Lesson 2 Wave Propagation

8/3/2019 Lesson 2 Wave Propagation

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Wave PropagationWave Propagation


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3/31

ObjectivesObjectives

Apply the relationship between Frequency, Wavelength and the

Speed of Wave Propagation

Distinguish between Reflection, Refraction, and Diffraction

Solve refraction angles using Snells Law

Explain the relationship between an electric field and its

magnetic field and how because of this relationship,

electromagnetic waves propagate

Explain Constructive or Destructive EM wave Interference and

calculate Phase Shift

Identify the range of frequencies associated with each EM band

designation

List the various wave propagation paths and the band

designations associated with the propagation

Solve for the radar horizon using the height relationship between

the target and sensor

Apply the relationship between Frequency, Wavelength and the

Speed of Wave Propagation



Explain the relationship between an electric field and its

magnetic field and how because of this relationship,

electromagnetic waves propagate

Explain Constructive or Destructive EM wave Interference and

calculate Phase Shift

Identify the range of frequencies associated with each EM band

designation

List the various wave propagation paths and the band


Solve for the radar horizon using the height relationship between

the target and sensor


4/31

Particles vs. WavesParticles vs. Waves

Two great concepts in physics

Particles suggest a tiny concentration of matter

capable of transmitting energy

Waves suggest just the opposite a broad

distribution of energy filling the space throughwhich it passes.

Two great concepts in physics

Particles suggest a tiny concentration of matter

capable of transmitting energy

Waves suggest just the opposite a broad

distribution of energy filling the space throughwhich it passes.


5/31

Wave CharacteristicsWave Characteristics

Two Types (for our purposes).

Mechanical ~ Requires medium for propagation Sound (Sonar) (Air or Water)

Electromagnetic ~ Doesnt require medium forpropagation

Light (Air or Water)

Radio (Air or Water)

Radar (Air)

Mechanical Waves Propagate as Longitudinal WavesDisturbance in line with direction of propagation

Electromagnetic Waves Propagate as Transverse Waves

Disturbance right angles to direction of propagation

Two Types (for our purposes).

Mechanical ~ Requires medium for propagation Sound (Sonar) (Air or Water)

Electromagnetic ~ Doesnt require medium forpropagation

Light (Air or Water)

Radio (Air or Water)

Radar (Air)

Mechanical Waves Propagate as Longitudinal WavesDisturbance in line with direction of propagation

Electromagnetic Waves Propagate as Transverse Waves

Disturbance right angles to direction of propagation


6/31

Energy FundamentalsEnergy Fundamentals

RAdio Detection And Ranging

Radar is an electromagnetic wave that acts likeany other electromagnetic wave (radio, light, etc.)

Characteristics of a radio wave assuming a

frequency of 50 Hertz:

RAdio Detection And Ranging

Radar is an electromagnetic wave that acts likeany other electromagnetic wave (radio, light, etc.)

Characteristics of a radio wave assuming a

frequency of 50 Hertz:

1 Cycle / .02 Sec

50 Cycles / 1 Sec


7/31


Spherical Wave (Near Field)

Undisturbed wave

Omni directional from source

Ripples on a pond.

Spherical Wave (Near Field)

Undisturbed wave

Omni directional from source

Ripples on a pond.

Plane Wave (Far Field)

Far from origin

Spreads out to appear to have sameamplitude everywhere on plane

perpendicular to direction of travel

Think of entire wave traveling in one

direction

Plane Wave (Far Field)

Far from origin

Spreads out to appear to have sameamplitude everywhere on plane

perpendicular to direction of travel

Think of entire wave traveling in one

direction


8/31

Wave TermsWave Terms

Frequency (f) Rate at which source disturbanceoscillates through one complete cycle (Hertz Hz sec 1)

Wavelength (l) Distance between two identical pointson adjacent waves or distance traveled by wave in onecycle. (Length cm, mm, m) = c/f

Velocity (c) EM waves travel at speed of light,

(c = 3 x 108 m/s)

Amplitude (A) Maximum displacement of wave fromconstant reference value.

Period (T) Time to complete one cycle (time, sec)

Frequency (f) Rate at which source disturbanceoscillates through one complete cycle (Hertz Hz sec 1)

Wavelength (l) Distance between two identical pointson adjacent waves or distance traveled by wave in onecycle. (Length cm, mm, m) = c/f

Velocity (c) EM waves travel at speed of light,

(c = 3 x 108 m/s)

Amplitude (A) Maximum displacement of wave fromconstant reference value.

Period (T) Time to complete one cycle (time, sec)


9/31

PhasePhase

Identical Waves shifted either

ahead or behind due to distanceseparations or time delay.

Pick one as a reference and

determine phase difference or

phase shift between the two.

Phase is measured in either degreesor radians.

