US2786979A - Microwave electronic switch - Google Patents

Description

LEW-" March 26, 1957 J. F. ZALESKI 2,786,979

MICROWAVE ELECTRONIC SWITCH 2 Sheets-Sheet 1 Filed March 9, 1954 POWER SUPPLY INVENTOR. JOHN-F. ZALE5K\ March 26, 1957 J. F. ZALESKI 2,786,979

MICROWAVE ELECTRONIC SWITCH Filed March 9, 1954 2 Sheets-Sheet 2 CATHODE CATHODE owsz PowEz POWE! SUPPLY SWH'CH swwcu 4 INVENTOR. JOHN F.ZALESK\ AT TOKNEY MICROWAVE ELECTRONIC SWITCH John F. Zaleski, Valhalla, N. Y., assignor to (general Precision Laboratory Incorporated, a corporation of New York Application March 9, 1954, Serial No. 415,071

Claims. (Cl. 333-7) This invention relates to electronic switches which employ streams of electrical particles as the only moving elements, and more particularly to electronic switches in which there is interaction between a stream of electrical particles and an electromagnetic field.

The present invention uses the principle of electron velocity variation to produce electronic bunching. By this means an electromagnetic field is caused to affect an electron stream which in turn is caused to excite a second electromagnetic field. By employing several electron streams or by deflecting a single electron stream the energy of an applied microwave field is caused to appear at a selected one of two or more output wave guide terminals. By appropriate direct-current switching of the electron stream generators or electron guns the micro wave energy may be switched between or among outlets, or may be cut ott altogether.

This invention avoids the use of ionizable gases and therefore the switching speed is not limited by gas ionization or deionization time, but is limited only by the switching speed of a direct-current circuit, which may be made very fast.

In one form of this invention microwave field energy is applied to a tuned chamber, causing it to resonate at the microwave frequency. A stream of electrons from an electron gun is passed through the chamber and in passing becomes velocity modulated, causing the electrons to become bunched. These bunched electrons are next passed between metallic charged plates so that the stream is deflected. The stream is then passed through a second resonant chamber tuned to resonate at the bunch frequency. Microwave energy is abstracted from this chamber by an output guide. By changing the direct-current charge on the plates, the deflection of the electron stream is changed so that the stream is removed from the second chamber and applied to a similar third chamber, which resonates and gives up its energy to a second output guide.

By appropriate constructions a number of output chambers and guides can be, employed, with appropriate switching arrangements to switch the electron beam with precision to any desired output chamber.

In place of the metallic charged plates for electrostatic deflection of the electron stream one or more magnetic solenoid coils may be substituted for the magnetic deflection of the electron stream.

In another form of this invention an input resonant chamber is sandwiched between two output resonant chambers, each provided with its input or output hollow waveguide or coaxial line. An electron gun is positioned on one side of the chambers to project its electron stream through all three chambers and another electron gun is positioned on the other side of the chambers to project its electron stream through all three chambers in the opposite direction. Application of the stream from one of these guns couples the input microwave line to one output line, and alternatively the stream from the other gun couples the input line to the other output line.

nited States Patent The time required to convert an electromagnetic field into a velocity varied stream of electrons, to pass this stream into an output cavity, and to reconvert the stream variations into an output electromagnetic field takes little longer than does the passage of the stream of electrons through the device, which is less than one thousandth of a microsecond. Some of the utility of this invention is attributable to this short operation time, because the fastest devices heretofore available have required times measured in microseconds for operation.

The employment of this switch as a radar antenna transfer switch provides one example of use. In the radar art it is general practice to employ TR tubes and ATR tubes in conjunction with resonant and anti-resonant lengths of guide to provide means for switching a single antenna between transmitting and receiving circuits, with isolation of the disconnected circuit on the order of 30 db. The switch of the present invention permits antenna switching from transmitter to receiver without the necessity for using resonant or anti-resonant lengths of waveguide, and at speeds limited only by direct current circuit speeds. It is therefore possible to reduce the minimum radar echo range to the neighborhood of five feet, instead of'a minimum range measured in hundreds of yards. Moreover, the isolation of the receiver during transmission is on the order of db, and may be considered to be infinite for all practical purposes. This in turn permits the employment of really sensitive and highly delicate apparatus in the receiver without danger of injury by leakage from the transmitter. This invention also removes the possibility of receiver injury as a limitation on increase of transmitter power.

