US3445718A

US3445718A - Mixed line magnetron circuits having strapped sections and tubes using same

Info

Publication number: US3445718A
Application number: US516272A
Authority: US
Inventors: Hunter L Mcdowell
Original assignee: SFD LAB Inc
Current assignee: S F D LAB Inc; SFD LAB Inc
Priority date: 1965-12-27
Filing date: 1965-12-27
Publication date: 1969-05-20
Anticipated expiration: 1986-05-20

Description

United States Patent US. Cl. 31539.3 9 Claims ABSTRACT OF THE DISCLOSURE A composite mixed line periodic slow wave circuit is disclosed together with tubes using same. The mixed line periodic slow wave circuit includes an array of conductive elements with a pair of conductive straps extending along the array. Adjacent ones of the conductive elements of the array are conductively connected at spaced points along the straps to alternate ones of the pair of straps. Over a portion of the length of the slow wave circuit, each of the straps is segmented with the segmentation occurring intermediate the points of connection of the straps to the conductive elements of the array to define adjacent segmented and unsegmented strapped sections of the composite slow wave circuit. The segmented strapped portion of the circuit will have a fundamental forward wave characteristic, Whereas the unsegmented strapped portion of the circuit will have a fundamental backward wave mode of propagation. Both modes will have a common operating point at the 11' mode such that only the desired 11- mode will propagate around the composite circuit. In this manner, certain undesired modes are prevented from interacting with an electron stream, thereby permitting improved electron efficiency and higher output power. Such a circuit is readily fabricated by strapping the array of conductors and then merely slotting through the straps to form a segmented section of the composite slow wave circuit.

Heretofore, it has been proposed to build mixed line interaction circuits such that the different sections have different dispersion characteristics with a common intersecting or operating point at the 11' mode of operation. Such a mixed interaction circuit permits a substantial increase in interfering mode frequency separation for a periodic interaction circuit with a given number of periodic elements; i.e., vanes, bars, slots and the like. In copending US. application 516,271, filed Dec. 27, 1965, there are described and claimed various composite mixed line circuits of the vane and bar type.

In the present invention, an improved composite mixed line magnetron interaction circuit is provided which offers enhanced ease of fabrication. The composite mixed line circuit is of the strapped vane or bar type whereinv a pair of straps pass along the length of the circuit with successive periodic elements, i.e., bars or vanes being conductively connected with alternate straps to form a fundamental backward wave circuit. This fundamental backward wave circuit is converted to fundamental forward wave circuit sections over certain portions of its length, to provide the composite mixed line circuit, by segmenting, as by slotting, the straps over one or more spaced circuit sections of the strapped circuit. This greatly facilitates ease of fabrication of the circuit as it may be completely assembled with the straps being connected to alternate periodic elements and then certain portions of this complete circuit may be converted to the forward wave sections by merely slotting or segmenting the straps to define the forward wave sections.

The principal object of the present invention is the provision of an improved mixed line magnetron interaction circuit and tube using same whereby ease of tube fabrication is obtained.

One feature of the present invention is the provision of a composite mixed line vane or bar periodic circuit having a pair of straps extending along the circuit and wherein adjacent regions of forward wave and backward wave sections are formed by segmenting the straps over regions of the circuit to define the forward wave sections whereby fabrication of the composite line circuit is facilitated.

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:

FIG. 1 is a schematic line diagram of a mixed line magnetron interaction circuit,

FIG. 2 is an w-B diagram for the mixed line circuit of FIG. 1,

FIG. 3 is a side elevational view of a mixed line strapped bar circuit incorporating features of the present invention,

FIG. 4 is a transverse sectional view of the structure of FIG. 3 taken along line 4-4 in the direction of the arrows,

FIG. 5 is a side elevational view of a mixed line strapped vane circuit incorporating features of the present invention,

FIG. 6 is a transverse sectional view of the structure of FIG. 5 taken along lines 66 in the direction of the arrows.

Referring now to FIG. 1, there is shown a magnetron tube incorporating a mixed line magnetron interaction circuit. More specifically, an anode electrode 1 coaxially surrounds a cathode electrode 2 defining an annular magnetron interaction 3 between the anode 1 and the cathode 2. A composite mixed line magnetron interaction circuit 4 is formed in the anode 1 in the face thereof adjacent the magnetron interaction region 3 for cumulative electronic interaction with a stream of electrons in the interaction region 3 in the presence of an axially directed magnetic field B to produce an output signal. The output signal is extracted from the anode circuit 4 via a suitable coupling device such as output coupling loop 5 for propagation to a suitable load, not shown.

The composite mixed line interaction circuit 4 comprises a backward wave section 4' and a forward wave circuit section 4". For the purposes of explanation the magnetron interaction circuit of FIG. 1 has been simplified by providing only one backward wave and one forward wave circuit section. As will be further described, below, this separation of the circuit into alternating backward and forward wave sections substantially reduces mode interference for a magnetron having a large number of periodic elements. Therefore, in practice, magnetrons for high power operation would include several alternately backward and forward wave circuit sections to accommodate a larger cathode electrode 2 and a larger anode 1 for greater power dissipation.

