Abstract:
An electron tube is provided with a plurality of supports, a portion of the support covered with conductive material abuts the inner wall of the shell, and another portion of the support covered with dielectric abuts the helix. The helix which is used as a high-frequency circuit for bringing about interaction between an electron beam and a high-frequency signal is supported and fixed within the shell by plurality of supports.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electron tube having a helix which will be used as a high-frequency circuit for bringing about interaction between an electron beam and a high-frequency signal.  
         [0003]     2. Description of the Related Art  
         [0004]     There are known electron tubes such as a traveling-wave tube or a klystron, for amplifying and oscillating a high-frequency signal by interaction between an electron beam emitted from an electron gun and a high-frequency circuit. One of these electron tubes, as shown in  FIG. 1 , is provided with electron gun  10  for emitting electron beam  50 , spiral-shaped helix  20  to be used as a high-frequency circuit for bringing about interaction between electron beam  50  emitted from electron gun  10  and a high-frequency signal (microwave), collector electrode  30  for capturing electron beam  50  passing through helix  20 , and anode  40  for introducing electron beam  50  emitted from electron gun  10  into the spiral structure of helix  20 .  
         [0005]     Electron gun  10  is provided with cathode  11  for emitting thermoelectrons, heater  12  for giving cathode  11  thermal energy for the emission of thermoelectrons, and Wehnelt electrode  13  for concentrating thermoelectrons to form electron beam  50 .  
         [0006]     Predetermined power supply voltages are respectively supplied to collector electrode  30  and electron gun  10  in the electron tube shown in  FIG. 1 , and anode  40  and helix  20  are each connected to the shell of the electron tube so as to be grounded.  
         [0007]     A common negative high voltage (cathode voltage) is supplied to cathode  11  and Wehnelt electrode  13  of electron gun  10  from power supply  60 ; a predetermined voltage is supplied to heater  12  based on the cathode voltage. Also, a positive high voltage is supplied to collector electrode  30  based on the cathode voltage. Alternatively, an electron tube is known in which anode  40  and helix  20  are separated and various power supply voltages are supplied to anode  40  and helix  20 .  
         [0008]     Electron beam  50  emitted from electron gun  10  is accelerated by anode electrode  40  and introduced into the spiral structure of helix  20 , and travels inside the structure of helix  20  while interacting with the high-frequency signal supplied from the input end of helix  20 . Electron beam  50  output from the spiral structure of helix  20  is captured by collector electrode  30  while the high-frequency signal amplified by interaction with electron beam  50  is output from the output end of helix  20 .  
         [0009]     Helix  20 , as shown in  FIGS. 2A and 2B , is supported by supports  22  (usually, three supports) made of dielectrics and fixed in shell  21 . On the inner wall of shell  21 , vein  23  (also called, solid) made of metal material is inserted in a radial direction in order to conduct signals over a wide range of frequencies by reducing changes with reference to the frequency in the phase speed of the high-frequency signal (microwave) supplied to helix  20  and with reference to the interaction impedance of electron beam  50  and the high-frequency signal. For example, a method for arranging vein  23  in shell  21  so that electron tube  1  can be used over a wide range of frequencies is described in Non-Patent Document (Onodera, Tsuji, “Dispersion Characteristic of Loading Helix for Ultra-Wide Band Traveling Wave Tube”, The Institute of Electronics, Information and Communication Engineers, September 1987, vol. J70-C, No. 9, pp. 1286-1287.). In this paper, the shell is called a barrel and the vein is called a metal segment.  
         [0010]     As shown in  FIGS. 2A and 2B , when helix  20  is fixed in shell  21 , helix  20  to which supports  22  are attached is fitted to shell  21  by means of heat shrinking, and then veins  23  are fixed to positions so as not to overlap with supports  22  on the inner wall of shell  21  (at intervals of angles of 120 degrees) by brazing. As a result, it is difficult to attach veins  23  and there is a problem in that the defective rate in the attaching process of veins  23  is high. In particular, recent electron tubes are used at higher frequencies in view of the large capacity of communications system and in view of the effective use of radio waves, and therefore, electron tubes become smaller to conform to higher frequencies. Hence, heat shrinking allowance between helix  20  and shell  21  tend to be small, there is a strong possibility that helix  20  or supports  22  will collapse during attachment of veins  23 , and attachment of veins  23  tends to be more difficult.  
