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Explore the fundamentals of radar systems, electromagnetic waves, and energy propagation in this comprehensive guide. Learn about polarization, wave propagation, transmission losses, and communication systems. Dive into topics like modulation, signal-to-noise ratio, and receiver tuning. Enhance your knowledge of naval weapons systems and energy fundamentals with practical insights and examples.
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Naval Weapons Systems Energy Fundamentals
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
Traveling Wave Characteristics • Frequency • Period • Wavelength • Velocity • Amplitude • ...examples....
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...
Generation of Electromagnetic Radiation + + - - - + a b c d = Alternating Current Source
Formation of Electric and Magnetic Fields around an Antenna E-line Mag field e- e- e- Electric field | Magnetic Field | Direction of Propagation.
What is Polarization? • The directionof polarization of an antenna is defined as the electric field vector. • 3 Kinds: • Horizontal • Vertical • Circular
Propagation Paths of E-M Waves • Reflection • Refraction • Diffraction
θ1 Medium 1 Medium 2 θ2 Snell’s Law n1*Sin θ1=n2*Sin θ2
...Reflection... Phase shift = 180 degrees. Angle of incidence = Angle of reflected wave. Reflected Wave IncidentWave
...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.
island not detected ...Diffraction... ...plane waves traveling in a straight path bend around a boundary or obstruction. detected
Wave Propagation – Distance and Frequency • Ground Waves • Sky Waves • Space Waves
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)
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.
Space Wave... • Above 30 MHz, ionosphere will not refract E-M waves back toward earth. • Energy tends to travel in straight line.
Transmission Range Factors • Antenna Height • Target Height • Ducting • Losses • Spreading • Absorption • Constructive / Destructive Interference
Transmission Losses • Spreading: Energy per unit area proportional to: • R is distance from xmitter • Absorption: Molecules of medium absorb some of the energy as it passes through. 1 R2
Basic Comms Path p. 40 in textbook
Transmitter • Transducers – Devices that change energy form • i.e. – acoustic waves to EM waves • Often boost the power of the signal to increase distance.
Transmission Channel • Air • Water • Wire • Co-axial • Fiber Optics • Beer
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.
Receiver • Tuner – this is what allows you to listen in on a particular frequency.
Modulation • The process of encoding information on the “Carrier Wave”. • A simple Sine wave. • The Sine wave has 3 independent parameters: • Amplitude • Frequency • Phase
Noise • Noise is bad on a communications circuit. • Two types: • Broadband Noise – “White Noise” • Narrowband Noise – “Interference”
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!!!