Patent Publication Number: US-7911390-B2

Title: Antenna structure

Description:
RELATED APPLICATIONS 
     The Application claims priority under 35 U.S.C. 119 to an application TAIWAN 097101505 filed Jan. 15, 2008, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna structure, and more particularly, to an antenna structure disposing a radiator around another radiator and to make at least one predetermined distance included between the two radiators for matching impedance and for increasing bandwidth of antenna. 
     2. Description of the Prior Art 
     With the trend of micro-sized mobile communications products, the location and the space arranged for antennas becomes increasingly limited. Therefore, built-in micro antennas have been developed. Some micro antennas such as chip antennas and planar antennas are commonly used and occupy very small volume. 
     The planar antenna has the advantages of small size, light weight, ease of manufacturing, low cost, high reliability, and can also be attached to the surface of any object. Therefore, micro-strip antennas and printed antennas are widely used in wireless communication systems. 
     Due to multimedia applications of present wireless communication products, such as notebook computers, getting more and popular every day, transmissions with a large number of data has become a basic requirement of the wireless communication products. Thus requirements for operations at wide bandwidth get more basic. Therefore, how to improve antenna efficiency, adjust impedance matching, improve radiation patterns, and increase bandwidths of the antennas become important topics in this field. 
     SUMMARY OF THE INVENTION 
     It is one of the objectives of the present invention to provide an antenna structure to solve the abovementioned problems. 
     The present invention discloses an antenna structure. The antenna structure includes a radiation element, a grounding element, a short point, and a feeding point. The radiation element has a first radiator and a second radiator, wherein the second radiator partially surrounds the first radiator and there is a predetermined distance included between the first radiator and the second radiator for matching impedance. The short point is coupled between the second radiator and the grounding element. The feeding point is coupled between a joint point of the first radiator and the second radiator and the grounding element. 
     In one embodiment, the second radiator includes a plurality of sections. A designated section of the plurality of sections overlaps the first radiator and is at a first designated distance from the first radiator in a designated direction, and the designated section is at a second designated distance from the grounding element in a direction opposite to the first designated direction. There is a fillister formed between the designated section of the second radiator, the short point, and the grounding element. 
     In one embodiment, the antenna structure further includes a third radiator coupled to the feeding point, wherein there is a third designated distance included between the third radiator and the second radiator for matching impedance. 
     In one embodiment, the radiation element and the grounding element locate on different planes, and the antenna structure presents a solid form. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an antenna structure according to a first embodiment of the present invention. 
         FIG. 2  is a diagram illustrating the return loss of the antenna structure shown in  FIG. 1 . 
         FIG. 3  is a diagram of an antenna structure according to a second embodiment of the present invention. 
         FIG. 4  is a diagram illustrating the VSWR of the conventional dual-frequency antenna. 
         FIG. 5  is a diagram illustrating the VSWR of the antenna structure shown in  FIG. 3 . 
         FIG. 6  is a diagram illustrating the return loss of the antenna structure shown in  FIG. 3 . 
         FIG. 7  is a diagram illustrating a radiation pattern of the antenna structure shown in  FIG. 3 . 
         FIG. 8  is a table illustrating an antenna gain of the antenna structure shown in  FIG. 3 . 
         FIG. 9  is a diagram of an antenna structure according to a third embodiment of the present invention. 
         FIG. 10  is a diagram of an antenna structure according to a fourth embodiment of the present invention. 
         FIG. 11  is a diagram illustrating the VSWR of the antenna structure shown in  FIG. 10 . 
         FIG. 12  is a diagram of an antenna structure according to a fifth embodiment of the present invention. 
