Patent Publication Number: US-11387576-B1

Title: Antenna system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Taiwan Patent Application No. 109146593 filed on Dec. 29, 2020, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The disclosure generally relates to an antenna system, and more particularly, it relates to an almost omnidirectional antenna system. 
     Description of the Related Art 
     With the advancements being made in mobile communication technology, mobile devices such as portable computers, mobile phones, multimedia players, and other hybrid functional portable electronic devices have become more common. To satisfy user demand, mobile devices can usually perform wireless communication functions. Some devices cover a large wireless communication area; these include mobile phones using 2G, 3G, and LTE (Long Term Evolution) systems and using frequency bands of 700 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, 2100 MHz, 2300 MHz, 2500 MHz, and 2700 MHz. Some devices cover a small wireless communication area; these include mobile phones using Wi-Fi and Bluetooth systems and using frequency bands of 2.4 GHz, 5.2 GHz, and 5.8 GHz. 
     Antennas are indispensable elements for wireless communication. If an antenna used for signal reception and transmission has a radiation pattern with any null, it will negatively affect the communication quality of the mobile device. Accordingly, it has become a critical challenge for antenna designers to design an almost omnidirectional antenna system. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment, the disclosure is directed to an antenna system that includes a first antenna element, a second antenna element, and a circuit region. The first antenna element includes a first nonconductive support element and a first main radiation element. The first main radiation element is disposed on the first nonconductive support element. The second antenna element includes a second nonconductive support element and a second main radiation element. The second main radiation element is disposed on the second nonconductive support element. The second main radiation element is at least partially perpendicular to the first main radiation element. The circuit region is positioned between the first antenna element and the second antenna element. 
     In some embodiments, the first antenna element and the second antenna element cover a first frequency band, a second frequency band, and a third frequency band. The first frequency band is from 699 MHz to 960 MHz. The second frequency band is from 1710 MHz to 2200 MHz. The third frequency band is from 2300 MHz to 2690 MHz. 
     In some embodiments, the second frequency band includes a first frequency interval, a second frequency interval, and a third frequency interval. The first frequency interval is from 1710 MHz to 1800 MHz. The second frequency interval is from 1800 MHz to 2000 MHz. The third frequency interval is from 2000 MHz to 2200 MHz. 
     In some embodiments, the first antenna element further includes a first feeding radiation element, a first radiation element, a shorting element, a second radiation element, a third radiation element, and a fourth radiation element. The first feeding radiation element has a first feeding point. The first main radiation element is coupled to the first feeding radiation element. The first radiation element is coupled to the first feeding radiation element. The first radiation element is coupled through the shorting element to a ground voltage. The second radiation element is coupled to the first feeding radiation element. The third radiation element is coupled to the first feeding point. The fourth radiation element is coupled to the ground voltage. The fourth radiation element is adjacent to the third radiation element. The first feeding radiation element, the first radiation element, the shorting element, the second radiation element, the third radiation element, and the fourth radiation element are disposed on the first nonconductive support element. 
     In some embodiments, the first main radiation element further includes a terminal U-shaped bending portion. 
     In some embodiments, the total length of the first feeding radiation element and the first main radiation element is shorter than or equal to 0.25 wavelength of the first frequency band. 
     In some embodiments, the first radiation element has a variable-width meandering shape. 
     In some embodiments, each of the second radiation element, the third radiation element, and the fourth radiation element substantially has an L-shape. 
     In some embodiments, the length of the first radiation element is shorter than or equal to 0.25 wavelength of the first frequency interval. 
     In some embodiments, the total length of the first feeding radiation element and the second radiation element is shorter than or equal to 0.25 wavelength of the second frequency interval. 
     In some embodiments, the length of the third radiation element is shorter than or equal to 0.25 wavelength of the third frequency interval. 
     In some embodiments, the length of the fourth radiation element is shorter than or equal to 0.25 wavelength of the third frequency band. 
