Patent Publication Number: US-10320077-B2

Title: Broadband antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Chinese application serial no. 201620016433.0, filed on Jan. 8, 2016. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an antenna, and more particularly, to a broadband antenna. 
     Description of Related Art 
     Since a small cell (including picocell and femtocell . . . etc.) supports a network listening (NL) technique of receiving function, different actual applications can be satisfied, and therefore small cell is a very promising solution. 
     In order to meet the bandwidth requirements of an NL system at 1 GHz or less, if the antenna structure having ¼ wavelength resonant mode of the prior art is used, then at low frequency, a portion of the resonant mode is degraded, and as a result the frequency band requirements of an NL system cannot be met. 
     SUMMARY OF THE INVENTION 
     The invention provides a broadband antenna capable of providing different resonant modes at low frequency band without the occurrence of resonant mode degradation. 
     The broadband antenna of the invention includes: a ground member; a first radiation member for providing a first resonant path to make the broadband antenna cover a first frequency band; and a second radiation member for providing a second resonance path to make the broadband antenna cover a second frequency band, wherein the first end of the second radiation member is connected to the first end of the first radiation member to form a first commonly-connected end, the first commonly-connected end has a feed point, the second end of the first radiation member is connected to the second end of the second radiation member to form a second commonly-connected end, and the second commonly-connected end is connected to the ground member, wherein the first radiation member is surrounded by the second radiation member and is spaced apart from the second radiation member by a gap. 
     The broadband antenna can provide 2 frequency bands, each of which has ½ wavelength resonant mode, in a frequency range less than 1 GHz without the occurrence of resonant mode degradation, and therefore the broadband antenna is suitable for application in network listening (NL) techniques. 
     In order to make the aforementioned features and advantages of the disclosure more comprehensible, embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic of a broadband antenna of an embodiment of the invention. 
         FIG. 2  is a schematic of a broadband antenna of another embodiment of the invention. 
         FIG. 3  is a schematic of a return loss test of a broadband antenna of an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic of a broadband antenna of an embodiment of the invention. Please refer to  FIG. 1 . A broadband antenna  100  includes a ground member  102 , a first radiation member  104 , and a second radiation member  106 , wherein the first end of the first radiation member  104  is connected to the first end of the second radiation member  106  to form a first commonly-connected end, and the first commonly-connected end has a feed point F 1 . Moreover, the second end of the first radiation member  104  is connected to the second end of the second radiation member  106  to form a second commonly-connected end, and the second commonly-connected end is connected to the ground member  102 . Moreover, the first radiation member  104  is surrounded by the second radiation member  106 , and the first radiation member  104  and the second radiation member  106  are spaced apart by a gap. 
     More specifically, the first radiation member  104  can include a first connecting segment  104 - 1 , a second connecting segment  104 - 2 , and a third connecting segment  104 - 3 , and the second radiation member  106  can include a fourth connecting segment  106 - 1 , a fifth connecting segment  106 - 2 , and a sixth connecting segment  106 - 3 . In particular, the first end of the first connecting segment  104 - 1  is connected to the first end of the fourth connecting segment  106 - 1  (i.e., the first end of the second radiation member  106 ) to form the first commonly-connected end, the first end and the second end of the second connecting segment  104 - 2  are respectively connected to the second end of the first connecting segment  104 - 1  and the first end of the third connecting segment  104 - 3 , and the second end of the third connecting segment  104 - 3  is connected to the second end of the sixth connecting segment  106 - 3  (i.e., the second end of the second radiation member  106 ) to form the second commonly-connected end. Moreover, the first end and the second end of the fifth connecting segment  106 - 2  are respectively connected to the second end of the fourth connecting segment  106 - 1  and the first end of the sixth connecting segment  106 - 3 . In the present embodiment, the second connecting segment  104 - 2  and the fifth connecting segment  106 - 2  are located on a first plane, and the first connecting segment  104 - 1 , the third connecting segment  104 - 3 , the fourth connecting segment  106 - 1 , and the sixth connecting segment  106 - 3  are located on a second plane. In particular, the first plane can be parallel to the ground member  102 , an angle can be between the first plane and the second plane, and as shown in  FIG. 1 , the angle can be, for instance, 90 degrees, but is not limited thereto. 
