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"ÆÓÐÍÀË ÐÀÄÈÎÝËÅÊÒÐÎÍÈÊÈ" "JOURNAL OF RADIOELECTRONICS" N 10, 1999 |
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Cyclotron Wave Electrostatic Amplifier
Hiroshi
Matsumoto, Naoki
Shinohara
Radio Atmospheric Science
Center, Kyoto University, Japan
Physics principles of a new type of microwave input amplifiers are described. Cyclotron wave electrostatic amplifier (CWESA) has a low noise level, broad band, switchable gain, super high self-protection against microwave overloads, rapid recovery and small DC consumption. CWESAs are widely used in Russian pulse Doppler radars and other systems.
1. INTRODUCTION
Development of modern microwave communication, radio, radar and Microwave Power Transmission Systems (MPTS) facilities places additional stringent requirements upon the microwave input amplifiers.
Together with improving the sensitivity of the input amplifier and reducing its intrinsic noises, the problems put to the forefront include the improving of the linearity of amplitude and phase-frequency characteristics over a wide dynamic range and stability to powerful pulsed and continuous overloads in the input signal level, the protection of subsequent receiver stages in case of such overloads and the reduction of the time needed for restoration of the serviceability after overloads.
Realization of such requirements on the basis of solid-state microwave amplifiers is a rather complicated problem, which necessitates the creation of special efficient and high-speed devices for protection of the input amplifiers and subsequent receiver stages.
In Russia active work is being carried on to create input microwave amplifiers (practically unknown today in the West) based on cyclotron waves -- Cyclotron Wave Parametric Amplifiers (CWPA) [1-4] and Cyclotron Wave Electrostatic Amplifiers (CWESA) [5-9] complying with the present-day requirements [10-39].
The operation of these devices is based on the principles of transverse grouping of the electron beam in the longitudinal magnetic field. In contrast to conventional longitudinal grouping of electrons into dense bunches, this principle employs the Lorenz force as an elastic force and leads to spatial distortion of the electric beam without electron bunches being formed (Fig. 1).
In this way it is possible to considerably overcome the fundamental restrictions which are characteristic of longitudinal grouping devices (both vacuum and solid-state ones) and are associated with non-linear influence of the space charge fields upon the process of the input signal amplification, thereby laying the basis for developing new input amplifiers with improved characteristics.
The oldest Russian microwave organization (The ISTOK State Research & Production Corporation) and Moscow State University are currently developing input amplifiers based on using cyclotron waves -- Cyclotron Wave Electrostatic Amplifiers (CWESA).
The CWESA has an unique
complex of characteristics: a low level of intrinsic noises (100-200 K and
lower), a remarkable linearity of the amplitude and phase-frequency
characteristics over a wide dynamic range (
W
and higher), a capability of sustain high overloads in the input signal (up to
200-500kW in the pulse), a highly efficient protection of subsequent receiver
cascades under overloads (60-120dB), a short time needed for restoration after
overloads (2-20ns), which explain its wide application in various communication,
radar and navigation systems.
The capability of CWESA to operate without any additional protection when it is connected directly to the receiving-transmitting antenna may be especially useful when employed in cases, where a great number of microwave systems are deployed and hence powerful overloads in the signal channel may arise.
GENERAL CWESA DESCRIPTION
2.1 The Principle of Operation of CWESA
The principle of operation of CWESA and the main elements of its structure are illustrated in Fig. 2.
forms a circular or
ribbon electron beam (150-300 
, 10-50V) passing through the series of the
input coupler (the input resonator), the region of electrostatic gain and the
output coupler (the output resonator) to the collector.
contains the
adiabatically decreasing magnetic field making it possible to reduce the
equivalent noise temperature 
of the fast (1+) and slow (1-) cyclotron waves [5]:
,
(1)
where 
is the cathode temperature.
In the CWESA construction this is realized with the help of specially designed thermo-cathodes which allow an additional magnet (see Fig. 2) to be placed near the emitting surface of the electron gun cathode.
The focusing magnetic
system creates an uniform longitudinal magnetic field 
corresponding to the resonance value of the cyclotron frequency in these regions
is the charge-to-electron mass ratio
i.e. in the input resonator, in the amplification region and in the output
resonator.
provides an efficient interaction of the electron beam with the uniform transverse electric field in the gap between the resonator pads. When the cyclotron resonance conditions are realized, the efficient energy exchange with the electron beam can take place [1,4]. Under the action of the transverse electric field there appear cyclotron rotations of the electrons in the electron beam, to be exact, a fast cyclotron wave is excited, whose amplitude is proportional to the input signal level. At the same time noises of the fast cyclotron wave within the operating frequency band can be removed (extracted) almost completely from the electron beam into the external load.
of the CWESA contains a
plane periodic structure (Fig. 2, Fig. 4) connected with the dc sources 
,
and creating a spatial periodic electrostatic field in the interaction channel.
