Patent Publication Number: US-10784578-B2

Title: Antenna system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 107134801 filed on Oct. 2, 2018, 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, to an antenna system for improving isolation. 
     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, and 2500 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. 
     An antenna system is indispensable in a mobile device supporting wireless communication. However, since the interior space in a mobile device is very limited, multiple antennas are usually disposed close to each other, and such a design causes serious interference between antennas. As a result, there is a need to design a new antenna system for solving the problem of bad isolation in conventional antenna systems. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment, the invention is directed to an antenna system including a first antenna, a second antenna, and a third antenna. The third antenna is disposed between the first antenna and the second antenna. Both the first antenna and the second antenna operate in a first frequency band. The third antenna operates in a second frequency band which is different from the first frequency band. The first antenna, the second antenna, and the third antenna are all disposed on the same plane. 
     In some embodiments, the distance between the first antenna and the third antenna is longer than or equal to 5 mm. The distance between the second antenna and the third antenna is longer than or equal to 5 mm. 
     In some embodiments, the first frequency band covers a first frequency interval from 2400 MHz to 2500 MHz and a second frequency interval from 4800 MHz to 6000 MHz. The second frequency band covers a third frequency interval from 680 MHz to 960 MHz, a fourth frequency interval from 1700 MHz to 2200 MHz, and a fifth frequency interval from 2500 MHz to 2700 MHz. 
     In some embodiments, the first antenna includes a first ground plane, a first feeding connection element, a first radiation element, and a first shorting element. The first feeding connection element has a first feeding point. The first radiation element is coupled to the first feeding connection element. The first feeding connection element is coupled through the first shorting element to the first ground plane. 
     In some embodiments, the first shorting element is surrounded by the first ground plane, the first feeding connection element, and the first radiation element. 
     In some embodiments, a combination of the first feeding connection element and the first radiation element substantially has an inverted U-shape. 
     In some embodiments, the first shorting element substantially has an inverted L-shape. 
     In some embodiments, the first feeding connection element, the first radiation element, and the first shorting element are excited to generate the first frequency interval. The first feeding connection element and the first shorting element are excited to generate the second frequency interval. 
     In some embodiments, the second antenna includes a second ground plane, a second feeding connection element, a second radiation element, and a second shorting element. The second feeding connection element has a second feeding point. The second radiation element is coupled to the second feeding connection element. The second feeding connection element is coupled through the second shorting element to the second ground plane. 
     In some embodiments, the second shorting element is surrounded by the second ground plane, the second feeding connection element, and the second radiation element. 
     In some embodiments, a combination of the second feeding connection element and the second radiation element substantially has an inverted U-shape. 
     In some embodiments, the second shorting element substantially has an inverted L-shape. 
     In some embodiments, the second feeding connection element, the second radiation element, and the second shorting element are excited to generate the first frequency interval. The second feeding connection element and the second shorting element are excited to generate the second frequency interval. 
     In some embodiments, the third antenna includes a third ground plane, a third feeding connection element, a third radiation element, a fourth radiation element, and a third shorting element. The third feeding connection element has a third feeding point. The third radiation element is coupled to the third feeding connection element. The fourth radiation element is coupled to the third feeding connection element. The third feeding connection element is coupled through the third shorting element to the third ground plane. 
     In some embodiments, the fourth radiation element is surrounded by the third feeding connection element, the third radiation element, and the third shorting element. 
     In some embodiments, the fourth radiation element further includes a terminal rectangular widening portion. 
     In some embodiments, the third radiation element substantially has an inverted U-shape. 
     In some embodiments, the third shorting element substantially has an inverted U-shape. 
     In some embodiments, the third feeding connection element, the third radiation element, and the third shorting element are excited to generate the third frequency interval. The third feeding connection element, the fourth radiation element, and the third shorting element are excited to generate the fourth frequency interval. The third feeding connection element and the third shorting element are excited to generate the fifth frequency interval. 
    
    
     
       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 diagram of an antenna system according to an embodiment of the invention; 
         FIG. 3A  is a diagram of isolation between a first antenna and a third antenna according to an embodiment of the invention; 
         FIG. 3B  is a diagram of isolation between a second antenna and a third antenna according to an embodiment of the invention; and 
         FIG. 3C  is a diagram of isolation between a first antenna and a second antenna according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to illustrate the foregoing and other purposes, features and advantages of the invention, the embodiments and figures of the invention will be described in detail as follows. 
