Electric lamp and discharge devices: systems – Cathode ray tube circuits – Combined cathode ray tube and circuit element structure
Patent
1990-09-13
1992-11-17
LaRoche, Eugene R.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Combined cathode ray tube and circuit element structure
315 5310, 331 79, 330 44, H01J 252, H03B 901
Patent
active
051646340
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an amplifier device for microwave frequencies and to an oscillator obtained from the amplifier device.
In order to generate and amplify microwaves, it is known to use in particular so-called velocity modulation electronic tubes. This type of tube comprises an electron gun, supplying an electron beam. The electrons of the beam undergo a periodic velocity modulation which causes their grouping into packets in certain zones of space. These packets then excite by impulse, according to their characteristic period, the oscillations of a microwave circuit (resonant cavity or line) by taking the energy necessary from their own kinetic energy.
In the electron beams of such tubes, the effects of the space charge are very large. In particular it is these which fix, for given voltages, a maximum value for the current which can be produced by the electron gun, or which can be carried in a given space, for an assembly of electrodes of given geometry. In the tubes of the type mentioned above, in order to obtain satisfactory results for gain, efficiency and signal quality, it is found necessary to limit the current carried by the electron beam to an intensity at least one order of magnitude less than the maximum intensity. Consequently, and considering the very principle of velocity modulation, these tubes must use long beams, usually requiring magnetic focussing; these generators are therefore heavy and bulky.
Devices are also known which are called vircators which, unlike the previous tubes, take advantage of the space charge effects. In a vircator there is injected, into a space, a current of electrons, usually equal to several times the maximum current which could actually pass through this space. There is therefore an accumulation of electrons which form a virtual cathode. This virtual cathode is unstable, i.e. it oscillates in space thus creating electromagnetic fields. With such a device, it is possible to obtain high microwave powers and to obtain this in a reduced volume. However, it is noted that the emitted signal is of mediocre quality, i.e. the power is emitted in numerous modes in a sequence of simultaneous or successive frequencies, and the applications of these types of signal are rather limited. Furthermore, the conversion efficiency is poor (in the order of 2 to 3% at best) with respect to the efficiency which can be obtained with velocity modulation tubes (often greater than 40%).
The subject of the present invention is a device intended to produce microwave energy from an electron beam, which overcomes the previous limitations, i.e. a conversion efficiency of the energy of the electron beam into microwave energy and a quality of the emitted signal comparable to those of velocity modulation tubes, having a weight and a volume comparable with those of vircators.
For this purpose, the device according to the invention comprises: current which it carries is slightly less than the maximum current capable of being carried in the generator; of an alternating voltage whose amplitude is sufficient for triggering, during one of its alternations, the formation of a virtual cathode no longer allowing the passage of electrons, the current transported by the beam thus being modulated at the so-called modulation frequency of the alternating voltage; modulation frequency, or a multiple or sub-multiple of the latter, this output circuit being excited by the previous modulated current.
Other objects, features and results of the invention will emerge from the following description, given by way of non-limitative example and illustrated by the appended drawings in which:
FIG. 1 shows a first embodiment of the device according to the invention;
FIG. 2 shows a second embodiment of the device according to the invention in which it comprises means conferring a post-acceleration on the electron beam;
FIG. 3 shows a third embodiment of the device according to the invention, in which the electron beam used is a full cylindrical beam.
In these various figures, the same references relate to the sam
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1988 IEEE International Conference on Plasma Science, 6-8 Jun. 1988, Seattle, Washington, Conference Record--Abstracts, IEEE, (New York, U.S.).
D. Price, et al.: "Mode and Phase Locking of a cavity vircator by injected microwave power from a relativistic magnetron", voir p. 114.
SPIE vol. 873 Microwave and Particle Beam Sources and Propagation (1988), "Relativistic klystron amplifier", pp. 92-103, Friedman et al.
Brasile Jean-Pierre
Convert Guy
"Thomson-CSF"
LaRoche Eugene R.
Lee Benny T.
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