Patent Publication Number: US-2012032870-A1

Title: Broadband antenna using coupling matching with short-circuited end of radiator

Description:
TECHNICAL FIELD 
     Example embodiment of the present invention relates to an antenna, more particularly relates to an antenna for implementing impedance matching for wide band. 
     BACKGROUND ART 
     In current mobile terminals, there is a demand for functions that allow a user access to mobile communication services of different frequency bands through a single terminal. That is, there is a demand for a terminal with which a user may simultaneously utilize signals of multiple bands as necessary, from among mobile communication services of various frequency bands, such as the CDMA service based on the 824˜894 MHz band and the PCS service based on the 1750˜1870 MHz band commercialized in Korea, the CDMA service based on the 832˜925 MHz band commercialized in Japan, the PCS service based on the 1850˜1990 MHz commercialized in the United States, the GSM service based on the 880˜960 MHz band commercialized in Europe and China, and the DCS service based on the 1710˜1880 MHz band commercialized in parts of Europe. 
     Furthermore, there is a demand for a composite terminal that allows the use of services such as Bluetooth, ZigBee, wireless LAN, GPS, etc. In this type of terminal for using services of multiple bands, a multi-band antenna is needed, which can operate in two or more desired bands. The antennas generally used in mobile terminals include the helical antenna and the planar inverted-F antenna (PIFA). 
     The helical antenna is an external antenna that is secured to an upper end of a terminal, and is used together with a monopole antenna. In an arrangement in which a helical antenna and a monopole antenna are used together, extending the antenna from the main body of the terminal allows the antenna to operate as a monopole antenna, while retracting the antenna allows the antenna to operate as a λ/4 helical antenna. While this type of antenna has the advantage of high gain, its non-directivity results in undesirable SAR characteristics, which form the criteria for levels of electromagnetic radiation hazardous to the human body. In addition, since the helical antenna is formed protruding outwards of the terminal, it is difficult to design the exterior of the terminal to be aesthetically pleasing and suitable for carrying. 
     The inverted-F antenna is an antenna designed to have a low profile structure in order to overcome such drawbacks. The inverted-F antenna has directivity, and when current induction to the radiating part generates beams, a beam flux directed toward the ground surface may be re-induced to attenuate another beam flux directed toward the human body, thereby improving SAR characteristics as well as enhancing beam intensity induced to the radiating part. Also, the inverted-F antenna operates as a rectangular micro-strip antenna, in which the length of a rectangular plate-shaped radiating part is reduced in half, whereby a low profile structure may be realized. 
     Since the inverted-F antenna has the directive radiation characteristics, the inverted-F antenna may have excellent electromagnetic radiation absorption rate compared to the helical antenna. However, the inverted-F antenna may have a narrow frequency bandwidth, and thus it is difficult to design an antenna operating in multiple bands. 
     In addition, the frequency characteristics of the inverted-F antenna may be easily changed due to external factors such as hand effect or head effect. 
     DISCLOSURE 
     Technical Problem 
     To resolve the problems in prior art described above, an objective of the present invention provides an antenna for implementing wide band characteristics with maintaining low profile characteristics. 
     Another objective of the present invention provides an antenna for implementing wide band characteristics through coupling matching. 
     Still another objective of the present invention provides an antenna of which frequency characteristics is less changed by external factors such as hand effect and head effect. 
     Technical Solution 
     To achieve the objectives above, an aspect of the present provides a wide-band antenna using a coupling method comprising: a first conductive element connected electrically to a first ground; a second conductive element connected electrically to a feeding part, and spaced from the first conductive element by a certain distance; and a third conductive element extending from the first conductive element and configured to output a RF signal, an end point of the third conductive element being coupled to a second ground, wherein the first conductive element and the second conductive element have a certain length to generate a travelling wave and implement adequate coupling. 
     The first conductive element and the second conductive element operate as an impedance matching/feeding part, and impedance matching between the first conductive element and the second conductive element is performed through coupling generated in the impedance matching/feeding part. 
     The first ground is identical to the second ground. 
     A radiation frequency is determined by a length of the first conductive element and a length of the third conductive element, and the electrical length of the first conductive element and the electrical length of the third conductive element are set 0.5 times the wavelength. 
     The wide-band antenna further comprises a fourth conductive element coupled to a third ground and spaced from the first conductive element by a certain distance, and configured to operate as another radiator. 
     Another aspect of the present invention provides a wide-band antenna using a coupling method comprising: a first conductive element connected electrically to a ground; a second conductive element connected electrically to a feeding part, and spaced from the first conductive element by a certain distance; and a third conductive element extending from the first conductive element and configured to output a RF signal, an end point of the third conductive element being coupled to the ground, wherein, a plurality of open stubs protrude from the first conductive element and the second conductive element, the plurality of open stubs protruding between the first conductive element and the second conductive element. 
     The open stubs protruding from the first conductive element and the second conductive element mesh with one another. 
     The open stubs have a uniform width and length. 
     The open stubs have partially varying widths and lengths. 
     The wide-band antenna further comprises a fourth conductive element coupled to the ground, the fourth conductive element being spaced from the first conductive element by a certain distance, and configured to operate as a radiator for another band. 
