Abstract:
A miniaturized ultra-wideband microstrip antenna, includes: a dielectric substrate; a feed line disposed on the dielectric substrate, and supplying an electromagnetic energy supplied from an external power source; a main radiating element radiating the electromagnetic energy inputted by the feed line; and at least one sub-radiating element disposed in proximity to the main radiating element for multi-radiation. Also, the antenna further includes at least one connection plate electrically connecting the main radiating element to at least one of the sub-radiating elements. The miniaturized ultra-wideband microstrip antenna can also be made ultralight, and include additional sub-radiating elements besides the main radiating element, whereby multi-radiation in UWB&#39;s range can be attained.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. § 119 from Korean Patent Application No. 2004-00384, filed on Jan. 5, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates in general to a wideband impulse transmitting/receiving antenna for use with communication systems employing electromagnetic impulses, such as, UWB (Ultra Wideband) communications. More specifically, the present invention relates to a miniaturized UWB microstrip antenna having excellent wideband characteristics by changing the notch structure of a main radiating element and a sub-radiating element connected to the main radiating element.  
         [0004]     2. Description of the Related Art  
         [0005]     UWB uses pulses which have the attribute of being spread over a frequency range measured in 3.1-10.6 gigahertz (GHz) for transmitting digital data as far as 10 m-1 km.  
         [0006]     As already known, impulse radio communications, unlike existing narrowband communications, use an ultra-wideband frequency band and transmit high-speed data consuming much power. To commercialize the impulse radio communication system for a mobile communication terminal, however, a small-sized antenna has to be used.  
         [0007]     A related art UWB antenna for transmitting/receiving impulses mainly has been used for radar feed, so its important features of radiating pattern are high power, wide bandwidth, high gain, and low sidelobe. In effect, there were few studies being done on impulse antennas for use with personal mobile communication terminals.  
         [0008]     The following will explain related art wideband antennas.  
         [0009]      FIG. 1  illustrates an ultra-wideband antenna disclosed in U.S. Pat. No. 5,428,364. This type of antenna requires an impedance taper featuring wide bandwidth impedance matching, in order to secure desired radiation patterns over every range of frequencies and to transmit electromagnetic energy inputted from a source without loss. Also, a slot line impedance taper is used in a matching circuit for wideband matching, so the size of the antenna has to be increased in proportion to a usable frequency range.  
         [0010]      FIG. 2  illustrates a single-layer wideband antenna using a stub, disclosed in Korean Pat. No. 2002-73660. For this type of antenna, an open or short stub is attached to a radiating patch to overcome weakness of an existing patch antenna, and as a result, excellent wideband impedance matching characteristics and wideband characteristics are obtained. However, the antenna could not accommodate the UWB waveform, and the patch antenna, being a single patch antenna by nature, is incapable of realizing omni-directional characteristics of antennas. In addition, when mounted in small-sized mobile communication equipment, the antenna&#39;s directivity interferes with smooth and proper communication, and thus, at least two antennas are required.  
         [0011]      FIG. 3  illustrates a print dipole antenna with wideband characteristics by constructing a matching circuit with more than one open stub on a microstrip line, disclosed in Japanese Pat. No. 5-3726. The print dipole antenna has the matching circuit on a signal line, so it occupies more space than necessary when designing an antenna combined with the dielectric substrate. It is practically impossible to implement a wideband matching circuit having a bandwidth greater than 3:1 in a relatively low (less than 5 GHz) frequency domain. Also, the disclosed antenna has a dual plane structure and thus, process cost thereof is higher than a single plane antenna.  
         [0012]      FIG. 4  illustrates an antenna disclosed in Europe Pat. No. WO 02/13313 A2. According to the disclosure, a large planar conductive plate and a small planer conductive plate inserted into an oval-shaped slot are formed in the large element. The suggested antenna size is 2.72×1.83 cm including a radiating slot, which is 8 times bigger than the antenna size of an embodiment of the present invention.  
         [0013]      FIG. 5  illustrates an antenna disclosed in U.S. Pat. No. 6,351,246 B1, titled “Planer ultra wide band antenna with integrated electronics”. According to the disclosed antenna, a difference signal is applied feed points, and a resistor is situated between a pair of radiating balance elements to improve voltage standing wave ratio (VSWR) of low frequency. Although this type of antenna has electric elements to meet the requirements of pulse communications in a desired frequency range, it is not proper to be miniaturized. Thus, the practicability of the antenna is basically limited. Moreover, because the resistor is employed in order to improve the VSWR in a low frequency range, it is not easy to maintain high reliability of the antenna.  
