Abstract:
A radio wave reception converter receives a radio wave and converts the radio wave into an electric signal, and includes a horn introducing a radio wave, and a waveguide arranged at the rear of the horn for guiding a radio wave introduced by the horn. An insulation sheet is located between the waveguide and the horn to seal hermetically the interior of the waveguide and the horn. The connecting part between the waveguide and the horn is covered with an exterior cabinet. The front opening of the horn is covered with a feedome. The structure facilitates the connecting work between the waveguide and the horn, and can ensure airtightness at the connecting part.

Description:
This nonprovisional application is based on Japanese Patent Application No. 2003-189431 filed with the Japan Patent Office on Jul. 1, 2003, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a radio wave reception converter (LNB: Low Noise Block down Converter) receiving radio waves such as those of satellite broadcasting and converting the radio wave into an electric signal, and an antenna apparatus including such a radio wave reception converter. 
   2. Description of the Background Art 
     FIG. 7  is a sectional view of a structure of a conventional radio wave reception converter. 
   As shown in  FIG. 7 , the conventional radio wave reception converter has a horn  102  secured by a screw  109   a  to a chassis main unit  101  having a waveguide  110 . Connection between horn  102  arid an exterior cabinet  105  is established by attaching a nut  124  to the screw portion of an output terminal  108  provided at chassis main unit  101 . Accordingly, exterior cabinet  105  is urged against and secured to horn  102 : At the front of horn  102 , a feedome  104  (also called horn cap) is secured by a screw  109   b.    
   An O ring  111  is located at the connection between horn  102  and exterior cabinet  105 . Additionally, an O ring  113  is located at the connection between exterior cabinet  105  and output terminal  108 . These O rings function to establish hermetic sealing of the interior of exterior cabinet  105  against outside air. Furthermore, an O ring  112  is located at the connection between feedome  104  and horn  102 . This O ring functions to establish hermetic sealing of the interior of horn  102  and the interior of waveguide  110  against outside air. 
     FIG. 8  is a sectional view of a structure of another conventional radio wave reception converter. 
   As shown in  FIG. 8 , this another conventional radio wave reception converter has a horn  202  press-fitted and secured at the front end of a waveguide  210  formed of a cylindrical metal pipe. At the rear of waveguide  210 , a circuit board  207  having a converter circuit formed is attached. Waveguide  210 , horn  202  and circuit board  207  are covered with bisected exterior cabinets  205   a ,  205   b  and feedome  204 . Connection of the bisected exterior cabinets  205   a  and  205   b  is established through press-fitting or adhesion-fixing. Additionally, connection between exterior cabinet  205   a  and feedome  204  is established by press-fitting or adhesion-fixing. Thus, the interior of the radio wave reception converter is maintained in an airtight manner. 
   The structure of other conventional radio wave reception converters is disclosed in, for example, Japanese Utility Model Laying-Open No. 64-5501, Japanese Utility Model Laying-Open No. 64-15410, Japanese Patent Laying-Open No. 2-75226, Japanese Utility Model Laying-Open No. 62-100710, Japanese Utility Model. Laying-Open No. 4-57927, and the like. 
   The radio wave reception converter of the structure shown in  FIG. 7  has the problem that extremely strict accuracy is required in the surface roughness of respective faces of feedome  104 , horn  102 , exterior cabinet  105  and the like brought into contact with O rings  111 – 113  as well as the dimension of the groove in which O rings  111 – 113  are fitted since airtightness is ensured by O rings  111 – 113 . If the accuracy of such elements are not maintained at a high level, moist air will flow into the radio wave reception converter to significantly degrade the product lifetime. It is therefore necessary to realize the high accuracy set forth above, imposing constraints on the fabrication cost. 
   The radio wave reception converter of the structure shown in  FIG. 8  is absent of O rings, and maintains airtightness by press-fitting or adhesion-fixing. This imposes the problem that strict dimension accuracy is required. However, exterior cabinets  205   a  and  205   b  as well as feedome  204  are generally resin-formed components, relatively harder to achieve critical dimension accuracy as compared to metal. Therefore, when the press-fitting process is employed, airtightness of a level that can prevent intrusion of rain can be ensured. However, it is extremely difficult to prevent intrusion of moist air. In the case where adhesion-fixing is employed, the working process becomes tedious since the adhesive must be applied evenly over the entire face of connection. Furthermore, overflow of the adhesion will become the cause of deterioration in appearance. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a radio wave reception converter that has the connecting work between a waveguide and a horn facilitated, and that can ensure airtightness at the connection thereof, and an antenna apparatus including such a radio wave reception converter. 
