US2881350A - Reflex klystron-type electron tube - Google Patents

Description

April 7,1959 W.-VElTH REF LEX KLYSTRON-TYPE ELECTRON TUBE Filed Nov. 24, 1954 United States Patent REFLEX KLYSTRON-TYPE ELECTRON TUBE Werner Veith, Munich, Germany, assignor to Siemens & Halske Aktiengesellschaft, Munich and Berlin, Germany, a German corporation Application November 24, 1954, Serial No. 470,913 Claims priority, application Germany December 23, 1953 Claims. (Cl. 315-519) This invention is concerned with an electron tube for very short waves, especially a tube of the reflex klystron type in which an electron reversal is effected in the space facing a reflection electrode.

The invention is particularly important for reflex klystrons and other similar tubes in which is obtained anelectron reversal. In the construction of eflicient reflex klystrons, care is usually taken to keep the plate voltage as low as possible while using a current as high as possible. The increase in the efliciency that may thereby be obtained is, however, limited by two conditions, namely, first by the yield of the tube and, second, by the effect of the space charge in the reflector area.

With constant current, the space charge, as is known, increases steadily with dropping voltage. At the reversal area of the electrons, facing the reflector plate, the space charge becomes theoretically infinitely great and the electrons scatter laterally instead of returning to the grid space in the direction of the injection path. Attempts have been made to prevent this spreading apart at the reflector plate by giving it and its vicinity suitable configuration.

The invention points another way, namely, the provision of means for considerably reducing the space charge in the reversal space. The spreading apart is in accordance with the invention not prevented; on the contrary, the space charge in the reversal space is appreciably reduced, for example, by the provision of a particularly large reflector surface. The invention accordingly deviates from the usual reflex klystrons in which the electrons move in a certain direction and permits the electrons to diverge ray-like in all directions. With high current densities, there is, due to the high space charge at any rate even in the nondelayed portion of the path a great outwardly directed force, and this force is preferably utilized for the production of the divergent ray beam.

The invention will now be explained with reference to the accompanying very much simplified drawings showing two embodiments each illustrating only the parts which are essential for the understanding of the structure.

Fig. 1 shows an arrangement comprising an anode and a large area concave cathode 1 with relatively low current density, which is in known manner employed so as to produce at a point Within the anode space a narrow beam. This beam diverges upon passing through the anode 10 and through the gap formed by grid electrodes 4 and 5 which are connected with walls 2 and 3 of the resonator and thereupon spreads strongly due to the previously described space charge forces. A concave plate is provided which serves as a reflector. The electron motion takes place within the beam indicated by the dotted lines 7 and 8.

Fig. 2 illustrates another embodiment. Instead of using a large-area cathode, there is provided a crosssectionally relatively small high-capacity cathode indicated at 9. This cathode may, for example, be a capillary metal cathode with high electron yield, which is disposed 2,881,350 Patented Apr. 7, 1959 so close to the anode 10 that very high current values can be produced at relatively low voltage. The result is again a, strongly diverging ray beam. The remaining numerals in Fig. 2 indicate parts corresponding to those indicated by like numerals in Fig. l.

The following aspects may be explained more. particularly as being essential for the operation of the reflex klystron according to the invention. The formation, in the reflector space, of a virtual cathode must be prevented. It was shown experimentally and theoretically, in the, case of. the formation of a virtual cathode, that the returning electrons are so far as their velocity is concerned only very indistinctly defined, such fact being reflected in particularly reduced steepness of the collector current-collector voltage characteristic. This steepness represents a criterion for the quality of the phase focusing of a reflex klystron, because it signifies that only few electrons of a certain velocity group return to the grid space and that the initiation of the oscill'ation with a certain frequency is possible only with a low degree of efiicieucy. Contrariwise, great steepness signifies the initiation of a certain frequency with a high degree of efliciency.

The two grids of the oscillation circuit are in the two figures concave with respect to the entering primary ray and are preferably not disposed directly at the narrowest area of the beam, so that the arrangement may have a relatively great grid capacitance. This arrangement causes a deterioration of the circuit quality, which is however compensated by the increased current and by the conditions in the reflector space which are improved by the invention.

The reflex klystrons according to the invention are due to their relatively great band width particularly suitable for modulation purposes.

The strict condition concerning the nonappearance of a virtual cathode is theoretically accurately known. Such condition constitutes a limitation for the length of the passage in the reflector space and may be mathematically formulated such that the length becomes l/V of the space between the cathode and the anode-all factors calculated in terms of a plane arrangement. Favorable data accordingly are obtained for the arrangement by applying the following simplified formula, namely wherein F is the effective reflector surface, K the cathode surface, a the spacing of the reflector area from the preceding grid electrode and k the cathode-anode spacing. It will be seen from the formula and referring to the figures, that the ratio of the effective reflection surface (F) to the cathode surface (K) is greater than twice the ratio of the square of the suppression path (a) preceding the reflector and the acceleration path (k).

Changes may be made within the scope and spirit of the appended claims in which is defined what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. In a reflex klystron-type electron tube for very short waves, having a cathode and an anode spaced therefrom and defining an electron acceleration space therewith and having grid means spaced from said anode and forming a gap, and having a reflector forming a reflection surface spaced from said grid means and defining therewith an entirely unobstructed electron reflection space, a resonator disposed entirely outside said reflection space and connected with said grid means, the electron beam emanating from said cathode progressively diverging along its passage from said anode and across said gap and thereupon strongly spreading on its passage across said reflection space. to said reflection surface, electron reversal being effected within said reflection space, the ratio of the effective reflection surface of said reflector to the cathode surface being greater than twice the ratio of the square of the suppression path across said reflection space and the acceleration ing across said acceleration space.

2. In an electron tube for very short waves operating in the manner of a reflex klystron and having a cathode and an anode spaced therefrom and defining an electron acceleration space therewith and having grid means spaced from said anode and mutually spaced by a gap, and having a concave reflector forming a relatively largearea reflection surface spaced from said grid means and defining an entirely unobstructed electron reflection space therewith, said reflector operating in the manner of a reflex electrode, a resonator disposed entirely outside said reflection space and connected with said grid means, said grid means controlling the electron beam emanating from said cathode to diverge progressively along its passage from said anode and across the gap therebetween, thereby causing said beam to spread strongly on its passage across said electron reflection space to said reflecpath extendv tion surface, electron reversal being efiected within said reflection space, the ratio of the effective reflection surface of said reflector to the'jcathode surface being greater than twice the ratio of the square of the suppression path extending across said reflection space and the acceleration path extending across said acceleration space for the purpose of considerably decreasing the space charge within said electron reversal space.

3. The structure defined in claim 2, comprising a concave relatively large-area cathode, said cathode being disposed relatively remote from said anode.

4. The structure defined in claim 2, comprising a crosssectionally relatively small high-capacity cathode disposed relatively close to said anode.

5. The structure defined in claim 2, comprising concave grid means disposed in the path of said divergent electron beam relatively considerably spaced from said anode.

References Cited in the file of this patent UNITED STATES PATENTS 2,460,332 Bowman-Manifold Feb. 1, 1949 2,513,371 Shepherd July 4, 1950 2,659,024 Bernier et a1. Nov. 10, 1953 FOREIGN PATENTS 7 602,796 Great Britain June 3, 1948 665,505 Great Britain Jan. 23, 1952

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