Abstract:
A coaxial waveguide converter circuit is provided for converting an input/output coaxial section of a traveling-wave tube to a waveguide. The circuit comprises a waveguide matching part for connecting an inner conductor of the coaxial section extending into the waveguide to a wall of the waveguide. The waveguide matching part includes a fitting hole for fitting the inner conductor thereinto, and a plurality of cantilever supports which define the fitting hole at leading end portions thereof. The leading end portions of the plurality of cantilever supports defining the fitting hole are uniformly kept in close contact with a peripheral surface of the inner conductor.

Description:
This application is based upon and claims the benefit of priority from Japanese patent application No. 2006-201882, filed on Jul. 25, 2006, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an input/output section of a traveling-wave tube for amplifying microwaves. In particular, the present invention relates to the structure of a coaxial waveguide converter circuit for converting the mode of the microwave when a microwave is applied from a waveguide to an input coaxial section of a traveling-wave tube, or for converting the mode of the microwave when a microwave is delivered from an output coaxial section of the traveling-wave tube to the waveguide. 
     2. Description of the Related Art 
       FIG. 1  is a longitudinal sectional view schematically illustrating the configuration of a general traveling-wave tube disclosed in Japanese laid-open patent publication No. 2005-339892A. Traveling-wave tube  100  generally comprises electron gun  101 , delay circuit  102 , and collector  103 . Delay circuit  102  comprises helix  105  securely supported by dielectric  106  within vacuum sheath  104 . Delay circuit  102  comprises, at both ends thereof, input circuit  107  for applying a microwave to helix  105  within traveling-wave tube  100 , and output circuit  108  for delivering a microwave which is amplified while it propagates through helix  105 , respectively. When waveguides  109  are used in input circuit  107  and output circuit  108 , a coaxial waveguide converter circuit is formed between waveguides  109  and input/output coaxial sections  110  of traveling-wave guide  100  for converting the mode of the microwave. 
     A structure as shown in Japanese utility model publication No. H02-32208 has been proposed for the coaxial waveguide converter circuit. As illustrated in  FIG. 2 , this structure comprises cylindrical coaxial outer conductor  203  which couples waveguide  201  with outer sheath  202  of a traveling-wave tube, and coaxial inner conductor  205  which extends within waveguide  201  along the center axis of coaxial outer conductor  203  from outer sheath  202  of the traveling-wave tube to connect helix  204  to waveguide  201 . Furthermore, a gap between coaxial outer conductor  203  and coaxial inner conductor  205  is sealed by ceramic window  206  under vacuum. In addition, waveguide matching part  207  is used at the joint of coaxial inner conductor  205  and waveguide wall  201   a  for impedance matching of a coaxial section comprised of coaxial outer conductor  203  and coaxial inner conductor  205  with waveguide  201 . 
     Waveguide matching part  207 , which comprises a cylindrical member, is fitted into a hole formed through waveguide wall  201   a  from the outside of waveguide tube  201  for fixation therein, and cylindrical coaxial inner conductor  205  is fitted into waveguide matching part  207 . A cylindrical hole of part  207  has its leading end portion narrower than the remaining portion, such that coaxial inner waveguide  205  is fitted into a narrow hole (hereinafter called “fitting hole  207   a ”) at the leading end of part  207 . Also, part  207  is made of a resilient material (for example, phosphor bronze), and is formed with a plurality of slits  207   b  from the leading end thereof, as illustrated in  FIGS. 3A and 3B . 
     Before such waveguide matching part  207  is fitted into waveguide  201  from the outside thereof, cantilever supports  207   c , divided by slits  207   b , are previously urged toward the center axis (in other words, fitting hole  207   a  is narrowed). By fitting coaxial inner conductor  205  into waveguide matching part  207  in this state, waveguide matching part  207  is brought into contact with coaxial inner conductor  205 . The contact between waveguide matching part  207  and coaxial inner conductor  205  is maintained by the resiliency of cantilever support  207   c.    
     According to the structure of the above waveguide matching part  207 , part  207  can be brought into contact with coaxial inner conductor  205  without requiring a high machining accuracy for part  207 , and is also assembled into waveguide  201  with ease. 