Such plane periodic electric field contains a quadruple component spatially
twisted along the z-axis. The electrons moving along such a system are now
affected by the electric field alternating in time, and if the frequency of such
a field is close to the double cyclotron frequency:
(2)
(
is the longitudinal velocity of the electrons in the amplification region
created by the “synchronism” potential
, 
is the periodic structure lag) the resonance interaction takes place and the
tangential force of such quadruple component of the field will accelerate or
decelerate cyclotron rotation of each electron in dependence on its initial
phase. The amplitudes of both the fast and slow cyclotron waves will be
increased.
The gain of the CWESA
can vary in a wide range as the “amplification” potential
varies.
The essential feature of signal amplification in the CWESA is the active coupling between the fast and slow cyclotron waves. Noises of the slow cyclotron wave are practically not removed from the beam in the input coupler and, due to the active coupling with the fast cyclotron wave, are transferred into this wave and are therefore present at the amplifier output. Thus, to realize a low level of intrinsic noises in the CWESA it is necessary to take additional steps to reduce noises of the slow cyclotron wave in the electron beam, i.e. in the drift region with the divergent magnetic field (Fig. 2).
is used to extract the fast cyclotron wave energy from the electron beam.
2.2 Main Advantages of CWESA
Operation of Cyclotron Wave Electrostatic Amplifiers is based on an essentially different method of grouping of the electron beam. Due to this fact, the CWESA possesses a unique combination of advantages of highly sensitive input amplifiers with improved linearity of the amplitude-phase characteristics with the ability to sustain considerable overloads in the input signal and protect the subsequent receiver stages.
Let us consider in brief some fundamental advantages of CWESA:
An additional magnet
placed in the near cathode surface allows the CWESA noise level to be reduced
considerably. As a result the CWESA noise factor 
is determined mainly by the cathode temperature 
and the ratio of the magnetic fields 
and 
:
(3)
where
is the cathode temperature on Kelvin’s scale, 
.
At 
and 
,
the CWESA noise factor does not exceed 0.8-1.2 dB.
The principle of transverse grouping of the electron beam imposes no physical restrictions on the amplitude of the signal carried by the fast cyclotron wave. Therefore the output amplitude characteristic of CWESA has a perfect linearity throughout the dynamic range.
The amplitude of the signal carried by the fast cyclotron wave is directly proportional to the radius of cyclotron rotation of the electron beam. Therefore the CWESA dynamic range is limited by the value of the input signal which causes the electron beam to deposit on the output resonator pads, i.e. when the double radius of cyclotron rotation of the electrons (plus the electron beam cross-section diameter) becomes greater than the gap between the output resonator bars.
The typical level of
the maximum input signal of CWESA (at linear amplification) reaches 
(may be done up to 
by additional device development and/or voltage control).
The Lorenz force used as an elastic force in transverse grouping of the electron beam in CWESA is always proportional to the amplitude of the signal at the fast cyclotron wave. Moreover, phase velocities of cyclotron waves are determined by the external parameters only (the value of the focusing magnetic field, the accelerating potential) and are independent of the internal parameters of the beams (the reduced plasma frequency, transverse dimensions, etc.). In addition, the amplification principle of CWESA is independent of the operation frequency.
Ultimately, all these factors lead to an improved linearity of the phase-frequency characteristics of CWESA.
When a powerful input signal (for example, that of an active or passive disturbance) impinges on the CWESA input, the amplitude of the fast cyclotron wave and, hence, the electron rotation radius increases so rapidly that the electron beam is absent in the second resonator (see Fig. 5).
In this case the electron beam will be totally intercepted by the input resonator pads and will change (increase) the value of VSWR (from 1.05-1.2 up to 20-30 and higher, see Fig. 9 also). Thus, the power input signal will be reflected from the CWESA input and will not damage the amplifier. In this case the electron beam does not enter the input resonator, which provides a reliable protection of the subsequent receiver stages against high power overloads in the input signal levels.
The electron beam interception by the resonator pads is not dangerous also owing low values of the beam current and the accelerating voltage (usually about 150-300m A and not higher than 50V). On removing the overload, the serviceability of CWESA is restored in a short period of time (usually 2-20 ns).
This unique property of CWESA allows the applications of this device without any additional protection when it is directly connected to the receiving-transmitting antenna circuits of radar and radio-navigation systems.
