Radar Technology Encyclopedia (Artech House Radar Library)

519 Pages·1997·9.65 MB·English

by  David K. Barton

Radar Technology Encyclopedia
(Electronic Edition)
David K. Barton
Sergey A. Leonov
Editors
Artech House
Boston London
•.
iv
Library of Congress Cataloging-in-Publication Data
Barton, David K.
Radar technology encyclopedia / David K. Barton and Sergey A. Leonov, editors
Includes bibliographical rteferences and index
ISBN 0-89006-893-3
1. Radar—Encyclopedias. I. Barton, David Knox, 1927-.
II. Leonov, S. A. (Sergey Alexandovich).
TK6574.R34 1997
621.3848’03—dc21 96-52026
CIP
British Library Cataloguing in Publication Data
Radar technology encyclopedia
1 Radar- encyclopedias
I. Barton, David K. (David Knox) II. Leonov, Sergey A.
ISBN 0-89006-893-3
© 1998 ARTECH HOUSE, INC.
685 Canton Street
Norwood, MA 02062
All rights reserved. Produced in United States of America. No part of this book may be reproduced or
utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or
by any information storage and retrieval system, without permission in writing from the publisher.
All terms mentioned in this book that are known to be trademarks or service marks have been appro-
priately capitalized. Artech House cannot attest to the accuracy of this information. Use of a term in this
book should not be regarded as affecting the validity of any trademark or service mark.
International Standard Book Number: 0-89006-893-3
Library of Congress Catalog Card Number: 96-52026
v
Table of Contents
Contributors ix carcinotron 72 display, radar 139
About the Authors ix cathode-ray tube 72 distribution 146
Introduction xi cell, radar (resolution) 73 diversity 149
Use of Hypertext Links xii centroiding 73 divider 149
cepstrum 74 doppler effect 149
A chaff 74 drive 151
channel 74 duct, ducting 151
absorber, radar 1
chart 75 duplexer 151
absorption 5 chirp 76 duty factor 152
accuracy 5
choke, microwave 76 dynamic range 153
acquisition 7 circuit 76
adapter, microwave 8
circulator 77 E
algorithm 8 clipping 78
aliasing 10 eclipsing 153
clutter 78
altimeter, radar 10 coast 88 echo, radar 154
ambiguity 11 effective echoing area 154
coaxitron 88
ambiguity function 12 code, coding 88 electromagnetic compatibility 154
amplifier, microwave 15 coherence 90 (EMC)
amplitron 22 conductance 91 electronic counter- counter mea- 154
amplitude 22
confusion area 91 sures ECCM)
analyzer 22 connector, microwave 91 electronic countermeasures 156
anechoic chamber 22
conopulse 91 (ECM)
angel (echo) 23 constant false alarm rate 91
angle 23 electronic intelligence 161
contrast, radar 93 electronic (warfare) support mea- 162
antenna 25 control 93
aperture 40 sures (ESM)
conversion, converter 94
approximation 41 convolution 96 electronic warfare 162
array (antenna) 42 equalization 163
coordinates, radar 96
astronomy, radar 51 correlation function 97 equivalence principle 163
atmosphere 51 error, measurement 164
correlator 98
atmospherics 55 Cotton-Mouton effect 98 exciter 172
attenuation 55
coupler, directional 99
attenuator 58 coverage, radar 100 F
autocorrelator 59
crossed-field amplifier 101 fading 173
autodyne 59 crowbar 103 failure 173
availability 59
false alarm 173
axis 60
D fantastron 174
Faraday 175
B data, radar 104 feed, antenna 175
deception, radar 105
backscatter, backscattering 60 feedback 180
decibel 105
backward-wave tube 60 decoder 106 feeder [feed line] 180
band 61 fence 180
decorrelation 106
bandwidth 61 decoy, radar 106 ferrite 181
