ninety degree angle with respect to one another. This can improve antenna isolation and introduce different polarities for each antenna element  204  and  206  at each frequency band (e.g., a 2.4-2.48 GHz frequency band, a frequency 4.9-5.9 GHz frequency band, etc.). 
     Each planar inverted-F antenna element  204  and  206  may include any suitable PIFA element configuration. For example, each antenna element  204  and  206  may include a planar radiator or upper radiating patch element having a slot, a lower surface spaced apart from the planar radiator or upper radiating patch element, first and second shorting elements electrically connecting the planar radiator or upper radiating patch element to the lower surface, a feeding element electrically connected between the planar radiator or upper radiating patch element and the lower surface, etc. Each antenna element  204  and  206  can include one or more solder pads  218  for forming appropriate electrical connections. 
     The circuit board  202  may be a flexible printed circuit board (PCB). In some cases, the first planar inverted-F antenna element  204 , the second planar inverted-F antenna element  206 , and the ground element  208  each comprises one or more copper traces  220  on the flexible printed circuit board  202 . In the example of  FIGS. 9A and 9B , the copper traces  220  have a grain direction at approximately a forty-five degree angle. 
     In some embodiments, an adhesive layer may be positioned on a side of the circuit board  202 . The adhesive layer can be used to mount the antenna  200  to a surface, which can reduce complexity when mounting the antenna  200 , etc. Example dimensions in millimeters (mm) are provided in  FIGS. 9A and 9B  for purposes of illustration only, and other embodiments may include components with smaller and/or larger dimensions. 
       FIG. 10  illustrates a flattened flexible PCB or pattern development of a dual-band multiple-input multiple-output (MIMO) antenna  300  according to another example embodiment of the present disclosure. The antenna  300  includes a circuit board  302 , a first planar inverted-F antenna element  304  positioned on the circuit board  302 , and a second planar inverted-F antenna element  306  positioned on the circuit board  302 . 
     A ground element (e.g., layer, isolator, plane, etc.)  308  is also positioned on the circuit board  302 . The ground element  308  includes a first arrow portion  312  and a second arrow portion  314 . As shown in  FIG. 10 , the second arrow portion  314  is larger than the first arrow portion  312 . 
     The first arrow portion  312  is connected with the second arrow portion  314  via a middle portion  316 . In some cases, the first arrow portion  312  may correspond to a 5 GHz band, and the second arrow portion  314  may correspond to a 2.4 GHz band. For example, the ground element  308  may have a ¼ wavelength for 2.4 GHz and a ½ wavelength for 5 GHz. Although  FIG. 10  illustrates a specific arrangement of the ground element  308 , other embodiments may include ground elements with different shapes, arrangements, orientations, dimensions, etc. 
     As shown in  FIG. 10 , the first planar inverted-F antenna element  304 , the second planar inverted-F antenna element  306 , and the ground element  308  are positioned on a same layer of the circuit board  302 . In this arrangement, the ground element  308  is positioned between the first planar inverted-F antenna element  304  and the second planar inverted-F antenna element  306 . 
     The circuit board  302  may be a flexible printed circuit board (PCB). In some cases, the first planar inverted-F antenna element  304 , the second planar inverted-F antenna element  306  and the ground element  308  each comprises one or more copper traces  320  on the flexible printed circuit board  302 . In the example of  FIG. 10 , the copper traces  320  have a grain direction at approximately a forty-five degree angle. 
     Each antenna element  304  and  306  can include one or more solder pads  318  for forming appropriate electrical connections. In some embodiments, an adhesive layer may be positioned on a side of the circuit board  302 . The adhesive layer can be used to mount the antenna  300  to a surface, which can reduce complexity when mounting the antenna  300 , etc. Example dimensions (in millimeters) are provided in  FIG. 10  for purposes of illustration only, and other embodiments may include components with smaller and/or larger dimensions. 
     As described above, each radiating element may include an upper planar radiator, and a lower surface electrically connected to the upper planar radiator.  FIGS. 11A-11C  illustrate optional placements of a ground element  408  with respect to the upper planar radiator  422  and the lower surface  424  of a radiating element  426 . 
     As shown in  FIG. 11A , the ground element  408  may be positioned below the lower surface  424  of the radiating element  426 . Alternatively, as shown in  FIG. 11B , the ground element  408  may be positioned above the lower surface  424  of the radiating element  426 , but below the upper planar radiator  422 . Therefore, the ground element  408  can be positioned between the upper planar radiator  422  and the lower surface  424 . As another option, and as shown in  FIG. 11C , the ground element  408  may be electrically connected to (e.g., integral with, etc.) the lower surface  424  of the radiating element  426 , etc. 