     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. 
       FIG. 1  is a diagram of an antenna system  100  according to an embodiment of the invention. As shown in  FIG. 1 , the antenna system  100  includes a first antenna  110 , a second antenna  120 , and a third antenna  130 . The third antenna  130  is substantially disposed between the first antenna  110  and the second antenna  120 . In a preferred embodiment, both the first antenna  110  and the second antenna  120  operate in a first frequency band, and the third antenna  130  operates in a second frequency band which is entirely different from the first frequency band. For example, the first antenna  110 , the second antenna  120 , and the third antenna  130  may all be disposed on the same plane or may all be arranged in the same straight line. The distance D 1  between the first antenna  110  and the third antenna  130  may be longer than or equal to 5 mm. The distance D 2  between the second antenna  120  and the third antenna  130  may be longer than or equal to 5 mm. Since the third antenna  130  has a different resonant frequency, such a design can prevent the third antenna  130  from interfering with the first antenna  110  and the second antenna  120 , so as to enhance the isolation between any two of the first antenna  110 , the second antenna  120 , and the third antenna  130 . In addition, the total size of the antenna system  100  is further reduced by designing the third antenna  130  into a gap between the first antenna  110  and the second antenna  120 . 
     In some embodiments, the aforementioned first frequency band is a WLAN (Wireless Local Area Network) band, and the aforementioned second frequency band is a WWAN (Wireless Wide Area Network) band. Specifically, the aforementioned first frequency band can cover a first frequency interval from 2400 MHz to 2500 MHz, and a second frequency interval from 4800 MHz to 6000 MHz, and the aforementioned second frequency band can cover a third frequency interval from 680 MHz to 960 MHz, a fourth frequency interval from 1700 MHz to 2200 MHz, and a fifth frequency interval from 2500 MHz to 2700 MHz. Accordingly, the antenna system  100  can support at least the wideband operations of WLAN and WWAN, but it is not limited thereto. 
     The following embodiments will introduce the detailed structure of the antenna system  100 . It should be understood that these figures and descriptions are merely exemplary, rather than limitations of the invention. 
       FIG. 2  is a diagram of an antenna system  200  according to an embodiment of the invention. As shown in  FIG. 2 , the antenna system  200  includes a first antenna  300 , a second antenna  400 , and a third antenna  500 . The third antenna  500  is disposed between the first antenna  300  and the second antenna  400 . Both the first antenna  300  and the second antenna  400  can operate in the aforementioned first frequency band (e.g., the WLAN band). The third antenna  500  can operate in the aforementioned second frequency band (e.g., the WWAN band). In some embodiments, the antenna system  200  further includes a dielectric substrate  210 , such as an FR4 (Flame Retardant 4) substrate, a PCB (Printed Circuit Board), or an FCB (Flexible Circuit Board). The first antenna  300 , the second antenna  400 , and the third antenna  500  are at least partially disposed on the dielectric substrate  210 . 
     The first antenna  300  includes a first ground plane  310 , a first feeding connection element  320 , a first radiation element  330 , and a first shorting element  340 . All of the above elements of the first antenna  300  may be made of metal materials. The first ground plane  310  may be a ground copper foil extending onto the dielectric substrate  210 . The first feeding connection element  320 , the first radiation element  330 , and the first shorting element  340  are all disposed on the dielectric substrate  210 . The first feeding connection element  320  may substantially have a rectangular shape. The first feeding connection element  320  has a first end  321  and a second end  322 . A first feeding point FP 1  is positioned at the first end  321  of the first feeding connection element  320 . The first feeding point FP 1  may be coupled to a first signal source (not shown). For example, the first signal source may be a first RF (Radio Frequency) module for exciting the first antenna  300 . The first radiation element  330  may substantially have an inverted L-shape. A combination of the first feeding connection element  320  and the first radiation element  330  may substantially have an inverted U-shape. The first radiation element  330  has a first end  331  and a second end  332 . The first end  331  of the first radiation element  330  is coupled to the second end  322  of the first feeding connection element  320 . The second end  332  of the first radiation element  330  is an open end extending toward the first ground plane  310 . The first shorting element  340  may substantially have an inverted L-shape. The first shorting element  340  has a first end  341  and a second end  342 . The first end  341  of the first shorting element  340  is coupled to the first ground plane  310 , and the second end  342  of the first shorting element  340  is coupled to a first connection point CP 1  on the first feeding connection element  320 , such that the first feeding connection element  320  is coupled through the first shorting element  340  to the first ground plane  310 . The first shorting element  340  is surrounded by the first ground plane  310 , the first feeding connection element  320 , and the first radiation element  330 . A first gap G 1  is formed between the first radiation element  330  and the first shorting element  340 . A second gap G 2  is formed between the first shorting element  340  and the first ground plane  310 . The width of the second gap G 2  is longer than the width of the first gap G 1 . In addition, the width W 1  of the first feeding connection element  320  is longer than the width of the first radiation element  330 , and is also longer than the width of the first shorting element  340 . Such a design can increase the high-frequency operation bandwidth of the first antenna  300 . 
