[4 1 June 13, 1972 3,397,339 8/1968 Beavereta1..,.........................3l5/3.5

[54] DELAY LINE STRUCTURE FOR 3,387,168 Beaver et al.

TRAVELING WAVE DEVICES 5 33 55 ll. 3 m n m mm SF. 91 67 99 H 00 ll 38 49 so 71 33 [72] Inventor: Robert McCowan Unger, Wayland,

[73] Assignee: Raytheon Company, Lexington, Mass. 3,610,999 10/1971 Falce......................................3l5/3.5

[22] Filed: Feb. 25, 1971 Primary Examiner-Herman Karl Sallbach Assistant Examiner-Saxfield Chatmon, Jr.

Attorney-Harold A. Murphy, Joseph D. Pannone and Edgar 0. Rest [21] Appl. No.:

[52] U.S. Cl. ....3l5/3.5, 333/31 A, 29/600,

[57] ABSTRACT An RF wave periodic delay line is disclosed having thermal [58] Field ofSearch.....................

energy dissipation and support structure of an insulating material with reduced dielectric loading between adjacent elements. For devices requiring internal attenuation to prevent undesired oscillations the appropriate attenuator References Cited structure is mounted independently of the dissipation and support structure.

UNITED STATES PATENTS 3,387,170 6/1968 Farney et a1. 5 3,505,730 4/1970 Nelson.....................................29/600 3,345,533 10/1967 Washburn, Jr............ 315/3 6 RF IN HELIX DELA Y -L/NE 20 minimum [912 3,670,197

swan 10F 2 RF IN 4-+ HEL/X DELAY/ LINE 20 F/G 2 F/G. 3

PATENTEDJUH 13 I972 3.670.197

sum ear 2 DELAY LINE STRUCTURE FOR TRAVELING WAVE DEVICES BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to slow wave propagating delay structures for traveling wave devices.

2. Description of the Prior Art Traveling wave devices conventionally utilize continuous wave propagating structures comprising a plurality of periodic circuit elements. Such structures reduce the velocity of RF electromagnetic circuit waves and permit interaction with an electron beam to result in growing waves with a net exchange of energy. A synchronous relationship between the relative velocities of the electron beam and a space harmonic of the traveling waves results in the establishment of the interaction phenomenon.

An example of such devices is the O-type which incorporates a periodic delay line structure with an electron beam traversing its axial length. These devices operate on the principle of the exchange of kinetic energy of the electrons with the RF circuit fields. The combined fields induce perturbations in the electron beam and form alternating energy electron packets which amplify RF energy on the delay line structure. The helix is a commonly employed structure in traveling wave amplifiers comprising a plurality of continuously wound circuit elements of a tape or conductive wire in a unifilar or bifilar arrangement supported by insulators. The helix is preferred due to, its broad bandwidth capabilities and high gain per unit length. At high RF power levels the helix becomes excessively heated by electron beam interception and RF losses. The supports, therefore, should dissipate the intense thermal energy.

Another factor to be considered in the utilization of a helix structure is the requirement for the attenuation of oscillations due to excessive helix length or reflections of energyat the input and output transitions from the delay line to transmission lines. Lossy material is, therefore, provided in a selected axial region of the delay line by a coating of, for example, carline bon or graphite on delay line supports such as parallel elongated ceramic or glass rods.

The principal difficulty in the design of efficient delay line structures in the prior art has resulted from the requirement for RF isolation and thermal energy dissipation coupled with the need for suppression of undesired oscillations. The art is replete with references to the utilization of supports of dielectric material such as sapphire rods extending along the longitudinal axis of a helix delay line structure. The net effect of sucha structure is that the dielectric material is disposed between the circuit elements where the electric fields of the.