         [0011]     To deal with these disadvantages, for example, Patent Document 1 (Japanese Patent Laid-Open publication No. 242817/1993) discloses that steps are arranged on one or both sides of the supports (dielectric) for supporting the helix and that metal plating is applied to the steps, so that the support functions as vein and veins are unnecessary.  
         [0012]     However, in the conventional structure disclosed in Patent Document 1, because a technique for accurately applying metal plating to the steps arranged on the support made of dielectrics has not been established, there is a problem that the defective rate in the process of forming supports is high.  
         [0013]     Therefore, the problems that occur are that cost of manufacturing electron tubes increases and electron tubes cannot be used over a wide range of frequencies.  
       SUMMARY OF THE INVENTION  
       [0014]     It is therefore an object of the present invention to provide an electron tube which has low manufacturing costs (in which manufacturing costs are suppressed) and which can be used over a wide range of frequencies.  
         [0015]     To achieve the object, according to the present invention, an electron tube is provided with a plurality of supports, a portion of which is covered with conductive material, these supports covered with conductive material abut an inner wall of the shell, and another portion of the supports covered with a dielectric abuts the helix, and a helix to be used as a high-frequency circuit for bringing about interaction between the electron beam and a high-frequency signal is supported and fixed within the shell by plurality of supports.  
         [0016]     In the electron tube according to this arrangement, the conductive material that included the support, rather than the veins, contributes to the electron tube being able to operate over a wide range of frequencies, and therefore it is not necessary to arrange veins on the inside of the shell. In particular, since the dielectric is formed on the surface of the conductive material, the supports can be formed by an established technique such as the CVD (Chemical Vapor Deposition) method and the defective rate in the process of forming the supports is improved. Therefore, it is possible to obtain an electron tube in which an increase of manufacturing costs is suppressed and which can be used over a wide range of frequencies.  
         [0017]     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  
       [0018]      FIG. 1  is a side sectional view showing an example of the configuration of an electron tube having a helix;  
         [0019]      FIG. 2A  is a sectional view showing the configuration of the conventional helix that is shown in  FIG. 1 ;  
         [0020]      FIG. 2B  is a side sectional view showing the configuration of the conventional helix that is shown in  FIG. 1 ;  
         [0021]      FIG. 3A  is a side sectional view showing a first embodiment of the configuration of an electron tube of the present invention;  
         [0022]      FIG. 3B  is a perspective view showing the configuration of a support that is shown in  FIG. 3A ;  
         [0023]      FIG. 4  is a perspective view showing the configuration of a modification of the support that is shown in  FIG. 3A ;  
         [0024]      FIG. 5A  is a sectional view showing a second embodiment of the configuration of an electron tube of the present invention; and  
         [0025]      FIG. 5B  is a perspective view showing the configuration of a support that is shown in  FIG. 5A . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0026]      FIG. 3A  is a side sectional view showing a first embodiment of the configuration of an electron tube of the present invention, and  FIG. 3B  is a perspective view showing the configuration of a support that is shown in  FIG. 3A .  FIG. 3A  shows a sectional view in a direction orthogonal to the flow of the electron beam.  
         [0027]     As shown in  FIGS. 3A and 3B , in the electron tube of the first embodiment, supports  2  for supporting helix  20  within shell  21  are different from those of the conventional electron tube. The construction is otherwise identical to an electron tube of the prior art shown in  FIGS. 2A and 2B  and explanation of this construction is therefore here omitted.  
