Patent Publication Number: US-6670760-B2

Title: Collector structure of traveling wave tube having a lossy ceramic member

Description:
This is a Continuation Application of application Ser. No. 09/190,009 filed Nov. 12, 1998 (issued as U.S. Pat. No. 6,291,935 on Sep. 18, 2001), the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a collector of a traveling wave tube. 
     BACKGROUND OF THE INVENTION 
     FIGS. 4,  5 ( a ),  5 ( b ) and  6  are longitudinal cross-sectional views of a conventional traveling wave tube. Specifically, FIG. 4 shows a conduction cooling type, FIG. 5 a forced air-cooling type and FIG. 6 shows a water-cooling type. 
     FIG. 7 shows a longitudinal cross-sectional view of a conventional collector, while FIG. 8 a  is a transverse cross-sectional view of another illustrative structure of a conventional collector and FIG. 8 b  is a longitudinal cross-sectional view of FIG. 8 a . FIG. 9 shows a two-stage version of the collector shown in FIG.  8 . Specifically, FIGS. 9 a  and  9   b  are a transverse cross-sectional view and a longitudinal cross-sectional view of the collector, respectively. 
     Among the devices which effect amplification of the micro-wave, using an electron beam, there is a traveling wave tube used as a relay station for micro-waves and for satellite communication. 
     Referring to FIGS. 4,  5 ( a ),  5 ( b ) and  6 , a traveling wave tube includes an electron gun  23  for radiating an electron beam  24 , a delay wave circuit  25  for producing interaction between the electron beam  24  and the input micro-wave, a collector  26  for collecting the electron beam  24  and a beam converging device  27  for converging the electron beam  24 . 
     For increasing the efficiency of the traveling wave tube, a method known as a collector potential lowering method is used. This method consists in progressively lowering the potential applied across the collector electrode  28  (see FIG. 4) relative to the delay wave circuit  25  to lower the speed of the electron beam  24  colliding against the collector to decrease the energy generated in the collector electrode  28 . To this end, there is provided a collector-insulating ceramic element  36  for maintaining insulation between the collector  26  and the delay wave circuit  25  against high voltage. 
     The electron beam  24  emitted by the electron gun  23  traverses the delay wave circuit  25  to amplify a signal and is collected by the collector  26 . At this time, the electron beam  24  captured by the collector  26  has its kinetic energy converted into thermal energy to raise the temperature of a collector electrode  28  (see FIG.  4 ). 
     For this reason, the heat generated in the collector electrode  28  (see FIG. 4) needs to be externally released. Among the methods for releasing the heat, there are a conduction cooling type collector  31  for releasing the heat from a base plate  30  to a heat sink  29 , as shown in FIG. 4, a forced air-cooling type collector  33  by providing a fin  32  on the outer periphery of the collector for flowing air thereon to release the heat with assistance from base plate  30 , as shown in FIG. 5, and a water-cooling type collector  35  by providing a water-cooled pipe  34  passed through by water to release the collector heat with assistance from base plate  30 , as shown in FIG.  6 . 
     Referring to FIG. 7, the collector structure of a conventional traveling wave tube includes an insulating enclosure  37  of ceramics etc. for insulating the collector electrode  28 , formed of copper, molybdenum or graphite etc., for maintaining vacuum and air-tightness, a base plate  30  for supporting the collector electrode  28  and passing heat generated in the collector electrode  28  through the insulating member to release heat to the outside and a collector-insulating ceramic element  36  for maintaining insulation against the delay wave circuit. These component parts are usually connected together by brazing or welding etc. This structure is termed an external insulation type collector  38 . 
     In the above-described collector, there are occasions where the collector electrode is displaced in the axial direction due to mechanical vibrations or impact. This positional deviation occasionally leads to changes in the colliding position of the electron beam leading to emission of gases or leading to an increased amount of retrogressive electrons to increase the helical current of the traveling wave tube, occasionally leading to destruction of the tube bulb. 
     Also, in such a collector structure, a problem arises in that RE components (TEM mode) of the electron beam incident on the collector are subjected to RE leakage through a collector lead line or collector-insulating ceramic element. 
     In JP Patent Kokai JP-A-2-101454 (1990), there is shown a structure in which the collector electrode  28  is supported by plural heat-conductive columnar ceramic elements  40  arranged between the collector electrode  28  and the external enclosure  41  to improve vibration-resistance and resistance against impact, while maintaining voltage withstand characteristics, as shown in FIGS. 8 a  and  8   b . This structure is termed an internal insulation type collector  39 . 
