US3591823A

US3591823A - Waveguide to coaxial to stripline transition for matching to slow circuits

Info

Publication number: US3591823A
Application number: US829639A
Authority: US
Inventors: Andrew S Wilczek
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1969-06-02
Filing date: 1969-06-02
Publication date: 1971-07-06
Anticipated expiration: 1988-07-06

Abstract

A microwave crossfield amplifier tube of circular format is disclosed. Transmission line transition sections are provided for impedance-matching the ends of a slow wave circuit to hollow rectangular waveguides axially directed of the tube. Each transition includes a T-bar connector inside the rectangular waveguide. The upright portion of the T-bar is connected to the end of the slow wave circuit via the intermediary of a section of coaxial line which tapers into a stripline portion which in turn is connected to the slow wave circuit.

Description

United States Patent [72] Inventor AndrewSJVilcuk 3,188,583 6/1965 Boyd 333/26 Old Brldge,N.J. 3,248,601 4/1966 Smith,.Ir, 315/35 X [21] Appl. No. 829,639 3,320,471 5/1967 Mims .4 315/393 (22] Filed June 2,1969 2,619,539 11/1952 Fano H 333/33 X [45] Patented July 6, 1971 2,786,981 3/1957 Zalcski 333/33 1 A lgn fl Primary ExaminerHerman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr.

Attorneys-Stanley Z. Cole and Gerald L, Moore [54] WAVEGUIDE T0 COAXIAL TO STRIPLINE TRANSITION FOR MATCHING T0 SLOW CIRCUITS 1 F 7 C 5 Drawing ABSTRACT: A microwave crossfie1d amplifier tube of circu- [52] U.S.Cl 315/393, lat f t is disclosed Transmission line transition Sections 3 l 333/25- 333/33, 3 l 3/ 35 are provided for impedance-matching the ends of a slow wave [51] lnt.Cl H01] 25/34 circuit to honow rectangmar waveguides axiauy directed f 0! u: 3 l the tube Each transition includes a T.bar connector inside the 16,393; 333/2526- 34,3312] rectangular waveguide. The upright portion of the T-bar, is 56 R i cud connected to the end of the slow wave circuit via the interl e mediary of a section of coaxial line which tapers into a UNITED STATES PATENTS stripline portion whichin turn is connected to the slow wave 2,922,956 1/1960 Dench 315/35 X circuit.

I 1 l 5 I 7/ 1/ A W v 22" 28 I l 8 RE 5 1 T 7 5 e PULSER PATENTH] JUL 8 1971 SHEET 2 0F 2 FIG. 5

FIG. 3

as i" INVENTOR.

"ANDREW S. WILCZEK 0& 3% ATTORNEY (24' FIG. 4

WAVEGUIDE TO COAXIAL T STRIPLINE TRANSITION FOR MATCHING TO SLOW CIRCUITS DESCRIPTION OF THE PRIOR ART Heretofore, crossed-field amplifier tubes of circular format have employed rectangular waveguides matched via the intermediary of transition sections to the ends of the slow wave circuit, such as a double-stripline helix-coupled bar circuit. In these prior transitions, the waveguide extended generally perpendicular to the axis of revolution of the circular tube and a transition was made from the rectangular waveguide to a stripline by means of a ridged waveguide, the ridge being connected to one strip of a stripline and the opposed waveguide wall being connected to the other strip. of the stripline. The stripline was connected to the helical stripline portion of the slow wave circuit. While such waveguide transitions provided relatively broadband high-power matches to the circuit, they had the problems that the waveguides projected at right angles from the body of the tube, thus interfering with placement of the magnetic circuit, such as a solenoid, around the tube. Therefore, it is desirable to provide a rectangular waveguide to a slow wave circuit transition which allows the waveguides to extend axially of the tube.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved transition for impedance-matching a slow wave circuit of a tube to hollow waveguide.

One feature of the present invention is the provision of a transition section including a T-bar connector disposed within a hollow waveguide with the upright portion of the T forming the center conductor of a short section of coaxialline which is connected to the microwave slow wave circuit, whereby the axis of the hollow waveguide may be brought out parallel to the axis of revolution of the tube.

