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29.Обучение чтению литературы на английском языке по специальности “Радиоэлектронные системы и устройства”

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Copyright ОАО «ЦКБ «БИБКОМ» & ООО «Aгентство Kнига-Cервис»
Московский государственный технический университет
имени Н.Э. Баумана
И.В. Стасенко, М.В. Куликова, И.Г. Сафарова
ОБУЧЕНИЕ ЧТЕНИЮ ЛИТЕРАТУРЫ
НА АНГЛИЙСКОМ ЯЗЫКЕ
ПО СПЕЦИАЛЬНОСТИ
«РАДИОЭЛЕКТРОННЫЕ СИСТЕМЫ
И УСТРОЙСТВА»
Методические указания
Москва
Издательство МГТУ им. Н.Э. Баумана
2012
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УДК 802.0
ББК 81.2 Англ-923
С21
Рецензент И.Ф. Беликова
С21
Стасенко И.В.
Обучение чтению литературы на английском языке по
специальности «Радиоэлектронные системы и устройства» :
метод. указания / И.В. Стасенко, М.В. Куликова, И.Г. Сафарова. — М.: Изд-во МГТУ им. Н.Э. Баумана, 2012. — 45, [3] с. : ил.
Представленный в методических указаниях учебный материал
предназначен для обучения студентов различным видам чтения.
Тексты, заимствованные из современных научных журналов, отражают передовые достижения в области радиосвязи, перспективы
новых технологий беспроводной связи, принципы работы радиоприемников, радиопередатчиков, мобильных телефонов и других
беспроводных устройств. Рассмотрены также различные виды антенн, принцип их действия, их сходство и различия. Задания на
составление плана изложения текста подготавливают студентов к
более осмысленному извлечению информации из научных источников, создают базу для развития умения писать аннотации и рефераты к научным статьям. Грамматические упражнения позволяют
повторить грамматический материал, вызывающий наибольшие
трудности при переводе. Содержание и лексическое наполнение
грамматических упражнений также связаны с технологиями беспроводной связи и системами коммуникации.
Для студентов третьего курса, обучающихся по специальности
«Радиоэлектронные системы и устройства».
Рекомендовано Учебно-методической комиссией НУК ФН
МГТУ им. Н.Э. Баумана.
УДК 802.0
ББК 81.2 Англ-923
© МГТУ им. Н.Э. Баумана, 2012
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ВВЕДЕНИЕ
Одной из основных целей данных методических указаний является формирование «зрелого» чтения научно-технической литературы на английском языке, т. е. умения быстро просматривать
большие объемы информации и прицельно отбирать ту, которая
необходима для пополнения знаний в области специализации студентов и для совершенствования их профессионального уровня.
Перед чтением текста следует ознакомиться с вокабуляром,
предваряющим текст и содержащим терминологическую лексику,
которую необходимо запомнить. Усвоение терминов создает
предпосылки для дальнейшего беспереводного понимания текста.
При работе с текстом вначале следует просмотреть весь текст,
фиксируя внимание на его структуре: заголовке, подзаголовках,
количестве абзацев, знакомых словах, включая интернациональную лексику, а также на рисунках, графиках, цифрах, именах собственных и т. п. Следует определить тему текста. Таким образом,
работу с текстом необходимо начинать с просмотрового чтения, а
не со «сплошного» дословного перевода. Такой подход к тексту
как к единому целому позволяет более целенаправленно выполнять с ним все другие виды работы.
Необходимо критически оценивать и переосмысливать прочитанное, пытаться понять логику изложения информации. Подготовиться к такой деятельности помогут задания на составление собственного плана изложения текста, что является необходимым
подготовительным этапом при написании собственных, так называемых вторичных текстов — аннотаций и рефератов. Полезно
выписывание ключевых фрагментов текста, т. е. структур текста,
несущих основную смысловую нагрузку.
Структура и содержание методических указаний создают базу
как для самостоятельной работы студентов, так и для аудиторных
занятий под руководством преподавателя.
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Послетекстовые упражнения подразделяются следующим образом:
1) упражнения на контроль понимания прочитанного позволяют сконцентрировать внимание студентов на основных фактах,
идеях, явлениях, законах, точках зрения, выводах и т. п., изложенных в текстах, с целью дальнейшего обсуждения научной проблемы, дополнения ее новыми фактами, полученными из других
источников, подготовки докладов и их презентаций с помощью
программы Power Point;
2) упражнения на развитие навыков аннотирования и реферирования, являющиеся наиболее сложными из всех видов упражнений, служат показателем эффективности работы студента и преподавателя;
3) грамматические упражнения нацелены на повторение наиболее сложных конструкций английского языка, представленных в
информативных предложениях, согласующихся с тематикой текстов и содержащих специальную терминологию.
Тексты на русском языке содержательно дополняют текстовой
материал методических указаний. Они предназначены для перевода
с русского языка на английский или для свободного изложения на
английском языке, что будет способствовать повторению терминологии и более полному осмыслению принципов работы медицинских приборов и изучению новых технологий, применяемых в
медицине.
Таким образом, данные методические указания подготавливают будущих специалистов в области радиоэлектроники к тому,
чтобы легче ориентироваться в огромном информационном потоке
публикаций на английском языке, определять их ценность для
собственной сферы деятельности и, следовательно, постоянно повышать свой профессиональный уровень.
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LESSON 1
Memorize the following basic vocabulary and terminology to
text 1A:
bearing n — пеленг
plane n — плоскость
in terms — в зависимости
magnetic field component — составляющая магнитного поля
electric field component — составляющая электрического поля
Read text 1A with its introduction and answer the questions.
Text 1A
Electromagnetic waves and antenna basics
Radio signals are a form of electromagnetic wave, and as they
are the way in which radio signals travel, they have a major
bearing on RF antennas themselves and RF antenna design.
Electromagnetic waves are the same type of radiation as light,
ultra-violet and infra red rays, differing from them in their
wavelength and frequency. Electromagnetic waves have both
electric and magnetic components that are inseparable. The
planes of these fields are at right angles to one another and to the
direction of motion of the wave.
The electric field results from the voltage changes occurring
in the RF antenna which is radiating the signal, and the magnetic
changes result from the current flow. It is also found that the lines
of force in the electric field run along the same axis as the RF
antenna, but spreading out as they move away from it. This
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electric field is measured in terms of the change of potential over
a given distance, e. g. volts per metre, and this is known as the
field strength. Similarly when an RF antenna receives a signal the
magnetic changes cause a current flow, and the electric field
changes cause the voltage changes on the antenna.
There are a number of properties of a wave. The first is its
wavelength (Fig. 1). This is the distance between a point on one
wave to the identical point on the next. One of the most obvious
points to choose is the peak as this can be easily identified
although any point is acceptable.
Fig. 1. Wavelength of an electromagnetic wave
The wavelength of an electromagnetic wave
The second property of the electromagnetic wave is its
frequency. This is the number of times a particular point on the
wave moves up and down in a given time (normally a second).
The unit of frequency is the Hertz and it is equal to one cycle per
second. This unit is named after the German scientist who
discovered radio waves. The frequencies used in radio are usually
very high.
The third major property of the wave is its velocity. Radio
waves travel at the same speed as light. For most practical
purposes the speed is taken to be 300 000 000 metres per second
although a more exact value is 299 792 500 metres per second.
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Frequency to wavelength conversion
Although wavelength was used as a measure for signals,
frequencies are used exclusively today. It is very easy to relate
the frequency and wavelength as they are linked by the speed of
light as shown:
lambda = c / f
where lambda = the wavelength in metres;
f = frequency in Hertz;
c = speed of radio waves (light) taken as 300 000 000 metres per
second for all practical purposes.