bang, main 62 field, electromagnetic 181
defruiter 106
baseband 62 delay 107 filter, filtering 182
baseline 62 fluctuation 197
delay line 107
beam, antenna 62 delta [Dirac] function 111 follower 197
bel 64 frequency 197
dematron 111
bimatron 64 demodulation 111 Friis transmission formula 203
bitermitron 64 “fruit” 203
demultiplexing 111
blanking, blanker 64 depolarization 111 function, random 203
blinking 64 fuze, radar 204
depth of focus 112
blip 65 designation 112
blocking 65 detectability factor 112 G
blooming 65 detection [of radar targets] 113 gain 204
Boltzmann’s constant 65
detector [demodulation, demodu- 125 garble 205
boresighting 65
lators[ gate, gating 205
Bragg 65
device, microwave 129 generator 206
bridge, microwave 65
diagram 132 ghost 207
burnthrough 67
Dicke fix 132 glint 207
buoy, radar 67
dielectric 133 goniometer 207
diffraction 133 “grass” 207
C diode, microwave 133 guidance, radar 207
calibration 67 diplex (mode) 137 gull 208
camouflage 68 dipole 137 Gunn effect 208
cancellation, canceler 68 direction finder, direction finding 137 gyrotron 208
capture effect 72 discrimination, discriminator 138
vi
refractivity 400
H N relay, radar 400
reliability, radar 400
height finder 209 navigation, radio 284 repair 400
heterodyning 210 navigator, doppler 285 resistance 401
hit 210 network 286 resolution 401
hole, radar 210 noise 286 resonator, microwave 404
hologram, holography, radar 210 nomenclature, radar 288 response 408
homing, radar 213 notcher 289 return loss 408
horizon, radar 213 nuclear effects 289 ring 408
Huygens’ source 213 nulling 290
hybrid (junction), microwave 213 Nyquist ‘ 290
S
O
I operator, radar 290 sample, sampling 408
scan, scanning 409
oscillation 290
illuminator 214 oscillator, microwave 291 scanner, antenna 411
image, imaging, radar 214 scatterer, scattering 414
impedance 216 scatterometer 415
inductance 217 P sea effect 416
information measure 217 parametric echo effect 296 searchlighting 416
integrated circuit 217 pattern, antenna 296 seeker, radar 416
integration, integrator 219 performance, radar 299 selectivity 418
intelligence, radar 223 permeability 299 sensitivity 418
interference 223 permittivity 300 sequence 418
interferometer, radar 223 phase 300 service, radar 419
interpolation 223 phase shifter 300 sextant, radar 420
interrogation, interrogator 224 phasor 304 shadow, radar 420
intrusion 224 platform 304 shift keying 420
ionosphere 224 platinotron 304 sidelobe 420
iris, matching 225 plumbing 304 sight, radar 421
Poincaré sphere 304 signal, radar 421
J polarization 304 signal processing, signal proces- 424
jaff 225 polarizer 307 sor
polyplexer 307 silence, radar 425
jammer, jamming 225
jitter 231 potential, radar 307 skiatron 425
power 307 slant-range effect 425
joint, microwave 232
Josephson effect 232 Poynting(’s) vector 310 slow-wave structure 425
precision 310 smoothing, data 426
preclassification 310 speckle 426
K principle 310 spectrometer, spectroscopy, radar 426
Kabanov effect 232 propagation, wave 310 spectrum 426
klystron 232 pulse 313 speed, blind 427
pulse compression 315 spoofing 427
L pulse repetition frquency (PRF) 318 squitter 427
pulser 319 stabilitron 427
lens 234 stability 427
likelihood 237
Q stealth 428
limiter 238 step function 428
line 240 Q(-factor) 320
strobe 428
load 240 Q-function 320 subsystem, radar 428
lobe 240 Quantization 320
local oscillator (LO) 241
superposition 428
loss, in radar 243 R