Another feature of the present invention is the same as the preceding feature wherein the end of the center conductor of the coaxial line which is connected to the slow wave circuit is curved toward an extension of the outer conductor of the coaxial line to form a short section of stripline, which connects to the slow wave circuit.

Another feature of the present invention is the same as any one or more of the preceding features wherein the crossarrns of the T are hollow to provide a coolant fluid passageway therethrough for cooling the transition in use.

Another feature of the present invention is the same as any one or more of the preceding features wherein the microwave slow wave circuit comprises a helix-coupled bar circuit with the stripline portion of the transition being connected to adjacent turns of the helix portion of the helix-coupled bar circuit.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a transverse schematic diagram of a crossfield amplifier tube incorporating features of the present invention,

FIG. 2 is an enlarged detailed view of a portion of the structure of FIG. I delineated by line 2-2,

FIG. 3 is a sectional view of a portion of the structure of FIG. 2 taken along the line 33 in the direction of the arrows,

FIG. 4 is a view similar to that of FIG. 3 depicting a similar portion of the circuit shown in FIG. 3 as modified to be utilized at the output transition, and

FIG. 5 is a detail view of the portion of the structure of FIG. 1 delineated by line 5-5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 there is shown a typical crossedfield microwave amplifier tube 1 of circular format including features of the present invention. The crossed-field amplifier tube 1 is of the general type disclosed and claimed in U.S. Pat. No. 3,255,422, issued June 7, 1966, and assigned to the same assignee as the present invention. Briefly, the tube 1 includes a generally cylindrical cathode electrode. structure 2 surrounded concentrically by an anode electrode'structure 3 to define an annular crossed-field interaction region-4 in the space between the cathode and anode electrode 2 and-3, respectively.

The anode electrode structure 3 includes a slow wave microwave circuit 5, such as an array of parallel'hollow conductive bars coupled at their back side by means of a pair of counterwound helices. Such a helix-coupled bar circuit is disclosed and claimed in copending US. application No. 541,088, filed Dec. 15, I965, and assigned to the same assignee as the present invention. The microwave circuit 5 is interrupted by a conductive circuit sever 6 positioned to define an upstream end 7 and a downstream end 8 at the respective ends of the circuit sever 6.

Microwave energy to be amplified is coupled to' the upstream end 7 of the microwave circuit 5 via the intermediary of a hollow rectangular waveguide 9 and waveguide-matching transition section 11, more fully described below. A similar waveguide and a similar transition section 9 and 11, respectively, are provided at the downstream end 8 of themicrowave circuit 5 for coupling amplified wave energy from the microwave circuit to a suitable load, not shown.

The cathode electrode structure 2 includes a secondary electron emissive portion 12 and a sector-shaped control electrode portion 13. The control electrode 13 is disposed facing the upstream end of the microwave circuit 5 and is insulatively supported relative to the secondary emission portion 12 of the cathode such that it may be operated at an independent potential for collecting the circulating stream of electrons to terminate operation of the tube.

In operation, a power supply 14 supplies a positive potential as of +25 kv. to the anode 3 relative to the potential applied to the secondary cathode emitter portion 12. The control electrode 13 is connected to the cathode end of the power supply 14 to be operated at the potential of the secondary emission portion 12 during amplification of the RF input pulses to' be amplified. A pulser 15, which is connected between the cathode secondary emitter 12 and the control in 13, pulses the control electrode 13 positive withrespect to the secondary emitter 12, as by +15 kv., to collect the electron stream and to terminate amplification of the tube, thereby preventing spurious output from the tube on termination of the input RF enery- Referring now to FIGS. 1, 2, 3 and 5, the hollow-waveguide 9 together with its transition section 11 is more fully described as it forms a transition between the microwave circuit 5 and the waveguide 9. The anode electrode structure 3 includesa conductive main body member of generally square cross section with a centrally disposed axially directed bore 10 which'is concentric with the cathode electrode structure 2. The rectangular waveguides 9 and 9 are axially directed of the cylindrical bore electrode the main body of the anode 3 with the broad walls of the waveguides 9 and 9' being'parallel to the corresponding flat side of the square main body member of the anode 3. A tubular conductive septum 16 extends across the waveguide 9 with the tubular septum 16 being generally parallel to the broad walls 17 and 18 of the waveguide and generally perpendicular to the planes of the narrowwalls I9 and 20 of the guide 9. As such, the bar 16 is perpendicular to the electric field vector E of the dominant waveguide transmission mode,'TE,, Suitable fittings, not shown,'are affixed to the tubular septum 16 for directing coolant fluid, such as water, through the tubular septum for cooling thereof in'use.

