Patent Publication Number: US-9425498-B2

Title: Wideband antenna module

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese Application No. 103113461, filed on Apr. 11, 2014. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wideband antenna module, more particularly to a wideband antenna module having a relatively small size and good isolation. 
     2. Description of the Related Art 
     Multiple-antenna systems (e.g., multiple-input and multiple-output systems, MIMO systems) are generally used to improve data rate, data throughput, spectrum efficiency, link reliability and channel capacity. However, since portable electronic devices are becoming increasingly smaller, distances among multiple antennas in the same portable electronic device are getting shorter. When two antennas are close to each other and operate at the same resonant frequency band, mutual coupling effect between the antennas will result in poor isolation therebetween, which degrades performances of the antennas. 
     A conventional antenna module as disclosed in U.S. Pat. No. 6,624,790 includes a protruded ground plane disposed between two antennas for improving isolation therebetween. Nevertheless, to add the protruded ground plane between two antennas may increase the size of the conventional antenna module. Moreover, a resonant frequency band at 5 GHz of the conventional antenna module is insufficient for covering WLAN 802.11a.n. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a wideband antenna module that has a relatively small size and good isolation. 
     Accordingly, a wideband antenna module of the present invention includes a ground conductor, a first radiating conductor, a second radiating conductor and a decoupling inductor. 
     The ground conductor has a first ground end part and a second ground end part. 
     The first radiating conductor includes a first feed-in portion, a first ground portion, a first radiating portion, a second radiating portion and a third radiating portion. 
     The first feed-in portion is spaced apart from the ground conductor, and has a first feed-in end part that is configured to be fed with a first radio frequency signal and that is adjacent to the first ground end part of the ground conductor. The first ground portion is connected to the first feed-in portion and the ground conductor. The first radiating portion is connected to the first feed-in portion. The second radiating portion is connected to the first radiating portion. The third radiating portion has a first connecting end part that is connected to the first radiating portion, and a first free end part that is opposite to the first connecting end part. 
     The second radiating conductor includes a second feed-in portion, a second ground portion, a fourth radiating portion, a fifth radiating portion and a sixth radiating portion. 
     The second feed-in portion is spaced apart from the ground conductor, and has a second feed-in end part that is configured to be fed with a second radio frequency signal and that is adjacent to the second ground end part of the ground conductor. The second ground portion is connected to the second feed-in portion and the ground conductor. The fourth radiating portion is connected to the second feed-in portion. The fifth radiating portion is connected to the fourth radiating portion. The sixth radiating portion has a second connecting end part that is connected to the fourth radiating portion, and a second free end part that is opposite to the second connecting end part and that is adjacent to the first free end part of the third radiating portion of the first radiating conductor. 
     The decoupling inductor is connected between the first free end part of the third radiating portion and the second free end part of the sixth radiating portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent in the following detailed description of the embodiment with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic view of an embodiment of a wideband antenna module according to the present invention; 
         FIG. 2  is a schematic view similar to  FIG. 1  for illustrating a current path and a size of the wideband antenna module; 
         FIG. 3  is a plot showing S-parameters of the wideband antenna module according to the present invention; 
         FIG. 4  is a radiation pattern of a first radiating conductor and a ground conductor of the wideband antenna module operating at a first frequency band; 
         FIG. 5  is a radiation pattern of a second radiating conductor and the ground conductor of the wideband antenna module operating at the first frequency band; 
         FIG. 6  is a radiation pattern of the first radiating conductor and the ground conductor of the wideband antenna module operating at a second frequency band; 
         FIG. 7  is a radiation pattern of the second radiating conductor and the ground conductor of the wideband antenna module operating at the second frequency band; and 
         FIG. 8  is a plot showing radiating efficiency of the wideband antenna module according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Referring to  FIG. 1 , an embodiment of a wideband antenna module  100  according to the present invention is shown to include a ground conductor  1 , a first radiating conductor  2 , a second radiating conductor  3  and a decoupling inductor  4 . 