     Advantageous Effects 
     Certain aspects of the present invention can provide antennas for implementing wide band characteristics with maintaining a low profile structure, and its frequency characteristics may be less changed by external factors such as hand effect and head effect. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       Example embodiments of the present invention will become more apparent by describing in detail example embodiments of the present invention with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a conceptual structure of a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to the first example embodiment of the present invention; 
         FIG. 2  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a first example embodiment of the present invention; 
         FIG. 3  illustrates a conceptual structure of a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a second example embodiment of the present invention; 
         FIG. 4  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to the second example embodiment of the present invention; 
         FIG. 5  illustrates a conceptual structure of a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a third example embodiment of the present invention; 
         FIG. 6  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to the third example embodiment of the present invention; 
         FIG. 7  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a fourth example embodiment of the present invention; and 
         FIG. 8  illustrates S 11  parameter of the antenna according to the fourth embodiment of the present invention. 
     
    
    
     MODE FOR INVENTION 
     Hereinafter, wide-band antennas using a coupling method according to embodiments of the present invention will be described in detail with reference to accompanying drawings. 
       FIG. 1  illustrates a conceptual structure of a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to the first example embodiment of the present invention.  FIG. 2  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a first example embodiment of the present invention. 
     In  FIG. 1 , the wide-band antenna of the present embodiment may include a first conductive element  100  connected electrically to a ground, a second conductive element  102  connected electrically to a feeding part and a third conductive element  104  extending from the first conductive element  100 . 
     The first conductive element  100  coupled to the ground and the second conductive element  102  coupled to the feeding part are formed with a particular gap in-between. It is desirable that the first conductive element  100  and the second conductive element  102  are arrayed in parallel, but this array is not necessary. The first conductive element  100  and the second conductive element  102  operate as an impedance matching/feeding part  130 . 
     The impedance matching/feeding part  130  performs impedance matching and coupling feeding. A traveling wave is generated between the first conductive element  100  and the second conductive element  102  in the impedance matching/feeding part  130 , and a certain power is fed to the first conductive element  100  from the second conductive element  102  through coupling. 
     If the impedance matching for wide band is implemented in the impedance matching/feeding part  130 , enough coupling should be performed between the first conductive element  100  and the second conductive element  102 . In order for enough coupling, the first conductive element  100  and the second conductive element  102  must assure a given length. When the conductive elements  100  and  102  have the greater length, the wider band may be realized. 
     The third conductive element  104  extends from the first conductive element  100  related to the coupling matching, and operates as a radiator. As shown in  FIG. 1  and  FIG. 2 , an end point of the third conductive element  104  operating as the radiator is connected electrically to the ground, and so the third conductive element  104  operates as a loop radiator. Since a radiation frequency of the antenna is determined by the lengths of the conductive elements  100  and  104  and the third conductive element  104  operates as the loop radiator, the lengths of the conductive elements  100  and  104  may have approximately 0.5 times the wavelength (λ) corresponding to frequency used. 
     As shown in  FIG. 1  and  FIG. 2 , in case that the coupling matching and the coupling feeding are performed with utilizing the loop radiator of which the end point is shorted, the antenna may be excellent in view of hand effect and head effect, and obtain the wide band characteristics. 
     In  FIG. 2 , the first conductive element  100  is connected electrically to the ground formed on a substrate  200 , and the second conductive element  102  is connected electrically to a feeding line. It is desirable that the ground, to which the end point of the third conductive element  104  is coupled, is identical to the ground to which the first conductive element  100  is coupled. 
     On the other hand, the first conductive element  100 , the second conductive element  102  and the third conductive element  104  included in the antenna in  FIG. 2  may be combined on a carrier of the antenna. 
       FIG. 3  illustrates a conceptual structure of a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a second example embodiment of the present invention.  FIG. 4  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to the second example embodiment of the present invention. 
     In  FIG. 3  and  FIG. 4 , the antenna of the present embodiment may include a first conductive element  300  connected electrically to a ground, a second conductive element  302  connected electrically to a feeding part, a third conductive element  304  extended from the first conductive element  300 , and plural open stubs  310  protruded from the first conductive element  300  and the second conductive element  302 . Here, an end point of the third conductive element  304  is shorted. 
     In the antenna of the second embodiment shown in  FIG. 3  and  FIG. 4  unlike in the first embodiment, the open stubs  310  protrude from the conductive elements  300  and  302 , operating as an impedance matching/feeding part  330 , between the conductive elements  300  and  302 .  FIG. 3  and  FIG. 4  show the open stubs  310  having a rectangular shape, but it will be immediately obvious to those skilled in the art that the open stubs  310  have another shape. 
     As described above, the wider band may be obtained when the conductive elements  300  and  302  have the greater length. This means that the impedance matching for the wider band may be obtained by increasing capacitance component between the first conductive element  300  and the second conductive element  302 . Accordingly, the impedance matching for the wide band may be obtained when the distance between the first conductive element  300  and the second conductive element  302  is short. 
