US2641733A - High-frequency tube - Google Patents

Description

Patented June 9, 1953 HIGH-FREQUENCY Donald E. Harris and Ralph L. McQreary, Cedar Rapids, Iowa, assignors to Collins Radio Company, Cedar Iowa Rapids, Iowa, at corporationof Application January 8, 1951, Serial No. 204,882

v2 Claims. (01. 31sec) This invention relates in general to electronic devices and in particular to ultra-high frequency tubes.

In the field of electronics, engineers have continuously pushed to higherfrequencies for transmission of radiant energy. Reasons for this are that, due to the large number of transmitting stations more frequencies are needed for new transmitters and secondly, transmission at the higher frequencies is oftentimes accomplished with a minimum of interference caused by variations in the Heavyside layer and similar disturbing factors. One highfrequency' electronic device is the klystron, which has a'bunching cavity through which an electron beam is passed and which bunches the electrons proportional to the frequency of the cavity. The electrons pass through a drift space where further punching occurs and into an anode cavity which is resonant at the bunched frequency and thus driven b the electron stream. The output of the anode cavity is removed by a coupling loop. The disadvantages of the klystron are that the electron gun is never turned off and thus the cathode gives a constant output. This'results in .a relatively low efficiency and a theoretical maximum efficiency of 57%.

The resnatron is another high frequency electronic device which has a resonant circuit comprising the gridand the cathode. An anode is placed so as to intercept electrons passing from the cathode. The resnatron is constructed as a radial structure wherein a center cathode is surrounded by a concentric grid structure and an outer concentric plate. The grid controls the electron flow from the cathode and can cut it off so that the tube can be operated in class C fashion. This results in greatly increased efficiency. Due to the concentric arrangement of the resnatron tube, the size of the cathode is of necessity relatively small and the emission current is limited thereby.

It is an object of this invention, therefore, to provide an electronic device which may be operated in class C fashion by obtaining a high emission current from the cathode.

Yet another object of this invention is to provide an axially aligned electronic device which has a control grid forming part of the resonant cathode that will turn oif the cathode during a part of the cycle.

Yet another object of this invention is to provide an improved highly efficient electronic dev1ce.

A feature of this invention is found in the provision for an anode and a cathode spaced in nated generally as ID, in which is mounted an anode H which is generally cylindrically shaped. The upper wall 12 oftheanode I I is formed with a cone shaped portion I3 at its center and the opposite wall I4 is formed with a central opening It. The anode II is supported from the envelope Ill by mechanical supports ll.

A cathode, designated generally as I3, is generally cylindrically shaped and is formed in two sections including an upper section l9 and a lower section 2 I. The lower section 2| has a bottom 2.2 and upwardly extending side walls '23. The bottom .22 is formed with a center cupshaped extrusion24. The upper section I9 is smaller in'radius than the lower section 2i and has a top 26 and downwardly extending walls 21. The walls 27 fit concentrically within the walls 23. Resistive material as, for example, a thin layer of ceramic 23, is placed between the outer edge of wall 21 and the inner edge of ,wall 23. The material 28 thus insulates the member [9 from the member 21 for a direct current potential. For alternating frequencies, however, the material 28 offers very little impedance and thus it provides means for maintaining the member :9 at a direct current potential differentfrom that of the member 2| while they are at the same high frequency potential. The cathode i8 is supported from the envelope it by the mechanical supports 28.

The cup-shaped portion 24 is coated on its inner surface with an emitting material 26 and a heater. '25 heats the cup-shaped portion 24 to cause electron emission from the inner surface thereof.

An input loop 29 passes through the wall 22 and has its end connected to it. In the anode cavity ll an output loop 3| passes through the wall 12 and connects to the inner wall.

