Abstract:
An antenna for ultra-wide band communication is disclosed. The antenna includes a substrate, a patch formed on one side of the substrate so as to be smaller than the substrate, and being excited when an electric current is supplied through a feeder line, so as so radiate energy, and a ground area formed by removing a portion of another side of the substrate so as to obtain a wide band characteristic.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Application No. P2003-049755, filed on Jul. 21, 2003, which is hereby incorporated by reference as if fully set forth herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an ultra-wide band antenna, and more particularly, to an antenna for ultra-wide band communication. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for fabricating an antenna having a compact size, being light weight, and having a low fabrication cost. 
   2. Discussion of the Related Art 
   The ultra-wide band (UWB) communication is a wireless communication method, which was first developed by the United States Department of Defense in the 1960&#39;s and used for military purposes. The UWB communication has a wide frequency band, a low power consumption, and a fast transmission speed. Also, the UWB communication forms a spectrum of a level lower than that of a white noise in a code division multiple access (CDMA) communication. Thus, the listening-in or cutting-off of signals becomes difficult, thereby being suitable for maintaining security. Moreover, unlike the conventional communication system, the UWB communication system performs communication using pulses. Recently, due to such characteristics, the UWB communication has been considered to be a next generation wireless data communication method, research on which is being extensively carried out worldwide. 
   Due to the many advantages of the UWB communication, the UWB communication is expected to be used extensively in various systems, such as personal communication networks or home networks connecting personal computers (PC), television receivers (TV), personal digital assistants (PDA), digital versatile discs (DVD), digital cameras, and printers, which are within a close range of 10 meters (m), global positioning systems, automobile collision avoidance systems, and medical apparatuses. The current UWB communication system is currently being standardized at a vast rate, starting from the United States. Many related corporations and university research laboratories have founded a mutual technology research group called the Ultra Wideband Working Group (UWBWG), which carries out many active studies. The level of interest is also increasing in the related fields in Korea by holding diverse forums and so on. 
   Recently, in the United States, the Federal Communications Commission (FCC) has approved the usages of the UWB communication bandwidth ranging from 3.1 to 10.6 gigahertz (GHz), in order to eliminate radio frequency interference with the conventional mobile communication system and the global positioning system (GPS). Herein, the transmission range has also been limited to within 9 meters (m). Therefore, in the related industry, the UWB communication is being considered as a new alternative for the wireless personal area network (WPAN), and applications of the UWB communication method are being actively and extensively developed. 
   However, one of the most important factors in the development of the UWB communication system is the development of an ultra-wide band antenna. More specifically, the UWB communication system has many advantages, such as very high speed communication, high amount of transmission, excellent obstacle transmission, a simple structure of receiver/transmitter, low transmission power, and so on. Herein, the UWB antenna acts as an essential assembly part for representing the UWB communication system having the above-described advantages. 
   In order to ensure the mobility of the UWB antenna, the UWB antenna should be formed to have the characteristics of compact size, simple and easily fabrication method, and low product cost. Additionally, the UWB antenna should also have a structure having a constant impedance value independent from the corresponding frequency. Furthermore, the UWB antenna should also have little distortion in the pulse signal. However, the development of such antenna has brought about many difficulties. And, a wide range of researchers has been globally participating in the development of an ultra-wide band antenna. Recently, only a few companies, such as Skycross, Timedomain, Taiyo-Yuden, and so on, have presented their mock-up products of the UWB antenna. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to an antenna for ultra-wide band communication that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
   An object of the present invention is to provide an antenna for ultra-wide band communication being of a compact size and light weight, and having a low fabrication cost. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
   To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an antenna for ultra-wide band communication includes a substrate, a patch formed on one side of the substrate so as to be smaller than the substrate, and being excited when an electric current is supplied through a feeder line, so as so radiate energy, and a ground area formed by removing a portion of another side of the substrate so as to obtain a wide band characteristic. 
   Herein, the substrate is a printed circuit board. The substrate may be formed of any one of low resistance silicon, glass, alumina, teflon, epoxy, low temperature co-fired ceramic. 
   The patch is formed to have a center frequency of 5.8 gigahertz (GHz). The patch may be formed in a shape of any one of a circle, a triangle, a rectangle, and a polygon. Herein, an air gap slot is formed in the patch, so as to control a frequency band. The air gap slot is formed in a shape of any one of a circle, a triangle, a rectangle, and a polygon. 
   Additionally, a plurality of matching stubs is formed between the patch and the feeder line, so as to perform an impedance matching between the patch and the feeder line. Each of the matching stubs may be formed in a shape of any one of a rectangle, a trapezoid, and a circle, and is formed in one of a singular form and an array form. Herein, one of the matching stubs being adjacent to the feeder line has a width smaller than that of another one of the matching stubs. 