     The open stubs  310  protruding from the first conductive element  300  and the second conductive element  302  in  FIG. 3  and  FIG. 4  substantially increase electrical lengths of the first conductive element  300  and the second conductive element  302 , and thus the impedance matching for the wide band may be performed though the conductive elements  300  and  302  have limited lengths. When the open stubs  410  protrude from the first conductive element  400  and second conductive element  402  in this manner to mesh with one another, the distance between the first conductive element  400  and the second conductive element  402  may be reduced, so that a greater capacitance value may be obtained during the coupling matching, and the impedance matching may be obtained for a wider band. 
     That is, the structure having plurality of open stubs protruding from the first conductive element and second conductive element and meshing with one another can not only substantially increase the electrical length of the first conductive element and second conductive element, but also reduce the distance between the first conductive element and second conductive element, so that a longer electrical length and a larger capacitance component may be obtained, which allow impedance matching for wider band even with a limited size. 
     The third conductive element  304  extending from the first conductive element  300  related to the coupling matching, and operates as a radiator. As shown in  FIG. 3  and  FIG. 4 , an end point of the third conductive element  304  operating as the radiator is connected electrically to the ground, and so the third conductive element  304  operates as a loop radiator. Since a radiation frequency of the antenna is determined by the electrical lengths of the conductive elements  300  and  304  and the third conductive element  304  operates as the loop radiator, the lengths of the conductive elements  300  and  304  may have approximately 0.5 times the wavelength (λ) corresponding to an use frequency. 
       FIG. 5  illustrates a conceptual structure of a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a third example embodiment of the present invention.  FIG. 6  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to the third example embodiment of the present invention. 
     In  FIG. 5  and  FIG. 6 , an antenna of the present embodiment may include a first conductive element  500  connected electrically to a ground, a second conductive element  502  connected electrically to a feeding part, a third conductive element  504  extending from the first conductive element  500 , first open stubs  510  protruding from the first conductive element  500  and second open stubs  512  protruding from the second conductive element  502 . 
     Shapes of the open stubs  510  and  512  protruding from the conductive elements  500  and  502  in the third embodiment shown in  FIG. 5  and  FIG. 6  are different from those in the second embodiment. In the second embodiment, the open stubs  301  protruding from the conductive elements  300  and  302  have the same widths and lengths. In other words, the open stubs  310  in the second embodiment are formed uniformly, but the open stubs  510  and  512  in the third embodiment are not formed uniformly. 
     In  FIG. 5  and  FIG. 6 , the first open stubs  510  protruding from the first conductive element  500  may be structured to increase in width and length and then decrease again, and the second open stubs  612  that protrude from the second conductive element  602  may be structured to increase in width and length and then decrease again, also. 
     Capacitance component for the coupling is diversified by varying the widths and the lengths of the open stubs  510  and  512  protruding from the conductive elements  500  and  502 . In case that the capacitance component between the first conductive element  500  and the second conductive element  502  is diversified, the impedance matching for wider band may be obtained. 
     The structure of the open stubs  510  and  512  shown in  FIG. 5  and  FIG. 6  is one example, and it will be obvious to those skilled in the art that the widths and the lengths of the open stubs  510  and  512  may be variously modified. For example, only the width of the first open stubs may be varied without varying length of the first open stubs. Otherwise, the width or the length may be varied for only one of the first open stub and the second open stub. 
       FIG. 7  illustrates a wide-band internal antenna, in which an end point of a radiator is shorted, using a coupling method according to a fourth example embodiment of the present invention. 
     In  FIG. 7 , the antenna of the present embodiment may include a first conductive element  700  connected electrically to a ground, a second conductive element  702  connected electrically to a feeding part, a third conductive element  704  extending from the first conductive element  700 , open stubs  710  protruding from the first conductive element  700  and the second conductive element  702 , and a fourth conductive element  750  spaced from the first conductive element  700  by a certain distance and connected electrically to the ground. 
     The antenna of the fourth embodiment further includes the fourth conductive element  750  compared with the second embodiment, the fourth conductive element  750  operating as a second radiator. In  FIG. 7 , the fourth conductive element  750  is adjacent to the first conductive element  700 , and a certain power is fed to the fourth conductive element  750  from the first conductive element  700  through a coupling method. On the other hand it will be immediately obvious to those skilled in the art that the fourth conductive element  720  may be adjacent to the second conductive element  702 , and a certain power may be fed to the fourth conductive element  720  from the second conductive element  702  through the coupling method, thereby outputting a RF signal. 
     The fourth conductive element  750  operating as the second radiator radiates the RF signal in higher frequency band than the third conductive element  704  operating as a first radiator. 
       FIG. 8  is a view illustrating S 11  parameter of the antenna according to the fourth embodiment of the present invention. 
     As shown in  FIG. 8 , in a low frequency band, a resonance band is formed by the third conductive element of which the end point is coupled to the ground. Here, the antenna has wide band characteristics due to the coupling between the first conductive element and the second conductive element. In a high frequency band of approximately 2 GHz, multiple resonance in accordance with the third conductive element and a resonance in accordance with the fourth conductive element are combined, i.e. dual resonance is generated, and so the wide band characteristics may be obtained.