Abstract:
An antenna structure having a ground element and an antenna element is provided. The antenna element is disposed on a dielectric substrate, and includes a first radiation portion, a second radiation portion, and a spiral metal line. An end of the first radiation portion is a feeding point of the antenna element, and another end is open. An end of the second radiation portion is electrically coupled to the ground element, and the length of the second radiation portion is greater than that of the first radiation portion. The first radiation portion is surrounded by the second radiation portion. An end of the spiral metal line is coupled to the first radiation portion. The spiral metal line contributes a parallel resonance outside the antenna&#39;s operating band, and results in a resonant mode generated within the antenna element&#39;s operating band such that the operating bandwidth of the antenna element is increased.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a communication electronic device and an antenna structure thereof, and more particularly, to a communication electronic device having a small-size planar antenna utilizing parallel resonance to generate multi-band operation. 
     2. Description of the Prior Art 
     With the rapid development of mobile communication technologies and markets, wireless access capabilities are indispensable to portable communication electronic devices. In addition to wireless local area network (WLAN), wireless wide area network (WWAN) is able to provide services over a wide coverage, and long term evolution (LTE) technology can provide higher data rates, thereby improving convenience and providing real time in wireless access while using the portable communication electronic devices. On the other hand, slim-profile design is becoming more attractive in market for the communication electronic device. Hence, it is critical to design a planar printed antenna having the capability of covering multi-band operation for a slim mobile device. 
     U.S. Patent (U.S. Pat. No. 7978141 B2) entitled “Coupled-fed multi-band loop antenna” discloses designing a dual-band antenna used in a communication electronic device, wherein the antenna has two operating bands. However, the lower operating band of the antenna fails to cover multi-band operation. As a result, such an antenna cannot be applied for covering all the lower operating bands in the WWAN or LTE system. 
     Apparently, it is necessary to provide a communication electronic device, which has two wide operating bands. For example, the operating bands can cover 824˜960 MHz as well as 1710˜2170 MHz. Additionally, the antenna element should have the attractive characteristics of planar structure and small size. 
     SUMMARY OF THE INVENTION 
     The present invention provides a communication electronic device having a built-in antenna element. The antenna element has a spiral metal line, which can increase an operating bandwidth of the antenna element. As the spiral metal line has a small size, it therefore does not increase the size of the antenna element. Therefore, the antenna element of the present invention has the advantages of small size, planar structure, and multi-band operation. 
     According to a first aspect of the present invention, a communication electronic device has an antenna structure. The antenna structure comprises a ground element and an antenna element that is disposed on a dielectric substrate. The antenna element comprises a first radiation portion, a second radiation portion and a spiral metal line, wherein a first end of the first radiation portion is a feeding point of the antenna element, and a second end is an open end. One end of the second radiation portion is electrically coupled to the ground element. The second radiation portion is extended around the open end of the first radiation portion. A first end of the spiral metal line is electrically coupled to the first radiation portion. The spiral metal line contributes a parallel resonance at a frequency outside an operating band of the antenna element. The parallel resonance further contributes a resonant mode in the operating band, thereby increasing an operating bandwidth of the antenna element. 
     According to a second aspect of the present invention, an antenna structure comprises a ground element and an antenna element that is disposed on a dielectric substrate. The antenna element comprises a first radiation portion, a second radiation portion and a spiral metal line, wherein a first end of the first radiation portion is a feeding point of the antenna element, and a second end is an open end. One end of the second radiation portion is electrically coupled to the ground element. The second radiation portion is extended around the open end of the first radiation portion. A first end of the spiral metal line is electrically coupled to the first radiation portion. The spiral metal line contributes a parallel resonance at a frequency outside an operating band of the antenna element. The parallel resonance further contributes a resonant mode in the operating band, thereby increasing an operating bandwidth of the antenna element. 
     In one exemplary embodiment of the present invention, the second radiation portion of the antenna element generates a resonant mode at lower frequencies. The higher-order resonant mode of the second radiation portion can further combine with a resonant mode generated by the first radiation portion at higher frequencies to increase the operating bandwidth. Additionally, with the addition of the spiral metal line, the first end of the spiral metal line is electrically coupled to the first radiation portion, which generates a parallel resonance at a frequency outside the lower operating band of the antenna element. The parallel resonance will in turn generate a resonant mode in the lower operating band, which will be combined with the original resonant mode generated by the second radiation portion to increase the operating bandwidth of the antenna element. 
     In one exemplary embodiment of the present invention, the size of the antenna is only 12×40 mm 2 , and is able to cover the penta-band WWAN operation (824˜960/1710˜2170 MHz), thereby obtaining the advantages of small size, planar structure, and multi-band operation. 
     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. 1A  is a structural drawing of a communication electronic device with an antenna structure according to a first exemplary embodiment of the present invention. 
         FIG. 1B  is a diagram illustrating input impedance of the communication electronic device with the antenna structure. 