   The ground area is formed in a single patch form, and an air gap slot is formed within the ground area. Herein, the air gap slot is formed in a shape of any one of a circle, a triangle, a rectangle, and a polygon. Furthermore, the patch is formed on the substrate in one of a single-layered structure and a multi-layered structure. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF TIRE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
       FIG. 1  illustrates a front side view of an ultra compact size antenna for ultra-wide band communication according to the present invention; 
       FIG. 2  illustrates a rear side view of the ultra compact size antenna for ultra-wide band communication according to the present invention; 
       FIG. 3  illustrates a graph showing measurements of return loss in the antenna for ultra-wide band communication according to the present invention; 
       FIG. 4  illustrates a graph showing a group delay in the antenna for ultra-wide band communication according to the present invention; 
       FIG. 5  illustrates samples showing measurements of radiation patterns in the antenna for ultra-wide band communication according to the present invention; 
       FIG. 6  illustrates a graph showing measurements of gain in the antenna for ultra-wide band communication according to the present invention; 
       FIGS. 7(   a )– 7 ( d ) illustrate different shapes of a patch; 
       FIGS. 8(   a )– 8 ( c ) illustrate different shapes of air gap slots; 
       FIGS. 9(   a )– 9 ( c ) illustrate different shapes of matching stubs; 
       FIG. 10  illustrates an array form of matching stubs; and 
       FIG. 11  illustrates a multi-structure patch antenna. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
   The antenna for ultra-wide band communication is a flat patch antenna, which has been devised to receive ultra-wide band (UWB) communication frequency band (i.e., ranging from 3.4 to 10.6 gigahertz (GHz)) and to have characteristics of compact size and light weight.  FIGS. 1 and 2  illustrate the ultra compact size antenna for ultra-wide band communication, wherein  FIG. 1  illustrates the front side view and  FIG. 2  illustrates the rear side view. 
   Referring to  FIG. 1 , in the antenna for UWB communication according to the present invention, a patch  101  is formed on a surface (or one side) of a substrate  108 , wherein the patch  101  is designed to have a center frequency of 5.8 gigahertz (GHz). At this point, as shown in  FIGS. 7(   a )–( d ), respectively, the shape of the patch  101  can be one of a circle, a triangle, a square or rectangle, a polygon, and so on, without limitations. However, the rectangular or round shapes are most widely used for the simplicity of the description. In the description of the present invention, the rectangular shaped patch  101  will be given as an example in the embodiment of the present invention. 
   In addition, an air gap slot  102  is formed in the patch  101 , so as to control the frequency and reduce the size of the antenna. More specifically, by controlling the bandwidth through the air gap slot  102 , the frequency can be controlled to be similar to the UWB communication bandwidth, which ranges from 3.1 to 10.6 gigahertz (GHz). As shown in  FIGS. 8(   a )– 8 ( c ), the shape of the air gap slot  102  can be one of a circle, a triangle, a square or rectangle, a polygon, and so on, without limitations. In the embodiment of the present invention, the air gap slot  102  has a rectangular shape. 
   As shown in  FIG. 2 , a set portion of another surface of the substrate  108  is removed to form a ground  107 . In the present invention, the surface area of the ground  107  is reduced, so that the frequency bandwidth can become a wide band. The ground  107  can be formed as a single patch shape, and an air gap slot of various shapes can also be formed on the ground  107 . 
   Referring to  FIG. 1 , matching stubs  104  and  105  are formed between a feeder line  103  and the patch  101  for an impedance matching between the feeder line  103  and the patch  101 . Herein, the feeder line  103  refers to a cable electrically connecting a receiver and an antenna or connecting a receiver and a feed point of the antenna, so as to transmit a high frequency power. The matching stub refers to a branch circuit or a lumped element fixed on a portion of a transmission cable, such as a twin parallel line, a coaxial line, a wave guide, and so on, so as to perform impedance matching. In other words, the matching stubs  104  and  105  are connected to the patch  101 , thereby matching a 50 ohm (Ω) feeder line  103 . Thus, the antenna for UWB communication can have a wider bandwidth (i.e., a bandwidth of 6 gigahertz (GHz)). 
   The matching stubs  104  and  105  can also be designed to have shapes other than a rectangle, such as shown in  FIGS. 9(   a )– 9 ( c ), respectively, a trapezoid, a polygon, or a circle, and the matching stubs  104  and  105  can also be designed to have an array form as shown in FIG  10 . Herein, the width of the matching stub  105  is formed to be smaller than the width of the matching stub  104 , thereby facilitating the flow of the radio waves. Moreover, the feeder line is formed of a coaxial cable having excellent characteristics of safety, shielding, low loss, voltage standing wave ratio (VSWR), and work efficiency. 
   In the embodiment of the present invention, a printed circuit board is used as the substrate  108 . More specifically, an FR-4 substrate, which is the most widely used among printed circuit boards, is used as the substrate  108 , thereby reducing the fabrication cost and allowing mass production of the present invention. Evidently, instead of the FR-4 substrate, low resistance silicon, glass, alumina, teflon, epoxy, low temperature co-fired ceramic, and so on can also be used as the substrate  108 . 