     The ground conductor  1  has a first ground end part  11  and a second ground end part  12 . 
     The first radiating conductor  2  includes a first feed-in portion  21 , a first ground portion  22 , a first radiating portion  23 , a second radiating portion  24  and a third radiating portion  25 . 
     The first feed-in portion  21  is spaced apart from the ground conductor  1 , and has a first feed-in end part  211  that is configured to be fed with a first radio frequency signal and that is adjacent to the first ground end part  11  of the ground conductor  1 . The first feed-in portion  21  in this embodiment extends from the first feed-in end part  211  along a first direction (D 1 ). 
     The first ground portion  22  is connected to the first feed-in portion  21  and the ground conductor  1 . The first ground portion  22  has a first ground segment  221  and a second ground segment  222 . The first ground segment  221  extends from the ground conductor  1  along the first direction (D 1 ). The second ground segment  222  extends, from an end of the first ground segment  221  away from the ground conductor  1 , to the first feed-in portion  21  along a second direction (D 2 ). In this embodiment, the second direction (D 2 ) is transverse to the first direction (D 1 ). 
     The first radiating portion  23  is connected to the first feed-in portion  21 . Specifically, the first radiating portion  23  extends, from an end of the first feed-in portion  21  away from the ground conductor  1 , along the second direction (D 2 ). 
     The second radiating portion  24  is connected to the first radiating portion  23 . Specifically, the second radiating portion  24  extends, from an end of the first radiating portion  23  away from the first feed-in portion  21 , along a fourth direction (D 4 ). The fourth direction (D 4 ) is opposite to the first direction (D 1 ). 
     The third radiating portion  25  has a first connecting end part  252  that is connected to the first radiating portion  23 , and a first free end part  255  that is opposite to the first connecting end part  252 . In this embodiment, the third radiating portion  25  has a first connecting segment  251 , a first meandering segment  253  and a first extension segment  254 . The first connecting segment  251  has the first connecting end part  252  and extends, from an end of the first radiating portion  23  away from the first feed-in portion  21 , along the first direction (D 1 ). The first meandering segment  253  extends, from an end of the first connecting segment  251  away from the first radiating portion  23 , along a third direction (D 3 ). The third direction (D 3 ) is opposite to the second direction (D 2 ). The first extension segment  254  has the first free end part  255  and extends, from an end of the first meandering segment  253  away from the first connecting segment  251 , along the third direction (D 3 ). 
     The second radiating conductor  3  includes a second feed-in portion  31 , a second ground portion  32 , a fourth radiating portion  33 , a fifth radiating portion  34  and a sixth radiating portion  35 . 
     The second feed-in portion  31  is spaced apart from the ground conductor  1 , and has a second feed-in end part  311  that is configured to be fed with a second radio frequency signal and that is adjacent to the second ground end part  12  of the ground conductor  1 . The second feed-in portion  31  in this embodiment extends from the second feed-in end part  311  along the first direction (D 1 ). 
     The second ground portion  32  is connected to the second feed-in portion  31  and the ground conductor  1 . The second ground portion  32  has a third ground segment  321  and a fourth ground segment  322 . The third ground segment  321  extends from the ground conductor  1  along the first direction (D 1 ). The fourth ground segment  322  extends, from an end of the third ground segment  321  away from the ground conductor  1 , to the second feed-in portion  31  along the third direction (D 3 ). 
     The fourth radiating portion  33  is connected to the second feed-in portion  31 . Specifically, the fourth radiating portion  33  extends, from an end of the second feed-in portion  31  away from the ground conductor  1 , along the third direction (D 2 ). 
     The fifth radiating portion  34  is connected to the fourth radiating portion  33 . Specifically, the fifth radiating portion  34  extends, from an end of the fourth radiating portion  33  away from the second feed-in portion  31 , along the fourth direction (D 4 ). 
