Abstract:
The present application provides a multi-band antenna, comprising at least one low-band sub-antenna; and at least one high-band sub-antenna comprising at least one high-band dipole and a reflector; wherein the high-band dipole and/or the reflector are/is structured and positioned so that current induced in the high-band sub-antenna by the low-band sub-antenna is directed to reflector over an extended effective distance in proportion to wavelength of the low-band sub-antenna.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to antennas, and in particular, relates to multi-band antennas. 
       BACKGROUND OF THE INVENTION 
       [0002]    Antennas play an important role in communication systems and directly affect communication qualities. As wireless technology continues to thrive, multi-band antennas are used to implement higher speed and various types of services. 
         [0003]    A multi-band antenna usually includes an array of sub antennas that are generally categorized as low-band antennas and high-band antennas, which can cooperate at different frequency bands, as illustrated in  FIG. 1( a ) . 
         [0004]    Due to the structure of multi-band antennas introduced above, coupling effect and parasitic radiation between the low-band antenna(s) and the high-band antenna(s) may greatly impair the performance of multi-band antennas and users&#39; experience.  FIG. 1( b )  shows radiation pattern of a low-band sub-antenna array of a conventional multi-band antenna, which is abnormal due to the inter-band coupling effect and parasitic radiation. 
         [0005]    Current solution to solve this problem is to add parasitic patches, shaped walls, bars, or arches to the multi-band antennas. 
       SUMMARY OF THE INVENTION 
       [0006]    Due to increase of sub-antennas in multi-band antennas, more and more above mentioned structures such as parasitic patches, shaped walls, bars, or arches need to be added to multi-band antennas in order to reduce coupling effect and parasitic radiation. However, that would greatly increase manufacture cost of multi-band antennas and space of the multi-band antennas would finally become a limit for further addition of such structures. 
         [0007]    One embodiment of the present application provides a multi-band antenna, comprising at least one low-band sub-antenna; and at least one high-band sub-antenna comprising at least one high-band dipole and a reflector; wherein the high-band dipole and/or the reflector are/is structured and positioned so that current induced by the low-band sub-antenna is directed to reflector over an extended distance in proportion to wavelength of the low-band sub-antenna. 
         [0008]    Specifically, the high-band dipole is spaced from the reflector, but is connected to the reflector over the extended distance which is in form of a metal line. 
         [0009]    Specifically, the high-band dipole is spaced from the reflector by a PCB board on which the metal line is located. 
         [0010]    Specifically, the metal line is spiral-shaped, and the metal line is positioned directly under the high-band dipole or beside the high-band dipole. 
         [0011]    Specifically, the metal line is spiral-shaped and is located on an insulated portion of the high-band dipole, wherein one end of the metal line is connected to a conductive portion of the high-band dipole and another end of the metal line is connected to reflector. 
         [0012]    Specifically, the extended distance is formed by a spiral-shaped slot punched in the reflector around the high-band dipole. 
         [0013]    Specifically, a metal box is located beneath the reflector configured to cover the spiral-shaped slot to improve front to back ratio of the high-band dipole. 
         [0014]    Specifically, the extended distance is in form of at least a cable and a metal box located beneath the reflector through which foot of the high-band dipole is connected to reflector. 
         [0015]    Specifically, the extended distance is in proportion to one fourth or one eighth of the wavelength of the low-band sub-antenna. 