     However, the waveguide matching part of the coaxial waveguide converter circuit as disclosed in Japanese utility model publication No. H02-32208 is configured to make a contact with the coaxial inner conductor by urging the cantilever support to narrow the coaxial inner conductor fitting hole. As such, when relying on manual operations, the fitting hole is non-uniformly narrowed, resulting in a non-circular fitting hole which is brought into contact with the cylindrical coaxial inner conductor. Consequently, the contact is exacerbated between the coaxial inner conductor and waveguide matching part. On the other hand, when the operation is automated to uniformly narrow the fitting hole, the manufacturing cost is increased. 
     On the other hand, the coaxial inner conductor fitting hole in the conventional waveguide matching part is a straight hole which has a diameter larger than that of the coaxial inner conductor. Specifically, as illustrated in  FIG. 4(   a ), wall surfaces of cantilever supports  207   c  which define fitting hole  207   a  are substantially parallel with the center line of fitting hole  207   a . Accordingly, when waveguide matching part  207  is brought into contact with coaxial inner conductor  205 , with cantilever supports  207   c  being previously urged, the wall surfaces of cantilever supports  207   c  which define fitting hole  207   a  are inclined, causing fitting hole  207   a  to come into point contact with coaxial inner conductor  205 , as illustrated in  FIG. 4(   b ). This further engraves the problem of the contact when the fitting hole is manually narrowed. 
     As described above, when the coaxial inner conductor is insufficiently in contact with the waveguide matching part, a problem arises in which the heat dissipation capability from the coaxial inner conductor is reduced. 
     Specifically, in a traveling-wave tube, as an electron beam passes through the delay circuit, the electron beam impinges on the inner wall of the helix to generate heat. Heat is also generated due to a high frequency loss when a microwave passes through the helix. Such heat generated in the helix is dissipated from the outer sheath of the traveling-wave tube, and is also dissipated from the waveguide through the coaxial inner conductor and waveguide matching part connected to the helix, and the like. 
     However, when the heat dissipation capability from the coaxial inner conductor is reduced, this causes the temperature to rise in the coaxial section and helix, which results in degraded electric characteristics and instable operations. In the worst case, discharge, sputtering and the like have occasionally occurred in the coaxial section to render the traveling-wave guide defective in operation. 
     Also, since the temperature rises during the operation of the traveling-wave guide, the contact exacerbates between the coaxial inner conductor and waveguide matching part due to a difference in thermal expansion between respective parts which make up the coaxial waveguide converter circuit, possibly resulting in a further degradation of the heat dissipation effect from the coaxial inner conductor. 
     SUMMARY OF THE INVENTION 
     In view of the problems of the related art mentioned above, it is an exemplary object of the present invention to improve contact between a coaxial inner conductor and a waveguide matching part to enhance heat dissipation capabilities over the conventional structure. 
     A coaxial waveguide converter circuit according to an exemplary embodiment of the present invention comprises a waveguide matching part for connecting the inner conductor of a coaxial section extending into a waveguide to a wall of the waveguide. This part comprises a fitting hole into which the inner conductor is fitted, and a plurality of resilient cantilever supports, the leading end portions of which define the fitting hole. To solve the problems mentioned above, the inner conductor is tapered only in its leading end portion, and an opening of the fitting hole, into which the inner conductor is inserted, has a diameter larger than the diameter of the inner conductor at the extreme leading end thereof, and smaller than the outer diameter of the body of the inner conductor except for the leading end portion. Thus, when the inner conductor is inserted into the fitting hole of the waveguide matching part, each cantilever support uniformly displaces outward in the radial direction of the waveguide matching part in conformity to the outer diameter of the inner conductor, and simultaneously, each cantilever support is kept in good contact with the inner conductor with the aid of resiliency of the cantilever supports. 
     According to the foregoing configuration, the heat conduction property is improved over the related art when heat is dissipated from the inner conductor to the waveguide through the waveguide matching part. Consequently, the waveguide matching part improves the effect of preventing the temperature from rising in the coaxial section and helix, thus allowing stable operation without causing degraded electric characteristics. In addition, the inner conductor is readily fitted into the waveguide matching part. 
     Further, the fitting hole of the waveguide matching part that is used is preferably tapered with its diameter being increasingly reduced toward the opening of the fitting hole into which the inner conductor is inserted, and the insertion opening has a diameter smaller than the outer diameter of the inner conductor. The fitting hole includes an opening opposite to the inner conductor insertion opening. The opening is formed with the same diameter as the outer diameter of the inner conductor, thereby allowing each cantilever support to come into plane contact with the inner conductor, when the inner conductor is fitted into the fitting hole. In other words, the heat dissipation capability is further improved. 
