Module 3 Radiation and Wave Propagartion PDF

Radiation and Wave Propagation Engr. Harry Bert G. Rolle Radiation The loss or escape of energy into free space. Wave Propagation is the travel of electromagnetic waves through a medium. Electromagnetic Waves are forms of radiant energy like heat, light, radio, x-ray, and television waves t...

Radiation and Wave Propagation Engr. Harry Bert G. Rolle Radiation The loss or escape of energy into free space. Wave Propagation is the travel of electromagnetic waves through a medium. Electromagnetic Waves are forms of radiant energy like heat, light, radio, x-ray, and television waves that are considered to the oscillatory disturbances in free space. Nomenclature of Frequency Bands Frequency Range Wave Metric Subdivision Designation Propagation Mode 3 – 30 kHz Myriametric Very Low Frequency Ground Propagation 30 -300 kHz Kilometric Low Frequency Ground Propagation 300-3000 kHz Hectometric Medium Frequency Ground Propagation 3-30 MHz Decametric High Frequency Sky Propagation 30-300 MHz Metric Very High Frequency Space Wave 300-3000 MHz Decimeric Ultra High Frequency Space Wave 3-30 GHz Centimeric Super High Frequency Space Wave 30-300 GHz Millimetric Extreme High Frequency Space Wave 300-3000 GHz Decimillimetric Space Wave Electromagnetic Wave Characteristic Space Time Relationship An electromagnetic wave has two components: an electric field and magnetic field. Each component varies sinusoidally in time at a fixed point in space. Both the electric and magnetic components of the wave are “in phase” in space, that is, their maxima and minima occur at the same intervals of the z-axis. Electromagnetic Wave Characteristic Wave Velocity Waves travel at characteristic speeds depending on the type of wave and the nature of the propagation or the medium. Electromagnetic waves travel the fastest n the free space, but may travel the fastest in free space, but may travel slowly in other propagation media. C=3x10^8 (m/s) where: c= velocity of electromagnetic C=186,000 (statute mi/s) wave in free space C=9.84 x 10^8 (ft/s) Electromagnetic Wave Characteristic Wavelength is the distance that a radio wave travels in the time of one cycle. It is also defined as the spatial separation of two successive oscillations. Frequency is the number of cycles per second of a radio wave. It is also defined as the rate at which the periodic motion repeats itself. λ = c/f Electromagnetic Wave Characteristic Polarization it refers to the physical orientation of the radiated waves in space. Linear Polarization electric vector has a particular direction in space. Waves have the same alignment in space. Vertical polarization electric vector is vertical, or it less in a vertical plane. Horizontal polarization electric vector is horizontal, or it lies in the horizontal plane. Circular Polarization electric vector is rotating about the axis of the direction of propagation. Elliptical Polarization electric vector rotates about the axis of the direction of propagation but the amplitudes of its two linearily polarized components are unequal. Random Polarization the is no fixed pattern of polarization variation. Electromagnetic Wave Characteristic Rays and wavefronts Ray is a line drawn along the direction of propagation of wave. Wavefront is a surface of constant phase of the wave. Electromagnetic Quantities and Parameters Permeability of free space The permeability of free space, μ0, is a physical constant used often in electromagnetism. It is defined to have the exact value of 4π x 10-7 N/A2 (newtons per ampere squared). It is connected to the energy stored in a magnetic field, see Hyperphysics for specific equations. It is related to the speed of light by the equation: C= 1/(√μ0є0) Electromagnetic Quantities and Parameters Permittivity of free space Vacuum permittivity, commonly denoted ε0 (pronounced "epsilon nought" or "epsilon zero"), is the value of the absolute dielectric permittivity of classical vacuum. It may also be referred to as the permittivity of free space, the electric constant, or the distributed capacitance of the vacuum. ε0 = (1/36π) x 10^-9 F/m Electromagnetic Quantities and Parameters Power Density (ҩ) It is defined as the rate at which energy flows through a unit area of surface in space. Inverse square law states that power density is inversely proportional to the square of the distance from the source. Ҩ = PtGt/(4πd^2 ) W/m^2 Where: Pt = transmitted power in W Ҩ = E^2/377 W/m^2 Gt = gain of transmitting antenna Ҩ = 377 H d = distance from point source in m E = electric fied intensity in V/m H = magnetic fields intensity in A/m Electromagnetic Quantities and Parameters Calculate the power density 25 km away from a 90% efficient