US2972083A

US2972083A - Sealing waveguide windows

Info

Publication number: US2972083A
Application number: US22290A
Authority: US
Inventors: Richard M Walker; William P Toorks
Original assignee: Microwave Associates Inc
Current assignee: MA Com Inc; Microwave Associates Inc
Priority date: 1957-05-07
Filing date: 1960-04-14
Publication date: 1961-02-14
Anticipated expiration: 1978-02-14
Also published as: GB843316A; US3101460A

Description

14, 1961 R. M. WALKER ETAL v2,

SEALING WAVEGUIDE WINDOWS Original Filed May 7, 1957 6 /95 F/[LED uZ/A United States Patent SEALING WAVEGUIDE WINDOWS Richard M. Walker, Roxbury, and William P. Toorks,

Beverly, Mass, assignors to Microwave Associates, Inc., Burlington, Mass., a corporation of Massachusetts 8 Claims. (Cl. 315-39) The present invention relates to waveguide windows for controlling the wave propagation as well as for establishing a high vacuum seal between two waveguide sections and is a division of our copending application Serial No. 657,585, filed May 7, 1957.

It is one of the principal objects of the invention to provide a window of the above indicated nature which allows practically reflectionless transmission of electromagnetic waves of a predetermined frequency through waveguides or other transmission lines requiring therewithin a hermetic, high vacuum-type seal.

Other objects are to provide a hermetically sealed iris construction which is especially suited for transmitreceive (TR) and .antitransmit-receive (ATR) tubes making it possible to achieve with such tubes performance characteristics heretofore considered impossible, to provide a mechanically effective sealing means whose geometry is not limited by the electrically effective configuration of an iris, the latter being not restricted to shapes and sizes that are compatible with the strain character istics of the sealing component, to provide a waveguide window construction of the above type which is particularly advantageous for the designing of so-called resonant windows giving access to broad band TR and ATR tubes, to provide a hermetically sealing iris structure which achieves particularly low insertion and are losses by eliminating sputtering across the iris thus avoiding the formation of a film across the sealing dielectric which film increases the insertion and arc losses, and generally speaking to provide a device of this type which has essentially improved reproducibility and design flexibility.

A brief summary of the invention will serve to indicate various aspects of its nature and substance for accomplishing the above objects, as follows.

In one aspect, a window device for the controlled propagation of electromagnetic energy in waveguides or other transmission lines comprises, in combination with a waveguide portion, the following elements:

A metallic iris component which fits the guide portion and has a wave controlling opening of any desirable configuration; a sealing component located adjacent to the iris component at a predetermined distance therefrom andincluding a dielectric window portion having around its entire periphery, where it fits the guide portion, a metallic frame portion; and between the guide portion and th frame portion of the sealing component a metallic seal (such as solder) in gas tight cohesive contact with the guide portion as well as the frame portion. In most instances it is preferable to arrange the iris component within the evacuated waveguide section. At any rate, the sealing and wave control functions can be strictly separated.

In another aspect, the invention involves the combination within a waveguide of a sealing component which has a metal frame portion and of an iris component,

both components fitting the guide and being arranged side-by-side therein, the dimensions of the iris opening and the opening'of the metal frame portion of the, seal- 'ice ing component being coordinated in such a manner that resonance results at a predetermined separation of the two openings.

In a preferred embodiment, the hermetic seal is provided by a metallic such as soldered, brazed, or welded joint between the metallic frame of the sealing component and the waveguide proper, the sealing metal flowing into the space between the waveguide and the metallic frame of the sealing component.

In an important practical embodiment, the sealing plate consists ofa metallic frame having an opening of proper configuration, which is closed by a dielectric plate joined thereto by a conventional glass-to-metal seal.

In another important practical embodiment, the sealing component consists of a dielectric (such as glass) plate to which a metallic coating is applied by conventional metallizing techniques for forming a frame or mat; this metallic frame can extend on either one or both sides towards the central part of the dielectric plate, forming iris openings of predetermined dimensions and configurations for the above-mentioned cooperation with the opening of the iris component, as affected by the distances of the several openings. The distance between the sealing and iris components can be exactly predetermined for example by dishing an iris plate, or by similarly dishing the sealing plate if it has a solidly metallic frame portion or, if both plates are essentially fiat, by providing a spacer therebetween.

