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Naval Weapons Systems. Energy Fundamentals. Energy Fundamentals. RA dio D etection A nd R anging 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.
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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...
Formation of Electric and Magnetic Fields around an Antenna E-line Mag field e- e- e- Electric field | Magnetic Field | Direction of Propagation.
Propagation Paths of E-M Waves • Reflection • Refraction • Diffraction
...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.
θ1 Medium 1 Medium 2 θ2 Snell’s Law n1*Sin θ1=n2*Sin θ2
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... • E-M energy travels along earth’s surface • Very low frequencies, 5-10Khz • Extremely wavelengths • Shore communications stations (HF-DF)
Sky Wave... • E-M energy refracts toward earth’s 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
Space Wave... • E-M energy refracts back toward earth’s surface in outer space (i.e. stratosphere) • Above 30 MHz, ionosphere will not refract E-M waves back toward earth.
Transmission Range Factors • Antenna Height • Target Height • Ducting • Losses • Spreading • Absorption • Constructive Interference • Destructive Interference
Transmitter • Transducers – Changes energy form • Acoustic waves to EM waves • Boosts power of 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 same time. • i.e. – “walkie-talkie” • Full-Duplex – both and at the same time • i.e. – shipboard telecommunications systems
Receiver • Tuner – allows particular frequency reception
Modulation • The process of encoding “Carrier Wave” • “Carrier 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 • 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!!!