Thedispersion characteristic for the composite mixed line circuits 4 of FIG. 1 is shown in FIG. 2. More specifically, the composite circuit 4 is seen to have two branches to its dispersion characteristic, an upper branch corresponding to the backward wave circuit 4', and a lower branch corresponding to the forward wave circuit section 4". When a circuit is made re-entrant upon itself as in FIG. 1, the dispersion characteristic becomes discontinuous and certain resonance modes of operation are established corresponding to the solid dots on the dispersion characteristic. For the composite mixed line type of interaction circuit it is found that there are N possible modes of operation on each branch of the dispersion curve, where N is the number of periodic elements in the corresponding section. For example, in the magnetron interaction circuit 4 of FIG. 1, the backward wave section includes four periodic elements, i.e., slot resonators, N, and thus, there are four possible resonant modes as indicated on the upper dispersion branch. The lower cutoff frequency for the backward wave circuit section occurs at the 1r mode and corresponds to series resonance of the slots 6 which occurs when the slots are approximately a quarter wavelength in radial extent. Likewise, the forward wave circuit section 4" has 4 possible modes of operation corresponding to the four periodic elements N, which as before, are the slots 6. The upper cutoff frequency of the forward wave section 4" occurs at the 1r mode and this frequency corresponds to resonance of the slots 6 and, as before in the backward wave section, occurs when the slots 6 have a radial extent of approximately a quarter wavelength. Thus, it is seen that the composite interaction circuit of FIG. 1 has a common operating frequency ca at the Ir mode with substantial mode separation obtained between all other possible modes of oscillation and the common 1.- mode.

The dispersion curve of FIG. 2 holds for the composite mixed line interaction circuit of FIG. 1 regardless of how many alternating sections of backward and forward wave comprise the total anode circuit. This means that the anode circuit 4 may be composed of several forward and several backward wave circuit sections, each preferably of relatively few elements, and the mode separation for the composite circuit will be characteristic at the mode separtion of each circuit section which, of course, is much greater than if the entire anode circuit 4 were completely composed of all identical elements.

Thus, for the composite mixed line circuit having alternate sections of forward and backward wave dispersion characteristic Wth relatively few elements per section, the only mode which can satisfy all boundary conditions leading to cumulative interaction will be the common 1r mode of the system. This means that this composite mixed line circuit leads to a powerful method for inhibiting all other types of mode interference. This inhibiting feature can be further enhanced by deliberately having the number of cells or periodic elements different in each circuit section to enhance the mode separation effect.

Referring now to FIGS. 3 and 4, there is shown a strapped bar composite mixed line magnetron interaction circuit incorporating features of the present invention. More specifically, the circuit comprises an array of parallel directed bars as of copper. The bars are shorted at their ends by a pair of conductor members 16 as of copper which may conveniently take the form of plate like members extending back to support the circuit from a common back wall as of copper. The bars 15 are dimensioned in length such as to have a length approximately equal to half an electrical wavelength at the frequency of the 1r mode of operation of the composite magnetron interaction circuit. The spaces between adjacent bars 15 define an array of half Wavelength slot resonators.

A pair of

conductive straps

17 and 18 as of copper extend lengthwise of the bar array and are connected to the bars intermediate their lengths. One of the straps 17 is connected to alternate bars 15 via conductive tabs 19 as of copper. Likewise the other strap 18 is conductively connected to alternate bars 15 via conductive tabs 21. The connections between the straps and the bars 15 alternate such that adjacent bars 15 are connected to

alternate strap members

17 and 18. In this manner, the two

straps

17 and 18 form the two wires of a two wire transmission line with the slot resonators, defined between adjacent bars 15, being connected in shunt across the two wire line. Such a circuit has a backward fundamental wave dispersion characteristic as shown in the upper branch of the dispersion curve of FIG. 2. Thus, in the absence of any further modification of the circuit, as thus far described, it would be entirely a backward wave over its entire length.

This fundamentally backward wave circuit is converted to forward Wave over certain sections of its length to form a composite magnetron interaction circuit by segmenting the

straps

17 and 18 intermediate their points of connection to the bars 15, as by slotting the straps with transverse slots 22. The slots 22 introduce series capacitance into the two wires of the transmission line formed by

straps

17 and 18 causing the dispersion characteristic for the circuit, over that portion which has been segmented, to be fundamentally forward wave as indicated by the lower branch of the dispersion characteristic of FIG. 2. The composite circuit will have a common mode of operation at the 1r mode corresponding to the bars 15 being approximately half an electrical wavelength long. The composite magnetron interaction circuit of FIGS. 3 and 4 may be used in either circular or linear form, the circular form being the preferred embodiment. In the circular geometry, as indicated in FIG. 1, the anode circuit 4 may conveniently surround or be surrounded by the cathode electrode to produce an annular magnetron interaction region in the space between the anode circuit and the cathode electrode 2.

