Abstract:
Disclosed is an antenna capable of micro-tuning and macro-tuning for a wireless terminal, comprising: a radiator radiating electromagnetic waves; a ground connected to the radiator; at least one switching element positioned at a lengthwise region of the radiator, for shorting or opening the region of the radiator; and a voltage controlling element positioned at the radiator between the switching element and the ground, for controlling the extent of a voltage potential applied across the radiator. In accordance with the present invention, the antenna is capable of the macro-tuning between the service bands and micro-tuning for channel control within the service bands. Furthermore, the size of the antenna is significantly reduced and the antenna is installed on a circuit board in a patch type, thereby simplifying a work process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2006-0062027, filed Jul. 3, 2006, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna capable of micro tuning and macro tuning for a wireless terminal, and more particularly, to an antenna capable of micro tuning and macro tuning for a wireless terminal, which is capable of control in a dual service band having a difference of a certain or higher frequency, and which is capable of frequency tuning between channels in each service band. 
     2. Description of the Related Art 
     As wireless communication has been developed, wireless network can be accessed by wireless terminals, such as personal computers, notebooks, mobile phones, PDA and so on. The technology for supporting the wireless access to network in real time in mobile working environment is called wireless local-area network (WLAN). 
     According to the WLAN standards of IEEE 802.11, in IEEE 802.11b, wireless signals are transmitted and received through the 2.4 GHz frequency band which is the industrial, scientific and medical (ISM) band, and in IEEE 802.11a, wireless signals are transmitted and received through the 5 GHz frequency band which is the unlicensed national information infrastructure (UNII) band. 
     In the 2.4 GHz, which is the frequency band for IEEE 802.11b, transmission at the bandwidth of 83.5 MHz, from 2.4 GHz to 2.4835 GHz, is permitted. In the 5 GHz, which is the frequency band for IEEE 802.11a, transmission at the bandwidth of a total of 300 MHz, from 5.15 GHz to 5.35 GHz and from 5.725 GHz to 5.825 GHz, is permitted. 
     The WLAN service has a different frequency band according to the standards utilized. Consequently, the standards may change at any time or in different localities. In this case, since an existing wireless terminal is manufactured so as to process signals within the frequency band according to one standard only, a user may need to purchase another terminal for a new standard. To prevent such waste, a wireless terminal which functions in different standards needs to be developed. 
     In order to operate a wireless terminal in the frequency bands of both standards, an antenna has to operate in both frequency bands. For this purpose, a wireless terminal is provided with an antenna operating in both frequency bands. That is, an antenna having a very broad frequency band may be installed to operate in the frequency band of 2.4 GHz to 5 GHz, or an antenna having a dual frequency band may be installed to separately operate in the frequency band of 2.4 GHz and in the frequency band of 5 GHz. 
     However, when using the antenna operating in the very broad frequency band of 2.4 GHz to 5 GHz, noise and interference occur in a non-use band. 
     Due to the aforementioned problem, antenna developing industries have developed an antenna separately operating in each of the 2.4˜2.5 GHz and 4.9˜5.9 GHz frequencies. However, this antenna has not yet been sufficiently small in size. When using the antenna separately operating in the both frequency bands, tuning performance between channels in each frequency band is not taken into consideration. 
     SUMMARY 
     Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above. 
     The present invention provides an antenna capable of micro-tuning and macro-tuning for a wireless terminal, which is capable of control between the dual service band having a difference of a certain or higher frequency and which is capable of frequency tuning between channels in each service band. 
     Also, the present invention provides an antenna capable of micro-tuning and macro-tuning for a wireless terminal, which is small in size. 
     According to an aspect of the present invention, there is provided an antenna capable of micro-tuning and macro-tuning for a wireless terminal, comprising: a radiator radiating electromagnetic waves; a ground connected to the radiator; at least one switching element positioned at a lengthwise region of the radiator, for shorting or opening the region of the radiator; and a voltage controlling element positioned at the radiator between the switching element and the ground, for controlling the extent of a voltage potential across the radiator. 
     Preferably, the radiator may comprise a meander line part being severally bent in zigzags. 
     Preferably, the switching element may be a PIN diode. 
     Preferably, the antenna may further comprise a switching controller for applying a certain or higher voltage to the switching element to be turned on. 
     Preferably, upon turning on the switching element, the radiator may operate in a lower frequency band than upon turning off the switching element, and upon turning off the switching element, the radiator may operate in a higher frequency band than upon turning on the switching element. 