In a further aspect, iris openings are formed at both, sealing and iris components, and used at a separation proper for providing a predetermined resonant condition rather than for cancellation of reflections from one by the other; both sealing and iris elements can be made resonant independently or together, or both elements may be nonresonant at a desired frequency but compensating to provide the desired resonant frequency for the dual unit.

In an additional aspect, difierent metals are used for iris and sealing components, respectively, in order to obtain specific characteristics not otherwise obtainable.

These and other objects and aspects of the invention will appear from the following description of several typical embodiments illustrating its novel characteristics. The description refers to a drawing in which Fig. 1 is the front elevation of a TR tube incorporat-- ing the invention;

Fig. 2 is a section on lines 2-2 of Fig. 1, with the electrodes in elevation;

Fig. 3 is a transverse section with the Window in elevation, of a waveguide incorporating another embodiment of the invention;

Fig. 4 is a section, corresponding to Fig. 2, on lines 4-4 of Fig. 3

Figs. 5 and 6 are elevations of sealing components illustrating additional embodiments of the invention;

Fig. 7 is a section on lines 77 of Fig. 6;

Figs. 8 and 9 are elevations of dished iris plates in accordance with the invention; and

Fig. 10 is a side elevation indicating the shape of plates according to Figs. 8 and 9.

Figs. 1 and 2 indicate at 21 a waveguide portion of a transmission-reflection tube which, as well known, is highly evacuated and instead filled with gas of exactly predetermined composition and pressure. 22 indicates the flange of the tube with the aid of which it can be joined to another Waveguide section of the system. 23 and 24 are electrodes which are kept at apredetermined potential difference, for purposes well known in the art but irrelevant to the present invention. A sealing component according to the invention is indicated at 25, and an iris component at 26, whereas the metallic seal is indicated at 28.

In the embodiment according to Figs. 3 and 4, two waveguide portions 31.1 and 31.2 contain near their juncture a sealing window which comprises a sealing com- ;ponent 35, an iris component 36,. a spacer 37 and. a .rnetal seal 33. If desired, the waveguide sections 31.1 and 31.2 may be joined by means of metal straps 32 extending over the entire joint of the waveguide sections. V

In the embodiment according to Figs. 1 and 2 the sealing'component is made according to Figs. 5, 6, and 7 and consists of a blank 25.1 of glass or ceramic material of a thickness 51 which has a metallized frame portion 25.2, applied to the blank by conventional methods, such as by painting or printing with metallic, for example silver paint followed by baking, or by gun spraying, or by vacuum depositionyin either case the metal of the frame is in intimate molecularly cohesive contact with the glass or ceramic plate, forming an impenetrable juncture therewith. In the embodiment shown in Figs. 1 and 2, the metallized frame 25.2 is restricted to the edge of the plate and serves only for providing a hermetic seal between the sealing plate and the waveguide, whereas in other embodiments the metallized frame can provide iris structures of selected dimensions and configurations, such as for example shown in Figs. and 6, respectively. As indicated in Fig. 7, both sides of the metallized frame can be extended toward the center of the sealing plate 25.1 so that two distinct iris structures of different or similar shape can be provided, the thickness of the plate 25.1 permitting the exact predetermination of the separation of two irises and the separation of one or two irises from the iris proper of the other component.

The sealing component according to Figs. 3 and 4 is a conventional window, consisting of a glass portion 35.1 which is joined to the metallic frame portion 35.2 by means of a standard glass-to-metal seal, the metal being an iron-nickel-cobalt alloy and the glass being of the boron-silicate type.

As indicated at 28 of Fig. 2 and at 38 of Fig. 4, the sealing component is joined to the waveguide by means of a sealing metal such as soldering, brazing or welding metal which completely fills the space between the frame portion 25.2 or 35.2 of the sealing plate and the waveguide 21 or 31.1, respectively, thus providing a hermetically tight seal independently of the

iris plate

26 or 36.

The iris component 26 according to Figs. 1 and 2 is dish-shaped, providing a. contact face 26.1 which determines the exactspacing between the sealing plate and the iris plate as clearly indicated at $2 in Fig. 2. The iris plate may be of any thickness s3 and of any configuration that is practicable or desirable for electrical purposes.

The iris component 36 according to Figs. .3and'4 is flat as indicated in Fig. 4, and the distance between sealing plate and iris plate is.determined by a spacer 37.

Although a complete seal is provided by the

metal

23 or 38 between the guide and the sealing plate, this metal seal can be extended into the space'between the guide and the iris plate.