2.3 Structure and Typical Parameters of CWESA
One of CWESA versions is shown in Fig. 6. CWESA has a compact magnetic system based on Sa-Co permanent magnets. The input signal enters the CWESA through the waveguide flange, which is directly connected with the receiving-transmitting antenna circuit. The input waveguide section is calculated for the transmitter power level.
Typical parameters of CWESA are summarized in the following table:
Frequency range, GHz.
0.7-11
Operation frequency
range, %
5-10
Noise factor, dB
0.8-4 *
Gain, dB
20-25
Dynamic range (input
signal), m W
10 **
Amplitude-phase noise
at the frequency 1 kHz,
dB/Hz
< -120
Third order
intercept point, dBm
18-20
Allowed input microwave
power level
pulsed, kW
up to
200-500
average, kW
up to
2-5
Protection of
subsequent stages, dB
60-120
Leakage power peak,
mW
< 0.1
Restoration time after
microwave
overload, ns
2-20 ***
DC power
consumption, W
1-2,5
Weight, kg
2-5
__________________________
*) Depends on operational frequency.
**) Additionally: +20 dB of dynamic
range extension by
CWESA voltage control.
***) Depends on input impact pulse intensity and its form.
Fig. 7-10 illustrate the main characteristics of CWESA in graphics form.
Equivalent nose
temperature 
as a function of operational frequency is shown in Fig. 7.
Fig. 8 illustrates the third-order intercept point, i.e. degree of linearity of amplitude-frequency characteristics.
Voltage Standing Wave Ratio of the
input of the CWESA is very low at the small signals (amplification regime) and
became very high when the beam is intercepted by input resonator bars at high
level of input signal (protection regime) - Fig. 9.
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The time dependence of the protection regime is shown in Fig. 10. Only a few percents of impact pulse power are accepted by input cavity. No electron beam in the output cavity and saturation (isolation) may reach -120 dB or even more.
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Fig. 10 Diagram illustrating the
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The level of the leakage power peak is restricted by the gaps of input and output resonator bars and does not exceed 1 mW in principle. The restoration time (up to full sensitivity) is 10-20 ns or less.
3. CONCLUSION
CWESA is one of the results of long-term academical and industrial research of Russia in the field of non-traditional microwave electronics based on electron beam transverse waves using [33, 36-39].
CWESA are designed for use as input amplifiers of super high quality radars, navigation communication systems. The CWESA possesses the properties and functions of a low noise and broad band input amplifier with switchable gain and a high degree of linearity and those of a self-protecting device with very small leakage spikes and rapid recovery after powerful microwave overloads.
4. APPENDIX
Cyclotron Wave Protectors (CWP)
If a powerful microwave signal (disturbance interference) impinges on the CWP input, the electron beam is deposited on the input resonator pads. As a result of mismatch between the resonator and the input stage this signal is reflected from the resonator and The unique self-protecting property of CWESA and its capability of protecting of subsequent receiver stages against powerful microwave overloads can be used to design on the basis of CWESA some simple special protective devices - Cyclotron Wave Protectors (CWP), whose principle of operation (protection) is illustrated in Fig. 11. When a powerful microwave signal (disturbance interference) impinges on the CWP input, the electron beam is deposited on the input resonator pads. As a result of mismatch between the resonator and input stage this signal is reflected from the resonator and reradiated.
Since the diameters of the openings and of the drift channel between the CWP resonators can be small enough, and the connection by the electron beam can be disrupted, a powerful microwave signal does not enter the output resonator and, hence, does not appear at the output of the protecting device.
Cyclotron waves protectors are likely to become promising devices for application at the short-wave range of the cm-wave band and in the mm-wave band. Fig. 12 illustrates the CW Protectors developed recently by Istok Corp. at the frequencies of 9 and 35 GHz.
REFERENCES
[1] C.L.Cuccia, ‘The Electron Coupler - a Developmental Tube for Amplitude Modulation and Power Control at UHF,’ RCA Rev., vol.10, no. 2, p. 270, 1949.
[2] R.Adler, ‘Parametric Amplification of the Fast Electron Wave,’ Proc. IRE, vol. 46, no. 6, p. 1300, 1958.
[3] R.Adler, G.Hrbek and G.Wade, ‘A Low-Noise Electron-Beam Amplifier,’ Proc. of IRE, vol. 46, no. 10, p. 1756, 1958.
[4] C.L.Cuccia, ‘Parametric Amplification, Power Control and Frequency Multiplication at Microwave Frequencies Using Cyclotron-Frequency Devices,’ RCA Rev., vol. 21, no. 2, p. 228, 1960.