The nature of the electronic switch of this invention is such that not only do signals suffer no attenuation during passage through the switch, but they may actually undergo amplification of as much as 28 db. When the switch is used as a radar antenna switch the transmitter signal may be amplified by 14 db and the echo signal may be amplified by 28 db before application to the receiver demodulator, which may in some circumstances greatly increase the overall sensitivity to echo signals. In addition the size of transmitter required is reduced and/or the radar range is extended.

The principal purpose of this invention is to provide a high speed electronic switch, employing electron stream velocity variation, for switching an input microwave circuit to any one of a plurality of output circuits.

Another purpose of this invention is to provide an electronic switch employing velocity variation of an electron stream eontrolled by an electrostatic field.

Another purpose of this invention is to provide an electronic switch employing velocity variation of an electron stream controlled by an electromagnetic field.

Another purpose of this invention is to provide a threeterminal electronic switch containing two electron guns alternatively used.

Another purpose of this invention is to provide an electronic device to connect a microwave transmission line to either of two other microwave transmission lines without attenuation of microwave energy passing through the device.

Another purpose of this invention is to provide an electronic device to switch microwave energy with concomitant amplification during passage through the device.

A further understanding of this invention may be secured from the detailed description and accompanying drawings, in which:

Figures 1, 2 and 3 depict one form of the microwave electronic switch of this invention, Fig. 3 being across section of Fig. 1 on the line 3-3.

Figure 4 represents a circuit for circularly deflecting an electron beam.

Figure 5 depicts a second form of the microwave electronic switch of the invention.

Referring now to Fig. 1, one form of microwave electronic switch employing the principles of this invention contains a conventional electron gun in a glass envelope 11, with terminals brought out through a base 12 in the usual manner. The electron gun contains a heater 13, cathode 14, control grid 16 and focusing cylinder 17. The electron stream leaves the focusing cylinder as a compact beam and passes through a smoothing grid 18, smoothing cylinder 19 and grid 21 into a resonant chamber 22; This chamber 22 is made of metal and is sealed to the gun envelope at 23. The chamber has the form of a short cylinder with a cylindrical Wall 24 and end discs 26 and 27. The end 'disc 27 contains the reentrant tubulation 28 terminated in a grid 29.

The electron stream leaves the resonant chamber 22 by passing through the grid 29, then passes between two parallel metal plates 31 and 32 having electrical connections 33 and 34 anchored in a surrounding tubular glass envelope 36 which is sealed to the outer surface of the resonant chamber end wall 27. The electron stream is electrostatically deflected at either one of two angles as it passes between the plates 31 and 32, after which the stream impinges on one of two similar catcher resonant chambers 37 and 38.

The construction of these chambers is exemplified by that of chamber 37, which has a cylindrical Wall 39 and discs 41 and 42, the disc .2 being provided with a reentrant tubulation 43. The chamber 37 has an axial input aperture covered by a grid 44 and an output aperture through tubulation 43 covered by a grid 46. The electron stream after passing through grids 44 and 46 enters an absorption chamber 47 where it is absorbed in a graphite cup 48. The cup 48 is held in a metal cup 49 sealed to the end disc 42 and provided with radiation fins 51. The purpose of the absorption chamber 47 is to prevent any electrons after passing through chamber 37 from being reflected back through that chamber, as such fed-back electrons may under some conditions cause self-oscillation. Any type of absorption device may be employed or, in some cases, it may be dispensed with as unnecessary.

The glass envelope 36 is flared at 52 and is joined by an annular seal 53 to a conical adapter ring 54 which is in turn sealed to the chambers 37 and 38. The construction is shown more clearly in the end view of Fig. 2, the ring 54 being sealed to the outside surfaces of chambers 37 and 38. The electron beam space is hermetically sealed and is highly evacuated in accordance with electronic tube practice.

The resonant chambers 22,37 and 38 are all tuned to the same frequency, and as they are high-Q chambers accurate tuning is highly desirable. Therefore in practice provision is made for final tuning adjustment after assembly. One way in which this can be done is by the provision of a flexible section of the cylindrical wall with V ascrew by which the volume enclosed by the cavitymay be slightly increased or decreased. The diaphragm 56, Fig. l, is such a section, adjusted by screw 57. The chambers 37 and 38 are similarly adjusted by screws 58 and 59, Fig. 2. Other methods of tuning will suggest themselves to one skilled in the art. 1

The input waveguide 61 is coupled to resonant chamber 22'by means of an iris 62, and output waveguides 63 and 64 are attached to chambers 37 and 38 and coupled to them by iris openings 66 and 67. In place of waveguides coaxial conductors can be used and in place of iris coupling magnetic loop couplings can be used in accordance with conventional practice.