Field measurements
It is also interesting to note that close to the RF antenna there
is also an inductive field the same as that in a transformer. This is
not part of the electromagnetic wave, but it can distort
measurements close to the antenna. It can also mean that
transmitting antennas are more likely to cause interference when
they are close to other antennas or wiring that might have the
signal induced into it. For receiving antennas they are more
susceptible to interference if they are close to house wiring and
the like. Fortunately this inductive field falls away fairly rapidly
and it is barely detectable at distances beyond about two or three
wavelengths from the RF antenna.
(2700)
Answer the following questions.
1. Which way radio signals travel in? 2. What components do
electromagnetic waves have? 3. What does electric field result
from? 4. What are the main properties of a wave? 5. How is the
electric field measured?
Task 1. Find the key-words to speak about electromagnetic
waves.
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Task 2. Find the passage describing the way in which
electromagnetic waves affect RF antenna.
Task 3. Write the summary of the text in Russian.
Read text 1B and answer the questions after the text.
Text 1B
Antenna polarisation
Polarisation (or polarization) is an important factor for RF
antennas and radio communications in general. Both RF antennas
and electromagnetic waves are said to have a polarization.
For the electromagnetic wave the polarization is effectively
the plane in which the electric wave vibrates. This is important
when looking at antennas because they are sensitive to
polarisation, and generally only receive or transmit a signal with
a particular polarization (Fig. 2).
Fig. 2. An electromagnetic wave
For most antennas it is very easy to determine the
polarization. It is simply in the same plane as the elements of the
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antenna. So a vertical antenna (i.e. one with vertical elements)
will receive vertically polarised signals best and similarly a
horizontal antenna will receive horizontally polarised signals.
It is important to match the polarization of the RF antenna to
that of the incoming signal. In this way the maximum signal is
obtained. If the RF antenna polarization does not match that of
the signal there is a corresponding decrease in the level of the
signal. It is reduced by a factor of cosine of the angle between the
polarisation of the RF antenna and the signal.
Accordingly the polarisation of the antennas located in free
space is very important, and obviously they should be in exactly
the same plane to provide the optimum signal. If they were at
right angles to one another (i. e. cross-polarised) then in theory no
signal would be received.
For terrestrial radio communications applications it is found
that once a signal has been transmitted then its polarisation will
remain broadly the same. However reflections from objects in the
path can change the polarisation. As the received signal is the
sum of the direct signal plus a number of reflected signals the
overall polarisation of the signal can change slightly although it
remains broadly the same.
Polarisation catagories
Vertical and horizontal are the simplest forms of antenna
polarization and they both fall into a category known as linear
polarisation. However it is also possible to use circular
polarisation. This has a number of benefits for areas such as
satellite applications where it helps overcome the effects of
propagation anomalies, ground reflections and the effects of the
spin that occur on many satellites. Circular polarisation is a little
more difficult to visualise than linear polarisation. However it can
be imagined by visualising a signal propagating from an RF
antenna that is rotating. The tip of the electric field vector will
then be seen to trace out a helix or corkscrew as it travels away
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from the antenna. Circular polarisation can be seen to be either
right or left handed dependent upon the direction of rotation as
seen from the transmitter.
Another form of polarisation is known as elliptical
polarisation. It occurs when there is a mix of linear and circular
polarisation. This can be visualised as before by the tip of the
electric field vector tracing out an elliptically shaped corkscrew.
However it is possible for linearly polarised antennas to
receive circularly polarised signals and vice versa. The strength
will be equal whether the linearly polarised antenna is mounted
vertically, horizontally or in any other plane but directed towards
the arriving signal. There will be some degradation because the
signal level will be 3 dB less than if a circularly polarised antenna
of the same sense was used. The same situation exists when a
circularly polarised antenna receives a linearly polarised signal.
Applications of antenna polarization
Different types of polarisation are used in different applications
to enable their advantages to be used. Linear polarization is by far
the most widely used for most radio communications applications.
Vertical polarisation is often used for mobile radio
communications. This is because many vertically polarized
antenna designs have an omni-directional radiation pattern and it
means that the antennas do not have to be re-orientated as positions
as always happens for mobile radio communications as the vehicle
moves. For other radio communications applications the
polarisation is often determined by the RF antenna considerations.
Some large multi-element antenna arrays can be mounted in a
horizontal plane more easily than in the vertical plane. This is
because the RF antenna elements are at right angles to the vertical
tower of pole on which they are mounted and therefore by using an
antenna with horizontal elements there is less physical and
electrical interference between the two. This determines the
standard polarisation in many cases.
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In some applications there are performance differences
between horizontal and vertical polarization. For example
medium wave broadcast stations generally use vertical
polarisation because ground wave propagation over the earth is
considerably better using vertical polarization, whereas horizontal
polarization shows a marginal improvement for long distance
communications using the ionosphere. Circular polarisation is
sometimes used for satellite radio communications as there are
some advantages in terms of propagation and in overcoming the
fading caused if the satellite is changing its orientation.
(4400)
Answer the following questions.
1. Why is polarization an important factor of RF antennas?
2. How can one determine the polarization? 3. Why is it
important to mach polarization? 4. What polarisation categories
do you know? 5. How are different types of polarization used?
6. What are performance differences between horizontal and
vertical polarization?
Task 1. Explain the difference between:
a. vertical antenna and polarization antenna;
b. magnetic field component and electric field component;
c. circular polarization and elliptical polarization.
Task 2. Find sentences which give the main idea of each
paragraph.
Task 3. Propose your own plan of the text in logical
consistency and put it down.
Memorize the following basic vocabulary and terminology to
text 1C:
antenna feeder — антенный фидер; питатель
feed impedance — сопротивление в точке питания
inductance n — индукция, самоиндукция, собственная
индукция
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capacitance cancel — отмена, подавление, емкости
radiation resistance — сопротивление излучения
dissipate v — рассеивать.
Read and translate the following text.
Text 1C
Antenna feed impedance
When a signal source is applied to an RF antenna at its feed
point, it is found that it presents a load impedance to the source.
This is known as the antenna “feed impedance” and it is a
complex impedance made up from resistance, capacitance and
inductance. In order to ensure the optimum efficiency for any RF
antenna design it is necessary to maximise the transfer of energy
by matching the feed impedance of the RF antenna design to the
load. This requires some understanding of the operation of
antenna design in this respect.
The feed impedance of the antenna results from a number of
factors including the size and shape of the RF antenna, the
frequency of operation and its environment. The impedance seen
is normally complex, i.e. consisting of resistive elements as well
as reactive ones.
Antenna feed impedance resistive elements
The resistive elements are made up from two constituents.
These add together to form the sum of the total resistive elements.
Loss resistance. The loss resistance arises from the actual
resistance of the elements in the RF antenna, and power
dissipated in this manner is lost as heat. Although it may appear
that the DC resistance is low, at higher frequencies the skin effect
is in evidence and only the surface areas of the conductor are
used. As a result the effective resistance is higher than would be
measured at DC. It is proportional to the circumference of the
conductor and to the square root of the frequency.
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The resistance can become particularly significant in high
current sections of an RF antenna where the effective resistance is
low. Accordingly to reduce the effect of the loss resistance it is
necessary to ensure the use of very low resistance conductors.
Radiation resistance. The other resistive element of the
impedance is the “radiation resistance”. This can be thought of as
virtual resistor. It arises from the fact that power is “dissipated”
when it is radiated from the RF antenna. The aim is to “dissipate”
as much power in this way as possible. The actual value for the
radiation resistance varies from one type of antenna to another,
and from one design to another. It is dependent upon a variety of
factors. However a typical half wave dipole operating in free
space has a radiation resistance of around 73 Ohms.
