Patent Publication Number: US-9431706-B2

Title: Multi-band antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 102128118, filed on Aug. 6, 2013. 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 
     1. Field of the Invention 
     The invention relates to an antenna, and more particularly, to a multi-band antenna. 
     2. Description of Related Art 
     In recent years, various wireless communication devices, such as smartphones, tablet PCs, personal wireless navigation systems, portable players and so on, tend to incorporate all known communication functions, instead of performing only a single wireless communication function. In addition, to reduce a hardware space of a device, these wireless communication devices adopt a single wireless communication chip that supports multiple wireless communication functions in various communication protocols such as wireless fidelity (WiFi), global positioning system (GPS), Bluetooth (BT) and so on. 
     With regard to corresponding antennas, current wireless communication devices usually require multiple antennas (e.g. WiFi antenna, GPS antenna, etc.) to be embedded therein in order to support the various wireless communication functions. However, as the embedded antennas are increased, more hardware space in the wireless communication devices is consumed for disposing the antennas, which limits the miniaturization of the wireless communication devices. In addition, for purposes of enhancing radiation efficiency or gain of antenna, in current design of antennas, laser direct structuring (LSD) technology or iron element is often utilized to form an antenna having an irregular three-dimensional structure. However, such design still requires larger hardware space for disposing the antenna. 
     SUMMARY OF THE INVENTION 
     The invention provides a multi-band antenna that generates coupling effects respectively with two extension elements through a radiation element, so as to generate multiple resonant modes and to support multiple communication functions. 
     The multi-band antenna of the invention includes a ground plane, a radiation element, a first extension element and a second extension element. The radiation element includes a first portion and a second portion electrically connected with each other. The first portion is adjacent to an edge of the ground plane and has a feeding point. The first extension element is extended from the edge of the ground plane and is spaced from the first portion by a first coupling distance. The second extension element is extended from the edge of the ground plane and is spaced from the second portion by a second coupling distance. The multi-band antenna is operated in a first band through the radiation element. A feeding signal from the radiation element excites the first and the second extension elements through the first and the second coupling distances so that the multi-band antenna is operated further in a second band and a third band. 
     Based on the above, the multi-band antenna of the invention generates coupling effects respectively with the two extension elements through the radiation element. Accordingly, the multi-band antenna generates multiple resonant modes, and thus is operated in multiple bands and supports multiple communication functions. In an actual application, a wireless communication device only requires a single multi-band antenna to be able to support a wireless communication chip having multiple communication functions. In this way, an effect of reducing hardware space is achieved, thus facilitating miniaturization. 
     To make the above features and advantages of the invention more comprehensible, embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a structure of a multi-band antenna according to an embodiment of the invention. 
         FIG. 2  is a graph showing return loss of a multi-band antenna according to an embodiment of the invention. 
         FIG. 3  is a graph showing gain of a multi-band antenna according to an embodiment of the invention. 
         FIGS. 4-5  show patterns of a multi-band antenna according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
       FIG. 1  is a schematic diagram of a structure of a multi-band antenna according to an embodiment of the invention. As shown in  FIG. 1 , a multi-band antenna  100  includes a ground plane  110 , a radiation element  120 , a first extension element  130  and a second extension element  140 . The radiation element  120  includes a first portion  121  and a second portion  122 . The first portion  121  is adjacent to an edge  111  of the ground plane  110  and has a feeding point FP. The first portion  121  is electrically connected to the second portion  122 . The first extension element  130  and the second extension element  140  are extended from the edge  111  of the ground plane  110 . The first extension element  131  and the first portion  121  are spaced by a first coupling distance CD1. The second extension element  140  and the second portion  122  are spaced by a second coupling distance CD2. 
     In terms of operation, the multi-band antenna  100  receives a feeding signal via the feeding point FP of the radiation element  120 . The radiation element  120  is excited by the feeding signal to generate a first resonant mode so that the multi-band antenna  100  is operated in a first band. In addition, the feeding signal from the radiation element  120  excites the first extension element  130  through the first coupling distance CD1 so that the multi-band antenna  100  generates a second resonant mode through the first extension element  130  and is operated further in a second band. Besides, the feeding signal from the radiation element  120  excites the second extension element  140  through the second coupling distance CD2 so that the multi-band antenna  100  generates a third resonant mode through the second extension element  140  and is operated further in a third band. 
     In other words, the radiation element  120  generates coupling effects respectively with the two extension elements  130  and  140 . In this way, the multi-band antenna  100  not only generates a resonant mode through the radiation element  120 , but also generates different resonant modes through the two extension elements  130  and  140 . Therefore, the multi-band antenna  100  may be operated in multiple bands so as to support multiple communication functions. 
       FIG. 2 , for example, is a graph showing return loss of a multi-band antenna according to an embodiment of the invention. As shown in  FIG. 2 , in the present embodiment, the radiation element  120 , the first extension element  130  and the second extension element  140  are equivalent to an antenna element. The antenna element has a length L and a height H of respectively 26 mm and 6 mm. In addition, the multi-band antenna  100  may be operated in a first band  210 , a second band  220  and a third band  230 . Moreover, the first band  210  covers a frequency band range (2300-2700 MHz) for 2G, the second band  220  covers a frequency band range (5150-5875 MHz) for 5G, and the third band  230  covers a frequency band range (1565-1612 MHz) for the Global Positioning System (GPS) and the GLObal NAvigation Satellite System (GLONASS). 