A lead 32 is connected to the anode H and passes out through the wall of the envelope lil. A second lead 33 connects to the wall 2! of the cathode and passes out through the wall of envelope It. A lead 34 connects to the wall 27 of the cathode and passes through the side Wall of the envelope. An accelerating direct current voltage Eb is connected between the leads 32 and 33 with the positive side connected to the lead 32. A direct current biasing voltage E is connected between the leads 34 and 33 with the negative side of the voltage connected to the lead 34.

In operation, the envelope i0 is evacuated and the heater 25 is connected to a heating voltage so as to raise the temperature of the cathode 24 high enough to cause electron emission from the material 26. The shape of the member 24 causes focusing of the electrons emitted from the inner surface and, providing that the correct bias is placed on the member 58, the electrons will pass through the cathode cavity and out the opening 36 formed in the wall 26. The electron stream will interact with the cathode cavity 18, and will be modulated by the resonant frequency of the cavity so that bunching will occur in the drift space between the opening 36 and opening [6. It may prove desirable to place an external magnetic field so as to pass flux between the cathode and anode and thus aid in focusing the electron beam.

The electrons enter the anode cavity through the opening 16 and impinge on the target 13. As they traverse the anode the bunched electrons excite and drive the anode cavity so that energy may be removed by the pick-off loop 3!. The operation thus far described is similar to that of a klystron. Because of the insulation between the members l9 and ill of the cathode, however, the electron beam may be turned off during a portion of the cycle so that the tube may be operated in class C fashion. This means that the electron beam is periodically interrupted so that greater efficiency may be obtained.

This is illustrated in Figure 2. The input exciting voltage supplied by the lead 28 is near the resonant frequency of the cavity Ill and the direct current voltage EC placed on the lead as prevents the electron beam from passing out of the opening 36 except on-the positive peaks of the exciting voltage. Thus, as shown in Figure 2, the electron beam emerges from the opening 35 only at times when it is above the biasing voltage, EC. This results in the tube operating in class C fashion, thus greatly increasing the efficiency. Thus the electron stream will be turned on and off so that pulses will be released from the cathode cavity. These pulses will be received through the opening IS in the anode which is tuned to substantially the same resonant frequency as the cathode and thus the pulses will excite oscillation of the anode cavity at a high energy level. The output loop 31 will remove this energy. Since the tube is operated in class C fashion the emission of the cathode is not constant and thus a. high level of emission is not constantly required.

The electrons which flow through the drift space between the cathode and anode tend to bunch due to the variable slope of the bias on the member l9. This increases the concentration of energy.

Although this invention has been described with respect to a preferred embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as deflned by the appended claims.

We claim:

1. A high frequency electronic device comprising, an evacuated envelope, an anode structure whollywithin and supported by said envelope, a cathode structure supported within said envelope in axial alignment with said anode, said anode comprising a relatively short hollow cylindrical member, one end wall of said hollow cylindrical member formed with a central opening,'

said cathode comprising, a pair of discs with short peripheral flanges, the flange of one of said discs mounted telescopicall within the flange of the other disc, said discs being spaced remote from each other, said flanges telescopically overlapping each other, and the first of said discs formed with a central opening in axial alignment with said anode.

2. A high frequency electronic device comprising, an evacuated envelope, a hollow cylindrical anode mounted within said envelope, a pair of end walls forming a part of said anode, the first end wall formed with a central opening, the other end wall formed with a central cone-shaped portion, a cathode mounted within said envelope, said cathode comprising first and second discs with short peripheral flanges, the flange of one of said discs mounted telescopically within the flange of the other disc, said discs being spaced remote from each other, the first of said discs formed with a central opening, the other disc depressed into a generally focusing cathode surface, a heater mounted adjacent the second disc behind the cathode surface, and the anode and cathode mounted in axial alignment so that a stream of electrons emerging from the opening in said first disc will pass into the anode through the opening formed in the first end wall.

DONALD B. HARRIS. RALPH L. MCCREARY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,425,748 Llewellyn Aug. 19, 1947 2,484,643 Peterson Oct. 11, 1949

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