Radio Wave Propagation Flashcards by chxngy Unknown

This wave is composed of two components, the magnetic field (H) and the electric field (E)

Transverse Electromagnetic Wave

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Each field in transverse electromagnetic wave varies ___________ at a fixed point in space

Sinusoidally in time

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What are the two components of transverse electromagnetic wave?

Magnetic field
Electric Field

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Transverse Electromagnetic Wave is transverse in nature and hence its direction of propagation is _______

perpendicular to its two components

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This velocity of TEM waves depends on the medium where it travels.

Wave Velocity

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It travels fastest at free space at approximately 3x10^8 m/s

Wave velocity

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Wave Velocity Formula

V = c / (square root of (Er))

Where:
C = speed of light: 3 x 10 ^8 m/s
Er = relative permittivity

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The number of cycles an electromagnetic wave completes in one second, expressed in Hz

Frequency

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Frequency formulas

f = 1 / T

f = v / λ

f = w / 2*pi

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The distance that the radio wave travels in the time of one cycle, expressed in meters

Wavelength

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Wave length formula

λ = c / f

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Refers to the physical orientation of the E field on space

Polarization

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Types of Polarization

Linear Polarization
Circular Polarization
Elliptical Polarization
Random Polarization

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E field has a particular direction in space either vertical or horizontal

LINEAR POLARIZATION

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E field is rotating about the axis of the direction of propagation

CIRCULAR POLARIZATION

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Similar to circular polarization except that E and H are unequal

ELLIPTICAL POLARIZATION

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Polarization with no fixed pattern

RANDOM POLARIZATION

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A line drawn along the direction of propagation of the wave

RAY

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A surface of constant phase of the wave

WAVEFRONT

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The definite ratio between the electric field intensity and magnetic field intensity
For free space: 120n or approximately 377 ohms

INTRINSIC CHARACTERISTIC IMPEDANCE (ZO)

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INTRINSIC CHARACTERISTIC IMPEDANCE (ZO) Formula

Zo = square root of (μo/εo)

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This refers to the rate at which energy flows through a unit area of surface in space

Power Density

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Power Density Formulas:

P = PtGt/[4pi*(r^2)]

P = E^2 / 377

P = 377*(H^2)

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This states that power density is inversely proportional to the square of the distance from the source

INVERSE SQUARE LAW

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The bending of radio wave as it passes from one medium to another at an angle due to the changing of direction and speed of an EM wave as it passes from one medium to another

Refraction

Refraction is the bending of radio wave as it passes from one medium to another at an angle due to the ____________ and ________ as it passes from one medium to another

Changing of direction and speed of an EM wave

The ratio of the speed of radio wave in free space to speed of radiowave in a specific meduim

Index of refraction (n)

This is dependent on the material and the number of electrons in a given medium

Index of refraction (n)

Index of refraction Formula:

N = c / v Where: v = propagation velocity c = free space or 3 x 10^8

Snell’s Law Formula:

N1sinθ1 = N2sinθ2 where: θ1: angle of incidence θ2: angle of refraction n1: index of refraction of the first medium n2: index of refraction of the second medium

Snell’s Law Formula:

N1sinθ1 = N2sinθ2 where: θ1: angle of incidence θ2: angle of refraction n1: index of refraction of the first medium n2: index of refraction of the second medium

tells us how fast light travels through a material.

The index of refraction

Higher index of refraction means _____

Slower light

When n2 > n1, light goes from a ________ to a more dense one.

Less dense medium (like air)

When n2 > n1, The light bends _______ because light slows down

toward the normal

When n2 < n1, light goes from ________ to a less dense one

More dense medium

When n2 < n1, light bends _______ because light speeds up

Away from the normal

Index of refraction can be calculated using the given equation:

N = squareroot of Er Er = relative permittivity of the medium since μr (relative permeability), is almost always 1 for the medium of interest , in practical term, this will be the equation to be used

TYpes of reflection

Diffuse Reflection Specular Reflection Rayleigh criterion

This states that a semirough surface will reflect as it if were smooth surface if the cosine of the angle of incidence is greater than λ/8d

Rayleigh criterion

Also called mirrorlike reflection this refers to the rflection at very smooth surface

Specular Reflection

Reflection at irregular and rough surfaces

Diffuse Reflection

This refer to the redistribution of energy within wavefront when it passes near the the edge of an opaque object while allowing seconday waves to sneak around the corner of an obstacle.