     The operation principle and element sizes of the first antenna  300  may be described as follows. The first feeding connection element  320 , the first radiation element  330 , and the first shorting element  340  are excited to generate the aforementioned first frequency interval (e.g., from 2400 MHz to 2500 MHz). The first feeding connection element  320  and the first shorting element  340  are excited to generate the aforementioned second frequency interval (e.g., from 4800 MHz to 6000 MHz). The total length of the first feeding connection element  320 , the first radiation element  330 , and the first shorting element  340  (e.g., the total length from the first end  341  through the first connection point CP 1  and the first end  331  to the second end  332 ) may be substantially equal to 0.25 wavelength (λ/4) of the central frequency of the first frequency interval. The total length of the first feeding connection element  320  and the first shorting element  340  (e.g., the total length from the first end  341  through the first connection point CP 1  to the second end  322 ) may be substantially equal to 0.25 wavelength (λ/4) of the central frequency of the second frequency interval. The width W 1  of the first feeding connection element  320  may be from 2.9 mm to 3.5 mm (e.g., 3.2 mm). The width of the first gap G 1  may be from 1.3 mm to 1.7 mm (e.g., 1.5 mm). The width of the second gap G 2  may be from 1.5 mm to 2.3 mm (e.g., 1.9 mm). The above ranges of elements are calculated and obtained according to many experimental results, and they help to optimize the operation bandwidth and impedance matching of the first antenna  300 . 
     The second antenna  400  includes a second ground plane  410 , a second feeding connection element  420 , a second radiation element  430 , and a second shorting element  440 . All of the above elements of the second antenna  400  may be made of metal materials. The second ground plane  410  may be a ground copper foil extending onto the dielectric substrate  210 . The second feeding connection element  420 , the second radiation element  430 , and the second shorting element  440  are all disposed on the dielectric substrate  210 . The second feeding connection element  420  may substantially have a U-shape, an H-shape, or a rectangular shape. The second feeding connection element  420  has a first end  421  and a second end  422 . A second feeding point FP 2  is positioned at the first end  421  of the second feeding connection element  420 . The second feeding point FP 2  may be coupled to a second signal source (not shown). For example, the second signal source may be a second RF module for exciting the second antenna  400 . The second radiation element  430  may substantially have an inverted L-shape. A combination of the second feeding connection element  420  and the second radiation element  430  may substantially have an inverted U-shape. The second radiation element  430  has a first end  431  and a second end  432 . The first end  431  of the second radiation element  430  is coupled to the second end  422  of the second feeding connection element  420 . The second end  432  of the second radiation element  430  is an open end extending toward the second ground plane  410 . The second shorting element  440  may substantially have an inverted L-shape. The second shorting element  440  has a first end  441  and a second end  442 . The first end  441  of the second shorting element  440  is coupled to the second ground plane  410 , and the second end  442  of the second shorting element  440  is coupled to a second connection point CP 2  on the second feeding connection element  420 , such that the second feeding connection element  420  is coupled through the second shorting element  440  to the second ground plane  410 . The second shorting element  440  is surrounded by the second ground plane  410 , the second feeding connection element  420 , and the second radiation element  430 . A third gap G 3  is formed between the second radiation element  430  and the second shorting element  440 . A fourth gap G 4  is formed between the second shorting element  440  and the second ground plane  410 . The width of the fourth gap G 4  is longer than the width of the third gap G 3 . In addition, the width W 2  of the second feeding connection element  420  is longer than the width of the second radiation element  430 , and is also longer than the width of the second shorting element  440 . Such a design can increase the high-frequency operation bandwidth of the second antenna  400 . 