     Preferably, a plurality of the switching elements may be positioned, at a predetermined distance, along the direction of the length of the radiator. 
     Preferably, the voltage-controlling element may be a varactor diode. 
     The antenna may further comprise a reverse voltage adjuster for supplying a reverse voltage to the voltage-controlling element. 
     The operation frequency may be controlled within a predetermined frequency bandwidth, according to the extent of the reverse voltage applied to the voltage-controlling element. 
     The operation frequency may increase within the predetermined frequency bandwidth as the extent of the reverse voltage applied to the voltage controlling element increases. 
     According to the extent of the reverse voltage applied to the voltage-controlling element, upon turning on the switching element, the operation frequency may be controlled within a predetermined frequency bandwidth included in a lower frequency band than upon turning off the switching element, and upon turning off the switching element, the operation frequency may be controlled within a predetermined frequency bandwidth included in a higher frequency band than upon turning on the switching element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawing figures, wherein; 
         FIG. 1  is a perspective view illustrating an antenna for a wireless terminal, in accordance with an embodiment of the present invention; 
         FIG. 2  is a front view illustrating the antenna of  FIG. 1 ; 
         FIG. 3  is a bottom view illustrating the antenna of  FIG. 1 ; 
         FIG. 4A  is a graph illustrating a resonance point of an antenna when a PIN diode is turned on; 
         FIG. 4B  is a graph illustrating a resonance point of an antenna when the PIN diode is turned off; 
         FIG. 5A  is a graph illustrating a result of micro-tuning by a varactor diode in the 2.4 GHz frequency band; 
         FIG. 5B  is a graph illustrating a result of micro-tuning by a varactor diode in the 5 GHz frequency band; 
         FIG. 6A  is a circuit diagram illustrating a via hole and a reverse voltage adjuster; 
         FIG. 6B  is a graph illustrating isolation by a via hole and a reverse voltage adjuster; 
         FIG. 7A  is a view illustrating a radiation pattern of an antenna when a PIN diode is turned on and a reverse voltage of 2V is applied to a varactor diode; and 
         FIG. 7B  is a view illustrating a radiation pattern of an antenna when a PIN diode is turned on and a reverse voltage of 3V is applied to a varactor diode. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawing figures. 
       FIG. 1  is a perspective view illustrating an antenna  1  for a wireless terminal, in accordance with an embodiment of the present invention;  FIG. 2  is a front view illustrating the antenna of  FIG. 1 ; and  FIG. 3  is a bottom view illustrating the antenna of  FIG. 1 . 
     The antenna  1  for a wireless terminal comprises a radiator  10 , a ground conductor  50 , a PIN diode  20 , a varactor diode  25 , a switching controller  30 , and a reverse voltage adjuster  35 . 
     The ground conductor  50  is attached to or formed onto one surface of a circuit board and is electrically connected to the radiator  10 . For this purpose, a protrusion  51  protruding from the ground  50  is formed at one side of the ground  50 . The protrusion  51  is electrically connected to one side of the radiator  10  through a via or contact hole. 
     The radiator  10  is attached to or formed onto the other surface of the circuit board in a patch antenna type. The radiator  10  includes a meander line part  15  being severally bent lengthwise, and a feeding part  11  being formed in a linear band shape. The length of the feeding part  11  is almost same as that of the ground  50 . The feeding part  11  is positioned to correspond to the region where the ground  50  is formed. 
     The meander line part  15  is extended, at a predetermined length, from an end of the feeding part  11  and is severally bent in zigzags. An end region of the meander line part  15  towards the feeding part  11  is electrically connected to the ground  50  through a via hole. 
     The size of the antenna  1  is significantly reduced compared with the conventional antenna since the radiator  10  is formed in the meander line. A conventional antenna has a length from a several tens of millimeters to several hundreds of millimeters. However, the antenna  1  of the present invention is formed to be 10.3×8 mm 2  in size. The manufacturing of antenna  1  is relatively simple since the radiator  10  is positioned on the circuit board as a patch type antenna. 
     The PIN diode  20  is positioned at one side region, along the direction of the length of the meander line part  15 . The PIN diode  20  electrically shorts or opens the meander line connected to both ends of the PIN diode  20 . 