Antenna reactive elements
There are also reactive elements to the feed impedance. These
arise from the fact that the antenna elements act as tuned circuits
that possess inductance and capacitance. At resonance where
most antennas are operated the inductance and capacitance cancel
one another out to leave only the resistance of the combined
radiation resistance and loss resistance. However either side of
resonance the feed impedance quickly becomes either inductive
(if operated above the resonant frequency) or capacitive (if
operated below the resonant frequency).
Efficiency
It is naturally important to ensure that the proportion of the
power dissipated in the loss resistance is as low as possible,
leaving the highest proportion to be dissipated in the radiation
resistance as a radiated signal. The proportion of the power
dissipated in the radiation resistance divided by the power applied
to the antenna is the efficiency.
A variety of means can be employed to ensure that the
efficiency remains as high as possible. These include the use of
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optimum materials for the conductors to ensure low values of
resistance, large circumference conductors to ensure large surface
area to overcome the skin effect, and not using designs where
very high currents and low feed impedance values are present.
Other constraints may require that not all these requirements can
be met, but by using engineering judgement it is normally
possible to obtain a suitable compromise.
It can be seen that the antenna feed impedance is particularly
important when considering any RF antenna design. However by
maximizing the energy transfer by matching the feeder to the
antenna feed impedance the antenna design can be optimized and
the best performance obtained.
(3400)
Task 1. Put questions to the text. Discuss the questions with
the group.
Task 2. Refer the text to your notes and give a spoken
summary.
Grammar exercise № 1
Point out Complex object Infinitive constructions in the
following sentences and translate them accordingly.
1. In the late 1990s the public expected broadcasting stations
to give up their analog frequencies by 2006. But that plan was a
failure.
2. TV viewers supposed conventional analog broadcasting to
end in 2007. They believed all broadcasts to be digital.
Subscribers (абоненты) assumed digital broadcasts to offer many
advantages such as crystal — clear pictures and new information
services.
3. We know the first high — definition broadcasts in the U.S.
to have started in 1998.
4. Consumers believe frequencies no longer used for analog
broadcasting to be available for emergency communication.
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5. The public found the idea of switching the country to
digital TV to have been approved by U.S. Congress in the 1980s.
6. Operators believe cable systems to be able to handle
750mhz of bandwidth with hundreds of channels, telephone
services and broadband Internet access.
7. Some people don t think that analog TV broadcasting to be
widely used in future.
8. Operators know digital signals to travel to televisions in
homes using 3 different routes — satellite, antenna or cable.
9. Consumers expect cable operators to provide them with
digital tuners.
10. Subscribers of TV channels found cable operators to have
begun employing a modified system architecture called switched
broadcasting.
11. Specialists expect a hybrid fiber coaxial cable system to
provide subscribers with limitless bandwidth.
12. Not everybody knows conventional signal distribution to
carry every channel broadcasts in parallel into each home.
13. Scientists expect satellite system to be changing
permanently. Consumers expect these systems to accommodate
twice as many channels.
14. Students believed adaptive antenna arrays to have
considerably improved wireless communications.
15. We know each of arrays to consist of up to a dozen
antennas and a powerful digital processor.
16. Millions of call-phone users consider adaptive antenna
arrays to have provided them with many benefits, among them
better quality of wireless communications.
17. Not only communication experts know the Global
Positioning System (GPS) to be a space-based navigation satellite
system (GNSS) that provides reliable information about the time
the message was transmitted.
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LESSON 2
Memorize the following basic vocabulary and terminology to
text 2A:
tuned circuit — резонансный контур
PMR (proton magnetic resonance) — протонный магнитный
резонанс
inductance n — индуктивность
capacitance n — электрическая емкость
reactance n — реактивное сопротивление
UHF (ultrahigh frequency) — ультравысокая частота
FM (frequency modulator) — частотный модулятор
Read text 2A and answer the questions after the text.
Text 2A
Antenna resonance and bandwidth
Two major factors associated with radio antenna design are
the antenna resonant point or center operating frequency and the
antenna bandwidth or the frequency range over which the antenna
design can operate. These two factors are naturally very
important features of any antenna design and as such they are
mentioned in specifications for particular RF antennas. Whether
the RF antenna is used for broadcasting, WLAN, cellular
telecommunications, PMR or any other application, the
performance of the RF antenna is paramount, and the antenna
resonant frequency and the antenna bandwidth are of great
importance.
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Antenna resonance
An RF antenna is a form of tuned circuit consisting of
inductance and capacitance, and as a result it has a resonant
frequency. This is the frequency where the capacitive and inductive
reactances cancel each other out. At this point the RF antenna
appears purely resistive, the resistance being a combination of the
loss resistance and the radiation resistance (Fig. 3).
Fig. 3. Impedance of an RF antenna
with frequency
The capacitance and inductance of an RF antenna are
determined by its physical properties and the environment where
it is located. The major feature of the RF antenna design is its
dimensions. It is found that the larger the antenna or more strictly
the antenna elements, the lower the resonant frequency. For
example, antennas for UHF terrestrial television have relatively
small elements, while those for VHF broadcast sound FM have
larger elements indicating a lower frequency. Antennas for short
wave applications are larger still.
(1351)
Answer the following questions.
1. What are the two main features of antenna design? 2. What
are the applications of RF antenna? 3. What is the idea of antenna
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resonance? 4. What do the capacitance and inductance of RF
antenna depend on? 5. Why are the dimensions of antenna design
so important?
Task 1. Prove the importance of antenna resonance in
designing RF antenna.
Task 2. Explain the dependence of the capacitance and
inductance of RF antenna on its physical properties and the
environment where it is located.
Memorize the following basic vocabulary and terminology to
text 2B:
impair v — ослаблять, уменьшать
SWR (standing wave ratio) — коэффициент стоячей волны
folded dipole — петлевой симметричный вибратор
antenna lobe — лепесток диаграммы направленности антенны
gain n — коэффициент усиления
Read text 2B and answer the questions after the text.
Text 2B
Antenna bandwidth
Most RF antenna designs are operated around the resonant
point. This means that there is only a limited bandwidth over
which an RF antenna design can operate efficiently. Outside this
the levels of reactance rise to levels that may be too high for
satisfactory operation. Other characteristics of the antenna may
also be impaired away from the center operating frequency.
The antenna bandwidth is particularly important where radio
transmitters are concerned as damage may occur to the
transmitter if the antenna is operated outside its operating range
and the radio transmitter is not adequately protected. In addition
to this the signal radiated by the RF antenna may be less for a
number of reasons.
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For receiving purposes the performance of the antenna is less
critical in some respects. It can be operated outside its normal
bandwidth without any fear of damage to the set. Even a random
length of wire will pick up signals, and it may be possible to
receive several distant stations. However, for the best reception it
is necessary to ensure that the performance of the RF antenna
design is optimum.
Impedance bandwidth
One major feature of an RF antenna that does change with
frequency is its impedance. This in turn can cause the amount of
reflected power to increase. If the antenna is used for transmitting it
may be that beyond a given level of reflected power damage may be
caused to either the transmitter or the feeder, and this is quite likely
to be a factor which limits the operating bandwidth of an antenna.
