US3324427A

US3324427A - Electromagnetic wave permeable window

Info

Publication number: US3324427A
Application number: US365253A
Authority: US
Inventors: Weiss Harry Max
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1964-05-06
Filing date: 1964-05-06
Publication date: 1967-06-06
Anticipated expiration: 1984-06-06
Also published as: NL6505712A; DE1256748B

Description

- June 6, 1967 H. M. wzlss ELECTROMAGNETIC WAVE PERMEABLE WINDOW Filed May 6, 1964 2 Sheets-Sheet 1 I as INVENT OR. HARRY MAX WEISS BY WW8;

June 6, 1967 H. M. WEISS 3,324,427

ELECTROMAGNETIC WAVE PERMEABLE WINDOW Filed May'6, 1964 2 Sheets-Sheet 2 INVENTOR. jg. 7 HARRY MAX WEISS BY Mffififi United States Patent 3,324,427 ELECTROMAGNETIC WAVE PERMEABLE WKNDUW Harry Max Weiss, San Jose, Caiifi, assignor, by mesne assignments, to Varian Associates, a corporation of California Filed May 6, 1964, Ser. No. 365,253 7 Claims. (Cl. 333-98) This invention relates to electromagnetic wave permeable windows and more particularly to gas tight electromagnetic wave permeable windows that may be utilized at the input or output of a source of electromagnetic wave energy, such as a microwave tube, to hermetically isolate the evacuated portion of the wave source.

Heretofore in the prior art, wave permeable windows have been inserted within hollow electromagnetic wave transmission devices, such as waveguides, to provide gas tight partitions thereacross. Such windows are fabricated from a suitable dielectric material, such as mica, ceramic, quartz or the like, and have their circumferential end portions hermetically secured to the inner walls of the waveguide. Such windows may be located within the waveguide to form a perpendicular transverse wall, a slanted wall, a conical wall, etc. Preferred use of some of these windows require that they be placed within the waveguide at an area containing strong electric fields. These electric fields, if of sufficient magnitude, cause arcing at the seal area, that is, where the circumferential edges of the window are hermetically sealed to the inner peripheral surface of the waveguide, thereby limiting the amount of electromagnetic power that can be passed through the window. The arcing also causes puncturing of the dielectric window assembly resulting in loss of the vacuum and destruction of the tube. Also, the circumferential edges of prior art windows and the inner peripheral surfaces of the waveguides to which they are sealed must be very accurately controlled to produce satisfactory hermetic seals which causes such prior art window assemblies to be relatively diflicult and expensive to fabricate.

Accordingly, an object of this invention is to overcome these and other disadvantages of the prior art.

Another object of this invention is to provide an improved wave permeable window assembly.

Another object of this invention is to provide a wave permeable window that is readily sealed to waveguide means.

Still another object of this invention is to provide a gas tight, wave permeable window capable of passing large amounts of electromagnetic energy therethrough.

A further object of this invention is to provide a gas tight, wave permeable window assembly capable of passing therethrough electromagnetic energy greatly in excess of several megawatts peak power without producing arc- These and other objects of the present invention are accomplished by a gas tight, electromagnetic wave permeable window which includes a single or unitary wave permeable, gas tight, body which is adapted to provide a path for electromagnetic energy therethrough. The unitary wave permeable body has an electromagnetic wave confining portion with an electrically conductive coating on the exterior surface thereof for providing a current path for electromagnetic energy and a window portion disposed within the wave confining portion to provide a gas tight portion across the wave confining portion. The window portion may be located transversely across the wave confining portion and may have a thickness substantially less than one-half an electrical wavelength of the center frequency of the passband of the wave confining portion whereas the wave confining portion may Too have a length of n/ 2 electrical wavelengths where n can be any odd integer value.

These and other objects, features and advantages of the present invention will be readily apparent from consideration of the following detailed description taken in conjunction with the annexed drawings wherein:

FIGURE 1 illustrates in partial cross-section one embodiment of the present invention used in conjunction with a microwave tube, such as a klystron;

FIGURE 2A illustrates a section taken along the line 2A2A of FIGURE 1;

FIGURE 2B illustrates a modification of the device shown in FIGURE 2A; and

FIGURES 3, 4, 5, 6 and 7 illustrate various embodiments of the present invention.