         FIG. 13  is a diagram of an antenna structure according to a sixth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 .  FIG. 1  is a diagram of an antenna structure  100  according to a first embodiment of the present invention. The antenna structure  100  includes a radiation element  110 , a grounding element  150 , a short point  160 , and a feeding point  170 . The radiation element  110  includes a first radiator  120  and a second radiator  130 , and the second radiator  130  surrounds the first radiator  120 . In this embodiment, the second radiator  130  includes a first section  132  and a second section  134 . The first section  132  is at a designated distance D 1  from the first radiator  120  in a first designated direction (i.e., +Z axis). The second section  134  is at a designated distance D 2  from the first radiator  120  in a second designated direction (i.e., +Y axis). The first radiator  120  is at a designated distance D 3  from the grounding element  150  in a direction opposite to the first designated direction (i.e., −Z axis). In addition, the short point  160  is coupled between the second section  134  of the second radiator  130  and the grounding element  150 . The feeding point  170  is coupled between a joint point of the first radiator  120  and the second radiator  130  and the grounding element  150 . In other words, the first radiator  120 , the second radiator  130 , the short point  160 , the grounding element  150 , and the feeding point  170  are disposed around along a sealed region  180 , wherein the sealed region  180  is a U type. 
     Please note that, the abovementioned “surround” does not mean that the second radiator  130  must completely surround the first radiator  120  but is disposed around the first radiator  120  partially. 
     Please keep referring to  FIG. 1 . A current I 1  flows through the first radiator  120  and a current I 2  flows through the second radiator  130  in the direction of the two arrows shown in  FIG. 1 . In this embodiment, through disposing the sections  132  and  134  of the second radiator  130  around the first radiator  120 , together with a capacitor effect generated from each section of the second radiator  130  and the first radiator  120  at more than one location and a capacitor effect generated from the first radiator  120  and the grounding element  150 , the impedance matching of the antenna structure  100  can be changed. Through adjusting parameters such as the designated distances D 1 , D 2 , and D 3 , a goal of increasing bandwidth of antenna can be achieved. 
     Please note that, as mentioned above, the first radiator  120  is a slender rectangle and the second radiator  130  has an L shape, but this is not a limitation of the present invention. Those skilled in the art should appreciate that various modifications of shapes of the first radiator  120  and the second radiator  130  may be made, and further description is omitted here for brevity. In addition, the location of the feeding point  170  is not unchangeable and can be moved to anywhere between locations A 1  and A 2  according to the arrow indicated in  FIG. 1 . 
     In this embodiment, the first radiator  120  resonates at an operating frequency band of higher frequency, wherein a length of the first radiator  120  is approximately one-fourth of a wavelength (λ/4) of a first resonance mode generated by the antenna structure  100 . The second radiator  130  resonates at an operating frequency band of lower frequency, wherein a length of the second radiator  130  is approximately one-fourth of a wavelength of a second resonance mode generated by the antenna structure  100 . Furthermore, through the capacitor effect generated from the second radiator  130  and the first radiator  120  at more than one location together with the capacitor effect generated from the first radiator  120  and the grounding element  150  (i.e., the capacitor effect generated by the designated distance D 1 , D 2 , and D 3 ), the two resonance modes can be combined to increase the bandwidth of antenna structure  100 . 
     Please refer to  FIG. 2 .  FIG. 2  is a diagram illustrating the return loss of the antenna structure  100  shown in  FIG. 1 . As shown in  FIG. 2 , the frequency 3.92 GHz and the return loss (−10.00 dB) of a first sign  1  and the frequency 5.45 GHz and the return loss (−9.83 dB) of a second sign  2  are marked. As is known from  FIG. 2 , the return loss falls below (−10 dB) for frequencies between 3.92 GHz and 5.45 GHz, which has a bandwidth approximately equaling 1.53 GHz (5.45 GHz−3.92 GHz=1.53 GHz). Thus an effective bandwidth percentage is substantially 1.53/4.685=32.65% ((5.45 GHz+3.92 GHz)÷2=4.685 GHz). Those skilled in the art should appreciate that the return loss can be transformed into the voltage standing wave ratio (VSWR) through equations, thus the return loss and the VSWR essentially have the same meaning. 