   A radio wave reception converter according to an aspect of the present invention receives a radio wave and converts the radio wave into an electric signal. The radio wave reception converter includes a horn for introducing a radio wave, and a waveguide arranged at the rear of the horn for guiding the radio wave introduced by the horn. An insulation sheet is located between the waveguide and the horn. The interior of the waveguide and the interior of the horn are sealed in an airtight manner by the insulation sheet. By the structure of providing and sandwiching the insulation sheet between the waveguide and the horn, the interior of the waveguide can be sealed hermetically against outside air. Since intrusion of moist air can be prevented thereby, the reliability of the apparatus is improved. 
   In the radio wave reception converter according to the aspect set forth above of the present invention, the connecting part between the horn and the waveguide is covered with a casing, and the opening at the front of the horn is preferably covered with a feedome. Since intrusion of air into the casing and the horn can be prevented by such a structure, the reliability of the apparatus is improved. 
   In the radio wave reception converter according to the aspect set forth above of the present invention, the inner diameter of the feedome is set smaller than the outer diameter of the horn to press-fit and secure the feedome into the horn. By such a structure, connection between the feedome and the horn is facilitated. 
   The radio wave reception converter according to the aspect set forth above of the present invention preferably has a structure in which a salient is formed at an end plane of the horn facing the waveguide, a reentrant is formed at an end plane of the waveguide facing the horn to receive the salient, and the circumferential edge of the insulation sheet is sandwiched by the salient and reentrant. In the radio wave reception converter according to the aspect set forth above of the present invention, a structure may be employed in which a salient is formed at an end plane of the waveguide facing the horn, a reentrant is formed at an end plane of the horn facing the waveguide to receive the salient, and the circumferential edge of the insulation sheet is sandwiched by the salient and reentrant. By such a structure, connection between the horn and the waveguide can be facilitated, and airtightness can be ensured by the insulation sheet. 
   In the radio wave reception converter according to the aspect set forth above of the present invention, preferably a structure is employed in which a horn side flange is provided at the rear end of the horn, and a waveguide side flange is provided at the front end of the waveguide. The horn side flange and the waveguide side flange are fastened by fastening means. By such a structure, the insulation sheet can be sandwiched reliably by the horn and the waveguide through a simple working process. 
   In the radio wave reception converter according to the aspect of the present invention set forth above, the insulation sheet is preferably a plastic sheet having an adhesive applied on the main surface. Application of an adhesive on the main surface of the insulation sheet allows one of the horn or waveguide to be attached to the insulation sheet, followed by connection between the horn and the waveguide. Therefore, the work is facilitated. The problem of the insulation sheet being shifted in position can also be eliminated. Hermetic sealing can be maintained reliably. 
   An antenna apparatus according to the present invention includes any of the radio wave reception converter set forth above, and a parabola reflecting and introducing into the radio wave reception converter a radio wave. By such a structure, an antenna apparatus of high reliability can be provided. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially fractured side view of an assembly structure of a radio wave reception converter according to a first embodiment of the present invention. 
       FIG. 2  is a sectional view of the connection between a waveguide and horn of the radio wave reception converter according to the first embodiment of the present invention. 
       FIG. 3  is an enlarged sectional view of region III of  FIG. 2 . 
       FIG. 4  is a sectional view of the connection when a horn having an angular aperture differing from that of the horn of  FIG. 2  is connected. 
       FIG. 5  is an enlarged sectional view of the connection between a waveguide and horn of a radio wave reception converter according to a second embodiment of the present invention. 
       FIG. 6  is a perspective view schematically showing a structure of an antenna apparatus according to a third embodiment of the present invention. 
       FIG. 7  is a sectional view of a structure of a conventional radio wave reception converter. 
       FIG. 8  is a sectional view of a structure of another conventional radio wave reception converter. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described hereinafter with reference to the drawings. 
   First Embodiment 
   A structure of a radio wave reception converter according to a first embodiment of the present invention will be described hereinafter with reference to  FIG. 1 . 
   Referring to  FIG. 1 , the radio wave reception converter of the present embodiment mainly includes a chassis main unit  1 , a horn  2 , an insulation sheet  3 , a feedome  4 , and exterior cabinets  5   a  and  5   b.    
   Chassis main unit  1  includes a cylindrical waveguide  10  for guiding a radio wave, high frequency circuitry  7  in which is sealed a high frequency circuit substrate (not shown) incorporated with a low noise amplifier and the like, and an F type attachment  8  that is a connection terminal. Waveguide  10  is formed of, for example, a metal pipe, or a resin pipe having metal plating on the inner circumferential face. A substrate antenna (not shown) extending from the high frequency circuit substrate is located at the rear of waveguide  10  to receive a radio wave guided by waveguide  10 . The received signal is frequency-converted by the high frequency circuit, amplified, and then output to an external source via F type attachment  8 . 
