Patent Publication Number: US-7710041-B2

Title: Microwave tube

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-053322, filed Feb. 28, 2006, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a microwave tube having a high frequency output section coupled to an output cavity. 
   2. Description of the Related Art 
   A large power klystron has been known as a microwave tube using the linear beam. The klystron is composed of: a klystron body including an electron gun for generating an electron beam, an input section for inputting high frequency power, a high frequency interacting section for amplifying high frequency power through the interaction of the electron beam with a high frequency electric field, a high frequency output section with a high frequency window for outputting the high frequency power that is amplified by the high frequency interacting section, and a collector section for collecting the electron beam that is no longer needed; and a magnetic field focusing device, mounted to and around the klystron body, for reducing the diameter of the electron beam to be a given diameter (Jpn. Pat. Appln. KOKAI Publication No. 11-149876, pages 2 to 3, FIGS. 1 and 2). 
   In some of this type of klystron, a plurality of high frequency output sections are coupled to the output cavity in order to cope with the power withstanding of the high frequency window or to meet client&#39;s requests. 
   If the coupling parts to the output cavity, the high frequency windows and the like, which are provided for one of those, for example, two high frequency output sections, are electrically and exactly the same as those for the other high frequency output section, the high frequency power output from one high frequency output section is exactly equal to that output from the other one. However, those high frequency output powers are minutely different from each other because of variations of the mechanical dimension of the coupling part to the output cavity and the high frequency window, variation of the relative permittivity of the dielectric member attached as the air-tight member to the high frequency window, and deformation of the wave guide. In the case where the matching of those high frequency output powers from the two high frequency output sections is lost, returning high frequency waves occur. This results in highering of VSWR (voltage standing wave ratio). 
   The difference between those two output powers is within 5% when the VSWR is low, in which case no problem arises. When the output power difference becomes a problem, a high frequency power mixer/divider  1  as shown in  FIG. 7  is used. Generally, in the power mixer/divider  1 , the high frequency powers output through two high frequency windows  2  are changed in traveling directions at corners  3 , are mixed by a magic tee  4 , and the mixed power is divided again into two high frequency powers at another magic tee  4 , and those high frequency powers are changed in traveling directions at corners  5 , and finally output to outside. 
   When the power mixer/divider  1  is used for the klystron, however, the external dimension of the klystron becomes large. Even when the power mixer/divider  1  is used, the two output powers could be exactly equal to each other if the electrical symmetry is secured. Actually, however, an output power difference inevitably occurs since the dimension accuracy variation of the magic tees  4  and other parts at the manufacturing stage is present. 
   BRIEF SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to provide a microwave tube in which the high frequency powers output from the high frequency output sections can be easily adjusted. 
   According to the present invention, there is provided a microwave tube having a high frequency output section coupled to an output cavity, wherein the high frequency output section includes: an output tube connected to the output cavity; and an output power adjusting mechanism which has a reflection adjusting part provided in the tube wall of the output tube so as to be displaceable in the inward and outward directions of the output tube, and which adjusts the output power by displacing the reflection adjusting part. 
   In the microwave tube constructed according to the present invention, the output powers of high frequency output from the high frequency output sections can be easily adjusted in a manner that a reflection adjusting part, which is provided in the tube wall of an output tube, is displaced in the inward or outward direction of the output tube by an output power adjusting mechanism. Therefore, when a plurality of high frequency output sections are used, the output powers of the high frequency output sections are easily adjusted for matching therebetween. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
       FIG. 1  is a cross sectional view showing an output cavity and high frequency output sections of a klystron, which is a first embodiment of the invention; 
       FIG. 2  is a plan view showing the output cavity and the high frequency output sections of the klystron; 
       FIG. 3  is an enlarged cross sectional view showing an output power adjusting mechanisms of the klystron; 
       FIG. 4  is a cross sectional view showing the klystron; 
       FIG. 5  is a cross sectional view showing an output cavity and high frequency output sections of a klystron, which is a second embodiment of the invention; 
       FIG. 6  is a plan view showing the output cavity and the high frequency output sections of the klystron; and 
       FIG. 7  is a perspective view showing a power mixer/divider used for a conventional klystron. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIGS. 1 to 4  show a first embodiment of the invention. 
   As shown in  FIG. 4 , a klystron  11  as a microwave tube is composed of a klystron body  12  and a focusing magnetic field device  13 . 
   The klystron body  12  includes an electron gun  16  for producing an electron beam, a high frequency interacting section  17  for amplifying high frequency power through the interaction of the electron beam with a high frequency electric field, an input section  18  for inputting high frequency power to the high frequency interacting section  17 , a plurality of, for example, two high frequency output sections  19  for outputting the high frequency power that is amplified by the high frequency interacting section  17 , and a collector section  20  for collecting the electron beam that has passed through the high frequency interacting section  17  and is no longer needed. 
