Introduction of Microwave.pdf
Transcript of Introduction of Microwave.pdf
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1.1 Introduction to Electromagnetic Spectrum
The term “Spectrum” was first introduced in the 17th century to explain
the range of colours observed when white light is passed through a prism.
It was soon applied to other waves like sound waves, electromagnetic
waves etc.
Now it is applied to any signal that can be decomposed into frequency
components.
“EM Spectrum” refers the range of all possible frequencies of EM
radiations and it extends from low frequencies, used for Radio
Communication to higher end at Gama radiation. Alternatively it covers
wavelengths from thousands of km down to the fraction of the size of an
atom.
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The term “Microwave” usually refers to that part of the EM spectrum which
is covered by wavelength range 1m to 1 cm or in frequency scale 300 MHz to30 GHz.
Above this frequency the wavelength becomes of the order of mm and is
called “Millimetre Wave” (30 GHz to 300 GHz).
The term “Micro” in the “Microwave” stands for “Extremely small in scale”
and it includes both the microwave and millimetre wave spectrum i.e., UHF,
SHF and EHF bands.
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Frequency Band Designations Typical Applications
3 kHz – 30 kHz Very Low Frequency(VLF)
Navigation & Sonar.
30 kHz – 300 kHz Low Frequency (LF) Radio beacons & Navigation.
300 kHz – 3 MHz Medium Frequency (MF) AM broadcasting & Coast guardcommunication
3 MHz – 30 MHz High Frequency (HF) Telephone, Telegraph, FAX, Ship
to coast and ship to aircraft
communication, Shortwave
international broadcasting,
Amateur radio and Citizen’s band.
30 MHz – 300 MHz Very High Frequency
(VHF)
Air traffic control, Police,
Television, FM, Taxicab mobile
radio and Navigational aids.
Table 1.1: Electromagnetic Frequency Band Designation
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Frequency Band Designations Typical Applications
300 MHz – 3 GHz Ultra High Frequency
(UHF)
Satellite communication,
Surveillance RADAR, Mobile
communication, Television and
navigational aids.
3 GHz – 30 GHz Super High Frequency
(SHF)
Airborne RADAR, Microwave
communication, Mobile
communication and Satellite
communication.
30 GHz – 300 GHz Extreme High
Frequency (EHF)
RADAR
300 GHz – 6 THz Far Infra-Red (FIR) Terahertz time domain
spectroscopy, Terahertz imaging
6 THz – 100 THz Mid Infra-Red (MIR) Guided missile and Thermal
imaging
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Frequency
Band
Designations Typical Applications
100 THz – 400
THz
Near Infra-Red (NIR) Fibre optic telecommunication, Night
vision, Long distance telecommunication
400 THz – 750
THz
Visible Light Optical communication
750 THz – 1PHz Near Ultra Violet(NUV)
Optical sensors, UV-ID, Label tracking,
Barcode, Forensic analysis, Drugdetection, Protein analysis, DNA
sequencing, Drug discovery, Medical
imaging of cells, Solid state lighting,
Curing of polymers and printer inks,
Light therapy in medicine and Bug
zappers.
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Frequency
Band
Designations Typical Applications
1 PHz – 30 PHz Extreme Ultra Violet
(EUV)
Extreme ultra violet lithography, Optical
sensors, Disinfection, Decontamination
of surface and water, UV-ID, Label
tracking, Barcode, Protein analysis,
DNA sequencing and Drug discovery.
30 PHz – 3 EHz Soft X-Ray (SX)
X-Ray microscopic analysis, X-Ray
crystallography, Medical imaging ofbones, Airport security, Border control,
Astronomy.
3 EHz – 30 EHz Hard X-Ray (HX) Absorption spectroscopy, Scanning
microprobe and Radiotherapy.
