Patent Publication Number: US-2007109203-A1

Title: Resonant frequency tunable antenna apparatus

Description:
CLAIM OF PRIORITY  
      This application claims the benefit of Korean Patent Application No. 2005-71583 filed on Aug. 5, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an antenna, and more particularly to an antenna apparatus which adjusts an electrical resonant length in a wide frequency bandwidth via a switching device to vary a resonant frequency into a desired available frequency band.  
      2. Description of the Related Art  
      With recent advancement in a mobile multimedia broadcasting technology, there has arisen a need to develop terrestrial broadcasting antennas and satellite broadcasting antennas suitable for a mobile telecommunication terminal.  
      But, in general, broadcasting antennas are low in frequency and wide in frequency bandwidth compared to wireless LANs or short-range wireless telecommunications. For example, DVB-H, the European portable broadcasting standard requires an antenna to be operable at a wide bandwidth of 475 to 702 MHz, thus adopting a large external antenna.  
      Furthermore, conventionally, to selectively transmit/receive a specified bandwidth for desired broadcasting, a resonant length of the antenna was adjusted via switching. But such a conventional switching method requires separate signal lines for switching on/off to be disposed in a narrow antenna space, which accordingly is a difficult process. In addition, the signal lines for switching on/off cause interruption and noises in the antenna.  
      Therefore in the art, there has been a demand for a smaller antenna apparatus which can adjust a resonant frequency by a switching device at a wide bandwidth and alleviate interference or noises resulting from the switching device.  
     SUMMARY OF THE INVENTION  
      The present invention has been made to solve the foregoing problems of the prior art and therefore an object according to certain embodiments of the present invention is to provide a resonant frequency tunable antenna apparatus which turns on/off a switching device in response to a DC voltage applied to a radiation pattern to simplify a signal line, and is designed in an adequate arrangement to enhance antenna properties.  
      According to an aspect of the invention for realizing the object, there is provided a resonant frequency tunable antenna apparatus comprising: a radiation pattern having a feeding part connected to a feeding source and a variable DC power; and at least one tuning pattern connected in series to the connecting pattern via at least one switching device, wherein the switching device is turned on/off in response to a voltage applied from the variable DC power, and wherein a resonant frequency is lowered in accordance with a length of the tuning pattern which is added by turn-on of the switching device.  
      According to another aspect of the invention for realizing the object, there is provided a resonant frequency tunable antenna apparatus comprising: a dielectric block; a part of a printed circuit board where the dielectric block is mounted; a radiation pattern having a feeding part formed on the dielectric block and connected commonly to a feeding source and a variable DC power; a connecting pattern extending from the radiation pattern onto the printed circuit board; and at least one tuning pattern formed on the printed circuit board, the tuning pattern connected in series to the connecting pattern via at least one switching device.  
      In this fashion, the main radiation pattern is disposed on the dielectric block, thereby maintaining superior antenna properties. Also, the switching device and related patterns are formed on the printed circuit board, thereby simplifying further the switching circuit.  
      Preferably, to select a variety of resonant frequencies, the resonant frequency tunable antenna apparatus comprises a plurality of the switching device and a plurality of the tuning pattern, wherein the switching devices are disposed such that the tuning patterns are connected in series to one another.  
      Preferably, a ground part is provided to the printed circuit board, wherein the switching device is disposed on the printed circuit board between the dielectric block and the ground part.  
      The tuning pattern employed in the invention may be partially or entirely disposed on the printed circuit board according to an embodiment of the invention.  
      According to an embodiment of the invention, the tuning pattern comprises first and second patterns, the first pattern formed on the printed circuit board and connected to the switching board, and the second pattern formed on an underside surface of the dielectric block and electrically connected to the first pattern, wherein the two conductive patterns are integrally connected to each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a basic conceptual view illustrating an antenna apparatus according to the invention;  
       FIG. 2  is a perspective view illustrating an antenna apparatus according to an embodiment of the invention;  
       FIG. 3  is a perspective view illustrating an antenna apparatus according to another embodiment of the invention;  
       FIG. 4   a  is a perspective view illustrating a chip antenna according to further another embodiment of the invention;  
       FIG. 4   b  is a perspective view illustrating an antenna apparatus in which the chip antenna of  FIG. 4   a  is employed;  
       FIGS. 5   a  to  5   d  are graphs illustrating a resonant frequency change in accordance with a voltage applied in the antenna apparatus according to an embodiment of the invention, respectively; and  
       FIGS. 6   a  to  6   d  are graphs illustrating a resonant frequency change in accordance with a voltage applied in the antenna apparatus according to another embodiment of the invention, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  
       FIG. 1  is a basic conceptual view illustrating an antenna apparatus according to the invention.  