suppression 429
(running) rabbits 320 surveillance, radar 429
M radar 320 switch, switching 429
magnetron 258 radar applications and types 321 synchronizer 429
map 262 radar cross section 361 synthesizer 429
mapping 262 radargrammetry 370
mark, calibration 263 radiation 371 T
matrix 263 radiator, radiating elements, of 372
tapering 430
measurement, radar 264 antenna
target, radar 430
meteorology, radar 265 radiometer, radiometry, micro- 373
target recognition and identifica- 432
microphone effect 266 wave
missile, antiradiation 266 radome 374 tion
mixer 266 railing 376 temperature, noise 436
model 269 range 376 test, testing, radar 438
modulation 269 range equation 378 tetrode 439
modulator 271 range finder, ranging, radar 385 threshold 439
monopinch 274 receiver, reception, radar 387 throughput capability 439
monopulse 275 reciprocity 393 thyristor 440
moving target detector 278 reflection 393 time 440
moving target indication 279 reflectivity 395 tomography, microwave 441
multiport, microwave 283 reflectometer 396 track, trackers, tracking 441
multivibrator 283 reflector 396 tradeoff 445
trainer, radar 446
vii
transceiver 446 waveform, radar 472
transducer 446 U waveguide 478
transfer function 446 uncertainty 465 weighting 483
transform 446
transformer, microwave 449 V X
transistor, microwave 450
varactor 466
transmission line, microwave 452
transmissivity 456 varicap 466 Y
vaxitron 466
transmitter, radar 456
transponder 459 vegetation factor 466 Z
velocity 466
traveling-wave tube (TWT) 460 zone, radar 484
trigatron 462 velodyne 466
video 466
trigger (flip-flop) circuit 462 Alphabetical Bibliography 485
triode, microwave 462 visibility 467
Bibliography by Subject 503
troposphere 462 W Radar Abbreviations and Acro- 507
tube, microwave 463
nyms
twystron 465 wave, electromagnetic 468
ix
CONTRIBUTORS
Barton, David K., Vice President, ANRO Engineering (U.S.A.), contributed as editor and author.
Barton, William F., Consulting Engineer, PictureTel (U.S.A.), contributed as translator.
Hamilton, Paul C., Vice President, ANRO Engineering (U.S.A.), contributed as author.
Leonov, Alexander I., Professor, Moscow Institute of Technology (Russia), contributed as author.
Leonov, Sergey A., Senior Engineer, Raytheon Canada Limited (Canada), contributed as editor,
author, and translator.
Michelson, Max, Senior Research Scientist, ANRO Engineering (U.S.A.), contributed as translator.
Morozov, Illya A., Senior Research Scientist, Aerospace Research Institute (Russia), contributed as
author.
ABOUT THE AUTHORS
Mr. David K. Barton is a well-known radar expert, lecturer, coauthor (with K. I. Fomichev) of Monopulse Radar (Soviet-
and author of several fundamental radar books published in skoe Radio, 1970, 1984; trans. Artech House 1986), and
the United States, United Kingdom, Russia, China, and many coauthor and editor of Modeling in Radar (Sovietskoe Radio,
other countries. Mr. Barton has had a long career in radar, 1979) and Radar Test (Radio i Svyaz, 1990). He holds the
including service with the U.S. Army Signal Corp., RCA, academic rank of professor and “All-Russian Honorable” title
Raytheon, and currently as Vice President for Engineering in the field of science and engineering. His contribution to the
with ANRO Engineering, Inc. He is an author of Radar Sys- Encyclopedia is identified by the initials AIL following the
tems Analysis (Prentice-Hall, 1964; Artech House, 1976) article.
