Fundamentals of Microwave Electronics

271 Pages·1963·13.355 MB·English

by  V. N. Shevchik and W. A. Gambling (Auth.)

OTHER TITLES IN THE SERIES
(FORMERLY PERGAMON SCIENCE SERIES ELECTRONICS AND WAVES)
Vol. 1 Signal, Noise and Resolution in Nuclear Counter Amplifiers
by A. B. GTTJ.ESPIE
Vol. 2 Scintillation Counters
by J. B. BIKES
Vol. 3 Probability and Information Theory with Applications to Radar
by P. M. WOODWARD
Vol. 4 Physics and Applications of Secondary Electron Emission
by H. BRUTNING
Vol. 5 Millimicrosecond Pulse Techniques (2nd edition)
by I. A. D. LEWIS and F. H. WELLS
Vol. 6 Introduction to Electronic Analogue Computers
by C. A. A. WASS
Vol. 7 Scattering and Diffraction of Radio Waves
by J. R. MENTZER
Vol. 8 Space-Charge Waves and Slow Electromagnetic Waves
by A. H. W. BECK
Vol. 9 Statistical Theory of Signal Detection
by C W. HELSTROM
Vol. 10 Laplace Transforms for Electronic Engineers
by J. G. HOLBROOE
Vol. 11 Frequency Modulation Theory—Application to Microwave Links
by J. FAGOT and Ph. MAGNE
Vol. 12 Theory of Microwave Valves
by S. D. GVOZDOVER
Vol. 13 Electronic Computers
by A. I. KIROV and N. A. KRINITSKII
Vol. 14 Topics in Engineering Logic
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Vol. 15 Environmental Testing Techniques
by G. W. A. DUMMER and N. B. GRIFFIN
V. N. SHEVCHIK
FUNDAMENTALS
of
MICROWAVE ELECTRONICS
Translated by
L. A. THOMPSON
Translation edited by
W. A. GAMBLING
UNIVERSITY OF SOUTHAMPTON
PERGAMON PRESS
OXFORD ' LONDON · NEW YORK · PARIS
1963
PERGAMON PRESS LTD.
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Distributed in the Western Hemisphere by
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Copyright © 1963
PEBOAMON PRESS LTD.
This is a translation from the original Russian
Osnovy elskironiki sverkhvysokikh chastot
published in 1969 by Izdatel'stvo "Sovetskoye Radio", Moscow
Library of Congress Card Number 62-9188
MADE IN GREAT BRITAIN
FOREWORD TO THE ENGLISH EDITION
PBOBABLY in no other field of scientific knowledge is the extremely
rapid progress being made by science better exemplified than in the
development of electronic devices. Progress in the understanding of
fundamental processes and in the evolution of new devices has been
very rapid since the initial impetus given to the work by the wartime
requirements for electronics. It has been aided, particularly in the
United States, by the emergence and establishment of electronics, or
light electrical engineering as it is sometimes called, as a distinct and
separate academic subject. Specific departments in Universities and
Technical Institutes have been set up to devote their attention to the
newly-recognized branch of science, and thus electronics, which pre-
viously had fallen between the two stools of physics and electrical
engineering, has flourished rapidly. In Britain, general recognition of
electronics as a distinct major subject has been slow to arrive, and
it is only within the last few years that some Universities have estab-
lished departments for its· study. This lag in academic studies is
apparent, particularly in the field of microwave electronics, by the
relatively small number of British contributions of a fundamental
nature since the end of the war. However, this state of affairs is
purely temporary and there are now definite signs that it is beginning
to disappear with the late, but steady growth of the academic study
of electronics in British Universities and research centres.
On the other hand, with the subject well established since the war
in the Universities, Research Institutes and industrial laboratories of
the United States a constant flow of new proposals and new achieve-
ments has continued to emanate from that country. Indeed, so rapid
is the progress of research and development that, in general, each
month the literature contains new contributions of a major nature
to the theory and application of electronic devices, and records
many minor advances and improvements in existing theories and
techniques.
In this volume devoted to microwave electronics, the author, V. N.
Shevchik, has given a detailed account of the subject up to 1957 and
a number of most important advances which have occurred within the
last four years are not recorded. Although very recent, these are of
such significance and are already so well established that this text-
xi
xili FOREWORD TO THE ENGLISH EDITION
book would be deficient without a general account of them to bring
the reader up to date in this rapidly developing field.
Whereas prior to about 1957 microwave electronics consisted al-
most entirely of the study of the interaction of electron beams with
microwave fields, most of the? new developments involve the use of
solid-state devices. These are included ?n the following review though
V. N. Shevchik has not discussed solid-state devices in his book
due, doubtless, to their relative unimportance at the time of writing.