     The sixth radiating portion  35  has a second connecting end part  352  that is connected to the fourth radiating portion  33 , and a second free end part  355  that is opposite to the second connecting end part  352  and that is adjacent to the first free end part  255  of the third radiating portion  25 . In this embodiment, the sixth radiating portion  35  has a second connecting segment  351 , a second meandering segment  353  and a second extension segment  354 . The second connecting segment  351  has the second connecting end part  352  and extends, from an end of the fourth radiating portion  33  away from the second feed-in portion  31 , along the first direction (D 1 ). The second meandering segment  353  extends, from an end of the second connecting segment  351  away from the fourth radiating portion  33 , along the second direction (D 2 ). The second extension segment  354  has the second free end part  355  and extends, from an end of the second meandering segment  353  away from the second connecting segment  351 , along the second direction (D 2 ). 
     The decoupling inductor  4  is connected between the first free end part  255  of the third radiating portion  25  and the second free end part  355  of the sixth radiating portion  35 . 
     In addition, the first ground end part  11  and the second ground end part  12  of this embodiment are connected electrically to two outer conductors of two respective coaxial cables (not shown) for receiving grounding signals, respectively. The first feed-in end part  211  and the second feed-in end part  311  of this embodiment are connected electrically to inner conductors of the coaxial cables for receiving the first radio frequency signal and the second radio frequency signal, respectively. Moreover, the first radiating conductor  2  of this embodiment cooperates with the ground conductor  1  to form an inverted-F antenna, and the second radiating conductor  3  of this embodiment cooperates with the ground conductor  1  to form another inverted-F antenna. 
     Referring further to  FIGS. 2 and 3 , the first feed-in portion  21 , the first radiating portion  23  and the second radiating portion  24  cooperate to forma first current path (C 1 ) for operating in a first resonant mode (m 1 ). The first resonant mode (m 1 ) covers a first frequency band. The second feed-in portion  31 , the fourth radiating portion  33  and the fifth radiating portion  34  cooperate to form a second current path (C 2 ) for operating in a second resonant mode (m 2 ). The second resonant mode (m 2 ) covers the first frequency band. The first ground segment  221  of the first ground portion  22 , the ground conductor  1  and the third ground segment  321  of the second ground portion  32  cooperate to form a third current path (C 3 ). A length of the third current path (C 3 ) is one-half of a wavelength corresponding to the first frequency band. 
     The second ground segment  222  of the first ground portion  22 , the first radiating portion  23  and the third radiating portion  25  cooperate to form a fourth current path (C 4 ) for operating in a third resonant mode (m 3 ). The third resonant mode (m 3 ) covers a second frequency band that has a frequency lower than the first frequency band. The fourth ground segment  322  of the second ground portion  32 , the fourth radiating portion  33  and the sixth radiating portion  35  cooperate to form a fifth current path (C 5 ) for operating in a fourth resonant mode (m 4 ) that covers the second frequency band. 
     Since the first resonant mode (m 1 ) and the second resonant mode (m 2 ) cover the first frequency band, and the third resonant mode (m 3 ) and the fourth resonant mode (m 4 ) cover the second frequency band, the effect of wideband transmission may be achieved by the wideband antenna module  100 . Particularly, in this embodiment, the first frequency band ranges between 5 GHz˜6 GHz, and the second frequency band ranges between 2.4 GHz˜2.5 GHz. That is to say, the first and second frequency bands of the wideband antenna module  100  may cover WLAN (Wireless Local Area Networks) 802.11a.b.g.n and ac. Moreover, since the length of the third current path (C 3 ) is one-half of the wavelength corresponding to the first frequency band, isolation when the wideband antenna module  100  operates at the first frequency band may be effectively improved. Furthermore, since the decoupling inductor  4  is connected between the first free end part  255  and the second free end part  355 , a capacitive coupling effect between the first and second radiating conductors  2 ,  3  may be reduced, thereby effectively improving isolation when the wideband antenna module  100  operates at the second frequency band. 
