Patent Publication Number: US-7212162-B2

Title: Horn antenna for circular polarization using planar radiator

Description:
FIELD OF THE INVENTION 
   The present invention relates to a horn antenna for circular polarization using a planar-type radiator; and, more particularly to a horn antenna for circular polarization using a planar-type radiator, the antenna which can be used for an antenna system for satellite communication using circular polarization in a high frequency band or which can be used as an element of an array antenna. 
   DESCRIPTION OF RELATED ART 
   Generally, a horn antenna, which is a waveguide antenna, propagates energy through a waveguide by exciting one end of the waveguide and opening the other end to thereby radiate the energy into space through the aperture. 
     FIG. 1  is a perspective view showing a typical horn antenna for circular polarization. 
   As shown, the conventional horn antenna has a complicated structure, which includes an exciter for providing signal power to the horn antenna, a circular polarizer  120  for inducing circular polarization, and a waveguide horn  130 . 
   Due to the structural complicacy, it is difficult to design and fabricate the conventional horn antenna and this leads to high production cost. 
   The structural complicacy also makes the physical size of the horn antenna bigger and thus prohibits it from being applied to various antenna systems using a high-gain array antenna. 
   In order to solve the problem, U.S. Pat. No. 4,051,476 discloses a horn antenna integrating a small power supplying horn for radiating linear polarization energy and a parabolic radiation horn on a dielectric substrate to thereby reduce a setup space. However, since the horn antenna of the cited patent radiates linear polarization energy, it cannot be applied to the antenna system for circular polarization. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a horn antenna for circular polarization using a planar radiator, the antenna that has a simplified and miniaturized structure by substituting a function of an exciter which provides signal power to the horn antenna with a function of a circular polarizer which induces circular polarization by using the planar radiator. 
   It is another object of the present invention to provide a wideband high-efficiency antenna that can minimize the narrowband characteristic of the planar radiator and the dielectric loss and radiation loss generated in a high-frequency band by applying a multilayer structure to which a metal plate having an aperture of a predetermined size is inserted in order to improve a narrowband characteristic of the planar radiator. 
   In accordance with an aspect of the present invention, there is provided a horn antenna for circular polarization, the antenna which includes: a horn for radiating signal power; and a planar radiator for providing the signal power to the horn to thereby induce circular polarization, the radiator including a radiating patch. 
   In accordance with another aspect of the present invention, the horn antenna further includes: a waveguide section for impedance matching between the planar radiator and the horn, the waveguide being placed between the planar radiator and the horn. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a perspective view showing a typical horn antenna for circular polarization; 
       FIG. 2  is a perspective view illustrating a horn antenna for circular polarization using a planar radiator in accordance with an embodiment of the present invention; 
       FIG. 3  is a cross-sectional view describing a horn antenna using a planar radiator of  FIG. 2  in accordance with an embodiment of the present invention; 
       FIG. 4  is a perspective view showing the planar radiator of  FIG. 2  in accordance with an embodiment of the present invention; 
       FIG. 5  is a perspective view showing a horn of  FIG. 2 ; 
       FIG. 6  is a graph describing impedance matching of the horn antenna for circular polarization using the planar radiator in accordance with an embodiment of the present invention; and 
       FIG. 7  is a graph describing gain of the horn antenna for circular polarization using the planar radiator and the axial characteristic for circular polarization in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. 
     FIGS. 2 and 3  present a perspective view and a cross-sectional view illustrating a horn antenna for circular polarization using a planar radiator in accordance with an embodiment of the present invention. 
   As shown, the horn antenna of the present invention comprises a planar radiator  210  and a horn  220 . The drawing presents a cross-section of the horn  220  to describe the planar radiator  210 . The complete form of the horn  220  will be described with reference to  FIG. 4 . 
   For general understanding, the present invention presents an embodiment where a corner-truncated square patch radiator is applied as the planar radiator  210 . However, the present invention is not limited to it and diverse forms of radiating patches can be used. 
   The planar radiator  210  induces circular polarization as well as providing signal power to the horn  220 . 
   Also, the horn  220  having a square aperture is not connected to the ground of the planar radiator  210  and, thus, there is an additional advantage that the planar radiator  210  can be inserted to and fixed in the inside of the horn  220  conveniently. 
     FIG. 4  shows a structure of the planar radiator of  FIGS. 2 and 3 . 
   As shown, the planar radiator  210  has a planar parasitic patch  320  in the upper part of a radiating patch  310  to extend the band of an axial ratio and thereby have a wideband characteristic based on dual resonance. It can have a high-efficiency characteristic by inserting the metal plate having an aperture of a predetermined size between the radiating patch and the parasitic patch to thereby induce the effect of a resonator and growing it. 
   Other than the examples of the planar radiator of  FIGS. 2 and 3 , the horn antenna of the present invention can utilize various forms of planar radiators. 
     FIG. 5  is a perspective view showing a horn of  FIG. 2 . As shown, the waveguide horn of the present invention further includes a waveguide section  410  having a square aperture for propagating the signal power of the circular polarization to which signal power is supplied through the planar radiator  210 . 
   The waveguide  410  achieves impedance matching between the planar radiator  210  and the horn  220  having a pyramid-shaped square aperture. 
   To the end of the waveguide section  410 , the horn  220  having a pyramid-shaped square aperture is connected so as to radiate circular polarization power propagating through the waveguide section  410  into free space. 
   The signal power of the circular polarization excited in the planar radiator  210  can be transmitted to the free space through the horn antenna horn antenna of the present invention efficiently. 
     FIG. 6  is a graph describing impedance bandwidth of the horn antenna for circular polarization using the planar radiator in accordance with an embodiment of the present invention. 
   As shown, the signal power excited in the planar radiator  210  can be transmitted to the free space efficiently by adjusting the size and length of the square aperture of the horn  220 . 
     FIG. 7  is a graph describing gain radiator and the axial ratio characteristic of the horn antenna in accordance with an embodiment of the present invention. 
   As shown, the horn antenna of the present invention has 10% 3 dB axial ratio bandwidth and has at least 9.0 dBi gain characteristic in the same band. 
   Also, it has 7% 2 dB axial ratio band and has at least 9.5 dBi gain characteristic in the same band. 
   Since the horn antenna of the present invention has a square structure in which the horizontal and vertical lengths are the same, the horn antenna having a simple structure can generate circular polarization without additional loss. 
   As described above, the present invention embodies a function of an exciter and a function of a polarizer in the conventional horn antenna for circular polarization simultaneously by applying the planar radiator to the horn antenna for circular polarization. 
   Also, the technology of the present invention can reduce the size of the horn antenna for circular polarization by removing a circular polarizer which has a considerable size of the conventional horn antenna, and it can reduce the production cost as well as providing convenience in designing. 
   In addition, it can be applied to a fabrication of a waveguide to form a parallel power supply structure in the waveguide. 
   It can also include a sort of a resonator effect by inserting a metal plate having an aperture of a predetermined size between the radiating patch and the parasitic patch and thereby provide wideband and high-efficiency characteristics. 
   The present application contains subject matter related to Korean patent application No. 2003-0083323, filed in the Korean Intellectual Property Office on Nov. 22, 2003, the entire contents of which is incorporated herein by reference. 
   While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.