US2929959A - Magnetrons - Google Patents

Description

' R. DUNSMUIR MAGNETRONS March 22, 1960 2 Sheets-Sheet 1 Filed Feb. 13, 1959 //V l/E' N TOR fPOEff/FT 00 IF? 147' TOFPNEY March 22, 1960 R. DUNSMUIR MAGNETRONS 2 Sheets-Sheet 2 Filed Feb. 13, 1959 Claims priority, application Great Britain February 13, 1958 2 Claims. (Cl. BIS-39.75)

.This invention relates to ultra-high frequency electron discharge devices. It has application in travelling wave amplifiers, oscillators and accelerators, including both magnetron and other types.

Magnetron oscillators in which alternate segments are strapped together by means of conductive connecting links are well known. Although these connecting links are substantially straight they nevertheless provide a measure of inductive coupling between the resonators. With such a form of coupling the dispersion curve, which is defined as the relationship between phase shift ,9 and frequency w is such that the group velocity B may be opposite in direction to the phase velocity Although this is of no consequence for magnetron oscillators it is unsuitable for magnetron amplifiers, where both phase and group velocity should preferably have the same direction.

It is an object of the present invention to ensure that the group velocity has the same direction as the phase velocity in the fundamental mode, throughout an appropriate frequency range.

Accordingly the present invention comprises an ultrahigh frequency electron discharge device having resonant cavities formed by a plurality of slotted laminae stacked so that the slots in successive laminae are aligned to define resonant cavities and wherein the slots in different laminae are so shaped that portions of slots defining adjacent cavities overlap, whereby mutual inductive coupling is obtained between successive resonant cavities.

The circuit may be in any one of several forms. It may form a complete ring, a portion of a ring or it may be straight and the invention is applicable to all these possible constructions.

It is important for the satisfactory operation of the device, that the interlaminar spaces should be of such a size that they do not resonate at any frequency within the pass-band of the device.

In a particular arrangement the anode block is composed of two annuli disposed coaxially. Each annulus has a number of slots opening into its inner periphery and forming segments between them. The corresponding segments of the two annuli are connected together to form complete segments extending along the whole axial length of the block, the connection being made near to the inner periphery. It is arranged that the inductance of the connecting portions is low compared with that of a slot. The unslotted edges of the annuli may also be connected together at the outer periphery. The slots are so shaped and the annuli so assembled with respect to each other that part of the inductive region of any slot on one side of a particular segment in one annulus is contiguous with a "ateint similar inductive region of a slot on'the other side of the same segment in the other annulus. Itwill be appreciated that with such an arrangement mutual inductive coupling is provided between adjacent resonant cavities.

In order that the invention may be more fully understood reference will now be made to the accompanying drawings,in which: p

Fig. l and Fig. 2 show linearly developed views of laminae suitable for the invention; I

Fig. 3 shows a linearly developed view of these laminae superimposed on each other to form an anode block;

Fig. 4 shows a desired dispersion curve of a device :in accordance with the invention; and p I N Fig. 5 is aplan sectional view, taken along line 5 5 of Fig. '6, illustrating a magnetron embodying the present invention; and

Fig. 6 is an elevational sectional view, taken along line 6-6 of Fig. 5.

Referring to Fig. 1 there is shown therein a lamina 1 having a plurality of slots such as 2. Slot 2 contains an entry portion 3 symmetrically disposed about a radial line bisecting the gap between adjacent segment tips 4 and 5 and an asymmetrically disposed end portion 6 of the slot. It now such a lamina is turned over it will appear as shown in Fig. 2 in which like parts have like reference numerals with a bar (1). Here end turns 6 of the slots are now on the opposite side of a radial line bisecting a slot. To construct an anode block the lamina 1 of Fig. 1 and lamina 1 of Fig. 2 are superimposed one on the other as shown in Fig. 3 and are connected together at or near the inner tips of the segments. If desired the laminae may also be connected at their outer peripheries so as to form a more stable structure. It will be seen that with such an arrangement the end portions 6 of the lamina of Fig. 1 will overlap the end portion 6' of the lamina of Fig. 2 so as to provide mutual inductive coupling between successive resonant cavities defined by the entry portions 3 and 3 of the slots.

When excited in the pi-mode, for which the magnetic flux tends to flow instantaneously in opposite directions in adjacent resonators, the flux associated with the mutual inductance opposes that associated with the self inductance. This is alternatively described by noting that the flux associated with current flowing around a given resonator opposes the flux due to current flowing simultaneously in the coupled resonators. When excited in the zero mode, in which the currents flow in the same direction round all the resonators, the fluxes in a given resona tor associated with self and mutual induction flow in the same direction. It follows that the stored magnetic energy per unit is lower for the pi-mode than for the zero mode and consequently the pi-mode resonant frequency is higher than that of the zero mode. By reference to the resulting dispersion curve shown in Fig. 4 it is clear that the group velocity for the fundamental component is in the same direction as the phase velocity.

It will be appreciated that more than two laminations could be used, and if desired they could be inverted a1 ternately or in packets, and it will be realised that the coupling could be modified by making the number of laminations of one hand diflerent from the number .of laminations of the other hand.

Figs. 5 and 6 illustrate a magnetron embodying the present invention. This magnetron is of a conventional type, such as the general type disclosed in Principles and Practice of Radar, Penrose and Boulding, 6th ed. (1958), page 282, 283, and 284, except for the features of the present invention, and comprises an annular anode 7 constructed of a plurality of slotted laminations 1 shaped as illustrated in Fig. l and Fig. 2 and stacked together in the manner illustrated in Fig. 3. The magnetron is sealed by two cover plates 10 and 11 placed at each end. A cathode 8, heated by a heater 9, emits electrons which are re pelled by a repeller electrode 15 to form a beam which traverses the annular space between anode 7 andsole plate 16 along the path indicated by dotted line 12 until they reach vcollector electrode 17. The input to the magnetron is provided by an input coupling loop 18 provided in the first cavity and the output from the magnetron is taken from an output coupling 19 provided in the last cavity. It will be appreciated that the magnetron illustrated in Fig. 5 and Fig. 6 will be placed between the poles of a magnet which provides a magnetic field extending axially of the magnetron.

What I claim is:

1. An ultra-high frequency electron discharge device including a plurality of walls defining cavities between the walls, said walls being formed by a stack of slotted laminae, the slots of each lamina having an entry portion and an end portion, the entry portions of the slots of each lamina being aligned with the entry portions of the corresponding slots of all the other laminae and the end portionsof each lamina being aligned with the end portions of some only of the other laminae.

2. A magnetron including an anode block comprising two coaxial annuli eachhaving a plurality of slots extending radially outwards from the inner periphery of the annuli, the entry portion of the slots of both annuli being aligned with each other and the end portion of the slots of each annulus extending in respective opposite directions and overlapping the end portions of the adjacent slot of the other annulus.

References Cited in the file of this patent UNITED STATES PATENTS 2,583,793 Nelson Jan. 29, 1952 2,606,307 Pease et a]. Aug. 5, 1952 2,817,789- Steirnel Dec. 24, 1957

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