Abstract:
A wideband dielectric resonator monopole antenna, which includes a dielectric resonator and a monopole antenna, combines two frequency bands having close resonant frequencies to achieve 49% of bandwidth and omnidirectional radiation patterns within the frequency band. It includes a column structure and a substrate, wherein the surface of the column structure is coated with a conductive layer, the column structure is kept upright to the substrate, and the substrate is coated or printed with two slot lines extended inward from an edge of the substrate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an antenna combining a dielectric resonator with a monopole. 
         [0003]    2. The Prior Arts 
         [0004]    With the advancement of wireless communication technology, portable devices have been widely used in various applications, such as industry, science, and medicine, and is also getting more diversified. Their major requirements are portability and low power. Therefore, how to reduce the size and power consumption of the product become important design considerations. For example, if the wireless LAN 802.11a in the 5.25 GHz frequency band adopts ordinary microstrip antenna, the ohmic loss will be excessive due to high operating frequency. Since the dielectric resonator basically has no ohmic loss, it has the advantages of low loss rate, high radiation efficiency and high gain, and is extremely suitable to be operated in high frequency. However, the dielectric constant of the prior dielectric resonators is approximately below 10, and its size is greater than that of the microstrip antenna. Thus, the dielectric resonator antenna is often designed using high dielectric constant to reduce the size. But increasing the dielectric constant often results in a reduction of the operating frequency bandwidth of the antenna, thereby not meeting with the bandwidth requirement within the frequency band. Therefore, it is desired to provide a novel and improved wideband dielectric resonator monopole antenna that can solve the above-mentioned problems. 
       SUMMARY OF THE INVENTION 
       [0005]    A primary objective of the present invention is to provide a novel antenna, which is a combination of the dielectric resonator and the monopole antenna, and combines the frequency bands of these two antennas by a coplanar waveguide feed system, to achieve 49% of bandwidth. 
         [0006]    Another objective of the present invention is to provide a novel antenna, which is a combination of the dielectric resonator and the monopole, with an omnidirectional radiation pattern, for reducing the poor signal reception conditions due to the changes and movements of signal reception location. 
         [0007]    Furthermore, the antenna structure in accordance with the present invention, which mainly utilizes the coplanar waveguide (CPW) feed, is simple and can be easily integrated into other planar circuits. It is a widely used and easily manufactured antenna structure. Since its antenna radiation pattern within the frequency band has the omnidirectional characteristic, it is suitable to be used in the wireless LAN such as WLAN 802.11a, which requires an omnidirectional radiation pattern. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view showing a preferred embodiment of the antenna structure in accordance with the present invention. 
           [0009]      FIG. 2  is a perspective view showing a resonator in  FIG. 1  in accordance with the present invention. 
           [0010]      FIG. 3  is a top view showing a feed-in/feed-out component in  FIG. 1  in accordance with the present invention. 
           [0011]      FIG. 4  is a graph showing the relation between frequency and return loss of the preferred embodiment of the antenna in accordance with the present invention. 
           [0012]      FIG. 5  is a radiation pattern of the antenna in accordance with the present invention in the XY-plane at the frequency of 5.3 GHz. 
           [0013]      FIG. 6  is a radiation pattern of the antenna in accordance with the present invention in the XY-plane at the frequency of 5.7 GHz. 
           [0014]      FIG. 7  is a radiation pattern of the antenna in accordance with the present invention in the XY-plane at the frequency of 6.1 GHz. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    In the following, the present invention will be described in detail with reference to the attached drawings and component numerals, and it can be carried into effect by those skilled in the art after reading it. 
         [0016]    With reference to  FIGS. 1 and 2 , an antenna structure  1  in accordance with the present invention is used to receive and transmit signals, which mainly comprises a resonator  11  and a feed-in/feed-out component  12 . The resonator  11  can receive electromagnetic signals in the space or transmit electromagnetic signals into the space. The feed-in/feed-out component  12  is used to import or export the signals received or transmitted by the resonator  11 . 
         [0017]    In the above-mentioned antenna structure in accordance with the present invention, the resonator  11  is a column structure. Part of the exterior surface of the resonator  11  is coated with a metal layer  11   a , which is made of conductive material, and a connector  11   b  is formed at the bottom end of the metal layer  11   a , to be electrically connected to the feed-in/feed-out component  12 . In particular, as  FIG. 2  shows, the resonator  11  is a rectangular column with a resonator width a, a resonator length b and a resonator height h. The connector  11   b  is a metal strip connector with a connector height hc and a connector width wc. The resonator width a, the resonator length b and the resonator height h of a preferred embodiment are 5.7 mm, 3.3 mm and 12 mm, respectively. The metal layer  11   a  is formed on the three adjacent surfaces of the column of the resonator  11 . The distance from the bottom end of the metal layer  11   a  to the bottom edge of the rectangular column of the resonator  11  is the connector height hc of the connector  11   b . Part of the bottom end of the metal layer  11   a  extends and forms the connector  11   b  to the bottom edge of the rectangular column of the resonator  11 . The connector height hc and the connector width wc of the preferred embodiment are 0.5 mm and 3.75 mm, respectively. 