In operation, a source 68 of direct potential is connectedbetween the terminals 33 and 34 of the electrostatic deflection plates 31 and 32, with provision for reversing polarity. This reversal may be eifected at very high speed by means of conventional electronic tube circuits energy at a selected frequency is applied from a generator to the wave guide 61 and the three resonant chambers are tuned to that selected frequency. Switch 69 is placed on terminal 73, making the deflector plate 31 positive and 32 negative.

Under these conditions the electron stream from the electron gun is subject, in the space between grids 21 and 29, to potentials of the resonating chamber 22 alternately accelerating and decelerating the electron passage. That is, the stream is velocity modulated. After leaving grid 29 the stream is not further accelerated or decelerated, and its electrons tend to collect in bunches. The greatest bunching effect is at a distance from the grid 29 depending upon parameters including the cathode-plate potential, and these parameters are preferably adjusted so that bunching is pronounced at the input grids 44 and 44 of the resonant chambers 37 and 38. As the stream of electrons passes between the plates 31 and 32 it'is deflected upward by an angle depending on the potential of source 68. This potential is made of such amount that the stream is deflected to enter grid 44. Upon entering grid 44 the stream produces alternations of potential between grids 44 and 46 at the resonant frequency of the chamber 37 setting it into oscillation, and microwave energy is abstracted from it by the waveguide 63. When the switch 69 is thrown to terminal 74 the electron stream is transferred to cavity 38 and the microwave energy output is thereby switched from guide 63 to guide 64.

The construction of the tube depicted in Fig. 1 may be modified to employ three or more receiving resonant chambers, and by the use of two pairs of electrostatic deflection plates or two sets of electromagnetic deflection coils to direct the electron stream into any selected one of the plurality of receiving resonant chambers. These chambers may be arranged in a circle or in any other convenientconfiguration which can be secured'to the large end of the flared tube 52. The deflection elements must be excited from an appropriate switching device such as the sine-cosine potentiometer of Fig. 4. In this figure the'knob 76 represents manual or automatic operation of the arm 77 of a cosine potentiometer 78 and of the arm 79 of a sine potentiometer 81. Both otentiometers are fed from the same constant potential source 82 and the outputs are applied to orthogonal plates 83 and 84 of a tube such as that of Fig. 1. The arms 77 and 79 maybe combined on a single resistance card. At constant input voltage E, rotation of knob 76 deflects an electron stream passing through plates 83 and 84 in a circle, and changeof E changes the stream radially, so that the entire area of the end of the flared tube is availablefor placement of receiving resonant chambers;

In the tube depicted in Fig. 1 the amount of velocity variation originated in chamber 22 is controlled by the gun cathode potential, and the velocity variation together with the distance between grid 29 and grid 44 control the bunchingefficiency of the tube. A different arrangement having a more'easily controlled drift distance'and requiring no deflection means, but necessitating the use of two electron guns,is illustrated in Fig. 5.

In Fig. 5 three similar resonant chambers of the reentrant cylinder for m, 86, 87 and 88, are positioned in axial alignment. These chambers are connected by drift tubes 89 and 91 having their ends closed to electromag netic field energy by grids 92, 93, 9.4 and. 96. Chambers 86 and 88 are provided with smoother tubes 97 and 98 closed by grids 99, 101, 102 and 103. Two similar electron guns are provided sealed to the smoother tubes 97 and 98 and axially aligned with them. These guns are enclosed in glass envelopes 104 and 106 and are provided with pin bases 107 and 108. The construction of these electron guns is exemplified by that of the electron gun in envelope 104. This electron gun has a helical filamentary cathode 109 and a control grid 111 enclosed in a focusing cylinder 112. An absorbent target 113 is made of dissipative material such as carbon. Power supplies 114 and 116 are connected to the pins of bases 107 and 108 so as to energize the filaments, apply control grid potentials and apply negative potentials to the cathodes relative to the metallic resonant chamber assembly, which is grounded. Each of the two cathode connections for applying cathode-anode potential to the guns is completed through a cathode power switch 117 and 118, for controlling the guns. Application of negative potential to a cathode initiates the electron stream and interruption of the potential interrupts the stream.

