Learning Objectives Comprehend basic communication theory, electromagnetic (EM) wave theory Comprehend radar and radio wave parameters including frequency, period, wavelength, velocity, and amplitude Know Maxwell’s theory, relationship between wave parameters Comprehend concepts of time and distance (wave phase angle) and interference
Learning Objectives (cont) Know EM wave propagation principles such as reflection, refraction, diffraction, and ducting Know the definition of sky, space, and ground waves
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
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... Electric FieldMagnetic FieldElectric Field
Formation of Electric and Magnetic Fields around an Antenna e- E-line Mag field Electric field | Magnetic Field | Direction of Propagation.
...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...
...Diffraction... island not detected detected...plane waves traveling in a straight path bend around a boundary or obstruction.
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 long 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.