   Horn  2  is the part where a radio wave reflected at the parabola of the antenna apparatus is introduced. The radio wave passing through a front opening  21  is guided towards the rear. Horn  2  is a metal shaped piece formed by, for example, press working, or a resin molded piece having metal plating applied on the inner face. 
   Insulation sheet  3  is a disk member formed of, for example, PET (polyethylene terephthalate) resin, PP (polypropylene) resin, polyimide resin, Teflon (registered trademark) resin or the like, having its thickness adjusted to several 10 μm. Insulation sheet  3  is formed in a desired shape by, for example, die-cutting a rectangular sheet. Insulation sheet  3  preferably has an adhesive (tenacious material) applied on one or both sides of the main surface. 
   Feedome  4  is a member attached to horn  2  so as to occlude front opening  21  of horn  2 . Feedome  4  is a formed piece such as a resin member. 
   Exterior cabinets  5   a  and  5   b  identified as the casing are divided into two, covering chassis main unit  1 . Exterior cabinets  5   a  and  5   b  are formed pieces of resin. 
   Assembly of respective components are carried out by the procedures set forth below. 
   First, insulation sheet  3  is attached at the front end side of waveguide  10  of chassis main unit  1 . Horn  2  is attached to the front end of waveguide  10  by means of a screw  9  which is a fastening means. Insulation sheet  3  is located between the front end plane of waveguide  10  and the back end plane of horn  2 . 
   Then, feedome  4  is attached to horn  2  so as to cover front opening  21  of horn  2 . Finally, bisected exterior cabinets  5   a  and  5   b  are fitted so as to cover the connecting part between waveguide  10  of chassis main unit  1  and horn  2 . Thus, the radio wave reception converter is assembled. 
   As shown in  FIGS. 2 and 3 , the radio wave reception converter of the present embodiment has insulation sheet  3  located and sandwiched between waveguide  10  and horn  2 . 
   Specifically, a salient  24  is provided at the end plane of horn  2  facing waveguide  10 , and a reentrant  14  is formed at the end plane of waveguide  10  facing horn  2 . Reentrant  14  of waveguide  10  receives salient  24  formed in horn  2 . Insulation sheet  3  is located between salient  24  and reentrant  14 . The circumferential edge of insulation sheet  3  is sandwiched between salient  24  and reentrant  14 . 
   A waveguide side flange  12  is provided at the front end of waveguide  10 . A horn side flange  22  provided at the rear end of horn  2 . A through hole  13  is formed in waveguide side flange  12 . A screw hole  23  is formed at horn side flange  22  at a position corresponding to through hole  13 . Screw  9  is inserted through through hole  13 . Waveguide  10  and horn  2  are secured by screw  9  fixed in screw hole  23 . By adjusting insulation sheet  3  to a predetermined thickness, insulation sheet  3  is compressed and deformed to be sandwiched between waveguide  10  and horn  2 . Therefore, hermetic sealing is ensured at this portion. 
   At the bottom of reentrant  14  provided at the end plane of waveguide  10 , a reentrant  15  of a size corresponding to the configuration of insulation sheet  3  is formed. By setting the depth of this reentrant  15  equal to or slightly smaller than the thickness of insulation sheet  3 , the gap between waveguide  10  and horn  2  can be reduced even if insulation sheet  3  is made thicker. Therefore, leakage of radio wave can be prevented. Since a thick insulation sheet  3  can be used by such a structure, hermetic sealing can be achieved more ensurely. 
   As shown in  FIG. 2 , feedome  4  is press-fitted and fixed at the front end of horn  2 . Specifically, the inner diameter of feedome  4  is set slightly smaller than the outer diameter of horn  2 . Press-fit fixation can be established by fitting feedome  4  to horn  2 . A claw  41  is provided at the rear end of feedome  4  to prevent feedome  4  from being detached from horn  2 . Fitting is established to engage claw  41  with projection  28  located at a predetermined position at the outer circumferential plane of horn  2 . This prevents rain from intruding through front opening  21  of horn  2 . 
   By the radio wave reception converter of the above structure, intrusion of rain through the connecting part of bisected exterior cabinets  5   a  and  5   b  and the connecting part between horn  2  and feedome  4  is prevented. Furthermore, the moist air introduced through the gaps thereof is prevented from flowing into waveguide  10  by insulation sheet  3 . Therefore, various electronic components such as the high frequency circuit substrate and the like arranged in high frequency circuitry  7  is protected from moisture. As a result, a radio wave reception converter of high reliability can be provided. 
   Since the connection structure set forth above can be realized by the simple working steps of attaching insulation sheet  3  to the end plane of waveguide  10 , and fastening waveguide  10  with horn  2  by means of screw  9 , the assembly work will not become tedious. Furthermore, the fabrication cost can be reduced significantly since critical surface roughness or dimension accuracy are not required. 
