Damped delay line for travelling-wave tubes
United States Patent Gross Apr. 8, 1975 DAMPED DELAY LINE FOR 3.354.347 11/1967 Hant 315/35 TRAVELLING WAVE TUBES 3.365.607 1/1968 Ruetz et al 315/35 3,453,491 7/1969 Cerko 3l5/3.5 [75] Inventor: Franz Gross, MllIllCll, Germany 3,602,766 8/1971 Grant 315/35 Assigneez Siemens Aktiengesenschafl, Berlin &amp; 3,771,010 ll/l973 Wll&#39;lSlOW 3l5/3.5  
  Munich, Germany Primarv Examiner-Alfred E. Smith F 2 [22] Dec 6 1973 Assistant Examiner-Saxfield Chatmon, Jr. [2]] Appl. N0.: 428,184 Attorney, Agent, or Firm-Hill, Gross, Simpson, Van  
  Santen, Steadman, Chiara &amp; Simpson [30] Foreign Application Priority Data Jan. 4, 1973 Germany 2300323 Oct. 5. 1973 Germany 2350239 [57] ABSTRACT 1 An improved delay line for travelling wave tubes com- [52] US. Cl. 3l5/3.5, 3l5/3.633333/3g prising a hollow cylindrical member formed with a plurality of resonant cavities and wherein the selected [5 :22- Cl. C sides of each of the partitions between the cavities is [581 lem of Search. 3 formed with depressions in which lossy material is References Cited :penged so as to provide matching and dissipation of UNITED STATES PATENTS 3.l53,767 lO/l964 Kyhl 315/35 X ll Claims, 4 Drawing Figures A S &#39;S S 1 l 13 a I M N z 4 g Y E Z SE51 1 BF 2 DUE]  NJ- h i DUEIEIUEJUEI I. [11:15am  
  muons UUEIUEI a g DEIDDCI u EJ001313 n u 5001:1055! mac] mum Fig.1  
 DAMPED DELAY LINE FOR TRAVELLING-WAVE TUBES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates in general to delay lines for travelling wave tubes and in particular to an improved delay line comprising a hollow cylinder divided into individual resonant cavities by successively arranged partitions which are provided with depressions and lossy material formed therein.  
 2. Description of the Prior Art Delay lines for travelling wave tubes and in particular drift wave tubes are well known, as, for example, German Letters Pat. No. 1,274,742 discloses a travelling wave tube which includes a plurality of resonant cavities arranged in line and with damping material pro vided in each cell which extends into the coupling opening of the partitions separating adjacent resonant cavities. Such a construction of the damping cell gives rise, however, to mounting and heat dissipation problems. As shown in German Letters Pat. No. 1,541,091, it is known to provide a damping element with cooling means which provide cooling fluid flow through one partition of a resonant cavity on one side thereof and to press the damping material firmly against the other side of the partition by use of a deformable part of the partition so as to remove heat for high powered tubes. Such arrangements are expensive to manufacture and give rise to problems in the operation of the tube.  
 SUMMARY OF THE INVENTION It is an object of the present invention to provide a delay line for a travelling wave tube which includes a hollow cylinder formed with a plurality of aligned resonant cavities separated from each other by partitions and wherein the partitions are formed with depressions on both sides thereof which are filled with lossy material.  
  So as to provide good heat dissipation characteristics the partition walls as well as the other conducting parts will be produced of good heat conducting material, as, for example, copper. The damping material which is mounted in the depressions of the partition could in some instances be omitted since the provision of depressions in the form of a raster on the partition provides a significant damping effect. In the specification, In the form ofa raster&#34; means that the depressions are formed substantially over the entire partition with many depressions formed in the surface of the partition. If a damping material is not used, a conductive material which does not conduct as well as copper, as, for example, V2a-steel, could be used for the rastered partitions. The proposed depressions formed into a raster on the partition provides a delay line which has a number of advantageous characteristics. The protuberances and depressions provide an arrangement which damps very intensively due to the local increase of the field intensity as well as due to the increase in length of the current paths in the partition. A damping material can be inserted and supported in the rastered depression and sticks very well. In addition, the contact surfaces between the damping material and the metallic partition are considerably increased in the raster. Also, heat generated due to energy losses developed in the damping material is easily removed due to its intimate contact with the partition. Another advantage of the invention is that since the damping material which is inserted into the raster partition does not function as a characteristic hollow space load, reflections and deformations of the electromagnetic waves are substantially reduced and discontinuities are not introduced by the material.  
