US2922124A - Microwave transmission control device - Google Patents

Description

Jan. 19, 1960 R. s. BRADEN 2,922,124

MICROWAVE TRANSMISSION CONTROL DEVICE File d June 4, 19 57 3 Sheets-Sheet 1 P2\O2 ART INVENTOR.

RAY S. BEADEM ATTC ENEY Jan. 19, 1960 R. s. BRADEN 2,922,124

MICROWAVE TRANSMISSION CONTROL DEVICE Filed June 4, 1957 3 Sheets-Sheet 2 INVENTOR. 'EAV S. BEADEN AT TORNEY v Jan. 19, 1960 R. s. BRADEN I 2,922,124

MICRQWAVE TRANSMISSION CONTROL DEVICE Filed June 4, 1957 3 Sheets-Sheet 3 INVEN TOR.

DAY 5. BEADEN ATTORNEY United States Patent 2,922,124 Patented Jan. 19, 1960 7 2,922,124 MICROWAVE TRANSMISSION coNTRor. DEVICE Ray Braden, Melrose, Mass., assignor to Roman Laboratories, Inc., Beverly, D'IQSS-g a corporation of Massachusetts Application June 4, 1957, Serial No. 663,536

8 Claims. Cl. 333-13 The present invention relates to gaseous discharge devices and more particularly to an electromagnetic energy sensitive element adapted to present an electrodeless gaseous discharge across a waveguide transmission path to thereby alter the conductive characteristics of the waveguide.

In the microwave transmission control art numerous devices have been developed for switching electromagnetic energy by means of an intense discharge of an ionizable atmosphere. In particular, transmit-receive devices provide for switching fi'om the transmitting to the receiving cycle of a radar system employing a single antenna. Generally such devices have inductive elements as well as capacitive discharge electrodes to provide a composite resonant circuit for transmission of low level energy and ionization of a gaseous atmosphere enclosed within a hermetically sealed envelope at high power levels. With improvements in the transmitter art, power levels are now available which present a problem in dissipation of heat generated by an intense gaseous discharge within conventional TR structures. Further, another problem exists in that at the higher power levels of long range radar systerns, the waveguide size has been increased to such an extent that conventional gaseous discharge switching devices become exceedingly difficult to fabricate. A need has, therefore, arisen for a simplified rapid switching structure capable of operation under conditions of severe thermal shock and intense heat. v

In recent years, one concept in the transmit-receive tube art has evolved in that more than one gaseous atmosphere may be incorporated within a resonant structure with each atmosphere selected for optimum electrical characteristics. An example of such devices is disclosed in U.S. Patent No. 2,791,720, issued May 7, 1957, to Ferdinand A. Lesch and assigned to the present assignee. In this embodiment, an encapsulated dielectric resonant window assembly of a single wall glass member encloses a resonant slot in a metallic window frame. The gas filling in this assembly is selected-for recovery time and are loss characteristics. The capacitive discharge gap electrodes are also encapsulated and filled with an atmosphere selected for such characteristics as flat leakage power and spike leakage energy. Both encapsulated structures are replaceable and easily mounted in a section of rectangular guide.

The present invention has for its primary object the provision of a novel structure for presenting a high frequency gaseous discharge in a high power waveguide transmission system to control propagation of energy.

Another object is to provide a novel gaseous discharge switching device capable of handling intense heat and thermal shock resulting from high power radio frequency discharges.

Still another object is to provide a novel gaseous discharge device for high power electromagnetic energy transmission control wherein the ratio of surface area per unit volume is considerably increased over prior art switching devices thereby enhancing thermal transfer and certain electrical charactertistics.

A further object is to provide a novel gaseous discharge device for high power microwave energy transmission control with an energy sensitive element having an annular folded cylinder configuration to produce a higher ionization density and shorter diffusion path than prior art switching devices.

