RU2152102C1 - Shf electronic device-istron - Google Patents

Abstract

FIELD: electronics. SUBSTANCE: invention refers specifically to SHF electronic devices in which formation of electron flux and its modulation by density are carried out in space " cathode-controlling grid " and interaction of grouped flux with SHF field and removal of useful energy are realized in output resonator. In this device electron flux is divided into separate beams thanks to special arrangement of individual beams in one drift tube. Device is intended for use in wide band of frequencies, predominantly, of decimeter television. EFFECT: provision for high efficiency and amplification factor and decreased value of accelerating voltages. 2 cl, 1 dwg, 1 tbl

Description

 The invention relates to electronic equipment, in particular, to microwave microwave devices, in which the formation of an electron beam and its modulation by density is carried out in the cathode-grid space, and the interaction of a grouped electron beam with a microwave field and the selection of useful energy in the output resonator. The electronic device we proposed is based on the same principle of operation, but differs significantly in design and, accordingly, in characteristics and capabilities, and therefore it is advisable to give it a new name. Let's call it "istron". Our device is designed to operate in a wide frequency band, mainly in the range used for decimeter television - 470 - 860 MHz.

 For the first time, an electrovacuum device with a similar operating principle was proposed by A. V. Gaev in 1938 and named the Inductive Output Tube (IOT) - an device with an inductive output [1]. However, at that time it was not possible to achieve a high output power due to overheating of the grid and the limitations associated with the insufficient emission ability of the then existing cathodes. In the 80s of the twentieth century, some technical problems of this plan were overcome. The American company Eimac-Varian, using metalloporous cathodes and grids of pyrolytic graphite, began to produce powerful IOT (tens of kW) with the brand name "klystrod".

 Known electrovacuum device IOT, in the design of which the electron beam is divided into separate beams ("rays") due to the implementation in space from the cathode to the collector of channels for the passage of electrons [2]. This design made it possible to provide the advantages known for multipath devices compared with single-beam advantages: to reduce the control voltage, intensity and magnitude of the focusing magnetic field. However, simply transferring the design solutions of multipath devices to an IOT device does not provide the ability to work in a wide frequency band, in particular, required for television. In a number of specific applications, devices [2] are generally unsuitable. So, when using a dual-gap output resonator, as proposed in [2], even if successfully overcome the difficulties associated with the mechanical tuning of the frequency of such a resonator in a wide frequency band (470 - 860 MHz), it is impossible to make the device of this class work effectively in the whole wide (almost octave) frequency band of the television decimeter range. Indeed, in such a wide frequency band, the electric length of the intergap gap of the two-gap resonator changes significantly, almost 2 times, which determines the efficiency of energy exchange of electrons and the high-frequency field. The operation of the device with a double-gap resonator is possible only in a limited narrow frequency band, many times smaller than required.

 The device [3], which we adopted as a prototype, is closest to the technical solution we proposed. The design of this known device includes a cathode, a control grid, an anode through which an electronic stream is passed in operating mode, single-gap input and active output resonators, drift tubes, an external passive output resonator, forming a chain of coupled resonators with an active output resonator, and a collector. The known device [3] allows you to provide an instantaneous frequency band of 6.9 MHz, required for transmitting a television signal, in a fairly wide passband of the transmitter 470.. . 860 MHz, high conversion efficiency (about 60%), high output power (at the level of tens of kW). Similar devices are now being developed and marketed by US firms (Eimac - Varian), UK (EEV), France (Thomson), Holland (Philips). A disadvantage of known devices of the type [3] is the need to use high accelerating voltages, and hence come to terms with the large dimensions of the power sources. The known design also has physical limitations on the maximum achievable gain. The known design requires the use of large diameter grids operating at high temperatures, for example, of pyrolytic graphite and thermal cathodes with high emissivity.

 The technical result of the present invention is to create a new type of powerful IOT-type devices designed to operate in the entire frequency band of the modern television decimeter range, which, in comparison with the well-known [3] IOTs, has lower accelerating voltages, a large gain, and greater operational reliability.

The technical result is achieved by using the idea of multipath, but implemented taking into account the features of IOT. Because of this, the proposed design of the device differs not only from [3], but also from the well-known multipath structures (in particular [2]), namely, by the arrangement of individual rays passing in their channels and by the current density in these rays. Specifically, the technical result of the present invention is achieved by the following set of essential features:
Known for [3] signs:
- the presence in the design of the device of the cathode, the control grid and the anode through which the electronic flow of the input and active output resonators, the drift tube, the external passive output resonator, forming a chain of coupled resonators with the active output resonator, and the collector are passed through in the operating mode.

Features other than [3]:
- the cathode is made in the form of a set of separate emitting surfaces forming individual electron beams,
- the grid is made in the form of a set of separate control grids, each of which is located above its emitting surface, and all together they are mounted on a single metal grid holder,
- the drift tube contains a set of separate longitudinal channels for the passage of individual electron beams, while the drift tube is performed subject to the conditions
0.1 ≤ D / λ ≤ 0.5,
where D is the diameter of the drift pipe,
λ is the wavelength of the short-wave end of the operating wavelength range,
and the centers of the channels and the emitting surfaces and grids corresponding to these channels are located on more than one concentric circle relative to the axis of the drift pipe.

 The proposed solution can be implemented in a number of options. We indicate some of them that are of the greatest interest in our opinion.

Option 1. To increase the efficiency of interaction of electron beams with a high-frequency field in the gaps of the resonators and achieve the instantaneous gain band required for television, separate electron beams (emitting surfaces, their corresponding grids and channels) are placed in such a way that their total number
N = 1 + 3n (n + 1),
where n is the given number of circles.