   The high frequency interacting section  17  includes a drift tube  21  through which the electron beam passes, an input cavity  22  coupled to the input section  18 , a plurality of intermediate cavities  23 , and an output cavity  24  coupled to the two high frequency output sections  19 . 
   The focusing magnetic field device  13  includes a main magnetic field generator  27  disposed around the high frequency interacting section  17 , and sometimes further includes an electron-gun side magnetic field generator (not shown) disposed around the electron gun  16  at one end of the main magnetic field generator  27 . The main magnetic field generator  27  includes main coils  28  disposed around the high frequency interacting section  17 , and an output coil  29  located on the outer side than the output cavity  24 . 
     FIG. 1  is a cross sectional view showing the output cavity  24  and the high frequency output sections  19  of the klystron  11 .  FIG. 2  is a plan view showing the output cavity  24  and the high frequency output sections  19  of the klystron  11 . 
   An cavity resonator  32  forming the output cavity  24  is provided with cylindrical cavity walls  33  and upper and lower faces  34 . The cavity walls  33  and the upper and lower faces  34  are made of good conductive metal, for example, copper. The drift tube  21  extends to the center axis part of the output cavity  24  through which the electron beam passes, through the upper and lower faces, to thereby form a semi-coaxial cavity resonator. 
   Formed in the side walls of the cavity resonator  32  are two opened rectangular windows each having a long side W extending in the peripheral direction. Those windows are called irises  35  through which the high frequency output sections  19  are coupled with each other. 
   Each high frequency output section  19  takes a rectangular shape having long sides  36  and short sides  37 , in conformity with the rectangular shape of each iris  35 . Each high frequency output section  19  includes a wave guide  38  as an output tube which is rectangular in cross section and coupled with the cavity resonator  32 . The wave guide  38  is provided with a high frequency window  39  and an output flange  40  located on the outer side than the high frequency window. A disc-like dielectric member  41  made of, for example, ceramic, which is for ensuring vacuum tightness, is placed within the high frequency window  39 . 
   An output power adjusting mechanism  44  is provided at a position of the wave guide  38  of each high frequency output section  19 , which is located at the central part of one of the long sides  36  of the wave guide  38  and is apart away from the cavity resonator  32  by a distance L. The output power adjusting mechanism  44  adjusts an output power by locally displacing the tube wall of the wave guide  38  in inward and outward directions of the wave guide. The distance L measured from the cavity resonator  32  is equal to ⅛ wavelength (λ) electrical length or distance of [(⅛λ)×odd number], measured from the cavity resonator  32 . 
   In the output power adjusting mechanism  44 , an annular thin part  45  is formed in the wall of the wave guide  38 . A circular reflection adjusting part  46  is formed on the inner side of the annular thin part  45 , and is displaceable in the inward and outward of the wave guide with the aid of the annular thin part  45 . An adjusting plate  48  having a screw hole  47  at the center is fastened to the outer surface of the reflection adjusting part  46 . 
   A plurality of supports  49  are protruded from the outer surface of the wave guide  38 , while surrounding the reflection adjusting part  46 . A support plate  50  is firmly mounted on the tips of those supports  49 . An adjusting screw  51  is rotatably inserted into the support plate  50 , and the tip of the adjusting screw  51  is screwed into the screw hole  47  of the adjusting plate  48 . 
   When the adjusting screw  51  is turned in one or the other direction, the reflection adjusting part  46  on the inner side of the annular thin part  45 , together with the adjusting plate  48 , is displaced in the inward or the outward direction of the wave guide with respect to the wave guide  38  and the support plate  50  to thereby adjust the high frequency reflection within the wave guide  38 . The high frequency reflection is capacitive and inductive, and an imaginary part reflection. Since the reflection adjusting part  46  is apart away from the cavity resonator  32  by the ⅛λ distance, the reflection is a real part reflection when viewed from the cavity resonator  32  distanced backward by the ⅛λ length. Accordingly, the load impedance when viewed from the cavity resonator  32  is adjusted by varying the coupling quantity to the load. When the reflection adjusting part  46  is displaced in the inward direction of the wave guide to decrease the diameter of the wave guide  38 , the high frequency reflection is capacitive. When it is displaced in the outward direction to increase the diameter of the wave guide  38 , the reflection is inductive. Accordingly, when the reflection adjusting part  46  is displaced inward to decrease the diameter of the wave guide  38 , the capacitive component increases, and when viewed from the cavity resonator  32  distanced backward by the ⅛λ length, the load impedance increases and the output power becomes low. Conversely, when it is displaced outward to increase the diameter of the wave guide  38 , the negative capacitance component, i.e., the inductive component, becomes large and the output power becomes high. 
