Abstract:
Provided is a microstrip patch antenna in which a unit cell of a planar metamaterial may be inserted to have a miniaturized size, a wide bandwidth, or multi-resonance.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2011-0018336, filed on Mar. 2, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a technology that may miniaturize an antenna and may extend a bandwidth, by greatly reducing a resonance frequency of the antenna. 
         [0004]    2. Description of the Related Art 
         [0005]    In early research, an antenna that may be operated in a zeroth-order resonance mode was developed using a unit cell of a metamaterial including a gap and a via hole, to have a resonance frequency independent of a size of the antenna. 
         [0006]    A technology has currently reached a stage of miniaturizing the size of the antenna and configuring the antenna in a planar form, using a metal-insulator-metal (MTM) capacitor, a virtual ground inductor, and the like. Also, a broadband and a high gain may be achieved using a triangular gap, and a cross-shaped line. It is expected that the antenna may replace the existing antenna technology since the antenna may have a miniaturized size compared to an existing antenna structure, and also may have characteristics of the broadband and the high gain. 
         [0007]    However, it may be difficult to commercialize the developed metamaterial antenna due to a complex manufacturing process, a narrow bandwidth, a low gain, and the like. Also, although antenna technologies have been developed to improve the aforementioned factors, it may also be difficult to use the antenna practically due to distortion of a radiation pattern. 
       SUMMARY 
       [0008]    An aspect of the present invention provides a microstrip patch antenna including a planar metamaterial having an isotropic radiation pattern as well as a wide bandwidth and a miniaturized size, in an operating frequency band. 
         [0009]    Another aspect of the present invention also provides a microstrip patch antenna including a planar metamaterial having an antenna configuration where a unit cell of the metamaterial, including a complementary split-ring resonator (CSRR) slot and an interdigital capacitor, may be inserted in the microstrip patch antenna. 
         [0010]    Another aspect of the present invention also provides a microstrip patch antenna that may change an operating frequency of an antenna, thereby miniaturizing the antenna, by matching impedance of the antenna by adjusting a size with respect to any of a radius, a width, a ring gap, and a ring split of the CSRR. 
         [0011]    Another aspect of the present invention also provides a microstrip patch antenna including a planar metamaterial that may miniaturize an antenna, and may broaden a bandwidth of the antenna, by inserting a configuration of a unit cell of a metamaterial in the microstrip patch antenna, and by adjusting an operating frequency by adjusting a length of an inserted interdigital capacitor. 
         [0012]    According to an aspect of the present invention, there is provided a microstrip patch antenna, including a patch disposed on an upper surface of a dielectric substrate, and a ground plane disposed on a lower part of the patch. Here, the patch may include an interdigital capacitor, and the ground plane may include a CSRR slot. 
         [0013]    The patch may further include a microstrip feed line. 
         [0014]    The patch may adjust an electrical size of the microstrip patch antenna, by adjusting a length of the interdigital capacitor. 
         [0015]    The CSRR slot may adjust an operating frequency of the microstrip patch antenna, by adjusting a size with respect to any of a radius, a width, a ring gap, and a ring split. 
         [0016]    The CSRR slot may match the impedance at the zeroth-order resonance, by adjusting a size with respect to any of a radius, a width, a ring gap, and a ring split. 
         [0017]    The microstrip patch antenna may be controlled to be operated in a dual band, by adjusting a length of the interdigital capacitor, or a size with respect to any of a radius, a width, a ring gap, and a ring split of the CSRR slot. 
         [0018]    The microstrip patch antenna may match impedance by adjusting a size of the patch. 
         [0019]    The patch may apply both TM 01  and TM 10  mode simultaneously to the microstrip patch antenna, by adjusting a length of the interdigital capacitor. 
         [0020]    The patch may combine two modes, each having a different frequency, by adjusting a length of the interdigital capacitor. 
         [0021]    The patch may extend a bandwidth of the microstrip patch antenna, through the combination of the two modes. 
         [0022]    The patch may enable the microstrip patch antenna to have an isotropic radiation pattern with respect to a horizontally polarized wave, through the combination of the two modes. 
         [0023]    According to another aspect of the present invention, there is provided a method of operating a microstrip patch antenna, including configuring a patch disposed on an upper surface of a dielectric substrate, including an interdigital capacitor and a microstrip feed line, and configuring a ground plane disposed on a lower part of the patch, including a CSRR slot. 