         FIG. 2A  is a structural drawing of a conventional communication electronic device with a conventional antenna structure. 
         FIG. 2B  is a diagram illustrating input impedance of the conventional communication electronic device with the conventional antenna structure. 
         FIG. 3  is a diagram illustrating return loss of the communication electronic device of  FIG. 1  and the conventional communication electronic device of  FIG. 2 . 
         FIG. 4  is a structural drawing of a communication electronic device with an antenna structure according to a second exemplary embodiment of the present invention. 
         FIG. 5  is a structural drawing of a communication electronic device with an antenna structure according to a third exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is of the best-contemplated mode of carrying out the present invention. A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     Certain terms are used throughout the following descriptions and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not differ in functionality. In the following discussion and in the claims, the terms “include”, “including”, “comprise”, and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “couple” and “coupled” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     Please refer to  FIG. 1A  in conjunction with  FIG. 1B .  FIG. 1A  is a structural drawing of a communication electronic device with an antenna structure  1  according to a first exemplary embodiment of the present invention.  FIG. 1B  is a diagram illustrating the input impedance of the communication electronic device with the antenna structure  1  according to the first exemplary embodiment of the present invention. In the first exemplary embodiment, the communication electronic device with the antenna structure  1  comprises a ground element  10  and an antenna element  11 . The antenna element  11  is disposed on a dielectric substrate  12 , and comprises a first radiation portion  13 , a second radiation portion  14  and a spiral metal line  15 . A first end of the first radiation portion  13  is a feeding point  131  of the antenna element  11 , the signal is fed through a coaxial line  16  connected thereto. Additionally, a second end of the first radiation portion  13  is an open end  132 . One end  141  of the second radiation portion  14  is electrically coupled to the ground element  10 . A length of the second radiation portion  14  is greater than that of the first radiation portion  13 . The second radiation portion  14  is extended around the open end  132  of the first radiation portion  13 . A first end  151  of the spiral metal line  15  is electrically coupled to the first radiation portion  13 . The spiral metal line  15  can contribute a parallel resonance  43  (as shown in  FIG. 1B ) at a frequency outside a lower band  31  (shown in  FIG. 3 ) of the antenna element  11 . The parallel resonance  43  generates an additional resonant mode  312  (as shown in  FIG. 3 ) in the lower band  31  such that an operating bandwidth of the antenna in the lower band  31  can be increased. It should be noted that, in this embodiment, the first radiation portion  13  is implemented using a monopole antenna. 
     Further, in this embodiment, a second end  152  of the spiral metal line  15  is an open end and spirals inward. The spiral metal line  15  spirals in a rectangular shape. However, these should not be considered as limitations of the present invention. Additionally, in this embodiment, the length of the spiral metal line  15  is close to one quarter of a wavelength of the center frequency of the parallel resonance  43  (as shown in  FIG. 1B ). 
     Please refer to  FIG. 2A  in conjunction with  FIG. 2B .  FIG. 2  is a structural drawing of a conventional communication electronic device with a conventional antenna structure  2  thereof.  FIG. 2B  is a diagram illustrates input impedance of the conventional communication electronic device with the conventional antenna structure  2 . As shown in  FIG. 2A , the communication electronic device and the antenna structure  2  comprise a ground element  20  and an antenna element  21 . The antenna element  21  is disposed on a dielectric substrate  22 , and comprises a first radiation portion  23  and a second radiation portion  24 . A first end of the first radiation portion  23  is a feeding point  231  of the antenna element  21 , and the signal is fed through a coaxial line  26  connected thereto. The second end of the first radiation portion  23  is an open end  232 . The first radiation portion  23  can contribute a resonant mode (as shown in  FIG. 3 ) at a higher band  32  of the antenna element  21 . A first end  241  of the second radiation portion  24  is electrically coupled to the ground element  20 . A length of the second radiation portion  24  is greater than that of the first radiation portion  23 . The second radiation portion  24  is extended around the open end  232  of the first radiation portion  23 . Also, the second radiation portion  24  can contribute a resonant mode (e.g. the resonant mode  313  shown in  FIG. 3 ) at a lower band  31  of the antenna element  21 . However, the bandwidth of the resonant mode is narrow, which fails to cover multi-band operation. 
     The difference between the communication electronic device with the antenna structure  1  of  FIG. 1  and the conventional communication electronic device with the conventional antenna structure  2  is that the antenna element  11  of the communication electronic device with the antenna structure  1  additionally includes the spiral metal line  15 . With the spiral metal line  15 , a parallel resonance can be generated at a frequency outside the lower band of the antenna element  11 . The parallel resonance will in turn generate a resonant mode in the lower band, which can be further combined with the original resonant mode of the second radiation portion, thereby increasing the operating bandwidth of the antenna element  11 . 
