Patent Publication Number: US-8525741-B2

Title: Multi-loop antenna system and electronic apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Chinese Application No. 201010274841.3, filed on Sep. 6, 2010. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna system and an electronic apparatus having the same, more particularly to a multi-loop antenna system and an electronic apparatus having the same. 
     2. Description of the Related Art 
     Conventionally, planar inverted-F antennas are used in wireless devices, such as wireless access points. Taiwanese Patent No. M377714 discloses a monopole antenna system, which includes three monopole antennas that are formed on a grounding plane by cutting or punching techniques, and which is applicable to multiple-input-multiple-output wireless communications. 
     Although such an antenna system may be disposed in a housing of an electronic apparatus, the antenna system, however, has a three-dimensional structure and hence occupies a larger space, which consequently reduces space in the housing available for disposing of other electronic components. Furthermore, such an antenna system generally has gain values ranging from 3 dBi to 5 dBi in the 2.4 GHz and 5 GHz frequency bands, and radiation patterns thereof generally show lower directivity. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a multi-loop antenna system capable of alleviating the aforesaid drawbacks of the antenna system of the prior art. 
     Accordingly, a multi-loop antenna system of the present invention includes an antenna module and a system module. The antenna module includes a substrate, and a plurality of loop antennas. The loop antennas are disposed on the substrate, and are arranged such that each of extending lines extending respectively from geometric centers of the loop antennas to a center point that is bounded by the loop antennas has a predetermined length, and that each of the loop antennas is spaced apart from an adjacent one of the loop antennas by a predetermined minimum distance. Each of the loop antennas includes: a first radiator portion operable in a first frequency band, and having opposite ends that respectively serve as a signal-feed section and a grounding section, and that are adjacent to and spaced apart from each other such that the first radiator portion substantially forms a loop; and a second radiator portion operable in a second frequency band, and having opposite ends that are connected electrically and respectively to the signal-feed section and the grounding section of the first radiator portion, such that the second radiator portion substantially forms a loop. The system module has a grounding plane that faces toward and that is spaced apart from and parallel to the substrate such that the grounding plane is able to reflect radiation from the antenna module so as to enhance gain and directivity thereof. 
     Another object of the present invention is to provide an electronic apparatus having an antenna module and a system module. 
     Accordingly, an electronic apparatus of the present invention includes a housing, and an antenna module and a system module disposed in the housing. The antenna module includes a substrate, and a plurality of loop antennas. The loop antennas are disposed on the substrate, and are arranged such that each of extending lines extending respectively from geometric centers of the loop antennas to a center point that is bounded by the loop antennas has a predetermined length, and that each of the loop antennas is spaced apart from an adjacent one of the loop antennas by a predetermined distance. Each of the loop antennas includes: a first radiator portion operable in a first frequency band, and having opposite ends that respectively serve as a signal-feed section and a grounding section, and that are adjacent to and spaced apart from each other such that the first radiator portion substantially forms a loop; and a second radiator portion operable in a second frequency band, and having opposite ends that are connected electrically and respectively to the signal-feed section and the grounding section of the first radiator portion, such that the second radiator portion substantially forms a loop. The system module has a grounding plane that faces toward and that is spaced apart from and parallel to the substrate such that the grounding plane is able to reflect radiation from the antenna module so as to enhance gain and directivity of the multi-loop antenna system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a perspective view of the first preferred embodiment of a multi-loop antenna system according to the present invention; 
         FIG. 2  is a schematic diagram to illustrate a loop antenna of the multi-loop antenna system; 
         FIG. 3  is a schematic diagram to illustrate the multi-loop antenna system; 
         FIG. 4  is a schematic diagram to illustrate a modification of the multi-loop antenna system according to the present invention; 
         FIG. 5  is a perspective view of another modification of the multi-loop antenna system according to the pre sent invention; 
         FIG. 6  is a perspective view of an electronic apparatus including a housing and the multi-loop antenna system, which is disposed in the housing, according to the present invention; 
         FIG. 7  is a schematic diagram to illustrate dimensions of the loop antenna of the multi-loop antenna system; 
         FIG. 8  is a schematic diagram to illustrate dimensions of the multi-loop antenna system; 
         FIG. 9  is a schematic diagram to illustrate dimensions of the multi-loop antenna system when viewed from the side; 
         FIG. 10  shows radiation patterns of the multi-loop antenna system in the x-z and y-z planes when operated at 2442 MHz; 
         FIG. 11  shows radiation patterns of the multi-loop antenna system in the x-z and y-z planes when operated at 5490 MHz; 
         FIG. 12  is a plot of reflection coefficient of the multi-loop antenna system; 
         FIG. 13  is a plot of isolation of the multi-loop antenna system; 
         FIG. 14  is a plot showing gain value and radiation efficiency of the multi-loop antenna system at different frequencies; 
         FIG. 15  is a perspective view of the second preferred embodiment of a multi-loop antenna system according to the present invention; and 
         FIG. 16  is a perspective view of the third preferred embodiment of a multi-loop antenna system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
     Referring to  FIG. 1 , the first preferred embodiment of a multi-loop antenna system  100  of the present invention is operable in the wireless local area network frequency bands, which range from 2400 MHz to 2484 MHz and from 5150 MHz to 5825 MHz, respectively, and includes an antenna module  10  and a system module  20 . The antenna module  10  includes a substrate  1  and a plurality of loop antennas  2 . The substrate  1  is preferably made of a dielectric material, such as glass fiber (FR4), has opposite first and second surfaces  11 ,  12 , and is formed with a through-hole  13  for extensions of cables  5  therethrough. 