       EFFECT OF THE INVENTION 
       [0024]    According to an embodiment of the present invention, a microstrip patch antenna may have an isotropic radiation pattern as well as a wide bandwidth and a miniaturized size, in an operating frequency band. 
         [0025]    According to another embodiment of the present invention, a microstrip patch antenna may have an antenna configuration where a unit cell of a metamaterial, including a complementary split-ring resonator (CSRR) slot and an interdigital capacitor, may be inserted in the microstrip patch antenna. 
         [0026]    According to another embodiment of the present invention, an antenna may be miniaturized and a bandwidth may be broadened by adjusting an operating frequency, by inserting a configuration of a unit cell of a metamaterial in a microstrip patch antenna, and by adjusting a length of an inserted interdigital capacitor. 
         [0027]    According to another embodiment of the present invention, an antenna may be miniaturized by changing an operating frequency of the antenna, by matching impedance of the antenna by adjusting a size with respect to any of a radius, a width, a ring gap, and a ring split of the CSRR, thereby miniaturizing the antenna. 
         [0028]    According to another embodiment of the present invention, an optimal impedance matching may be induced, by supporting a flexible adjustment of parameter values of a patch and a CSRR slot, with respect to multiple resonances caused by a characteristic of an inserted metamaterial. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    These and/or other aspects, features, and advantages of the invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0030]      FIG. 1  illustrates a configuration of a microstrip patch antenna according to an embodiment of the present invention; 
           [0031]      FIG. 2  illustrates a characteristic of impedance matching of a microstrip patch antenna according to a change in a size of a patch; 
           [0032]      FIG. 3  illustrates a characteristic of impedance matching of a microstrip patch antenna according to a change in a size of a complementary split-ring resonator (CSRR) slot; 
           [0033]      FIG. 4  illustrates a characteristic of impedance matching of a microstrip patch antenna according to a change in a size of parameters of a CSRR slot; 
           [0034]      FIG. 5  illustrates an example of a change in a return loss of a microstrip patch antenna according to a change in a length of an interdigital capacitor; 
           [0035]      FIG. 6  illustrates another example of a change in a return loss of a microstrip patch antenna according to a change in a length of an interdigital capacitor; 
           [0036]      FIG. 7  illustrates electric field distribution of a microstrip patch antenna in modes, each having a different frequency; 
           [0037]      FIG. 8  illustrates electric field distribution in a hybrid mode where two modes may be combined, according to a change in input phase; 
           [0038]      FIG. 9  illustrates a characteristic of a return loss of an optimized microstrip patch antenna; 
           [0039]      FIG. 10  illustrates three-dimensional (3D) radiation patterns of a microstrip patch antenna; 
           [0040]      FIG. 11  illustrates a gain characteristic of a microstrip patch antenna; and 
           [0041]      FIG. 12  illustrates a sequence of a method of operating a microstrip patch antenna according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Exemplary embodiments are described below to explain the present invention by referring to the figures. 
         [0043]      FIG. 1  illustrates a configuration of a microstrip patch antenna  100  according to an embodiment of the present invention. 
         [0044]    Referring to  FIG. 1 , the microstrip patch antenna  100 , which will be hereinafter referred to as an ‘antenna’ may include a microstrip feed line  110 , a patch  120 , an interdigital capacitor  130 , a complementary split-ring resonator (CSRR) slot  140 , and a ground plane  150 . 
         [0045]    On an upper surface of a dielectric substrate, the patch  120 , which may be conductive and in which the microstrip feed line  110  and the interdigital capacitor  130  may be inserted, may be included. The patch  120  may adjust an electrical size of the antenna  100 , by adjusting a length of the interdigital capacitor  130 . For example, when a size of the patch  120  is fixed and the length of the interdigital capacitor  130  is increased, the antenna  100  may have increased series capacitance, and thus may have an effect of having an increased electrical size while the physical length may remain fixed. 
         [0046]    The size of the patch  120 , L 1 ×W 1 , may be adjustable for impedance matching of the antenna  100 . That is, an operating frequency of the antenna  100  may be changed when impedance of the antenna  100  is matched by adjusting the size of the patch  120 . Generally, a width W 0  of the microstrip feed line  110  may be determined to have characteristic impedance of the line corresponding to  50  Ω. 