     In some embodiments, the first antenna element further includes a first matching element and a second matching element. The first matching element and the second matching element are coupled to the first radiation element, and substantially extend away from each other. The first matching element and the second matching element are disposed on the first nonconductive support element. 
     In some embodiments, second antenna element further includes a second feeding radiation element, a fifth radiation element, a sixth radiation element, a seventh radiation element, and an eighth radiation element. The second feeding radiation element has a second feeding point. The second main radiation element is coupled through the fifth radiation element to the second feeding radiation element. The fifth radiation element is coupled through the sixth radiation element to the ground voltage. The seventh radiation element is coupled to the second feeding radiation element. The eighth radiation element is coupled to the ground voltage. The second feeding radiation element, the fifth radiation element, the sixth radiation element, the seventh radiation element, and the eighth radiation element are disposed on the second nonconductive support element. 
     In some embodiments, the fifth radiation element and the second feeding radiation element are substantially perpendicular to each other. 
     In some embodiments, the total length of the second feeding radiation element, the fifth radiation element, and the second main radiation element is shorter than or equal to 0.25 wavelength of the first frequency band. 
     In some embodiments, each of the sixth radiation element, the seventh radiation element, and the eighth radiation element substantially has an L-shape. 
     In some embodiments, the total length of the second feeding radiation element, the fifth radiation element, and the sixth radiation element is shorter than or equal to 0.5 wavelength of the first frequency interval. 
     In some embodiments, the total length of the second feeding radiation element and the seventh radiation element is shorter than or equal to 0.25 wavelength of the second frequency interval or the third frequency interval. 
     In some embodiments, the length of the eighth radiation element is shorter than or equal to 0.25 wavelength of the third frequency band. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a diagram of an antenna system according to an embodiment of the invention; 
         FIG. 2  is a perspective view of a first antenna element according to an embodiment of the invention; 
         FIG. 3  is a perspective view of a second antenna element according to an embodiment of the invention; 
         FIG. 4  is a radiation pattern of a conventional antenna system; and 
         FIG. 5  is a radiation pattern of an antenna system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to illustrate the purposes, features and advantages of the invention, the embodiments and figures of the invention are shown in detail below. 
     Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. The term “substantially” means the value is within an acceptable error range. One skilled in the art can solve the technical problem within a predetermined error range and achieve the proposed technical performance. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Furthermore, spatially relative terms, such as “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 or feature as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
       FIG. 1  is a diagram of an antenna system  100  according to an embodiment of the invention. The antenna system  100  may be applied to a mobile device, such as a phone, a tablet computer, or a notebook computer. As shown in  FIG. 1 , the antenna system  100  includes a first antenna element  200 , a second antenna element  300 , and a circuit region  400 . The first antenna element  200  includes a first main radiation element  220  and a first nonconductive support element  299 . The first main radiation element  220  is disposed on the first nonconductive support element  299 . The second antenna element  300  includes a second main radiation element  330  and a second nonconductive support element  399 . The second main radiation element  330  is disposed on the second nonconductive support element  399 . The shapes of the first main radiation element  220  and the second main radiation element  330  are not limited in the invention, and they may both be made of metal materials, such as silver, copper, aluminum, iron, or their alloys. The circuit region  400  is positioned between the first antenna element  200  and the second antenna element  300 . The circuit region  400  may be coupled to a system ground plane (not shown). The circuit region  400  can accommodate one or more circuit components, such as a processor, a memory device, and/or a battery, although they are not displayed in  FIG. 1 . It should be noted that the second main radiation element  330  of the second antenna element  300  is at least partially perpendicular to the first main radiation element  220  of the first antenna element  200 . For example, the angle θ between a portion of the second main radiation element  330  and the first main radiation element  220  may be from 45 to 135 degrees, or may be from 60 to 120 degrees, such as about 90 degrees. According to practical measurements, such an at least partially orthogonal design can effectively suppress all of the nulls of the antenna system  100 , and therefore the antenna system  100  can provide an almost omnidirectional radiation pattern. 