     The operation principle and element sizes of the second antenna  400  may be described as follows. The second feeding connection element  420 , the second radiation element  430 , and the second shorting element  440  are excited to generate the aforementioned first frequency interval (e.g., from 2400 MHz to 2500 MHz). The second feeding connection element  420  and the second shorting element  440  are excited to generate the aforementioned second frequency interval (e.g., from 4800 MHz to 6000 MHz). The total length of the second feeding connection element  420 , the second radiation element  430 , and the second shorting element  440  (e.g., the total length from the first end  441  through the second connection point CP 2  and the first end  431  to the second end  432 ) may be substantially equal to 0.25 wavelength (λ/4) of the central frequency of the first frequency interval. The total length of the second feeding connection element  420  and the second shorting element  440  (e.g., the total length from the first end  441  through the second connection point CP 2  to the second end  422 ) may be substantially equal to 0.25 wavelength (λ/4) of the central frequency of the second frequency interval. The width W 2  of the second feeding connection element  420  may be from 3.1 mm to 3.7 mm (e.g., 3.4 mm). The width of the third gap G 3  may be from 1 mm to 1.4 mm (e.g., 1.2 mm). The width of the fourth gap G 4  may be from 1.6 mm to 2.2 mm (e.g., 1.9 mm). The above ranges of elements are calculated and obtained according to many experimental results, and they help to optimize the operation bandwidth and impedance matching of the second antenna  400 . 
     The third antenna  500  includes a third ground plane  510 , a third feeding connection element  520 , a third radiation element  530 , a fourth radiation element  540 , and a third shorting element  550 . All of the above elements of the third antenna  500  may be made of metal materials. The third ground plane  510  may be a ground copper foil extending onto the dielectric substrate  210 . The third feeding connection element  520 , the third radiation element  530 , the fourth radiation element  540 , and the third shorting element  550  are all disposed on the dielectric substrate  210 . The third feeding connection element  520  may substantially have a width-varying straight-line shape. The third feeding connection element  520  has a first end  521  and a second end  522 . The width of the second end  522  of the third feeding connection element  520  is longer than the width of the first end  521  of the third feeding connection element  520 . A third feeding point FP 3  is positioned at the first end  521  of the third feeding connection element  520 . The third feeding point FP 3  may be coupled to a third signal source (not shown). For example, the third signal source may be a third RF module for exciting the third antenna  500 . The third radiation element  530  may substantially have an inverted U-shape. The third radiation element  530  has a first end  531  and a second end  532 . The first end  531  of the third radiation element  530  is coupled to the end  522  of the third feeding connection element  520 . The second end  532  of the third radiation element  530  is an open end extending toward the third shorting element  550 . The width of the first end  531  of the third radiation element  530  may be longer than the width of the second end  532  of the third radiation element  530 . The fourth radiation element  540  may substantially have a straight-line shape. The fourth radiation element  540  has a first end  541  and a second end  542 . The first end  541  of the fourth radiation element  540  is coupled to a third connection point CP 3  on the third feeding connection element  520 . The second end  542  of the fourth radiation element  540  is an open end. In some embodiments, the fourth radiation element  540  further includes a terminal rectangular widening portion  545 , such that the width W 3  of the second end  542  of the fourth radiation element  540  is longer than the width of the first end  541  of the fourth radiation element  540 . Such a design can increase the median-frequency operation bandwidth of the third antenna  500 . The fourth radiation element  540  is surrounded by the third feeding connection element  520 , the third radiation element  530 , and the third shorting element  550 . The third shorting element  550  may substantially have an inverted U-shape. The third feeding point FP 3  may be positioned in a notch region  556  which is defined by the third shorting element  550 . The third shorting element  550  has a first end  551  and a second end  552 . The first end  551  of the third shorting element  550  is coupled to the third ground plane  510 , and the second end  552  of the third shorting element  550  is coupled to a fourth connection point CP 4  on the third feeding connection element  520 , such that the third feeding connection element  520  is coupled through the third shorting element  550  to the third ground plane  510 . In some embodiments, the third shorting element  550  further includes a median rectangular widening portion  555 . The width W 4  of the median rectangular widening portion  555  is longer than the width of the other portion of the third shorting element  550 , so as to fine-tune the impedance matching of the third antenna  500 . A fifth gap G 5  is formed between the third radiation element  530  and the third feeding connection element  520 . A sixth gap G 6  is formed between the fourth radiation element  540  and the third shorting element  550 . The width of the sixth gap G 6  is longer than the width of the fifth gap G 5 . 
