Abstract:
The present invention relates to a circularly-polarized dielectric resonator antenna (DRA). The antenna comprises a substrate, a Wilkinson power divider, a phase shifter, a ground plane and a dielectric resonator, wherein the phase shifter is connected to the Wilkinson power divider. Besides, the dielectric resonator is disposed on the ground plane, and includes a dielectric main body and a well disposed above the substrate. Additionally, the antenna is adopted to increase the linear radiation bandwidth by utilizing the well, and transceives a circularly-polarized electromagnetic wave by utilizing the Wilkinson power divider. Consequently, the circularly-polarized dielectric resonator antenna can be applied in the fields of satellite communication, Worldwide Interoperability for Microwave Access (WiMAX), and wireless communication.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an antenna, and more particularly, to a circularly-polarized dielectric resonator antenna (DRA), applied in the fields of satellite communication, Worldwide Interoperability for Microwave Access (WiMAX), and wireless communication. 
       BACKGROUND OF THE INVENTION 
       [0002]    Two types of polarization of antenna are frequently used, linear polarization (LP) and circular polarization (CP). When wave of CP is used for satellite communication, it is less sensitive to Faraday rotation of polarization through ionosphere than the LP wave; hence it is applied in satellite and other wireless systems like GPS. 
         [0003]    DRA is usually operated in a TE 111  mode, and the mode has a wide beam linearly-polarized radiation pattern with a bandwidth of approximately 5-8% and having advantages of low loss and high radiation efficiency. In a common circularly-polarized DRA, an oblique aperture can be used to excite two modes with mutually orthogonal electric fields, in order to radiate circularly-polarized wave. Alternatively, a metal sheet is adhered to the surface of the dielectric resonator of the antenna, to perturb its original electric field distribution to generate two mutually orthogonal electric fields and generate the circular polarization. Alternatively, an annular or U-shaped aperture is used to excite the circularly-polarized electromagnetic wave from the dielectric resonator, but the bandwidth having an axial ratio (AR) smaller than 3 dB is approximately 3%, which is much smaller compared with a common linearly-polarized DRA which can reach 5-8% of bandwidth. The linearly-polarized bandwidth of the DRA is mainly affected by the dielectric constant of the antenna and the shape thereof, and generally, if a material with lower dielectric constant (e.g., εγ□10) is used, the bandwidth can be increased by about 10%. 
         [0004]    U.S. Pat. No. 6,147,647 B1 published on Nov. 14, 2000, entitled “Circularly polarized dielectric resonator antenna” discloses a dual-band dielectric resonator antenna, comprising: a first resonator formed of a dielectric material; a first ground plane formed of a conductive material on which said first resonator is mounted; a second resonator formed of a dielectric material; a second ground plane formed of a conductive material on which said second resonator is mounted, said first and second ground planes being separated from each other by a predetermined distance; and first and second probes electrically coupled to each of said resonators spaced approximately 90° apart around the perimeter of each resonator providing first and second signals, respectively, to each resonator, wherein each of said resonators resonates in a predetermined frequency band that differs from each other. 
         [0005]    Additionally, U.S. Pat. No. 6,995,713 B1 published on Feb. 7, 2006, entitled “Dielectric resonator wideband antenna” discloses a wideband antenna consisting of a dielectric resonator or DRA mounted on a substrate with a ground plane. The resonator is positioned at a distance x from at least one of the edges of the ground plane, x being chosen such that 0.1 toreq.x.ltoreq.Lamda . . . sub. die ½, with .lamda . . . sub. die ½ where the wavelength is defined in the dielectric resonator. 
         [0006]    Also, U.S. Pat. No. 7,196,663 B1 published on Mar. 27, 2007, entitled “Dielectric resonator type antennas” discloses a dielectric resonator antenna comprising a block of dielectric resonator having a first face intended to be mounted on ground plane and entirely covered with a first metallic layer, wherein at least one second face perpendicular to the first face is covered with a second metallic layer contacting said metallic layer covering said first face, said second metallic layer covering said second face extending over a width less than the width of the second face and over a height less than or equal to the height of the second face, and wherein said block of dielectric resonator comprises a third face being at least partially unbounded by conductive material so as to emit radiation from said third face. 
         [0007]    The above-mentioned DRAs, U.S. Pat. No. 6,147,647 “Circularly polarized dielectric resonator”, U.S. Pat. No. 6,995,713 “Dielectric resonator wideband antenna”, and U.S. Pat. No. 7,196,663 “Dielectric resonator type antennas”, all related to a rectangle DRA, huge effect will be brought to the wireless communication field. 
       SUMMARY OF THE INVENTION 
       [0008]    According to the prior arts mentioned above, the present invention is provided with a wideband circularly-polarized dielectric resonator antenna. The antenna comprises a substrate including a first surface and a second surface, a Wilkinson power divider and a phase shifter are formed on the first surface, a ground plane and a dielectric resonator are formed on the second surface; wherein the phase shifter formed on the first surface and having a main microstrip line, a reference microstrip line, a first microstrip line, and a second microstrip line, in which input ports of the main microstrip line and the reference microstrip line are respectively connected to two output ports of the Wilkinson power divider, and the first microstrip line and the second microstrip line are respectively connected to output ports of the main microstrip line and the reference microstrip line; a ground plane formed on the second surface and having a first hollow portion and a second hollow portion; and a dielectric resonator disposed above the ground plane, which includes a dielectric main body and a well carved off the main body. 