> 30 EHz Gamma Rays ( - Ray) Container security initiative, Irradiation,
Gamma-knife surgery and Nuclear
medicine.
g
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Table 1.2: Letter designation of Microwave bands as per as per Radio
Society of Great Britain
Frequency Bands Frequency Range (GHz)
L 1 – 2
S 2 – 4
C 4 – 8
X 8 – 12
Ku 12 – 18
K 18 – 26.5Ka 26.5 – 40
Q 33 – 50
U 40 – 60
V 50 – 75
E 60 – 90
W 75 – 110F 90 – 140
D 110 – 170
G 140 – 220
H 170 – 260
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Table 1.3: Letter designation of microwave bands as per US Navy and
International Telecommunication Union (ITU)
Band US Navy ITU
L 0.390 – 1.55 1.215 – 1.400
S 1.55 – 3.90 2.300 – 2.500
2.700 – 3.700
C 3.90 – 6.20 5.250 – 5.925
X 6.20 – 10.90 8.500 – 10.680
Ku 15.25 – 17.25 13.40 – 14.0015.70 – 17.70
K 10.90 – 36.00 24.05 – 24.25
24.65 – 24.75
Ka 33.00 – 36.00 33.40 – 36.00
Q 36.00 – 46.00
V 46.00 – 56.00 59.00 – 64.00W 56.00 – 100.00 76.00 – 81.00
92.00 – 100.00
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1.2 Characteristics Features of Microwave
Upto around a frequency of 1 GHz, most circuits are designed andconstructed using lumped parameter circuit components.
Above 1 GHz the propagation time of the signal becomes comparable
with the time period of the signal. The lumped parameter circuit
component length also becomes comparable to the wavelength.This results in a rapid amplitude and phase variation of the signal
with the distance.
The phase difference caused by the interconnection of different
components is also not negligible above 1 GHz.
As a result at high frequencies KCL, KVL and normal voltage –
current concepts are not applicable. Instead field theory is required.
Limitations:
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Above 1 GHz the lumped circuit elements are replaced by the
distributed circuit element.
The distributed circuit elements are small transmission line sections
and the are defined over an infinitesimal length.
In this model the connecting wires between different elements are not
perfect conductor.
At high frequencies the distributed circuit model is more accurate
than the lumped element circuit model and also more complex in nature.
The existence of non-uniform current in the branches and non-uniform
voltages at the nodes further complicates the analysis of the circuit.The use of infinitesimals in distributed circuit model requires the
application of calculus rather than linear algebra.
Distributed circuit theory
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The high frequency nature of microwave has also brought the
complexity and challenges in designing microwave active components.
At microwave frequencies the transit time of the carriers through
ordinary low frequency triode and transistors becomes comparable with
the time period of the wave which restricts its operation at these
frequencies.
A number of new principles of operation namely velocity modulation,
interaction of space charge waves with EM field, quantum mechanical
tunnelling, avalanche breakdown and transferred electron techniques etc.
have been employed to generate microwave signals.
Challenges in designing microwave sources
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At microwave frequencies measurements of voltages and currents are
not possible with a multimeter or any other low frequency circuits.
At microwave frequencies the impedance of the parasitic of the
measurement cables and connectors become large enough and frequently
cross the component values. Thus special cable and connectors are
required.
The meter impedance and capacitance also affect the measurement.
The most common method to do microwave measurement is to measure
the field amplitudes, phase difference and power carried by the waves.
Another very common used method is based on the standing wave
pattern measurement.
Challenges in measurement
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1.3 Advantages of Microwave
High bandwidth
Improved gain / directive propertiesReduction in antenna size
Low power requirement
Fading effect and reliability
Transparency property of microwave
1.4 Disadvantages of Microwave
Line of sight propagationSubject to electromagnetic interference
Affected by bad weather
Costly equipments
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1.3 Applications of Microwave
Radio detection and ranging
Terrestrial microwave link
Transmission of many television channels over one link
Satellite communication
Radio astronomyLinear particle accelerator
Studies on basic properties of materials
Microwave oven
Industry
Medical Science