Abstract:
One dual-band monopole antenna composed of a microwave substrate, radiation devices and transmission line is disclosed. The radiation device includes the central radiation body and two radiation arms. The central radiation body is used to generate one resonance mode, and the two radiation arms are used to generate another resonance mode. Thus, the dual-band monopole antenna is capable of operating at two different frequencies. In practical applications, radiation arms can be put symmetrically on two opposite sides and close to the central radiation body.

Description:
[0001]    This application claims the benefit of Taiwan application Serial No. 091116519, filed on Jul. 24, 2002.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention is related to a dual-band antenna, and more particularly to a dual-band monopole antenna.  
           [0004]    2. Description of the Related Art  
           [0005]    As a result of the prosperous growth of the communication industry, various radio frequency (RF) products are commercially available in a short period of time. For the wireless local area network, its related products own rather high market value and attraction. Antenna design is one of the key techniques in wireless system. Monopole antennas with long linear conductors are widely used in wireless local area network (WLAN) related products. Its large volume and complicated structure limit its application. Furthermore, the monopole antennas with long linear conductors need additional matching circuit, which results in high manufacturing cost.  
           [0006]    On the other hand, high frequency RF signal (5.2 GHz for example) transmission can be easily interfered by landforms and decays rapidly. For this reason, the transmission distance and signal quality will be affected seriously. In terms of wireless transmission applications, not only the convenience of dual-band operation but also high frequency antenna gain must be considered. Thus, how to enhance the performance and the operation of all communication system in high-frequency band (such as the 5.2 GHz band (5.15-5.35 GHz), is the hot issue nowadays.  
         SUMMARY OF THE INVENTION  
         [0007]    It is therefore an object of the invention to provide a dual-band monopole antenna of low manufacturing cost.  
           [0008]    Another object is to provide a dual-band monopole antenna with both characteristics of high antenna gain and dual-band operation.  
           [0009]    In accordance with the object of the invention, it provides a dual-band monopole antenna, which is concisely described as follows.  
           [0010]    Dual-band monopole antenna can be manufactured by microwave substrate, and the radiation devices can be formed on surface of microwave substrate by printing technology or etching technology. Radiation device is composed of a central radiation body and two radiation arms. To make dual-band antenna capable of performing two different frequency operations, the central radiation body is used to generate a resonance mode, and the two radiation arms are used to generate another resonance mode. In practical applications, the radiation arms can be arranged symmetrically and on opposite sides of the central radiation body. In addition, the use of two radiation arms makes the antenna radiation field enhanced to increase antenna gain.  
           [0011]    Further, in order to make the purpose, feature and advantage of the invention more obviously understood, one preferred embodiment is described in detail with figures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The description is made with reference to the accompanying drawings in which:  
         [0013]    [0013]FIG. 1 illustrates a dual-band monopole antenna according to the preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 2 illustrates assembly of radiation device in FIG. 1;  
         [0015]    [0015]FIG. 3 illustrates measurement of return loss of dual-band monopole antenna in FIG. 1;  
         [0016]    [0016]FIG. 4 illustrates measurement of antenna gain of dual-band monopole antenna operating in the 2.4 GHz band;  
         [0017]    [0017]FIG. 5 illustrates measured value of antenna gain of dual-band monopole antenna operating in the 5.2 GHz band;  
         [0018]    [0018]FIG. 6 illustrates a transformation of the radiation device in FIG. 1; and  
         [0019]    [0019]FIG. 7 illustrates another transformation of radiation device in FIG. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Referring to FIG. 1, a dual-band monopole antenna  11  is provided according to the preferred embodiment of the present invention. The dual-band monopole antenna  11  can be manufactured by using a microwave substrate  10  as a substrate. On the microwave substrate  10 , a radiation device  100  can be formed by printing technology or etching technology to generate two resonance modes. For signal transmission, while a microstrip line is used as a transmission line, the microstrip line  150  can be settled on the topside of the microwave substrate  10  for connecting the radiation devices  100 , and a grounding surface (Gnd) corresponding to the microstrip line  150  is set on the backside of microwave substrate  10 . As one skilled in the art knows, a coplanar waveguide (CPW) or coaxial cable can also be used to be the transmission line for connecting radiation device  100  to transmit antenna signal.  