     A feed point F 1  on the first commonly-connected end can receive a feed signal, and under the excitation of the feed signal, currents in the same direction can be respectively formed on the first radiation member  104  and the second radiation member  106 . In particular, the first resonance path provided by the first radiation member  104  can generate a resonant mode, such that the broadband antenna  100  covers a first frequency band, and the second resonance path provided by the second radiation member  106  can generate another resonant mode, such that the broadband antenna  100  covers a second frequency band. In the present embodiment, the length of the first resonance path is less than the length of the second resonance path (as shown in  FIG. 1 ), and therefore the center frequency of the first frequency band is higher than the center frequency of the second frequency band. In particular, the first frequency band can be between 869 MHz and 894 MHz, and the second frequency band can be between 729 MHz and 756 MHz. That is, the antenna structure of the present embodiment can provide 2 similar center frequencies in a frequency range less than 1 GHz, and each of the band has a frequency band of ½ wavelength resonant mode without the occurrence of resonant mode degradation. As a result, the frequency band requirements of network listening (NL) techniques in low frequency range can be met. Moreover, in the structure of the broadband antenna  100  of the present embodiment, a height H 1  of the broadband antenna can be as low as 18 mm, and a length D 1  and a width W 1  thereof can respectively only be 70 mm and 20 mm. That is, the broadband antenna  100  has the advantage of small size and can be readily applied in various communication devices. 
     It should be mentioned that, in the embodiment of  FIG. 1 , although the first radiation member  104  and the second radiation member  106  include a bent section (such as a portion interconnecting the first connecting segment  104 - 1  and the second connecting segment  104 - 2 ), in some embodiments, the first radiation member  104  and the second radiation member  106  can also not include a bent section. That is, the first radiation member  104  and the second radiation member  106  can also be implemented as planar antennas. Moreover, in the embodiment of  FIG. 1 , the first radiation member  104  and the second radiation member  106  are conformal. For instance, in the embodiment of  FIG. 1 , the second connecting segment  104 - 2  and the fifth connecting segment  106 - 2  are both U-shaped connecting segments, but are not limited thereto in actual application. In some embodiments, the second connecting segment  104 - 2  and the fifth connecting segment  106 - 2  can also be other shapes, such as an oval having a notch. Alternatively, in other embodiments, the first radiation member  104  and the second radiation member  106  can also be different shapes. 
     Moreover, the center frequencies of the first frequency band and the second frequency band can be adjusted by changing the lengths of the first radiation member  104  and the second radiation member  106 . For instance,  FIG. 2  is a schematic of a broadband antenna of another embodiment of the invention. Please refer to  FIG. 2 . In the embodiment of  FIG. 2 , by changing the length of the first radiation member  104 , i.e., changing the length of the resonance path provided by the first radiation member  104 , the center frequency of the first frequency band can be adjusted. As shown in the return loss test schematic of a broadband antenna of  FIG. 3 , when the length of the first radiation member  104  is increased, the length L shown in  FIG. 2  is also increased, and curve L 1 , curve L 2 , curve L 3 , curve L 4 , and curve L 5  in  FIG. 3  respectively represent the curves corresponding to the length L of  FIG. 2  at 69 mm, 65 mm, 55 mm, 45 mm, and 35 mm. It can be known from  FIG. 3  that, when the length L is increased, i.e., the length of the first radiation member  104  is increased, the center frequency corresponding to the first radiation member  104  is also reduced. As shown in  FIG. 3 , when the length L is 69 mm, 65 mm, 55 mm, 45 mm, and 35 mm, the center frequencies corresponding thereto are respectively about 0.85 GHz, 0.91 GHz, 1.04 GHz, 1.21 GHz, and 1.45 GHz. Even when the center frequency of the first frequency band is reduced to 0.85 GHz and close to the center frequency of the second frequency band (about 0.77 GHz), it can still be clearly seen from  FIG. 3  that the resonant modes generated by the first radiation member  104  and the second radiation member  106  are both still significant. It can therefore be known that, the broadband antenna  100  of the embodiments can indeed solve the issue of degradation to resonant mode of the current antenna at low frequency, and can satisfy the frequency band requirements of an NL system. Similarly, the center frequency of the second frequency band can also be adjusted by changing the length of the second radiation member  106 , and the adjustment method thereof is similar to the adjustment method of the first frequency band, and is therefore not repeated herein. 
     The broadband antenna of the above embodiments can provide 2 frequency bands, each having ½ wavelength resonant mode in a frequency range less than 1 GHz, and even if the center frequencies of two low frequency bands are close, resonant mode degradation still does not occur.