     In some embodiments, both the first antenna element  200  and the second antenna element  300  of the antenna system  100  can cover a first frequency band, a second frequency band, and a third frequency band. For example, the first frequency band may be from 699 MHz to 960 MHz, the second frequency band may be from 1710 MHz to 2200 MHz, and the third frequency band may be from 2300 MHz to 2690 MHz. Specifically, the second frequency band may include a first frequency interval from 1710 MHz to 1800 MHz, a second frequency interval from 1800 MHz to 2000 MHz, and a third frequency interval from 2000 MHz to 2200 MHz. Therefore, the antenna system  100  can support at least the wideband operations of LTE (Long Term Evolution) and the next 5G (5th Generation Wireless System) communication. 
     The following embodiments will introduce the detail structures of the first antenna element  200  and the second antenna element  300 . It should be understood that these figures and descriptions are merely exemplary, rather than limitations of the invention. 
       FIG. 2  is a perspective view of the first antenna element  200  according to an embodiment of the invention. In the embodiment of  FIG. 2 , the first antenna element  200  includes a first feeding radiation element  210 , a first main radiation element  220 , a first radiation element  230 , a shorting element  240 , a second radiation element  250 , a third radiation element  260 , a fourth radiation element  270 , and a first nonconductive support element  299 . The first feeding radiation element  210 , the first main radiation element  220 , the first radiation element  230 , the shorting element  240 , the second radiation element  250 , the third radiation element  260 , and the fourth radiation element  270  may all be made of metal materials, and they may all be disposed on the first nonconductive support element  299 . In addition, the first nonconductive support element  299  has a first surface E 1  and a second surface E 2  which are substantially perpendicular to each other. 
     The first feeding radiation element  210  may substantially have a straight-line shape, which may be positioned on the first surface E 1  of the first nonconductive support element  299 . Specifically, the first feeding radiation element  210  has a first end  211  and a second end  212 . A first feeding point FP 1  is positioned at the first end  211  of the first feeding radiation element  210 . The first feeding point FP 1  may be further coupled to a signal source (not shown). For example, the signal source may be an RF (Radio Frequency) module for exciting both the first antenna element  200  and the second antenna element  300 . 
     The first main radiation element  220  may substantially have a meandering shape, which may extend from the second surface E 2  onto the first surface E 1  of the first nonconductive support element  299 . Specifically, the first main radiation element  220  has a first end  221  and a second end  222 . The first end  221  of the first main radiation element  220  is coupled to the second end  212  of the first feeding radiation element  210 . The second end  222  of the first main radiation element  220  is an open end. In some embodiments, the first main radiation element  220  further includes a terminal U-shaped bending portion  225 , which is adjacent to the second end  222  of the first main radiation element  220 . It should be noted that the term “adjacent” or “close” over the disclosure means that the distance (spacing) between two corresponding elements is shorter than a predetermined distance (e.g., 5 mm or shorter), or means that the two corresponding elements are touching each other directly (i.e., the aforementioned distance/spacing therebetween is reduced to 0). 
     The first radiation element  230  may substantially have a variable-width meandering shape (with a widening portion  235 ), which may be positioned on the first surface E 1  of the first nonconductive support element  299 . Specifically, the first radiation element  230  has a first end  231  and a second end  232 . The first end  231  of the first radiation element  230  is coupled to a first connection point CP 1  on the first feeding radiation element  210 . The second end  232  of the first radiation element  230  is an open end. 
     The shorting element  240  may substantially have a straight-line shape, which may be positioned on the first surface E 1  of the first nonconductive support element  299 . The widening portion  235  of the first radiation element  230  is coupled through the shorting element  240  to a ground voltage VSS (e.g., 0V). 
