Patent Publication Number: US-2013241784-A1

Title: Communication device and tunable antenna element therein

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 101108578 filed on Mar. 14, 2012, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure generally relates to a communication device, and more particularly, relates to a communication device and a tunable antenna element therein. 
     2. Description of the Related Art 
     With progress in mobile communication technology, the users use communication devices not only for talking but also for a variety of requirements. In order to meet the requirements using slim and small-size communication devices, the limited space for the internal antennas in the communication devices is very valuable. As a matter of fact, it is important to effectively use the limited space for the internal antennas in the communication devices. 
     Therefore, there is a need for an antenna element of a mobile communication device to operate in different communication bands by switching to different circuit elements without changing the size and the structure of the antenna element in the mobile communication device. The antenna element should have more operating bands without increasing the space for antenna design. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a communication device and a tunable antenna element therein. The communication device comprises an antenna element which is a loop antenna, and the communication device selectively electrically couples one of at least two separate circuit element sub-groups to a feeding end of the antenna element. Therefore, the antenna element can operate in different communication bands, covering WWAN/LTE bands. 
     In one exemplary embodiment, the disclosure is directed to a communication device, comprising: a ground element; an antenna element, wherein the antenna element is a loop antenna, one end of the antenna element is a grounding end coupled to the ground element, and the other end of the antenna element is a feeding end close to the grounding end; a circuit element group comprising at least two separate circuit element sub-groups; and a communication module coupled to the circuit element group, wherein one of the circuit element sub-groups of the circuit element group is selectively coupled to the feeding end so as to make the antenna element operate in different communication bands. 
     In the invention, the antenna element is a loop antenna, and each circuit element sub-group of the circuit element group may comprise at least a capacitive element and an inductive element that are electrically coupled in series. Note that each circuit element sub-group has different capacitances of the capacitive element and different inductances of the inductive element. By a selection circuit, when the antenna element is electrically coupled to one of these circuit element sub-groups, different capacitances and inductances can correspond to multiple communication bands for optimal impedance matching, thereby making the antenna element operate in multiple communication bands. The communication device with the loop antenna is capable of covering different communication bands (e.g., WWAN/LTE bands) by electrically coupling to different capacitive and inductive elements in series without changing the size of the antenna element. In an embodiment, the antenna element has a feeding end which is close to a grounding end, and the antenna element substantially has an inverted L-shape or an L-shape. This antenna structure can lead to easy adjustment of the frequency ratio of higher-order resonant modes to a fundamental (lowest frequency) resonant mode of the antenna element so as to cover dual bands or multiple bands of mobile communications. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1A  is a diagram for illustrating a communication device according to a first embodiment of the invention; 
         FIG. 1B  is a diagram for illustrating a communication device according to another embodiment of the invention; 
         FIG. 2  is a diagram for illustrating a communication device according to a second embodiment of the invention; 
         FIG. 3  is a diagram for illustrating return loss when an antenna element is electrically coupled through a selection circuit to a first circuit element sub-group according to the second embodiment of the invention; 
         FIG. 4  is a diagram for illustrating antenna efficiency when the antenna element is electrically coupled through the selection circuit to the first circuit element sub-group according to the second embodiment of the invention; 
         FIG. 5  is a diagram for illustrating return loss when the antenna element is electrically coupled through the selection circuit to a second circuit element sub-group according to the second embodiment of the invention; 
         FIG. 6  is a diagram for illustrating antenna efficiency when the antenna element is electrically coupled through the selection circuit to the second circuit element sub-group according to the second embodiment of the invention; 
         FIG. 7  is a diagram for illustrating return loss when the antenna element is electrically coupled through the selection circuit to a third circuit element sub-group according to the second embodiment of the invention; and 
         FIG. 8  is a diagram for illustrating antenna efficiency when the antenna element is electrically coupled through the selection circuit to the third circuit element sub-group according to the second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to illustrate the foregoing and other purposes, features and advantages of the invention, the embodiments and figures thereof in the invention are shown in detail as follows. 