The objects enumerated are attained chiefly by the provision of a structure having a metallic plate member with a centrally located resonant aperture. A tubular member is provided within the aperture and may be either cemented or removably mounted therein for easy replacement. This member comprises two dielectric cylinders concentrically disposed and hermetically sealed at their ends to form an enclosed folded cylinder with an axial hollow passageway. By controlling the spacing between the cylinders an annular gas storage chamber is defined. In selecting the dimensions of the gas envelope, it has been observed that such characteristics as recovery time and leakage power have been vastly improved over available prior art devices. Possible explanations of the improved electrical results obtained are that the annular cylinder configuration leads to a reduced cross section of gas volume which increases conductivity by reason of a higher ionization density, shorter diffusion path and increased surface recombination. Furthermore, since half the cylinder element is exposed to the high power microwave energy generator the mechanism of deionization may be accelerated.

With this structure it is possible to fiow a dielectric coolant having a low loss tangent through the axial passageway defined therein to conduct heat away from the cylinder. Additionally the ratio of surface area per unit volume is increased many times which leads to ionization energy levels lower than comparable prior art devices with lower leakage power readings.v

The novel structure disclosed is useful either as a pre-TR device positioned before a TR tube or it may be mounted on a section of waveguide to form a resonant input window assembly of a complete TR tube employ ing demountable elements. Further, numerous dielectric materials may be selected which are desirable in handling the high heat requirements. Quartz, ceramic or hard glass cylinders have produced excellent results at power levels as high as 20 megawatts peak power.

Further objects, features and advantages will be evident after consideration of the following detailed description and accompanying drawings, in which:

Fig. l a cross section of prior art'encapsulated window;

Fig. 2 is a perspective view of .the illustrative embodi ment;

Fig. 3 is a detailed cross sectional view taken along the line 22 in Fig. 2;

Fig. 4 is a perspective View of an alternative mounting structure;

- Fig. 5 is a longitudinal cross section of the envelope member of the invention;

Figs. 6 and 6A are enlarged fragmentary views of a portion of the structure shown in Fig; 5. before and after assembly;

Fig. 7 is a perspective view of an embodiment of the invention useful in TR devices; and

Fig. 8 is a cross section of the embodiment mounted in waveguide structure as a pre-TR device. 7

Referring now to the drawings, Fig. 1 is illustrative of the prior art encapsulated window structure disclosed in the aforementioned patent application. The assembly comprises a relatively short section of waveguide 1 having brazed thereto a flange 2 which mates with similar flange structure mounted on a tube assembly. Plate member 3 is secured to waveguide 1 and defines a central resonant accurately determined.

opening covered by a glass closure 4. The entire inner surface of plate 3 is glazed as at 5 by a beaded powdered glass suspension and a glasstrough member 6 is heat sealed tothe glazed surface. An exhaust stem 7 provides means for evacuation and filling with-an ionizable atmospl ere under reducedpressure. p

. Figs. 2 to 6 show the embodiment of the present invention which may be employed either as a separate structure mounted between flanges or incorporated as an element in a transmit-receive device. A plate member 8 having a central resonant aperture 9 may be fabricated from any metal such as aluminum, steel or brass and need not be of a metal having'a matching coeflicient of expansion similar to the closure material which is necessary in prior art dielectric windows. Supportedwithin resonant aperture 9 by means of mounting members 10 secured on opposite walls of plate ,8 adjacent the aperture is tubular energy sensitive member 11. Mounting members 10 are desirably of a resilient metal in strip form and are V-shaped to define a trough. Suchia mounting provides for easy insertion and removal. To

further assure good contact between the tubular member 11 and mounting strips 10, thin-walledcopper shims may be inserted underneath strips 10. Other methods of mounting include the use of silicone rubber cement or a spring coil, however, the structure shown' is' desired. Fig. 4 illustrates an alternative mounting structure incorporating serrated fingers 12 in mounting members 10.