      Referring to  FIG. 1 , the antenna apparatus of the invention includes at least two antennas ANT 1  and ANT 2 . The first antenna ANT 1 , as a radiation component, has an electrical resonant length corresponding to a first resonant frequency. Meanwhile, the second antenna ANT 2 , as a tuning radiation component, is combined with the first antenna ANT 1  to provide a second resonant frequency, lower than the first resonant frequency. The first and second antennas  5  and  6  are connected with each other by a diode D, which is a switching device.  
      According to the invention, the diode is not connected to a separate driving signal line. However, the first antenna  5  is connected to a feeding source and a variable driving power supply  3 , thereby receiving both an AC signal from the feeding source  1  and a DC signal for a driving voltage. That is, a switching of the invention is structured such that the first antenna  5  is provided with an AC voltage for feeding the first antenna  5  and a DC voltage for driving the diode D through an identical signal line. The variable driving power supply may be configured as a Pulse Wave Modulator, and a desired available frequency is adjustable by turning on/off the diode D in response to a driving voltage.  
      In this fashion, according to the invention, a desired available frequency can be adjusted through a simple switching circuit structure. Especially, the invention does not require a separate signal line for driving the switching device, thereby preventing interference and noises arising therefrom.  
      The invention provides a method for adequately arranging the chief component of the antenna, i.e., a radiation pattern and a tuning pattern for changing an available frequency in order to improve antenna properties and make the switching circuit easily arranged in actual fabrication of the antenna apparatus.  
      According to the invention, the radiation pattern is structured as a chip antenna using a dielectric block to attenuate insertion loss of the antenna. Also, the tuning pattern is disposed on the printed circuit board having the chip antenna mounted thereon or formed integrally with the chip antenna pattern. Preferably, the switching device is disposed on the printed circuit board to fabricate the antenna more easily.  
       FIG. 2  is a perspective view illustrating an antenna apparatus  10  according to an embodiment of the invention. This embodiment employs a tuning pattern  24  and a switching device  25 .  
      The antenna apparatus according to this embodiment basically includes a radiation pattern  12  disposed on a dielectric block  11 , and a tuning pattern  24  and a switching device  25  each disposed on a printed circuit board  21  where the dielectric block  11  is mounted.  
      The radiation pattern  12  is formed of a conductive pattern on the dielectric block  11 , thereby ensuring superior radiation properties in a main radiation part of the antenna. Also, the tuning pattern  24  is formed of a conductive pattern on the printed circuit board  21 . The tuning pattern  24  formed on the printed circuit board allows the switching device  25  to be easily mounted on the printed circuit board.  
      The radiation pattern  12  includes a feeding part  12   a  and a connecting pattern  12   b . The feeding part  12   a  is connected to a feeding source (not illustrated) for providing transmission/reception signals and a variable DC power supply (not illustrated) for adjusting on/off of the switching device  25 . The connecting pattern  12   b  is formed on the printed circuit board  21 , extending toward the tuning pattern  24 . The switching device  25  is connected between the connecting pattern  12   b  and the tuning pattern  24 .  
      The tuning pattern  24  connected to the switching device  25  is connected to a resistance device  27  connected to a ground plate  29 , ensuring a voltage difference for a switching operation. To connect easily as just described, as in this embodiment, preferably, the tuning pattern  24  and switching device  25  are disposed between the dielectric block  11  of the printed circuit board  21  and the ground plate  29 . In a case where the switching device  25  is turned off, an electrical resonant length of the antenna  10  is determined by a radiation pattern  12  (including a connecting pattern  12 ( b )) and a first resonant frequency is determined correspondingly.  
      But with a predetermined level of a voltage applied from the variable DC power supply (not illustrated), the switching device  25  is turned on, and thus an electrical resonant length L corresponding to the tuning pattern is added. As a result, the resonant frequency of the antenna apparatus  10  is adjusted to a second resonant frequency which is lower than the first resonant frequency.  