Modern Radar System Analysis (Artech House, 1988), coau-
thor (with H. R. Ward) of Handbook of Radar Measurement
Dr. Sergey A. Leonov is known in both Russia and the West
(Prentice-Hall, 1969; Artech House, 1984), with W. F. Barton
as a bilingual radar expert. He started his radar career work-
of Modern Radar System Analysis Software (Artech House,
ing for Russian space programs; later he designed and tested
1993), with C. E. Cook and P. C. Hamilton of Radar Evalua-
shipborne and spaceborne radars, headed a research labora-
tion Handbook (Artech House, 1991), and editor of Radars
tory in Moscow Aerospace Institute, and currently is with
(Artech House, 1975). Mr. Barton is an editor of Artech
Raytheon Canada Limited. He is an author of Air Defense
House Radar Library, and a Fellow of the IEEE. His contribu-
Radars (Voenizdat, 1988), coauthor (with A. I. Leonov) of
tion to the Encyclopedia is identified by the initials DKB fol-
Radar Test (Radio i Svyaz, 1990), and (with W. F. Barton) of
lowing the article.
the Russian-English and English-Russian Dictionary of
Radar and Electronics (Artech House, 1993). He holds the
Dr. Paul C. Hamilton is a leading expert on radar and sys- academic rank of associate professor, “All-Russian Honor-
tems design. He has much experience having served with the able” title in the field of science and engineering, and a Senior
U.S. Air Force, Hughes Aviation Co., and Raytheon and now Member of IEEE. His contribution to the Encyclopedia is
as Vice President for Radar Studies with ANRO Engineering, identified by the initials SAL following the article.
Inc. He is coauthor (with D. K. Barton and C. E. Cook) of the
Radar Evaluation Handbook (Artech House, 1991). His con-
Dr. Ilya A. Morozov is a leading Russian expert on radar and
tribution to the Encyclopedia is identified by the initials PCH
microwave technology. He has participated in a series of pro-
following the article.
grams involving design and test of Russian state-of-the-art
phased-array radars, and currently is a Senior Research Scien-
Dr. Alexander I. Leonov is well known in Russia as a scien- tist at the Moscow Aerospace Institute. Dr. Morozov is a
tist and engineer in the field of radar. For about 25 years he coauthor of a book Ships of National Control (Moskovskiy
was a senior member of teams that designed and tested state- Litsey, 1991), and Sophisticated Radio Systems Performance
of-the-art radars for Soviet ABM programs, and now he is a Estimation (Mashinostroenie, 1993). His contribution to the
professor at the Moscow Institute of Technology. He is an Encyclopedia is identified by the initials IAM following the
author of Radar in Anti-Missile Defense (Voenizdat, 1967), article.
xi
INTRODUCTION
The Radar Technology Encyclopedia is a joint product of and so forth.
leading United States and Russian radar experts with decades
of experience on design, development, and test of state-of- The subarticles are alphabetized without regard to
the-art radar systems and technology. The Encyclopedia cov- whether the qualifying adjective precedes or follows the main
ers the entire field of radar fundamentals, design, engineering, word: broadband antenna precedes antenna control.
systems, subsystems, and major components. It contains
Within each article and subarticle, if applicable, the
about 5000 entries, each giving the depicted term definition,
cross-reference to another subarticle is indicated in lower-
and, if applicable, the standard notation, brief description,
case bold, e.g.:
evaluation formulas, relevant block diagrams, performance
summary, and a reference to the literature in which the more “The RCS of this type of clutter is calculated using the
detailed information is available. The purpose is to provide, volume of the clutter cell V and the volume reflectiv-
c
in a single volume, the reference material for researchers and ity h (see volume clutter). “
v
engineers in radar and related disciplines, representing the
That subarticle is found alphabetically within the same top-
most modern information available in both the former Soviet
level article, e.g., CLUTTER. If the cross-reference refers to
Union and in the West. It includes an extensive bibliography
another top-level article, then the name of this article is given
of sources from both regions. This bibliography covers practi-
in capital letters. For example, a reader is referred to an article
cally all monographs and textbooks in radar and related sub-
NOISE, and will find that article alphabetically under N.
jects published after World War II in English (in the U.S.A.