     The second radiation element  250  may substantially have an L-shape, which may be positioned on the first surface E 1  of the first nonconductive support element  299 . Specifically, the second radiation element  250  has a first end  251  and a second end  252 . The first end  251  of the second radiation element  250  is coupled to the second end  212  of the first feeding radiation element  210 . The second end  252  of the second radiation element  250  is an open end. 
     The third radiation element  260  may substantially have an L-shape, which may be positioned on the first surface E 1  of the first nonconductive support element  299 . Specifically, the third radiation element  260  has a first end  261  and a second end  262 . The first end  261  of the third radiation element  260  is coupled to the first feeding point FP 1 . The second end  262  of the third radiation element  260  is an open end. For example, the second end  262  of the third radiation element  260  and the second end  232  of the first radiation element  230  may extend in the same direction. 
     The fourth radiation element  270  may substantially have an L-shape, which may be positioned on the first surface E 1  of the first nonconductive support element  299 . Specifically, the fourth radiation element  270  has a first end  271  and a second end  272 . The first end  271  of the fourth radiation element  270  is coupled to the ground voltage VSS. The second end  272  of the fourth radiation element  270  is an open end. For example, the second end  272  of the fourth radiation element  270  and the second end  262  of the third radiation element  260  may extend in opposite directions and away from each other. The fourth radiation element  270  is adjacent to but separate from the third radiation element  260 . A coupling gap GC 1  may be formed between the fourth radiation element  270  and the third radiation element  260 . 
     In some embodiments, the first antenna element  200  further includes a first matching element  280  and a second matching element  290 , which may both be made of metal materials. The first matching element  280  may substantially have a bending straight-line shape, which may extend from the first surface E 1  onto the second surface E 2  of the first nonconductive support element  299 . Specifically, the first matching element  280  has a first end  281  and a second end  282 . The first end  281  of the first matching element  280  is coupled to a second connection point CP 2  on the first radiation element  230 . The second end  282  of the first matching element  280  is an open end. The second matching element  290  may substantially have a straight-line shape, which may be positioned on the first surface E 1  of the first nonconductive support element  299 . Specifically, the second matching element  290  has a first end  291  and a second end  292 . The first end  291  of the second matching element  290  is coupled to a third connection point CP 3  on the first radiation element  230 . The second end  292  of the second matching element  290  is an open end. For example, the second end  292  of the second matching element  290  and the second end  282  of the first matching element  280  may extend away from each other. In addition, a crisscross shape may be formed by the first radiation element  230 , the first matching element  280 , and the second matching element  290 . It should be understood that the first matching element  280  and the second matching element  290  are optional components, which are removable in other embodiments. 
     With respect to the antenna theory of the first antenna element  200 , the first feeding radiation element  210  and the first main radiation element  220  are excited to generate the aforementioned first frequency band. The first feeding radiation element  210 , the first radiation element  230 , the second radiation element  250 , and the third radiation element  260  are excited to generate the aforementioned second frequency band. The fourth radiation element  270  is excited to generate the aforementioned third frequency band. Furthermore, the incorporations of the shorting element  240 , the first matching element  280 , and the second matching element  290  can help to fine-tune the impedance matching of the first antenna element  200 . 
     In some embodiments, the element sizes of the first antenna element  200  are described as follows. The total length L 1  of the first feeding radiation element  210  and the first main radiation element  220  may be shorter than or equal to 0.25 wavelength (λ/4) of the first frequency band of the antenna system  100 . The length L 2  of the first radiation element  230  may be shorter than or equal to 0.25 wavelength (λ/4) of the first frequency interval of the antenna system  100 . The total length L 3  of the first feeding radiation element  210  and the second radiation element  250  may be shorter than or equal to 0.25 wavelength (λ/4) of the second frequency interval of the antenna system  100 . The length L 4  of the third radiation element  260  may be shorter than or equal to 0.25 wavelength (λ/4) of the third frequency interval of the antenna system  100 . The length L 5  of the fourth radiation element  270  may be shorter than or equal to 0.25 wavelength (λ/4) of the third frequency band of the antenna system  100 . The width of the coupling gap GC 1  may be shorter than 4 mm. The above ranges of element sizes and element parameters are calculated and obtained according to many experiment results, and they help to optimize the operation bandwidth and the impedance matching of the first antenna element  200 . 