Today most transmitters have some form of SWR protection circuit
that prevents damage by reducing the output power to an acceptable
level as the levels of reflected power increase. This in turn means
that the efficiency of the station is reduced outside a given
bandwidth. As far as receiving is concerned the impedance changes
of the antenna are not as critical as they will mean that the signal
transfer from the antenna itself to the feeder is reduced and in turn
the efficiency will fall. For amateur operation the frequencies below
which a maximum SWR figure of 1.5 : 1 is produced is often taken
as the acceptable bandwidth.
In order to increase the bandwidth of an antenna there are a
number of measures that can be taken. One is the use of thicker
conductors. Another is the actual type of antenna used. For example,
a folded dipole has a wider bandwidth than a non-folded one.
Radiation pattern
Another feature of an antenna that changes with frequency is
its radiation pattern. In the case of a beam it is particularly
noticeable. In particular the front to back ratio will fall off rapidly
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outside a given bandwidth, and so will the gain. In an antenna
such as a Yagi this is caused by a reduction in the currents in the
parasitic elements as the frequency of operation is moved away
from resonance. For beam antennas such as the Yagi the radiation
pattern bandwidth is defined as the frequency range over which
the gain of the main lobe is within 1 dB of its maximum.
For many beam antennas, especially high gain ones it will be
found that the impedance bandwidth is wider than the radiation
pattern bandwidth, although the two parameters are inter-related
in many respects.
(2790)
Answer the following questions.
1. What is the role of the resonant point in RF antenna design?
2. Why is antenna bandwidth important in radio transmitters
performance? 3. What can cause damage for transmitting
function of RF antenna? 4. How is it possible to prevent the
damage? 5. When are impedance changes of antenna more
crucial? 6. What are the ways of increasing the bandwidth?
7. What are the main parameters of RF antennas?
Task 1. Speak about the functions of antenna bandwidth in
RF antenna design.
Task 2. Explain the importance of impedance bandwidth
and radiation pattern in antennas that change with frequency.
Task 3. Tell about the impact of RF antenna resonance and
bandwidth on radio communications systems.
Grammar exercise № 2
Point out Complex Subject Infinitive constructions in the
following sentences and translate them.
1. Cognitive radio is reported to be a smart wireless
communications technology that will be able to find and connect
with any nearby open radio frequency.
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2. A typical cell phone is known to incorporate several
hundred million instructions per second of processing capacity
that is largely dedicated to unique cellular standards.
3. The new generation wireless technology is supposed to use
both embedded (встроенный) signal-processing algorithms and
reconfigurable code structures to receive and transmit new radio
protocols.
4. A monthly cell service bill is considered to contain, for
instance charges for leasing radio spectrum and renting cell
towers.
5. The charges for leasing radio spectrum are assumed to drop
dramatically when cognitive radio appears in the marketplace.
6. Wireless signals are considered to jump automatically to an
available, open frequency in cognitive radio.
7. Smart radios and other new wireless devices are likely to
avoid transmission bottlenecks by switching instantly to nearby
frequencies that are clear.
8. The smartest antennas are considered to employ digital
processors to manipulate incoming and outgoing signals.
9. These smart antennas, also called adaptive antenna arrays,
are supposed to enhance reception.
10. An adaptive array is reported to contain four to twelve
antennas.
11. The digital processor embedded in the antenna array is
known to perform complex mathematical operations on the signal
from the antenna.
12. The terahertz (THz) region of the electromagnetic
spectrum is known to lie in the gap between microwaves and
infrared region.
13. Much of the interest in terahertz science and technology is
believed to have grown out of the natural overlap between the
electronics and optics points of view.
14. The idea of using terahertz radiation for imaging and
sensing is assumed to have been discussed for at least several
decades.
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15. Digital TV (or DTV) is known to use electrical pulse to
transmit information precisely and efficiently. Thus, DTV is sure
to offer very sharp pictures and to enable new interactive
features.
16. DTV proved to be able to pack enormous amounts of
information in scarce (в небольшом количестве) bandwidths.
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LESSON 3
Memorize the following basic vocabulary and terminology to
text 3A:
discrete quanta — раздельные части
active devices — активное устройство, активный элемент
logic gate — логический элемент, логическая схема
charge-coupled device — устройство с зарядной связью
field-effect microwave power devices — полевое СВЧустройство
strip line circuits — полосковая схема, полосковая линия
micro-strip circuits — микрополосковая схема
Text 3A
Why Digital Transmission?
Communication is the transmission of information to a remote
place or a remote time. Digital communication transmits
information in discrete quanta. The increasingly complex
activities of mankind have forced an exponential growth in
communication to sustain them, and revolutions in hardware and
in our understanding of electrical communication have decimated
the cost of communication and completely changed how it
occurs. The foremost innovation in communication has been the
advent of digital transmission and the understanding of its
importance.
All about us we see a revolution in which the older methods
of analog transmission are being replaced by digital transmission.
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Obvious reasons for this include the advent of new, incredibly
cheap hardware and of customers with nonanalog data to
transmit. A more subtle factor is the nature of communication
theory, which may require a digital format in the transmissions
systems that we find convenient to use.
New Hardware. Rapidly advancing electronic technology has
caused a revolution in the hardware used in digital
communication.
Digital circuits have been reduced to microscopic size, weight,
power consumption, and cost. In addition, huge numbers of active
devices can be combined into a single integrated circuit. Other
types of circuits not based on logic gates have also appeared with
all the above advantages, including charge-coupled devices,
switched capacitor filters, and various analog integrated circuits.
Several future generations of integrated circuit technology
beyond those now in commercial use exist at this writing in the
development stage. These generations relate to the use of
submicron structures, new semiconductor materials, fault-tolerant
or self-repairing architectures and computer-aided design aids. It
is a fact, however, that knowledge of how to apply these circuits,
as opposed to how to construct them, lags behind appearance of
the circuits.
Microwave hardware has undergone a less publicized but
equally exciting development. New solid-state hardware has
appeared, such as the Gunn device and field-effect microwave
power devices. Strip line and micro-strip circuits have appeared,
along with new methods for phase shifting and switching
microwave energy. Surface acoustic wave devices have under-gone a rapid development. These are thin film planar devices that
operate over the uhf range by means of elastic waves propagating
through a piezoelectric substrate. Since these waves are on the
surface, they can be easily tapped, guided, and modified; as a
consequence, complex signal filtering can be realized cheaply, at
great speed and in a small space. Other propagating wave
devices, such as magnetostatic devices, are on the horizon.
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Disadvantages of digital transmission exist. Some are
notorious to the communications engineer; an example is the
tendency of digital formats to consume unreasonably wide signal
bandwidths.
Some more subtle short-comings exist, however. Digital
equipment contains complex and recent technology known only
to a few and very expensive to design. To tap the advantages of
digital transmission requires the organization of large research
efforts.
(2730)
Answer the following questions.
1. What caused the development of digital transmission?
2. Why is analog transmission replaced by digital transmission?
3. What are the advantages of digital circuit technology? 4. What
new devices have appeared due to the development of digital
circuit technology? 5. What are the disadvantages of digital
transmission?
Task 1. Explain the idea why the public wants to
communicate in digital manner.
Task 2. Tell about a revolution in digital communication.
Text 3B
Fidelity of Reproduction and Error Control
Digital transmission
Fidelity of Reproduction and Error Control Digital
transmission may be favored by the nature of the channel. Long
distance channels are for the most part of two types, terrestrial
channels consisting of long chains of repeaters or of other tandem
processors such as switches, and satellite transponders. In either
case aspects of the channel favor digital signaling. As an example
of a channel with many repeaters, consider the microwave radio
channel. Microwaves propagate in a line-of-sight fashion so that
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individual links are limited to about 50 km. If 100 such links are
chained to form a 5000-km channel, communications theory
shows how much the signal-to-noise ratio (SNR) must be
improved in each link so that the total performance is that of an
original single link. For an analog system the link SNR must be
improved by 20 dВ while for a digital system operating at an
error rate of ~105 only 2 dB is required.
