Patent Publication Number: US-2015077307-A1

Title: Antenna structure and wireless communication device employing same

Description:
FIELD 
     The subject matter herein generally relates to antenna structures, and particular to a multiband antenna structure and wireless communication device employing same. 
     BACKGROUND 
     With improvements in the integration of wireless communication systems, antennas have become increasingly important. For a wireless communication device to utilize various frequency bandwidths, antennas having wider bandwidths have become a significant technology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
         FIG. 1  is an isometric view of one embodiment of a wireless communication device employing an antenna structure. 
         FIG. 2  is similar to  FIG. 1 , but showing the wireless communication device in another view angle. 
         FIG. 3  is a circuit diagram showing an impedance matching circuit of the antenna structure as shown in  FIG. 1 . 
         FIG. 4  is a diagram showing return loss (“RL”) measurement of the antenna structure when a value of a variable capacitor of the impedance matching circuit is 2.3 pF. 
         FIG. 5  is a diagram showing total efficiency measurement of the antenna structure when the value of the variable capacitor of the impedance matching circuit is 2.3 pF. 
         FIG. 6  is a diagram showing RL measurement of the antenna structure when a value of a variable capacitor of the impedance matching circuit is 7 pF. 
         FIG. 7  is a diagram showing total efficiency measurement of the antenna structure when the value of the variable capacitor of the impedance matching circuit is 7 pF. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts have been exaggerated to better illustrate details and features of the present disclosure. 
     Several definitions that apply throughout this disclosure will now be presented. 
     The term “coupled” is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently connected or releasably connected. The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series and the like. 
       FIG. 1  illustrates an isometric view of one embodiment of a wireless communication device  100  employing a printed circuit board  10  and an antenna structure  20 . The printed circuit board  10  includes a feeding point  14  configured to feed current signal and a grounding point  16  electronically coupled to ground. 
       FIG. 2  is similar to  FIG. 1 , but showing the wireless communication device  100  in another view angle. The antenna structure  20  includes a feeding portion  21  electronically coupled to the feeding point  14  (also see  FIG. 1 ), a grounding portion  22  electronically coupled to the grounding point  16  (also see  FIG. 1 ), a first radiating body  23 , a second radiating body  24 , a first coupling portion  25 , and a second coupling portion  26 . The first radiating body  23  is electronically coupled to the grounding portion  22  and the feeding portion  21 . The second radiating body  24  is positioned apart from the first radiation body  23 . The first coupling portion  25  is electronically coupled between the first and second radiating bodies  23  and  24 . The second coupling portion  26  faces the first coupling portion  25 , and is electronically coupled between the first and second radiating bodies  23  and  24 . The first and second radiating bodies  23  and  24 , and the first and second coupling portions  25  and  26  cooperatively define a loop antenna. 
     The first radiating body  23  and second radiating body  24  are metal sheets, and are parallel to each other. The printed circuit board  10  is parallel to the first and second radiating bodies  23  and  24 , and is positioned between and apart from the first and second radiating bodies  23  and  24 . In one embodiment, the first radiating body  23  is a portion of a front cover (not shown) of the wireless communication device  100 , and is insulative from the remaining portion of the front cover of the wireless communication device  100 . The second radiating body  24  is a portion of a back over of the wireless communication device  100 , and is insulative from the remaining portion of the back cover of the wireless communication device  100 . 
     The first coupling portion  25  and second coupling portion  26  are meander strips, and are positioned in a plane that is substantially perpendicular to a plane in which the first radiating body  23  is positioned. In particular, the first coupling portion  25  includes a first arm  251 , a second arm  252  and a third arm  253  which are coupled sequentially. The first arm  251  is substantially perpendicularly coupled to an edge of the first radiating body  23 . The second arm  252  is substantially U-shaped and positioned at a side of the first arm  251  facing the second coupling portion  26 . The third arm  253  is substantially perpendicularly coupled to an edge of the second radiating body  24  facing the edge of first radiating body  23 . 