       SUMMARY OF THE INVENTION  
       [0014]     It is, therefore, an aspect of the present invention to provide a miniaturized ultra-wideband (UWB) microstrip antenna combined with a substrate for use in personal and military mobile communication terminals for high-speed impulse radio communications.  
         [0015]     It is another aspect of the present invention to provide a miniaturized UWB microstrip antenna having improved narrowband and multi-harmonic features, by employing a main radiating element and a sub-radiating element connected to the main radiating element.  
         [0016]     It is still another aspect of the present invention to provide a miniaturized UWB microstrip antenna with improved wideband-matching properties in a desired frequency range through a specific notch structure constructed of a main radiating element and a sub-radiating element connected thereto.  
         [0017]     Yet another aspect of the present invention is to provide a miniaturized UWB microstrip antenna, capable of wideband impedance matching between an antenna and sky wave, by completely irradiating electric impulses on the interface.  
         [0018]     To achieve the above and/or aspects and advantages, there is provided a miniaturized ultra-wideband microstrip antenna, including: a dielectric substrate; a feed line disposed on the dielectric substrate, and supplying an electromagnetic energy supplied from an external power source; a main radiating element for radiating the electromagnetic energy inputted by the feed line; and at least one sub-radiating element disposed in proximity to the main radiating element for multi-radiation.  
         [0019]     According to an aspect of the present invention, the antenna further includes at least one connection plate for electrically connecting the main radiating element to at least one of the sub-radiating elements.  
         [0020]     According to another aspect of the present invention, an upper end of the main radiating element has a rectangular shape, the sub-radiating elements are symmetrically arranged with respect to the main radiating element, and an upper end of each sub-radiating element preferably has a rectangular shape among other possible shapes in order to reduce the size of the antenna.  
         [0021]     According to another aspect of the present invention, the length of a long side of the sub-radiating element is smaller than or equal to the length of a long side of the main radiating element.  
         [0022]     According to another aspect of the present invention, the feed line includes at least one slot of a predetermined size through an etching process.  
         [0023]     According to another aspect of the present invention, one lower side of the main radiating element and the connection plate form a 90° angle, and the connection plate and one lower side of the sub-radiating element form a 90° angle.  
         [0024]     According to another aspect of the present invention, one lower side of the main radiating element and the connection plate form a 90° angle, and the connection plate and one lower side of the sub-radiating element form a (90°+θ 1 ) angle, where θ 1  is a predetermined angle.  
         [0025]     According to another aspect of the present invention, one lower side of the main radiating element and the connection plate form a (90°+θ 2 ) angle (where θ 2  is a predetermined angle), and the connection plate and one lower side of the sub-radiating element form a 90° angle.  
         [0026]     According to another aspect of the present invention, one lower side of the main radiating element and the connection plate form a (90°+θ 3 ) angle, and the connection plate and one lower side of the sub-radiating element form a (90°+θ 4 ) angle, where, θ 3  and θ 4  are predetermined angles.  
         [0027]     According to another aspect of the present invention, the main radiating element and the sub-radiating elements are disposed on the same planar surface.  
         [0028]     According to another aspect of the present invention, the main radiating element and the sub-radiating elements are disposed on a different planar surface.  
         [0029]     According to another aspect of the present invention, the main radiating element and the sub-radiating elements are indirectly connected to each other through an electromagnetic coupling, and are spaced apart by a predetermined distance.  
         [0030]     According to another aspect of the present invention, the dielectric substrate is an epoxy laminate (FR-4) substrate of which relative dielectric constant (ε r ) is approximately 4.4.  
         [0031]     According to an aspect of the present invention, the length of a long side of the main radiating element is approximately 11.5 mm.  
         [0032]     According to an aspect of the present invention, the length of a long side of the feed line is approximately 55 mm.  
         [0033]     According to an aspect of the present invention, the sum of the length of a short side of the main radiating element, the length of the connection plate, and the length of a short side of the sub-radiating element is approximately 6.272 mm.  
         [0034]     According to an aspect of the present invention, the connection plates are formed on the upper end, center, or lower end of the main and sub-radiating elements.  