       FIG. 12  is an exemplary line graph illustrating port to port isolation in decibels (dB) versus frequency in megahertz (MHz) measured for a prototype of the antenna  300  positioned on a metal base. Generally,  FIG. 12  shows that the antenna  300  is operable with good port to port isolation in frequency bands from about 2400 MHz to about 2480 MHz and from about 4900 MHz to about 5900 MHz. 
       FIGS. 13A-13C  illustrates performance summary data measured for prototypes of the antennas  200  and  300  illustrated in  FIGS. 9 and 10 , on a plastic base and on a metal base. As shown in  FIGS. 13A-13C , the antennas  200  and  300  have good isolation, peak gain, VSWR, etc. at desired operating frequencies. 
       FIG. 14  is an exemplary line graph illustrating VSWR versus frequency in megahertz (MHz) measured for a prototype of the antenna  200  and/or  300 . Generally,  FIG. 14  shows that the antenna  200  and/or  300  has a low VSWR in frequency bands from about 2400 MHz to about 2480 MHz and from about 4900 MHz to about 5900 MHz. 
       FIG. 15  is an exemplary line graph illustrating port to port isolation in decibels (dB) versus frequency in megahertz (MHz) measured for a prototype of the antenna  200  and/or  300 . Generally,  FIG. 15  shows that the antenna  200  and/or  300  is operable with good port to port isolation in frequency bands from about 2400 MHz to about 2480 MHz and from about 4900 MHz to about 5900 MHz. 
       FIG. 16  illustrates various polarizations of radiation patterns for the simulated design of the antenna  200 . More specifically,  FIG. 16  illustrates far-field realized gain at Phi=90° Plane at frequencies of 2440 MHz and 5400 MHz. 
       FIG. 17-19  illustrate various radiation patterns for the simulated design of the antenna  200 . More specifically,  FIG. 17-19  illustrate farfield realized gain at Azimuth Plane (left), Phi=0° Plane (center), and Phi=90° Plane (right) at frequencies of 2400 MHz, 2440 MHz, 2480 MHz, 4900 MHz, 5400 MHz, and 5900 MHz. 
     The antennas disclosed herein including the antennas, the ground elements, antenna elements, etc., may be any suitable size (e.g., height, diameter, width, length, etc.). The size of each component of an antenna may be determined based on particular specifications, desired results, etc. 
     Exemplary embodiments of the antenna systems disclosed herein may be suitable for a wide range of applications, e.g., that use more than one antenna, such as LTE/4G applications and/or infrastructure antenna systems (e.g., customer premises equipment (CPE), terminal stations, central stations, in-building antenna systems, etc.). An antenna disclosed herein may be configured for use as an omnidirectional MIMO antenna, although aspects of the present disclosure are not limited solely to omnidirectional and/or MIMO antennas. An antenna disclosed herein may be implemented inside an electronic device, such as machine to machine, vehicular, in-building unit, etc. In which case, the internal antenna components would typically be internal to and covered by the electronic device housing. As another example, the antenna may instead be housed within a radome, which may have a low profile. In this latter case, the internal antenna components would be housed within and covered by the radome. Accordingly, the antennas disclosed herein should not be limited to any one particular end use. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. In addition, advantages and improvements that may be achieved with one or more exemplary embodiments of the present disclosure are provided for purpose of illustration only and do not limit the scope of the present disclosure, as exemplary embodiments disclosed herein may provide all or none of the above mentioned advantages and improvements and still fall within the scope of the present disclosure. 
     Specific numerical dimensions and values, specific materials, and/or specific shapes disclosed herein are example in nature and do not limit the scope of the present disclosure. The disclosure herein of particular values and particular ranges of values for given parameters are not exclusive of other values and ranges of values that may be useful in one or more of the examples disclosed herein. Moreover, it is envisioned that any two particular values for a specific parameter stated herein may define the endpoints of a range of values that may be suitable for the given parameter (i.e., the disclosure of a first value and a second value for a given parameter can be interpreted as disclosing that any value between the first and second values could also be employed for the given parameter). For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, and 3-9. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     The term “about” when applied to values indicates that the calculation or the measurement allows some slight imprecision in the value (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If, for some reason, the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring or using such parameters. For example, the terms “generally”, “about”, and “substantially” may be used herein to mean within manufacturing tolerances. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements, intended or stated uses, or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.