     In addition,  FIG. 3  is a graph showing gain of a multi-band antenna according to an embodiment of the invention, and  FIGS. 4-5  show patterns of a multi-band antenna according to an embodiment of the invention. As shown in  FIG. 3 , the multi-band antenna  100  has a good antenna gain in all of the first band  210 , the second band  220  and the third band  230 . Particularly in the first band  210 , the multi-band antenna  100  has a gain as high as −1 dB, which means that the multi-band antenna  100  achieves an antenna efficiency of 90%. In addition,  FIGS. 4-5  show radiation patterns of the multi-band antenna  100  on Y-Z and X-Z planes in the first band  210 . As shown in  FIGS. 4-5 , the multi-band antenna  100  has an omni-directional radiation pattern in the first band  210 , and difference between an upper pattern and a lower pattern of the multi-band antenna  100  is within 1 dB. Accordingly, in real practice, whether the multi-band antenna  100  is disposed on an upper side or a lower side of a wireless communication device, the multi-band antenna  100  is able to receive a GPS signal. 
     It is to be noted that since the multi-band antenna  100  supports multiple communication functions through multiple resonant modes, only a single multi-band antenna  100  is required to be embedded in the wireless communication device for supporting a wireless communication chip having multiple communication functions. In this way, an effect of reducing hardware space is achieved, thus facilitating miniaturization. In addition, the multi-band antenna  100  is provided with good radiation pattern and gain without use of LDS technology or iron element. Thus the hardware space is reduced even further. 
     Still referring to  FIG. 1 , in terms of details of the structure of the multi-band antenna  100 , the radiation element  120 , the first extension element  130  and the second extension element  140  are arranged in sequence along the edge  111  of the ground plane  110 . In addition, a first end  131  of the first extension element  130  is electrically connected to the edge  111  of the ground plane  110 , and a second end  132  of the first extension element  130  is an open end. Similarly, a first end  141  of the second extension element  140  is electrically connected to the edge  111  of the ground plane  110 , and a second end  142  of the second extension element  140  is an open end. Moreover, the first end  131  of the first extension element  130  is opposite to the first portion  121  of the radiation element  120 , and the second end  142  of the second extension element  140  is opposite to the second portion  122  of the radiation element  120 . 
     The first extension element  130  is configured to provide a first resonant path. The first resonant path is from the first end  131  of the first extension element  130  to the second end  132  of the first extension element  130 . In addition, the first extension element  130  adopts a quarter wavelength resonance. Hence the first resonant path has a length of approximately one-fourth a wavelength of a lowest frequency in the second band. Similarly, the second extension element  140  is configured to provide a second resonant path. The second resonant path is from the first end  141  of the second extension element  140  to the second end  142  of the second extension element  140 . In addition, the second extension element  140  also adopts a quarter wavelength resonance. Hence the second resonant path has a length of approximately one-fourth a wavelength of a lowest frequency in the third band. 
     In the whole configuration, the first end  131  of the first extension element  130  is adjacent to the first portion  121  of the radiation element  120 . A spacing DT between the first end  131  of the first extension element  130  and the first end  141  of the second extension element  140  is larger than one-twentieth the wavelength of the lowest frequency in the third band. The first coupling distance CD1 is between one and two times the wavelength of the lowest frequency in the second band, while the second coupling distance CD2 is between one and two times the wavelength of the lowest frequency in the third band. Meanwhile, in an embodiment, the second extension element  140  further includes at least one bend so as to further reduce the hardware space consumed by the multi-band antenna  100 . 
     Furthermore, the radiation element  120  further includes a third portion  123  and a fourth portion  124 . Both the third portion  123  and the fourth portion  124  are electrically connected to the second portion  122 . In addition, the third portion  123  is configured to extend the resonant path of the radiation element  120  to meet actual application requirements. The fourth portion  124  is opposite to the second end  142  of the second extension element  140  so as to increase the coupling effect between the radiation element  120  and the second extension element  140 . In an embodiment, the ground plane  110 , the radiation element  120 , the first extension element  130  and the second extension element  140  are located on the same horizontal plane (e.g. X-Z plane). In other words, the multi-band antenna  100  may have a planar structure and may be disposed on a surface of a substrate, such as a printed circuit board or a flexible printed circuit board. 
     In summary, the multi-band antenna of the invention generates coupling effects respectively with the two extension elements through the radiation element. Accordingly, the multi-band antenna forms multiple resonant modes, and thus may be operated in multiple bands and may support multiple communication functions. In an actual application, a wireless communication device only requires the multi-band antenna to be able to support a wireless communication chip having multiple communication functions. In this way, an effect of reducing hardware space is achieved, thus facilitating miniaturization. 
     Although the invention has been described with reference to the above embodiments, it will be apparent to one of ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims and not by the above detailed descriptions.