Satellite channels, on the other hand, are marked by lower
power and wide bandwidth. These qualities predispose the channel
to digital transmission in another way, as we shall develop.
These channels have a special character that tends to favor
digital transmission, but a digital format in any communications
network makes it easier to guarantee a given data error rate or
fidelity of reproduction. For analog signals that have been
digitized, the fidelity of reproduction is set almost entirely by the
fineness of the digitizing, and it is easily controlled throughout
the system. The error rate in a digital channel generally obeys a
threshold rule: Beyond a certain signal power, the receiver error
rate falls very rapidly so that as long as signal power exceeds this
threshold, a performance level can be virtually guaranteed
throughout a system, even if many links and processors are
chained. If error performance is not sufficient in one link, digital
error correction methods can be used to improve it; in addition,
performance of this coding will improve rapidly as a threshold
signal power is exceeded.
Cost. In cases where one can choose between digital or analog
means to transmit information, digital transmission may be
cheaper. This may be true because of the availability of wide
bandwidth, the low cost of manufacturing digital equipment,
difficulties with error control, or customer factors, like
compatibility, flexibility, or need for security.
(2300)
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Text 3C
The Satellite Channel
No event has more strongly motivated digital transmission
research than the communications satellite. This channel consists
of a relatively linear high-power amplifier on the ground that
feeds an “uplink” and a highly nonlinear low-power amplifier in
the satellite that feeds a “downlink” to the ground. Microwave
carrier frequencies are normal. The satellite offers an attractive
star network topology; it allows communication over long
distances at wide bandwidths at relatively low cost.
It appears that digital modulation will eventually predominate
in this channel. Compared to other channels, the satellite
transmission path is characterized by wide bandwidth, a nonlinear
amplitude response, and low power, that is, by very long
distances. These factors all point to digital transmission, but the
most telling constraint is the low-power one.
As transmitter power drops it becomes increasingly
necessary to resort to bandwidth-spreading modulations,
including digital ones. Simple analog modulation has at best
the same SNR as the radiofrequency channel; and for single
sideband modulation, it has the same bandwidth as the
information source. Once the SNR drops below 30 dB or so,
transmission of telephone-quality voice, for instance, becomes
impossible without a bandwidth-spreading modulation like
FM. As the SNR drops into the 10–20 dB range encountered in
satellite channels, the degree of bandwidth expansion must
increase, and the analog transmitter and receiver components
must be increasingly wideband. Eventually it becomes more
efficient to convert analog signals to digital form and make use
of a digital modulation method. New modulation methods will
soon become available which, when combined with an
efficient analog-to-digital conversion method like adaptive
differential PCM, should be more efficient than analog FM
over present-day commercial satellites.
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Another hallmark of the satellite channel is its nonlinearity.
All rf power amplifiers must operate nonlinearly in order to be
highly efficient. At the same time, dc power generation on board
a satellite is a heavy contributor to launch weight. Satellites are
thus compelled to operate as nonlinear amplifiers. The
modulations that fare best under these conditions are constantamplitude modulations, those that have little or no envelope
variation; and this narrows the choice to either analog FM or
digital phase modulation. A second factor that promotes the use
of constant-amplitude modulation is their apparent ability to
suppress interference. Interference arises naturally in a satellite
link from closely spaced adjacent channels, from the multiple
carriers that appear in a multiple-access system, or from spurious
carriers that sweep the satellite.
The low power and nonlinearity of the satellite channel require
precisely what the channel has in abundance, bandwidth.
Bandwidth reduction remains a worthwhile goal, however, since a
reduction in signaling bandwidth per data symbol in any channel
leads to a correspondingly higher rate of information transfer.
(2632)
Answer the following questions.
1. What does the satellite channel consist of ? 2. Why is the
satellite channel used for digital transmission? 3. What are the
advantages of the satellite channel? 4. What are the main features
of the satellite channel?
Task 1. Find the main sentences which give the idea of each
paragraph. Write down the key words to each paragraph.
Task 2. Find information from the text and tell about the role
of bandwidth-spreading modulation in the satellite channel.
Task 3. Explain the importance of nonlinearity in the
satellite channel.
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Grammar exercise № 3
Point out Adverbial Participle constructions and Absolute
Constructions in the following sentences and translate them
accordingly.
1. The basic concept of radar being relatively simple, its
practical implementation is not.
2. A radar operates by radiating electromagnetic energy and
detecting the echo returned from reflecting objects (targets)
(отражение).
3. The nature of the echo signal provides information about the
target, the range (or distance) to the target being found from the time
it takes for the radiated energy to travel to the target and back.
4. Resolution being sufficiently high, a radar can discern
(рассмотреть) target’s size and shape, radar resolution being
obtained in range or angle, or both.
5. Radar resolution may be in range or angle, range resolution
requiring large antennas.
6. Resolution in the cross — range (боковое отклонение)
dimensions being not very good, it is possible to use the resolution
in Doppler frequency to resole the cross — range dimensions.
7. Being not dependent on ambient radiation, radar can detect
relatively small targets at near or for distances and can measure
their range.
8. Though the location of a target in range and angle having
been determined by radar, the echo signal also can provide
information about the nature of the target.
9. Automatic detection and track (сопровождение) (ADT)
being available, the operator is usually presented with the
processed target track rather than raw radar detections.
10. The transmitter power being radiated into space by a
directive antenna, the latter immediately concentrates the energy
into a narrow beam.
11. Though deployment (развертывание) having been
delayed, 40-Gbit/s transmission will enable service providers
(поставщик услуг) to deliver necessary signal bandwidth.
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12. Wireless signal being able to jump automatically to an
available frequency, transmissions will be more reliable.
13. The service specific parameters having been studied, the
linear system of equations can be solved.
14. The cost of a base station having been reduced due to
semiconductor advances, the station could be a laptop or home
computer.
15. Though conventional NRZ (non-return-to zero)
modulation format being adequate for transmitting over relatively
short distances, special formats may be required for longer routes.
16. Fiber with high effective mode area having been used,
possible damage of the system was reduced.
17. A receiver being set to many cycles per second, you can
tune the antenna circuit to any stations frequency.
18. Other transmitters interfering with your reception, your
only real option will be to wait out the problem.
19. If provided with new adaptive software, nearly any
wireless system will be able to locate and link to any locally
available unused radio spectrum.
20. The Global Positioning System (GPS) is a space-based
navigation satellite system (GNSS) that provides reliable location
and time information, GPS satellites continually transmitting
messages about the time the message was transmitted.
21. After many years of anticipation (ожидание) the end of
conventional analog broadcasting is evident, digital broadcasts
offering consumers many advantages such as crystal-clear
pictures and new information services.
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LESSON 4
Memorize the following basic vocabulary and terminology to
text 4A:
inhibit v — задерживать, тормозить
disrupt v — разрушать
din — шум
pursue v — наступать, следовать за
subtract v — вычитать
wave trough — минимальная амплитуда огибающей
бегущей волны
Text 4A
Adaptive antenna arrays
Each of us is immersed in a sea of radio-frequency waves.
The invisible electromagnetic energy comes from many sources:
broadcast towers, cellular-phone networks and police radio
transmissions, among others. Although this radiation may be
harmless to our bodies, it can severely inhibit our ability to
receive and transmit information. Excess radio energy is a kind of
pollution, because it can disrupt useful communications. As the
intensity of radio-frequency interference in our environment
grows we have to raise the volume of radio signals so that they
can be heard over the electromagnetic background noise. And as
our electronic communications become more intense, they simply
add to the din of radio interference.