SUMMARY OF THE INVENTION In accordance with the teachings of the invention, a delay line structure is supported by insulator and thermal dissipation means contacting each of the circuit elements. The configuration of the support means is selected to avoid high electric fields of the RF wave associated with the circuit. In an illustrative embodiment, an arch-shaped notch is provided in the interval between the circuit elements to form an undulating wall configuration. The high gain traveling wave amplifiers are provided with internal attenuation means, which may be of the bulk or surface type, separately and independently of the support and thermal dissipation means. Strips or vanes of a lossy material, in any desired shape to provide both axial and radial adjustment, are disposed on the perimeter of the delay line structure and span a plurality of desired periodic circuit elements. In alternative embodiments the configuration of the attenuator material may be patterned to introduce such material in the interstices between the circuit elements with a max imum concentration of such material disposed in only a few elements and then being gradually reducedover a portion of the axial dimension.

A wide range of selection of materials, as well as the overall quantity utilized, is now available in traveling wave devices by reason of the separation of the support and attenuation functions. The invention can be utilized in different delay line configurations such as the ring and bar arrangement in addition to the helix type. The bulk attenuator provided by the structure of the invention represents a marked improvement over the surface type attenuation heretofore utilized in prior art structures. In addition, a mechanically simplified delay line structure is provided with improved electrical characteristics by the elimination of lossy coatings on support structures.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the details for the provision of a preferred embodiment, will be readily understood after consideration of the following detailed description and reference to the accompanying drawings, wherein:

FIG. 1 is a detailed cross-sectional view of a traveling wave device embodiment utilizing the delay line structure of the present invention;

FIG. 2 is an enlarged detailed cross-sectional view of a portion of the insulator support and thermal energy dissipation structure of the delay line in FIG. 1;

FIG. 3 is an enlarged cross-sectional view of a portion of the attenuator structure associated with the delay line in FIG. 1;

FIG. 4 is a detailed cross-sectional view of the embodiment of the invention taken along the line 44 in FIG. 1;

FIG. 5 is a detailed cross-sectional view of an alternative embodiment of the present invention; and

FIG. 6 is a detailed cross-sectional view of a portion of an alternative attenuator structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 the traveling wave device 2 incorporating the embodiment of the invention comprises a conductive envelope 4having mounted at one end an electron gun assembly 6 including, in the order named, a cathode 8, focusing electrode 10 and accelerating electrode 12. Appropriate voltages are applied by means of leads 14 for operation of the device and the electron gun assembly. A collector electrode 16 is provided at the opposing end of the envelope 4 to intercept and dissipate the electrons in the beam traversing the path defined along the longitudinal axis of helix delay line structure 20 which is illustrated as being of the unifilar configuration.

A magnetic field is produced by electromagnetic means 22, such as a solenoid, to assist in the orientation of the electron beam within the delay line structure 20. In the traveling wave amplifier illustrated, the electron beam has a phase and group velocity and the RF energy propagating along the helix delay line structure has a circuit phase and group velocity characteristic. With the proper synchronism condition, beam energy is transferred to the circuit. The electron beam and the RF waves are illustrated as traveling in the same direction. Since there is coupling of only the waves traveling in the forward direction, the device is referred to as a forward traveling wave amplifier. The RF energy is coupled into the delay line 20 by means of an input coaxial line 24. The amplified energy is coupled from the delay line structure adjacent to the collector end of the envelope by means of output coaxial line 26. If the electron beam is synchronized with backward space harmonic waves, the positioning of the input and output coaxial coupling lines is reversed. Numerous systems for the circulation of fluid coolants in or around the elements of the delay line structure have been disclosed in the art and need not be further described herein to assist in an understanding of the invention.

Delay line structure defines a plurality of continuously wound periodic elements 28, of a tape or conductive wire to evolve the conventional helix sheath structure employed in traveling wave devices. The delay line structure 20 is supported by a pair of insulator members 30, of a dielectric material in contiguous relationship with each of the periodic circuit elements 28 and envelope 4. Referring now to FIGS. 2 and 4, the support members 30 are provided with a plurality of arch-shaped notches 32 in the regions defined between circuit elements 28. The removal of the support material in what may be referred to as the perturbing region, follows an undulating pattern closely analogous to the RF electric field provided between the circuit elements. Exemplary dielectric insulating materials having the desired properties for support members 30 include beryllia, alumina or boron nitride. The removal of the dielectric material from the region spanning all the circuit elements by means of the notches 32 reduces the dielectric loading" phenomenon. An insulator support structure is thus provided which is principally outside of the high intensity electric field region associated with the RF circuit waves. Paths established between the respective periodic circuit elements 28 and the conductive envelope 4, which acts as a heat sink, are still efiiciently maintained to provide for the rapid dissipation of the thermal energy generated by the interaction process.

