MICROWAVE DEVICES
LECTURE ONE
EBEN NORNORMEY
MICROWAVE SPECTRUM
Short History of Microwave Technology
• The fundamental concepts of Microwave
Engineering were developed more than 50 years ago.
• Radar is the first major application of Microwave
technology.
• Radar was intensively developed as far back as
World War II
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Today, microwave technology has developed and
continued to be developed in the following:
• High-frequency solid-state devices
• Microwave integrated circuits
• Computer-aided design techniques
• The ever-widening applications of RF and microwave
technology to wireless communications
• Networking
• Sensing
• Security
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• The above development has kept the Microwave
Engineering field active and vibrant.
• The foundation of microwave technology is
electromagnetic theory.
• Some of the geniuses in electromagnetic theory
are:
• James Clerk Maxwell
• Oliver Heaviside
• Heinrich Hertz
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Some of the geniuses that work intensively in the
microwave field are:
• N. Marcuvitz
• I. Rabi
• J. S. Schwinger
• H. A. Bethe
• E. M. Purcell
• C. G. Montgomery
• R. H. Dicke,
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• Microwave Spectrum forms part of the Electromagnetic
Spectrum with typical wavelengths from 1 millimetre to 100
centimetres.
• Its frequencies range from about 300 MHz – 300 GHz.
• It is in between light waves and radio waves.
• Microwave is composed of both electric and magnetic fields,
which are perpendicular to each other and propagates at the
speed of light throughout space.
• Speed of light “c” in vacuum is roughly 300,000,000 metres
per second, or 300,000 kilometres per Second (3x10⁸m/s or
3x10⁵Km/s).
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NB:
The entire universe is filled with microwave
radiation left by the Big Bang Explosion of the
early Universe.
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Applications of Microwave
• Communications:
used in Telecommunications, Wireless Computer
Networks, Broadcasting, Mobile Phones and
Transmission of T.V signal
• Baking:
Cooking using Microwave Oven ie the food is cooked
directly by using microwave radiation
• Radars
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• Navigation Systems:
To keep track of the position of airplane
• Electronic Warfare:
Intelligent gathering and counter measure
• RADER:
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Properties of Microwave
• Microwave is an electromagnetic radiation of short
Wavelength
• Microwave are composed of bundles of energy that
travel through a vacuum in a sine waveform
• Microwave are easily attenuated within short distances
• Microwaves communication systems are used to carry
telephony, television and data signals
• Microwaves are not reflected by the ionosphere
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Safety of microwave:
• Do not put metallic objects into microwave
radiation can pass through plastic and glass, but not metallic
objects. This is why the glass window of the door of microwave
oven is laced with metal wiring; the metal wiring keeps the
microwaves from leaving the cooking chamber. If you put a
metal object, such as a fork, into the oven, microwaves hitting
the fork will get reflected back to the source. The extent to
Which microwaves are reflected varies from the types of metal.
Certain metal composites actually absorb microwave energy.
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• Do not put boiled water into microwave
A phenomenon known as superheating is known to occur when
a cup of water is heated in a microwave oven. The water is
referred to as superheated when its temperature increases
above its normal boiling point (the boiling point for water at
standard atmospheric pressure is 100 ). The superheated
state is an unstable state. When water is superheated, the
presence of an external agent such as a spoon or even milk
powder can cause the water to boil vigorously into explosion. If
one litre of water is superheated by only 1 ᴼC, it can produce
about 3 litres of steam.
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• Almost all microwave ovens emit microwaves
whilst in operation the amount of microwave
emission decreases with the distance, therefore keep
a distance from microwave ovens when they are in
operation.
The official recommended value of microwave
emission for all domestic ovens is about 10mW/cm².
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• Cellular or mobile phones
As cellular or mobile phones are getting increasingly
popular in recent years, the effect of microwaves on our
health has also been a subject of study. The main concern
is the effect of heat produced by microwave radiation on
our body, particularly the brain. Despite the fact that the
recorded temperature rise on our body caused by
microwave radiation emitted from mobile phones was so
low, just a fraction of a degree Celsius, some researchers
believe that radiation emitted from mobile phones could
increase the risk of brain diseases.
Electromagnetic Spectrum
Microwave Bands and their Applications
Frequency Bands
Frequency Range
Uses
VLF
3-30KHz
Used for long distance
Communication.
LF
30-300KHz
Used For Marine
Communication.
MF
300-3000KHz
Used for Radio
broadcasting.
HF
3-30MHz
For long distance
Communication
VHF
30-300MHz
FM Radio, Television
broadcasting.
UHF
300-3000MHz
For short distance
communication.
SHF
3-30GHz
Satellite/Space
communication.
EHF
30-300GHz
Radar, Space
communication.
Electromagnetic Spectrum
Designation Microwave
Some Applications
Band
(GHz)
L-Band
1-2
World Space Digital Radio
S-Band
2-4
Wi-Fi, Bluetooth, UWB, heating,
WiMax
C-Band
4-8
Satellite(big dishes), WiMax
X-Band
8-12
Satellite Communication, MultiTV,
DSTV, etc
Ku-Band
12-18
Satellite Communication, MultiTV,
DSTV, etc
K-Band
18-27
Satellite Communication
Ka-Band
27-40
V
40-75
W
75-110