Referring now to the drawings, there is illustrated in FIGURE 1 a microwave tube, such as a klystron, which includes a gun section 11 for producing an electron beam, a radio frequency interaction section 12 and a collector section 13. As is well known to those skilled in the art, the electron gun section, the interaction section and the collector section are united in axial alignment to enable the projection of the electron beam produced by the gun section 11 through a series of drift tube sections 14. Each drift tube section terminates within a

cavity

15, 16 or 17 and has a conically tapered end portion 18 spaced from the end of an associated drift tube section to provide an interaction gap 19 therebetween. The drift tube sections are supported in axially spaced alignment by relatively heavy transversely extending annular metallic plates 20 which form end portions of-the

cavities

15, 16 and 17.

The cavity 17, adjacent the collector 13, illustrated in cross-section in FIGURE l-is an output cavity. High frequency electromagnetic energy contained within the output cavity is withdrawn therefrom by Way of a first tubular waveguide 25, which may be rectangular. The end of the first waveguide remote from the output cavity is flanged 26 in a manner as illustrated in FIGURE 1.

A second tubular waveguide 31, which also may be a rectangular waveguide, likewise has a flanged 32 end portion. The flanged portions 26 and 32 of the first 25- and second 31 waveguides, respectively, are spaced apart but adjacent one another and the first and sec-0nd waveguides have their longitudinal axis in substantial alignment.

Disposed between the flanged portions is a unitary or single, gas tight, electromagnetic wave permeable body 27. The wave permeable body includes a Wave confining portion, such as a flanged, tubular or hollow cylindrical portion 28. An electrically conductive coating or surface 29 is secured to the exterior surface and edges of the electromagnetic wave confining portion 28. Opposite ends of the wave confining portion 28 are hermetically sealed to the flanged portions 26 and 32, respectively, thereby electrically coupling the coating 29 to the first and

second waveguides

25 and 31. The unitary wave permeable body 27 also includes a window portion 30 which extends transversely of and is enclosed within the wave confining portion 28 to provide a gas tight, wave permeable partition across the wave confining portion.

The single wave permeable member 27 and the flanged portions 26 and 32 of the first and

second waveguides

25 and 31, respectively, form a circular broadband waveguide wherein refiections from various discontinuities and irregularities associated therewith cancel with out over a very broad band of frequency. In accordance with a preferred embodiment of the present invention, the tubular portion 28 of the unitary wave permeable body has a length parallel to the longitudinal axis of the first 25 and second 31 waveguides of about 11/2 electrical wavelengths long at the center frequency of the passband of the tubular portion 28, where n can be any odd integer value. Although it may be any odd integer value, a value of n equal to one produces a wider bandpass than when n is greater than one. Also, the window portion of the wave permeable member has a thickness substantially less than one-half of an electrical Wevelength at the center frequency of the passhand of the tubular waveguide portion 28 and is substantially equally spaced from opposite ends of the waveguiding portion 28. The broadband device comprising the wave permeable body 27 and the flanged portions 26 and 32 of the first and second waveguides have a bandwidth that approaches 30%, that is, 30% between standing wave ratio points of 1.2.

The operation of the device illustrated in FIGURE 1 is such that electromagnetic energy contained Within the output cavity 17 passes through the first waveguide 25, the unitary wave permeable body 27 and the second waveguide 31. Current paths associated with this electromagnetic energy is along the inner walls of the first waveguide 25, the flanged portion 26 of the first waveguide 25, the electrically conductive coating 29 on the unitary ceramic body 27, the flanged portion 32 of the second waveguide 31 and the inner peripheral walls of the second waveguride 31.

The broadband device, comprising the unitary ceramic body 27 and the flanged waveguide portions 26 and 32, operates such that a standing wave is created therein that has a maximum electric field intensity at an area substantially equally spaced between the ends of the waveguiding portion 28 which field decreases to substantially zero intensity at the opposite ends of the waveguiding portion 28 adjacent the flanged portions 26 and 32. Accordingly, no arcing occurs where the flanged portions 26 and 32 are sealed to opposite ends of the waveguiding portion 28 of the wave permeable body 27 since substantially no electric field is present at the seal area. Due to the unitary construction of the wave permeable body 27, there is no metallic sealing material intermediate the ends of the waveguiding portion (for example, where the window portion 30 intercepts the waveguiding portion 28) at which arcing may take place as is the case in prior art devices. An excess of 100 megawatts of peak power in the S band has been transmitted through the device of FIGURE 1 without producing arcing, whereas with prior art windows arcing occurs in the vicinity of twenty megawatts of peak power in the S band. The arcing in prior art broadband devices is due to the fact that heretofore sealing material has been required at areas of high electric field intensity in order to preserve the wide bandwidth characteristics. For example, the bandwidth of the tubular waveguiding portion 28 is largest when the window portion 30 is located substantially an equal distance between the ends of the waveguiding portion 28 where the electric field intensity is a maximum.