A section of coaxial line 21 (see FIG. 5) intersects the waveguide 9 centrally of one of the broad walls 18 with the center conductor 22 of the coaxial line 21 being conductively connected to the conductive septum 16 at a point substantially midway along the length thereof and extending perpendicularly from the tubular septum 16 through the conductive block of the anode 3. A cylindrical bore in the conductive block 3, such bore intersecting with the rectangular waveguide 9, defines the outer conductor 23 of the coaxial line 21. The septum 16 defines the crossarms of a T-bar connector and the center conductor 22 defines the upright of such T-bar connector.

The inner end of the center conductor 22 (see FIG. 2) of the coaxial transmission line 21 is connected to the severed end of the microwave circuit 5. The microwave circuit 5 includes a pair of counterwound stripline helices 25 and 25 (see H6. 3) which are conductively connected at successive turns of the

stripline helices

25, 26 to adjacent hollow conductive bars 27 of the array of axially directed bars of the microwave circuit 5. The axial ends of the hollow bars 27 communicate with fluid distribution and collection manifolds, not shown, for passing a fluid coolant through the bars for cooling same in use. v

The outer conductor 23 of the coaxial transmission line 21 includes a radially directed extension 28 to define one conductor of a stripline 31 having its inner end connected across the first full turn 29 of the

countrawound helices

25 and 26. The inner end of the center conductor 22 of the coaxial line 21 is reduced in thickness while retaining substantially its entire maximum width to define with the extension 28 of the outer conductor 23 a section of stripline 31. In addition, the center conductor is curved toward the conductive extension 28 of the outer conductor 23 to concentrate the microwave energy in the stripline 31 and for matching the impedance of the stripline 31 to the impedance of the

stripline helices

25 and 26, respectively.

Referring now to FIGS. 1 and 4, there is shown the stripline connection to the downstream terminal end 8 of the microwave circuit 5. More particularly, the inner end of the center conductor 22' is conductively connected to the last pair of outwardly directed leg portions 32 of the last turn of the

helices

25 and 26. The stripline extension 28 of the outer conductor 23 is connected to the next to last turn 24 of the helices. The microwave energy on the circuit flows in the direction as indicated by the arrows of FIG. 4.

In the T-bar-to-coaxial-line-to-stripline transition 11 of the present invention, the transition members are cooled by means of the fluid coolant flowing through the tubular septum 16. in addition, the center conductor 22 and stripline portion 31 is' cooled by means of thermal conduction of energy to the fluid streams within the hollow bars 27. This arrangement has been found to be adequate for cooling such a circuit operating at 2 megawatts peak and kilowatts average power at C- band. In addition, the transition 11 provided, in this case, a relatively wide band of operation, namely, a bandwidth of from 4 to 6.5 gigal-lertz between VSWR points of 1.1. If additional cooling is desired the center conductor 22 may be hollow and provided with a longitudinally directed septum to partition the hollow center conductor 22 into two fluid channels to be connected for series flow of coolant through the tube 16 and through the partitioned center conductor 22.

Although a contrawound helix-coupled bar-type slow wave circuit is disclosed for use with the transition section 11 of the present invention, other types of slow wave circuits may also be employed with the transition of the present invention. Such other circuits include wave circuits, stripline circuits, other types of bar circuits, etc.