     The operation principle and element sizes of the third antenna  500  may be described as follows. The third feeding connection element  520 , the third radiation element  530 , and the third shorting element  550  are excited to generate the aforementioned third frequency interval (e.g., from 680 MHz to 960 MHz). The third feeding connection element  520 , the fourth radiation element  540 , and the third shorting element  550  are excited to generate the aforementioned fourth frequency interval (e.g., from 1700 MHz to 2200 MHz). The third feeding connection element  520  and the third shorting element  550  are excited to generate the aforementioned fifth frequency interval (e.g., from 2500 MHz to 2700 MHz). The total length of the third feeding connection element  520 , the third radiation element  530 , and the third shorting element  550  (e.g., the total length from the first end  551  through the fourth connection point CP 4  and the first end  531  to the second end  532 ) may be substantially equal to 0.25 wavelength (λ/4) of the central frequency of the third frequency interval. The total length of the third feeding connection element  520 , the fourth radiation element  540 , and the third shorting element  550  (e.g., the total length from the first end  551  through the fourth connection point CP 4  and the third connection point CP 3  to the second end  542 ) may be substantially equal to 0.25 wavelength (λ/4) of the central frequency of the fourth frequency interval. The total length of the third feeding connection element  520  and the third shorting element  550  (e.g., the total length from the first end  551  through the fourth connection point CP 4  to the second end  522 ) may be longer than or equal to 0.25 wavelength (λ/4) of the central frequency of the fifth frequency interval. The width W 3  of the terminal rectangular widening portion  545  of the fourth radiation element  540  may be from 2.3 mm to 2.9 mm (e.g., 2.6 mm). The width W 4  of the median rectangular widening portion  555  of the third shorting element  550  may be from 5 mm to 5.6 mm (e.g., 5.3 mm). The width of the fifth gap G 5  may be from 2.9 mm to 3.5 mm (e.g., 3.2 mm). The width of the sixth gap G 6  may be from 0.5 mm to 0.9 mm (e.g., 0.7 mm). The above ranges of the elements are calculated and obtained according to many experimental results, and they help to optimize the operation bandwidth and impedance matching of the third antenna  500 . 
     In some embodiments, the main beam of the first antenna  300  is arranged toward a first direction (e.g., the direction of the −Y axis), the main beam of the second antenna  400  is arranged toward a second direction (e.g., the direction of the +X axis) which is perpendicular to the first direction, and the main beam of the third antenna  500  is arranged toward a third direction (e.g., the direction of the +Y axis) which is opposite to the first direction, so as to increase the spatial diversity gain of the antenna system  200 . In order to increase the isolation between antennas, the distance D 3  between the first antenna  300  and the third antenna  500  may be longer than or equal to 5 mm, and the distance D 4  between the second antenna  400  and the third antenna  500  may be also longer than or equal to 5 mm. The distance D 6  between the second ground plane  410  and the third ground plane  510  may be much longer than the distance D 5  between the first ground plane  310  and the third ground plane  510 . For example, the aforementioned distance D 6  may be at least 5 times the aforementioned distance D 5 , thereby further reducing the interference between the second antenna  400  and the third antenna  500 . 
       FIG. 3A  is a diagram of isolation between the first antenna  300  and the third antenna  500  according to an embodiment of the invention.  FIG. 3B  is a diagram of isolation between the second antenna  400  and the third antenna  500  according to an embodiment of the invention.  FIG. 3C  is a diagram of isolation between the first antenna  300  and the second antenna  400  according to an embodiment of the invention. According to the measurement of  FIG. 3A ,  FIG. 3B , and  FIG. 3C , within the wide operation bandwidth from 600 MHz to 6000 MHz, the isolation between any two of the first antenna  300 , the second antenna  400 , and the third antenna  500  can be higher than 17 dB (or the corresponding S 21  parameter is lower than −17 dB), and it can meet the requirements on the practical application of general antenna systems. 
     The invention proposes a novel antenna system. By incorporating an antenna having a different frequency into two antennas having the same frequency, the invention not only increases the isolation of the antenna system but also minimizes the total size of the antenna system, and therefore it is suitable for application in a variety of mobile communication devices with small sizes. 
     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. 1-3 . The invention may include any one or more features of any one or more embodiments of  FIGS. 1-3 . 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. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the invention. It is intended that the standard and examples be considered as exemplary only, with the true scope of the disclosed embodiments being indicated by the following claims and their equivalents.