         [0035]     According to an aspect of the present invention, the antenna further includes a plurality of ground plates disposed on the top of the dielectric substrate, each being symmetrically spaced apart by a predetermined distance with respect to the feed line.  
         [0036]     According to an aspect of the present invention, the antenna further includes a ground plate having a predetermined size to be disposed at the bottom of the dielectric substrate.  
         [0037]     According to an aspect of the present invention, the antenna further includes a ground plate having a predetermined size to be disposed at the bottom of the dielectric substrate.  
         [0038]     According to an aspect of the present invention, an insertion loss in a frequency range from 3.0 GHz to 12 GHz is less than 10 dB.  
         [0039]     According to an aspect of the present invention, VSWR in a frequency range from 3.0 GHz to 12 GHz is less than 2.0.  
         [0040]     According to an aspect of the present invention, if the center frequency is 5 GHz, the current is mainly induced to the lower end of the main radiating element.  
         [0041]     According to an aspect of the present invention, if the center frequency is 10 GHz, the current is mainly induced to the main radiating element, and a certain part of the sub-radiating element.  
         [0042]     According to an aspect of the present invention, also, if the center frequency is 10 GHz, the current is mainly induced to the main radiating element, the connection plate, and a certain part of the sub-radiating element.  
         [0043]     According to an aspect of the present invention, the antenna further includes at least one additional sub-radiating element disposed at a predetermined position improving wideband characteristics of the antenna.  
         [0044]     According to another aspect of the present invention, VSWR in a frequency range from 3.0 GHz to 18 GHz is less than 2.0.  
         [0045]     According to another aspect of the present invention, the antenna further includes a plurality of connection plates for electrically connecting the main radiating element, the sub-radiating elements, and the additional sub-radiating elements to each other.  
         [0046]     According to another aspect of the present invention, the antenna further includes at least one connection plate electrically connecting the main radiating element to the additional sub-radiating elements.  
         [0047]     According to another aspect of the present invention, the antenna further includes at least one connection plate electrically connecting the sub-radiating elements to the additional sub-radiating elements.  
         [0048]     According to another aspect of the present invention, the additional sub-radiating elements are disposed on the same planar surface with the main radiating element or with the sub-radiating elements.  
         [0049]     According to another aspect of the present invention, the additional sub-radiating elements are disposed on the same planar surface with the main radiating element and the sub-radiating elements.  
         [0050]     According to another aspect of the present invention, the antenna further includes at least one additional sub-radiating element disposed at a predetermined position improving wideband characteristics of the antenna.  
         [0051]     According to another aspect of the present invention, the sub-radiating elements and the additional sub-radiating elements are indirectly connected to each other through an electromagnetic coupling, and are spaced apart by a predetermined distance.  
         [0052]     According to another aspect of the present invention, the antenna further includes at least one connection plate electrically connecting the sub-radiating elements to the additional sub-radiating elements.  
         [0053]     According to another aspect of the present invention, the additional sub-radiating elements are disposed on the same planar surface with the main radiating element or with the sub-radiating elements.  
         [0054]     According to another aspect of the present invention, the additional sub-radiating elements are disposed on the same planar surface with the main radiating element and the sub-radiating elements.  
