Naval Weapons Systems

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Naval Weapons Systems

• Energy Fundamentals

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Energy FundamentalsOverview

• RADAR
• Electromagnetic (E-M)Wave Characteristics
• Maxwells Theory
• Polarization
• Interference
• Propagation of E-M waves
• Transmission Range factors

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Energy FundamentalsRADAR

• RAdio Detection And Ranging
• Radar is an electromagnetic wave that acts like
  any other electromagnetic wave (i.e. - radio,
  light, etc.)
• Characteristics of a radio wave assuming a
  frequency of 2 Hertz

Cycle
Amplitude
1 second
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Traveling Wave Characteristics

• Frequency
• Measured
• in Hertz (Hz)
• (Cycles/sec)
• ?(Wavelength) c (Speed of Light)

f (frequency)
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Traveling Wave Characteristics

• Period
• The time required
• for a full cycle
• Inverse of Frequency
• T1/f

T
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Traveling Wave Characteristics

• Wavelength
• The distance
• between 2 identical
• points on adjacent
• waves

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Traveling Wave Characteristics

• Phase
• The angular
• difference where a
• wave begins relative
• to an arbitrary starting
• point

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Traveling Wave Characteristics

• Velocity
• The speed of light
• Amplitude
• Distance from the
• baseline to the crest of the wave

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Maxwells Theory

• An accelerating electric field will generate a
  time-varying magnetic field.
• A time-varying magnetic field will generate a
  time-varying electric field.
• ...and so on...and so on...and so on...

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Generation of Electromagnetic Radiation


-
-
-

a
b
c
d
Alternating Current Source
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Formation of Electric and Magnetic Fields around
an Antenna
E-line
Mag field
e-
e-
e-
Electric field Magnetic Field
Direction of Propagation.
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Energy Fundamentals

• Part II
• Polarization
• Interference
• Wave Propagation
• Wave Types

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What is Polarization?

• The direction of polarization of an antenna is
  defined as the electric field vector.

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Interference

• Electromagnetic wave interference can be both
• Constructive
• Destructive

• Interference varies with phase angle

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Constructive Interference

• Constructive Interference

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Constructive Interference

• Destructive Interference

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End of Part 1

• Questions ?

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Propagation Paths of E-M Waves

• Reflection
• Refraction
• Diffraction

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...Reflection...
Phase shift 180 degrees. Angle of incidence
Angle of reflected wave.
Reflected Wave
Incident Wave
?R
?I
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...Refraction...
- Incident wave passes through two transparent
media in which the velocity of light differs... -
Incident wave divides into a reflected wave and a
refracted wave.
Snells Law
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...Diffraction...
...plane waves traveling in a straight path bend
around a boundary or obstruction.
detected
island
not detected
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Wave Propagation - relationship between distance
and frequency

• Ground Waves
• Sky Waves
• Space Waves

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Ground Wave...

• Very low frequencies (VLF)
• Vertical polarization
• Waves travel along earths surface.
• 5-10Khz
• Very long wavelengths - unsuitable for ships
  aircraft, except comms
• Shore-based installations (HF-DF)

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Draw on board
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Sky Wave...

• E-M energy refracts back towards the earths
  surface in upper ionosphere layer.
• E-M energy then reflects back toward upper layer
  again.
• Frequencies used up to 550 KHz effectively (LF
  and MF region)
• Wavelengths still too long for anything but comms
  by aircraft and ships.

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Draw on board
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Space Wave...

• Above 30 MHz, ionosphere will not refract E-M
  waves back toward earth.
• Energy tends to travel in straight line.

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Electromagnetic Spectrum
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Transmission Range Factors

• Antenna Height
• Target Height
• Ducting
• Losses
• Spreading
• Absorption
• Constructive / Destructive Interference

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Transmission Losses

• Spreading Energy per unit area proportional to
  1/R.
• Absorption Molecules of medium absorb some of
  the energy as it passes through.

2
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Communication Systems
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Basic Comms Path
p. 40 in textbook
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Transmitter

• Transducers Devices that change energy form
• i.e. acoustic waves to EM waves
• Often boost the power of the signal to increase
  distance.

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Transmission Channel

• Air
• Water
• Wire
• Co-axial
• Fiber Optics
• Beer

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Transmit/Receive Capability

• Simplex one or the other
• i.e. car radio
• Half-Duplex both, but not at the same time.
• i.e. walkie-talkie or BTB
• Full-Duplex both and at the same time
• i.e. telephone system and most shipboard
  communications.

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Receiver

• Tuner this is what allows you to listen in on a
  particular frequency.

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Modulation

• The process of encoding information on the
  Carrier Wave.
• A simple Sine wave.
• The Sine wave has 3 independent parameters
• Amplitude
• Frequency
• Phase

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Noise

• Noise is bad on a communications circuit.
• Two types
• Broadband Noise White Noise
• Narrowband Noise Interference

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Signal-to-Noise Ratio

• Can be expressed in a pure number
• Signal power / Noise power
• More commonly expressed in Decibels.
• Signal level is on a relative scale compared to
  the noise.
• The more positive the dB number, the clearer the
  signal.
• Unless you want to hide it!!!

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Questions ?
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Assignment

• Read
• Chapter
• Radar Principles and Systems