As indicated at Figs. 8 to 10, the opening 26.5 or 26.6 of the iris plate is of selected dimensions and configurations similarly to the opening of the sealing plate shown in Figs. 5 to 7.

The iris plate is preferably arranged on the vacuum side of the sealing plate, as indicated in Fig. 2, for the reasons presentlyto be pointed out; however, if the reverse order should be preferable in a given instance, various unique advantages of'the invention such as the perfect seal and the availability of several irises are still present.

In an actual embodiment according to Figs. 1 to 4, ncorporating a sealing plate as shown at 35 of Fig. 4 in combination with an aperture plate .as shown at 26 4 K of Fig. 2, the dimensions which are indicated in these figures were as follows: a=.900" b=.400" m=.530" s1=.020" s2=.030" 53:.020

The iris plate was made of stainless steel and the metal seal consisted of soft solder applied by means of a gas-air torch. Characteristic electric data indicating the quality of this construction are as follows:

Insertion loss db-.. .05 Are loss db..- .10 Bandwidth percent 15 Peak power rating (kilowatts) 500 Average power rating watts 500 Frequency (kilomegacycles) 9 Insertion loss db .25 Are loss db .25 Bandwidth percent 12 Peak power rating (kilowatts) 200 Average power rating watts 200 After operation for hours or more, sputtering and film deposition on the dielectric seal is always visible when these previous structures are used.

The above figures show a considerable advancement in this art in the following aspects: (a) a reduction of insertion loss to /s of the former value; (b) a reduction of arc loss to /5 of the former value; (c) an increase of bandwidth of 3 percent; (d) an increase of power handling to 250 percent of its former value.

It has been proposed (compare for example US. Patent No. 2,407,069 of September 3, 1956 to Milan D. Fiske) to seal irises by means of fiat or bulbous dielectric bodies which do not fill the iris opening but are joined to the aris structure in some other manner. Such constructions however do not provide hard vacuum seals nor do they have the advantages of the present invention which are based on the strict separation of the sealing and iris functions, namely lower insertion loss, lower arc loss, elimination of sputtering, and better reproducibility and design flexibility. I

The insertion loss in a standard window (such as part 35 of Fig. 4 if it were used by itself without part 36) is inversely proportional to b/b namely the heights of window and waveguide as marked in Fig. 3. The bandwidth of the unit is proportional to b/b, and the arc loss 18 proportional to (b'/b)2. It can readily be seen that b'/b must be small for low arc loss and large for low insertion loss. In conventional TR tubes the bandwidth is usually adjusted to a value which is about 2 /2 times that of the tuning elements of the tube in which the window is used. The value of b'/b for this condition is normally about A to /3 for tubes designed for a 12 percent bandwidth. The insertion loss for standard Windows in this b'/b range is 3 to 5 times the loss in windowswhere b/b is This loss is contributed by dielectric losses in the glass and heating losses in the metal. Therefore, the design of a TR tube using the standard window represents a compromise between high power handling (low arc loss), desirable bandwidth and insertlon loss The insertion loss is reduced by increasing the separation between the dielectric and the iris which decreases the field strength in the dielectric, and the dual element window according to the present invention therefore eliminates the requirement .for the above-discussed compromise. In such a Window, b'lb can be made or larger in

parts

25 or 35, thereby reducing the be plated with high conductivity materials, so that the insertion loss contribution by part 21 or 31.2, the waveguide proper, can be made negligible.

The arc loss in a TR tube is proportional to (b'/b)2 in the input window and the value of b'/b is dictated by the bandwidth as indicated above. This is also true of the dual element window according to the present invention where

parts

26 or 36, the iris windows, determine the bandwidth. However, the value of b/b for a given bandwidth is in this case about /2 that of the standard window. Still further improvements can be made by using more complex iris shapes such as shown in Figs. 8 and 9. This means that the arc loss can be reduced by the present dual element window by a factor of 4 or more as compared to the standard glass-metal seal type.