       FIG. 3  is a perspective view illustrating an antenna apparatus  30  according to another embodiment of the invention. This embodiment employs three tuning patterns  44   a ,  44   b  and  44   c  and three switching devices  45   a ,  45   b  and  45   c.    
      The antenna apparatus  30  of this embodiment basically includes a radiation pattern  32  disposed on a dielectric block  31 , and the three tuning patterns  44   a ,  44   b  and  44   c  and the three switching devices  45   a ,  45   b  and  45   c  disposed on the printed circuit board  41  where the dielectric block  31  is mounted.  
      In the similar manner to  FIG. 2 , the radiation pattern  32  is formed of a conductive pattern on the dielectric block  31 . The first to third tuning patterns  44   a ,  44   b  to  44   c  are connected in series to one another by the second and third switching devices  45   b  and  45   c . Of course, the first tuning pattern  44   a  is connected to the connecting pattern  32   b  extending from the radiation pattern  32  and the first switching device  45   a . Here, the first to third tuning patterns  44   a ,  44   b  and  44   c  are connected to resistance devices  47   a ,  47   b  and  47   c  grounded on the ground pate  49  to turn on/off the switching devices  45   a ,  45   b  and  45   c.    
      A feeding part  32   a  of the radiation pattern  32  is connected to a feeding source (not illustrated) for applying transmission/reception signals and a variable DC power supply (not illustrated) for adjusting on/off of the switching devices. The first to third switching devices  44   a ,  44   b  and  44   c  may be turned on sequentially with increase in a voltage applied from the variable DC power supply. Consequently, the resonant frequency decided by the radiation pattern  32  is gradually adjusted to a lower resonant frequency. Also, resonant frequencies determined correspondingly to resonant lengths can be used selectively depending on a voltage applied. For example, a voltage is selected by which the first and second switching devices  45   a  and  45   b  are turned on and the third switching device  45   c  is turned off, thereby allowing selection of a resonant frequency corresponding to a combined resonant length of the first and second tuning patterns  44   a  and  44   b.    
      In this fashion, with the three switching devices  45   a ,  45   b  and  45   c  turned on/off sequentially according to a voltage applied, the three tuning patterns  44   a ,  44   b  and  44   c  are added, thereby producing four resonant frequency ranges. The antenna apparatus  30  shown in  FIG. 3  can be used as an antenna having four available frequencies depending on the voltage applied.  
      In the aforesaid embodiment, the tuning patterns are disposed on the printed circuit board, which accordingly allows the switching device to be mounted on the printed circuit board. The switching device, if disposed on the printed circuit board, is more advantageous for designing and fabrication of the antenna apparatus. Therefore, only a portion of the tuning patterns connecting to the switching device may be disposed on the printed circuit board and the other portion of the tuning patterns may be disposed on the dielectric block, especially on an underside surface thereof to be integrally connected with each other.  FIG. 4   a  is an exploded perspective view illustrating a chip antenna according to this embodiment of the invention.  
      Referring to  FIG. 4   a , the chip antenna has a radiation pattern  52  formed on a dielectric block  51 . The radiation pattern  52  has a feeding part  52   a  formed on an end, and two connecting patterns  52   b  formed on the other end. The connecting patterns  52   b  extend from the radiation pattern  52  onto an underside surface of the dielectric block  51 .  
      Moreover, the dielectric block  51  has first to third conductive lines  54   a ,  54   b  and  54   c  formed on the underside surface of the dielectric block  51  to constitute portions of the first to third tuning patterns. The first to third conductive lines each have two separate patterns, which however may be designed to different sizes and shapes according to an adjustment range of a desired resonant frequency.  
      The chip antenna shown in  FIG. 4   a  is mounted on a printed circuit board  61  where other conductive lines are formed as in  FIG. 4   b . The conductive lines  52   b ,  54   a ,  54   b  and  54   c  on the underside surface of the dielectric block  51  shown in  FIG. 4   a  are apparently arranged as indicated with dotted lines in  FIG. 4   b . That is, the connecting pattern  52   b  is connected to a connecting pattern  62  of the printed circuit board to integrally form a connecting pattern.  