       FIG. 3  is a perspective view of the second antenna element  300  according to an embodiment of the invention. In the embodiment of  FIG. 3 , the second antenna element  300  includes a second feeding radiation element  310 , a fifth radiation element  320 , a second main radiation element  330 , a sixth radiation element  340 , a seventh radiation element  350 , an eighth radiation element  360 , and a second nonconductive support element  399 . The second feeding radiation element  310 , the fifth radiation element  320 , the second main radiation element  330 , the sixth radiation element  340 , the seventh radiation element  350 , and the eighth radiation element  360  may all be made of metal materials, and they may all be disposed on the second nonconductive support element  399 . In addition, the second nonconductive support element  399  has a third surface E 3  and a fourth surface E 4  which are substantially perpendicular to each other. 
     The second feeding radiation element  310  may substantially have a straight-line shape, which may be positioned on the third surface E 3  of the second nonconductive support element  399 . Specifically, the second feeding radiation element  310  has a first end  311  and a second end  312 . A second feeding point FP 2  is positioned at the first end  311  of the second feeding radiation element  310 . The second feeding point FP 2  may be further coupled to the aforementioned signal source. 
     The fifth radiation element  320  may substantially have a straight-line shape, which may be positioned on the third surface E 3  of the second nonconductive support element  399 . The fifth radiation element  320  may be substantially perpendicular to the second feeding radiation element  310 . Specifically, the fifth radiation element  320  has a first end  321  and a second end  322 . The first end  321  of the fifth radiation element  320  is coupled to the second end  312  of the second feeding radiation element  310 . 
     The second main radiation element  330  may substantially has a meandering shape, which may extend from the third surface E 3  onto the fourth surface E 4  of the second nonconductive support element  399 . Specifically, the second main radiation element  330  has a first end  331  and a second end  332 . The first end  331  of the second main radiation element  330  is coupled to the second end  322  of the fifth radiation element  320 . The second end  332  of the second main radiation element  330  is an open end. That is, the second main radiation element  330  is coupled through the fifth radiation element  320  to the second feeding radiation element  310 . In some embodiments, the second main radiation element  330  further includes a terminal extension bending portion  335 , which is adjacent to the second end  332  of the second main radiation element  330 . The terminal extension bending portion  335  of the second main radiation element  330  may be substantially perpendicular to the aforementioned first main radiation element  220 . In some embodiments, the angle between the terminal extension bending portion  335  of the second main radiation element  330  and the first main radiation element  220  may be from 45 to 135 degrees, or may be from 60 to 120 degrees, such as about 90 degrees. 
     The sixth radiation element  340  may substantially have an L-shape, which may be positioned on the third surface E 3  of the second nonconductive support element  399 . Specifically, the sixth radiation element  340  has a first end  341  and a second end  342 . The first end  341  of the sixth radiation element  340  is coupled to the ground voltage VSS. The second end  342  of the sixth radiation element  340  is coupled to the second end  322  of the fifth radiation element  320 . That is, the fifth radiation element  320  is coupled through the sixth radiation element  340  to the ground voltage VSS. In some embodiments, the first end  341  of the sixth radiation element  340  is adjacent to the second feeding point FP 2 , such that a loop structure is almost formed by the second feeding radiation element  310 , the fifth radiation element  320 , and the sixth radiation element  340 . 
     The seventh radiation element  350  may substantially have an L-shape, which may be positioned on the third surface E 3  of the second nonconductive support element  399 . Specifically, the seventh radiation element  350  has a first end  351  and a second end  352 . The first end  351  of the seventh radiation element  350  is coupled to the second end  312  of the second feeding radiation element  310 . The second end  352  of the seventh radiation element  350  is an open end. For example, the second end  352  of the seventh radiation element  350  may extend toward the second main radiation element  330 . 