   In the structure where the two high frequency output sections  19  are coupled to the cavity resonator  32 , the respective load impedances can be adjusted by using the output power adjusting mechanisms  44 . Accordingly, the output power to the output flanges  40  coupled to the wave guides  38  may be adjusted as desired. 
   The irises  35  provided in the cavity resonator  32  may become capacitive and inductive, and the electric field expands from the cavity resonator  32  into the wave guide  38  through the irises  35 . For this reason, the distance L from the end face of the wave guide  38  to the center of each output power adjusting mechanism  44  is not simply determined to be the ⅛λ length wave guide. However, the output power is most effectively adjusted when the distance L is electrically selected to be the ⅛λ length. 
   In the case where the distance L is selected to be [(⅛λ)×odd number], it is replaced with [⅛+(¼×n)]. In the expression, if n=even number, the reflection adjustment acts in the same direction as in the case of ⅛λ length. If n=odd number, the adjustment acts in the opposite direction as in the case of ⅛λ length. 
   Thus, the high frequency output power output from each high frequency output section  19  is easily adjusted in a manner that the reflection adjusting part  46  provided in the tube wall of the wave guide  38  is displaced in the inward or outward direction of the wave guide by means of the output power adjusting mechanisms  44 . 
   For this reason, in the case where a plurality of high frequency output sections  19  are used, it is possible to adjust the output powers of the high frequency output sections  19  for matching therebetween. In other words, the output powers that are minutely different from each other can be adjusted to be equal to each other without using the power mixer/divider. 
   The output power adjusting mechanisms  44  may be provided on both the long sides  36  of the wave guide  38 , one or both short sides  37  of the wave guide  38 , or the long side  36  and/or the short side  37  of the wave guide  38 . In the case where the output power adjusting mechanisms  44  is provided on the short side  37  of the wave guide  38 , the inductive component is adjusted through the inward displacement. 
   The annular thin part  45  and the reflection adjusting part  46  of the output power adjusting mechanisms  44  are annular and circular, but may be elliptical, square or the like. 
   A second embodiment of the present invention will be described with reference to  FIGS. 5 and 6 . 
   The two high frequency output sections  19  include coaxial tubes  63  as output tubes, each having an outer tube  61  and an inner tube  62 . The outer tube  61  of each coaxial tube  63  is coupled to the cavity walls  33  of the cavity resonator  32 . The inner tube  62  is connected to a coupling loop  64  located in the cavity resonator  32 . A vacuum tightness of each coaxial tube  63  is secured by a disc-like dielectric member  65  which is made of ceramic, for example, and has a hole allowing the inner tube  62  to pass therethrough. 
   Each coaxial tube  63  is provided with the output power adjusting mechanisms  44 , which is located at a position apart away from the cavity resonator  32  by an electrical distance of ⅛λ or (⅛λ×odd number). In each output power adjusting mechanism  44 , an annular thin part  45 , elongated in the axial direction of the coaxial tubes  63 , is formed in the tube wall of the outer tube  61  of the coaxial tubes  63 . An elliptical reflection adjusting part  46  is formed on the inner side of the elongated annular thin part  45 , and is displaceable in the inward and outward of the coaxial tube with the aid of the annular thin part  45 . An adjusting plate  48  having a screw hole  47  at the center is fastened to the outer surface of the reflection adjusting part  46 . 
   A plurality of supports  49  are protruded from the outer surface of the outer tube  61  of the coaxial tubes  63 , while surrounding the reflection adjusting part  46 . A support plate  50  is firmly mounted on the tips of those supports  49 . An adjusting screw  51  is rotatably inserted into the support plate  50 , and the tip of the adjusting screw  51  is screwed into the screw hole  47  of the adjusting plate  48 . 
   When the adjusting screw  51  is turned in one or the other direction, the reflection adjusting part  46  on the inner side of the annular thin part  45 , together with the adjusting plate  48 , is displaced in the inward or the outward direction of the wave guide with respect to the coaxial tubes  63  and the support plate  50  to thereby adjust the high frequency reflection within the coaxial tubes  63 . 
   This reflection is an imaginary part reflection, and is a real part reflection when viewed from the cavity resonator  32  distanced backward by the ⅛λ length. Accordingly, the load impedance when viewed from the cavity resonator  32  can be adjusted, and the output power to output terminals  66  connected to the two coaxial tubes  63  can be adjusted. 
   Each embodiment mentioned above may be modified as follows. A part of the tube wall of the wave guide  38  or the coaxial tube  63  is formed separately from the latter, and hermetically fastened to the latter. The annular thin part  45  and the reflection adjusting part  46  of the output power adjusting mechanism  44  are incorporated into the separate portion. 
   The microwave tube is not limited to the klystron  11 , but may be a linear accelerator, a traveling-wave tube or the like. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.