     Please refer to  FIG. 3 .  FIG. 3  is a diagram of an antenna structure  300  according to a second embodiment of the present invention, which is a varied embodiment of the antenna structure  100  shown in  FIG. 1 . In  FIG. 3 , the architecture of the antenna structure  300  is similar to that of the antenna structure  100 , and the difference between them is described in the following. The antenna structure  300  includes a radiation element  310 . A number of sections included by a second radiator  330  of the antenna structure  300  is different from that of the second radiator  130  of the antenna structure  100 . In  FIG. 3 , the second radiator  330  includes a first section  332 , a second section  334 , and a third section  336 , wherein the third section  336  partially overlaps the first radiator  120  and is at the designated distance D 3  from the first radiator  120  in the first designated direction (i.e., +Z axis), and is at a designated distance D 4  from grounding element  150  in the direction opposite to the first designated direction (i.e., −Z axis). There is a fillister  390  formed between the third section  336 , the short point  360 , and the grounding element  150  for generating capacitor effect. Furthermore, the shape and the location of the short point  360  included by the antenna structure  300  are different from that of the short point  160  in  FIG. 1 . Those skilled in the art should appreciate that this is not a limitation of the present invention and various modifications of the shape, size, and location of the short point may be made. For example, the short point can be implemented by the symbol  160  marked in  FIG. 1  or the symbol  360  marked in  FIG. 3 . Or the short point can be extended from the rear end of the second radiator  330 , such as the symbol  336  marked in  FIG. 3  or the symbol  960  marked in  FIG. 9 , which should also belong to the scope of the present invention. 
     Please keep referring to  FIG. 3 . The current I 1  flows through the first radiator  120  and a current I 3  flows through the second radiator  330  in the direction of the two arrows shown in  FIG. 3 . In this embodiment, through disposing each section  332 ,  334  and  336  of the second radiator  330  around the first radiator  120 , together with the capacitor effect generated from each section of the second radiator  330  and the first radiator  120  at more than one location, the capacitor effect generated from the first radiator  120  and the grounding element  150 , and the capacitor effect generated from the second radiator  330  and the grounding element  150 , the impedance matching of the antenna structure  300  can be changed. Through adjusting parameters such as the designated distances D 1 , D 2 , D 3 , and D 4 , a goal of increasing bandwidth of antenna can be achieved. 
     In addition, a comparison of the antenna structure disclosed in the present invention with a conventional dual-frequency antenna further expands advantages of the antenna structure disclosed in the present invention. Please refer to  FIG. 4  together with  FIG. 5 .  FIG. 4  is a diagram illustrating the VSWR of the conventional dual-frequency antenna, and  FIG. 5  is a diagram illustrating the VSWR of the antenna structure  300  shown in  FIG. 3 . The horizontal axis represents frequency (Hz), between 2 GHz and 6 GHz, and the vertical axis represents the VSWR. The conventional dual-frequency antenna mentioned herein means a planar inverted F antenna (PIFA) having two radiators, wherein the two radiators are located on different sides of the feeding point and extend in different directions. As shown in  FIG. 4 , there is only a bandwidth of 250 MHz having the VSWR fall below 2 near the frequency 2450 MHz. Thus an effective bandwidth percentage is substantially 250/2450=10.2%. As shown in  FIG. 5 , the VSWR falls below 2 for frequencies between 3.168 GHz and 4.752 GHz, which has an effective bandwidth percentage substantially equaling 1.584/3.96=40%. As can be known by comparing them, the effective bandwidth of the antenna structure  300  shown in  FIG. 3  is much better than that of the conventional dual-frequency antenna (1.58 GHz&gt;250 MHz). 
     Please refer to  FIG. 6 .  FIG. 6  is a diagram illustrating the return loss of the antenna structure  300  shown in  FIG. 3 . As shown in  FIG. 6 , the frequency 3.63 GHz and the return loss (−9.93 dB) of a third sign  3  and the frequency 5.24 GHz and the return loss (−10.20 dB) of a fourth sign  4  are marked. As is known from  FIG. 6 , the return loss falls below (−10 dB) for frequencies between 3.63 GHz and 5.24 GHz, which has a bandwidth approximately equaling 1.61 GHz (5.24 GHz−3.63 GHz=1.61 GHz). Thus an effective bandwidth percentage is substantially 1.61/4.435=36.3% ((5.25 GHz+3.63 GHz)÷2=4.435 GHz). 