         [0021]    Referring now to FIG. 2, it illustrates the assembly of the radiation device  100 . The radiation device  100  includes a central radiation body  110  and radiation arms  133 ,  135 . The central radiation body  110  is used to generate the first resonance mode of the first operating frequency, and the radiation arms  133 ,  135  are used to generate the second resonance mode of the second operating frequency. The length of the central radiation body  110  can be designed to be longer than the length of the radiation arms  133  and  135 , so that the central radiation body  110  can resonate at lower frequency. Taking the wireless local area network as an example, the antenna is preferred to have two operating frequency bands at 2.4 GHz and 5.2 GHz. The length of the central radiation body  110  is accordingly a quarter of the wavelength of 2.4 GHz and the lengths of the radiation arms  133 ,  135  are accordingly a quarter of the wavelength of 5.2 GHz. According to the spirit of the invention, the radiation arms  133  and  135  are symmetrical and are respectively positioned on two opposite sides of the central radiation body  110  by bending for a specific angle. Referring to the radiation body shown in FIG. 2, wherein the central radiation body  110  is a rectangular structure, the radiation arms  133  and  135  are bent for about 90 degrees to be positioned on the left and right sides of the central radiation body  110 . The radiation arms  133  and  135  are both close to the central radiation body  110 , which makes the proposed antenna have a smaller lateral width.  
         [0022]    In order to have high antenna gain during operation, two radiation arms are used. The radiation arms  133  and  135  are preferably set symmetrical and extended in the same directions (along y-axis as shown in FIG. 2). By this arrangement, the radiation field of the antenna is nearly omnidirectional in azimuth angle plane. As a result, good impedance match for the proposed antenna can be obtained without additional match circuit, and consequently a dual-band antenna can be manufactured in lower cost.  
         [0023]    Referring to FIG. 3, it shows the return loss of the dual-band monopole antenna  11 . The dielectric coefficient of the microwave substrate  10  is about 4.4, the thickness of the microwave substrate  10  is about 0.4 mm, and the length of the microwave substrate  10  is about 57 mm. The length of the central radiation body  110  is about 25 mm. The resonance mode  21  and the resonance mode  23  are generated when the central radiation body  110  is excited. The corresponding operating frequency of the resonance mode  21  is 2.4 GHz, and the operating frequency of the resonance mode  23  is two times of the frequency of the resonance mode  21 . And the lengths of the radiation arms  133 ,  135  are about 13 mm. The resonance mode  22  is generated when the radiation arms  133 ,  135  are excited. The corresponding operating frequency of the resonance mode  22  is about 5.2 GHz. In terms of frequency band, if 1.5:1 voltage standing wave ratio (VSWR) or 14 dB return loss is defined, the frequency band is 112 MHz when operating at about 2.4 GHz, and the frequency band is 310 MHz when operating at about 5.2 GHz, which meet respectively the frequency band requirements of wireless local area network when operating in the 2.4 GHz (2.4˜2.484 GHz) and 5.2 GHz (5.15˜5.35 GHz) bands.  
         [0024]    Referring to FIG. 4, it shows the antenna gain of the dual-band monopole antenna  11  operating in the 2.4 GHz band. It is revealed that the antenna gain can reach up to 2.1 dBi. FIG. 5 shows the antenna gain of the dual-band monopole antenna  11  operating in the 5.2 GHz band. It is revealed that the antenna gain can reach up to 5.7 dBi. By FIG. 4 and FIG. 5, the dual-band monopole antenna provided by the present invention is capable of having high antenna gain for dual-band operation, especially for operating in the higher frequency band.  
         [0025]    Some trivial deformations of the feature of the central radiation body or the radiation arms for the proposed invention are also within the scope of the invention. For example, the width of the central radiation body  610  in FIG. 6 can be modified to increase linearly, the width of the central radiation body  710  in FIG. 7 can be modified to increase in stepping or the widths of the radiation arms  713 ,  715  can be modified to increase linearly. These modifications of the features do not influence the applicability of the present invention. Other modifications like forming slot or slit at the edge or internal of the central radiation body  710  or the radiation arms  713 ,  715  for the purpose of miniaturizing the product size, do not substantially affect the performance of the invention.  
         [0026]    The width of the dual-band monopole antenna operating in the 2.4 GHz and 5.2 GHz bands according to the embodiment of present invention is only about 12 mm, which is very close to the popular long linear monopole antenna and is ideal for dual-band operations of wireless local area network. In addition, the embodiment of present invention provides almost omni-directional radiation field operation at azimuth angle plane, and good antenna gain performance at two operating frequency. Low frequency antenna gain is 2.1 dBi and high frequency antenna gain is 5.7 dBi, which is very suitable for application in the base station or access point of current wireless local area networks.  
         [0027]    While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.