Since many changes could be made in the above construction andmany apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

ln a crossed-field tube, means forming a cathode electrode structure for producing a stream of electrons, means forming an anode electrode having a microwave circuit portion spaced from said cathode to define a crossed-field interaction region between said cathode and anode electrodes, a hollow waveguide structure, means for coupling wave energy between said microwave circuit and said hollow waveguide, the improvement wherein, said couplingv means includes an elongated conductive septum extending across said hollow waveguide in abutment with a pair of opposite, facing walls of said waveguide with the longitudinal axis of said septum being disposed approximately at right angles to the electric field vector of the dominant transmission mode within said waveguide for wave energy of a frequency within the passband of said microwave circuit, means forming a length of coaxial transmission line intersecting said hollow waveguide with the center conductor of said coaxial line extending into said waveguide and being electromagnetically coupledto said septum within said hollow waveguide, the axis of the portion of said center conductor within said hollow waveguide being directed generally parallel to the electric field vector for the dominant transmission mode within said hollow waveguide, and said center conductor of said coaxial line being coupled to I said microwave circuit portion for coupling wave energy between said microwave circuit and said hollow waveguide.

2. The apparatus of claim 1 wherein said conductive septum is hollow to define a fluid coolant passageway thercwithin for cooling said coupling means in use.

3. The apparatus of claim 1 wherein said conductive septum is tubular, and means for directing a fluid coolant through said tubular septum for cooling same.

4. The apparatus of claim 1 including a coaxial line to stripline transition section between said coaxial line and said microwave circuit, said transition section including a length of said center conductor of said coaxial line which is flattened, said length of center conductor thereby forming one conductor of said stripline, said length of center conductor furthermore being shaped to more closely approach one interior surface portion of the outer conductor of said coaxial line than the diametrically opposite interior surface portion of said outer conductor to define said stripline between said length of center conductor and said more closely spaced surface of the outer conductor of said coaxial line.

5. The apparatus of claim 4 wherein said microwave circuit portion of said anode comprises a helix-coupled bar circuit, and said stripline portion of said transition section being connected to adjacent turns of the helix portion of said helixcoupled bar circuit.

6; The apparatus of claim 5 wherein said helix-coupled bar circuit comprises an array of conductive bars interconnected by a pair of contrawound helices, said stripline portion being connected to adjacent turns of both of said helices.

7. The apparatus of claim 1 wherein said anode electrode is concentrically disposed of said cathode electrode to define an annular crossed-field interaction region in the space therebetween, and wherein the longitudinal axis of said hollow waveguide is substantially parallel to the axis of revolution of said annular interaction region.

Claims

1. In a crossed-field tube, means forming a cathode electrode structure for producing a stream of electrons, means forming an anode electrode having a microwave circuit portion spaced from said cathode to define a crossed-field interaction region between said cathode and anode electrodes, a hollow waveguide structure, means for coupling wave energy between said microwave circuit and said hollow waveguide, the improvement wherein, said coupling means includes an elongated conductive septum extending across said hollow waveguide in abutment with a pair of opposite, facing walls of said waveguide with the longitudinal axis of said septum being disposed approximately at right angles to the electric field vector of the dominant transmission mode within said waveguide for wave energy of a frequency within the passband of said microwave circuit, means forming a length of coaxial transmission line intersecting said hollow waveguide with the center conductor of said coaxial line extending into said waveguide and being electromagnetically coupled to said septum within said hollow waveguide, the axis of the portion of said center conductor within said hollow waveguide being directed generally parallel to the electric field vector for the dominant transmission mode within said hollow waveguide, and said center conductor of said coaxial line being coupled to said microwave circuit portion for coupling wave energy between said microwave circuit and said hollow waveguide.

2. The apparatus of claim 1 wherein said conductive septum is hollow to define a fluid coolant passageway therewithin for cooling said coupling means in use.

5. The apparatus of claim 4 wherein said microwave circuit portion of said anode comprises a helix-coupled bar circuit, and said stripline portion of said transition section being connected to adjaCent turns of the helix portion of said helix-coupled bar circuit.

6. The apparatus of claim 5 wherein said helix-coupled bar circuit comprises an array of conductive bars interconnected by a pair of contrawound helices, said stripline portion being connected to adjacent turns of both of said helices.