       FIG. 1A  is a diagram for illustrating a communication device  100  according to a first embodiment of the invention. As shown in  FIG. 1A , the communication device  100  comprises a ground element  10 , an antenna element  11 , a circuit element group  12 , and a communication module  13 . The antenna element  11  is a loop antenna. One end of the antenna element  11  is a grounding end  110  which is electrically coupled to the ground element  10 , and the other end of the antenna element  11  is a feeding end  111  which is close to the grounding end  110 . In a preferred embodiment, the antenna element  11  substantially has an inverted L-shape or an L-shape. In other embodiments, the antenna element  11  may have other shapes, such as a C-shape, a U-shape, or an I-shape. The circuit element group  12  comprises two separate circuit element sub-groups, that is, a first circuit element sub-group  121  and a second circuit element sub-group  122 . The communication module  13  is electrically coupled to the circuit element group  12 . Either the first circuit element sub-group  121  or the second circuit element sub-group  122  is electrically coupled through a selection circuit  14  to the feeding end  111  of the antenna element  11  so as to make the antenna element  11  operate in different communication bands. Each of the first circuit element sub-group  121  and the second circuit element sub-group  122  comprises at least an inductive element (e.g., a chip inductor) and a capacitive element (e.g., a chip capacitor), wherein the inductive element and the capacitive element are electrically coupled in series. In some embodiments, the selection circuit  14  is electrically coupled to either the first circuit element sub-group  121  or the second circuit element sub-group  122  according to a user input or a control signal generated by a processor (not shown). Note that the first circuit element sub-group  121  and the second circuit element sub-group  122  have different capacitances of the capacitive elements and different inductances of the inductive elements. The capacitive elements are configured to adjust a low-frequency band of the antenna element  11 , and the inductive elements are configured to adjust a high-frequency band of the antenna element  11 . When the feeding end  111  is electrically coupled to the first circuit element sub-group  121 , the antenna element  11  operates in a first band and a second band. When the feeding end  111  is electrically coupled to the second circuit element sub-group  122 , the antenna element  11  operates in a third band and a fourth band. Each of the first band, the second band, the third band and the fourth band covers at least one mobile communication band. 
       FIG. 1B  is a diagram for illustrating a communication device  100  according to another embodiment of the invention. As shown in  FIG. 1B , the selection circuit  14  may be electrically coupled between the circuit element group  12  and the communication module  13  instead, and the selection circuit  14  switches between the first circuit element sub-group  121  and the second circuit element sub-group  122 . 
       FIG. 2  is a diagram for illustrating a communication device  200  according to a second embodiment of the invention. As shown in  FIG. 2 , an antenna element  21  is a loop antenna. One end of the antenna element  21  is a grounding end  210  which is electrically coupled to a ground element  20 , and the other end of the antenna element  21  is a feeding end  211  which is close to the grounding end  210 . In the embodiment, a circuit element group  22  comprises three different circuit element sub-groups, that is, a first circuit element sub-group  221 , a second circuit element sub-group  222 , and a third circuit element sub-group  223 . Similarly, one of the first circuit element sub-group  221 , the second circuit element sub-group  222  and the third circuit element sub-group  223  is electrically coupled through a selection circuit  24  to the feeding end  211  of the antenna element  21  so as to make the antenna element  21  operate in different communication bands. Each of the first circuit element sub-group  221 , the second circuit element sub-group  222  and the third circuit element sub-group  223  comprises at least an inductive element and a capacitive element, wherein the inductive element and the capacitive element are electrically coupled in series. In some embodiments, the selection circuit  24  is electrically coupled to one of the first circuit element sub-group  221 , the second circuit element sub-group  222  and the third circuit element sub-group  223  according to a user input or a control signal generated by a processor (not shown). Note that the first circuit element sub-group  221 , the second circuit element sub-group  222  and the third circuit element sub-group  223  have different capacitances of the capacitive elements and different inductances of the inductive elements. The capacitive elements are configured to adjust a low-frequency band of the antenna element  21 , and the inductive elements are configured to adjust a high-frequency band of the antenna element  21 . When the feeding end  211  is electrically coupled to the first circuit element sub-group  221 , the antenna element  21  operates in a first band and a second band. When the feeding end  211  is electrically coupled to the second circuit element sub-group  222 , the antenna element  21  operates in a third band and a fourth band. When the feeding end  211  is electrically coupled to the third circuit element sub-group  223 , the antenna element  21  operates in a fifth band and a sixth band. Each of the first band, the second band, the third band, the fourth band, the fifth band and the sixth band covers at least one mobile communication band. In other embodiments, the selection circuit  24  may be electrically coupled between the circuit element group  22  and a communication module  23  instead, and the selection circuit  24  switches between the first circuit element sub-group  221 , the second circuit element sub-group  222  and the third circuit element sub-group  223 . 