     Also, to solve the problems mentioned above, in the structure according to the other exemplary aspect of the present invention, the waveguide may include a hole formed through its wall for fitting thereinto a portion of the waveguide matching part comprised of the plurality of cantilever supports to fix the portion therein, where the hole is tapered with its diameter being increasingly reduced from the outside to the inside of the waveguide. A waveguide matching part for use in this structure comprises a fitting hole for fitting the inner conductor thereinto, and a plurality of resilient cantilever supports, the leading ends of which define the fitting hole. When the waveguide matching part is inserted into the tapered hole formed through the waveguide wall, each cantilever support displaces inward in the radial direction of the waveguide matching part in conformity with the increasingly reduced diameter of the tapered hole to firmly come into close contact with the inner conductor. Accordingly, this structure can also be expected to improve the heat dissipation capability over the related art. 
     The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view schematically illustrating the configuration of a general traveling-wave tube; 
         FIG. 2  is a longitudinal sectional view schematically illustrating the configuration of a conventional coaxial waveguide converter circuit for use in a traveling-wave tube; 
         FIG. 3A  is a front view illustrating a waveguide matching part shown in  FIG. 2 , when not assembled; 
         FIG. 3B  is a plan view illustrating only the waveguide matching part shown in  FIG. 2 , when not assembled, viewed from the leading end side (near the traveling-wave guide); 
         FIG. 4  is a diagram for describing how the waveguide matching part is brought into contact with a coaxial inner conductor, both shown in  FIG. 2 ; 
         FIG. 5  is a longitudinal sectional view schematically illustrating the configuration of a coaxial waveguide converter circuit for a traveling-wave tube according to a first exemplary embodiment of the present invention; 
         FIG. 6  is a longitudinal sectional view illustrating how a coaxial inner conductor is fitted into a simple waveguide matching part used in the first exemplary embodiment of the present invention; 
         FIG. 7  is a longitudinal sectional view schematically illustrating the configuration of a coaxial waveguide converter circuit for a traveling-wave tube according to a second exemplary embodiment of the present invention; and 
         FIG. 8  is a longitudinal sectional view illustrating how a coaxial inner conductor is connected to a waveguide through a waveguide matching part in the second exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, the same reference numerals are used to designate the same components as those in the conventional coaxial waveguide converter circuit illustrated in  FIG. 2 . 
     First Exemplary Embodiment 
     A first exemplary embodiment of the present invention will be described with reference to  FIGS. 5 and 6 . Both  FIGS. 5 and 6  illustrate waveguide matching part  207 A on a plane taken along a slit. 
     In  FIGS. 5 and 6 , a cylindrical conductor is used for the coaxial inner conductor  205 . The coaxial inner conductor  205  is fitted into the waveguide matching part  207 A of this exemplary embodiment. Specifically, waveguide matching part  207 A comprises a cylindrical member which has a cylindrical hole that is narrower only in a leading end portion  207   d  ( FIG. 6 ) of part  207 A than in the remaining portion, to define fitting hole  207   a . In addition, this part  207 A is made of a resilient material (for example, phosphor bronze), and is formed with a plurality of slits  207   b  from the leading end thereof. In this way, aided by their resiliency, cantilever supports  207   c , that are divided by respective slits  207   b , can displace towards the center axis of fitting hole  207   a . As illustrated in  FIG. 5 , when coaxial inner conductor  205  is fitted into fitting hole  207   a  of waveguide matching part  207 A, each cantilever support  207   c  aided by its resiliency is in contact with coaxial inner conductor  205 . It should be noted that a plurality of cantilever supports  207   c  of waveguide matching part  207 A protrude into the inside of waveguide wall  201   a , and no waveguide wall  201   a  exists around cantilever supports  207   c  (outside of waveguide matching part  207 A in the radial direction). 
     In particular, in this exemplary embodiment, coaxial inner conductor fitting hole  207   a  of waveguide matching part  207 A, when coaxial inner conductor  205  is not fitted thereinto, has a tapered circular shape, the diameter of which is gradually reduced toward the leading end  207   d  of part  207 A (opening into which coaxial inner conductor  205  is inserted), as illustrated in  FIG. 6 . Further, leading end portion  205   a  of cylindrical coaxial inner conductor  205 , which extends into the waveguide, is tapered with its diameter gradually reduced toward the leading end, or leading end portion  205   a  has its edge chamfered. 