      The first to third conductive lines  54   a ,  54   b  and  54   c  formed on the underside surface of the dielectric block  51  are connected to the first to third conductive patterns  64   a ,  64   b  and  64   c  formed on the printed circuit board, respectively, thereby constituting first to third tuning patterns, respectively. A first switching device  65   a  is disposed between the connecting patterns and the first tuning pattern. Likewise, a second switching device  65   b  is disposed between the connecting patterns and the second tuning pattern, and also a third switching device  65   c  is disposed between the connecting patterns and the third tuning pattern. In addition, the respective first to third tuning patterns  54   a ,  54   b  and  54   c ;  64   a ,  64   b  and  65   c  are connected to respective resistance devices  67   a ,  67   b  and  67   c  grounded on a ground plate  69  to turn on/off switching devices  65   a ,  65   b  and  65   c.    
      In this structure, with the switching devices  65   a ,  65   b  and  65   c  turned on/off sequentially, the tuning patterns  54   a ,  54   b  and  54   c ;  64   a ,  64   b  and  65   c  are added, thereby producing four resonant frequency ranges. Accordingly, the four resonant frequencies can be selected as an available frequency depending on a voltage applied.  
       FIGS. 5   a  to  5   d  are graphs illustrating a resonant frequency change in response to a voltage applied in an antenna apparatus according to an embodiment of the invention.  
      The graphs plot changes in the resonant frequency in response to the voltage applied using the antenna apparatus of the invention. The antenna apparatus used in the measurement employs three tuning patterns and three switching devices as shown in  FIG. 3 . Each of the switching devices is a Positive Intrinsic Negative (PIN) diode for switching on at a voltage of 0.7V, and the radiation pattern and tuning patterns are designed to have a resonant frequency ranging from about 475 to 702 MHz.  
      When no voltage is applied, a resonant frequency is decided by a radiation pattern of the dielectric block with all switching devices turned off. At this time, as shown in  FIG. 5   a , the resonant frequency is measured at 695 MHZ. When a voltage of 0.7 is applied, as shown in  FIG. 5   b , a first tuning pattern is connected to the radiation pattern and the resonant frequency is moderately lowered to 659 MHZ.  
      When a voltage of 1.4V is applied, the first to second tuning patterns are connected to the radiation pattern, and the resonant frequency is further lowered to 598 MHZ. Also, with a voltage of 2.1V applied, all switching devices are turned on and a resonant length is prolonged to the third tuning pattern. Thus the resonant frequency is reduced to 547 MHZ.  
      In this fashion, the resonant length can be properly adjusted by sequential switching-on in order to select a desired resonant frequency.  
       FIGS. 6   a  to  6   d  are graphs illustrating changes in a resonant frequency in accordance with a voltage applied in an antenna apparatus according to further another embodiment of the invention.  
      The graphs illustrate a measurement result for the antenna apparatus designed similarly to  FIG. 2 . That is, as shown in  FIG. 2 , a tuning pattern is designed to be connected to a radiation pattern via a switching device. The switching device employed is a PIN diode which is turned on at a voltage of about 0.7V.  
      As in  FIG. 6   a , when no voltage is applied, a resonant frequency is 685 MHZ. But when the tuning pattern is integrally connected to the radiation pattern with the switching device turned on, the resonant frequency is lowered to 614 MHZ as in  FIG. 6   b  (0.7V). This change in  FIG. 6   b  apparently results from increase in the resonant length by turn-on of the switching device.  
      Further, as shown in  FIGS. 6   c  and  6   d , when a voltage is raised to 1.4V and 2.1V even with the switching device turned on, the resonant frequency is confirmed to be lowered to 522 MHZ and 515 MHZ, respectively. This is not ascribed to a change in the resonant length by the turn-on the switching device as shown in  FIG. 6   b . But this is apparently because current flows in different amounts between the radiation pattern and the tuning patterns, thereby affecting impedance. Consequently, the resonant frequency can be changed by additional increase in the voltage applied even with the switching device turned on.  
      As set forth above, according to certain embodiments of the invention, a resonant frequency tunable antenna apparatus turns on/off a switching device via a DC voltage inputted to a radiation pattern, thereby simplifying a signal line structure. Also, according to the invention, a main radiation pattern and switching devices can be arranged in adequate proportions on a dielectric circuit board and a printed circuit board, thereby enhancing antenna properties.  
      While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.