         [0016]    By extending the effective distance proportionally to the frequency of a low-band sub-antenna for induction current, induced by the low-band sub-antenna in the high-band sub-antenna, to flow from the high-band sub-antenna dipole to the reflector, the coupling effect and parasitic radiation between the sub-antennas are reduced. Extending the effective distance for the induction current means extending connection between the high-band sub-antenna and the reflector, or having the same effect as such extension. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other objects and features of the present invention will become more apparent from the following detailed description considered in connection with the accompanying drawings, in which: 
           [0018]      FIG. 1 ( a )  shows block diagrams of a plurality of multi-band antennas; 
           [0019]      FIG. 1( b )  shows radiation pattern of a low-band sub-antenna array of a conventional multi-band antenna; 
           [0020]      FIGS. 2 ( a ) and ( b )  show a high-band sub-antenna in accordance with one embodiment of the present application; 
           [0021]      FIG. 3  is a top view of a multi-band antenna with four high-band sub-antennas illustrated in  FIG. 2 ; 
           [0022]      FIG. 4  is a radiation pattern of the low-band sub-antenna array cooperating with high-band sub-antenna array including high-band sub-antennas as illustrated in  FIG. 2 ; 
           [0023]      FIGS. 5 ( a )-( b )  show a high-band dipole in accordance with another embodiment of the present application; 
           [0024]      FIG. 6  is a radiation pattern of the low-band sub-antenna array cooperating with high-band sub-antenna array including high-band dipoles as illustrated in  FIG. 5 ; 
           [0025]      FIGS. 7 ( a )-( d )  show a high-band dipole in accordance with another embodiment of the present application; 
           [0026]      FIGS. 8 ( a )-( b )  show a high-band dipole in accordance with another embodiment of the present application; 
           [0027]      FIGS. 9 ( a )-( b )  are radiation pattern of a low-band sub-antenna array cooperating with high-band sub-antenna array including high-band dipoles as illustrated in  FIG. 8 ; 
           [0028]      FIGS. 10 ( a )-( b )  are radiation pattern of a high-band sub-antenna array with and without the structure illustrated in  FIG. 8 ; 
           [0029]      FIG. 11 ( a )  shows a high-band sub-antenna in accordance with another embodiment of the present application; 
           [0030]      FIG. 11( b )  shows a high-band sub-antenna with the structures illustrated in  FIG. 11( a )  and  FIGS. 2( a )-( b ) ; 
           [0031]      FIGS. 12 ( a ) and ( b )  are radiation pattern of a low-band sub-antenna array cooperating with high-band sub-antenna array including high-band sub-antennas as illustrated in  FIG. 11( a ) ; and 
           [0032]      FIGS. 13 ( a ) and ( b )  are radiation pattern of a low-band sub-antenna array cooperating with high-band sub-antenna array including high-band sub-antennas as illustrated in  FIG. 11( b ) . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0033]    Reference will now be made to embodiments of the invention, one or more examples of which are illustrated in the figures. The embodiments are provided by way of explanation of the invention, and are not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. It is intended that the invention encompass these and other modifications and variations as come within the scope and spirit of the invention. 
         [0034]      FIG. 2( a )  is a 3-D illustration and  FIG. 2( b )  is schematic drawing of a high-band sub-antenna  200  of a multi-band in accordance with one embodiment of the present application. As illustrated in  FIGS. 2( a ) and ( b ) , high-band sub-antenna  200  may include dipole arms  202 , a support portion  204 , and a reflector  208 , wherein the support portion  204  is not connected to reflector  208  directly. Support portion  204  is separated from reflector  208  by a PCB board and is coupled to reflector  208  via a metal line  206  extending on the PCB board. Length of metal line  206  may be in proportion to a low-band sub antenna that is to cooperate with high-band sub-antenna  200 . 
         [0035]      FIG. 3  is a top view of a multi-band antenna including high-band sub-antenna as illustrated in  FIG. 2  in accordance to one embodiment of the present application. In  FIG. 3 , multi-band antenna may include four high-band sub-antennas  200   a - d , each of which may have the same structure as high-band sub-antenna  200  in  FIG. 2 . In particular, each of high-band sub-antennas  200   a - d  may be connected to the reflector via a metal line extending on a PCB board. 
         [0036]    In the center of the four high-band antennas  200   a - d , stands a low-band sub-antenna  210 , which may have a frequency F. Length of each of the metal lines respectively coupling high-band sub-antenna  200   a - d  to the reflector may be proportional to F, for example ¼ or ⅛ of F. 
         [0037]      FIG. 4  shows a radiation pattern of the low-band sub-antenna array of the multi-band antenna illustrated in  FIG. 3 . Compared to  FIG. 1( b ) , the pattern becomes much more normal, regarding the respective of linear beam-width and normal cross-polarization discrimination (XPD). 
         [0038]      FIG. 5  shows a high-band dipole of another multi-band antenna in accordance with another embodiment of the present application. High-band dipole may include dipole arms  502 , a support portion  504   a  made of conducting materials such as metal, and support portion  504   b  made of insulating materials such as plastic. Foot  506  of the high-band dipole may be made of conducting materials as well. A conductive line  505  may be spirally around or embedded in support portion  504   b  and configured to couple support portion  504   a  to dipole foot  506  and further to the reflector. 
         [0039]      FIG. 6  shows a radiation pattern of the low-band sub-antenna array of the multi-band antenna which includes high-band dipole as illustrated in  FIG. 5 . Compared to  FIG. 1( b ) , the pattern also is much more normal, regarding the respective of linear beam-width and normal cross-polarization discrimination (XPD). 