Obviously the filament 109 can be enclosed in a cylindrical enclosure having an axial aperture, and the end of the cylindrical enclosure facing the resonant chamber assembly can be coated with electron-emitting material. The filament then becomes a heater and the cylinder is an indirectly heated cathode.

The three resonant chambers must as a practical matter be tuned after assembly and while operating. Any of a number of conventional forms of tuning structure may be employed such as that shown in Figs. 1 and 2. Another form is shown in Fig. 5. It uses flexible chamber end disc 119, 121 and 123, and screws to adjust the amounts by which the reentrant drift tube ends project into the chambers. These screws are connected between the outer end discs 124 and 126 and the inner chamber end disc 122 and intermediate flanges 127 and 128, which are connected to drift tubes 89 and 91 respectively. The adjustment screws are positioned at several points around the periphery of the chamber assembly, one screw 129 being shown.

Microwave connections are made to the chambers by means of three rectangular microwave guides 131, 132 and 133, coupling being effected by hermetically sealed irises 134, 136 and 137. Alternatively connections can be made by any other conventional method.

In operation, microwave energy is applied to the middle resonant chamber 87 through its input guide 132. The resonant chamber 87 is excited and oscillates at its tuned frequency, which is also the input frequency. No field energy can pass through the grids 93 and 94, which behave so far as the field is concerned as if they were solid walls. When the electron gun 104 is energized, gun 106 being left deenergized, an electron beam is generated and passes through focusing tube 97, drift tube 89, drift tube 91, and focusing tube 98 to the right-hand electron gun structure. The filamentary cathode 138 being cylindrical, the electron beam passes through it axially and impinges on the carbon block 139, where it is absorbed. In the passage of the electron beam the several grids 99, 101, 92, 93, 94, 96, 102 and 103 have little obstructive effect. However if desired these grids can be made very coarse or even omitted without greatly increasing the microwave field leakage. As the electron beam passes through resonant chamber 87 it is velocity modulated by the field therein, so that the electrons entering chamber 88 are bunched and generate resonation therein. Energy is abstracted from this chamber by guide 133.

The excitation of gun 104 thus elfectively couples chamber 87 to chamber 88 so that the energy applied through guide 132 is effectively abstracted through guide 133. In general it is easy to employ such parameters as to effect zero attenuation in the circuit from the input guide to the output guide. Moreover, at selected parameter values considerable voltage and/or power amplification takes place so that the output voltage and/or power is" greater than at the input.

The structure is symmetrical and when excitation is removed from gun 104 and applied to gun 106 the cathode beam is passed from right to left and is absorbed at target 113. The beam is velocity modulated in chamber 87 and gives up its energy to chamber 86, from which it is abstracted by guide 131.

Any one of the three chambers, 86, 87 and 88, can be excited and serve as the input chamber, with either of the other two chambers serving as the output chamber, provided only that an electron beam passes first through the inputchamber and second through the output chamber. It is not necessary that the chamber serving as input when one of the electron guns is used also serve as input when the other electron gun is used. For example, when the gun 104 is used chamber 87 may be the input chamber and chamber 88 the output chamber. When gun 104 is switched off the gun 106 is switched on the chamber 88 may be used as the input chamber and chamber 86 as output chamber. There are obviously several possible cases: when gun 104 is used chamber 86 may be the input chamber, with either chamber 87 or chamber 88 the output chamber, or chamber 87 may be the input chamber and chamber 88 the output chamber.

It is in addition possible under some conditions to employ two input circuits simultaneously or two output circuits simultaneously in this microwave switch.

What is claimed is:

l. A microwave switch comprising, an input microwave chamber and at least a pair of output microwave chambers, each of said chambers being resonant at the same microwave frequency, passageways extending in diiferent directions interconnecting said input chamber with each of said output chambers, said passageways be ing .impervious to microwave energy at said frequency but pervious to an electron stream, electron gun means for projecting an electron stream through respective passageways to intercouple the microwave energy in said input chamber into selected ones of said output chambers, switch actuated means for altering the direction of said electron stream in said different directions selectively to intercouple selected ones of said output chambers with said input chamber, and microwave transmission circuits coupled to each of said microwave chambers.