         [0055]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0056]     These and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiments of the present invention with reference to the accompanying drawings, of which:  
         [0057]      FIG. 1  illustrates an ultra-wideband antenna disclosed in U.S. Pat. No. 5,428,364;  
         [0058]      FIG. 2  illustrates a single-layer wideband antenna using a stub, disclosed in Korean Pat. No. 2002-73660;  
         [0059]      FIG. 3  illustrates a print dipole antenna with wideband characteristics by constructing a matching circuit with more than one open stub on a microstrip line, disclosed in Japanese Pat. No. 5-3726;  
         [0060]      FIG. 4  illustrates an antenna disclosed in Europe Pat. No. WO 02/13313 A2;  
         [0061]      FIG. 5  illustrates an antenna disclosed in U.S. Pat. No. 6,351,246 B1, titled “Planer ultra wide band antenna with integrated electronics;” 
         [0062]      FIG. 6  is a perspective view of a CPW (Coplanar waveguide) fed microstrip antenna according to an aspect of the present invention;  
         [0063]      FIG. 7  is a perspective view of a GCPW (Ground coplanar waveguide) fed microstrip antenna according to an aspect of the present invention;  
         [0064]      FIG. 8  is a perspective view of a microstrip fed antenna according to an aspect of the present invention;  
         [0065]      FIG. 9  is a plan view of a radiating element of a miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention;  
         [0066]      FIG. 10  illustrates another embodiment of  FIG. 9 ;  
         [0067]      FIG. 11  is a plan view of  FIG. 6 ;  
         [0068]      FIG. 12  illustrates current distribution of a miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention, where the amplitude of the antenna is 1 and the phase of the antenna is 0 degree, respectively;  
         [0069]      FIG. 13  is a three-dimensional diagram illustrating a radiation pattern of a miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention plotted on spherical coordinates;  
         [0070]      FIG. 14  is a graph illustrating an insertion loss (S 11 ) of a miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention;  
         [0071]      FIG. 15  illustrates an insertion loss (S 11 ) of  FIG. 14  plotted on a smith chart; and  
         [0072]      FIG. 16  is a graph illustrating VSWR of a miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0073]     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0074]      FIG. 6  is a perspective view of a CPW (Coplanar waveguide) fed microstrip antenna according to an aspect of the present invention;  FIG. 7  is a perspective view of a GCPW (Ground coplanar waveguide) fed microstrip antenna according to another aspect of the present invention; and  FIG. 8  is a perspective view of a microstrip fed antenna according to another aspect of the present invention  
         [0075]     As shown in FIGS.  6  to  8 , the miniaturized ultra-wideband microstrip antenna  100  of the present invention includes a dielectric substrate  10 , a feed line  20 , a main radiating element  30 , a plurality of connection plates  35   a,    35   b,  a plurality of sub-radiating elements  40   a,    40   b,  and ground plates GND 1 -GND 6 . In the interest of brevity and convenience, the dielectric substrate  10 , the feed line  20 , the main radiating element  30 , the connection plates  35   a,    35   b,  and the sub-radiating elements  40   a,    40   b  are represented by like reference numerals throughout FIGS.  6  to  8 .  
         [0076]     Preferably, but not necessarily, the feed line  20 , the main radiating element  30 , the connection plates  35   a,    35   b,  and the sub-radiating elements  40   a,    40   b  are conductors, and more preferably, but not necessarily, each is plated with tin against corrosion.  
         [0077]     Referring to the CPW fed microstrip antenna shown in  FIG. 6 , the main radiating element  30 , the connection plates  35   a,    35   b,  the sub-radiating elements  40   a,    40   b,  the feed line  20 , and the first, and second ground plates GND 1 , GND 2  conductively coat the top planar surface of the dielectric substrate  10 .  
         [0078]     A typically used coating method is the PCB (Printed Circuit Board) process. Preferably, but not necessarily, an epoxy laminate (FR-4) substrate whose relative dielectric constant (ε r ) is approximately 4.4 is used for the dielectric substrate  10 .  
         [0079]     Referring now to  FIG. 7 , the GCPW fed microstrip antenna, unlike the CPW fed microstrip antenna, is constructed in such a manner that a fifth ground plate GND 5  is disposed at the bottom, and the dielectric substrate  10  is layered on the fifth ground plate GND 5 .  
         [0080]     Except for the above, the GCPW fed microstrip antenna and the CPW fed microstrip antenna have the same construction, that is, the main radiating element  30 , the connection plates  35   a,    35   b,  the sub-radiating elements  40   a,    40   b,  third and fourth ground plates GND 3 , GND 4 , and the feed line  20  conductively coat the top planar surface of the dielectric substrate  10 .  
         [0081]     Referring to the microstrip fed antenna shown in  FIG. 8 , a sixth ground plate GND 6  is disposed at the bottom, and the dielectric substrate  10  is layered on the top of the sixth ground plate GND 6 . In contrast with the CPW fed microstrip antenna or the GCPW fed microstrip antenna, there is no ground plate formed on the dielectric substrate, but the main radiating element  30 , the connection plates  35   a,    35   b,  the sub-radiating elements  40   a,    40   b,  and the feed line  20  conductively coat the top of the dielectric substrate  10 .  