         [0040]      FIG. 7  shows a high-band dipole of a multi-band antenna in accordance with one embodiment of the present application. High-band dipole may include dipole arms  702 , a support portion  704  and an extension portion  706 , each of which may be made of conducting materials. Support portion  704  may be not in direct connection with the reflector but is coupled to the reflector via extension portion  706 . In particular, extension portion  706  may be a spirally shaped metal bracket with one end contacting support portion  704  and the other end contacting the reflector. Length of extension portion  706  may be in proportion to frequency of a low-band sub-antenna that is to be used cooperating with high-band dipole to form the multi-band antenna. 
         [0041]      FIGS. 7( a ) and ( b )  show an example of extension portion  706  positioned right under support portion  704 .  FIGS. 7( c ) and ( d )  show an example of extension portion  706  positioned beside support portion  704 . People of ordinary skills in art would know that any position of extension portion  706  in relative to support portion  704  would be within the scope of the present application. 
         [0042]      FIGS. 8 ( a ) and ( b )  show a high-band sub-antenna of a multi-band antenna in accordance with a further embodiment of the present application. High-band sub-antenna may include dipole arms  802 , a support portion  804  and a reflector  806 . In particular, a spiral shaped slot  805  is carved in the reflector  806  around support portion  804 . Slot  805  brings the same effect as current inducted in high-band sub-antenna by a low-band sub-antenna is directed to the reflector  806  via an extended distance that is proportional to the wavelength of the low-band sub-antenna. 
         [0043]    In order to improve the front to back ratio of high-band sub-antenna, a box/block  808  may be added beneath reflector  806  and to cover slot  805 . 
         [0044]      FIG. 9 ( a )  shows a radiation pattern of the low-band sub-antenna array of a multi-band antenna which includes high-band sub-antennas as illustrated in  FIG. 8 .  FIG. 9( b )  is the curve of beam-width in  FIG. 9( a ) , which shows that the beam-width is almost linear and therefore can meet the need of communication well. 
         [0045]      FIG. 10 ( a )  is a radiation pattern of high-band sub-antenna array without the slot structure shown in  FIG. 8 .  FIG. 10 ( b )  is a radiation pattern of high-band sub-antenna array with the slot structure shown in  FIG. 8 , which shows that the front to back ratio is not deteriorated due to the addition of the metal box/block  808 . Patterns in  FIGS. 10 ( a ) and ( b )  are similar which means low band performance is greatly improved because of the slot and box/block structures. 
         [0046]      FIG. 11 ( a )  shows a high-band sub-antenna of a multi-band antenna in accordance with one embodiment of the present application. High-band sub-antenna may have dipole arms  1102 , a support portion  1104 , dipole feet  1106 , cables  1108  connecting dipole feet  1106  to a reflector, and a metal box  1110  positioned beneath the reflector and is passed through by cables  1108 . In particular, support portion  1104  and dipole feet  1106  are made of conducting materials but are not in direct contact with the reflector. 
         [0047]    In one embodiment, length of cables  1106  and size of metal box  1110  are designed to have current induced in high-band sub-antenna by a low-band sub-antenna directed to the reflector via an extended distance that is proportional to wavelength of the low-band sub-antenna. 
         [0048]      FIG. 11( b )  shows a high-band sub-antenna with the metal line structure illustrated in  FIGS. 2( a )-( b )  and the cable and metal box/block structure illustrated in  FIG. 11( a ) . 
         [0049]      FIG. 12 ( a )  shows radiation pattern of a low-band sub-antenna array of a multi-band antenna including high-band sub-antennas as illustrated in  FIG. 11( a ) . Compared to  FIG. 1( b ) , the pattern also is much more normal.  FIG. 12( b )  is the curve of beam-width in  FIG. 12( a ) , which shows that the beam-width is almost linear and therefore can meet the need of communication. 
         [0050]      FIG. 13 ( a )  shows radiation pattern of a low-band sub-antenna array of a multi-band antenna including high-band sub-antennas as illustrated in  FIG. 11( b ) . Compared to  FIG. 1( b ) , the pattern also is much more normal.  FIG. 13( b )  is the curve of beam-width in  FIG. 13( a ) , which shows that the beam-width is almost linear and therefore can meet the need of communication. 
         [0051]    In the present application, the reflectors described are directed to ground. Length/size of the extended distance, such as the metal line and the various structures for extending the effective distance, may be proportional to ¼ or ⅛ of the frequency of the low-band sub-antenna cooperating with the high-band sub-antenna. 
         [0052]    It should be noted that the above described embodiments are given for describing rather than limiting the invention, and it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the invention and the appended claims. The protection scope of the invention is defined by the accompanying claims. In addition, any of the reference numerals in the claims should not be interpreted as a limitation to the claims. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The indefinite article “a” or “an” preceding an element or step does not exclude the presence of a plurality of such elements or steps.