halfwave dipole if the transmit power is 125 W. Electromagnetic Quantities and Parameters At 20 km in free space from a point source, the power density is 200μW/m^2. What is the power density 25 km away from this source? Electromagnetic Quantities and Parameters Electric Field Intensity (E) Electric field intensity is directly proportional to the square root of the power density an inversely proportional to the distance from the source. E = √30Pt/d V/m Magnetic Field Intensity (H) H = E/377 Electromagnetic Quantities and Parameters Attenuation (ɑ) It is due to the spherical spreading of the wave. It is also called space attenuation. It is proportional to the square of the distance traveled. Since power density decrease with distance, we can say that electromagnetic waves are attenuated as they travel outward from their source. ɑ = 10 log 10 (ҩ1/ ҩ2) dB where: ҩ1= power density at point 1 ɑ = 20 log 10 (d1/ d2) dB ҩ2= power density at point 2 d1= distance of pt 1 from source d2= distance of pt 2 from source Electromagnetic Quantities and Parameters Absorption Some of the energy from the electromagnetic waves is transferred to the atoms and molecules of the atmospheric thereby causing some radio waves to be absolved. If humidity is increased or if there is fog, rain, or snow, then absorption is greatly increased.  Reflection Role of Environment It occurs at any boundary between materials of differing dielectric constants. on Wave Propagation The angle of incidence is equal to the angle of reflection. Role of Environment on Wave Propagation Reflection Coefficient is defined as the ratio of the electric intensity of the reflected wave to that of the incident wave. Complete reflection occurs only for a theoretically perfect conductor and when the electric field is perpendicular to the reflecting element. Role of Environment on Wave Propagation Refraction It is defined as the bending of a ray as it passes from one medium to another at an angle. It occurs when electromagnetic waves pass from one propagating medium to another medium having a different density. The degree of bending of a wave at boundaries increases with frequency. Role of Environment on Wave Propagation Snell’ s Law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air. In optics, the law is used in ray tracing to compute the angles of incidence or refraction, and in experimental optics to find the refractive index of a material. 𝑛1 sin 𝜃1 = 𝑛2 sin 𝜃2 Where: 𝑛1 = refractive index of incident medium 𝑛2 = refractive index of refractive medium sin 𝜃1 = angle of incidence sin 𝜃2 = angle of reflection  Diffraction Role of Environment It is defined as the bending of a ray that is traveling in a straight on Wave Propagation path as it hits an obstacle (either an edge or an object or an opening.) This is caused largely by the spreading of the wave around the obstacle and by the interference of one part of the beam with another. Role of Environment on Wave Propagation Interference It occurs when two waves that left one source and traveled by different path arrive at a point. This happens very often in high- frequency sky waves propagation and in microwave space-wave propagation. Role of the Sun on the Wave Sunspots It is the tendency of the sun to have a grayish-black blemishes, seemingly at random times and at random places on the its feiry surface. The 11 year sunspot cycle affects propagations because there is a direct correlation between sunspot activity and ionization. Role of the Sun on the Wave Solar Flux It is a measure of energy received per unit time, per unit area, per unit frequency interval. The radio fluxes, which originates from atmospheric layers, high in the sun chromosphere and low in its corona change gradually from day to day, in response to activity causing sunspots. Daily solar flux information is of value in determining current propagation conditions. Role of the Sun on the Wave Solar Flare It is the sudden eruption on the sun that causes high spread atomic particle to be ejected far into space from the surface of the sun. The results in dramatic ionization of the thin atmosphere over the arctic and Antartic. Role of the Sun on the Wave Maunder Minimum Based on evidence, there have been long periods with a lack of any solar activity. The most recent of these periods was 70 yrs period beginning 1646. This period has been named the Mauder minimum after EW Munder, who was the superintendent of the solar department of Greenwich observatory n the late 1600’s.  https://www.ess.uci.edu/~yu/class/ess200a/lecture.2.global.pdf https://www.sciencedirect.com/topics/earth-and-planetary- sciences/solar-flux https://earthsky.org/sun/sun-news-activity-solar-flare-cme- aurora-updates/