Referring next to FIG. 3, as well as FIG. 4, which is rotated 90 from the plane of FIG. 3, the attenuation means for the suppression of undesired oscillation is provided by the vanetype attenuator members 34. In this embodiment each attenuator member has a slight inner tapered edge 36. Attenuator members 34 are arranged in oppositely disposed pairs in the backwall region oriented 90 from the positioning of support members 30. A strip or vane of a dielectric material similar to the support member material is coated with a lossy or resistive material such as graphite or carbon. The attenuation means is thus provided over a selected region spanning a number of periodic circuit elements. The attenuator members may be thinner than the support members and have a minimal effect on dielectric or backwall loading to disrupt the delay line electrical characteristics. The attenuator members, if desired, can contact the circuit elements 28 and are easily adjusted axially, as well as radially, to vary the quantity of attenuating material. Any resistive materials may also be employed for the attenuation means.

FIG. 5 illustrates another feature of the invention relating to the separate support and attenuator members. In the selected regions adjacent to the helix delay line structure, additional attenuation is provided by additional attenuator members 38 angularly displaced as illustrated. In addition, further attenuation may be provided by similar members 40. The provision of the attenuating material as an independent component results in an attenuator which is superior to the surface coatings applied to the insulator support members in prior art delay line structures.

Referring next to FIG. 6, another feature of the invention is illustrated. A pair of oppositely disposed attenuator members 42 supported by the envelope 4 are disposed in the backwall region of the helix delay line structure 20. A tapered undulating edge 44 provides for the disposition of a gradually reducing quantity of the attenuating material in the interstices between circuit elements 28. It is, therefore, possible to provide for the introduction of the attenuation means in the regions of high electric fields over a shorter span of the overall delay line length. A smaller attenuator would be required so that a shorter tube length or higher output powers may be realized.

Many other variations, modifications or alterations will occur to those skilled in the art. Numerous other materials for the support and attenuation functions may also be utilized.

The independent provision of the support and attenuation means optimizes the output power capability of the traveling wave device with the reduction of "dielectric loading" bridging the delay line elements. The disclosed new and novel structure also provides conformation to the RF electric field intensity pattern with higher efiiciency in the electron beamcircuit wave coupling. It is intended, therefore, that the foregoing description of preferred embodiments be considered in the broadest aspects and not in a limiting sense.

What is claimed is:

1. A traveling wave device comprising:

an envelope;

means for propagating electromagnetic wave energy along a predetermined path; and

dielectric means for supporting said wave propagating means contacting said envelope;

said dielectric means having an undulating wall configuration contacting said wave propagating means with said Wall conforming substantially to the intensity pattern of the electric fields associated with the propagated electromagnetic waves with the lesser amount of dielectric material being disposed in the regions of high electric field intensity.

2. A traveling wave device comprising:

an envelope;

means for propagating electromagnetic wave energy along a predetermined path;

dielectric means for supporting said wave propagating means contacting said envelope;

said dielectric means having an undulating wall configuration contacting said wave propagating means with said wall conforming substantially to the intensity pattern of the electric fields associated with the propagated electromagnetic waves with the lesser amount of dielectric material being disposed in the regions of high electric field intensity; and

lossy energy absorbing means for attenuating said wave energy appended to said envelope in the spaces between said dielectric means.

3. A traveling wave device comprising:

an envelope;

a plurality of spaced periodic circuit elements forming an electromagnetic wave energy propagating structure; dielectric means for supporting said circuit elements contacting an inner wall of said envelope;

said dielectric means contacting each of said circuit elements and having arch-shaped notches in the intervals between said circuit elements; and

lossy energy absorbing means for attenuating said wave energy appended to said envelope in the spaces between said dielectric means.

4. A device according to claim 3 wherein said attenuating means comprise vane members defining wall structure providing a larger amount of attenuating material in the intervals between said circuit elements over a portion of the vane member axial length.