Much of what follows took place in the period 1957-1958, which
w as a truly remarkable year of progress in the evolution of new electronic
devices and in the development of existing ones. So much new
material was published in the three years 1957,1958 and 1959 that to
attempt more than a review of the basic principles of the devices con-
cerned would be beyond the scope of a Foreword. Details of the work
may be obtained in the selected papers listed in the bibliography.
The trend of advances during the four years since 1957 has been
in two principal directions. Success, nothing less than spectacular, has
been achieved in the development of microwave amplifiers with very
low noise figures by the establishment in the microwave field of two
new types of amplifier which had been proposed only a few years
earlier. One employs the parametric principle whereby the energy
source for the amplified signal is not the d.c\ power supply of conven-
tional amplifiers, but a microwave source.The other, called the MASER,
employs the principle of the stimulated emission of radiation from
a solid or gas having energy levels separated by amounts equivalent
to the microwave frequency to be amplified. Energy is supplied by
a microwave source which establishes an abnormal, non-Boltzmann,
distribution between the permitted states and thus primes the system
so that the signal to be amplified initiates emission at the signal fre-
quency with an amplitude greater than the signal amplitude.
Important advances have also been made in utilizing techniques
to reduce the size and weight of existing microwave amplifiers and
oscillators without loss of performance. These include methods for
the electrostatic focusing of longitudinal beam devices, and improved
designs of lightweight, periodic-permanent-magnet focusing systems to
replace the heavy and bulky uniform-field magnetic focusing systems.
The cyclotron resonance oscillator, which employs no slow-wave circuit
and thus simplifies the design of very high frequency oscillators, has
made considerable progress, as also has the Piatinotron.
Let us consider first the remarkable success which has been achieved
in the field of low-noise microwave amplifiers In 1957 travelling-
wave tubes were the principal and best low-noise microwave amplifiers
FOREWORD TO THE ENGLISH EDITION xiii
in practical usé. Noise figures of 6 dB had been achieved at S-band
using large solenoids to focus the beam, and it was then believed that
the ultimate minimum in noise performance had been achieved. The
existing theory was in good agreement with experimental measure-
ments of noise figure, and no better noise figures were expected to be
obtained from travelling-wave tubes. Then came, in a practical form,
the Maser, which has reduced the achievable noise figure to a fraction
of a decibel corresponding typically to noise temperatures of some
5°K at 5650 Mc/s. The word MASER stands for Microwave Amplifica-
tion by Stimulated Emission of Radiation; similar devices operating
at infrared and visible light frequencies are known as IRASERS and
LASERS. This great advance gave very low noise performance at the
cost, to the application engineer, of providing liquid helium facilities,
and a microwave power source known as the "pump". This is not a
large price to pay for such excellent noise performance and modern
technological methods have already solved the engineering problems
associated with the requirement of a continuous» supply of liquid
helium.
The essential operation of the maser is briefly as follows. Consi-
der a system with three energy levels, E E and E in ascending
lf 2 3
order, such that the energy differences (E — E ) and (E — E ) cor-
3 x 3 2
respond to microwave frequencies and (E — E ) > (E — E ). Such
2 x 3 2
a system is found in a crystal of ruby at low temperatures. In thermal
equilibrium the population of molecules in each state follows a Boltz-
mann distribution, but if an electromagnetic field of frequency / ,
p
corresponding to (E — E ) is applied then the populations in states
3 t
E and E can be equalized. Under these conditions the population of
x 3
E will be greater than that of E and a weak signal at frequency / ,
3 2 s
corresponding to (E — E ), will induce more transitions from E to
3 2 3
E> than from E to E , so that the system can give a net emission of
2 3
radiation at f which can be made greater than the applied signal
s
at/ . Thus amplification occurs, and the mechanism is such that the
s
noise caused by spontaneous emission is extremely low, and the thermal
noise contribution is small because of the low temperature.
As a low-noise device the travelling-wave tube was overshadowed.
if not forgotten, and engineers were becoming resigned to accepting
and solving the problems associated with liquid helium temperatures
to achieve these remarkably low noise figures when the first micro-
wave PARAMETRIC AMPLIFIERS were announced.
These do not require operation at low temperatures, but like the
maser they utilize a microwave source to supply the energy required
for amplification. The noise figures attainable are not so extremely
Xiv FOREWORD TO THE ENGLISH EDITION
low as those of the maser, values of I to 3 dB being typical, but this
level of noise is really the minimum which can, in practice, be used in
most operational environments where the background noise is also of
this order. Only in selected sites and with carefully designed aerials
can amplifiers having noise temperatures of the order of 1° to 10°K
be utilized to full advantage. With these considerations in mind, most
application engineers welcomed the parametric amplifier and turned
their attention away from the maser which, however, still represents
the ultimate in low-ncise amplification,
The principle of parametric amplification is not new, but its adap-
tation to successful low-noise microwave amplifiers is very recent.