         [0047]    The ground plane  150 , which may be conductive, may be disposed on a lower surface of the dielectric substrate, and the ground plane  150 , in which the CSRR slot  140  may be inserted, may be disposed under the patch  120 . A relative permittivity of a dielectric substance may correspond to ε r , and a dielectric substrate having a predetermined value may be used. 
         [0048]    The CSRR slot  140  may adjust an operating frequency of the antenna  100 , by adjusting a size with respect to any of a radius R 2 , a width W 2 , a ring gap D 2 , and a ring split G 2  to optimum sizes. 
         [0049]    For example, the radius R 2  may correspond to 8 mm, the ring gap D 2  may correspond to 1.5 mm, the width W 2  may correspond to 2 mm, the ring split G 2  may correspond to 1 mm, the length L 1  of the patch  120  may correspond to 19 mm, the width W 1  of the patch  120  may correspond to 19 mm, and the width WO of the microstrip feed line  110  may correspond to 5 mm. 
         [0050]      FIG. 2  illustrates a characteristic of impedance matching of a microstrip patch antenna according to a change in a size of a patch. 
         [0051]    As illustrated in  FIG. 2 , a graph  210  may indicate input resistance, that is, impedance at a zeroth-order resonance frequency, and a first-order resonance frequency of the antenna  100 , according to the length L 1  and the width W 1  of the patch  120 . Also, a graph  220  may indicate a return loss at the zeroth-order resonance frequency, and the first-order resonance frequency of the antenna  100 , according to the length L 1  and the width W 1  of the patch  120 . 
         [0052]    In  FIG. 2 , when an overall size of the patch  120  becomes greater, the overall impedance of the antenna  100  may be reduced. The antenna  100  may have a metamaterial characteristic, and accordingly may have a zeroth-order resonance, a first-order resonance, and the like. When the size of the patch  120  becomes greater, the impedance of the antenna  100  at the zeroth-order resonance, and the first-order resonance may be reduced. Accordingly, the impedance may be matched by tuning the size of the patch  120  and the size of parameters of the CSRR slot  140 , for example, the radius R 2 , the width W 2 , the ring gap D 2 , and the ring split G 2 . 
         [0053]      FIG. 3  illustrates a characteristic of impedance matching of a microstrip patch antenna according to a change in a size of a CSRR slot. 
         [0054]    As illustrated in  FIG. 3 , when the radius R 2  of the CSRR slot  140  becomes greater, an operating frequency of the antenna  100  including a zeroth-order resonance frequency, and a first-order resonance frequency may be reduced. A graph  310  may indicate input resistance at the zeroth-order resonance frequency, and the first-order resonance frequency of the antenna  100 , according to a change in the radius R 2  of the CSRR slot  140 . Also, a graph  320  may indicate a return loss at the zeroth-order resonance frequency, and the first-order resonance frequency of the antenna  100 , according to the change in the radius R 2  of the CSRR slot  140 . 
         [0055]    It is because the operating frequency of the metamaterial antenna  100  may be unrelated to a physical size of the antenna  100 , whereas the operating frequency of the metamaterial antenna  100  may be dependent on valid inductance and capacitance. 
         [0056]      FIG. 4  illustrates a characteristic of impedance matching of a microstrip patch antenna according to a change in a size of parameters of a CSRR slot. 
         [0057]    As illustrated in  FIG. 4 , the parameters of the CSRR slot  140  may correspond to the width W 2 , the ring gap D 2 , and the ring split G 2 . When the parameters are changed, an operating frequency and input impedance of the antenna  100  may be changed. 
         [0058]    A graph  410  may indicate input resistance at the zeroth-order resonance frequency, and the first-order resonance frequency of the antenna  100 , according to a change in the width W 2  of the CSRR slot  140 . A graph  420  may indicate input resistance at the zeroth-order resonance frequency, and the first-order resonance frequency of the antenna  100 , according to a change in the ring gap D 2  of the CSRR slot  140 . Also, a graph  430  may indicate input resistance at the zeroth-order resonance frequency, and the first-order resonance frequency of the antenna  100 , according to a change in the ring split G 2  of the CSRR slot  140 . 