Phase is measured in either degreesor radians.

radians = (2T/360o) x degreesdegrees = (360o/2T) x radians

57.3o per radian

radians = (2T/360o) x degreesdegrees = (360o/2T) x radians

57.3o per radian

Positive phase shift wave is advanced

Negative phase shift wave is retarded

Positive phase shift wave is advanced

Negative phase shift wave is retarded


10/31

Fourier AnalysisFourier Analysis

French mathematician Jean Baptist Fourier explained how the

principles of interference can be used to analyze non-sinusoidalwave forms.

Specifying amount and frequency of each component (cosine and

sine waves) is representative of frequency domain.

8 Hz easily

recognizable,

other freqs.

questionable.

8 Hz easily

recognizable,

other freqs.

questionable.


11/31

Propagation Paths of Electromagnetic WavesPropagation Paths of Electromagnetic Waves

Reflection

Refraction Diffraction

Absorption

Reflection

Refraction Diffraction

Absorption


12/31

ReflectionReflection

Medium boundaries with dissimilar propagation result

in reflection

Medium boundaries with dissimilar propagation result

in reflection

Specular

reflection is

reflected at equal

but opposite

angle from

smooth surface

Diffuse reflection

results from

waves striking in

irregular surfaceand reflecting

over a broad

range


13/31

ReflectionReflection

When we examine at the particle level When we examine at the particle level


14/31

RefractionRefraction

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.

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.

As the angle of incidence

increases, angle ofrefraction increases

When the angle of

refraction = 90o then

critical angle

For a range of incidence

greater than 90o, no

refraction, only internal

reflection

As the angle of incidence

increases, angle ofrefraction increases

When the angle of

refraction = 90o then

critical angle

For a range of incidence

greater than 90o, no

refraction, only internal

reflection

No internal reflection when starting in alowern because sin e 1

No internal reflection when starting in alowern because sin e 1

!

1

21sinn

n

cU


15/31

RefractionRefraction

Electromagnetic waves propagate at speed of light (c) =

3 x 108

m/s (in vacuum)Speed of light varies in different medium (Cm)

Light refracts at medium boundary layer.

Index of refraction, n, defined as;

n = c/cm

Electromagnetic waves propagate at speed of light (c) =

3 x 108

m/s (in vacuum)Speed of light varies in different medium (Cm)

Light refracts at medium boundary layer.

Index of refraction, n, defined as;

n = c/cm

We can determine

either indices of

refraction or angle ofrefraction by applying

Snells Law

We can determine

either indices of

refraction or angle ofrefraction by applying

Snells Law

n1sinU

1= n

2sinU

2n1sinU

1= n

2sinU

2


16/31

DiffractionDiffraction

Spreading of wave along

edge of an object Amount of diffraction is

wavelength and size

related

Wave bends whenwavelength is larger than

object or opening

Can hear around corner,

but cant see around acorner.

Radar can detect around

an object under the right

conditions

Spreading of wave along

edge of an object Amount of diffraction is

wavelength and size

related

Wave bends whenwavelength is larger than

object or opening

Can hear around corner,

but cant see around acorner.

Radar can detect around

an object under the right

conditions


17/31

InterferenceInterference

Interference when two or more waves collide,

superposition of amplitudes add to produce a resultingwave.

Described as either constructive or destructive

interference, depending on phase shift between waves.

Constructive phase difference between 0o and 120o orbetween 240o and 360o .

Destructive phase difference between 120o and 240o .

Interference when two or more waves collide,

superposition of amplitudes add to produce a resultingwave.

Described as either constructive or destructive

interference, depending on phase shift between waves.

Constructive phase difference between 0o and 120o orbetween 240o and 360o .

Destructive phase difference between 120o and 240o .

Destructive

0o

240o 120o


18/31

Electromagnetic Signal LossElectromagnetic Signal Loss

Spreading - energy distributed over an

increasingly larger area. Energy per unit area

proportional to 1/R2.

Absorption - energy dissipated into medium.

Molecules of medium absorb some of the energy

as it passes through.

Scattering - energy bouncing off suspended

particles within a medium. Scattering is going tobe particulate size/radar frequency dependent.

Spreading - energy distributed over an

increasingly larger area. Energy per unit area

proportional to 1/R2.

Absorption - energy dissipated into medium.

Molecules of medium absorb some of the energy

as it passes through.

Scattering - energy bouncing off suspended

particles within a medium. Scattering is going tobe particulate size/radar frequency dependent.