Various analogues may be used to illustrate the principle, of which
the most direct is that of the energy stored in a capacitor by an applied
a.c, signal. This is given by the expression y CV2, where C is the
2
capacitance and V the applied voltage. ïf C is varied at twice the
frequency of the signal in such a way that it is increased when F is a
maximum and decreased when V is zero, it is clear that the energy
stored may be increased and the increase will be provided by the
agency which varies C. Actually it is not essential for the frequency
of variation of C to be exactly twice that of F, nor for the above phase
condition to be true. Through a variation of the reactive parameter
£7, energy may be exchanged from one system to another and the
change may also be associated with a change of frequency giving fre-
quency conversion with gain. In the past, frequency conversion has
been carried out with valve or diode mixers, which are effectively non-
linear resistorse These are unable to store energy and the frequency
conversion is achieved with a loss, not a gain, of signal power. The
possibility of frequency conversion with gain represents a major ad-
vance in receiver techniques. The parametric principle allows gain with
frequency conversion only when the conversion is upwards in frequency ;
down-conversion with gain may be obtained using the tunnel diode,
a negative resistance device introduced by Esaki [40] in 1958.
The other useful analogue for the parametric amplifier is that of a
swinging pendulum whose bob is pushed inwards at each extremity
of the swing. The amplitude of the oscillation will build up and if this
represents the signal while the pushing force, at double the signal
frequency, represents the pump, we can see a similarity between this
model of the pendulum (which is also an energy storage device) and
the capacitor.
Parametric amplifiers and frequency convertors are of two princi-
pal types, the electron- beam type and the diode type. Of the electron-
beam parametric amplifiers outstanding success has been achieved by
PORBWOED TO THE ENGLISH EDITION xv
the transverse-wave version announced by Adler [17] in 1958. This
amplifier employs the fast space-charge wave mode of an electron
beam to carry the signal from the input coupler, through the amplifi-
cation region to the output coupler. The fast-wave mode, unlike the
slow space-charge wave mode used in conventional travelling-wave
tubes, is a positive a.c. energy carrier in the sense that the fast-wave
mode, electrons have a higher energy content than the average electron
energy of the beam. This means firstly, that to establish the fast-wave
mode, energy must be supplied to the beam, and secondly, that the
noise energy of this mode can be coupled off the beam. Now in the
Âdler amplifier the beam noise energy in the fast-wave mode, which
is excited by the random electron motion of the beam, is stripped off
by a coupler and at the same time the signal is fed on to the beam
in the fast-wave mode. Thus, the signal is impressed on the beam in
a mode which, in theory, carries no noise waves. The fast-wave mode
cannot be amplified by the same process as is used in travelling-wave
tubes as this is applicable only to the slow-wave mode and it is now
that the parametric process is used. The beam is immersed in a longi-
tudinal magnetic field of such a value that cyclotron resonance occurs
at the signal frequency, so that when the signal is applied through
a parallel plate CTJCCIA coupler the electrons take up a spiral trajec-
tory. The amplifying section is a four-plate quadrupole structure
coaxial with and surrounding the beam; the pump, at double the
signal frequency, is applied to these plates in such a way that the
spiralling electrons always experience an outward deflecting force as
they move round the axis. Thus the transverse excursion of the
electrons increases and amplification of the signal occurs in a manner
similar to the pendulum analogy. The amplified signal is coupled out
by a similar Cuccia coupler and, with the fast-wave noise mostly strip-
ped from the beam, the resultant noise figure of the amplifier is be-
tween 1 and 3 dB in practice.
Parametric amplifiers of the diode type use a semiconductor diode
the capacitance of which is governed largely by the depletion layer in
the semiconductor. The depth of the depletion layer may be varied
by varying the voltage across the diode and this variation may occur
at microwave frequencies. Thus, a microwave pump field is applied
to the diode which then behaves as a time-varying capacitance. The
signal is also applied to the diode and energy exchange giving signal
amplification occurs in the manner of the capacitor analogue. Noise
figures with devices of this type are typically in the range 1 to 3 dB
and a very large number of amplifiers based on this principle have
been successfully built and operated within the last three years.