, The tubular energy sensitive member 11 comprises an envelope formed by two concentrically disposed-spaced cylinders 13 and 14 joined together at their outer ends as at 15. By reducing the diameter of the inner cylinder 13 an appropriate dimension an annular gap 16 is defined which provides the chamber for storage of an ionizable gaseous atmosphere under reduced pressure introduced through a tubulation 17. The inner wallsof the cylinder 13 provide an axial. hollow passageway 18 to allow passage of a dielectric coolant to thereby conduct" heat generated by the intense ionization away from the tubular member. lllusrative embodiments have been manufactured having gap dimensions varying from .005 to .060 inch for a tubular member having an outer diameter of 1.000 to 1.500 inches and a lengthof 4.50 inches. viding the best electrical characteristics lie in the region of one-sixteenth the outer diameter of the outer cylinder \14orless.

Alignment of the concentric cylinders may be achieved by conventional techniques employing spacers or appropriate jigging. An alternative method of controlling the gap is shown in Fig; 6 and comprises undercutting the outer wall of the inner cylinder 13 as at 19 by any just the inductive parameters of the resonant circuit to assure resonance at a desired frequency, I next provide metallic means enclosing an equal distance on each end of tubular member restricting the area of dielectric material exposed to the electromagnetic waves propagated through the waveguide system. A conductive coating of a metallic paint such as DuPont conductive silver paint may be applied on. each end aswell as a portion of the plate member to assure electrical continuity. It may be desirable to employ metallic strips 28 secured to plate member 24 by screws 29 with a slot 30 to permit horizontal movement of the strips. The arrangement shown will be duplicated on the reverse side of the window assembly which is exposed to the interior of waveguide 20. By adjusting the spacing between the metallic means it is possibleto tune the window assembly to be resonant at a desired frequency. v

In some high power transmission systems it may be advantageous to employ the embodiment of the invention as a pre-TR device preceding the conventional TR tube. In such applications. the window assembly may be mounted as shown in Fig. 8 between flanges 31 and 32 Results indicate that the gap dimensions prosecured to waveguides 33 and 34. Bolts 35 maintain the assembly in position.

The embodiment may also be employed as a window assembly for an anti-TR device which is essentially the same construction as a TR device with the exception of having one end closed and a length of only one-quarter of a wavelength.. 7

- The ionizable gaseous atmosphere employedin the annular gas chamber may be any noble gas, desirably argon at reduced pressure of approximately 4 millimeters of mercury. Such a filling has resulted in recovery time readings of 5 microseconds at 1000 kilowatts, whereas prior art structures are capable of only'300400 microseconds for similar power levels and gas content. The device disclosed when ionized will attenuate radio frequency signal energy propagated in a waveguide system by values of 30 db or better.

While a specific embodiment has been described and illustrated, various modifications may occur to those skilled in the art. It is my intention that such modifications be included Within the spirit and scope of the invention as set forth in the appended claims.

What is claimed'is:

.wave transmission control devices comprising a metallic of the known techniques such as grinding or etching.

When the cylinders are sealedtogt'ether as at-15 the assembly resembles Fig. 6A with the desired gapspacing The total volume of the annular chamber 16 defined between the cylinders'is substantially reduced in comparison with the prior art concept of a single'wall' gas envelope. Calculations indicate that the reducedvolume 0f the tubular member of the'invention isone quarter plate member defining a centrally'located rectangular opening, an energy sensitive tubular element of a d1elec tric material mounted within said opening by resilient metallic members secured to the wall surfaces of said plate member extending parallel to the axis of said tubular element, said tubular element comprising an outer cylinder having a diameter and length substantially equal to the dimensions of said opening, an inner cylinder of reduced diameter concentrically disposed within. said outer cylinder to definetherewith an annular gap, said cylinders being joined together at their outer ends to form a vacflange 21 by means of screws or bolts 23 on all four uum tight envelope, metallic means enclosing a portion of the ends of said tubular element electrically connected to'said plate member, said means restricting the exposed dielectric walls of said tubular element to thereby alter the electrical characteristics to tune the assembly to a desiredresonant frequency, and a filling of an ionizable gaseous atmosphere contained within said envelope under reduced pressure. V 7

2. A resonant window assembly according to claim 1, wherein said metallic means comprise a metallic coating extending over said tubular element walls and a portion of said plate member.