DIFFRACTION

This states that any point on a wavefront of light may be regarded as the source of secondary waves.

Huygen’s Principle

this occur when two waves that left one source and travelled by different paths arrive at a point

INTERFERENCE

Memorize radio frequency spectrum table

Refer to table in page 24 of Radio wave propagation powerpoint

Modes of Wave Propagation

Ground/surface wave propagation Sky wave propagation Space wave/LOS propagation

an Earth-guided electromagnetic wave that travels over the surface of the Earth.

Groundwave propagation

It follows the contour of the Earth and given enough transmit power, it can communicate between any two locations in the world.

Groundwave propagation

can be used with frequencies up to 2 MHz and must be vertically polarized.

Ground Wave propagation

______ and ______ of the surface play an important role in ground wave propagation

Conductivity and permittivity

Relative conductivity of sea water

Good

Relative conductivitiy of flat, loamy soil

Fair

Relative conductivity of large bodies of fresh water

Fair

Relative conductivity of rocky terrain

Poor

Relative conductivity of desert

Poor

Relative conductivity of Jungle

Unusable

As the ground wave move further away from the source, it can experience ________ and _______

Tilting and eventually disappear

Groundwave propagation is effective on __________ frequency bands and commonly used in AM radio broadcasting

VLF, LF and MF frequency bands

Formula for Ground Wave Propagation

Vind = Lr * E E = 120*pi * ht * I / λ * d

Also called ionospheric propagation

Sky Wave Propagation

Its wave strikes the ionosphere and is reflected back to the ground

Sky Wave Propagation

Sky wave propagation employed on the

High Frequency band

Ionospheric Propagation Parameters

Critical frequency Maximum Usable Frequency (MUF) Optimum Working Frequency (OWF) Virtual Height Skip Zone Skip Distance

It is the highest frequency that will be returned down to Earth when beamed vertically upward

Critical Frequency of Ionospheric Propagation

How is critical frequency in ionospheric propagation measured? And what process does it utilizes?

Measured in ionosonde Process: Ionospheric sounding

Formula for Critical Frequency in Ionospheric Propagation

fc = square root of (81*Nmax)

The highest frequency that will be returned down to Earth at a given distance when beamed at specific angle other than the normal.

Maximum Usable Frequency (MUF) of Ionospheric Propagation

Maximum Usable Frequency (MUF) formula

MUF = fc * sec θi

The frequency that gives the most consistent communication

Optimum Working Frequency of Ionospheric Propagation

It is chosen to avoid irregularities of the ionosphere

Optimum Working Frequency of Ionospheric Propagation

Optimum working frequency is chosen to be ________ than the MUF

15% lower

Optimum workingfrequency formula:

OWF = 0.85 * MUF

It is the apparent height of the ionized layer and measured by sending a wave vertically to the layer and measuring the time it takes to come back at the receiver.

Virtual Height of Ionospheric Propagation

How is virtual height in ionospheric propagation measured?

Using an ionosonde

Virtual Height formula

hv = d / 2tan θi

is the area that is between the outer limit of the ground wave range and the inner edge of the energy of return from the ionosphere.

Skip zone

is the distance between the originating site and the beginning of the atmospheric return.

Skip distance

It is called the Line-of-Sight (LOS) propagation

Space wave propagation

Space Wave propagation is employed on _____

Very High Frequency and Ultra High Frequency

In space wave propagation, This refers to the boundary line beyond which direct rays of the radio waves cannot be propagated over the Earth’s surface..

Radio Horizon

Radio horizon is usually _______ the optical horizon.

4/3 greater than

Radio Horizon of Space Wave Propagation formulas:

If D = miles, formula is: D(mi) = square root of 2*hT(in ft) + square root of 2*hR(in ft) If D = kilometers, formula is D(km) = square root of 17*hT(in m) + square root of 17*hR(in m)

Occurs when incident wave strikes the boundary of two media aand some or all the incident power does not enter the second material.

Reflection