One solution to this problem lies in a new class of radio
antennas that could dramatically reduce man-made interference.
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Instead of wastefully broadcasting personal communications such
as cell-phone calls — in all directions, these innovative antennas
track the positions of mobile users and deliver radio signals
directly to them. These antenna systems also maximize the
reception of an individual cell-phone user's signal while
minimizing the interference from other users. In effect, the
antennas create a virtual wire extending to each mobile phone.
These systems are generically referred to as smart antennas,
but the smartest members of the class are called adaptive antenna
arrays. In 1992 ArrayComm, a San Jose, Calif., company focused
on developing adaptive arrays that can be incorporated into both
new and existing wireless networks. Each of our arrays consists
of up to a dozen antennas and a powerful digital processor that
can combine and manipulate the incoming and outgoing signals.
The technology, which is also being pursued by Lucent
Technologies, Nortel Networks and other firms, promises to
decrease the cost and improve the quality of wireless
communications. Adaptive antenna arrays are already providing
these benefits to millions of cell-phone users. Moreover, these
smart antennas may become the linch-pins of the wireless
Internet because they are ideally suited to transmitting and
receiving large amounts of data.
What makes the adaptive array so smart? The key step is
processing the information received by its antennas. An adaptive
antenna array can pinpoint the source of a radio signal and
selectively amplify it while canceling out competing signals.
The array's brain is a digital processor that can manipulate the
signals coming down the wires from the antennas. A typical
adaptive array contains 4 to 12 antennas, but for simplicity's
sake let us consider an array of two antennas, separated by a
distance equal to half the wavelength of the radio signal. In an
ordinary array the signals from the two antennas are just added
together, but in an adaptive array the signals are sent to the
adjoining processor, which can for many number of
mathematical operations on them.
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For example, suppose that the array is aligned north to south
and a signal from a cell-phone user comes in from the east. The
processor can quickly determine the direction of the signal
because the radio waves reach both antennas at the same time,
they must be coming from a direction perpendicular to the array.
To maximize reception the processor adds the signals together,
doubling their intensity. When transmitting back to the user, the
array emits identical signals from both antennas.
But now suppose that another cell-phone user sends a signal
from the south. Because the radio waves hitting the north antenna
are 180 degrees out of phase from antenna, the processor can tell
that the signal is coming from a direction parallel to the array. So the
processor now subtracts one signal from the other — that is, it
inverts the signal from the north (or south) аntenna, turning wave
peaks into wave troughs and vice versa, and adds this mirror image
to the signal from the south (or north) antenna. Again, the signal's
intensity is doubled. And when the array transmits back to the cellphone user, the processor sends an out-of-phase signal to one of the
antennas, generating a radio beam that runs from north to south.
Notice that in both these examples the radio beam generated
for one cell-phone user does not reach the other. The two users
could be communicating with the adaptive array at the same time
and on the same frequency channel, but their signals would not
interfere with each other. The array's processor can create radio
beams pointing in other directions as well by performing more
complex mathematical operations on the signals from the two
antennas . The task of selective transmission and reception is thus
reduced to solving a series of simultaneous equations. To direct
beam at users who are moving around, the processor must
repeatedly solve the equations with constantly updated
information from the antenna array.
(4133)
Answer the following questions.
1. What are the sources of electromagnetic energy? 2. Why is
it necessary to raise the volume of radio signals? 3. What led to
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the appearance of a new class of radio antennas? 4. What does
each of adaptive antenna arrays consist of? 5. What are the
significant features of adaptive antenna arrays? 6. What is the
difference between the signals in an ordinary array and the ones
in an adaptive antenna array? 7. What do the examples in the text
show? 8. In what way is the signal intensity doubled in both
examples?
Task 1. Tell about the benefits of a new class of radio
antennas.
Task 2. Explain what makes the adaptive array so smart.
Task 3. Discuss the role of the processor in adaptive
antenna array with your fellow students and explain your point
of view to the class.
Memorize the following basic vocabulary and terminology to
text 4B:
faint adj — слабый, неясный
juggle v — изменять
trigger v — запускать, вызывать
discard v — отбрасывать
leap n — скачок
erroneous adj — ложный, ошибочный
bounce v — ударяться
Read text 4B and give the title to the text.
Text 4B
Adding more antennas to the adaptive array increases the
locating precision and the gain of the signal. An array with
12 antennas can hear signal a dozen times as faint as those that
can be heard by a single antenna. The array can also transmit 12
times as loudly and much more directly. And the processor can
juggle the antenna signals to create beam patterns that ensure the
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greatest possible gain for a desired signal and the greatest
possible rejection for other signals on the same frequency.
Because the processor is fast enough to perform this task
many times a second, the array can continually readjust the radio
beam as the cell-phone user walks or drives across the array's
coverage area. The system is designed so that stray reflections of
the user's signal against vehicles or buildings do not trigger
abrupt changes in the direction of the beam. By tracking the user's
route, the array can estimate the like hood of future movements
and discard erroneous information indicating sudden leaps in
position.
Furthermore, the most advanced adaptive arrays can take
advantage of the multipath phenomenon to focus radio signals
still further. The processors in these arrays are so powerful that
can handle information from all the reflected signals that bounce
along various routes between cell phone and the adaptive array.
By including the multipath reflections in the mathematical
equations, the processor can extrapolate not only the direction of
the signal, but also the exact position of the user's cell phone. In
an urban environment where there are numerous reflections the
adaptive array can receive numerous reflections from and
transmit to a small area surrounding the phone. Instead of
generating a radio beam, the array creates a “personal cell” that
can be only centimeters in radius. And because the array is
constantly recalculating the phone's position this personal cell can
follow the user as he or she moves about.
(1624)
Task 1. Make questions to the text and address them to the
other students.
Task 2. Give the proper name to the text.
Task 3. Tell about the advantages of an array with
12 antennas.
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Memorize the following basic vocabulary and terminology to
text 4C:
deploy v — разворачиваться
scarce adj — скудный, недостаточный
allotte v — наделять
congest v — перегружать, переполнять
barrage n — огромное количество
slump n — резкое падение интереса, цен
chunk n — зд. область
bounce v — зд. перемещаться
Text 4 C
Benefits and Applications of adaptive antenna arrays
Wireless networks that employ adaptive antenna arrays have
several advantages over conventional cellular networks. Because
a base station equipped with an adaptive array has a far greater
range than an ordinary station transmitting at the same power,
fewer stations are needed to cover a given area. Although
adaptive arrays may be more expensive than traditional antennas,
reducing the number of base stations dramatically cuts the overall
cost of deploying and operating a wireless network.
Adaptive arrays also enable a cellular service company to
make better use of a scarce resource: the spectrum of frequencies
allotted to the company for its radio signals. Many cellular
systems are becoming overloaded with customers in certain
congested sectors, the barrage of signals sometimes exceeds the
amount that can be carried on the limited number of radio
channels. Customers feel the crunch when their calls are dropped
or they hear poor-quality signals. But because adaptive arrays
allow several cell-phone users within a base station coverage area
to share the same radio channel the technology increases the
capacity of the spectrum. The improvement over ordinary
antennas is significant: base stations outfitted with adaptive
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arrays can serve about six times as many people for voice
communications and up to 40 times as many for data
transmission. The result is better service and less interference, not
to mention less wasted energy and radio pollution.