     In this type of collector, the outer enclosure  41 , collector electrode  28  and the highly heat-conductive columnar ceramic elements  40  are secured in position by deforming the outer enclosure  41  such as by press-working. If, in this structure, plural collector electrodes  28 , specifically a first collector electrode  42  and a second collector electrode  43 , are used and arranged in this order from the upstream to the downstream side of the electron beam, it is possible to lower the potential of the second collector electrode  43  relative to the first collector electrode  42  to improve the overall efficiency of the traveling wave tube. 
     A two-stage collector  44  is illustrated in FIGS.  9 ( a ) and  9 ( b ). An electron beam emitted by the electron gun is passed through the delay wave circuit to amplify the signal and is captured by the first collector electrode  42  and the second collector electrode  43  which are supported by heat-conductive columnar ceramic elements  40 . 
     For improving the efficiency of the traveling wave tube, there is usually employed a method of lowering the potential of the first collector electrode  42  to approximately 50% of that of the delay wave circuit and of lowering the potential of the second collector electrode  43  to approximately one-half that of the first collector electrode  42 . This method consists in sequentially lowering the collector potential with respect to the potential of the delay wave circuit to lower the speed of the electron beam impinging against the collector in order to lower the energy produced in each collector electrode while improving the overall efficiency of the traveling wave tube. 
     Referring to FIG.  9 ( b ), in the case of a two-stage internal insulation type collector  44 , it is necessary to take out a first collector lead wire  45  of the first collector electrode  42  to a position forwardly or rearwardly of the outer enclosure  41 . In the present case, the collector lead wire is taken out to a position rearward of the outer enclosure  41  and is passed through the inside of an insulator tube  46  for maintaining insulation of the first collector lead wire  45  to reduce the size of the collector as shown in FIG.  9 ( b ). This insulator tube  46  is led rearwardly of the collector via a groove  47  (see FIG.  9 ( a )) formed in a portion of the outer periphery of the second collector electrode  43  so as to be led to outside vacuum in an insulated state from a second collector lead line  48  (see FIG.  9 ( b )). 
     In this structure, the electrical field is unavoidably concentrated in an edge portion of the insulator tube  46 . Since there is a corner portion of the groove  47  in this edge portion, a problem arises in that the withstand voltage is deteriorated between the first collector lead line and the ground potential. 
     In addition to this structure, a demand is raised in recent years for providing a small-sized lightweight structure easy to manufacture for communication or loading on a satellite to lower the cost. 
     SUMMARY OF THE INVENTION 
     The above-described collector structure of the conventional traveling wave tube is vulnerable to RF leakage from the collector lead line, such that, the RF power leakage occurs from the lead line portion if, in the case of the internal insulation type collector having a co-axial structure, impedance matching is taken between the collector lead line and the collector inlet end. 
     Meanwhile, in JP Patent Kokai JP-A-4-306538 (1992), for example, there is disclosed a coupling cavity type traveling wave tube in which a loss member having loss in a high-impedance area and which is designed to suppress oscillations caused by the non-continuous coupling impedance in the high impedance area is arranged in the cavity. The conventional technique of inserting this loss member is used in a high frequency circuit system (cavity  49  in FIG. 10) because the loss member  50  is of an electrically conductive material, as shown in the cross-sectional view of FIG.  10 . 
     It is therefore an object of the present invention to provide a collector of a traveling wave tube capable of maintaining vibration-resistance, impact-resistance and voltage withstand characteristics and yet capable of suppressing or eliminating RF leakage. 
     For accomplishing the above object, the present invention provides a collector of an internal insulation type of a traveling wave tube having a structure in which a collector electrode is supported by a plurality of heat conductive columnar ceramic elements arranged between the collector electrode and an outer enclosure of the collector, wherein a loss ceramic member is arranged between the outer surface of the collector electrode and the inner surface of the outer enclosure of the collector. 
     Preferably, the loss ceramic member is cylindrically-shaped (or annular) and contacted at outer corners thereof with the outer enclosure of the collector. The loss ceramic member is contacted with the collector electrode at its inner corner diagonally opposite to the contacted portion thereof with the outer enclosure of the collector. 
     Preferably, the loss ceramic member(s) is (are) those on the outer peripheral surface of which is coated with a conductive layer such as graphite coating. 