[5] R.Adler and G.Wade, ‘Beam Refrigeration by Means of Large Magnetic Fields,’ J. of Appl. Phys., vol. 31, no. 7, p. 1201, 1960.
[6] A.E.Siegman, ‘The DC-Pumped Quadrupole Amplifier - a Wave Analysis,’ Proc. of IRE, vol. 48, no. 10, p. 1750, 1960.
[7] W.H.Louisell, ‘Coupled Mode and Parametric Electronics,’ John Wiley & Sons, Inc., New York, London, 1960.
[8] V.Dubravec, ‘Wave Theory of Cuccia Couplers’, Arch. Elektr. Ubertrag., vol. 18, no. 10, p. 585, 1964 (in German).
[9] G.Hrbek and. R.Adler, ‘Low-Noise DC-Pumped Cyclotron-Wave Amplifier,’ Proc. of 5th In tern. Congress on Microwave Tubes (Paris, 1964), N.Y.-London, Acad. Press, p. 17, 1965.
[10] V.A.Vanke, L.P.Grigorenko and V.B.Magalinsky, ‘Investigation of Amplitude-Phase Characteristics of Quadrupole Region of Electron-Beam Parametric Amplifier,’ Radiotechnique & Electronics, vol. 10, no. 12, p. 2187, 1965 (in Russian).
[11] V.A.Vanke and V.B.Magalinsky, ‘Statistical Properties of Output Signal of Quasi-Degenerative Electron-Beam Parametric Amplifier,’ Radiotechnique & Electronics, vol. 11, no. 7, p. 1210, 1966 (in Russian).
[12] V.A.Vanke and V.B.Magalinsky, ‘On the Role of Space Charge at the Amplification of Intrinsic Noise Orbits in High-Frequency Quadrupole Field,’ Higher School Reports, Series Radiophysics, vol. 9, no. 5, p. 831, 1966 (in Russian).
[13] V.M.Lopukhin, V.B.Magalinsky, V.P.Martynov and A.S.Roshal, ‘Noises and Parametric Pheomena in Electron Beams,’ Nauka, Moscow, 1966 (in Russian).
[14] V.M.Lopukhin, and A.S.Roshal, ‘Electron-Beam Parametric Amplifiers,’ Sov. Radio, Moscow, 1968 (in Russian).
[15] V.A.Vanke and V.L.Savvin, ‘Shaping of Magnetic Field in Near-Cathode Region of Cyclotron-Wave Electrostatic Amplifier,’ Electron Technique, vol. Microwave Electronics, no. 12, p. 143, 1969 (in Russian).
[16] V.A.Vanke and V.L.Savvin, ‘Field Structure and Parameters Calculation of Quadrupole Spiral for Cyclotron-Wave Electrostatic Amplifier,’ Electron Technique, vol. Microwave Electronics, no. 12, p. 159, 1969 (in Russian).
[17] V.A.Vanke, V.M.Lopukhin and V.L.Savvin, ‘Super Low-Noise Cyclotron-Wave Amplifiers,’ Sov. Phys. Usp., vol. 99, N 4, p. 545, 1969 (in Russian).
[18] V.A.Vanke and V.L.Savvin, ‘To the Theory of Amplification Processes in Cyclotron-Wave Electrostatic Amplifier,’ Radiotechnique & Electronics, vol. 15, no. 11, p. 2317, 1970 (in Russian).
[19] V.A.Vanke and V.L.Savvin, ‘Transformation of Transverse Waves of an Electron Beam in Axially-Symmetric Fields,’ Radiotechnique & Electronics, vol. 15, no.11, p. 2408, 1970 (in Russian).
[20] V.A.Vanke, S.P.Kryukov and Yu.M.Timofeev, ‘On the Minimum Noise Level of Cyclotron-Wave Electrostatic Amplifier with Taped Electron Beam’, Higher School Reports, Series Radiophysics, vol. 14, no. 1, p. 142, 1971 (in Russian).
[21] A.S Bondarev and S.P.Kantyuk, ‘Influence of Electron Deceleration in the Beams with Finite Density on the Dynamic Range of Cyclotron-Wave Electrostatic Amplifiers,’ in ‘Design of New Types of UHF Amplifiers,’ Kiev Polytech. Inst. Ed., Kiev, 1971 (in Russian).
[22] V.A.Vanke and S.P.Kryukov, ‘Longitudinal Electron Velocity Spread and Gain Limitation in Cyclotron-Wave Electrostatic Amplifiers,’ Radiotechnique & Electronics, vol. 17, no. 10, p. 2230, 1972 (in Russian).