     Please refer to  FIG. 7  together with  FIG. 8 .  FIG. 7  is a diagram illustrating a radiation pattern of the antenna structure shown in  FIG. 3 , and  FIG. 8  is a table illustrating an antenna gain of the antenna structure shown in  FIG. 3 .  FIG. 7  shows measurement results of the antenna structure  30  in the YZ plane. As can be seen, the radiation pattern of the antenna structure  300  is similar to a circle and is an omni-directional antenna.  FIG. 8  is a diagram marking out positions and values of the maximum, minimum, and average values of the antenna gain in each frequency band in  FIG. 7 . As can be seen, the average gains of the antenna structure  300  all fall above −2 dB in each frequency band. 
     Of course, the antenna structures  100  and  300  are merely one of the embodiments of the present invention, and, as is well known by persons of ordinary skill in the art, suitable variations can be applied to the antenna structures. In the following, several embodiments illustrate various modifications of the antenna structure disclosed in the present invention. 
     Please refer to  FIG. 9 .  FIG. 9  is a diagram of an antenna structure  900  according to a third embodiment of the present invention, which is a varied embodiment of the antenna structure  300  shown in  FIG. 3 . In  FIG. 9 , the architecture of the antenna structure  900  is similar to that in  FIG. 3 , and the difference between them is described in the following. In  FIG. 3 , the antenna structure  900  includes a radiation element  910 . A distance between the first radiator  120  and the third section  336  of the second radiator  330  is the same as a distance between the first radiator  120  and the grounding element  150 , wherein both of the distances are D 3 . In  FIG. 9 , a distance between the first radiator  120  and the third section  336  is D 3 , but a distance between the first radiator  120  and the grounding element  950  is D 5 , which are different from each other. In addition, an area of a first section  932  of the second radiator  930  is much greater than an area of the first section  332  of the second radiator  330  shown in  FIG. 3 , therefore, radiation efficiency of the second radiator  930  can be improved. Moreover, the shape and position of a short point  960  included by the antenna structure  900  are different from that of the short point  360  included by the antenna structure  300  shown in  FIG. 3 . 
     Please refer to  FIG. 10 .  FIG. 10  is a diagram of an antenna structure  1000  according to a fourth embodiment of the present invention, which is a varied embodiment of the antenna structure  900  shown in  FIG. 9 . In  FIG. 10 , the architecture of the antenna structure  1000  is similar to that in  FIG. 9 , and the difference between them is that the antenna structure  1000  further includes a third radiator  970  coupled between the feeding point  170  and the grounding element  950 . The third radiator  970  overlaps the second radiator  930  and is at a designated distance D 6  from the second radiator  930  in the second designated direction (i.e., +Y axis). Therefore, through adding the third radiator  970  into the antenna structure  1000 , a third resonance mode with another frequency band can be generated to form a three-frequency antenna. In addition, the impedance matching of the antenna structure  1000  can be changed through adjusting the capacitor effect (i.e., adjusting the designated distance D 6 ) generated from the third radiator  970  and the second radiator  930 . Furthermore, if the short point  960  is removed, the first radiator  120 , the second radiator  930 , the grounding element  950 , and the feeding point  170  are disposed around along a region with an inverted S type shape. At this time, the distance between the first radiator  120  and the second radiator  930  still can be adjusted to change the impedance matching and the distance between the second radiator  930  and the third radiator  970  can also be adjusted to change impedance matching. 