xvi FOREWORD TO THE ENGLISH EDITION
With the advent of the maser and the parametric amplifier the
conventional traveliing-wave tube with a noise figure of some 6 dB
had been virtually discarded as a low-noise device. Events then took
a surprising turn when Dr. Currie [33] proposed in 1958 a new theory
for the noise performance of travelling-wave tubes which did not pre-
dict a minimum noise figure of 6 dB, but showed that the noise figure
could be reduced to a value approaching 0 dB. Currie designed a new
type of electron gun and with it travelling-wave tubes have now been
constructed with noise figures of less than 3 dB at S-band and 4 dB
at X-band. This work has brought the travelling-wave tube back to
the front rank of competitive low-noise amplifiers. It now has a noise
figure comparable with parametric amplifiers and it employs no micro-
wave pump nor does it require to operate at a low temperature. Its
frequency bandwidth of approximately an octave is considerably
greater than most present-day parametric amplifiers and masers.
The present situation in the low-noise amplifier field is that the
lowest noise temperatures are given by the maser, and in this respect it
has no proven competitor, while as more practical devices with ade-
quately-low noise performance the travelling-wave tube and the para-
metric amplifier are competitive. It has been predicted by Watkins
and Wade [39] that travelling-wave tubes of the future will achieve
noise figures of about 1% dB at 300 Mc/s, iV dB at 3000 Mc/s, 2 dB
2
at 10,000 Mc/s and 3 l/ dB at 50,000 Mc/s. With tins noise performance,
2
and with their inherently wide bandwidths and simple power supply
requirements, it is clear that travelling-wave tubes will be extremely
valuable devices for most modern applications. It remains to be seen
how they will compare with parametric amplifiers as practical com-
ponents for use in systems.
In 1958, the Annus Mirabilis of the low-noise amplifier, yet another
important new device was introduced. This is now called the TUNNEL
DIODE and it was first described by Dr. Esaki [40] who discovered
that a large increase in the normal impurity concentration in semi-
conductor diodes causes a significant change in their energy-band
distribution and performance. The current-vol tage characteristic of
the tunnel diode is similar to that of a tetrode in that it has a region
of reverse slope corresponding to a negative resistance. Just as the
negative resistance of the tetrode was used in the dynatron oscillator
the same property of the tunnel diode can be used to make microwave
oscillators and amplifiers. The negative-resistance effect is due to
the tunnelling of charge carriers through a thin potential barrier, and
unfortunately classical physics cannot explain this phenomenon nor
can it help us to understand it by analogy. The quantum-mechanical
FOREWORD TO THE ENGLISH EDITION xv ii
concept of the nature of an electron is not as a discrete particle, but
as a centre of waves of probability having the greatest density at the
centre and a diminishing density radially outwards. If a number of
such charge carriers are on one side of a thin potential barrier which
they have insufficient energy to surmount, the probability waves will
extend through it and give a finite probability of there being some
charge carriers on the other side. As these charge carriers cannot have
surmounted the barrier they may be regarded as having tunnelled
through it due to its extreme thinness. This phenomenon, by a process
which we will not discuss in detail here, but refer to the bibliography,
gives rise to the negative-resistance characteristic. Tunnel-diode ampli-
fiers do not, at present, give promise of extremely low noise figures
as the negative-resistance region of the characteristic has an associated
high standing current that contributes an appreciable amount
of shot-noise. Typical noise figures are 3 dB at 300 Mc/s and 6 dB
at 3000 Mc/s, however one must remember that amplification is ob-
tained at these low noise figures from an extremely small, simple and
rugged device requiring no microwave pump, no liquid helium facili-
ties and no d.c. power supply in the conventional sense. With these
characteristics it is ideally suited for use in satellites where space and
power are at a premium and ruggedness is very important.
The tunnel diode has one other important characteristic which has
already been mentioned. It can be used as a frequency convertor and
the conversion, which may be from a high to a low frequency, is
accompanied by gain. As indicated above, conventional mixers give
frequency conversion through their behaviour as variable-resistance
devices. The local oscillator sweeps the operating point through a non-
linear part of the current-voltage characteristic and the mixer behaves
as a variable, non-linear resistance. The local oscillator and signal
frequencies beat together to give sum and difference components which
constitute the frequency-converted signal. A loss of signal power is
associated with this conversion process. The tunnel diode can be made
to behave as a variable, negative, non-linear resistance, and frequency
conversion in this case has an associated gain of signal power. Energy
for the amplification is supplied from the local oscillator and the energy
exchange is made possible by the negative-resistance characteristic.
Conversion gains of some 20 dB have been achieved and it is most
likely that this property of tunnel diodes will grow in importance.
The past four years have produced new and interesting proposals
for low-noise amplifiers which are as yet unproven and this review
would be incomplete without a discussion of the more interesting of
them.