Referring now to FIGS. 5 and 6 there is shown an alternative embodiment of the present invention. In this embodiment, an array of T shaped vane members 25 as of copper outwardly project from a conductive back wall 20 as of copper. Alternate tips of the vanes 25 are axially offset from the intermediate vane to make electrical contact with one of a pair of

conductive strap members

26 and 27 extending longitudinally of the vane circuit over the top and bottom side edges of the vanes, preferably near the outermost ends of the vanes 25. In this manner, adjacent vanes 25 are connected to

alternate straps

26 and 27. In the absence of further modification of the periodic circuit formed by the strapped vanes the circuit will have a backward fundamental dispersion characteristic as shown by the upper branch of the dispersion curve of FIG. 2. The circuit may be considered as a strapped vane circuit or as a choke supported interdigital line either description being valid.

The upper cutoff frequency of the backward wave circuit occurs when the distance around the interdigital line 1 between successive stream field interaction regions corresponds to approximately half an electrical wavelength. This distance will be half an electrical wavelength when the vanes have a height 1 which is approximately a half of an electrical wavelength. The low frequency cutoff, which corresponds to the 1r mode of the backward wave section, occurs when the vanes 25 have a length 1 corresponding to approximately a quarter of an electrical wavelength. Thus, the slot resonators defined by the space inbetween adjacent vane members 25 become resonant at the 11' mode and determine the low frequency cutoff for the backward wave section. V

The forward wave section 4" of the composite mixed line circuit 4 is formed by segmenting, as by slotting, the

straps

26 and 27 at points intermediate their points of connection to alternate vanes 25. This introduces a series capacitance in the two wire line formed by the

conductive straps

26 and 27 in the forward wave section. This series capacitive loading of the straps shifts the dispersion curve for the segmented portion of the circuit to that as indicated by the lower branch of the dispersion characteristic of FIG. 2. The 1r mode frequency for the forward wave section 4" now becomes its high frequency cutoff and is essentially the same frequency as the low frequency cutoff of the backward wave section. Thus, the composite circuit has a common operating point at the 1r mode. The zero mode frequency for the segmented section of line has been substantially reduced in frequency for the for-= ward wave section due to the capacitive series loading of the

segmented straps

26 and 27 formed by the slots 28.

The composite magnetron interaction circuit 4 of FIGS. 5v and 6 is easily fabricated by strapping the vane array and then merely slotting the strapped array at slots 28 over alternate circuit sections in order to obtain alternating sections of forward and backward wave characteristics having a common 11' mode.

Since many changes could be made in the above construction and many 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:

1. A composite mixed line periodic circuit including, means forming an array of conductive elements, means forming a pair of spaced conductors defining a pair of straps extending along said array with adjacent ones of said conductive elements of said array being conductively connected at spaced points along said straps to alternate ones of said pair of straps, said pair of straps each being segmented intermediate their points of connection to alternate elements of said array with said segmentation extending only over a portion of the length of said straps to define adjacent segmented and unsegmented strapped circuit sections of plural conductive elements and forming fundamental forward wave and fundamental backward wave circuit portions, respectively, thereby defining the composite mixed line circuit.

2. The apparatus according to claim 1 wherein said array comprises an array of conductive parallel bars conductively joined together at their ends to define an array of half wavelength slot resonators in the spaces between adjacent bars at the 1r mode frequency of the composite circuit.

3. The apparatus according to claim 1 wherein said array comprises an array of conductive element conductively connected together at one end to define in the spaces between adjacent elements an array of quarter Wave slot resonators at the 1r mode frequency of the composite mixed line circuit.

4. The apparatus according to claim 3 wherein said conductive elements are T shaped vanes, and said straps overlie opposite side edges of said vanes.

5. The apparatus according to claim 1 including, means for providing a stream of charged particles adjacent the composite mixed line circuit for cumulative electronic interaction with the fields thereof to produce an output R.F. signal, and means for extracting the output signal.

6. The apparatus according to claim 5 wherein said stream producing means includes a cathode electrode and including an anode electrode spaced from said cathode to define an electron interaction region therebetween, said anode having the mixed line composite periodic circuit formed as a part thereof for collecting the stream of charged particles.

7. The apparatus according to claim 6 wherein said cathode and anode electrodes are coaxially disposed of each other to define an arcuate electronic interaction region, and including means for producing an axially directed magnetic field in said interaction region to obtain magnetron type electronic interaction.

8. The apparatus according to claim 7 wherein said pair of straps are arcuate taken in a direction along the composite circuit, and wherein said straps are segmented by slots traversing same.

9. The apparatusaccording to claim 1 wherein the composite mixed line circuit includes plural periodic circuit sections of segmented straps alternating with plural circuit sections of unsegmented strapped circuit portions.

References Cited UNITED STATES PATENTS 3,069,595 12/1962 Sibley 315-39.69 3,219,882 11/1965 Zawada et al 31539.69 3,308,336 3/1967 McDowell 3l539.69 2,504,329 4/1950 Heising 31S39.69 3,121,820 2/1964 Wilbur 3l5-39.69 3,121,821 2/1964 Yu 31539.69 3,121,822 2/1964 Boyd 3l539.69 3,176,188 3/1965 Wilbur 3l539.69

HERMAN K. SAALBACH, Primary Examiner.

S. CHATMON, Assistant Examiner.

US. Cl. X.R.