and England) and Russian (in the former Soviet Union) lan- Parentheses in the name of an article or subarticle mean
guages that covers the overwhelming majority of the world- that the word is optional. For example, phased array
wide library of radar books. (antenna) means that the term is used both as phased array
or phased array antenna. Square brackets mean that the
The Encyclopedia format is alphabetical by subject. It
word in the brackets can be used instead of the previous one.
consists of top-level articles, which are identified with bold
For example, bed of spikes [nails] ambiguity function
capital letters (e.g., MAGNETRON), and, if applicable, are
means that the term is used as bed of spikes ambiguity func-
followed by subarticles, which are identified in lowercase
tion or bed of nails ambiguity function.
bold (e.g., rising-sun magnetron). The top-level articles are
arranged in the way so the key word (typically, a noun) deter- For definitions of terms, extensive use has been made of
mines its alphabetical position (e.g., microwave antenna is IEEE Standard Dictionary of Electrical and Electronics
cited as ANTENNA, microwave, radar targets as TARGET, Terms and IEEE Standard Radar Definitions. The standard
radar, data smoothing as SMOOTHING, data). Subarticles definitions reproduced from these dictionaries and other
within a top-level article are given in a conventional word acknowledged sources are put into quotes. The Encyclopedia
order typically used in literature and alphabetically arranged, does not contain separate articles with the description and
for example: performance of concrete radar stations and facilities, because
even brief description of the major radars developed through-
AMPLIFIER, microwave out the world requires to provide additional volume as thick
amplifier-attenuator as this one. This information is systematized in Jane’s Radar
amplifier chain and Electronic Warfare Systems, updated and issued annually,
aperiodic amplifier and the Encyclopedia does not duplicate this material. How-
backward-wave tube amplifier ever, where applicable, extensive examples of modern radars
balanced amplifier are provided.
bandpass amplifier
xii
Each article and subarticle contains references, primarily listed in the Alphabetical Bibliography, and for the readers
to textbooks, which are listed alphabetically by author in the interested in a full bibliography on a corresponding subject
Alphabetical Bibliography at the end of Encyclopedia. The the Bibliography by Subject is provided. It contains a full bib-
combination of the surname of the first author and a year of liography list of the identifiable radar and radar-related books
edition identifies the cited book: published during the last 50 years and is arranged in 35 sec-
Ref.: Skolnik (1980) tions by subject. Within each section the books are given in
chronological order, and alphabetically by author within one
refers to the book listed in the bibliography as:
year. At the end of Encyclopedia is a list of the most common
Skolnik, M. I., Introduction to Radar Systems, McGraw- radar abbreviations and acronyms.
Hill, 1980;
and the brief reference: The author of each article and subarticle is identified by
the corresponding initials following the entry, when that entry
Ref.: Barton (1969)
exceeds a few lines of definition (see About the Authors). The
identifies the book listed with both authors and two editions
original generation of the list of entries, compiling of the Bib-
or publishers:
liography, and final editing of Encyclopedia material was
Barton, D. K., and Ward, H. R., Handbook of Radar Mea- done by David K. Barton and Sergey A. Leonov.
surement, Prentice-Hall, 1969; Artech House, 1984.
In rare cases where there is no applicable textbook, reference David K. Barton and Sergey A. Leonov,
is made to a professional journal article. Typically, each arti- Editors
cle is followed by references to the major current books, as
Use of Hypertext Links
In this electronic edition of the Radar Technology Ency- text. Clicking on any blue entry initiates an immediate trans-
clopedia, hypertext links have been added to transfer rapidly fer to the related entry. The program keeps track of the history
from one article to a related or referenced subject. The words of these transfers, and the reader can retrace steps by clicking
or phrases from which links can be exercised appear in blue in either the right or left page margins.
ABSORBER, radar absorber, Dahlenbach 1
A conductivity of the deposition on the film. An example of a
pattern deposited on a CA sheet in shown in Fig. A1.