     Please refer to  FIG. 3 , which is a diagram illustrating return loss of the communication electronic device  1  as shown in  FIG. 1A  and the conventional communication electronic device  2  as shown in  FIG. 2A . In the first exemplary embodiment, the first radiation portion  13  of the communication electronic device  1  generates at least one resonant mode in a second (higher frequency) operating band  32 . The second radiation portion  14  of the communication electronic device  1  generates at least one resonant mode in the first (lower frequency) operating band  31 . 
     Please refer to  FIG. 1B  in conjunction with  FIG. 2B  and  FIG. 3 .  FIG. 1B  is a diagram illustrating the input impedance of the communication electronic device with the antenna structure  1 .  FIG. 2B  is a diagram illustrating the input impedance of the conventional communication electronic device with the antenna structure  2 .  FIG. 3  is a diagram illustrating return loss of the communication electronic device  1  of  FIG. 1A  and the conventional communication electronic device  2  of  FIG. 2A . As shown in  FIG. 1B , the input impedance of the communication electronic device  1  has a real part  41  and an imaginary part  42 . As shown in  FIG. 2B , the input impedance of the communication electronic device  2  has a real part  51  and an imaginary part  52 . 
     In the communication device shown in  FIG. 2A , a length of the ground element  20  is about 150 mm and a width of the ground element  20  is about 200 mm; a length of the dielectric substrate  22  is about 40 mm, a width of the dielectric substrate  22  is about 12 mm and a thickness of the dielectric substrate  22  is about 0.8 mm. A length of the first radiation portion  23  is about 30 mm and a length of second radiation portion  24  is about 75 mm. The second radiation portion  24  can cause a quarter-wavelength resonant mode  313 . Since the impedance of the resonant mode  313  has a larger real part, the bandwidth of the resonant mode  313  will be narrow and fail to cover multi-band operation with the 6-dB return-loss definition (which is the design specification widely used for the mobile communication device antennas). In the communication electronic device  1  as shown in  FIG. 1 , the sizes of the elements are chosen as the similar sizes of the elements of the conventional communication electronic device  2  shown in  FIG. 2A . Further, a length of the spiral metal line  15  is about 60 mm. The second radiation portion  14  can cause the quarter-wavelength resonant mode  311  and the higher-order resonant mode. The spiral metal line  15  can contribute a parallel resonance  43  (having a center frequency at about 1.1 GHz) at a frequency outside the lower band  31  of the antenna element  11 . The parallel resonance  43  generates an additional resonance around the resonant mode  311  (e.g. the zero imaginary part of the impedance as shown in  FIG. 1B ), thereby generating a resonant mode  312 . The resonant mode  312  and the resonant mode  311  generated by the second radiation portion  14  collectively generate the first (lower frequency) operating band (e.g. the operating band  31  shown in  FIG. 3 ) . The first radiation portion  13  can cause a quarter-wavelength resonant mode. The quarter-wavelength resonant mode and the higher-order resonant mode generated by the second radiation portion  14  collectively generate the second (higher frequency) operating band (e.g. the operating band  32  shown in  FIG. 3 ). Under the definition of  6  dB return loss, the first operating band  31  covers at least the dual-band operation of GSM850/900 (from about 824 to 960 MHz). The second operating band  32  covers at least the triple-band operation of GSM1800/1900/UMTS (from about 1710 to 2170 MHz). Compared to the conventional communication electronic device  2 , the operating bandwidth of the communication electronic device  1  is significantly increased by the spiral metal line  15 , thereby allowing the first operating band  31  to achieve multi-band operation. 
     Please refer to  FIG. 4 , which is a structural drawing of a communication electronic device with an antenna structure  6  thereof according to a second exemplary embodiment of the present invention. In the second exemplary embodiment, the antenna structure is basically similar to the antenna structure of the first exemplary embodiment. However, the difference between these two exemplary embodiments is that structures of the antenna element  61  and the spiral metal line  65  are changed. In the second exemplary embodiment, the spiral metal line  65  can spiral in circular shapes. Since the antenna structure of the second exemplary embodiment is similar to that of the first exemplary embodiment, effects of the second exemplary embodiment are also similar to those of the first exemplary embodiment. 
     Please refer to  FIG. 5 , which is a structural drawing of a communication electronic device with an antenna structure  7  according to a third exemplary embodiment of the present invention. The antenna structure of the third exemplary embodiment is basically similar to the antenna structure of the first exemplary embodiment. The difference between the antenna structures of these two exemplary embodiments is that the position to which the antenna element  71  and the spiral metal line  75  are electrically coupled is changed. Also, the spiral metal line  75  is adjusted to determine the center frequency of the parallel resonance generated by the spiral metal line  75 . Since the antenna structure of the third exemplary embodiment is similar to that of the first exemplary embodiment, effects of the third exemplary embodiment are also similar to those of the first exemplary embodiment. 
     The abovementioned embodiments are presented merely to illustrate practicable designs of the present invention, and in no way should be considered to be limitations of the scope of the present invention 
     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. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.