Patent Publication Number: US-9431696-B2

Title: Communication device with ground plane antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 102115722, filed on May 2, 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 a communication device, and more particularly, to a communication device with a ground plane antenna. 
     2. Description of Related Art 
     In recent years, with the rapid advances in the wireless communication technology, the communication device not only is demanded for its function, but the appearance thereof is also designed to be thinner and lighter to attract the consumer&#39;s attention. Therefore, how to utilize limited space to design an antenna element having a small size and achieve broadband or multi-frequency operation has become an important issue in the design of the antenna. 
     Accordingly, when it comes to designing an antenna for a communication device, how to combine an antenna element having a small size with a ground plane of the device to form a ground plane antenna with a broadband resonant mode and improve the impedance matching and the antenna efficiency in an operating band of the ground plane antenna has become a major issue in the design of the antenna. 
     SUMMARY OF THE INVENTION 
     The invention provides a communication device that uses an antenna element and a ground element in the communication device to form a ground plane antenna with an asymmetric dipole antenna structure, and two metal portions disposed on different surfaces of a dielectric substrate in the antenna element are connected with each other through a conductive via-hole. In this way, the impedance matching of the resonant mode of the ground plane antenna can be improved, and thus the operating bandwidth and the antenna efficiency of the ground plane antenna can be increased. 
     The communication device of the invention includes a ground element, a dielectric substrate, and an antenna element. The dielectric substrate is disposed nearby the ground element and has a first surface and a second surface. The antenna element includes a first metal portion and a second metal portion. The first metal portion is disposed on the first surface and has a feeding point. The second metal portion is disposed on the second surface. The first metal portion is electrically connected to the second metal portion through a conductive via-hole, and the conductive via-hole is located at or nearby a first edge of the first metal portion. The first edge is away from the ground element. The projection of the second metal portion on the first surface is covered by the first metal portion. 
     To make the above features and advantages of the invention more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       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 diagram illustrating a structure of a communication device according to a first embodiment of the invention. 
         FIG. 2  is a return loss diagram of the communication device according to the first embodiment of the invention with a second metal portion and without a second metal portion. 
         FIG. 3  is an antenna efficiency diagram of the communication device according to the first embodiment of the invention with a second metal portion and without a second metal portion. 
         FIG. 4  is a schematic diagram illustrating a structure of a communication device according to a second embodiment of the invention. 
         FIG. 5  is a schematic diagram illustrating a structure of a communication device according to a third embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In order to make the above objectives, features and advantages of the invention more comprehensible, several specific embodiments accompanied with figures are described in detail as follows. 
       FIG. 1  is a schematic diagram illustrating a structure of a communication device according to a first embodiment of the invention. Referring to  FIG. 1 , a communication device  1  includes a ground element  11 , a dielectric substrate  12 , and an antenna element  10 . The dielectric substrate  12  has a first surface  121  and a second surface  122 , and the antenna element  10  has a first metal portion  13  and a second metal portion  14 . 
     A shape of the first metal portion  13  is approximately an inverted U shape and the first metal portion  13  is disposed on the first surface  121 . Moreover, the first metal portion  13  has a feeding point  131  and a first edge  132 , and the first edge  132  is an edge of a middle section of the inverted U shape and is away from the ground element  11 . From another perspective, the first metal portion  13  further includes a second edge opposite to the first edge  132 . The second edge of the first metal portion  13  includes a notch such that the shape of the first metal portion  13  is approximately the inverted U shape. Moreover, the feeding point  131  is disposed on the second edge of the first metal portion  13  and is nearby a sidewall of the notch. Furthermore, an opening of the notch of the first metal portion  13  is opposite to the ground element  11 , and the first edge  132  and the ground element  11  are spaced by a first distance d. A length of the first edge  132  is between 0.5 to 2.0 times the first distance d. 
     A shape of the second metal portion  14  is also approximately an inverted U shape, and the second metal portion  14  is disposed on the second surface  122 . Moreover, a middle section  141  of the inverted U shape is disposed nearby the first edge  132  and is substantially parallel to the first edge  132 . Furthermore, a projection of the second metal portion  14  on the first surface  121  is covered by the first metal portion  13 . That is, the second metal portion  14  is opposite to the first metal portion  13  with the dielectric substrate  12  in between. 
     In addition, the first metal portion  13  is electrically connected to the second metal portion  14  through a conductive via-hole  15 . The conductive via-hole  15  passes through the first metal portion  13 , the dielectric substrate  12 , and the second metal portion  14 . Moreover, regarding the first metal portion  13 , the conductive via-hole  15  is located at or nearby an end of the first edge  132 , and the conductive via-hole  15  and the feeding point  131  are nearby two ends of a diagonal  133  of the first metal portion  13 , respectively. Furthermore, regarding the second metal portion  14 , the conductive via-hole  15  is located at or nearby a corner of the second metal portion  14 . 