     Generally, when a certain prescribed or higher voltage is applied, the PIN diode  20  is turned on. In accordance with the embodiment of the present invention, when a voltage of 5V or higher is applied, an intrinsic series resistance is 1Ω, and the PIN diode  20  is turned on. Accordingly, the meander line connected by the PIN diode  20  shorts, resulting in the length of the radiator  10  being the total length which is derived by adding the length of the feeding part  11  to the length of the meander line part  15 . In the embodiment of the present invention, the total length of the radiator  10  is 56.5 mm, and the antenna  1  has a resonance point in the frequency band of 2.4 GHz, as illustrated in  FIG. 4A . The bandwidth of the antenna  1  in the frequency band of 2.4 GHz is 150 MHz based on −10 dB. Since the bandwidth of 150 MHz is expanded, compared to the common bandwidth of 80 MHz, it may be understood that the performance of the antenna  1  is improved. 
     When no voltage is applied to the PIN diode  20 , the series resistance is 10 kΩ, and the PIN diode  20  is turned off. Accordingly, the meander line connected by the PIN diode  20  opens, and the length of the radiator  10  is a value which is derived by adding the length of the feeding part  11  to the length of the portion of the meander line part  15  up to the PIN diode  20 . Then, the length of the radiator  10  is 14.65 mm, and the antenna  1  resonates at, or has the resonance point of 5.3 GHz, as illustrated in  FIG. 4B . In this case, the bandwidth of the antenna  1  in the frequency band of 5.3 GHz is 400 MHz based on −10 dB. 
     That is, when the PIN diode  20  is turned on and the length of the radiator  10  is its full length, the antenna  1  has the resonance point of 2.4 GHz. When the PIN diode  20  is turned off and the length of the radiator  10  is shortened, the antenna  1  has the resonance point of 5.3 GHz. 
     Accordingly, the antenna  1  is capable of selectively changing frequency between the 2.4 GHz frequency band for IEEE 802.11b and the 5.3 GHz frequency band for IEEE 802.11a by the PIN diode  20 . That is, the antenna  1  is capable of macro tuning. In the above-described embodiment, the length of the radiator  10  is designed to form appropriate operation frequency for the WLAN band. However, the operation frequency band may be changed by changing the length of the radiator  10 . Further, since the voltage of 5V applied when the PIN diode  20  is turned on is generally used for a wireless terminal, any additionally voltage supply source is not required, thereby reducing costs and simply constituting a circuit. 
     The varactor diode  25  is positioned at the meander line part  15  between the feeding part  11  and the PIN diode  20 . According to the extent of a reverse voltage applied to the varactor diode  25 , the frequency of the antenna  1  changes between channels within the service band. A reverse voltage which continuously changes within the range of 0˜3V is applied to the varactor diode  25 . Before a reverse voltage bias is applied, a depletion region of the varactor diode  25  is smallest, so as to have highest capacitance. The antenna  1  has the resonance point in a channel with the lowest frequency within the 2.4 GHz frequency band or the 5.3 GHz frequency band. 
     When the reverse voltage is applied to the varactor diode  25 , the depletion region increases and thus the capacitance decreases. Then, the resonance point of the antenna  1  moves to a channel with the highest frequency within the service band. That is, as the reverse voltage increases, the varactor diode  25  moves the resonance point of the antenna  1  to the channel with the highest frequency. Thus, the antenna  1  is capable of changing the channels within the service band by controlling the reverse voltage applied to the varactor diode  25 . That is, the antenna  1  is capable of micro-tuning. 
       FIG. 5A  is a graph illustrating a result of micro-tuning by the varactor diode  25  in the 2.4 GHz frequency band, and  FIG. 5B  is a graph illustrating a result of micro-tuning by the varactor diode  25  in the 5 GHz frequency band. 
     When the PIN diode  20  is turned on, the meander line shorts, so that the resonance point is formed in the 2.4 GHz frequency band. In such a state, the micro-tuning of the resonance point is performed by controlling the reverse voltage applied to the varactor diode  25 . As illustrated in  FIG. 5A , when the reverse voltage of 2V is applied to the varactor diode  25 , the resonance point is formed at 2.4 GHz, and when the reverse voltage of 3V is applied to the varactor diode  25 , the resonance point is formed at 2.48 GHz. S 11  at 2.4 GHz is −21 dB, and S 11  at 2.48 GHz is −20 dB. A resonance point between 2.4 GHz and 2.48 GHz may be formed by applying the reverse voltage of 2V˜3V to the varactor diode  25 . 
     As illustrated in  FIG. 5B , when the reverse voltage of 2V is applied to the varactor diode  25 , the resonance point is formed at 5.3 GHz, and when the reverse voltage of 3V is applied to the varactor diode  25 , the resonance point is formed at 5.46 GHz. S 11  at 5.3 GHz is −27 dB, and S 11  at 5.46 GHz is −26 dB. A resonance point between 5.3 GHz and 5.46 GHz may be formed by applying the reverse voltage of 2V˜3V to the varactor diode  25 . 