         [0082]     In FIGS.  6  to  8 , the connection plates  35   a,    35   b  electrically connect the main radiating element  30  with the sub-radiating elements  40   a,    40   b.  However, when the radiating elements are connected indirectly to each other through electromagnetic coupling, the main radiating element  30  and the sub-radiating elements  40   a,    40   b  are naturally spaced apart. If this is the case, the connection plates  35   a,    35   b  are unnecessary.  
         [0083]     Although FIGS.  6  to  8  illustrate an embodiment where the main radiating element  30  and the sub-radiating elements  40   a,    40   b  are disposed on the same planar surface, this is illustrative only. That is, the main radiating element  30  and the sub-radiating elements  40   a,    40   b  can be disposed on different planar surfaces. In this case, the main radiating element  30  and the sub-radiating elements  40   a,    40   b  are indirectly connected to each other, or can be connected directly to each other via hole (not shown).  
         [0084]     According to an embodiment of the invention shown in FIGS.  6  to  8 , the top end of the feed line  20  is etched to form a slot (not shown) of a predetermined size. Preferably, but not necessarily, the slots come in various shapes. When etched to form the slot, the feed line functions as a matching circuit for impedance matching. The feed line can be fed with a coaxial cable, and a center conductor (not shown) of the coaxial cable is connected directly to a lower end of the main radiating element  30  of the antenna  100 , and an outer conductor (not shown) is connected directly to the ground plates GND 1 -GND 6 .  
         [0085]     In the case of a related art antenna, an open stub is employed to the feed unit of the antenna to create impedance matching with respect to frequencies in a specific range. According to an embodiment of the invention, however, the slot is formed by etching the top end of the feed line, so any additional element like the open stub is not required.  
         [0086]      FIG. 9  is a plan view of a radiating element of the miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention.  
         [0087]     As shown in  FIG. 9 , the radiating element  50  includes a main radiating element  30 , and a plurality of sub-radiating elements  40   a,    40   b.  The upper ends of the main radiating element  30  and the sub-radiating elements  40   a,    40   b  have a rectangular shape, respectively. Although the lower ends of the main radiating element  30  and the sub-radiating elements  40   a  and  40   b  in  FIG. 9  have a rectangular shape, they are illustrative only. In effect, the lower ends of the radiating elements can have various shapes including a taper or inverted triangle.  
         [0088]     The main element  30  and the sub-radiating elements  40   a,    40   b  are electrically connected to each other through connection plates  35   a,    35   b.  The connection plates  35   a,    35   b  can be formed on the upper end, center, or lower end of the main and sub-radiating elements  30 ,  35   a,  and  35   b.  If the radiating elements are indirectly connected to each other through a medium like an electromagnetic coupling, the main radiating element  30  and the sub-radiating elements  40   a,    40   b  are naturally spaced apart. If this is the case, the connection plates  35   a,    35   b  are not necessary.  
         [0089]     The main radiating element  30  and the sub-radiating elements  40   a,    40   b  are made by etching one conductor plate and forming a slot therebetween. This type of structure is called a ‘notch’ structure.  
         [0090]     For convenience in explaining the notch structure, the lower-right end of the main radiating element  30 , the right side connection plate  35   b,  and the lower-left end of the right side sub-radiating element  40   b  are illustrated.  
         [0091]     As shown in  FIG. 9 , the notch structures come in various types. For example, (I) illustrates a structure where sides AB, BC, and CD meet at right angles to each other; and (II) illustrates a structure where sides AB and BC meet at right angles, while sides BC and CD form a (90°+θ 1 ) angle.  
         [0092]     (III) illustrates a structure where sides BC and CD are perpendicular to each other, and sides BC and AB form a (90°+θ 2 ) angle; and (IV) illustrates a structure where sides AB and BC form a (90°+θ 3 ) angle, and sides BC and CD form a ( 90  ° + 04 ) angle, wherein θ 1 , θ 2 , θ 3 , and θ 4  are arbitrary angles.  
         [0093]     The length of side AB, namely H 1 , is a controlling factor of the input impedance of the antenna. In other words, if the length of side AB (or H 1 ) is increased, the wideband characteristics of the antenna are limited and low frequency radiation patterns become distorted. Meanwhile, if H 2  is increased, high frequency radiation patterns are improved gradually to a certain limit, but when H 2  exceeds a predetermined length, the radiation patterns are distorted again.  