[23] Yu.N.Dudin and S.P.Kantyuk, ‘Analysis of Cyclotron-Wave Electrostatic Amplifiers with Flatly-Symmetric Periodic System,’ Electron Technique, vol. Microwave Electronics, no. 4, p. 126, 1973 (in Russian).
[24] V.A.Vanke and S.P.Kryukov, ‘Interaction of Cyclotron Waves of Multivelocity Electron Beam with Electrodynamics Systems,’ Higher School Reports, Series Radiophysics, vol. 16, no. 8, p. 1271, 1973 (in Russian).
[25] A.S Bondarev and S.P.Kantyuk, ‘Dynamic Dissynchronisation in Cyclotron-Wave Electrostatic Amplifiers with due Account of Space Charge Influence,’ Higher School Reports, Series Radioelectronics, vol. 116, no. 12, p. 30, 1973 (in Russian).
[26] A.S Bondarev and S.P.Kantyuk, ‘Sectionalised Cyclotron-Wave Electrostatic Amplifiers,’ Higher School Reports, Series Radioelectronics, vol. 19, no. 10, p. 74, 1976 (in Russian).
[27] V.A.Vanke, ‘Interaction of Transverse Oscillations and Waves in the Electron Beams and Electromagnetic Fields,’ Doctor of Sciences (Phys. & Math.) Thesis, Faculty of Physics, Moscow State University, Moscow, pp. 1-430, 1979 (in Russian).
[28] S.P.Kantyuk and V.B.Petrovsky, ‘Characteristics of Resonant Coupler with Fast Cyclotron Wave of an Electron Beam in the Non-Uniform Magnetic Field,’ Electron Technique, vol. Microwave Electronics, no. 8, p. 29, 1982 (in Russian).
[29] A.K.Balyko and V.B.Petrovsky, ‘Influence of Dismatched Load on the Bandwidth of Resonant Couplers,’ Electron Technique, vol. Microwave Electronics, no. 2, p. 64, 1988 (in Russian).
[30] Yu.A.Budzinsky and S.P.Kantyuk, ‘Cyclotron-Wave Electrostatic Amplifiers,’ Electron Technique, vol. Microwave Electronics, no. 1, p. 21, 1993 (in Russian).
[31] Yu.A.Budzinsky and S.P.Kantyuk, ‘A New Class of Self-Protecting Low-Noise Microwave Amplifiers,’ Proc. IEEE MTT-S Microwave Symposium, Atlanta, USA, Digest vol. 2, p. 1123, June 1993.
[32] S.V.Bykovsky and V.A.Vanke, ‘Transverse Waves of an Electron Beam in Flatly-Symmetric Fields,’ Radiotechnique & Electronics, vol. 38, no. 8, p. 1475, 1993 (in Russian).
[33] Yu.A.Budzinsky and S.V.Bykovsky, ‘Cyclotron-Wave Electrostatic Amplifiers - Main Parameters and Application Features’, Abstracts of the Conf. on Actual Problems of Electron Device Manufacturing, Saratov, Russia, p. 19, October 1994 (in Russian).
[34] Yu.A.Budzinsky and S.V.Bykovsky and A.A.Murskov, ‘Magnetic System of Electron-Vacuum UFH Device’, Russian Fed. Patent 2024098, Appl. 08.01.91, Bulletin of Inventions., no. 22, 1994 (in Russian).
[35] S.V.Bykovsky and V.A.Vanke, ‘Transverse Waves of an Electron Beam in the Quadrupole Electric Field,’ Radiotechnique & Electronics, vol. 40, no. 8, p. 1277, 1995 (in Russian).
[36] V.A.Vanke and V.L.Savvin, ‘On Some Microwave Physics Research at Moscow State University and Russian Industries,’ (Plenary Talk), 23rd IEEE Int. Conference on Plasma Science, Boston, June 3-5, 1996. Abstracts, pp. 62, 226.
[37] V.A.Vanke and V.L.Savvin, ‘CWESA-High Sensitive Input Amplifier with Super High Self Protection for Use in Radar and Communication System,’ Final Report, ONREUR Contract N68171-95-C-9145, September 1996.
[38] V.A.Vanke and V.L.Savvin, ‘Non-Traditional Microwaves Tubes Based on Electron Beam Cyclotron and Synchronous Waves Using. Status & Perspective,’ (Invited Presentation), ESA/NATO Workshop on TWTA, April 7-10, 1997, Noordwijk, Netherlands.
[39] V.A.Vanke, H. Matsumoto., N. Shinohara, ‘A New Microwave Input Amplifier with High Self-Protection and Rapid Recovery,’ IEICE Trans. on Electronics (Japan), vol. E81-C, pp. 788-794, 1998.
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