         [0028]     Support  2  in the electron tube of the first embodiment is formed by covering dielectric  4  onto the surface of conductive material  3  in such a manner that dielectric  4  is exposed at the region abutting on the inner wall of shell  21 . Hence, conductive material  3  comes in contact with the inner wall of shell  21  in the radial direction. Additionally,  FIGS. 3A and 3B  show that dielectrics  4  are arranged on both sides of plate-shaped conductive material  3 , however, conductive material  3  is not limited to the plate shape and may be formed in any shape such as a trapezoid and a L-shape. Further, support  2  may be formed in any shape as long as conductive material  3  is arranged at the region abutting the inner wall of shell  21 , and as long as a region that is in contact with helix  20  is covered with dielectric  4 . For example, dielectric  4  is formed in a L-shape on the surface of conductive material  3  as shown in  FIG. 4 .  
         [0029]     Non-magnetic material such as copper and graphite is used for conductive material  3 . Boron nitride or aluminum nitride is used for dielectric  4  that covers conductive material  3 . On the surface of conductive material  3 , for example, dielectric  4  is deposited by CVD (Chemical Vapor Deposition) method.  
         [0030]     In the electron tube of the first embodiment, conductive material  3  in support  2  reduces changes with reference to the frequency in the phase speed of high-frequency signal (microwave) supplied to helix  20 , and reduces changes in the interaction impedance of electron beam and high-frequency signal so as to contribute to the electron tube being used over a wide rage of frequencies. Hence, veins  23  are unnecessary, the process of attaching veins  23  is not required, and therefore, the cost of electron tube is reduced.  
         [0031]     Also, in the first embodiment, compact electron tubes being able to operate over a wide range of frequencies can be obtained by the same manufacturing method as the conventional method because veins  23  is not needed.  
         [0032]     Further, in the first embodiment, it is possible to produce support  2  by forming dielectric  4  on the surface of conductive material  3  with established techniques such as the CVD method rather than by applying metal plating to support  2  which is made of dielectric as described in Patent Document 1. The defective rate is improved during the process of forming support  2 . Hence, an increase in the cost of electron tubes can be suppressed while the electron tube can be used over a wide range of frequencies.  
       Second Embodiment  
       [0033]      FIG. 5A  is a sectional view showing a second embodiment of the configuration of an electron tube of the present invention, and  FIG. 5B  is a perspective view showing the configuration of a support that is shown in  FIG. 5A .  FIG. 5A  shows a sectional view in a direction orthogonal to the flow of the electron beam.  
         [0034]     As shown in  FIGS. 5A and 5B , in the electron tube of the second embodiment, conductive material  6  is used for the material in as support  5  for supporting helix  20  within shell  21 , and a region abutting helix  20  is covered with dielectric film  7 . The construction is otherwise identical to an electron tube of the prior art shown in  FIGS. 2A and 2B  and explanation of this construction is therefore here omitted.  
         [0035]     Non-magnetic material such as copper and graphite is used for conductive material  6 , as in the first embodiment. Boron nitride or aluminum nitride is used for dielectric film  7 . On the region abutting helix  20 , dielectric film  7  is formed by the CVD method.  
         [0036]     In the electron tube of the second embodiment, as with the first embodiment, conductive material  6  which is used in support  5 , rather than vein  23  shown in  FIG. 2 , contributes to the electron tube being able to operate over a wide range of frequencies. Hence, veins  23  are unnecessary, the process of attaching veins  23  is not required, and therefore, the cost of electron tubes is reduced.  
         [0037]     Also, in the second embodiment, compact electron tubes operating over wide range frequencies can be obtained by the same manufacturing method as the conventional method because veins  23  are not needed in the construction of the electron tube.  
         [0038]     Further, in the second embodiment, it is possible to produce support  5  by forming dielectric film  7  on the surface of conductive material  6  with established techniques such as the CVD method. The defective rate is improved in the process of forming support  5 . Hence, an increase in the cost of electron tube can be suppressed while the electron tube can be used over a wide range of frequencies.  
         [0039]     While preferred 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.