         [0009]    The antenna further includes a signal input/output device disposed on a side edge of the substrate. The Wilkinson power divider includes two output ports respectively connected to the input ports of the main microstrip line and the reference microstrip line of the phase shifter. The Wilkinson power divider and the phase shifter are combined such that the circularly-polarized DRA generates two TE 111  modes with the same magnitude and a phase difference of 90° when feeding a signal. The disposed positions of the first microstrip line and the second microstrip line of the phase shifter are respectively extended to correspondingly pass through centers of the first hollow portion and the second hollow portion of the ground plane. The ground plane is made of a conductive material, for example, copper, in which axis lines of the first hollow portion and the second hollow portion are mutually orthogonal. The dielectric resonator is disposed on the ground plane, and correspondingly above the first hollow portion and the second hollow portion, in which the dielectric main body has a square cross section, the well is a square or a rectangle structure, and the dielectric constant of the dielectric resonator is between 10 and 100. 
         [0010]    To sum up, there is a rectangular well embedded into the main body of the rectilinear dielectric resonator in the present invention, and the resonator is formed to cause a discontinuity such that the electric field in the well is enhanced, to improve the radiation efficiency and reduce the quality factor, thereby increasing the bandwidth. The Wilkinson power divider and the phase shifter are joined to generate two signals with the same magnitude and a phase difference of 90°. Through a coupling aperture, signals are fed into the dielectric resonator to generate the circularly-polarized characteristics. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0011]    The foregoing aspects, as well as many of the attendant advantages and features of this invention will become more apparent by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a perspective diagram of the circularly-polarized DRA of the present invention; 
           [0013]      FIG. 2  is a schematic exploded view of the circularly-polarized DRA of the present invention; 
           [0014]      FIG. 3  is a diagram illustrating return loss of the signal radiation of the circularly-polarized DRA according to the embodiment of the present invention; 
           [0015]      FIG. 4  is a diagram of directivity and AR of the antenna radiation of the circularly-polarized DRA according to the embodiment of the present invention; and 
           [0016]      FIGS. 5A to 5C  are radiation pattern diagrams of the circularly-polarized DRA according to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0017]    Referring to  FIGS. 1 and 2 , a perspective and a schematic exploded view of the circularly-polarized dielectric resonator antenna of the present invention are respectively illustrated. 
         [0018]    The circularly-polarized DRA  1  comprises: a substrate  11  including a first surface  111  and a second surface  112 , which is a printed circuit board made of a material having a dielectric constant of 2-13, for example, an FR4 substrate with the dielectric constant of 4.4; a Wilkinson power divider  12  formed on the first surface  111  and having an input port and two output ports  121  and  122 , in which the Wilkinson power divider  12  can generate two signals with the same magnitude and a phase difference of 90°; a phase shifter  13  formed on the first surface  111  and connected to the Wilkinson power divider  12 , and having a main microstrip line  131 , a reference microstrip line  132 , a first microstrip line  133 , and a second microstrip line  134 , in which input ports of the main microstrip line  131  and the reference microstrip line  132  are respectively connected to the two output ports  121  and  122  of the Wilkinson power divider  12 , and the first microstrip line  133  and the second microstrip line  134  are respectively connected to output ports of the main microstrip line  131  and the reference microstrip line  132 , in which an open-circuited microstrip line  1311  with a quarter wavelength and a short-circuited microstrip line  1312  with a quarter wavelength are connected in parallel at the input port of the main microstrip line  131 , an open-circuited microstrip line  1313  with a quarter wavelength and a short-circuited microstrip line  1314  with a quarter wavelength are connected in parallel at the output port, and the short-circuited portions are connected to a ground plane  14  through two vias; a ground plane  14  formed on the second surface  112 , which can be a metal layer, in which the ground plane  14  further includes a first hollow portion  141  and a second hollow portion  142  that are long-rectangular shaped, and axis lines of the first hollow portion  141  and the second hollow portion  142  are orthogonal; and a dielectric resonator  15  disposed above the ground plane  14  and including a dielectric main body  151  and a well  152 , in which the dielectric main body  151  is a square or rectangular structure, the dielectric main body  151  is overlapped above the first hollow portion  141  and the second hollow portion  142  of the ground plane  14 , and the well  152  has an annular rectangle shape embedded in the main body  151 . 
