•electromagnetic waves with frequencies that
range (500MHz – 300 GHz)
• high frequencies, short wavelength
•An electromagnetic wave with a wavelength
in the range 0.001–0.3 m.
•Microwaves are used in radar, in
communications, and for heating
• Microwaves are electromagnetic waves which
consists of both electric and magnetic fields
perpendicular to each other and propagates at the
speed of light.
• Microwaves form parts of the electromagnetic
spectrum with typical wavelengths from 1 millimetre to
10 centimetres – something in between light waves
and radio waves.
• Microwaves are also used in telecommunications, e.g.,
radars, wireless computer networks and mobile
• The entire universe is filled with microwave radiation
left by the Big Bang explosion of the early Universe.
• Visible Light is only one form of electromagnetic
• Radio waves, heat, ultra-violet rays and X-rays
are other familiar forms.
• All of this energy is inherently similar, and
radiates in accordance with basic wave theory.
Electromagnetic radiation consists of an electrical
field (E) which varies in magnitude in a direction
perpendicular to the direction in which the radiation
is travelling, and a magnetic field (M) oriented at
right angles to the electrical field.
Both these fields travel at the speed of light (c)
Wavelength and Frequency
• Wavelength is measured in metres (m) or some factor
of metres such as:
▫ nanometers (nm, 10-9 metres),
▫ micrometers (mm, 10-6 metres) or
▫ centimetres (cm, 10-2 metres).
• Frequency refers to the number of cycles of a wave
passing a fixed point per unit of time. Frequency is
normally measured in hertz (Hz), equivalent to one
cycle per second, and various multiples of hertz.
From basic physics, waves obey the general
Since c is essentially a constant (3 x 108 m/sec),
frequency v and wavelength λ for any given wave
are related inversely, and either term can be used
to characterise a wave into a particular form.
• The electromagnetic spectrum ranges from the
shorter wavelengths (including gamma and x-rays)
to the longer wavelengths (including microwaves
and broadcast radio waves).
• There are several regions of the electromagnetic
spectrum which are useful for remote sensing.
• The light which our eyes - our "remote sensors"
- can detect is part of the visible spectrum.
• It is important to recognise how small the visible
portion is relative to the rest of the spectrum.
• There is a lot of radiation around us which is
"invisible" to our eyes, but can be detected by
other remote sensing instruments and used to
• The visible wavelengths cover a range from
approximately 0.4 to 0.7 mm.
• The longest visible wavelength is red and the
shortest is violet.
• It is important to note that this is the only portion
of the EM spectrum we can associate with the
concept of colours.
• Blue, green, and red are the primary colours or
wavelengths of the visible spectrum.
• They are defined as such because no single primary
colour can be created from the other two, but all other
colours can be formed by combining blue, green, and
red in various proportions.
• Although we see sunlight as a uniform or homogeneous
colour, it is actually composed of various wavelengths.
• The visible portion of this radiation can be shown when
sunlight is passed through a prism
• The IR Region covers the wavelength range
from approximately 0.7 mm to 100 µm - more
than 100 times as wide as the visible portion!
• The infrared region can be divided into two
categories based on their radiation properties the reflected IR, and the emitted or thermal IR.
Needs for microwaves in communication
• Microwave transmission refers to the technology of transmitting
information or energy by the use of radio waves whose wavelengths are
conveniently measured in small numbers of centimeter; these are called
• This part of the radio spectrum ranges across frequencies of roughly
1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from
30 centimeters down to 1.0 cm.
• Microwaves are widely used for point-to-point communications
because their small wavelength allows conveniently-sized antennas to
direct them in narrow beams, which can be pointed directly at the
• This allows nearby microwave equipment to use the same frequencies
without interfering with each other, as lower frequency radio waves do.
Needs for microwaves in communication
• A disadvantage is that microwaves are limited to line of sight
propagation; they cannot pass around hills or mountains as lower
frequency radio waves can.
• Microwave radio transmission is commonly used in point-to-point
communication systems on the surface of the Earth, in
satellite communications, and in deep space radio communications.
Other parts of the microwave radio band are used for radars, radio
navigation systems, sensor systems, and radio astronomy.
Radiation Hazard (RADHAZ) describes the hazards of electromagnetic radiation
1) Hazards of Electromagnetic Radiation to Personnel (HERP)
2) Hazards of Electromagnetic Radiation to Ordnance (HERO)
3) Hazards of Electromagnetic Radiation to Fuel (HERF)
Hazard of Electromagnetic Radiation to Personnel
Effect only possible at 10x permissible exposure limits.
Cause harmful effects to humans.
Electromagnetic radiation from antennas fed by high–powered
transmitters can potentially injure personnel in the vicinity of the
radiating antennas. Transmitters on aircraft, aboard ship, and at
air stations are potential sources of harmful electromagnetic
The danger of HERP occurs because the body absorbs
radiation and significant internal heating may occur without the
individuals knowledge because the body does not have internal
sensation of heat, and tissue damage may occur before the
excess heat can be dissipated.
Hazard of Electromagnetic Radiation to Fuel
Create sparks of sufficient magnitude to ignite flammable
There is a potential for accidentally igniting fuel vapors by RF–
induced arcs during fuel
handling operations close to high–powered radio and radar
transmitting antennas. The facility
conducts radiation surveys to determine if the hazard exists in
fuel handling or fueling areas.
Hazards of Electromagnetic Radiation to Ordnance
Extremely high power electromagnetic radiation can cause electric currents strong
enough to create sparks (electrical arcs) when an induced voltage exceeds the
breakdown voltage of the surrounding medium (e.g.air). These sparks can then
ignite flammable materials or gases, possibly leading to an explosion.
This can be a particular hazard in the vicinity of explosives or pyrotechnics, since
an electrical overload might ignite them.
This risk is commonly referred to as HERO(Hazards of Electromagnetic Radiation
MIL-STD-464A mandates assessment of HERO in a system, but Navy document
OD 30393 provides design principles and practices for controlling electromagnetic
hazards to ordnance.
Radiation Hazard (RADHAZ)
Surveys are conducted to determine the RADHAZ
distance and appropriate safety precautions to
ensure personnel are not exposed to power
intensities exceeding established safe limits.