1. Naval Weapons Systems Energy Fundamentals
Weapons system must detect the target
Detect energy emitted or reflected from the target
We will talk about these different types of energy
Electromagnetic
Audio
Heat
Light

2. 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
Measured in units of Frequency, or HERTZ, cycles per second
Sound: Amplitude of the sound waves
Electromagnetic: Amplitude of electric and magnetic fields
Represent energy as a SINE wave.
The nature of the energy (heat, light, electromagnetic, audio) and its frequency are directly related.
Amplitude
1 second

3. Traveling Wave Characteristics
Frequency
Period
Wavelength
Velocity
Amplitude
...examples....
Point out that the sinusoid wave graph represents the energy level seen over time.
1. Amplitude - The maximum amount of energy of the wave.
2. Wave length - Distance between two identical points on the sine wave.
i.e.... one wave cycle.
- If you know how fast the wave moves then your can use wave length to
determine the distance the energy travels in one cycle.
3. Frequency - How many cycles (complete patterns) in a second. (hertz)
- This is principle distinguishing characteristic of energy.
- The nature of energy (and its behavior) is directly related to the
frequency
Make sure everyone understands what a cycle means.
- Wave length relates to frequency: wave length= propagation speed
propagation speed for electromagnetic energy is speed of light in air.
Note that as wave frequency gets bigger the wave length gets smaller.
4. Period - Is the time required to go one cycle (T=1/freq..)

4. Maxwell’s 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...
1. The students must know Maxwell's Theory. Must Memorize.
2. Theory means there is an energy transfer taking place between electrical and magnetic fields when changes occur in electrical or magnetic energy. Each affects the other. i.e... A changing electrical field produces a changing magnetic field that produces a change in the electrical field....etc
3. Relate to students knowledge that an electrical wire with current flowing will effect a magnetic compass (magnetic field it measures).
4. Since the electrical and magnetic fields effect each other they go on
forever (and travel at the speed of light).
5. Bottom line: If we produce a varying electrical field we can produce a corresponding varying magnetic field and together they will propagate together as electromagnetic waves.

5. Generation of Electromagnetic Radiation+ + -
1. Principle mean of propagation of electromagnetic waves is dipole antenna.
- suitable conducting material.
- 1/2 of wave length long
2. Explain how it works:
a. Electrical energy difference on antenna conductor produces an electrical
field. (Voltage difference between two ends - current flow).
NOTE:
- Field lines (represent points where the field strength
(force) is the same magnitude).
- Outer lines are further apart due to natural repulsion force
between forces that move in the same direction.
b. Shows how the force lines collapse when the voltage difference between ends reduces.
c. Because of delay in reaction of Maxwell's theory the outer field lines do not collapse as fast as inner one and they close in around themselves forming a loop.
d. As the electrical field is reversed, opposite field lines are produced. Since the field lines are in same direction as the one that collapsed on themselves the like polarity repulsion forces push the closed loop fields away at nearly the speed of light. - - + a b c d
= Alternating Current Source

6. Formation of Electric and Magnetic Fields around an Antenna
E-line
Mag field e- e- e-
1. Show Slide and show electrical and magnetic fields.
2. Point out that:
- The magnetic field lines are at 90 degrees to the electrical fields lines.
- The field strengths are greater at the center of the antenna and less at
the ends.
3. Another good picture is fig. 2-9 on p.29 of text.
Electric field | Magnetic Field | Direction of Propagation.

7. What is Polarization?
The direction of polarization of an antenna is defined as the electric field vector.
3 Kinds:
Horizontal
Vertical
Circular
Polarization based on the electric field
Electric field direction determined by ANTENNA DIRECTION
Vertically oriented antenna poor reception of horizontally polarized signal.
Refer to figure 2-9, page 29 and the example on the same page.
Commercial radio broadcasts over a vertical antenna, a car receiver must be vertical as well to receive a good signal.