2. A microwave electronic switch comprising, an input microwave resonant chamber and a plurality of output micnowave resonant chambers, means for applying a microwave field .to said input chamber, electron gun means for projecting an electron stream through said input chamber whereby said electron stream is velocity modulated by the field excited in said input chamber, switch means for selectively directing said velocity modulated electron stream into selected ones of said output chambers, and means for abstracting microwave energy from said output chambers.

3. A microwave electronic switch comprising, an input microwave resonant chamber and a plurality of output microwave resonant chambers, passageways interconnecting said input chamber and respective ones of said output chambers, means for rendering said passageways impervious to the transmission of microwave field energy, means for applying a microwave field to said input chamber, electron gun means projecting an electron stream through said input chamber whereby said electron stream is velocity modulated by the field excited in said input chamber, switch means for varying the direction of said velocity modulated electron stream through said passageways into alternately selected ones of said output chamhers, and means for abstracting microwave energy from said output chambers.

4. -A microwave electronic switch comprising, an input microwave resonant chamber, a pair of output microwave resonant chambers, a first passageway interconnecting said input chamber and one of said pair of output chambers, a second passageway interconnecting said input chamber and the other of said pair :of, output chambers, means'for rendering 'said passageways impervio to the transmission of microwave field energy, means for applying a microwave field to said ,input chamber, electron gun means proiecting an electron. Stream through said input chamber whereby said electron stream is velocity modulated by the field excited in said input chamber, means for selectively projecting said velocity modulated electron beam through said first and second passageways into said one or the other of said output chambers, and means for abstracting microwave energy from said output chambers.

5. A microwave switch for transferring microwave energy between one or another pair of three microwave circuits comprising, three microwave chambers resonant at the same frequency, means coupling said three microwave circuits to respective ones of said three microwave chambers, passageways interconnecting said chambers, said passageways being nonconductive of microwave electromagnetic field energy but permitting passage of. an electron stream, electron gun means for passing an electron stream through said passageways, and means for switching said electron stream from travel between one pair of said three chambers to travel between another pair of said three chambers.

6. A switch for transferring microwave energy from an input microwave circuit 'to any one of a plurality of output microwave circuits comprising, an input microwave resonant chamber connected for excitation by said input microwave circuit, a plurality of output microwave resonant chambers each connected to a respective one of said plurality of output microwave circuits for the excitation thereof, passageways connecting said input microwave resonant chamber to each of said output microwave resonant chambers, said passageways having high impedance to the passage of microwave electromag'-" netic field energy but allowing the passage of electrons, an electron gun positioned vto pnoject an electron stream through said input microwave resonant chamber, means for selectively controlling the direction of said electron stream after passage through said input microwave resonant chamber to direct its passage through a selected one of said passageways and into a selected one of said output microwai e resonant chambers 7. A switch in accordance with claim 6 in which said meansior controlling'the direction of the electron stream is electrostatic.

8. A microwave switch comprising, three resonant chambers axially aligned including a central input chamber .flankedoneach side by an output chamber, an electron-beam gun connected axially to each of said output chambers for directing an electron beam axially of said chambers andthereby transferring microwave energy from said input chamber to said output chambers and switch means for selecting one or the other of said guns.

9. A microwave switch comprising, three resonant chambers axially aligned including a central input chamber flanked on each side by an output chamber, microwave transmission circuits respectively coupled to each of said resonant chambers, passageways interconnecting said chambers, said passageways having very high impedance to passage of electromagnetic field energy but transmitting an electron stream, a first electron gun connected to one of said output chambers and positioned to direct a stream of electrons through said chambers and said passageways in one direction, a second electron gunoonnected to the other output chamber and positinned to direct a stream of electrons through said chambets and said passageways in the opposite direction, and means for selecting and alternately operating said electron guns.

10. A microwave switch comprising, three microwave chambers resonant at the same frequency positioned in axial alignment and provided with interconnecting passageways therebetween, means in each of said passagewalys peivious to an electron stream for preventing the passage of elcctnomagn'ctic'field energy therethrough, an electron gun connected to one end chamber positioned to direct a stream of electrons through said chambers and said passageways in one direction, a second electron gun connected to the other end chamber positioned to direct a streamof electrons through said chambers and said passageways in the opposite direction, means for alternately energizing said electron guns, and microwave transmission circuits connected to each of said chambers.

References Cited in the file of this patent UNITED STATES PATENTS

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