Option 2. For devices operating under high thermal loads, a design is suitable in which the central beam is excluded from the topology of the placement of individual electron beams in the total flow, i.e. the number of individual electron beams is
N = 3n (n + 1),
where n is the given number of circles.

 The efficiency of the device will clearly increase and noise will decrease if the collector is multistage in the proposed device. The use of such a collector will provide a positive effect in a high-pivot device due to the fact that the first-response of individual beams is low.

 Thus, the central point of the proposed design is the implementation in it of a special multipath system.

The meaning of this feature can be explained as follows:
A characteristic feature of the proposed design, which fundamentally differs from [3], is the presence of a plurality N of individual passage channels within a single drift pipe located in several layers on concentric circles relative to the drift pipe. Each channel has its own separate electron beam. Thus, in contrast to the single-beam prototype, the fundamental physical limitation associated with the strong and harmful influence of the intrinsic space charge of a high-output low-voltage beam is eliminated.

 Separate electron beams with relatively low current and low current are easier to focus, easier to control in the input cavity, and more efficiently transfer their energy to the high-frequency field in the output cavity. The microwave power in the output cavity is formed by summing the powers given to the field by many low-current beams.

We found that the diameter of a single drift tube, within which N individual channels are located, is limited by the value at which the change in the electric field along the cavity radius does not exceed 10%. This condition is satisfied when the relation
D / λ <0.5.
In this case, an equally high efficiency of interaction of electrons and a high-frequency field is achieved for all individual electron beams.

The restriction in the direction of reducing the diameter of the pipe
D / λ> 0.1
due to a sharp increase in current density in individual electron beams with a decrease in the diameter of the drift tube.

 The proposed technical solution, which we called "Istron", can be illustrated by a drawing, which schematically shows a section of the device. Here are indicated: 1 — cathode assembly, 2 — individual emitting surface forming a separate electron beam, 3 — grid holder, 4 — individual grid, 5 — cathode-grid gap, 6 — anode, 7 — parts of the drift tube, 8 — individual channel for a separate electron beam, 9 — input resonator, 10 — high-frequency gap of the output active resonator, 11 — output active resonator, 12 — passive output resonator, 13 — communication device, 14 — energy output, 15 — blocking capacitors, 16 — focusing electromagnets, 17 - collector.

Istron works as follows:
The high-frequency voltage between the cathode 1 and the grids 4 located on the holder of the grids 3, determined by the parameters of the input resonator 9 and the input signal, as well as a constant grid voltage (bias voltage) and the voltage of the anode 6 provide for the formation in the cathode-grid space 5 periodic with the frequency of the input signal the sequence of electron bunches is similar to what happens in triodes and tetrodes operating in class "B" or "AB". Further, these electron bunches are accelerated by the anode voltage in the space between the grid 4 and the anode 6, pass through the individual passage channels 8 of the first part of the drift tube 7 and reach the working gap 10 of the active output resonator 11, where they give their kinetic energy to the high-frequency electric field of the output resonator system, consisting of resonators 11, 12 and device 13, providing amplification of the input signal. Then, having passed the second part of the drift tube 7, the spent multipath electron beam falls into the collector 17 common to all beams and is scattered in it. Blocking capacitors 15 isolate the outer casing of the input resonator 9 by a high constant voltage and at the same time ensure the closure of high-frequency currents in the presence of isolation of the cathode and grid parts of the input resonator 9. The output coupled system of resonators, consisting of an active resonator 11, a passive resonator 12, and a communication device between them 13 , provides an instantaneous frequency band of 9 - 14 MHz at each frequency of the operating range of 470 - 860 MHz. The electron beams are focused by a magnetic field created by electromagnets 16. To increase the efficiency, the collector can be made in the form of several steps, to which voltages are applied, which provide multi-stage energy recovery of the spent electrons.

 During experimental testing, a number of samples were made that differed in the requirements of the output parameters and, therefore, were made with a different arrangement and number of beams. The test results are shown in the table.

 The bottom row of the table shows the data from Eimac-Varian advertising for single-beam devices with similar parameters. The comparison is clearly in favor of our device.

 Thus, the Istron turned out to be a fully feasible operable microwave device, comparing favorably with known devices of the same type in terms of control voltages and gain. And due to the lower temperature of the grid, it also has greater operational reliability.

Sources of information taken into account when preparing the application:
1. AV Haeff, Electronics, p. 30 - 32, Feb. 1939.

 2. RF patent N 2084042, cl. HOIJ 25/02, 1994.

 3. US patent N 4480210, CL. 315-4, 1984 (prototype).

Claims (3)

1. Microwave vacuum device, including a cathode and a control grid, anode and drift tube, through which an electronic stream is passed in operating mode, a single-gap input active output resonator, an external passive output resonator, forming a chain of coupled resonators with an active output resonator, and a collector that differs the fact that the cathode is made in the form of a set of separate emitting surfaces forming individual electron beams; the grid is made in the form of a set of separate control grids, each of which is placed above its emitting surface, and all together they are mounted on a single metal grid holder; drift pipe is made in compliance with the ratio
0.1 ≤ D / λ ≤ 0.5,
where D is the diameter of the drift pipe;
λ is the wavelength of the short-wave end of the operating wavelength range,
and contains a set of individual longitudinal channels intended for the passage of individual electron beams parallel to the axial axis of the device, and the centers of the channels and the emitting surfaces and grids corresponding to these channels are located on more than one concentric circle. 2. Microwave vacuum device according to claim 1, characterized in that the total number of individual electron beams
N = 1 + 3n (n + 1),
where n is the given number of circles. 3. Microwave vacuum device according to claim 1, characterized in that the total number of individual electron beams
N = 3n (n + 1),
where n is the given number of circles.

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