     Further, as illustrated in  FIG. 6 , at the leading end  207   d  of waveguide matching part  207 A, diameter A of the opening in tapered fining hole  207   a  is smaller than diameter B of an opening in fitting hole  207   a  at the rear end of waveguide matching part  207 A. On the other hand, coaxial inner conductor  205  has diameter C at the leading end  205   a  thereof, which is smaller than diameter D of body  205   b  of coaxial inner conductor  205 , and which is also smaller than diameter A of the opening of fitting hole  207   a . In addition, diameter D of body  205   b  of coaxial inner conductor  205  may be larger than diameter B of the opening of fitting hole  207   a , but preferably diameter D is substantially the same size as diameter B of the opening of fitting hole  207   a . Stated another way, a relationship D&gt;B&gt;A&gt;C may exist, but preferably D≈B&gt;A&gt;C. 
     As described above, since fitting hole  207   a  at the leading end  207   d  of waveguide matching part  207 A has the opening, the diameter A of which is larger than diameter C at the leading end of coaxial inner conductor  205 , and smaller than diameter D of body  205   b  of coaxial inner conductor  205 , coaxial inner conductor  205  is readily inserted into fitting hole  207   a  of waveguide matching part  207 A. Then, while coaxial inner conductor  205  is being inserted into fitting hole  207   a , each cantilever support  207   c  deforms in conformity to the outer diameter of coaxial inner conductor  205 . Consequently, a good contact can be maintained between waveguide matching part  207 A and coaxial inner conductor  205  as best shown in  FIG. 5 . Specifically, since each cantilever support  207   c  uniformly extends outward in the radial direction of waveguide matching part  207 A in conformity to the outer diameter of coaxial inner conductor  205  while coaxial inner conductor  205  is inserted into fitting hole  207   a , the resiliency of cantilever supports  207   c  can serve to maintain a good contact with coaxial inner conductor  205 . 
     In particular, when diameter D of body  205   b  of coaxial inner conductor  205  is substantially the same as diameter B of the opening of fitting hole  207   a  at the rear end of waveguide matching part  207 A, wall surfaces of cantilever supports  207   c  which define fitting hole  207   a  are in contact with the peripheral surface of the body  205   b  of coaxial inner conductor  205 , as illustrated in  FIG. 5 . Stated another way, in this event, they are in plane contact with each other to have a larger contact area which further improves the heat conduction property. 
     As described above, waveguide matching part  207 A can maintain good contact with coaxial inner conductor  205  by simply inserting coaxial inner conductor  205  into fitting hole  207   a , without the need for a step of previously bending cantilever supports  207   c , as compared with the conventional counterpart. As a result, the heat conduction property is improved over the related art when heat generated in the helix of the traveling-wave tube is dissipated from coaxial inner conductor  205  to waveguide  201  through waveguide matching part  207 A. In addition, waveguide matching part  207 A improves the effect of preventing the temperature from rising in the coaxial section and helix, thus allowing stable operation without causing degraded electric characteristics. 
     Second Exemplary Embodiment 
     Next, a second exemplary embodiment of the present invention will be described with reference to  FIGS. 7 and 8 . Both  FIGS. 7 and 8  illustrate waveguide matching part  207 B on a plane taken along a slit. 
     Likewise, this exemplary embodiment employs cylindrical coaxial inner conductor  205  and a cylindrical coaxial outer conductor  203  ( FIG. 7 ). The waveguide matching part  207 B comprises a cylindrical member which has a cylindrical hole that is narrower only at a leading end portion  207   d  ( FIG. 8 ) of part  207 B in than the remaining portion, to define fitting hole  207   a . In addition, this part  207 B is made of a resilient material (for example, phosphor bronze), and is formed with a plurality of slits  207   b  from the reading end of part  207 B. In this way, aided by their resiliency, cantilever supports  207   c , that are divided by respective slits  207   b , can displace towards the center axis of fitting hole  207   a . It should be noted that slits  207   b  have a width large enough such that the leading end of each cantilever support  207   c  can largely displace toward the center axis of fitting hole  207   a  simultaneously with the other cantilever supports  207   c.    