     As for the plural heat conductive columnar ceramic elements, a number corresponding to the number of the collector electrodes less 1 of the columnar ceramic elements is designed as cylindrically-shaped ceramic elements, if the number of the collector electrodes is two or more. The cylindrically-shaped ceramic elements have a diameter equal to or less than the other heat conductive columnar ceramic elements. The cylindrically-shaped ceramic elements are arranged in an area of the collector electrode from which heat is most unlikely to be released. 
     Other features of the present invention are disclosed in the appended claims, the contents thereof being incorporated herein by reference thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a transverse cross-sectional view of a collector of a traveling wave tube according to the present invention taken along line II—II of FIG.  1 ( b ), and FIG. 1 b  is a longitudinal cross-sectional view taken along line I—I of FIG. 1 a.    
     FIG. 2 shows transmission characteristics (S 21 ) of the collector of a traveling wave tube according to the present invention and transmission characteristics (S 21 ) in the absence of loss ceramic elements as a comparative embodiment. 
     FIG. 3 a  is a transverse cross-sectional view of a second embodiment according to the present invention taken along line I—I of FIG.  3 ( b ), and FIG. 3 b  is a longitudinal cross-sectional view taken along line II—II of FIG. 3 a.    
     FIG. 4 is a longitudinal cross-sectional view showing a structure of a conventional traveling wave tube of the conduction cooling type. 
     FIG.  5 ( a ) is a longitudinal cross-sectional view and FIG.  5 ( b ) is a transverse view of FIG.  5 ( a ) of a structure of a conventional traveling wave tube of the forced air cooling type. 
     FIG. 6 is a longitudinal cross-sectional view showing a structure of a conventional traveling wave tube of the water cooling type. 
     FIG. 7 is a longitudinal cross-sectional view showing an example of a conventional collector. 
     FIG. 8 a  is a transverse cross-sectional view of another conventional collector taken along line I—I of FIG. 8 b , and FIG. 8 b  is a longitudinal cross-sectional view taken along line II—II of FIG. 8 a.    
     FIG. 9 a  is a transverse cross-sectional view of a two-stage collector configuration and FIG. 9 b  is a longitudinal cross-sectional view taken along line I—I of FIG.  9 ( a ). 
     FIG. 10 is a transverse cross-sectional view of a cavity employing a conventional loss ceramic element. 
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     Preferred embodiments of the invention are explained further. In a preferred embodiment of the present invention, there is provided an internal insulating collector of the type in which a collector electrode ( 2  of FIGS.  1 ( a ) and  1 ( b )) is supported by plural heat conductive columnar ceramic elements ( 3  of FIGS.  1 ( a ) and  1 ( b )) arranged between the electrode and an outer enclosure ( 4  of FIGS.  1 ( a ) and  1 ( b )), in which loss ceramic members displaying significant loss (high frequency loss or dielectric loss) and superior insulating properties ( 5  of FIG.  1 ( b )) are arranged between the outer surface of the collector electrode (surface not illuminated with an electron beam) and the inner surface of the outer enclosure of the collector (surface contacting with insulating ceramics). These loss ceramic members may be coated on their outer peripheral surface with a substance such as Aquadag ( 7  of FIG.  1 ( b )). 
     Preferably, according to a preferred embodiment of the present invention, the loss ceramic members are cylindrically-shaped (annular ring), the outer diametrical portion of each loss ceramic member contacts with the outer enclosure of the collector and the corner of the inner diametrical portion of the loss ceramic member disposed diametrically to the contacting portion contacts with the collector electrode. This realizes axial positioning of the collector while maintaining vibration-resistance and impact-resistance. 
     Among the plural heat conductive columnar ceramic elements, a number corresponding to the number of the collector electrodes less 1 of the columnar ceramic elements are designed as cylindrically-shaped (e.g., hollow) ceramic element(s), if the number of the collector electrodes is two or more. The cylindrically-shaped ceramic element(s) has a diameter equal to or smaller than the other heat conductive columnar ceramic elements. For improving voltage withstand characteristics, these cylindrically-shaped ceramic elements are disposed without any groove formed in the second collector (on the outer periphery thereof) for laying conventional insulating tubes as in the conventional collector. Meanwhile, the cylindrically-shaped ceramic element(s) is positioned in an area from which heat of the collector electrode is most unlikely to be released (or dissipated), for example, on the opposite side to the base plate in case of conduction cooling, towards the base plate in case of the forced air cooling, and in an area of lesser congestion of water-cooling pipes in case of forced water cooling. 