       FIG. 3  is a plot showing S-parameters of the wideband antenna module  100  according to the present invention. A curve (S 11 ) shows a return loss related to the first feed-in end part  211  of the first feed-in portion  21  of the first radiating conductor  2 . A curve (S 22 ) shows a return loss related to the second feed-in end part  311  of the second feed-in portion  31  of the second radiating conductor  3 . A curve (S 21 ) shows isolation between the first feed-in end part  211  of the first radiating conductor  2  and the second feed-in end part  311  of the second radiating conductor  3 . According to  FIG. 3 , the curves (S 11 , S 22 ) indicate that the return loss of the first frequency band covered by the first and second resonant modes (m 1 , m 2 ) is less than −6 dB, and the return loss of the second frequency band covered by the third and fourth resonant modes (m 3 , m 4 ) is less than −6 dB. The curve (S 21 ) indicates that the isolation between the first and second radiating conductors  2 ,  3  at the first and second frequency bands is lower than −15 dB. 
       FIG. 4  is a radiation pattern of the first radiating conductor  2  and the ground conductor  1  of the wideband antenna module  100  operating at the first frequency band.  FIG. 5  is a radiation pattern of the second radiating conductor  3  and the ground conductor  1  of the wideband antenna module  100  operating at the first frequency band. A y axis shown in  FIGS. 4 and 5  extends along the first and fourth directions (D 1 , D 4 ). An x axis shown in  FIGS. 4 and 5  extends along the second and third directions (D 2 , D 3 ). The radiation pattern shown in  FIG. 4  is symmetrical with the radiation pattern shown in  FIG. 5  about the y axis, which represents that correlation between the radiation patterns of the first and second radiating conductors  2 ,  3  operating at the first frequency band is low. Therefore, the wideband antenna module  100  of this embodiment is suitable for application to multiple-input multiple-output (MIMO) antenna systems. 
       FIG. 6  is a radiation pattern of the first radiating conductor  2  and the ground conductor  1  of the wideband antenna module  100  operating at the second frequency band.  FIG. 7  is a radiation pattern of the second radiating conductor  3  and the ground conductor  1  of the wideband antenna module  100  operating at the second frequency band. The radiation pattern shown in  FIG. 6  is symmetrical with the radiation pattern shown in  FIG. 7  about the y axis, which represents that correlation between the radiation patterns of the first and second radiating conductors  2 ,  3  operating at the second frequency band is low. Therefore, the wideband antenna module  100  of this embodiment is suitable for application to MIMO antenna systems. 
       FIG. 8  is a plot showing radiating efficiency of the wideband antenna module  100  according to the present invention. The radiating efficiency of the wideband antenna module  100  operating at the first frequency band ranges between 78%˜85%. The radiating efficiency of the wideband antenna module  100  operating at the second frequency band ranges between 50%˜62%. Therefore, it is evident that the radiating efficiencies of the wideband antenna module  100  operating at the first and second frequencies are good. 
     Referring once again to  FIGS. 1 and 2 , it is noted that a combination of the first and second radiating conductors  2 ,  3  has a length (L) and a width (W). In this embodiment, the length (L) is 23 mm and the width (W) is 12 mm. It is evident that the wideband antenna module  100  of the present invention has a relatively small size. 
     To conclude, by virtue of the first, second, fourth and fifth current paths (C 1 , C 2 , C 4 , C 5 ) of the present invention, the wideband antenna module  100  may operate at the first and second frequency bands to thereby achieve wideband transmission. Moreover, the length of the third current path (C 3 ) is one-half of the wavelength corresponding to the first frequency band, and the decoupling inductor  4  is connected between the first free end part  255  and the second free end part  355 . As a result, isolation of the wideband antenna module  100  of the present invention operating at the first and second frequency bands may be effectively improved. Furthermore, the wideband antenna module  100  of the present invention has a relatively small size. 
     While the present invention has been described in connection with what is considered the most practical embodiment, it is understood that this invention is not limited to the disclosed embodiment 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.