Naval Weapons Naval Weapons SystemsSystems

Energy Energy FundamentalsFundamentals

Learning ObjectivesLearning Objectives

Comprehend basic communication theory, Comprehend basic communication theory, electromagnetic (EM) wave theoryelectromagnetic (EM) wave theory

Comprehend radar and radio wave Comprehend radar and radio wave parameters including frequency, period, parameters including frequency, period, wavelength, velocity, and amplitudewavelength, velocity, and amplitude

Know Maxwell’s theory, relationship Know Maxwell’s theory, relationship between wave parametersbetween wave parameters

Comprehend concepts of time and distance Comprehend concepts of time and distance (wave phase angle) and interference(wave phase angle) and interference

Learning Objectives (cont)Learning Objectives (cont)

Know EM wave propagation principles such Know EM wave propagation principles such as reflection, refraction, diffraction, and as reflection, refraction, diffraction, and ductingducting

Know the definition of sky, space, and Know the definition of sky, space, and ground wavesground waves

Energy FundamentalsEnergy Fundamentals

RARAdio dio DDetection etection AAnd nd RRanginganging Radar is an Radar is an electromagnetic wave electromagnetic wave that acts like any that acts like any

other electromagnetic wave (i.e. - radio, light, etc.)other electromagnetic wave (i.e. - radio, light, etc.) Characteristics of a radio wave assuming a Characteristics of a radio wave assuming a

frequency of 2 Hertz:frequency of 2 Hertz:

Cycle

Amplitude

1 second

Traveling Wave CharacteristicsTraveling Wave Characteristics

FrequencyFrequency PeriodPeriod WavelengthWavelength VelocityVelocity AmplitudeAmplitude

Maxwell’s TheoryMaxwell’s Theory

An accelerating electric field will generate a An accelerating electric field will generate a time-varying magnetic field.time-varying magnetic field.

A time-varying magnetic field will generate a A time-varying magnetic field will generate a time-varying electric field.time-varying electric field.

...and so on...and so on...and so on......and so on...and so on...and so on...

Electric Field Magnetic Field Electric Field

Formation of Electric and Magnetic Formation of Electric and Magnetic Fields around an AntennaFields around an Antenna

e- e- e-

E-line

Mag field

Electric field | Magnetic Field | Direction of Propagation.

Electromagnetic SpectrumElectromagnetic Spectrum

Propagation Paths of E-M WavesPropagation Paths of E-M Waves

ReflectionReflection RefractionRefraction DiffractionDiffraction

...Reflection......Reflection...

Incident Wave

Reflected Wave

Phase shift = 180 degrees.

Angle of incidence = Angle of reflected wave.

-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.

...Refraction......Refraction...

Snell’s LawSnell’s Law

n1 * Sin θ1 = n2 * Sin θ2

...Diffraction......Diffraction...

islandnot detected

detected

...plane waves traveling in a straight path bend around a boundary or obstruction.

Wave Propagation – Wave Propagation – Distance and FrequencyDistance and Frequency

Ground WavesGround Waves Sky WavesSky Waves Space WavesSpace Waves

Ground Wave...Ground Wave...

E-M energy travels along earth’s surfaceE-M energy travels along earth’s surface Very low frequencies, 5-10KhzVery low frequencies, 5-10Khz Extremely long wavelengthsExtremely long wavelengths Shore communications stations (HF-DF)Shore communications stations (HF-DF)

Sky Wave...Sky Wave...

E-M energy refracts toward earth’s surface E-M energy refracts toward earth’s surface in upper ionosphere layerin upper ionosphere layer

E-M energy then reflects back toward upper E-M energy then reflects back toward upper layer againlayer again

Frequencies to 550 KHz effectivelyFrequencies to 550 KHz effectively Fairly long wavelengthsFairly long wavelengths Ship and Aircraft Communications Ship and Aircraft Communications

Space Wave...Space Wave...

E-M energy refracts back toward earth’s E-M energy refracts back toward earth’s surface in outer space (i.e. stratosphere)surface in outer space (i.e. stratosphere)

Above 30 MHz, ionosphere will not refract Above 30 MHz, ionosphere will not refract E-M waves back toward earth.E-M waves back toward earth.

Transmission Range Factors

Antenna HeightAntenna Height Target HeightTarget Height DuctingDucting LossesLosses

– SpreadingSpreading– AbsorptionAbsorption– Constructive InterferenceConstructive Interference– Destructive InterferenceDestructive Interference

ModulationModulation

The process of encoding The process of encoding “Carrier Wave”“Carrier Wave” ““Carrier Wave”Carrier Wave” has 3 independent parameters has 3 independent parameters

– AmplitudeAmplitude– FrequencyFrequency– PhasePhase

WHEW!WHEW!

Questions?Questions?