It is clear that the flanged portions 26 and 32 function as transition means which electrically couple the conductive coating 29 on the unitary permeable body to the first 25 and second 31 waveguides. Also, it is clear that the wave permeable body 27 being air tight and hermetically sealed to at least the flanged portion 26 of the first waveguide serves to hermetically isolate the evacuated portion of the klystron. A suitable dielectric material which is vacuum tight, such as mica, quartz, ceramic and the like, can be used to fabricate the unitary wave permeable body 27.

The flanged portions 26 and 32 of the first 25 and second 31 waveguides, respectively, are readily hermetically secured to opposite ends of the waveguiding portion 28 of the unitary body 27 by an ordinary butt seal in a manner as illustrated in FIGURE 1. As will be obvious to those skilled in the art, this type of seal eliminates the exact dimensioning of the circumferential edges of prior art windows and the inner peripheral surfaces of the waveguides to which they are sealed necessary to fabricate prior art output window assemblies. Accord- 4 ingly, the output window assembly illustrated in FIGURE 1 is readily and economically fabricated.

The electrically conductive coating 29 on the exterior surface of the waveguiding portion 28 of the wave permeable body may be evaporated, flame sprayed, metalized or otherwise suitably applied to the wave permeable body. For example, FIGURE 2A, which is a section taken along the line 2A2A of FIGURE 1 shows a metalized layer 35 over the exterior surface of the tubular waveguiding portion 28 which is then plated with a layer of a low electrical resistance material 36, such as copper. The waveguiding portion 28 of the wave permeable body is not limited to being circular, as shown in FIGURE 2A, for it may take any desired geometric shape. For example, FIGURE 2B illustrates a single, wave permeable body with a rectangular waveguiding portion 37 having an electrically conductive surface 38 on the exterior surface thereof.

FIGURES 3 through 8 illustrate various modifications of the device illustrated in FIGURE 1. For example, FIG- URE 3 illustrates a unitary wave permeable member 39, substantially similar to the member 27 of FIGURE 1, having a hollow passageway 40 extending through the window portion whereby a gas or liquid may be readily passed through the window portion to prevent the window from overheating as a result of absorbing electromagnetic energy propagated therethrough. The gas or liquid enters and leaves the window area by any suitable means, such as an inlet tubulation 41 and an outlet tubulation 42, respectively. A further modification of this device is illustrated in FIGURE 4 where the hollow passageway within the window portion is greatly increased by using two

parallel window portions

45 and 46. This removes the window portions from the area of maximum electrical field thereby decreasing the bandwidth of the device. However, this disadvantage is overcome by the large amounts of electromagnetic energy that may be passed through the device of FIGURE 4 without overheating the

Window portions

45 and 46.

Another embodiment of the present invention is illustrated in FIGURE 5 wherein there is shown a unitary wave permeable body 50 having a window portion 51 which comprises a section of a hollow sphere. This type of construction mechanically strengthens the window portion 51 and enables it to withstand great pressure differentials existing on opposite sides thereof. Also, electromagnetic energy traveling from left to right through the device of FIGURE 5, from a vacuum source, will produce substantially less multipactor at the window 51 than would a flat transverse window. A modification of this embodiment is illustrated in FIGURE 6 which shows a hollow window portion 52 which is adapted to be cooled by passrng liquids or gases therethrough and in which each side of the window portion 52 comprises a section of a hollow sphere. This embodiment permits multipactor reduction regardless of which side is connected to the source of electromagentic energy and also provides a strong window assembly capable of withstanding differential pressures.

FIGURE 7 illustrates still another embodiment of the present invention wherein a unitary, wave permeable body has a window portion 55 that slants across a waveguiding or confining portion 56.