         [0059]    When the width W 2 , the ring gap D 2 , and the ring split G 2  of the CSRR slot  140  become greater, input impedance of the antenna  100  may be reduced at the zeroth-order resonance frequency. Here, the antenna  100  may independently perform impedance matching at the zeroth-order resonance frequency. Also, as illustrated in  FIG. 2 , the antenna  100  may be operated as a dual-resonance antenna, by adjusting a size of parameters of the CSRR slot  140  in a status that the impedance matching may have been achieved at the first-order resonance. 
         [0060]      FIG. 5  illustrates an example of a change in a return loss of a microstrip patch antenna according to a change in a length of an interdigital capacitor. 
         [0061]    Referring to  FIG. 5 , in the antenna  100 , when a length L 3  of the interdigital capacitor  130  is adjusted to optimally be 1 mm to 5 mm, series capacitance may be increased and accordingly a first-order resonance frequency may be reduced. Here, an operating frequency of the antenna  100  may be changed, and miniaturization of the antenna  100  may be achieved by changing the length of the interdigital capacitor  130  only, without changing an overall size of the antenna  100 . In this instance, a zeroth-order resonance frequency may not be changed, however impedance matching may be damaged due to reduction of input impedance. In order to operate the antenna  100  in a dual band, the impedance may be matched at the zeroth-order resonance frequency by adjusting the size of the parameters of the CSRR slot  140 . 
         [0062]      FIG. 6  illustrates another example of a change in a return loss of a microstrip patch antenna according to a change in a length of an interdigital capacitor. 
         [0063]    As illustrated in  FIG. 6 , when the length L 3  of the interdigital capacitor  130  is continuously increased, a first-order resonance frequency may be continuously reduced and an effect that a size of the antenna  100  may be reduced may be achieved. The first-order resonance frequency of the antenna may correspond to a TM 10  mode. However, when the length L 3  of the interdigital capacitor  130  is greater than 7 mm, a TM 01  mode may be generated along with the TM 10  mode. In this instance, the TM 01  mode may be a mode in which an operating frequency may be determined based on the width W 1  of the antenna  100 , which may be different from a mode in which the operating frequency may be determined based on the length L 1  of the antenna  100 . 
         [0064]      FIG. 7  illustrates electric field distribution of a microstrip patch antenna in modes, each having a different frequency. 
         [0065]    As illustrated in a lower diagram  720  of  FIG. 7 , an electric field may have a half-wavelength resonance in a direction of a Y-axis, in a TM 01  mode. Accordingly, an operating frequency of the TM 01  mode may be adjusted by adjusting a width of the antenna  100 . Conversely, the electric field may have a half-wavelength resonance in a direction of an X-axis, in a TM 10  mode in which a general patch antenna may be operated, as illustrated in an upper diagram  710  of  FIG. 7 . 
         [0066]    The TM 10  mode and the TM 01  mode may be determined based on a direction of the antenna. For example, when the antenna is disposed in the direction of the X-axis, the TM 10  mode may be used, and when the antenna is disposed in the direction of the Y-axis, the TM 01  mode may be used. Accordingly, both the TM 10  mode and the TM 01  mode may be simultaneously used in a single antenna. 
         [0067]    The diagrams  710  and  720  may illustrate the electric fields in the TM 10  mode and the TM 01  mode when the length L 3  of the interdigital capacitor  130  corresponds to 8 mm The diagram  710  may indicate the electric field at 3.497 GHz corresponding to the first-order resonance frequency, and the diagram  720  may indicate the electric field at 3.812 GHz corresponding to the resonance frequency in the TM 01  mode. 
         [0068]      FIG. 8  illustrates electric field distribution in a hybrid mode where two modes may be combined, according to a change in input signal phase. 
         [0069]    As illustrated in  FIG. 8 , when the length L 3  of the interdigital capacitor  130  corresponds to 7 mm, there may be a hybrid mode in which a first-order resonance mode and a TM 01  mode may be combined in a band of 3.80 GHz. When the input signal phase corresponds to 0° and 180°, the TM 01  mode may occur as illustrated in diagrams  810  and  830  respectively. When the input signal phase corresponds to 90° and 270°, a TM 10  mode may occur as illustrated in diagrams  820  and  840  respectively. That is, when the length of the interdigital capacitor  130  is adjusted, the TM 10  mode and the TM 01  mode may form the hybrid mode, and the two modes may have a phase difference of 90° from each other, and accordingly may be operable without destructive interference from each other. 