It is not surprising then, that adaptive antenna arrays are
already in commercial use. Arrays using technology created by
ArrayComm Eave Seen have been mounted on more than
150,000 cellular base stations in Japan, China, Thailand and other
countries in Asia and Africa. All told, the arrays provide phone
service to more than 15 million people. Commercial adoption has
been slower in the US and Europe, partly because the
telecommunications industry's economic slump has curtailed new
investment in cellular networks. But one U.S. manufacturer,
Airnet in Melbourne, Fla., is currently making cellular base
stations that employ ArrayComm’s technology. And Marconi,
British telecommunications company, is developing an advanced
base station that will contain adaptive arrays.
Adaptive arrays are also a boon to wireless data networks.
Because the arrays minimize interference, they can receive and
transmit more data to users in a given chunk or frequency
spectrum. A base station equipped with an adaptive array could
deliver data to as many as 40 concurrent users at a rate of one
megabit a second, which is about 20 times as fast as the typical
data rate for existing long-range wireless networks. Because all
the users in such a network do not usually require peak data rates
at the same time, one station with an adaptive array could serve
several thousand people. Users with laptops or other portable
devices would be able to get uninterrupted high-speed access to
the Internet walking or driving across the coverage area.
Since late 1990s the telecommunications industry has been
heralding the advent of the wireless Internet. The new networks
have been developing more slowly than originally predicted, but
work is nonetheless progressing. As wireless carriers continue to
pursue 3G networks — next-generation cellular systems that
transmit data in packets — other companies are offering a variety
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of competing solutions for high-speed data transmission. Smart
antennas have been incorporated into some of these solutions and
can be put to use in existing networks as well. A data network is
now operating in Sydney, Australia, and similar networks.
Several major manufacturers of telecommunications equipment
plan to incorporate smart-antenna technology into their next
generation. For almost 100 years after Alexander Graham Bell
invented the telephone, voice communications relied on a
physical connection — a copper wire or a coaxial cable —
between the caller and the network. Over the past 30 years,
though, cellular phones have given us a taste of the freedom to
communicate without wires. With the help of adaptive-array
technology, wireless carriers will be able to offer far better
performance at a much lower cost than wired networks do. Only
then we will rid ourselves of the copper cage.
(3649)
Answer the following questions.
1. What are the advantages of adaptive antenna arrays over
the conventional arrays? 2. What is the role of frequencies
spectrum in wireless networks? 3. Where are adaptive antenna
arrays commonly used now? 4. Why can adaptive arrays transmit
more data to the users? 5. What is a new class of systems for high
speed data transmission? What do you know about it?
Task 1. Discuss the application of adaptive antenna arrays
with your partner and give additional information about it.
Task 2. Justify the idea that adaptive arrays provide
cellular-phone services.
Task 3. Summarize the information about the benefits of
adaptive antenna arrays in wireless communication and give
your presentation.
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Grammar exercise № 4
Translate the following sentences.
1. In 1997 there were 5 channels on TV in the U.K. — BBC1,
BBC2, ITV, Channel 4 and Channel 5. Provided the subscriber
(абонент) wanted to receive satellite TV programs, he had to pay
extra for a satellite dish.
2. Provided with satellite dish, the subscriber can receive
satellite TV programs.
3. Lately TV viewers provided their old analog TV sets with
digital tuners that enable them to receive surprisingly sharp
pictures.
4. Even if your TV set can receive over-the-air digital signals,
that does not guarantee the high resolution pictures.
5. Provided cable TV operators supply all households with
DTV tuners, TV viewers all over the country will get access to
hundreds of channels.
6. Unless cable subscribers provided their TV sets with new
high-definition recorder, they wouldn’t be able to record
programs at the highest resolution.
7. Provided other transmitters interfere with your reception,
your only real option is to wait.
8. Were cognitive radio as new smart wireless communication
technology available everywhere, it would provide connection
with any open (free) radio frequency that is particularly important
in an emergency.
9. When cable and satellite subscribers provided their TV sets
with new high definition recorder, they could record programs at
the highest resolution.
10. Providing cognitive radio were now used even in remote
rural areas, the cost of wireless services could drop dramatically.
11. Unless we install a satellite dish, we won’t be able to
watch satellite TV programs.
12. Hadn’t the aerial of your TV set been grounded (earthed),
the lightning might have caused a lot of damage.
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13. Adaptive antenna arrays can vastly improve wireless
communication provided they connect mobile users with virtual
wires.
14. Provided with powerful digital procession that
manipulates the incoming and outgoing signals adaptive antenna
arrays can maintain and offer cellular-phone service to more than
15 million people.
15. Unless your home electrical appliances are safely
grounded, you may get electric shock if you accidentally touch
the machinery.
16. Provided the number of base station for wireless
communication is reduced, the cost of operating a wireless
network will go down (fall).
17. Adaptive antenna arrays provided a vast quality
improvement of wireless communication.
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SUPPLEMENTARY TEXTS
Task 1. Read and translate the following text with a
dictionary
Task 2. Discuss plasma antenna technology.
Plasma antenna technology
On earth we live upon an island of “ordinary” matter. The
different states of matter generally found on earth are solid,
liquid, and gas. Sir William Crookes, an English physicist
identified a fourth state of matter, now called plasma, in 1879.
Plasma is by far the most common form of matter. Plasma in the
stars and in the tenuous space between them makes up over 99 %
of the visible universe and perhaps most of that which is not
visible. Important to ASI’s technology, plasmas are conductive
assemblies of charged and neutral particles and fields that exhibit
collective effects. Plasmas carry electrical currents and generate
magnetic fields.
The essence of a plasma antenna is that it is equal to
performance of a metal antenna but is lighter. When a plasma
antenna is turned off, it is transparent — immune to electronic
countermeasures and allowing other adjacent antennas to transmit
or receive without interference.
Since the discovery of radio frequency (RF) transmission,
antenna design has been an integral part of virtually every
communication and radar application. Technology has advanced
to provide unique antenna designs for applications ranging from
general broadcast of radio frequency signals for public use to
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complex weapon systems. In its most common form, an antenna
represents a conducting metal surface that is sized to emit
radiation at one or more selected frequencies. Antennas must be
efficient so the maximum amount of signal strength is expended
in the propogated wave and not wasted in antenna reflection.
Plasma antenna technology employs ionized gas enclosed in a
tube (or other enclosure) as the conducting element of an antenna.
This is a fundamental change from traditional antenna design that
generally employs solid metal wires as the conducting element.
Ionized gas is an efficient conducting element with a number of
important advantages. Since the gas is ionized only for the time
of transmission or reception, “ringing” and associate effects of
solid wire antenna design are eliminated. The design allows for
extremely short pulses, important to many forms of digital
communication and radars. The design further provides the
opportunity to construct an antenna that can be compact and
dynamically reconfigured for frequency, direction, bandwidth,
gain and beam width. Plasma antenna technology will enable
antennas to be designed that are efficient, low in weight and
smaller in size than traditional solid wire antennas.
When gas is electrically charged, or ionized to a plasma
state it becomes conductive, allowing radio frequency (RF)
signals to be transmitted or received. We employ ionized gas
enclosed in a tube as the conducting element of an antenna.
When the gas is not ionized, the antenna element ceases to
exist. This is a fundamental change from traditional antenna
design that generally employs solid metal wires as the
conducting element. We believe our plasma antenna offers
numerous advantages including stealth for military
applications and higher digital performance in commercial
applications. We also believe our technology can compete in
many metal antenna applications.
Initial studies have concluded that a plasma antenna’s
performance is equal to a copper wire antenna in every respect.
