Abstract:
A miniature monopole antenna used in a wireless communication system. The monopole antenna has a radiation body, a feeding point and a short point. The radiation body has a plurality of slits alternatingly arranged at two opposite edges of the radiation body, and every slit is perpendicular to the sides of the radiation body and extends toward the inner of the radiation body. The radiation body resonates with a signal of a predetermined frequency, and is connected to the signal processing unit via the feeding point. In addition, the operational stability can be enhanced when the short point is grounded.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Taiwan Application Serial Number 93123533, filed Aug. 5, 2004, the disclosure of which is hereby incorporated by reference herein in its entirety.  
       BACKGROUND  
       [0002]     1. Field of Invention  
         [0003]     The present invention relates to an antenna apparatus. More particularly, the present invention relates to a miniature monopole antenna apparatus built in a wireless communication system.  
         [0004]     2. Description of Related Art  
         [0005]     According to the progress of communication technology, the key development is the transfer from wired to wireless communication, such as the popularization of wireless household phones and mobile phones. In the field of wireless communication, the signal carrier is invisible air waves, where the bridge between the electrical signal and the air waves is an antenna. That is to say, an antenna is certainly needed by a wireless communication device to transmit or receive air waves. An antenna is therefore an essential component in a wireless communication device.  
         [0006]     In the conventional wireless communication device, the antenna apparatus is usually attached to the exterior of the device, and causes a variety of problems. For example, an antenna is easily damaged by external force, and the overhead of the circuit design is rising and hard to carry. In addition, in accordance with the present design trend, many functions are integrated into a device, such as a mobile phone with the data processing function of a personal digital assistant (PDA) or a portable computer system with Bluetooth communicating function and wireless local area network (WLAN). Thus, the amount of components and antennas will substantially increase in the device, but the volume of the device must be maintained within a range. For these reason, the external antenna is increasingly unsuited to use in advanced wireless communication devices.  
         [0007]     Ii is apparent that the miniature antenna built in the wireless communication devices will be a mainstream trend in the communications field. The conventional built-in miniature antenna techniques comprise chip antenna and planer antenna, and have some problems. For example, a chip antenna connects with a communication system via a carrier, and the relations between the dielectric constant of the carrier and the operation frequency of the antenna, and between the dielectric constant of the carrier and the performance of the antenna, all are an inverse proportion. That is to say, if the chip antenna needs a lower operation frequency, the dielectric constant of the carrier must be higher, and causes a lower performance of the chip antenna. Besides, the mounting technique used by some of built-in miniature antennas may be different from the mounting techniques used by the communication system. Thus, the antenna and the system are difficult to integrate and expensive.  
       SUMMARY  
       [0008]     It is therefore an objective of the present invention to provide a built-in miniature antenna apparatus.  
         [0009]     It is another objective of the present invention to provide a miniature antenna apparatus, which has a stable performance and is easily integrated into a wireless communication system.  
         [0010]     It is still another objective of the present invention to provide a wireless communication device with a built-in miniature antenna, where the wireless communication device is small and easily carried.  
         [0011]     In accordance with the foregoing and other objectives of the present invention, the invention provides a rectangular radiation body made of metal, which has a feeding point, a short point, and a plurality of threadlike slits. The slits are alternatingly arranged on opposite edges of the radiation body and perpendicularly extend to the interior of the radiation body. Due to a zigzag path formed by the slits on the radiation body, the radiation body resonates with a signal of a specific frequency. In addition, the feeding point is used to connect the radiation body and a signal processing unit, and the short point is used as a ground for enhancing the matching ability of the antenna and the operational stability thereof.  
         [0012]     The radiation body also has many pins to allow perpendicular mounting of the radiation body on the substrate of a communication system by the identical surface mounting technique (SMT) used by the others components.  
         [0013]     It is to be understood that both the foregoing general description and the following detailed description are by examples and are intended to provide further explanation of the invention as claimed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:  
         [0015]      FIG. 1  illustrates the structure of a monopole antenna in accordance with an embodiment of the present invention;  
         [0016]      FIG. 2A  illustrates the structure of a monopole antenna in accordance with an embodiment of the present invention;  
         [0017]      FIG. 2B  illustrates the structure of a monopole antenna in accordance with an embodiment of the present invention; and  
         [0018]      FIG. 2C  illustrates the installation of a monopole antenna in accordance with an embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
         [0020]     The basic concept of the present invention is defining a current conducting path on a antenna body made by metal for resonating with a signal has a predestinate frequency, wherein the frequency is determined by the length of the current conducting path.  
         [0021]      FIG. 1  shows the structure of a built-in miniature monopole antenna according to an embodiment of the present invention. The body of a monopole antenna  100  comprises a rectangular region and a section  110 , where the rectangular is constituted by edges  102 - 108  and the section  110  can be connected with any edge of the rectangular region. In the embodiment, the section  110  is extended and formed from the edge  106 , and is perpendicular to the edge  104 . The monopole antenna  100  is made of metal, such as nickel-plated copper. Many pins perpendicularly extend from the edge  106 ; these pins comprise a short point  112 , a feeding point, and pins  116 - 120  used to fix the monopole antenna  100 . In addition, many slits are alternatingly arranged at the edge  102  and the edge  106 ; that is, slits  122 - 126  in the embodiment, but the number of slits is not limited by the embodiment in practice. Slits  122 - 126  are perpendicular to the edge  102  or the edge  106 , respectively, and all extend to the interior of the monopole antenna  100 .  