         [0094]      FIG. 10  illustrates another embodiment of  FIG. 9 .  
         [0095]     Referring to  FIG. 10 , the main radiating element  30  and the sub-radiating elements  40   a,    40   b  can be spaced apart from each other. In this case, the main radiating element  30  and the sub-radiating elements  40   a,    40   b  are indirectly connected to each other through an electromagnetic coupling.  
         [0096]     As shown in  FIG. 10 , the main radiating element  30  is located on the x-axis, and the sub-radiating elements  40   a,    40   b  are symmetric with respect to the xz plane. It should be noticed that more than two sub-radiating elements could be symmetrically arranged with respect to the xz plane.  
         [0097]     Also, additional sub-radiating elements  45   a,    45   b  can be formed on the dielectric substrate  10 . For example, in  FIG. 10 , the additional sub-radiating elements  45   a,    45   b  are indirectly connected to the main radiating element  30  or the sub-radiating elements  40   a,    40   b,  respectively, being spaced apart from each. Alternatively however, the additional sub-radiating elements  45   a,    45   b  can be connected directly to the main radiating element  30  and the sub-radiating elements  40   a,    40   b  through connection plates (not shown). Also, the main radiating element  30  and the sub-radiating elements  40   a,    40   b  and the additional sub-radiating elements  45   a,    45   b  can be all connected directly to each other through connection plates.  
         [0098]     Besides the shapes shown in  FIG. 10 , the additional sub-radiating elements  45   a,    45   b  come in various shapes, e.g., rectangular shapes, cross shapes, and ‘T’ shapes.  
         [0099]      FIG. 11  is a plan view of  FIG. 6 . Referring to  FIG. 11 , the upper end of the main radiating element  30  has a rectangular shape, and the short side of the bottom of the main radiating element  30  is directly connected with the short side of the top of the feed line  20 . In particular,  FIG. 11  illustrates the radiating element, in which the length of the short side of the bottom of the main radiating element  30 , a, is longer than the length of the short side of the top of the feed line  20 , c. Preferably, but not necessarily, the length of the long side, L, of the feed line  20  is about    55   mm.  
         [0100]     In an embodiment of the invention, the length of the short side of the bottom of the main radiating element  30 , a, is longer than or equal to the length of the short side of the top of the feed line  20 , c. That is, a≧c. Even though  FIG. 11  illustrates a rectangular-shaped lower end for the main radiating element  30 , a taper- or inverted triangle-shaped lower end is also possible.  
         [0101]     The shape of the upper ends of the sub-radiating elements  40   a,    40   b  can be arbitrary, but preferably it has a rectangular shape in the interest of reducing the size of the antenna  100 . Also, the shape of the lower ends of the sub-radiating elements  40   a,    40   b  does not have to be limited to the rectangular shape, but can be diverse like a taper or inverted triangle shape.  
         [0102]     If the sub-radiating elements  40   a,    40   b  are connected directly to the main radiating element  30 , the connection plates  35   a,    35   b  preferably but not necessarily, have taper shapes. That is, the width of the sub-radiating elements  40   a,    40   b  located lower than the connection plates  35   a,    35   b  is gradually reduced. The length of the long side of the sub-radiating elements  40   a,    40   b  is smaller than or equal to the length of the long side, d, of the main radiating element  30 . Preferably, but not necessarily, the length of the long side of the main radiating element  30  is about 11.5 mm.  
         [0103]     The width W 1  of the antenna, the sum of the length of the short side, a, of the main radiating element  30 , the length, b, of the connection plate, and the length of the short side, e, of the sub-radiating element. As shown in  FIG. 11 , W 1 =a+2b+2e≈6.272 mm.  
         [0104]     The ground plates GND are composed of broad planar conductors. The shape of the ground plates GND varies, depending on the feed structure being used. In other words, in case of the microstrip feeding, the ground plate GND 6  is formed by coating the bottom of the dielectric substrate with a conductor plate.  
         [0105]     In case of the CPW fed microstrip antenna, the first and second ground plates GND 1 , GND 2  are disposed on the dielectric substrate, each being spaced apart in both sides of the feed line. Meanwhile, in case of the GCPW fed microstrip antenna, the fifth ground plate GND 5  is formed at the bottom of the dielectric substrate, and the third and fourth ground plates GND 3 , GND 4 , similar to the ones in the CPW fed microstrip antenna, are disposed on the dielectric substrate, each being spaced part in both sides of the feed line.  