     The eighth radiation element  360  may substantially have an L-shape, which may be positioned on the third surface E 3  of the second nonconductive support element  399 . Specifically, the eighth radiation element  360  has a first end  361  and a second end  362 . The first end  361  of the eighth radiation element  360  is coupled to the first end  341  of the sixth radiation element  340  and the ground voltage VSS. The second end  362  of the eighth radiation element  360  is an open end. For example, the second end  362  of the eighth radiation element  360  and the second end  352  of the seventh radiation element  350  may substantially extend in orthogonal directions. 
     With respect to the antenna theory of the second antenna element  300 , the second feeding radiation element  310 , the fifth radiation element  320 , and the second main radiation element  330  are excited to generate the aforementioned first frequency band. The second feeding radiation element  310 , the fifth radiation element  320 , the sixth radiation element  340 , and the seventh radiation element  350  are excited to generate the aforementioned second frequency band. The eighth radiation element  360  is excited to generate the aforementioned third frequency band. 
     In some embodiments, the element sizes of the second antenna element  300  are described as follows. The total length L 6  of the second feeding radiation element  310 , the fifth radiation element  320 , and the second main radiation element  330  may be shorter than or equal to 0.25 wavelength (λ/4) of the first frequency band of the antenna system  100 . The total length L 7  of the second feeding radiation element  310 , the fifth radiation element  320 , and the sixth radiation element  340  may be shorter than or equal to 0.5 wavelength (λ/2) of the first frequency interval of the antenna system  100 . The total length L 8  of the second feeding radiation element  310  and the seventh radiation element  350  may be shorter than or equal to 0.25 wavelength (λ/4) of the second frequency interval or the third frequency interval of the antenna system  100 . The length L 9  of the eighth radiation element  360  may be shorter than or equal to 0.25 wavelength (λ/4) of the third frequency band of the antenna system  100 . The distance D 1  between the first end  341  of the sixth radiation element  340  and the second feeding point FP 2  may be from 0.5 mm to 1.5 mm. The distance D 2  between the second end  352  of the seventh radiation element  350  and the second main radiation element  330  may be from 3 mm to 4 mm. The above ranges of element sizes and element parameters are calculated and obtained according to many experiment results, and they help to optimize the operation bandwidth and the impedance matching of the second antenna element  300 . 
       FIG. 4  is a radiation pattern of a conventional antenna system. As shown in  FIG. 4 , the radiation pattern of the conventional antenna system usually has a non-ideal null (indicated by a dash-line box  410 ), and thus the whole communication quality is degraded. 
       FIG. 5  is a radiation pattern of the antenna system  100  according to an embodiment of the invention. According to the measurement of  FIG. 5 , if the second main radiation element  330  of the second antenna element  300  is designed to be at least partially perpendicular to the first main radiation element  220  of the first antenna element  200 , the null of the antenna system  100  will be effectively eliminated (indicated by a dash-line box  510 ). Therefore, the whole communication quality is significantly improved. 
     The invention proposes a novel antenna system. In comparison to the conventional technology, the proposed antenna system of the invention can almost eliminate all nulls and provide an almost omnidirectional radiation pattern, and therefore it is suitable for application in a variety of mobile communication devices. 
     Note that the above element sizes, element shapes, and frequency ranges are not limitations of the invention. An antenna designer can fine-tune these settings or values according to different requirements. It should be understood that the antenna system of the invention is not limited to the configurations of  FIGS. 1-5 . The invention may merely include any one or more features of any one or more embodiments of  FIGS. 1-5 . In other words, not all of the features displayed in the figures should be implemented in the antenna system of the invention. 
     Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having the same name (but for use of the ordinal term) to distinguish the claim elements. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.