       FIG. 3  is a diagram for illustrating return loss when the antenna element  21  is electrically coupled through the selection circuit  24  to the first circuit element sub-group  221  according to the second embodiment of the invention. In response to the capacitance and inductance provided by the first circuit element sub-group  221 , the antenna element  21  can obtain optimal impedance matching and operate in the first band  31  and in the second band  32 . In the embodiment, the first band  31  and the second band  32  at least cover the GSM900 band and the GSM1800/1900/UMTS bands, respectively. 
       FIG. 4  is a diagram for illustrating antenna efficiency when the antenna element  21  is electrically coupled through the selection circuit  24  to the first circuit element sub-group  221  according to the second embodiment of the invention. The antenna efficiency curve  41  represents the antenna efficiency of the antenna element  21  which operates in the GSM900 band. The antenna efficiency curve  42  represents the antenna efficiency of the antenna element  21  which operates in the GSM1800/1900/UMTS bands. No matter which band the antenna element  21  operates in, the GSM900 band or the GSM1800/1900/UMTS bands, the communication device  200  of the invention has good antenna efficiency (S parameters included in the antenna efficiency). 
       FIG. 5  is a diagram for illustrating return loss when the antenna element  21  is electrically coupled through the selection circuit  24  to the second circuit element sub-group  222  according to the second embodiment of the invention. In response to the capacitance and inductance provided by the second circuit element sub-group  222 , the antenna element  21  can obtain optimal impedance matching and operate in the third band  51  and in the fourth band  52 . In the embodiment, the third band  51  and the fourth band  52  at least cover the GSM850 band and the GSM1800/1900/UMTS bands, respectively. 
       FIG. 6  is a diagram for illustrating antenna efficiency when the antenna element  21  is electrically coupled through the selection circuit  24  to the second circuit element sub-group  222  according to the second embodiment of the invention. The antenna efficiency curve  61  represents the antenna efficiency of the antenna element  21  which operates in the GSM850 band. The antenna efficiency curve  62  represents the antenna efficiency of the antenna element  21  which operates in the GSM1800/1900/UMTS bands. No matter which band the antenna element  21  operates in, the GSM850 band or the GSM1800/1900/UMTS bands, the communication device  200  of the invention has good antenna efficiency (S parameters included in the antenna efficiency). 
       FIG. 7  is a diagram for illustrating return loss when the antenna element  21  is electrically coupled through the selection circuit  24  to the third circuit element sub-group  223  according to the second embodiment of the invention. In response to the capacitance and inductance provided by the third circuit element sub-group  223 , the antenna element  21  can obtain optimal impedance matching and operate in the fifth band  71  and in the sixth band  72 . In the embodiment, the fifth band  71  and the sixth band  72  at least cover the LTE Band  13  and the LTE2300/2500 bands, respectively. 
       FIG. 8  is a diagram for illustrating antenna efficiency when the antenna element  21  is electrically coupled through the selection circuit  24  to the third circuit element sub-group  223  according to the second embodiment of the invention. The antenna efficiency curve  81  represents the antenna efficiency of the antenna element  21  which operates in the LTE Band  13 . The antenna efficiency curve  82  represents the antenna efficiency of the antenna element  21  which operates in the LTE2300/2500 bands. No matter which band the antenna element  21  operates in, the LTE Band  13  or the LTE2300/2500 bands, the communication device  200  of the invention has good antenna efficiency (S parameters included in the antenna efficiency). 
     In an embodiment, the antenna element  21  (or  11 ) of the invention is approximately 23 mm in length and 8 mm in width and 3 mm in height. The total length of the resonant path of the antenna element  21  (or  11 ) is approximately 62 mm. The small-size antenna element  21  will be easily applied into a variety of communication devices, such as smart phones, and tablet computers. 
     Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the invention. It is intended that the standard and examples be considered as exemplary only, with a true scope of the disclosed embodiments being indicated by the following claims and their equivalents.