     The antenna element  10  and the ground element  11  form a ground plane antenna having an asymmetric dipole antenna structure. Moreover, the communication device  1  transmits a signal source  17  to the feeding point  131  to excite the antenna element  10 . Therefore, the first metal portion  13  can generate a resonant mode in a frequency band such that the antenna element  10  is operated in the frequency band. Moreover, as shown in  FIG. 1 , in an embodiment, the communication device  1  further includes a matching circuit  16 , and the matching circuit  16  is electrically connected to the first metal portion  13 . During the operation, the matching circuit  16  provides an impedance value such that the antenna element  10  is operated in the frequency band. Moreover, with the arrangement of the matching circuit  16 , the sum of the lengths of the first edge  131  and the first distance d is less than 0.1 times a wavelength of a lowest frequency of the frequency band and is far less than a resonance path length of a quarter wavelength required by a conventional antenna element. 
     It should be mentioned that, in the situation where the second metal portion  14  is not arranged, the distribution of the surface current of the first metal portion  13  may not be very uniform. For instance, since the first edge  132  of the first metal portion  13  is away from the feeding point  131 , a region nearby the first edge  132  in the first metal portion  13  becomes the region having weaker surface current in the first metal portion  13 . However, with the arrangement of the second metal portion  14 , since the first metal portion  13  can be electrically connected to the second metal portion  14  through the conductive via-hole  15  and the conductive via-hole  15  is located at or nearby the first edge  132 , the surface current of the first metal portion  13  can be distributed more uniformly through the second metal portion  14 . Hence, the effects of improving the impedance matching of the ground plane antenna formed by the antenna element  10  and the ground element  11  and increasing the antenna efficiency and the operating bandwidth of the ground plane antenna can be achieved. 
     For instance,  FIG. 2  is a return loss diagram of the antenna element  10  according to the first embodiment of the invention with the second metal portion  14  and without the second metal portion  14 . The dimension of the antenna element  10  in the present embodiment is only about 10×10×1 mm 3 , and the dimension of the antenna element  11  is about 110×60 mm 2 . As shown in  FIG. 2 , the antenna element  10  is operated in a frequency band  21  and the frequency range of the frequency band  21  is about 746-960 MHz, and covers the frequency bands of LTE band  13  and GSM850/900. Moreover, a return loss curve  22  is used to represent the return loss of the antenna element  10  without the second metal portion  14 , and the return loss curve  23  is used to represent the return loss of the antenna element  10  with the second metal portion  14 . By comparing the return loss curves  22  and  23 , it is apparent that, with the arrangement of the second metal portion  14 , the return loss of the antenna element  10  can be improved from the return loss curve  22  to the return loss curve  23 . Moreover, the improvement of the return loss is at least about 1 dB, and the maximum improvement is about 2.7 dB. Therefore, the operating bandwidth of the antenna element  10  is effectively increased. 
       FIG. 3  is an antenna efficiency diagram of the antenna element  10  according to the first embodiment of the invention with the second metal portion  14  and without the second metal portion  14 . An antenna efficiency curve  31  (the mismatching loss of the antenna is included) is used to represent the antenna efficiency of the antenna element  10  without the second metal portion  14 , and the antenna efficiency curve  32  (the mismatching loss of the antenna is included) is used to represent the antenna efficiency of the antenna element  10  with the second metal portion  14 . By comparing the antenna efficiency curves  31  and  32 , it is apparent that, with the arrangement of the second metal portion  14 , the antenna efficiency of the antenna element  10  can be improved from the antenna efficiency curve  31  to the antenna efficiency curve  32 . Moreover, the average improvement of the antenna efficiency in the frequency band  21  is about 10%, and the maximum improvement is about 14%. 
       FIG. 4  is a schematic diagram illustrating a structure of a communication device according to a second embodiment of the invention. The communication device  4  in the second embodiment is similar to the communication device  1  in the first embodiment. The difference between the second embodiment and the first embodiment is that a shape of the second metal portion  44  in the antenna element  10  is approximately an inverted L shape. Moreover, a section  441  of the inverted L shape is nearby the first edge  132  and is substantially parallel to the first edge  132 . Under the similar structure, the communication device  4  in the second embodiment can also achieve an effect similar to the first embodiment. 
       FIG. 5  is a diagram illustrating a structure of a communication device according to a third embodiment of the invention. The communication device  5  in the third embodiment is similar to the communication device  1  in the first embodiment. The difference between the third embodiment and the first embodiment is that the first metal portion  13  is electrically connected to the second metal portion  14  through two conductive via-holes  551  and  552 . Under the similar structure, the communication device  5  in the third embodiment can also achieve an effect similar to the first embodiment. 
     Based on the above, in the invention, the antenna element and the ground element in the communication device are used to form the ground plane antenna having the asymmetric dipole antenna structure. Moreover, the antenna element has two metal portions respectively disposed on different surfaces of the dielectric substrate, and the two metal portions are connected with each other through the conductive via-hole. In this way, the impedance matching of the resonant mode of the ground plane antenna can be improved, and thus the operating bandwidth and the antenna efficiency of the ground plane antenna can be increased. 
     Although the invention has been described with reference to the above embodiments, it will be apparent to one of the 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 is defined by the attached claims not by the above detailed descriptions.