     With the collector of the present embodiment of the present invention, in which loss ceramic members superior in insulation properties are arranged forwardly and rearwardly of the collector for preventing RF leakage from the collector, and collector lead wire is passed through the inside of the cylindrically-shaped (hollow) heat conductive columnar ceramic elements designed for collector insulation, voltage withstand characteristics can be improved while vibration-resistance and impact-resistance equivalent to those in the conventional system are maintained, and also RF leakage may be prevented from occurring from the collector. 
     Embodiments 
     Referring to the drawings, preferred embodiments of the present invention will be explained in detail. 
     [First Embodiment] 
     FIGS.  1 ( a ) and  1 ( b ) show a collector structure of a traveling wave tube (or guide) embodying the present invention. Specifically, FIG. 1 a is a transverse cross-sectional view of an internal insulating type collector of a traveling wave tube and FIG. 1 b  is a longitudinal cross-sectional sectional view taken along line II—II of FIG. 1 a.    
     Referring to FIGS.  1 ( a ) and  1 ( b ), a collector  1  of a travelling wave tube of the present embodiment is made up of a collector electrode  2 , heat conductive columnar ceramic elements  3 , an outer enclosure  4  for maintaining vacuum and loss ceramic members  5  (see FIG.  1 ( b )) provided forwardly or rearwardly of the collector electrode  2 . 
     The heat conductive columnar ceramic elements  3  are axially arranged (distributed) over the entire area (circumference) of an annular gap defined between the outer peripheral surface of the cylindrically-shaped collector electrode  2  and the inner peripheral surface of the cylindrically-shaped outer enclosure  4 . The heat conductive columnar ceramic elements  3  are kept in contact with the collector electrode  2  by an outer flange thereof so that the ceramic elements  3  are not deflected at their axial ends. For improving voltage withstand characteristics, the inner peripheral surface of the outer enclosure  4  is spaced apart at the axial end portions from the heat conductive columnar ceramic element  3  by annular gaps  6 , each of several mm. As a matter of course, the broader this gap, the lesser is the degree of concentration of the electrical field and the higher are voltage withstand characteristics. 
     Also, there is a small axial clearance between the columnar ceramic elements  3  and the rear loss ceramic member  5 , which in turn is axially secured on a shoulder formed at the outer peripheral corner of the end plate of outer enclosure  4  leaving an axial clearance. The forward loss ceramic member  5  is axially and radially secured by an inward flange formed within the outer enclosure  4 , while the diagonally opposite corner of the loss ceramic member  5  is axially secured by the outward flange at the forward end of the collector electrode  2 . The rear loss ceramic member  5  is radially secured on a small annular rib or protrusions axially extending from the rear end of the collector electrode  2 . 
     The cylindrically-shaped (annular ring) loss ceramic members  5  (see FIG.  1 ( b )) are arranged at both ends of the heat conductive columnar ceramic elements  3  so that a portion of the inner surface  5   b  (see FIG.  1 ( b )) of each member  5  (see FIG.  1 ( b )) is contacted with (secured by) the collector electrode  2  and the corner of the outer surface  5   a  (see FIG.  1 ( b )) of the loss ceramic member lying diagonally opposite to the contacted portion with the collector electrode  2  is contacted with (secured by) the outer enclosure. 
     The loss ceramic members  5  are of alumina material etc. coated on outer sides with a graphite layer of Aquadag E (trade name of Nihon Atisson K. K., a mixture of graphite and an aqueous binder). 
     After assembling the above structure of the entire collector, the resulting assembly is pressed from outside such as press-working to take heat conduction into account to deform the outer enclosure  4  to secure the various components in situ. 
     FIG. 2 shows characteristics  8  as a transmission circuit (S 21 ) in the TEM mode of the collector  1  of the structure of the preset embodiment. FIG. 2 shows, as a comparative embodiment, transmission characteristics  9  (S 21 ) in the absence of the loss ceramic members  5 . 
     As a measurement method, RF signals were entered at an electron beam incident end of the collector  1  and the signal level thereof was measured from a collector terminal  11  (see FIG.  1 ( b )) connecting to a collector lead wire  10  (see FIG.  1 ( b )). As may be seen from FIG. 2, the signal level was improved by approximately 20 dB in the present embodiment. 
     It may be surmised that the forward side loss ceramic member accounts for a loss of 10 dB, while the rear side loss ceramic member accounts for a loss of 10 dB, thus achieving improvement of 20 dB. 