Window sputterng occurs in high power pulse operation where a high intensity discharge is maintained across the input window on the inside of the TR or ATR tube. This discharge presents a short circuit across the transmission line, thereby preventing high frequency energy from reaching the receiver. The intensity of the discharge is so great that localized heating occurs and chemical action takes place between gas within the tube, vapors, and the metal. This phenomena causes erosion of the metal and sputtering of metallic particles across the opening. These particles form a metallic film across the glass of the conventional window or of the above-mentioned window with an incompletely separated sealing element. This causes the insertion loss to increase during tube life. The chemical reaction also changes the gas composition inside the tube until all of the water vapor has been converted to hydrogen and metallic oxides. Sputtering rates in metals vary a great deal and some are for this purpose much better than others, but the metals used for glass-to-metal sealing are particularly bad in this respect. In the dual element window according to the invention the discharge takes place within the opening in

part

26 or 36 which can be made of any metal so that those having low sputtering rates can be employed.

The reproducibility and design flexibility of the window according to the invention are definitely more favorable than in the heretofore known glass-to-metal seal constructions, because it is not necessarily dependent on glass-to-metal seals with their well-known unavoidable variations in resonant frequency, arc losses and insertion loss which are functions of technological factors such as sealing temperature, cleanliness of materials and surface roughness of the metal. Similar problems are introduced by the sealing cement and the spacers of the abovementioned previously suggested window with an incompletely separated sealing body. All this is avoided by the present window construction With its complete separation of the sealing function, with its metallic joint between sealing plate and waveguide, and with its avoidance, if desired (Figs. 1, 2) of any glass-to-metal seal. If a sealing plate according to Figs. 1 and 2 is used to supply an electrically effective iris, the metal frame 25.2 of element 25 (Figs. 1 and 2) which forms this iris can be arranged outside of the vacuum so that it is not subject to sputtering. The separation of the sealing and iris components can be selected and exactly incorporated at will, and both components can be made resonant independently or together or both elements can be made nonresonant at a desired frequency but compensating to provide the desired resonant frequency for the unit as a whole.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

6 What is claimed is: 1. A waveguide transmit receive switch device comprising, in combination: a metallic waveguide portion constituted of a first metal; gap electrodes across said Waveguide portion providing a gap adapted to break down electrically in the presence of electromagnetic wave energy propagating in said waveguide portion at an energy level exceeding a prescribed level; a metallic iris component located within said waveguide portion a given distance from said gap electrodes and having a wave controlling iris opening, said iris component being made essentially of a second metal different from said first metal which substantially will not sputter onto dielectric window material in close proximity thereto in the presence of an electric discharge across said iris opening; a hermetic sealing component having dielectric window means framed in a frame metal hermetically sealed to said dielectric window means located adjacent the outer side of said iris component relative to the interior of said Waveguide portion containing said gap electrodes, the frame aperture of said frame metal being everywhere larger than said iris opening and located so that all points on the periphery of said iris opening confront substantially only the dielectric material of said window means, said dielectric window means and said iris component in the vicinity of said iris opening being both substantially planar and parallel to each other, said iris component and the frame metal of said sealing component being peripherally hermetically sealed to each other, said frame metal being hermetically sealed to said waveguide portion by a totally metallic seal, and the distance between the outer surface of said dielectric window means and the interior surface of said iris element being a minor fraction of said given distance from said gap electrodes, whereby said window means and said iris element are located essentially the same electrical distance from said gap electrodes.

2. A waveguide transmit-receive switch device comprising in combination: a metallic Waveguide portion constituted of a first metal; gap electrodes across said waveguide portion providing a gap adapted to break down electrically in the presence of electromagnetic wave energy propagating in said waveguide portion at an energy level exceeding a prescribed level; a metallic iris component located within said waveguide portion a given distance from said gap electrodes and having a Wave controlling iris opening, said iris component being made essentially of a second metal different from said first metal which substantially will not sputter onto dielectric window material inclose proximity thereto in the presence of an electric discharge across said iris opening; a hermetic sealing component having dielectric window means framed in a frame metal hermetically sealed to said dielectric window means located adjacent the outer side of said iris component relative to the interior of said waveguide portion containing said gap electrodes, the frame aperture of said frame metal being everywhere larger than said iris opening and located so that all points on the periphery of said iris opening confront substantially only the dielectric material of said window means, said dielectric window means and said iris component in the vicinity of said iris opening being both substantially planar and parallel to each other, one of said components being bent along a line substantially parallel to its periphery and having its peripheral region directed from said line toward the other element, said iris component and the frame metal of said sealing component being peripherally hermetically sealed to each other, said frame metal being hermetically sealed to said waveguide portion by a totally metallic seal, and the distance between the outer surface of said dielectric window means and the interior surface of said iris element being a minor fraction of said given distance from said gap electrodes, whereby said window means and said iris element are located essentially the same electrical distance fromsaid gap electrodes.