     In particular, in this exemplary embodiment, waveguide matching part  207 B is fitted into waveguide wall  201   a  together with a plurality of cantilever supports  207   c . Then, as illustrated in  FIG. 8 , hole  208  is formed through waveguide wall  201   a  for inserting thereinto a portion of waveguide matching part  207 B, comprised of the plurality of cantilever supports  207   c . Hole  208  is a tapered circular hole, the diameter of which is increasingly reduced toward the inside of waveguide  201 . The outer surface of the portion of waveguide matching part  207 B, comprised of the plurality of cantilever supports  207   c , is also tapered, with its outer diameter being increasingly reduced toward the leading end  207   d  of part  207 B (the opening into which coaxial inner conductor  205  is inserted). The angle of the tapered outer surface is designed to be smaller than the angle of tapered hole  208  formed through waveguide wall  201   a.    
     Further, as best shown in  FIG. 8 , waveguide matching part  207 B has outer diameter B at the leading end thereof which is smaller than diameter F of hole  208  open to the outer surface of waveguide wall  201   a , and larger than diameter J of hole  208  open to the inner surface of waveguide wall  201   a . In addition, diameter F outside of waveguide wall  201   a  in hole  208  is designed to be slightly larger than the outer diameter I of waveguide matching part  207 B at proximal ends of the plurality of cantilever supports  207   c.    
     Also, fitting hole  207   a  of waveguide matching part  207 B has diameter G which is designed to be larger than diameter H of coaxial inner conductor  205 . 
     By designing waveguide matching part  207 B in the foregoing shape, coaxial inner conductor  205  goes into fitting hole  207   a  of waveguide matching part  207 B as waveguide matching part  207 B is inserted into hole  208  through waveguide wall  201   a . In this process, the leading end  207   d  of waveguide matching part  207 B hits against the side surface of tapered hole  208 , causing each cantilever support  207   c  to deform toward the center line of fitting hole  207   a  in conformity to the increasingly reduced diameter of tapered hole  208 . In other words, respective cantilever supports  207   c  are urged together inward in the radial direction of waveguide matching part  207 B to gradually reduce the diameter of fitting hole  207   a . Subsequently, when waveguide matching part  207 B has been completely inserted into hole  208  of waveguide wall  201   a  as illustrated in  FIG. 7 , each cantilever support  207   c  is firmly in close contact with coaxial inner conductor  205 . 
     As described above, waveguide matching part  207 B does not have the requirement that the cantilever supports  207   c  be previously bent, as compared with the conventional counterpart. In addition, simply by inserting waveguide matching part  207 B into tapered hole  208  formed through waveguide wall  201   a  and fixing waveguide matching part  207 B in tapered hole  208 , close contact is firmly maintained between waveguide matching part  207 B and coaxial inner conductor  205 . As a result, the heat conduction property is improved over the related art when heat generated in the helix of the traveling-wave tube is dissipated from coaxial inner conductor  205  to waveguide  201  through waveguide matching part  207 B. In addition, waveguide matching part  207 B improves the effect of preventing the temperature from rising in the coaxial section and helix, thus allowing stable operations without causing degraded electric characteristics. 
     In this exemplary embodiment, the outer surface of waveguide matching part  207 B is tapered in the portion comprised of a plurality of cantilever supports  207   c  for the following reason. The tapered outer surface prevents inclination of the wall surfaces of cantilever supports  207   c  which define fitting hole  207   a , when waveguide matching part  207 B is inserted into hole  208  of waveguide wall  201   a . Accordingly, cantilever supports  207   c  are brought into plane contact with coaxial inner conductor  205 . In contrast, when the outer surface of waveguide matching part  207 B has the same outer diameter in the portion comprised of the plurality of cantilever supports  207   c , cantilever supports  207   c  can be brought into point contact with coaxial inner conductor  205 , as illustrated in  FIG. 4(   b ), when such a waveguide matching part is inserted into hole  208  of waveguide wall  201   a . In this event, however, a plane contact can be achieved, as described above, by tapering fitting hole  207   a  with its diameter being increasingly reduced toward the direction opposite to the opening into which coaxial inner conductor  205  is inserted. 
     In any case, each part is preferably designed to prevent cantilever supports  207   c  from coming into point contact with coaxial inner conductor  205 . This is because, by designing waveguide matching part  207 B in such a way, resulting waveguide matching part  207 B further improves the heat dissipation property from coaxial inner conductor  205  to waveguide  201 . 
     As described above, the present invention can improve contact between the coaxial inner conductor and waveguide matching part over the conventional structure. As a result, the present invention can increase the heat dissipation effect from the coaxial inner conductor to stabilize the operation, as compared with the conventional traveling-wave tube. 
     While exemplary embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.