     The switching controller  30  and the reverse voltage adjuster  35 , which apply the reverse voltage to the PIN diode  20  and the varactor diode  25 , are positioned on the surface where the ground  50  is positioned. The switching controller  30  is connected to the PIN diode  20  through the via hole, and the reverse voltage adjuster  35  is connected to the varactor diode  25  through the via hole, as illustrated in  FIG. 1 . 
     The switching controller  35  applies a reverse voltage of 0V or 5V to the PIN diode  20  and is formed in a RLC (resistive-inductive-capacitive) circuit. The reverse voltage adjuster  35  continuously provides a reverse voltage of between 0V to 3V to the varactor diode  25  and is formed in a RLC circuit, as illustrated in  FIG. 6A . 
     As illustrated in  FIG. 6A , the via hole connecting the varactor diode  25  and the reverse voltage adjuster  35  is indicated as an inductor, and the reverse voltage adjuster  35  includes a resistance, an inductor and a capacitor. The voltage provided by the reverse voltage adjuster  35  should not affect the resonance frequency of the antenna  1 , i.e., 2.4 GHz and 5.5 GHz. For this purpose, resistance, inductance and capacitance values are designed to be appropriated. According to such design, as illustrated in  FIG. 6B , the via hole and the reverse voltage adjuster  35  form high isolation at 2.4 GHz and 5.5 GHz and overall have S 11  being less than −100 dB. Since the via hole and the reverse voltage adjuster  35  form the high isolation at 2.4 GHz and 5.5 GHz, these do not affect the antenna  1 . 
     The switching controller  30  is designed based on the same principles for the reverse voltage adjuster  35 , and thus it does not affect the antenna  1 . 
       FIG. 7A  illustrates a radiation pattern of the antenna  1  when the PIN diode  20  is turned on and the reverse voltage of 2V is applied to the varactor diode  25 . 
     When the PIN diode  20  is turned on and the reverse voltage of 2V is applied to the varactor diode  25 , the resonance point is formed at 2.4 GHz. As illustrated in  FIG. 7A , the radiation pattern of the antenna  1  has omni-directionality and a gain is indicated as −0.096 dB. 
       FIG. 7B  illustrates a radiation pattern of the antenna  1  when the PIN diode  20  is turned on and the reverse voltage of 3V is applied to the varactor diode  25 . 
     When the PIN diode  20  is turned on and the reverse voltage of 3V is applied to the varactor diode  25 , the resonance point is formed at 2.48 GHz. As illustrated in  FIG. 7B , the radiation pattern of the antenna  1  has the omni-directionality and a gain is indicated as −0.194 dB. 
     Accordingly, since the antenna  1  is omni-directional and the gain is sufficiently excellent, it is usable as a wireless antenna for the WLAN. 
     As described above, the antenna  1  performs the macro-tuning between the service bands by the PIN diode  20  and the micro-tuning to control the channel frequency within the service band by the varactor diode  25 . Accordingly, since it is possible to manufacture an antenna for a wireless terminal receiving signals in the two service bands, which correspond to the two standards of IEEE 802.11, usability is improved and manufacturing cost is reduced. 
     Furthermore, since the radiator  10  is formed in the form of a meander line, the size of the antenna  1  is significantly reduced compared to that of a conventional antenna, and since the radiator  10  is positioned on the circuit board, it makes it easy to manufacture the antenna  1 . 
     In the above-described embodiment, the antenna is designed to operate in the dual frequency band by placing only one PIN diode  20  on the radiator  10 . However, when plurality of the PIN diodes  20  are placed, an antenna may be designed to operate in a plurality of frequency bands. 
     The results of simulation illustrated in  FIGS. 4A ,  4 B,  5 A and  5 B are obtained by designing the length of the radiator  10  and controlling the voltage applied to the varactor diode  25 , to form appropriate operation frequency for any specific service. Accordingly, the operation frequency band of the antenna  1  may be variously realized by changing the length of the radiator  10  and the voltage applied to the varactor diode  25 . 
     As described above, in accordance with the present invention, the antenna is capable of the macro-tuning between the service bands and the micro-tuning for the channel control within the service bands. Furthermore, the size of the antenna is significantly reduced and the antenna is installed on the circuit board in a patch type, thereby simplifying a manufacturing process. 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, the use of the term ground herein may refer to any reference potential and not necessarily earth ground.