     Referring to  FIG. 2 , in this embodiment, each of the loop antennas  2  is a one-wavelength loop antenna made of metal, is disposed on the first surface  11  of the substrate  1 , and includes first and second radiator portions  3 ,  4 . 
     The first radiator portion  3  of each of the loop antennas  2  is operable in a first frequency band preferably ranging from 2400 MHz to 2484 MHz, and has opposite ends that respectively serve as a signal-feed section  31  and a grounding section  32 , and that are adjacent to and spaced apart from each other such that the first radiator portion  3  substantially forms a circular loop. The second radiator portion  4  of each of the loop antennas  2  is operable in a second frequency band preferably ranging from 5150 MHz to 5825 MHz, and has opposite ends  41 ,  42  that are connected electrically and respectively to the signal-feed section  31  and the grounding section  32  of the first radiator portion  3  of the loop antenna  2 , such that the second radiator portion  4  substantially forms a circular loop. 
     In this embodiment, the second radiator portion  4  has a substantially circular loop-shaped radiator section  40  having opposite ends, and a pair of parallel extending sections  410 ,  420  extending from the opposite ends of the radiator section  40  and serving as the opposite ends  41 ,  42  of the second radiator portion  4 , respectively. The pair of extending sections  410 ,  420  and the radiator section  40  cooperate to define a slot  430 . 
     Referring to  FIG. 3 , the loop antennas  2  are arranged along a peripheral portion of the substrate such that each of extending lines extending respectively from geometric centers of the loop antennas  2  to a center point “A” that is bounded by the loop antennas  2  has a predetermined length. That is to say, lengths “La”, “Lb”, and “Lc” are identical to one another. Moreover, each of the loop antennas  2  is spaced apart from an adjacent one of the loop antennas  2  by a predetermined minimum distance. That is to say, distances “L 1 ”, “L 2 ”, and “L 3 ” are identical to one another. Furthermore, each of the extending lines forms a predetermined angle with an adjacent one of the extending angles. That is to say, “θ 1 ”, “θ 2 ”, and “θ 3 ” are identical to one another and are equal to 120 degrees in this embodiment. Such a symmetrical arrangement of the loop antennas  2  ensures substantially equal degrees of isolation there among and a relatively symmetrical radiation coverage. 
     It is worth noting that, in this embodiment, the through-hole  13  corresponds in position to the center point “A”, and the cables  5  are connected electrically and respectively to the loop antennas  2  via the through-hole  13  so as to avoid overlapping of the loop antennas  2  by the cables  5 , thereby reducing interference between the cables  5  and the loop antennas  2 . 
     In this embodiment, for each of the loop antennas  2 , the first radiator portion  3  substantially encloses the second radiator portion  4 . Such a configuration of the second radiator portion  4  with respect to the first radiator portion  3  ensures efficient usage of space. Specifically, the geometric center of each of the loop antennas  2  is bounded by the first radiator portion  3  instead of the second radiator portion  4  of the loop antenna  2 . In this embodiment, for each of the loop antennas  2 , the slot  430  opens in a direction that forms a predetermined included angle “a” with the respective one of the extending lines, and the first and second radiator portions  3 ,  4  are respectively symmetrical in the direction in which the slot  430  opens. The predetermined included angle “a” is preferably 45 degrees such that signals radiated by each of the loop antennas  2  are characterized by bipolar propagation in a direction perpendicular to the first surface  11  of the substrate  1 . 