,3. A resonant window assembly according to claim 1, whereinsaid metallic means comprise strips of a conductive metal secured at their ends to said plate member.

4, A resonantwindow assembly according to claim 1,

wherein said metallic means are adjustable to alter the exposed dielectric Wall area.

5. In combination with hollow-pipe Waveguide structure for propagation of ultra high frequency electromagnetic wave energy, an electrodeless gaseous discharge switching device for control of transmission of such energy comprising a metallic plate member extending transversely to the direction of wave propagation in said waveguide, said metallic plate member defining a central rectangular aperture resonant at a selected frequency, a tubular member of a dielectric material enclosing substantially all of said resonant aperture with its axis lying within the plane of the plate member, said tubular member comprising a plurality of concentrically disposed cylindrical members joined together at their outer ends to form an hermetically sealed envelope with an openended axial passageway therethrough and an ionizable gaseous atmosphere contained within said envelope under reduced pressure.

6. In combination with hollow-pipe Waveguide structure for propagation of ultra high frequency electromagnetic energy, an electrodeless gaseous discharge switching device for control of transmission of such energy comprising a metallic plate member extending transversely to the direction of wave propagation in said waveguide, said metallic plate members defining a central rec- (angular aperture resonant at a selected frequency, a tubular member of a dielectric material disposed Within said resonant aperture with its axis lying Within the plane of the plate member, said tubular member comprising a first cylindrical member having substantially the same dimensions as said aperture, a second cylindrical member of reduced diameter concentrically disposed within and spaced from said first cylindrical member, said cylindrical members being joined together at their outer ends to form an hermetically sealed envelope With an openended axial passageway therethrough, the total volume of said envelope being one-quarter or less the total volume of a single Wall envelope having the same dimensions as said first cylindrical member and a filling of an ionizable gaseous atmosphere contained within said envelope under reduced pressure.

7. In combination with hollow-pipe waveguide structure for propagation of ultra high frequency electromagnetic energy, an electrodeless gaseous discharge switching device for control of transmission of such energy comprising a metallic plate member extending transversely to the direction of wave propagation in said waveguide, said metallic plate members defining a central rectangular aperture resonant a selected frequency, a tubular member of a dielectric material enclosing substantially all of said resonant aperture with its axis lying within the plane of the plate member, said tubular member comprising a first cylindrical member having a diameter substantially equal to the height of said resonant aperture, a second cylindrical member concentrically disposed within said first cylindrical member, the diameter of said second cylindrical member being reduced to provide an annular gap between said cylindrical members of one-sixteenth or less of the outer diameter of the first cylindrical member, said cylindrical members being joined together at their outer ends to form an hermetically sealed envelope with an open-ended axial passageway therethrough and a filling of an ionizable gaseous atmosphere contained within said envelope under reduced pressure.

8. In combination with hollow-pipe waveguide structure for propagation of ultra high frequency electromagnetic energy, an electrodeless gaseous discharge switching device for control of transmission of such energy comprising a metallic plate member extending transversely to the direction of wave propagation of said Waveguide, said metallic plate member defining a central rectangular aperture resonant at a selected frequency, a tubular member of a dielectric material enclosing substantially all of said resonant aperture with its axis lying within the plane of the plate member, by means of resilient metallic supports secured to the wall surfaces of said plate member extending parallel to the wide dimension of said aperture, said tubular member comprising a plurality of concentrically disposed cylindrical members spaced apart to define an annular gap said cylindrical members being joined together at their outer ends to define an hermetically sealed gas storage envelope with an open-ended axial passageway therethrough and an ionizable gaseous atmosphere contained within said envelope under reduced pressure.

References Cited in the file of this patent UNITED STATES PATENTS Re. 13,093 Burger Mar. 15, 1910 2,048,491 Cartun July '21, 1936 2,114,175 Cartun Apr. 12, 1938 2,832,004 Teeter Apr. 22, 1958

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