  In the drift wave tube according to the invention the distance between adjacent partitions become progressively closer together due to the action of the delay line and the partitions further along the line require a smaller absorbing area since the damping increases continuously with raster tapering and reflections and mismatch of the waves can thus be avoided. The variations of the length of the cavities reduces the cavity impedance and effects higher current damping and ultimately results in shorter construction length with increased damping per cavity.  
  The depth of the raster and, if necessary, the cavity length can be advantageously changed uniformly such that in each cavity the same heat loss is incurred and thus the amount of heat dissipated in each cavity will be uniform. This prevents overheating and maintains a constant temperature gradient throughout the structure.  
  The partitions for the delay line of the present invention can be produced by using a spark erosion means comprising, for example, a comb-shaped member which has a plurality of finger shape electrodes and which are placed adjacent a partition so as to erode material from the partition. After the raster has been formed in this manner the lossy material can be rubbed into the depressions formed in the partition and sintered so as to provide a seal between the lossy material and the partition. Samples of lossy material are well known and conventional lossy materials may be utilized.  
  Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a lateral sectional view of the novel delay line of the invention;  
  FIG. 2 is a plan view of a partition of the invention; FIG. 3 is a sectional view illustrating the delay line of the invention; and  
 FIG. 4 is a plan view of a second partition embodiment.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS The figures illustrate the constructions of portions of a stacked delay line, however &#34;the input and output coupling and decoupling circuits are not illustrated since such structures are well known to those skilled in the art and do not constitute the novel features of the present invention.  
  FIG. 1, for example, illustrates a section of a delay line of the stacked type illustrating merely that portion of the delay line for a single conduction cycle. The portion of the delay line illustrated comprises a pair of profile disks 2 and 3 with a spacer ring 4 separating the disks 2 and 3 and with a spacer ring 6 mounted adjacent the ring 3 and separating it from the next adjacent profile disk, not shown. The delay line 1 is formed by arranging the profile disks 2 and 3 180 relative to the central axis of the delay line as shown such that the generally crescent-shaped coupling opening 8 of each of the disks 2 and 3 is offset by 180 as shown. Each of the disks 2 and 3 are provided with extending portions which extend beyond the center axis of the delay line and are formed with electron beam openings 7 through which the electron beam of the drift tube passes.  
  Each of the disks 2 and 3 are formed with protuberances 9 and depressions 11 on opposite side surfaces of the disks in which damping material 12 is inserted. The electron beam openings 7 remain free of raster and damping material for high frequency reasons. The disk 2 shown in plan view in FIG. 2 has the rastered portion of the disk at the bottom relative to FIG. 2, whereas the disk 3 would have the rastered portion at the top relative to FIG. 1 as shown, thus being rotated 180 relative to the disk 2. Also, the coupling openings 8 in disks 2 and 3 would be rotated 180 as shown in FIG. 1.  
  FIG. 3 illustrates a modification of the invention and discloses a plurality of resonant cavities which comprise several conduction cycles. The delay line illustrated in FIG. 3 is constructed according to stacking construction methods and comprises a plurality of conduction disks 13 and 14 arranged directly behind one another in the electron beam direction which is injected from the left relative to FIG. 3. The conduction disks 13 and 14 are connected together, as, for example, by welding, to form a solid structure. Spacer rings 15 are mounted between the disks 13 and 14 so as to provide resonant cavities. Each of the conduction disks 13 and 14 has cavity separating partitions 17 formed with electron beam openings 7 through which the electron beam passes and further include coupling openings 8 as illustrated, for example, in FIG. 4.  
  Adjacent conduction disks 13 and 14 are mutually staggered about 180 and each pair forms a cycle of the delay line. The illustrated cavity group section is closed at its right end by disk 18 which has a central electron beam through opening 19.  
  The lateral surfaces of the conduction disks 13 and 14 are provided with a raster of protuberances 9 and depressions 11 as shown in FIG. 4 into which damping material 12 is inserted. As shown, for high frequency and productional reasons it is desirable to keep the coupling openings 8 raster free as well as the electron beam through openings 7.  
  The raster depth and length of the cavities are tapered so as to provide non-reflecting, high concentrated and complete dampening of the electromagnetic waves to be processed.  