19/31

SpreadingSpreading


20/31

AbsorptionAbsorption


21/31

AbsorptionAbsorption


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There is a relationship between distanceand frequency

There is a relationship between distanceand frequency

Propagation Modes

Ground WaveSky Wave

Space Wave

Propagation Modes

Ground WaveSky Wave

Space Wave


23/31

Frequency Band Range (nm) Power Rate

SpaceWaves

Sho

rtRange(Tactical)

30-300 GHz EHF Attenuationsusceptible

100 Mbps

3-30 GHz SHF 4

0 (G/ LOS)100-300 (Tropo)

P/G limit (Satellite)

25

0 kbps

300-3000 MHz UHF 15-100 (LOS)

300 (LOSAir)

1000s (Satellite)

10-100 W

2500-10000 W

56 kbps

30-300 MHz VHF 25-50 (G)

LOS (D)

.25-120 W 75 baud

9600 bps

3-30 MHz HF 30-300 (G)

Span Globe (S)

2-100 kW 2400 bps Sky

Wave

Long

Range

300-3000 kHz MF 100-1000 (G)

1

000-3000 (S)

75 baud G

roundWaves

VeryLongRange

(Strategic)

30-300 kHz LF 1000-5000 50-100 kW 75 baud

3-30 kHz VLF 5000+ 100-200 kW 50 baud

3-3000 Hz ELF 5000+ 100 MW 1-2 baud


24/31

Ground WaveGround Wave

Very low frequencies (5-

10Khz) Vertical polarization

Waves travel along earths

surface. Very long wavelengths -

unsuitable for ships &

aircraft, but used for subcomms

Shore-based installations

(HF-DF)

Very low frequencies (5-

10Khz) Vertical polarization

Waves travel along earths

surface. Very long wavelengths -

unsuitable for ships &

aircraft, but used for subcomms

Shore-based installations

(HF-DF)


25/31

Sky WaveSky Wave

E-M energy refracts in upper ionosphere and is

directed back to Earth. May occur multiple times Frequencies used up to 550 KHz effectively

Wavelengths still too long for anything but

comms by aircraft and ships. (Antenna Length)

E-M energy refracts in upper ionosphere and is

directed back to Earth. May occur multiple times Frequencies used up to 550 KHz effectively

Wavelengths still too long for anything but

comms by aircraft and ships. (Antenna Length)


26/31

Space WaveSpace Wave

Higher frequency signals that penetrate the

ionosphere and travel through space. Above 30 MHz, ionosphere will not refract E-M

waves back toward earth.

Energy tends to travel in straight line.

Higher frequency signals that penetrate the

ionosphere and travel through space. Above 30 MHz, ionosphere will not refract E-M

waves back toward earth.

Energy tends to travel in straight line.


27/31

Atmospheric effects on Space WavesAtmospheric effects on Space Waves

Ionospheric Scatter

Scattered reflection of VHF and up signals

600 1000 miles

Tropospheric Scatter

Scattering signal off of troposphere.

Air turbulence, irregularities in refractive index,homogeneous discontinuities.

Boundary layers between stratified pockets of air.

Strong function of weather.

400 miles.

Tropospheric ducting

Present in inversion conditions (as is all ducting).

Refraction curve matches curvature of the earth.

Ionospheric Scatter

Scattered reflection of VHF and up signals

600 1000 miles

Tropospheric Scatter

Scattering signal off of troposphere.

Air turbulence, irregularities in refractive index,homogeneous discontinuities.

Boundary layers between stratified pockets of air.

Strong function of weather.

400 miles.

Tropospheric ducting

Present in inversion conditions (as is all ducting).

Refraction curve matches curvature of the earth.


28/31


29/31

Radar Line of SightRadar Line of Sight

Due to

refraction,

certain

electromagneti

waves cantransmit farthe

than the

visual Line o

Sight (LOS).

Due to

refraction,

certain

electromagneti

waves cantransmit farthe

than the

visual Line o

Sight (LOS).


30/31

Radar Horizon (LOS)Radar Horizon (LOS)

To compute the maximum detection range

between a target and electromagnetictransmitting antenna, the following equation can

be employed:

HT = Target Height in METERS HR= Radar Antenna Height in METERS

Resultant Range is in Kilometers!

To compute the maximum detection range

between a target and electromagnetictransmitting antenna, the following equation can

be employed:

HT = Target Height in METERS HR= Radar Antenna Height in METERS

Resultant Range is in Kilometers!

RT HHkmR 1717)( !


31/31

ObjectivesObjectives

Apply the relationship between Frequency, Wavelength andthe Speed of Wave Propagation



Explain the relationship between an electric field and itsmagnetic field and how because of this relationship,

electromagnetic waves propagate Explain Constructive or Destructive EM wave Interference

and calculate Phase Shift

Identify the range of frequencies associated with each EM

band designation List the various wave propagation paths and the band


Solve for the radar horizon using the height relationshipbetween the target and sensor

Apply the relationship between Frequency, Wavelength andthe Speed of Wave Propagation



Explain the relationship between an electric field and itsmagnetic field and how because of this relationship,

electromagnetic waves propagate Explain Constructive or Destructive EM wave Interference

and calculate Phase Shift

Identify the range of frequencies associated with each EM

band designation List the various wave propagation paths and the band


Solve for the radar horizon using the height relationshipbetween the target and sensor

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Lesson 2 Wave Propagation

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