     [Second Embodiment] 
     As a second embodiment, an internal insulation type two-staged collector is explained. 
     FIGS.  3 ( a ) and  3 ( b ) show the collector structure  12  of the second embodiment of the present invention. Specifically, FIG. 3 a  is a transverse cross-sectional view of the collector structure and FIG. 3 b  is a longitudinal cross-sectional view taken along line II—II thereof. Referring to FIGS.  3 ( a ) and  3 ( b ), the second embodiment of the present invention includes a first collector electrode  13  (see FIG.  3 ( b )), a second collector electrode  14  (see FIG.  3 ( b )), highly heat conductive columnar ceramic elements  15  (see FIG.  3 ( a )), an outer enclosure  16  for maintaining vacuum, loss ceramic members  17  (see FIG.  3 ( b )), arranged forwardly of the first collector electrode  13  and rearwardly of the second collector electrode  14 , a first collector lead wire  18  (see FIG.  3 ( b )) extending from the first collector electrode  13  along the outer peripheral surface of the second collector electrode  14  to the rear side of the second collector via a cylindrically-shaped (hollow) ceramic element  19  for maintaining the insulation of the collector lead wire. 
     The first and second loss ceramic members  17  are axially secured between flanges formed on the collector electrodes  13 ,  14  and outer enclosure  16 . Namely, the forward loss ceramic member  17  is secured between an inward protruding flange of the outer enclosure  16  and the outward protruding flange at the forward end of the first collector electrode  13 . The rearward loss ceramic member is secured between the inward protruding flange of the outer enclosure  16  and the outward flange at the rear end of the second collector electrode  14 . The columnar ceramic elements are axially secured between two outward flanges of the first and second collector electrodes  13 ,  14 . 
     The first collector lead wire  18  is lead to outside vacuum via a first collector terminal  20  (see FIG.  3 ( b )). In addition, a second collector lead wire  21  (see FIG.  3 ( b )) is led to outside vacuum via a second collector terminal  22  (see FIG.  3 ( b )). 
     The first collector lead wire  18  is passed through the inside of cylindrically-shaped ceramic elements  19 , placed in lieu of the heat conductive columnar ceramic elements  15 , so as to be led to the rear side of the collector. The outer diameter of the cylindrically-shaped ceramic elements  19  is equal to or less than the diameter of the heat conductive columnar ceramic elements. 
     If the collector cooling method is of the conduction cooling type, the collector is placed on the opposite side of a portion of a base plate where the collector is contacted with a heat sink, that is on the side where heat dissipation is at the least level. If the collector cooling method is of the forced air cooling type or the water cooling type, the collector is placed on the side of the base plate carrying the collector where there is no air or water flow, that is towards the base plate carrying the collector. In short, the collector position is directly opposite to the conduction cooling position. 
     The present embodiment has an advantage that voltage withstand characteristics, vibration-resistance or impact-resistance and heat conductivity are equivalent to those of the first embodiment, even though the number of the collector stages is increased, thus assuring facilitated multi-stage collector designing. 
     It is noted that the Aquadag can be applied not only on the outer peripheral surfaces but also on the inner peripheral surfaces of the loss ceramic elements. Moreover, Aquadag can be applied to both surfaces of the loss ceramic elements if voltage withstand characteristics permit. Alternatively, Aquadag can be applied to a portion of the surfaces of the loss ceramic elements depending on the amount of RF leakage. 
     The meritorious effects of the present invention are summarized as follows. 
     According to the present invention, as described above, there may be provided an internal insulation type collector in which, by placing loss ceramic elements on the collector, RF leakage from the collector may be prevented and axial position setting can also be achieved while vibration-resistance and impact-resistance equivalent to those of the conventional system are maintained, and yet the voltage withstand characteristics can be improved. 
     Moreover, according to the present invention, high heat conductivity and voltage withstand characteristics can be maintained in achieving multi-stage collecting designing in consideration of arrangement of the collector lead wires. 
     The present invention may be used in combination with other structures and elements of the conventional devices other than the specific features of the present invention. Thus the entire disclosure relating to the prior art is also incorporated by reference in the disclosure of the present invention. 
     Further any arbitrary combination of the disclosed features and/or elements may be done within the gist of the present invention irrespective of the place of disclosure including the entire claims. 
     It should be noted that other objects of the present invention will become apparent in the entire disclosure and that modifications may be done without departing the gist and scope of the present invention as disclosed herein and appended herewith.