         [0070]    The patch  120  may combine the two modes, thereby extending the bandwidth of the antenna  100 . An operating frequency of the TM 01  mode may be constant when the width of the antenna  100  is constant, and accordingly the bandwidth may be extendable when the hybrid mode is formed by properly adjusting the length L 3  of the interdigital capacitor  130 . 
         [0071]      FIG. 9  illustrates a characteristic of a return loss of an optimized microstrip patch antenna. 
         [0072]    Referring to  FIG. 9 , the length L 3  of the interdigital capacitor  130  may correspond to 7.3 mm in order to extend a bandwidth of the antenna  100  up to a maximum width. In this instance, a characteristic of the return loss of the antenna  100  may be the same as described with respect to  FIG. 8 . 
         [0073]    The bandwidth of a 10 dB return loss of the antenna  100  may correspond to 6.8%, and may be expendable to be three times greater than an existing patch antenna. Also, a physical size of the antenna  100  may correspond to 0.24 λ 0 ×0.24 λ 0 ×0.02 λ 0  at a central operating frequency, and the antenna  100  may have a size reduced by 55% when compared to a microstrip patch antenna designed at the same frequency on the same substrate. 
         [0074]      FIG. 10  illustrates three-dimensional (3D) radiation patterns of a microstrip patch antenna. 
         [0075]    Referring to  FIG. 10 , the antenna  100  may have a near-isotropic radiation pattern  1010  with respect to a horizontally polarized wave. Also, with respect to a vertically polarized wave, the antenna  100  may have a directional radiation pattern  1020  in a direction of a ±z-axis, and may be null with respect to all directions on an x-y plane. 
         [0076]      FIG. 11  illustrates a gain characteristic of a microstrip patch antenna. 
         [0077]    Referring to  FIG. 11 , the antenna  100  may have a gain greater than 5 dB within a range of an operating frequency, and may have a maximum gain of 6.4 dB. In spite of its miniaturized size, the antenna  100  may have the same electrical length due to a characteristic of a metamaterial, and thus, may enable maintaining a high gain. 
         [0078]      FIG. 12  illustrates a sequence of a method of operating a microstrip patch antenna according to an embodiment of the present invention. 
         [0079]    Referring to  FIG. 12 , the antenna  100  may configure the patch  120  disposed on an upper surface of a dielectric substrate, including the interdigital capacitor  130  and the microstrip feed line  110 , in operation  1210 . 
         [0080]    In operation  1220 , the antenna  100  may configure the ground plane  150  disposed on a lower part of the patch  120 , including the CSRR slot  140 . 
         [0081]    In operation  1230 , the antenna  100  may adjust an operating frequency by adjusting a size of the interdigital capacitor  130 . That is, in operation  1230 , the operating frequency of the antenna  100 , for example, a first-order resonance frequency may be adjusted, and a TM 01  mode may be additionally applied. The size of the interdigital capacitor  130  may be adjusted in a state that the size of the antenna  100  may be fixed. 
         [0082]    As an embodiment of the present invention, the antenna  100  may be controlled to be operated in a dual band, by adjusting the length L 3  of the interdigital capacitor  130 , or a size with respect to any of the radius R 2 , the width W 2 , the ring gap D 2 , and the ring split G 2  of the CSRR slot  140 . 
         [0083]    As another embodiment of the present invention, the antenna  100  may apply the TM 01  mode, by adjusting the length L 3  of the interdigital capacitor  130 . 
         [0084]    As still another embodiment of the present invention, the antenna  100  may combine two modes, for example, a TM 10  mode and the TM 01  mode, each having a different frequency, by adjusting the length L 3  of the interdigital capacitor  130 . The antenna  100  may extend a bandwidth of the antenna  100 , through the combination of the two modes. Also, the antenna  100  may enable having a near-isotropic radiation pattern with respect to a horizontally polarized wave, through the combination of the two modes. 
         [0085]    The aforementioned methods may be recorded, stored, or fixed in one or more non-transitory computer-readable storage media that includes program instructions to be implemented by a computer to cause a processor to execute or perform the program instructions. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. The media and program instructions may be those specially designed and constructed, or they may be of the kind well-known and available to those having skill in the computer software arts. 
         [0086]    Although a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.