         [0022]     According to the antenna structure from the foregoing description, a zigzag path with a specific length is formed by segmenting the body of the monopole antenna  100  by slits  122 - 126 , and the path allows the monopole antenna  100  to resonate with a signal of a specific frequency. The frequency value of the signal is determined by the length of the path, because the relation between the resonance frequency value and the length of the path is an inverse proportion. That is to say, when more slits are in the monopole antenna  100 , the path is longer and the resonance frequency value is lower. Thus, the resonance frequency value can be determined by the number of slits on the monopole antenna  100 .  
         [0023]     For example, if the resonance frequency value of the monopole antenna  100  shown in  FIG. 1  is to be about 2.4 GHz or 5.2 GHz, the monopole antenna  100  can be used in a Bluetooth or a wireless local area network (WLAN) communication system. Furthermore, if the monopole antenna  100  is to be uses in a communication system with a higher operation frequency, a reduction in the length of the path achieves the objective. The length of the path can be reduced by decreasing the number of slits or reducing the length of the slits. Comparatively, if the monopole antenna  100  is to be used in a communication system with a lower operation frequency, an increase in the length of the path achieves the objective. That is, the number or the length of the slits is increased.  
         [0024]     The short point  112  can be connected to a ground potential or floated. If the short point  112  is grounded, the matching ability of the monopole antenna  110  will be enhanced, and then the operation of the monopole antenna  100  will be more stable. The pins  116 - 120  are floated and are used to perpendicularly fix the monopole antenna  100  on the system substrate. The number of floating pins is not limited as long as the monopole antenna  100  can be fixed.  
         [0025]     Reference is made to  FIG. 2A  and  FIG. 2B . The shape of the monopole antenna may be changed from flat to three-dimensional. For example, a monopole antenna  200  shown in  FIG. 2A  has the same structure and operation as the monopole antenna  100  shown in  FIG. 1 , and the monopole antenna  200  also can be bent into a shape shown in  FIG. 2B . For this purpose, a section  202  of the monopole antenna  200  is bent along an edge  204 , and the monopole antenna  200  is bent along a folding line  210  with a distance  208  from a edge  206 . The bending direction of the section  202  and the monopole antenna  200  is the same and the distance  208  is approximately between the length of the section  202  and the distance between the folding line  210  and the edge  204 . Referring to  FIG. 2B , the bent monopole antenna  200  can be divided into three parts, comprising the section  202 , a flat  212  and a flat  214 . In this embodiment, the range of an angle  216  between the section  202  and the flat  212  is about 60° to 90°, and an angle  218  between the flat  212  and the flat  214  is about 90° to 120°.  
         [0026]      FIG. 2C  shows the installation of the monopole  200  on a substrate  220 , where the substrate  220  is a general circuit board used in a circuit system, such as an isolated region in a printed circuit board (PCB). The monopole antenna  200  is perpendicularly installed on the substrate  220 ; that is to say, the section  202 , flat  212  and flat  214  shown in  FIG. 2B  all are perpendicular to the substrate  220 . Then, any fixing technique used in the circuit board field may be used to fix a short point  222 , a feeding point  226  and pins  226 - 230 . In this embodiment, the short point  222 , feeding point  224  and pin  230  is bent to the inside and then fixed on the surface of the substrate  220  by a surface mounting technique (SMT). Furthermore, the pins  226  and  228  are buried in the substrate  220  at first, and then are fixed. Different fixing techniques may be used to fix these pins for different applications, and the embodiment is not to be construed as a limitation on the scope of the invention.  
         [0027]     After the monopole antenna  200  is fixed, the pins  226 - 230  can be kept floating. The feeding point  224  is connected with a radio frequency (RF) component (not shown) of a wireless communication system, such as a mobile phone or PDA system with a Bluetooth or WLAN function, for signal communication. Thus, the monopole antenna  200  is integrated with the communication system. Furthermore, the short point  222  may be kept floating or grounded. If the short point  222  is grounded, the matching ability of the monopole antenna  200  can be enhanced, and the operation of the monopole antenna  200  can also be more stable. The connections between the components referred herein can be formed by any wiring technique used in a circuit board.  
         [0028]     According to the foregoing description, the monopole antenna of the present invention has many characteristics, such as simple material, low cost high performance and ease of integration. According to the description of the embodiment of the present invention, the monopole antenna is formed from sheet metal to avoid material that is complicated or hard to acquire, thus reducing the cost of the wireless communication system. However, the monopole antenna still keeps the operational performance at a level. Compared with conventional chip antennas, the monopole antenna of the present invention can be installed without any carrier; therefore, the performance of the antenna will not be degraded by the effect of the carrier. On the whole, the monopole antenna of the present invention is evidently better than the chip antenna in the aspects of power consumption and sensitivity. In addition, the monopole antenna of the present invention can be easily integrated with the whole system, because the monopole antenna of the present invention has a smaller volume and only fixing and wiring techniques used in the general circuit board, such as PCB, are needed. For example, if the monopole antenna shown in  FIG. 2C  is designed to be used in the band of 2.4 GHz, the size thereof may only be 9.5×4.5×4.3 mm. Similarly, if the monopole antenna is designed to be used in a higher band, the size thereof will smaller; that is to say, the length thereof will not be more than 10 mm, and the monopole antenna is well suited to be used in a small system.  
         [0029]     When a monopole antenna of the present invention starts to be integrated with a system where a PCB is to be used as a substrate, an isolated region for placement of the monopole antenna is first planed on the circuit board. Then, the monopole antenna is fixed on the isolated region in the circuit board by the same SMT used to fix the other components, such as integrated circuits or passive devices, on the circuit board. Finally, the monopole antenna can be connected to the other components in the system by a general wiring technique of PCB.  
         [0030]     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.