         [0106]     Preferably, but not necessary, the width W 2  of the ground plates GND 1 -GND 6  is approximately 35 mm. However, the size of the ground plates GND 1 -GND 6  can be varied according to what kind of the miniaturized ultra-wideband microstrip antenna  100  is applied.  
         [0107]     The following will now explain the operational principles of the present invention.  
         [0108]     Electromagnetic energy transmitted through the microstrip fed antenna, the CPW fed antenna, or the GCPW fed antenna is transmitted in TEM or QuasiTEM mode to the radiating element  50 . This transmitted energy is expressed as the current flow at the surface of the radiating element  50 .  
         [0109]      FIGS. 12A and 12B  illustrate current distribution of the miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention, where the amplitude of the antenna is 1 and the phase of the antenna is 0 degree, respectively  
         [0110]     More specifically,  FIG. 12A  illustrates the current distribution when the center frequency is 5 GHz. Referring to  FIG. 12A , the current is mainly induced around the lower end of the main radiating element  30 .  FIG. 12B  illustrates the current distribution when the center frequency is 10 GHz. Referring to  FIG. 12B , the current is induced even to a certain area of the sub-radiating elements  40   a,    40   b  through the connection plates  35   a,    35   b.    
         [0111]     Then, an electromagnetic field is generated perpendicular to the current flow, and as a result, spherical electromagnetic waves are radiated from the antenna.  
         [0112]      FIGS. 13A and 13B  are three-dimensional diagrams illustrating a radiation pattern of the miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention plotted on spherical coordinates. More specifically,  FIG. 13A  illustrates the radiation pattern in a spherical shape, wherein the pattern is calculated at a central frequency of 5 GHz.  FIG. 13B  illustrates the radiation pattern in an elliptical shape, wherein the pattern is calculated at a central frequency of 10 GHz.  
         [0113]      FIG. 14  is a graph illustrating an insertion loss S 11  of the miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention. As shown in  FIG. 14 , the insertion loss S 11  in a frequency range extending from 3.0 GHz to 12 GHz is less than 10 dB, so that the present invention antenna satisfies UWB&#39;s range.  
         [0114]      FIG. 15  illustrates the insertion loss (S 11 ) of  FIG. 14  plotted on a smith chart. The chart shows a frequency trajectory when standard input power is applied, and amplitude and phase of the antenna with respect to different frequencies.  
         [0115]      FIG. 16  is a graph illustrating VSWR of the miniaturized ultra-wideband microstrip antenna according to an aspect of the present invention. As shown in  FIG. 16 , the VSWR in a frequency range from 3.0 GHz to 12 GHz is less than 2.0, that is the present invention antenna satisfies UWB&#39;s range.  
         [0116]     In case of constructing an antenna having additional sub-radiating elements according to an embodiment of the invention, the VSWR in a frequency range from 3.0 GHz to 18 GHz can be reduced to lower than 2.0. Thus, excellent wideband characteristics can be obtained.  
         [0117]     Therefore, it is possible to construct a miniaturized ultra-wideband microstrip antenna having no reflection in a desired frequency range.  
         [0118]     In conclusion, according to an aspect of the present invention, it is possible to construct a miniaturized, ultra-light antenna combined with the dielectric substrate. Also, applying the PCB process, the microstrip antenna can be more easily and cost-effectively manufactured.  
         [0119]     Also, according to an aspect of the present invention, the antenna includes additional sub-radiating elements besides the main radiating element, whereby multi-radiation in the UWB range can be realized.  
         [0120]     According to an aspect of the present invention, the antenna has an improved notch structure for the radiating element. Thus, it is easy to adjust a frequency range and to control multi-band and band stop characteristics.  
         [0121]     According to another aspect of the present invention, the current distribution can be changed in dependence of changes of radiation frequency, and through these changes, the radiation area can be changed also. In this manner, radiation patterns in wideband can be improved.  
         [0122]     Lastly, the microstrip antenna of the present invention can be advantageously used for high-speed radio communication antennas employing electromagnetic impulses. This is because in case of the present invention antenna, time delay in transmitting/receiving impulses in different frequencies is insignificant compared to existing antennas and thus, pulses are hardly distorted.  
         [0123]     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.