     Of course, those skilled in the art should appreciate that the extending directions of the first radiator  120 , the second radiator  930 , and the third radiator  970  are not a limitation of the present invention. For example, an antenna structure, wherein extending directions of each radiator included by the antenna structure are totally opposite to the extending directions of each radiator included by the antenna structure  1000 . In other words, the antenna structure is the same as a bottom-view diagram of the antenna structure  1000  (+Y axis and −Y axis are swapped), which should also belong to the scope of the present invention. At this time, the first radiator  120 , the second radiator  930 , the grounding element  950 , and the feeding point  170  are disposed around along a region with an S type shape. 
     Please refer to  FIG. 11 .  FIG. 11  is a diagram illustrating the VSWR of the antenna structure  1000  shown in  FIG. 10 . The horizontal axis represents frequency (Hz), between 2 GHz and 6 GHz, and the vertical axis represents the VSWR. As shown in  FIG. 11 , the VSWR falls below 2 for frequencies between 2.4 GHz and 5.875 GHz, which has an effective bandwidth percentage substantially equaling 3.475/4.138=83.98%. Moreover, the antenna structure  1000  covers three frequency bands 2.4 GHz-2.702 GHz, 3.3 GHz-3.8 GHz and 5.15 GHz-5.875 GHz in total. 
     Please refer to  FIG. 12 .  FIG. 12  is a diagram of an antenna structure  1200  according to a fifth embodiment of the present invention, which is a varied embodiment of the antenna structure  1000  shown in  FIG. 10 . In  FIG. 12 , the architecture of the antenna structure  1200  is similar to that in  FIG. 10 , and the difference between them is that each element of the antenna structure  1200  presents a solid form and locates on different planes. For example, a radiation element  1210  locates on the YZ plane, and a first part  1252  of a grounding element  1250  locates on the XY plane but a second part  1254  of the grounding element  1250  locates on the YZ plane. As shown in  FIG. 10 , each element of the antenna structure  1000  locates on the same plane. As can be known, the locating plane of each element of the antenna structure should not be considered to be limitations of the scope of the present invention. Those skilled in the art should appreciate that various modifications of the locating plane of each element of the antenna structure may be made without departing from the spirit of the present invention. 
     Please refer to  FIG. 13 .  FIG. 13  is a diagram of an antenna structure  1300  according to a sixth embodiment of the present invention, which is another varied embodiment of the antenna structure  900  shown in  FIG. 9 . In  FIG. 13 , the antenna structure  1300  includes a radiation element  1310 . The architecture of the antenna structure  1300  is similar to that in  FIG. 9 , and the difference between them is that a location of a feeding point  1370  of the antenna structure  1300  is different from that of the feeding point  170  shown in  FIG. 9 . In addition, an area of a first section  1332  of a second radiator  1330  shown in  FIG. 13  is much greater than the area of the first section  932  of the second radiator  930  in  FIG. 9 , therefore, radiation efficiency of the second radiator  1330  can be improved. 
     From the above descriptions, the present invention provides the antenna structures  100 - 1300 . Through disposing each section of the second radiator around the first radiator, together with the capacitor effect generated from each section of the second radiator and the first radiator at more than one location, the capacitor effect generated from the second radiator and the grounding element, the capacitor effect generated from the first radiator and the grounding element, the impedance matching of antenna can be changed. In addition, through adjusting parameters such as the designated distances D 1 -D 6 , a goal of increasing bandwidth of antenna can be achieved. Compared with the conventional dual-frequency antenna, the effective bandwidth of the antenna structure disclosed in the present invention is much better than that of the conventional dual-frequency antenna. Hence, the antenna structures disclosed in the present invention are suitably applied to wireless communication products requiring transmission of a large number of data. In addition, because the antenna structures disclosed in the present invention can be easily manufactured without extra cost, disclosed the antenna structures are suitable for mass production. As can be known from the VSWR and the radiation pattern, the antenna structures disclosed in the present invention have the advantages of providing omni-directional radiation patterns, small size, low cost, and covering multiple frequency bands of wireless communication systems. Therefore, the antenna structures disclosed in the present invention are suitably applied to portable device or wireless communication devices of other types. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.