CA absorbers can be tuned, as with an RLC circuit,
ABSORBER, radar. The term absorber refers to a radar-
enabling the designer to improve the bandwidth of the multi-
absorbing structure or material (RAS or RAM), the purpose
sheet configuration. In general, CA absorber is a lossy ver-
of which is to soak up incident energy and reduce the energy
sion of a class of printed patterns known as frequency-
reflected back to the radar. Its main objective is to achieve
selective surfaces (FSS). SAL
reduction in the radar cross section (RCS) of radar targets.
Other applications are to suppress wall reflections in anechoic Ref.: Knott (1993) p. 326; Bhattacharyya (1991), pp. 215–217.
chambers and reflections from nearby structures at fixed
radar sites.
Absorbers can be classified from the point of view of
scattering phenomena as specular and nonspecular types, and
from the point of view of their bandwidth as narrowband
RAS and wideband RAS. The major representatives of nar-
rowband RAS are the Salisbury screen and the Dahlenbach
absorber. Wideband RAS are represented by m = e type
r r
absorbers, circuit analog absorbers, frequency-selective sur-
faces, geometric transition absorbers, Jaumann absorbers, and
graded absorbers. Some of these types can be combined to
form hybrid absorbers with improved performance. All these
types are specular absorbers designed to reduce specular
reflections from metallic surfaces. Nonspecular absorbers are
intended primarily for suppression of surface traveling-wave
echoes. SAL
Figure A1 Circuit analog absorbers (after Knott, 1993,
Absorbers for anechoic chambers are applied to the internal Fig.8.18, p. 326).
surfaces of an anechoic chamber to absorb the incident radio
A Dahlenbach absorber (Fig. A2) consists of a thick homo-
waves. The basic requirements are wideband performance
geneous lossy layer backed by a metallic plate. It is a simple
and low reflection coefficient.
narrowband absorber that is flexible and can be applied to dif-
Usually the absorber is a plastic foam frame with filler
ferent kinds of curved surfaces. It is characteristic of single-
that readily absorbs radio waves (microspheres of polysty-
rene, teflon, etc.), the density of the material and the concen- e , m
tration growing with depth. Radar-absorbing material is most
convenient in the form of pyramids with an angle of 30(cid:176) to
q
60(cid:176) at the apex, which assures multiple re-reflections that
increase absorption. To reduce the reflection coefficient to - q
20 dB, the height of the pyramids must be 0.5l to 0.6l , but to
reduce it to - 50 dB, a height of 7l to 10l is required. In this
L
case thinner structures are used, made, for example, from fer-
rite absorbing materials. IAM
Z = 0 Z = L
Ref.: Finkel'shteyn (1983), p. 145; Knott, 1993, pp. 528–532.
Chirosorb absorbing material is a novel RAM typically Figure A2 Dahlenbach absorber (after Bhattacharyya, 1991,
fabricated by embedding randomly oriented identical chiral Fig.4.65, p. 211).
microstructures (e.g., microhelices), in an isotropic host layer absorbers backed by metal plates that it is impossible to
medium. In comparison with conventional RAMs, it pos- achieve zero reflection because the layer material must be
sesses an excellent low-reflectivity property and may be prac- such that low reflection occurs on its front face, and using
tically invisible to radar. SAL physically realizable materials it is impossible to force reflec-
Ref.: Bhattacharyya (1991), p. 233. tion from both the front face and the metal backing to zero.
The main objective in this case is to choose electrical proper-
Circuit analog (CA) absorbers are sheets of low-loss mate-
ties of the layer to make two reflections to cancel each other.
rial on which specific conducting patterns have been depos-
Reflectivity curves for dominantly electrical and magnetic
ited. The patterns constitute resistance, inductance, and
layer materials are shown in Figs. A3 and A4, respectively.
capacitance. The deposited film can be represented by an
The optimum layer thickness in the first case is near a quarter
equivalent RLC circuit, parameters of which can be con-
wavelength, in the second case it is near a half wavelength.
trolled by the geometric configuration, film thickness, and
SAL
Ref.: Knott (1993), pp. 314–320; Bhattacharyya (1991), pp. 208–212.