Plasma antennas can be used for any transmission and/or
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modulation technique: continuous wave (CW), phase modulation,
impulse, AM, FM, chirp, spread spectrum or other digital
techniques. And the plasma antenna can be used over a large
frequency range up to 20 GHz and employ a wide variety of
gases (for example neon, argon, helium, krypton, mercury vapor
and xenon). The same is true as to its value as a receive antenna.
(3300)
Suppose you invented cognitive radio. Prepare a talk to
make presentation of a new device.
Cognitive Radio
Cognitive radio is an emerging smart wireless
communications technology that will be able to find and connect
with any nearby open radio frequency to best serve to user. Thus,
a cognitive radio should be able to switch from a band of the
radio spectrum that is blocked by interference to a free one to
complete a transmission link, a capability that is particularly
important an emergency.
Adaptive software will enable these intelligent devices to
reconfigure their functions to meet the demands of
communications networks or consumers as needed. These
alterations will be based on the ability to sense and remember
various factors such as the radio-frequency spectrum, user
behavior, or network state in different transmission environments
at any one place and time. As a result, wireless communications
should become far more dependable and convenient.
The new flexibility afforded by cognitive radio may also
eventually enable consumers to take advantage of cheaper wireless
network paths available locally to make calls, a future that would
do much to revolutionize the communications business.
The cognitive radio unit would build an internal database that
defines how it should best operate in different places and at
specific times of day.
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In contrast, the frequency bands and transmission protocol
parameters of current wireless systems have been mostly fixed.
As cognitive radios send and receive signals, they will nimbly
bound in and out of free bands as required, avoiding those that
are already in use. This lightning-fast channel jumping should
permit cognitive radio systems to transmit voice and data streams
at reasonable speeds. By making much more efficient use of
existing radio-frequency (RF) resources to work around
spectrum-availability traffic jams, wireless communications
should become far more dependable and convenient and perhaps
considerably cheaper than it is today. Indeed, if cognitive radio
technology progresses as its developers hope, a glut of RFspectrum options may actually arise in time. The airwaves will
never be the same again.
The next-generation wireless technology, called softwaredefined radio (SDR), uses both embedded signal-processing
algorithms to sift out weak radio signals and reconfigurable code
structures to receive and transmit new radio protocols. Experts
anticipate that in the relatively near term this software-driven
advance will produce a seismic shift in radio design.
The change means, for example, that SDR code and other
programmable radio-frequency front-end interface technologies
running on a standard laptop computer (fitted with a small RF
peripheral component interconnect card) could receive TV signals
and display them. If the laptop were then equipped with an analog
RF SDR card, it could upload software programming that would
allow it to behave as a cellular handset or base station, a wireless
personal organizer or even a military-frequency radio — whatever
is required (and permitted) for the task at hand.
Cognitive radio is arriving on the heels of SDR technology
and building on it. This new wireless paradigm involves SDR
systems that can reconfigure their analog RF output and that
incorporate “self-awareness” and knowledge of transmission
protocols, etiquette and procedures. These developments will
yield a cognitive radio able to sense its RF environment and
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location and then alter its power, frequency, modulation and other
operating parameters so as to dynamically reuse whatever
spectrum is available.
Self-awareness refers to the unit's ability to learn about itself
and its relation to the radio networks it inhabits. Engineers can
implement these functions through a computational model of the
device and its environment that defines it as an individual entity
(“Self”) that operates as a “Radio”; the model also defines a
“User” about whom the system can learn.
A cognitive radio will be able to autonomously sense how its
RF environment varies with position and time in terms of the
power that it and other transmitters in the vicinity radiate. These
data structures and related software will enable a cognitive radio
device to discover and use surrounding networks to the best
advantage while avoiding interference from other radios. In the
not too distant future, cognitive radio technology will share the
available spectrum optimally without instructions from a
controlling network, which could eventually liberate the user
from user contracts and fees.
Cognitive radio will be smart enough to introduce etiquette —
sensible transactional practices — into RF-spectrum operations. It
will also intelligently detect and interact with nearby picocells to
keep the cognitive radio user connected by the means that best
serve his or her needs, which may differ among various times and
situations.
To accomplish these tasks, a cognitive radio unit requires
several things. First, it must “know” how radiated RF power at its
location varies with distance along the ground, among
obstructions and up in the air. Cell phones do not need this
information because the fixed network employs dedicated radio
spectrum that has been previously calibrated for existing radiated
power patterns. Cognitive radios instead sense the entire local RF
environment of low, medium and high bands, mapping its
features as a function of space, time and frequency propagation.
The development of spectrum-sensing cognitive radio will
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require the design of high-quality sensor devices and practical
algorithms for exchanging spectrum-monitoring data between
cooperating communications nodes. Systems that feature
multiple-input/multiple-output
capabilities
will
direct
transmissions along complex multipath components—thereby
accounting for reflections of signals from objects such as
buildings and vehicles — and away from other potentially
interfering radios.
A fully functional cognitive radio system will be smart
enough to sense the local RF “scene”, to choose the radio band,
mode and service it needs as well as the SDR upload connections
to the selected band and mode. It will then direct its transmission
energy toward the intended receiver while minimizing
interference with other radios, including cognitive ones. Thus, it
will display a high level of spectrum etiquette and connect the
user securely and privately.
The accuracy of such operations could be improved by the
development of three-dimensional computer representations of
the full local cityscape stored on gigabyte hard drives, which
would be accessed wirelessly as needed.
Just as the emergence of cell-phone technology has led to
wide social and business consequences, cognitive radio's adoption
will induce similar changes as advanced devices exploit the
wireless Web to displace now traditional cell phones. The growth
of cognitive radio will take some time to occur, but the effect on
all our lives will be significant.
(5800)
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CONTENTS
Введение.......................................................................................................3
Lesson 1.........................................................................................................5
Text 1A. Electromagnetic waves and antenna basics ...................................5
Text 1B. Antenna polarisation ....................................................................8
Text 1C. Antenna feed impedance ............................................................12
Grammar exercise № 1.............................................................................14
Lesson 2.......................................................................................................16
Text 2A. Antenna resonance and bandwidth..............................................16
Text 2B. Antenna bandwidth ....................................................................18
Grammar exercise № 2.............................................................................20
Lesson 3.......................................................................................................23
Text 3A. Why Digital Transmission?........................................................23
Text 3B. Fidelity of reproduction and error control digital transmission.....25
Text 3C. The satellite channel...................................................................27
Grammar exercise № 3.............................................................................29
Lesson 4.......................................................................................................31
Text 4A. Adaptive antenna arrays .............................................................31
Text 4B....................................................................................................34
Text 4C. Benefits and applications of adaptive antenna arrays...................36
Grammar exercise № 4.............................................................................39
Supplementary texts......................................................................................41
Plasma antenna technology.......................................................................41
Cognitive Radio .......................................................................................43
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Учебное издание
Стасенко Ирина Валентиновна
Куликова Маргарита Владимировна
Сафарова Ирина Григорьевна
ОБУЧЕНИЕ ЧТЕНИЮ ЛИТЕРАТУРЫ
НА АНГЛИЙСКОМ ЯЗЫКЕ
ПО СПЕЦИАЛЬНОСТИ
«РАДИОЭЛЕКТРОННЫЕ СИСТЕМЫ
И УСТРОЙСТВА»
Корректор Е.К. Кошелева
Компьютерная верстка С.А. Серебряковой
Подписано в печать 18.01.2012. Формат 60×84/16.
Усл. печ. л. 2,79. Тираж 500 экз. Изд. № 21. Заказ
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Издательство МГТУ им. Н.Э. Баумана.
Типография МГТУ им. Н.Э. Баумана.
105005, Москва, 2-я Бауманская ул., 5.
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