Wave Propagation Ec

8/12/2019 Wave Propagation Ec

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WAVE PROPAGATION

1. Free space is space that does not interfere with the normal radiation and propagation of radio waves. Thus, it has no magnetic or gravitational fields.No, solid bodies and noionized particles.

2. Electromagnetic waves are oscillations that propagate through free space with thevelocity of light equal to 2. ! 2"#$% &m's.3. Electro Electromagnetic waves are transverse waves. Electromagnetic waves are

reflected, refracted, diffracted, attempted and scattered. (agnetic waves are transversewaves.

4. Propagation of radio waves )adio communication uses electromagnetic wavespropagated through earth*s atmosphere or space to carry information over longdistances without use of wires. )adio waves with frequencies ranging from about $%+h z in the -F band to well above %% /0 z in the E0F band have been used forcommunication purposes.

!. The direction of the electric field, the magnetic field and propagation are mutually

perpendicular in electromagnetic waves.". #ree spa$e para%eter =0 1ermeability of free space 3 )/(10 7 M H X

1ermittivity of free space )/(1036

19 m F X

4 velocity of propagation00

1

#$%&m's

5 intrinsic impedance of free space0

0

$2% = 377

&. Free space path loss 2.362% log $%F62% log $%7.8hen F and 7 are e9pressed in (05 and :m respectively.

'. Free space is unli+ely to e9ist anywhere; it certainly does not e9ist near the earth.0owever the concept of free space is used because it simplifies the approach to wavepropagation, since it is possible to calculate the conditions if the space were free, andthen to predict the effect of its actual properties.

(. 8hen the antenna is vertical to the ground, the polarization is called vertical polarizationi.e. the electric field is vertical and magnetic field is horizontal while the wave ispropagated.0orozontal antennas produce waves whose polarization is horizontal .

1). 1olarization refers to the physical orientation of the radiated waves in space.11. ertical and horizontal polarizations are called linearly polarized where as light emitted

by coherent sources r $ and they are the distance from

the source.13. ?bsorption of ratio waves does not occur in free space. ?bsorption of E( waves of

frequencies of below $% /05 is insignificant in space.

0


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14. ?t certain frequencies absorption is greatly reduced. and $$% /05 are suchfrequencies.

1!. @% and $2% /05 frequencies are restricted for long distance propagation in theatmosphere.

1". ?bsorption of power


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2(. 8aves in the 0F range, are reflected by the ionized layers of the atmosphere, and arecalled s+y waves. uch signals are beamed into the s+y and come down again afterreflection, returning to earth well beyond the horizon.

3). Tropospheric catter and stationary satellite communications are the two more developedmeans of beyond the horizon propagation.

31. /round wave propagationi= Earth behaves li+e a lea+y capacitance.ii= /round wave should be vertically polarized. Gtherwise the electric

component is grounded. o the electric vector must be normal to the earth*ssurface.

iii= /round wave induces charges in the earth when travel along the earth*ssurface.

iv= There will be loss in this moment. Bnduced current will flow through earth*sresistance and this will be dissipation loss.

v= The field strength at a distance Dd* is

Ed

ih t

.

.120

and velocity receivered by receiving antenna is

d ihh r t

.120

8here $2% is the characteristic impedance of free space.h t and h r are the effective heights of transmitting and receiving

antennas respectively.B is the antenna currentd is the distance from the transmitting antenna is the wave length

vi=. /round loss is a function of a= Earth*s limited conductivity.b= 7ielectric constant of ground level.c= 7istance from transmitter.d= Frequency of the electromagnetic wave used as carrier.

vi= the degree of the electromagnetic wave used as carrier 32. Bf 0F signals are propagated using surface wave propagation they can not travel longer

distance.33. -ong term signal strength variations ta+es place due to $$ years solar cycle also.34. -F antennas are certain to be insufficient high powers and the tallest masts are used.

7ue to these problems they are not used much.3!. ?ll broadcast radio signals received in day time propagate by means of surface waves.3".+,- wave propagation Bt is also called ionospheric wave propagation.

i The ionosphere is the upper portion of the atmosphere. The upper reachesof the earth*s atmosphere are ionized i.e electrons are detached fromatmospheric gas atoms mainly as a result of receiving ultraviolet radiationand and , radiation form the sun as well as cosmic says and meters

ii arious pea+s


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layers are 7 layer, E layer, F $ and F 2 layes.7uring night time 7 and E layersdisappear and F $ is mi9ed with F 2 as a result only F 2 layer is present

iii The E s layer is a thin layer of very high ionization density. Bt is also called thesporadic E layer. ome times appears with E $ layer often persists during thenight.

iv Ref/e$tion %e$0anis% ElectroHmagnetic waves returned to earth by oneof the layers of the ionosphere appear to have been reflected. Bn actual factthe mechanism involved is refraction, ?s the ionization*s density increasesfor a wave approaching the given layer at an angle, so the refractive inde9

of the layer is reducted.0ence the incident wave is gradually bent furtherand further away from the normal. Bs the rate of change of refractive inde9 per unit height is

sufficient, the refracted ray will eventually became parallel to the layer. Bt will then be bent downward finally emerging from the ionized layer at an angle equal to the angle of incidence. some absorption ta+es place, but the wave has been returned by the ionosphere.