         [0018]    The coating area or coating height of the metal layer  11   a  of the above-mentioned resonator  11  is used to adjust the resonant frequency of the resonator  11 . 
         [0019]    With reference to  FIGS. 1 and 3 , in the above-mentioned antenna structure in accordance with the present invention, the feed-in/feed-out component  12  is made up of a wire pattern  122  coated or printed on a substrate  121 . Wherein the substrate  121  with a substrate thickness t is made of a dielectric material such as FR4, Teflon, Duriod, fiberglass, aluminum oxide, ceramic materials, and so on; and, the wire pattern  122  is made of metal, with a grounding length LG and a grounding width WG, respectively. The wire pattern  122  comprises a grounding part  122   a , parallel slot lines  122   b  and open-circuited slot lines  122   c , and defines a resonator foot-print region  122   d . The grounding part  122   a  is made of conductive material. It is used to ground the feed-in/feed-out component  12 , and to electrically connect with the connector  1   b . The parallel slot lines  122   b  and the open-circuited slot lines  122   c  are the part of the wire pattern  122  that conductive material is removed. The parallel slot lines  122   b  are made up of two parallel slot lines, with a parallel slot length L, a parallel slot width g 1  and a parallel slot spacing w. The open-circuited slot lines  122   c  are made up of two open-circuited slot lines, with an open-circuited slot width g 2  and an open-circuited slot length s. Each open-circuited slot line  122   c  is vertically extended from the end of the parallel slot line  122   b  close to the resonator foot-print region  122   d , and the distance between the open-circuited slot line  122   c  and the backside of the resonator  11  is d. The wiring pattern  122  may incur a coupling effect of the electromagnetic signals associated with the resonator  11 . In particular, as  FIG. 3  shows, the feed-in/feed-out component  12  according to the preferred embodiment is coated or printed on a rectangular substrate  121 , on which the feed-in/feed-out length, feed-in/feed-out width, and feed-in/feed-out height are 75 mm, 75 mm, and 0.5 mm, respectively. The parallel slot spacing w, which is the distance between the parallel slot lines  122   b , is 0.5 mm. The parallel slot length L is 39 mm. The inner end of each parallel slot line  122   b  turns 90 degrees and extends toward the other parallel slot line  122   b  to form the open-circuited slot line  122   c . An open-circuited slot opening, which is between the two ends of the two open-circuited slot lines  122   c , is approximately 0.25 mm long. In addition, the distance d between the backside of the resonator  11  and the open-circuited slot line  122   c  is 0.5 mm. 
         [0020]    The open-circuited slot width g 2  and the open-circuited slot length s of the above-mentioned open-circuited slot lines  122   c  are used to adjust the impedance matching. The open-circuited slot length s is chosen slightly shorter than the parallel slot spacing w, and the open-circuited slot width g 2  is chosen close to the parallel slot width g 1 . 
         [0021]    Furthermore, the dimensions of the rectangular column of the resonator  11  and the open-circuited slot length s of the open-circuited slot lines  122   c  are used to adjust the impedance matching and the resonant frequency. When the distance d between the open-circuited slot line  122   c  and the backside of the resonator  11  is about one-seventh to one-sixth of the resonator width a of the rectangular column of the resonator  11 , the antenna structure is optimized. 
         [0022]    With reference to  FIG. 4 , the relevant parameters according to another preferred embodiment are: the resonator width a is 3.3 mm; the resonator length b is 5.7 mm; the resonator height h is 12 mm; the parallel slot spacing w is 10 mm; the parallel slot width g 1  is 0.5 mm; the open-circuited slot width g 2  is 0.5 mm; the distance d between the backside of the resonator and the open-circuited slot line is 0.5 mm; the open-circuited slot length s is 5.375 mm; the connector height hc is 0.5 mm; the connector width wc is 3.75 mm; the parallel slot length L is 39 mm; the grounding length LG is 75 mm; the grounding width WG is 75 mm; and the substrate thickness t is 0.6 mm.  FIG. 4  shows the relation between frequency and return loss of the preferred embodiment of the antenna structure in accordance with the present invention, wherein the solid line shows the data measured from experiments, and the dash line shows the data simulated by a software package.  FIG. 4  shows that the bandwidth measured from experiments is close to the simulated bandwidth. 
         [0023]      FIGS. 5-7  are the radiation patterns of the antenna structure in accordance with the present invention in the XY-plane at the frequencies 5.3 GHz, 5.7 GHz, and 6.1 GHz, respectively, wherein the scale from the origin to the perimeter in radial direction is 40 dB. Curve  501  shows the Eθ component measured from experiments, and curve  502  shows the Eφ component measured from experiments. Curve  503  shows the Eθ component simulated by software, and curve  504  shows the Eφ component simulated by software. It is apparent from the figures that the radiation pattern of the antenna structure in accordance with the present invention has omnidirectional characteristic, and the frequency bandwidth is greater than that of conventional antennas. 
         [0024]    The above-presented description is only intended to illustrate the preferred embodiment in accordance with the present invention, and must not be interpreted as restrictive to the present invention. Therefore, it is apparent that a variety of modifications and changes may be made without departing from the scope of the present invention, which is intended to be defined by the appended claims.