  For example, in FIG. 3 the resonant cavities become progressively shorter from the left to the right as the beam traverses from the left to the right.  
  For example, the depth of the raster of the first partition 13 which is designated 5 becomes progressively deeper toward the right relative to the figure so that the raster depth of the last disk adjacent the end member 18, which is designated as 5 is much greater than 5,. The length of the resonant cavities which are designated as h decrease uniformly from the left to the right relative to FIG. 3 from a first height h for conduction disk 13 to a height h,, for the disks adjacent the member 18. For subsequent disks to the right of the first disk which has the dimensions s and h,,, the raster depth and cavity length remains constant. In the illustrated example, the cavity lengths are varied by providing spacer rings of different heights while maintaining the wall thickness of the partitions 17 constant. As an alternative, uniform conduction disk heights could be utilized and the width of the partition 17 could be varied so as to provide variable length in the resonant cavities.  
  The depth of the raster as well as the length of the resonant cavity can be tapered with only one cell resonant cavity group section as the first embodiment illustrates. The raster depth dimensions and the resonant cavity length dimensions should change approximately symmetrically starting at the two ends of the damping area and proceeding toward their center.  
  It would also be possible to modify the invention by increasing the number of protuberances per surface unit area such as by increasing the protuberance cross,- section itself or alternatively by varying the surface of the sector upon which the raster is formed from partition to partition.  
  It might also be desirable for heat dissipation purposes to provide the electron beam through openings 7 in the rastered partitions to be somewhat larger with respect to the openings of the remaining partitions and thus to reduce the impact ratio of electrons in the beam.  
  It is seen that this invention provides for an improved delay line wherein the resonant cavities are separated by partitions having electron beam coupling openings as well as electron beam center passage openings and in which the side walls of the partitions are formed with depressions and protuberances in which lossy material is formed so as to attenuate undesirable energy.  
  As shown in the embodiment illustrated in FIG. 3, since the incident energy at the left side of the delay line is greater than that arriving at the right side of the delay line relative to FIG. 3, the attenuating characteristics of the partitions including the protuberances and the lossy material of the partitions on the left relative to FIG. 3 should be such that the quantity of energy dissipated in the partitions to the left equals the quantity of the energy dissipated in the partitions further to the right. For this to occur, the protuberances must become deeper at the right than they are at the left. This results in uniform heat dissipation throughout the length of the delay line and results in an improved structure.  
  It is seen that this invention provides an improved delay line and although it has been described with respect to preferred embodiments it is not to be so limited as changes and modifications may be made which are within the full intent and scope as defined by the appended claims.  
 I claim as my invention:  
  1. A delay line for travelling wave tubes in the form of a hollow tube divided into individual resonant cavities by means of successively arranged partitions, whereby at least some of said partitions absorb energy in order to form damped cavities and said some partitions have side walls formed with rasters of many protuberances and many depressions.  
  2. A delay line according to claim 1, in which said some partitions forming the damped cavities have lossy material mounted in said rasters.  
  3. A delay line according to claim 1 wherein in the raster depth of adjacent partitions having a raster become progressively deeper in the direction of beam travel in the delay line.  
  4. A delay line according to claim 1 wherein the length of the resonant cavities become progressively shorter in the direction of beam travel in the delay line.  
  5. A method for the production of a delay line wherein a partition with a raster of many depressions is formed by spark erosion by means of a comb which is arranged on the front surface of an electrode with the cross section of the latter corresponding to the desired cross section of the partition of the delay line and applying lossy material into said raster and sintering it.  
  6. The method according to claim 5, wherein after said raster is formed, it is sanded before applying the lossy material.  
  7. A delay line for a travelling wave tube having a plurality of aligned resonant cavities through which an electron beam passes comprising a plurality of lossy partitions comprising outer cylindrical portions, segment portions of said partitions extending to the center of said travelling wave tube and formed with electron beam openings, and the side walls of said partitions formed with a raster of many depressions for attenuating energy.  
  8. A delay line for a travelling wave tube according to claim 7 including lossy material mounted in said depressions of said side walls of said partitions.  
  9. A delay line according to claim 8 further including sector shaped energy coupling openings formed in said partitions.  
  10. A delay line according to claim 9 wherein said sector shaped openings of adjacent partitions are angularly offset 11. A delay line according to claim 10 wherein said sector shaped openings of adjacent partitions are offset by