   Furthermore, since the connection between bisected exterior cabinets  5   a  and  5   b  and the connection between horn  2  and feedome  4  are conducted by press-fitting, it is no longer necessary to use an adhesive. The problem of deterioration in the outer appearance caused by overflow of the adhesive can be eliminated. 
   Complete blocking of the path of waveguide  10  and the path of horn  2  by means of insulation sheet  3  in the radio wave reception converter of the present embodiment allows the interior of waveguide  10  to be sealed hermetically against outside air. By virtue of insulation sheet  3  having the thickness of several 10 μm as set forth above, most of the radio waves introduced into horn  2  will pass through insulation sheet  3  and reach the interior of waveguide  10 . There is little, if any, loss in radio wave by such arrangement of an insulation sheet  3 . 
   By the structure of dividing the feed horn that guides a radio wave into waveguide  10  and horn  2  as in the present embodiment, most of the components of a radio wave reception converter having a different angular aperture depending upon the specification can be used in common. Specifically, a horn  2 ′ having an angular aperture differing from that of  FIG. 2  is additionally prepared, as shown in  FIG. 4 . By setting the configuration of the connecting part between horn  2 ′ and waveguide  10  identical to that of horn  2  shown in  FIG. 2 , the components of chassis main unit  1  including waveguide  10  and external cabinets  5   a  and  5   b  can be used in common. Versatility can be improved. Accordingly, a radio wave reception converter differing in angular aperture can be produced economically. 
   Second Embodiment 
   The connection structure of the waveguide and horn of a radio wave reception converter according to a second embodiment of the present invention will be described with reference to  FIG. 5 . Elements similar to those of the first embodiment have the same reference characters allotted in the drawings, and description thereof will not be repeated. 
   As shown in  FIG. 5 , the radio wave reception converter of the present embodiment has insulation sheet  3  located and sandwiched between waveguide  10  and horn  2 . 
   Specifically, a salient  16  is formed at the end plane of waveguide  10  facing horn  2 , and a reentrant  26  is formed at the end plane of horn  2  facing waveguide  10 . Reentrant  26  of horn  2  receives salient  16  of waveguide  10 . Insulation sheet  3  is located between salient  16  and reentrant  26 . The circumferential edge of insulation sheet  3  is sandwiched between salient  16  and reentrant  26 . 
   Waveguide side flange  12  is provided at the front end of waveguide  10 . Horn side flange  22  is provided at the rear end of horn  2 . Through hole  13  is formed at waveguide side flange  12 . Screw hole  23  is formed at horn side flange  22  at a position corresponding to through hole  13 . Screw  9  is inserted through through hole  13 . Waveguide  10  is secured with horn  2  by screw  9  being fixed in screw hole  23 . By adjusting insulation sheet  3  to a predetermined thickness, insulation sheet  3  is compressed and deformed by waveguide  10  and horn  2  to be sandwiched therebetween. Therefore, hermetic sealing at this region can be ensured. 
   A reentrant  27  of a size corresponding to the configuration of insulation sheet  3  is formed at the bottom of reentrant  26  provided at the end plane of horn  2 . By setting the depth of reentrant  27  equal to or slightly smaller than the thickness of insulation sheet  3 , the gap between waveguide  10  and horn  2  can be reduced even if insulation sheet  3  is made thicker. Therefore, radio wave leakage can be prevented. Since a thick insulation sheet  3  can be used by such a structure, hermetic sealing can be achieved more ensurely. 
   The structure set forth above has an advantage similar to that of the first embodiment. 
   Third Embodiment 
   A structure of an antenna apparatus according to a third embodiment of the present invention will be described with reference to  FIG. 6 . 
   Referring to  FIG. 6 , the antenna apparatus of the present embodiment includes a radio wave reception converter  50  and a parabola  52 . Radio wave reception converter  50  corresponds to the radio wave reception converter of the first or second embodiment set forth above. 
   The radio wave from a satellite is reflected and concentrated by parabola  52  to be introduced into the horn of radio wave reception converter  50  arranged in front of parabola  52 . The radio wave from a satellite is a circularly polarized wave, including a right-handed polarized wave and a left-handed polarized wave. Radio wave reception converter  50  separates these two components, amplifies respective components, and converts the radio wave in a band of ten several GHz to a signal of the frequency band of 1 GHz. The converted signal passes through a cable connected to the F type attachment of radio wave reception converter  50  and an indoor receiver (for example, a satellite receiver) to be send to a television. 
   By the above-described structure, an antenna apparatus maintaining high reliability can be provided. 
   Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.