Naval Weapons Systems

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Naval Weapons Systems

• Energy Fundamentals

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Energy Fundamentals

• 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
• Period
• Wavelength
• Velocity
• Amplitude
• ...examples....

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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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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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Electromagnetic Spectrum
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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
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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.
• The result is that the energy ray will bend
  toward the area of higher density.

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Snells Law
n1Sin ?1n2Sin ?2
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...Diffraction...
...plane waves traveling in a straight path bend
around a boundary or obstruction.
detected
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Wave Propagation Distance and Frequency

• Ground Waves
• Sky Waves
• Space Waves

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Ground Wave...

• E-M energy travels along earths surface
• Very low frequencies, 5-10Khz
• Extremely wavelengths
• Shore communications stations (HF-DF)

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Sky Wave...

• E-M energy refracts toward earths surface in
  upper ionosphere layer
• E-M energy then reflects back toward upper layer
  again
• Frequencies to 550 KHz effectively
• Fairly long wavelengths
• Ship and Aircraft Communications

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Space Wave...

• E-M energy refracts back toward earths surface
  in outer space (i.e. stratosphere)
• Above 30 MHz, ionosphere will not refract E-M
  waves back toward earth.

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Transmission Range Factors

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

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Communication Systems
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Basic Comms Path
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Transmitter

• Transducers Changes energy form
• Acoustic waves to EM waves
• Boosts power of 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 same time.
• i.e. walkie-talkie
• Full-Duplex both and at the same time
• i.e. shipboard telecommunications systems

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Receiver

• Tuner allows particular frequency reception

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Modulation

• The process of encoding Carrier Wave
• Carrier 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

• Expressed as a ratio of
• Signal power / Noise power
• Unit of measure in Decibels
• The more positive the number, clearer the signal.
• Unless you want to hide it!!!

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• Questions?