.metal which substantially will not sputter onto dielectric window material in close proximity thereto in the presence of an electricdischarge across said iris opening; a hermetic sealing component having dielectric window means framed in a frame metal hermetically sealed to said dielectric window means located adjacent the outer side of said iris component relative to the interior of said waveguide portion containing said gap electrodes, the frame aperture of said frame metal being everywhere larger than said iris opening and located so that all points on the periphery of said iris opening confront substantially only the dielectric material of said window means, said dielectric window means and said iris component in the vicinity of said his opening being both substantially planar and parallel to each other, one of said components being bent along a line substantially parallel to its periphery and having its peripheral region directed from said line toward the other element, said iris component and the frame metal of said sealing component being peripherally in contact with each other, said frame metal being hermetically sealed to said waveguide portion by a totally metallic seal, and the distance between the outer surface of said dielectric window means and the interior surface of said iris element being a minor fraction of said given distance from said gap electrodes, whereby said window means and said iris element are located essentially the same electrical distance from said gap electrodes.

4. A vwaveguide transmit-receive switch device coniprising in combination: a metallic waveguide portion constituted of a first metal; gap electrodes across said waveguide portion providing a gap adapted to break down electrically in the presence of electromagnetic wave energy propagating in said waveguide portion at an energy level exceeding a prescribed level; a metallic iris component located within said waveguide portion a given distance from said gap electrodes and having a wave controlling iris opening, said iris component being made essentially of a second metal different from said first metal which substantially will not sputter onto dielectric Window material in close proximity thereto in the presence of an electric discharge across said iris opening; a hermetic sealing component having dielectric window means framed in a frame metal hermetically sealed to said dielectric window means located adjacent the outer side of said iris component relative to the interior of said waveguide portion containing said gap electrodes, the frame aperture of said frame metal being everywhere large than said iris opening and nonresonant at the intended frequency of operation of said switch device and located so that all points on the periphery of said iris opening confront substantially only the dielectric material of said window means, said dielectric window means and said iris component in the vicinity of said iris opening being both substantially planar and parallel to each other,

'said iris component and theframemetal of said sealing component being peripherally hermetically sealed to each other. said frame metal being hermetically sealed to said waveguide portion bya'totally metallic seal, and the distance between the outer surface of said dielectric window means and the interior surface of said iris element being a minor fraction of said given distance from said gap electrodes, whereby said window means and said iris element are located essentially the same electrical distance from said gap electrodes.

5 A waveguide transmit-receive switch device comprising, in combination: a metallic waveguide portion constituted of a first metal; gap electrodes across said waveguide portion providing a gap adapted to break down electrically in the presence of electromagnetic wave energy propagating in said waveguide portion at anj energy level exceeding a prescribed level; a metallic iris component located within said waveguide portion a given distance from said gap electrodes and having a wave controlling iris opening, said iris component being made window material in close proximity thereto in the presence of an electric discharge across said iris opening; a

hermetic sealing component having dielectric window means farmed in a frame metal hermetically sealed to said dielectric window means located adjacent the outer side of said iris component relative to the interior of said waveguide portion containing said gap electrodes, the frame aperture of said frame metal being everywhere larger than said iris opening and nonresonant at the intended frequency of operation of said switch device and located so that all points on the periphery of said iris opening confront substantially only the dielectric material of said window means, said dielectric window means and said iris'component in the vicinity of said iris opening being both substantially planar and parallel to each other, one of said components being bent along a line substantially parallel to its periphery and having its peripheral region directed from said line toward the other element, said iris component and the frame metal of said sealing component being peripherally in contact with each other, said frame metal being hermetically sealed to said waveguide portion by a totally metallic seal, and the distance between the outer surface of said dielectric window means and the interior surface of said iris element being forming an outwardly open recess, and wherein said iris and sealing components fit into said recess where said sealing means is in contact with said guide.

7. Device according to claim 1 wherein said guide portion has an internal peripheral recess for receiving said iris and sealing components.

8. Device according to claim 1 wherein at least the surface of said iris component consists of stainless steel, whereby metal sputtering onto the sealing component is essentially eliminated for the useful life of said apparatus.

References Cited in the file of this patent UNITED STATES PATENTS Bondley Apr. 7, 1959 Stanney et al May 31, 1960