What has been described is an electromagnetic wave permeable window including a single, gas tight, wave permeable body adapted to provide a path for electromagnetic energy therethrough. The wave permeable body includes a wave confining portion having an electrically conductive coating on the exterior surface thereof for providing a current path for electromagnetic energy and also includes at least one window portion that extends across the path of the electromagnetic energy and which is enclosed in the wave confining portion of the wave permeable body.

Since many changes could be made in the above embodiments, and since many apparent widely different embodiments of the present invention could be made without departing from the spirit and scope thereof, it is intended that all material contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not in a limiting sense.

What is claimed is:

1. An electromagnetic wave permeable window assembly for transmitting electromagnetic energy comprising: a pair of waveguides having their longitudinal axis in substantial alignment, adjacent ends of said waveguides being flanged, a broadband device located between and secured to said flanged portions for providing a path for electromagnetic energy between said pair of waveguides, said broadband device including a unitary ceramic body having a window portion extending across the path of electromagnetic energy at a point of high electric field, said ceramic body also including a flanged portion around the circumference of said window portion which flanged portion is parallel to the longitudinal axis of said pair of waveguides, and an electrically conductive coating on the exterior surface of said wave permeable body flanged portion, said conductive coating being electrically coupled to said waveguides by way of hermetic seals between said ceramic body and said waveguide flanged portions at a distance from said window portion along said longitudinal axis corresponding with points of reduced electric field.

2. The window assembly according claim 1 wherein said window portion slants across the path of electromagnetic energy.

3. The window assembly according to claim 1 wherein said window portion is characterized as being a section of a hollow sphere.

4. A gas tight electromagnetic wave permeable window assembly for transmitting electromagnetic energy therethrough comprising: first and second tubular waveguide members having adjacent end portions, window means including a unitary wave permeable body having an electrically conductive coating on the exterior surface thereof located between said adjacent end portions of said first and second waveguide members, said wave permeable body including a circumferential electromagnetic waveguiding portion having a length of n/2 electrical wave lengths at the center frequency of the passband of said waveguiding portion where n can be any odd integer value, said wave permeable body also including a window portion disposed within said waveguiding portion to form a gas tight wave permeable partition across said wave guiding portion substantially at the center thereof, and transition means including hermetic seals connecting said first and second Waveguide members to opposite ends of said waveguiding portion of said Wave permeable body whereby said transition means are electrically coupled to said conductive coating on the exterior of said waveguiding portion.

5. The combination according to claim 4 wherein n is equal to one.

6. A high frequency gas tight wave permeable window assembly for transmitting electromagnetic energy comprising: first and second tubular waveguide members having adjacent end portions, window means including a unitary wave permeable body located between said adjacent end portions of said first and second waveguide members, said wave permeable body including a circumferential electromagnetic waveguiding portion having an electrically conductive coating on the exterior surface thereof for providing a current path for electromagnetic energy, said waveguiding portion having a length approximately n/ 2 electrical wavelengths long at the center frequency of the passband of said waveguiding portion where n can be any odd integer value, said wave permeable body also including a window portion disposed transversely of and within said waveguiding portion to form a gas tight wave permeable partition across the waveguiding portion, said window portion disposed substantially midway the length of said waveguiding portion and having a thickness substantially less than one-half an electrical wavelength at the center frequency of the passband of the wave con fining portion, and transition means hermetically connecting said first and second waveguide members to opposite ends of said waveguiding portion of said wave permeable body whereby said transition means are electrically coupled to said conductive coating on the exterior of said waveguiding portion of said Wave permeable body.

7. The combination according to claim 4 wherein said first and second waveguide members are rectangular and said waveguide portion of said permeable body is circular, the diameter of said circular waveguide portion being greater than the width of said first and second waveguides.

References Cited UNITED STATES PATENTS 2,683,863 7/1954 Curtis 33398 2,706,275 4/1955 Clark 33398 2,958,834 11/1960 Symons 33398 2,971,172 2/1961 Hamilton 33398 2,990,526 6/ 1961 Shelton 33398 3,101,461 8/1963 Henry-Bezy 33398 3,100,881 8/1963 Edson 33398 3,110,000 11/1963 Churchill 33398 3,210,699 10/ 1965 Hisashi-Tagano 33398 FOREIGN PATENTS 1,341,625 9/1963 France.

HERMAN KARL SAALBACH, Primary Examiner.

L. ALLAHUT, Examiner.