   Herein, when the FR-4 printed circuit board is used as the substrate  108 , the value of the dielectric constant (or permittivity) is 4.4, the height is 1.6 millimeters (mm), and the overall size of the antenna including the substrate is 30×35 square millimeters (mm 2 ), thereby allowing the antenna for UWB communication to be formed in a compact size. Meanwhile, the antenna for UWB communication according to the present invention can be formed substrate  108  in a single-layer form or a multi-layered form (see  FIG. 11 ). The UWB antenna having the above-described structure can be formed in a patch structure having a rectangular shape, and can use the FR-4 printed circuit board, thereby reducing the fabrication cost and allowing mass production. 
   Meanwhile, the bandwidth of the antenna for UWB communication does not vary much depending upon the increase or decrease of the size of the rectangular patch  101 , shown  FIG. 1 . However, if the size of the patch  101  increases, the frequency of the antenna for UWB communication makes a downward movement. Conversely, if the size of the patch  101  decreases, the frequency of the antenna for UWB communication makes an upward movement. 
   Also, by controlling the surface area of the ground  107 , the antenna for UWB communication may have the characteristic of a wide band. More specifically, when a ground height  106  approaches a distance approximate to the rectangular patch  101 , the voltage standing wave ratio (VSWR) becomes small. On the other hand, when the ground height  106  becomes further away from the rectangular patch  101 , the VSWR becomes large. In other words, the VSWR value exceeds 2:1 at 6.5 gigahertz (GHz). In this case, the return amount becomes smaller as the VSWR decreases. Accordingly, if the VSWR is less than 2:1, it can be considered that the matching has been performed relatively accurately. 
   Therefore, an optimized value obtained through simulation is applied as the height of the ground  107 . Similarly, optimum values of the matching stubs  104  and  105  are also obtained through simulation. Moreover, the rectangular slot  102  in the rectangular patch  101 , shown in  FIG. 1 , not only controls the frequency, but can also reduce the size of the antenna, the optimum value of which can also be decided through simulation. The optimum value is decided while taking into consideration that the VSWR value becomes deficient as the width of the rectangular slot  102  becomes larger, and that an excessively long or short length of the rectangular slot  102  influences the bandwidth. 
   When performing the simulation in the present invention, the MicroWave Studio (MWS) of Computer Simulation Technology, Inc. (CST) is used as the simulation tool. However, the actual measurement results measured and obtained after fabricating the antenna for UWB communication were found to be similar to the simulation results. More specifically, the bandwidth was measured to be within the range of 3.4 to 12 gigahertz (GHz), which generally accommodates the frequency bandwidth required in the UWB communication system, which is within the range of 3.1 to 10.6 gigahertz (GHz). 
     FIG. 3  illustrates a graph showing measurement results of return loss in the antenna for ultra-wide band (UWB) communication according to the present invention. Herein, the return loss is measured by using a network analyzer. Referring to  FIG. 3 , the antenna for UWB communication is shown to have a bandwidth ranging from 3.4 to 12 gigahertz (GHz) at a voltage standing wave ratio (VSWR) of 2:1. 
     FIG. 4  illustrates a graph showing a group delay in the antenna for ultra-wide band communication according to the present invention. The level of distortion in the pulse signal can be determined based depending upon the group delay. Therefore, the group delay may act as an essential parameter for the design and analysis of the antenna for UWB communication. Referring to  FIG. 4 , the antenna for UWB communication is shown to have a group delay of 2 nanoseconds (ns) demonstrating an excellent performance. This result may be considered to be similar to that of an antenna developed by other manufacturing companies. 
     FIG. 5  illustrates samples showing measurements of radiation patterns in the antenna for ultra-wide band communication according to the present invention. Referring to  FIG. 5 , the antenna for UWB communication is shown to have an omni-directional characteristic in an XZ plane. Herein, such radiation pattern is similar to that of a dipole antenna. 
     FIG. 6  illustrates a graph showing measurements of gain in the antenna for ultra-wide band communication according to the present invention. Referring to  FIG. 6 , when the antenna for UWB communication is at a UWB communication bandwidth of 3 gigahertz (GHz), the maximum gain is 6.03 decibels-isotropic (dBi) and the minimum gain is −6.67 decibels-isotropic (dBi). 
   The antenna for UWB communication and the UWB communication system according to the present invention can be extensively used in the areas of electric household appliance industry, personal computer industry, mobile phones, personal digital assistants (PDAs), medical equipments, automobile industry, and so on. As described above, the antenna for UWB communication according to the present invention can be formed to have the characteristics of compact size, light weight, excellent performance, and low product cost, by being fabricated as a flat patch antenna accommodating UWVB communication frequency bandwidth. 
   Moreover, the surface of a ground area is reduced, and a plurality of matching stubs is formed between the patch and the feeder line, thereby obtaining a wider bandwidth. Also, an FR-4 substrate is used, thereby reducing the fabrication cost and enabling mass production. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.