     However, referring to  FIG. 4 , in a modification, the pair of the extending sections  410 ,  420  and the radiator section  40  of the second radiator portion  4  of each of the loop antennas  2  may be configured such that the slot  430  opens toward the center point “A”. Furthermore, referring to  FIG. 5 , in another modification, each of the first and second radiator portions  3 ,  4  of each of the loop antennas  2  may be a rectangular radiator portion. 
     In this embodiment, the system module  20  is a system circuit board having a grounding plane  201  that faces toward and that is spaced apart from and parallel to the second surface  12  of the substrate  1  such that the grounding plane  201  is able to reflect radiation from the antenna module  10 . Radiation patterns of the multi-loop antenna system  100  thus exhibit high directivity and gain. Moreover, the system module  20  preferably has a multi-layer structure, of which the top layer is a thin metal layer serving as the grounding plane  201 , and each of remaining layers is independently one of a substrate layer and a circuit layer. It is to be noted that, in other embodiments, the antenna module  10  and the system module  20  may be spaced apart from each other by a distance not smaller than 5 mm (e.g., 8.4 mm) so as to enable disposing of various electronic components therebetween. Furthermore, the substrate  1  occupies an area not larger than that occupied by the system module  20  such that the system module  20  is able to substantially reflect signals radiated by the antenna module  10 . 
     Referring to  FIG. 6 , the multi-loop antenna system  100  of the first preferred embodiment may be disposed in a housing  210  of an electronic apparatus  200 , which may be a wireless access point or a wireless router. 
     Each of the cables  5  is preferably a mini-coaxial cable connected electrically to the feed-in segment  31  of the respective loop antenna  2  for transmission and reception of signals therethrough. 
       FIGS. 7 to 9  show dimensions of the multi-loop antenna system  100  in millimeters. However, configuration of the multi-loop antenna system  100  is not limited to such. 
       FIGS. 10 and 11  show two-dimensional radiation patterns of the first and second radiator portions  3 ,  4  at 2442 MHz and 5490 MHz, respectively. It is apparent that the multi-loop antenna system  100  is characterized by high directivity and bipolar propagation in the direction perpendicular to the first surface  11 . 
       FIG. 12  shows a plot of reflection coefficient, of which “S 11 ”, “S 22 ”, and “S 33 ” represent reflection coefficients of the loop antennas  2 , respectively. It is apparent that the reflection coefficients of the loop antennas  2  are lower than −10 dB in the first and second frequency bands. 
       FIG. 13  shows a plot of isolation, of which “S 21 ”, “S 32 ”, and “S 32 ” represent isolations between different pairs of the loop antennas  2 , respectively. It is apparent that an average value of the isolations among the loop antennas  2  is below −15 dB. 
       FIG. 14  shows a plot of radiation efficiency of the multi-loop antenna system  100 . It is apparent that the multi-loop antenna system  100  has a maximum gain of 7.6 dBi and a radiation efficiency of 76% in the first frequency band, and a maximum gain of 9 dBi and a radiation efficiency of 83% in the second frequency band. 
       FIG. 15  shows the second preferred embodiment of a multi-loop antenna system  100  according to the present invention, of which the loop antennas  2  are disposed on both the first and second surfaces  11 ,  12  of the substrate  1 . 
       FIG. 16  shows the third preferred embodiment of a multi-loop antenna system  100  according to the present invention. The sole difference between the first and third preferred embodiments resides in that the second radiator portion  4  of each of the loop antennas  2  includes only the radiator section  40 , and that the opposite ends of the radiator section  40  serve as the opposite ends  41 ,  42  of the second radiator portion  4 . 
     In summary, the multi-loop antenna system  100  is applicable to multiple-input-multiple-output communications, is operable in the wireless local area network frequency bands, radiates signals with high directivity, and is characterized by relatively high isolation. In addition, because printed circuit board techniques are used to form the loop antennas  2 , fabrication is relatively easy and costs less, and the multi-loop antenna system  100  has a low-profile of planar configuration suitable for application to small outdoor wireless devices. 
     While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.