     The second coupling portion  26  includes a first strip  261 , a second strip  262 , and a third strip  263  which are coupled sequentially. The first strip  261  is substantially perpendicularly coupled to the edge of the first radiating body  23 . The second strip  262  is substantially U-shaped and positioned at a side of the first strip  261  facing the first coupling portion  25 . The third strip  263  is substantially perpendicularly coupled to the edge of the second radiating body  24 . In one embodiment, the second strip  262  aligns with the second arm  252 . 
     The feeding portion  21  and the grounding portion  22  are substantially perpendicularly coupled to a same surface of the first radiating body  23 . 
     In use, the loop antenna generates a low frequency resonate mode and a first high frequency resonant mode that is a harmonic of the low frequency resonate mode; the first and second coupling portions  25  and  26  generates a second high frequency resonate mode and a third high frequency resonate mode respectively. 
       FIG. 3  illustrates a circuit diagram of an impedance matching circuit  27  of the antenna structure  20  as shown in  FIG. 2 . The impedance matching circuit  27  includes a first inductor L1, a second inductor L2 and a variable capacitor C. The variable capacitor C and the first inductor L1 are electronically coupled in series between the feeding portion  21  and the feeding point  14 . The second inductor  12  is electronically coupled to a node between the first inductor  11  and the feeding portion  21 , and further electronically coupled to ground. 
     By changing the capacitance value of the variable capacitor C, the operation frequency at low frequency band of the antenna structure  100  can be adjusted and the antenna characteristic can be improved. In one embodiment, the variable capacitor C can be a digital tuned capacitor that is an integrated circuit capacitor, such as a variable capacitor based on micro-electro-mechanical systems (MEMS) technology. In another embodiment, the variable capacitor C is a capacitance-variable diode of which the capacitance value can be changed by changing an applied voltage. In one embodiment, the capacitance value of the variable capacitor C can be set to either 2.3 pF or 7 pF. 
       FIG. 4  illustrates a return loss (“RL”) measurement of the antenna structure  20  when the capacitance value of the variable capacitor C is set to 2.3 pF. As shown in  FIG. 4 , the RL is lower than −5 dB when the antenna structure  20  operates at a low frequency band from about 704 MHz to about 746 MHz and a high frequency band from about 1710 MHz to about 2170 MHz. 
       FIG. 5  illustrates a total efficiency measurement of the antenna structure  20  when the capacitance value of the variable capacitor C is set to 2.3 pF. The total efficiency of the antenna structure  20  is in a range from about 60% to about 80% at the low frequency band from about 704 MHz to about 746 MHz, and the total efficiency of the antenna structure  20  is in a range from about 52% to about 76% at the high frequency band from about 1710 MHz to about 2170 MHz. 
       FIG. 6  illustrates a RL measurement of the antenna structure  20  when the capacitance value of the variable capacitor C is set to 7 pF. As shown in  FIG. 4 , the RL is lower than −5 dB when the antenna structure  20  operates at a low frequency band from about 824 MHz to about 960 MHz and a high frequency band from about 1710 MHz to about 2170 MHz. 
       FIG. 7  illustrates a total efficiency measurement of the antenna structure  20  when the capacitance value of the variable capacitor C is set to 7 pF. The total efficiency of the antenna structure  20  is in a range from about 70% to about 79% at the low frequency band from about 824 MHz to about 960 MHz, and the total efficiency of the antenna structure  20  is in a range from about 47% to about 79% at the high frequency band from about 1710 MHz to about 2170 MHz. 
     Therefore, the antenna structure  20  can operate a low frequency band from about 704 MHz to about 960 MHz, and a high frequency band from about 1710 MHz to about 2170 MHz with an exceptional communication quality. 
     The embodiments shown and described above are only examples. Many details are often found in the art. Therefore, many such details are neither shown nor described. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size and arrangement of the parts within the principles of the present disclosure up to, and including the full extent established by the broad general meaning of the terms used in the claims. It will therefore be appreciated that the embodiments described above may be modified within the scope of the claims.