8. Propagation Paths of E-M Waves
Reflection
Refraction
Diffraction
Reflection: When waves strike a medium boundary and are reflected back. (Mirror)
Refraction: Another effect when waves strike a medium boundary, direction of travel changed, but allowed to pass through the boundary. (Pool of water)
Diffraction: How waves can be bent around a boundary or obstruction. (How radar can detect something “over the horizon”

9. Snell’s Law
n1*Sin θ1=n2*Sin θ2 θ1 θ2
Medium 1
Medium 2

10. Angle of incidence = Angle of reflected wave.
...Reflection...
Phase shift = 180 degrees.
Angle of incidence = Angle of reflected wave.
Reflected Wave
Incident Wave
About reflection:
a. The reflected wave will be 180 degrees out of phase with the original
wave of incident.
b. The only way to get reflected energy back to the source (as needed for
radar to work) is to hit the material perpendicular to the surface.
c. If the surface is not flat then reflected rays will not go in the same
direction. (scattering)
d. Many other things besides targets can cause reflections (dust, rain, snow,
and water vapor, sandstorms in the gulf).
e. Can get reflections off ionosphere.

11. ...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.
About Refraction:
a. The refracted ray will remain in; the same plane as incident ray.
b. Although there are no clear boundaries of medium in air, there are
different densities. The result is that the energy ray will bend
toward the area of higher density.
Example: A Prism!!

12. ...Diffraction...
...plane waves traveling in a straight path bend around a boundary or obstruction.
island
not detected
detected
1. Classic example of diffraction is waves around a break water.
Same is true for electromagnetic energy waves.
Low frequency waves bend much more readily than high frequency. (VLF vs. EHF)

13. Wave Propagation – Distance and Frequency
Ground Waves
Sky Waves
Space Waves
Go over the following three slides.

14. Ground Wave... Very low frequencies, 5-10Khz Vertical polarization
Waves travel along earth’s surface.
Very long wavelengths - unsuitable for ships & aircraft, except comms
Shore-based installations (HF-DF)
Ground Waves
a. Low frequencies, travels along earth’s surface.
b. Ask what are the advantages?
OTH targeting
Long range communications

15. Sky Wave...
E-M energy refracts back towards the earth’s surface in upper ionosphere layer.
E-M energy then reflects back toward upper layer again.
Frequencies used up to 550 KHz effectively
Wavelengths still too long for anything but comms by aircraft and ships.
Sky Waves
a. Rays bend back toward the earth, Higher density air down lower! Then reflected off the earth/ocean surface back toward the upper layer.
Draw picture of sky wave.
b. If too steep of angle ray travels through and doesn’t bounce back. Causes skip zones.

16. Space Wave...
Above 30 MHz, ionosphere will not refract E-M waves back toward earth.
Energy tends to travel in straight line.
Space Waves are not reflected or refracted by the ionishpere
Higher frequencies less susceptible to Refraction and Diffraction
Add to first picture, show straight line out of ionisphere, discuss how Snell’s law applies.

17. Electromagnetic Spectrum
p. 32 out of text
LOS is considered from the VHF range and above.

18. Transmission Range Factors
Antenna Height
Target Height
Ducting
Losses
Spreading
Absorption
Constructive / Destructive Interference
Ducting: When a cold layer of air is above a warmer layer below. EM waves travel slower in cold air (more dense) than warm air and will curve away from the cold air mass. This causes a ‘duct’ to form, increasing radar and comms by at least 10%.
Destructive Interference: p. 31 of text.

19. Transmission Losses Spreading: Energy per unit area proportional to: 1
R is distance from xmitter
Absorption: Molecules of medium absorb some of the energy as it passes through. 1 R2
1. Demonstrate spreading by dropping rock in lake. Draw Picture. Near center the energy waves are bigger. As they spread out they get smaller.
a. Energy per unit area decreases. Same amount of energy but more area, so at any point further away from the source the energy measured at a point in space is less than if closer.
b. Loss is proportional to 1/(R squared) where R is the distance from the transmitter.
2. Molecules of the medium absorb the energy instead of reflect or refract it.
Absorption is where the work in radar stealth is effective. Cover the object with radar absorbing material! Applied to ships, aircraft, and submarines!!

20. Communication Systems

21. Basic Comms Path
p. 40 in textbook

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

23. Transmission Channel
Air
Water
Wire
Co-axial
Fiber Optics
Beer

24. 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.

25. Receiver
Tuner – this is what allows you to listen in on a particular frequency.

26. Modulation The process of encoding information on the “Carrier Wave”.
A simple Sine wave.
The Sine wave has 3 independent parameters:
Amplitude
Frequency
Phase
The information signal can be used to vary any one of these parameters to encode it’s signal.

27. Noise Noise is bad on a communications circuit. Two types:
Broadband Noise – “White Noise”
Narrowband Noise – “Interference”

28. 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!!!

29. Questions?