2 absorber, dielectric absorber, geometric transition
A dielectric absorber uses dielectric absorbing materials for absorbing wall consisting of individual magnetic rods
its construction. An example of a simple, single-layer dielec- arranged vertically and horizontally. IAM
tric absorber is the Salisbury screen. In practical applications, Ref.: Stepanov (1968), p. 62; Bhattacharyya (1991), pp. 177, 217–218.
multilayer dielectric absorbers are used, such as Jaumann
Frequency-selective surface (FSS) types of absorbers usu-
absorbers and graded dielectric absorbers. Practical graded
ally take the form of a thin metallic patterns etched into or
dielectric absorbers are made of discrete layers with proper-
deposited onto lossless substrates or films. The desired effect
ties changing from layer to layer. SAL
is to pass waves of a given range of frequencies, or all waves
Ref.: Knott (1993), pp. 313–327.
except those in a required band (bandpass or bandstop filter-
ing). Other uses are high-pass or low-pass filtering. Some
configurations used in FSS are shown in Fig. A5. Frequency
selective surfaces find many practical applications: in antenna
reflectors, wave polarizers, RCS control, and so forth. The
Jaumann and circuit analog absorbers are versions of FSS.
SAL
Ref.: Bhattacharyya (1991), pp. 224, 228.
Figure A3 Reflectivity of dominantly electric materials. Solid (a) Rectangular slot (b) Circular slot,
trace: |e r| = 16, |m r| = 1, d e = 20(cid:176) , d m = 0(cid:176) ; dashed trace: |e r| = 25, circular hole (c) Annular slot
|m r| = 16, d e = 30(cid:176) , d m = 20(cid:176) ; diagonal trace: |e r| = |m r| = 4, d e = d m
= 15(cid:176) . e r = |e r|exp(id e ) and m r = |m r|exp(id m ) are the complex per-
mittivity and permeability of the material relative to those of free
space (from Knott, 1993, Fig. 8.12, p. 319).
(d) Single loaded slot
(e) Four-legged (f) Three-legged
symmetrically loaded slot
loaded slot
Figure A5 Frequency-selective surfaces (after Knott, 1993,
Fig. 8.22, p. 330).
A geometric transition absorber is based on geometric tran-
sition from free space to the highly lossy medium that pro-
vides an effective dielectric gradient and minimizes
reflections. The major shapes available are convoluted,
wedge-shaped, twisted-wedge-shaped, rectangular, triangular,
conical, and pyramidal. The pyramidal profile is most often
used, usually having the structure of a planar array of pyrami-
Figure A4 Reflectivity of dominantly magnetic materials. Solid dal absorbers (Fig. A6). Geometric transition absorbers are
trace: |m r| = 16, |e r| = 1, d m = 10(cid:176) , d e = 0(cid:176) ; dashed trace: |m r| = 25, used in anechoic chambers to reduce reflection from the
|e r| = 16, d m = 20(cid:176) , d e = 30(cid:176) ; diagonal trace: |e r| = |m r| = 4, d e = d m
= 15(cid:176) (from Knott, 1993, Fig. 8.13, p. 319).
Ferrite absorbing material provides attenuation of a radio
wave passing through it. Ferrite absorbing coatings are
marked by their low weight and thickness. Usually they are
used for masking the warheads of ballistic missiles and vari-
ous reflective parts of short-range missiles. They provide an
attenuation of 15 to 30 dB. With a thickness of 5 mm, a
square meter of coating has a weight of up to 5 kg. Ferrite
absorbing materials are used for camouflage in a wide wave-
band, from the meter to the centimeter range.
Ferrite material is used for coatings of anechoic cham-
Figure A6 Geometric transition absorber (from Knott, 1993,
bers, taking the form of a layer of tightly placed tiles or an
Fig. 8.18, p. 326).