         [0019]    The circularly-polarized DRA  1  further includes a signal input/output device  16  disposed on a side edge of the substrate  11 , for inputting and outputting signals. The first microstrip line  133  and the second microstrip line  134  of the phase shifter  13  must be disposed to respectively extend to pass through the centers of the first hollow portion  141  and the second hollow portion  142 . Next, the material of the dielectric resonator  15  has the characteristics of high dielectric constant and low loss, the range of dielectric constant is between 10 and 100, the loss tangent is usually smaller than 0.005, so as to have the feature of high radiation efficiency. When electric line passes through the well  152 , the dielectric constant of the dielectric resonator  15  is greater than the dielectric constant of air (εγ=1), such that the electric field is enhanced by several times, the more efficient the electromagnetic wave radiation, the lower the quality factor Q, consequently the bandwidth of the signal transmission is increased. 
         [0020]    In addition, the design of the width of the microstrip line of the Wilkinson power divider  12  and the selection of bridged resistance make the fed signal to have no reflection when the two output ends of the Wilkinson power divider  12  match with their respective load. The design of the width and the length of the microstrip line of the phase shifter makes the main microstrip line and the reference microstrip line to have a phase difference of 90°, the same amplitude, and a minimum return loss at the operating frequency. 
         [0021]    Sizes of different parts of the DRA  1  are given as follows. The main body  151  includes a length a, a width b, and a height d. A width of the well  152  is s, and the substrate  11  and the ground plane  14  respectively have a length W x  and a width W y . The phase shifter  13  has a width W m  and is joined with the Wilkinson power divider  12 . The first microstrip line  133  and the second microstrip line  134  of the phase shifter  13  respectively extend to exceed the first hollow portion  141  and the second hollow portion  142  by a length L s , and the first hollow portion  141  and the second hollow portion  142  all have a length L a  and a width W a . 
         [0022]    In addition, it should be noted that some performance indices of the DRA  1  provided by the present invention can be controlled by adjusting related elements. For example, (1) the position of the dielectric resonator  15  is fine-adjusted to match the input impedance with the input signal line, (2) the size of the main body  151  is adjusted to adjust the radiation frequency of the antenna, and (3) the width of the well  152  is adjusted to fine-tune the resonance frequency of the antenna and to increase the radiation bandwidth. 
         [0023]    Next, one of the preferred embodiments of the present invention is disclosed as follows, in which size parameters of the main body  151  and the well  152  of the dielectric resonator are defined to be a=22 mm, b=22 mm, d=4 mm, s=6 mm. 
         [0024]    The first hollow portion  141  and the second hollow portion  142  respectively have a length W a  and a width L a , wherein W a =1 mm and L a =9 mm, and the substrate  11  and the ground plane  14  respectively have a length W x , a width W y  and a thickness t wherein W x =80 mm, W y =55 mm, and t=1.6 mm, the dielectric constant is 4.4, and the dielectric constant εγ of the dielectric resonator  15  is 20. 
         [0025]    Subsequently, the length and width of the output end of the Wilkinson power divider are respectively 9.5 mm and 3 mm, and in the phase shifter  13 , the length and width of the main microstrip line are respectively 20 mm and 2.3 mm, the length and width of the reference microstrip line are respectively 27 mm and 3 mm, the length and width of the first microstrip line are respectively 11 mm and 2.3 mm, and the length and width of the second microstrip line are respectively 13.5 mm and 3 mm. Further, the length of the first microstrip line  133  and the second microstrip line  134  exceeding the first hollow portion  141  and the second hollow portion  142  by L s  which is 3 mm. 
         [0026]      FIG. 3  is a diagram of return loss of the signal radiation of the embodiment, showing the simulation result and practical measurement of the return loss of the signal radiation, in which dashed line represents a result of simulated return loss A of the signal radiation, and solid line represents a result of practically measured return loss B of the signal radiation. When the return loss is lower than 10 dB, the signal radiation band is between 4.43 GHz and 5.85 GHz. 
         [0027]    Next, referring to  FIG. 4 , illustrating a radiation performance diagram of the antenna according to the embodiment of the present invention, in which the solid line represents the result of practically measured AR, the dashed line represents the result of simulated AR, and broken line and circled line are respectively measured and simulated antenna directivity. It can be observed from the drawing that when the AR is smaller than or equal to 3.5 dB and the return loss is lower than −10 dB, the frequencies range is between 4.4 GHz and 5.3 GHz, over which the directivity is between 1.8 dBi and 4 dBi. 
         [0028]    Referring to  FIGS. 5A to 5C , radiation pattern diagrams of the embodiment of the present invention are shown.  FIGS. 5A to 5C  sequentially represent radiation patterns of the embodiment of the present invention in the x-y plane at frequencies of 4.45 GHz, 4.9 GHz, and 5.2 GHz, respectively, in which the solid line is the measurement of the left-hand circular polarization (LHCP) D, and the dashed line is the measurement of the right-hand circular polarization (RHCP) at the frequency of 4.9 GHz, a broadside radiation of LHCP is observed, and the 3 dB AR beamwidth is about 25°(−10°□φ□−15°). The antenna gain of LHCP is about 3.8 dBi. The front-to-back ratio is more than 12 dB. 
         [0029]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, these are merely examples to help clarify the invention and are not intended to limit the invention. It will be understood by those skilled in the art that various changes, modifications, and alterations in form and details may be made therein without departing from the spirit and scope of the invention, as set forth in the following claims.