3&.Virt a/ 0eig0t Bt is the height which would be reached by an E( 1ulse of energy within the same time as the actual pulse. Bt is called virtual height to distinguish it fromactual


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44. sing/e 0op or % /ti 0op trans%ission 8hen the s+y wave is received on earth afterbeing reflected from the ionosphere only once then the transmission is termed as singlehop. Bf more than once, it is called multiHhop transmission.

4!. 8ith multi hop transmission e9tremely long distance communication is possible.4". B7< uddenly Bonospheric disturbances or 7ellinger 7ropouts= are caused by solar

flares. 7ue to this, long distance communication may disappear completely, B7improves the -F propagation.4&.+pa$e wave propagation 8hen the frequency of CF e9ceed (0z ground wave

does not propagate. Bt gets shortHcircuited to earth. Bn the range of (0zH %(0zionosphere reflects waves, on the basis of ionospheric reflections. 0owever above

%(0z ionosphere refracts the )F wave, which is consequently last to earth, e9cept byutilizing satellite base equipment to receive it and retransmit the same to the earth.

Frequencies above % (0z are propagate by means of space waves in thespace immediately above the earth called troposphere,upto a height of roughly$"+m

4'. pace waves travel in straight lines. The radio horizon for space waves

d kmhh r t )4 +

8here h t Transmitting antenna height in mts.above the groundh r )eceiving antenna height above the ground in mts

4(. )adio horizon 3' # optical horizon!). 7ue to the temperature inversion, atmospheric ducts are formed. The temperature

inversion ta+es with in % meters from the earth*s surface.!1. Ising super refraction or duct propagation micro waves are propagated for distances

more than $%%% +m also.!2. uper refraction ta+es place between the inversion layer and earth surface where as

multi hop ta+es place between ionosphere and earth surface.!3. Bn the standard atmosphere the atmosphere the decrease in temperature is @." %4'+m

!4. Troposphere or forward scatter propagation is a means of beyond the horizonpropagation for I0F signals!!. Troposphere is the nearest portion of the atmosphere and it is within $"

+ms.Troposphere is not a sporadic phenomenon. Bt is a permanent state of affair. Thebest suitable frequencies are %%.2%%% and "%%%(05.The troposphere propagationmay be due to blobs in atmosphere.

!". )adio broadcasts


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"". To reduce the fading effect generally diversity reception systems are used. Juadruplediversity systems are employed to reduce the fading effect in case of troposphericscatter propagation.

"&. )efraction becomes insignificant at frequencies above $%% (0z and atmosphericabsorption is negligible up to about $3 /05.

"'. The polarization of the radio wave rotate as it passes through the ionosphere and it maynot possible to receive a signal using the same polarized antenna. The effect is calledFaraday Effect to overcome this helical antennas are used.

"(. The Faraday effect is negligible above $/05 frequency.&). The satellite which is orbiting at the lower orbit ta+es % minutes to circum navigate the

earth.

O*7E TIVE PRO*8E5+ 9 +O86TION+$. ? certain radio station broadcasts at a frequency of %% + 4ycles'sec.The wave length of

the wave transmitted by the station isa= %m b= %cm c= . cm d= . m

so/ elocity of radio waves 9$% &m'sec, Frequency f %%+ cycles'sec %% :0z

8ave length of the wave transmitted m X

x f v

33.33310900

1033

8

===

2. 8hat is the critical frequency for reflection at vertical incidence if the ma9imum electron density is 3# $% @'44

a= @ :0z b= $& :05 c= $& (05 d= @ (05

so/ 4ritical frequency f c max N (a9imum electron density N ma9 3#$% @'44 3#$% $2 'm MHZ X X X f c 1810291049 612 ===

. Two points which are %% +m apart on earth are communicated by beams of 0F for a single hop transmission; the critical frequency at that time is " (05 all conditions are idealized. Find the (IF for those two points if the height of the ionospheric layer

is 2%% +ma= .%2 :0z b= $2. $ (0z c= &. (0z d= $$.@2 (0z+o/ /iven data,f c "(0z, 7 %% +m, h 2%% +m

(IF


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". ?t 2% +m in free space form appoint source, the power density is 2%% 2/ m .what is the power density 2" +m away form this sourceM

a= @3 )/( 2m b= $2& m


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&. The troposphere e9tends from earth surface to a height ofa= $" +m b= %+m c= $2%+m d= 2"% +m

. The intrinsic impedance of free space is a= $!! b= 2!! c= !! d= 3!!

$%. ?udio frequency range lies between

a= 2%0z and 2% :0z b= 2%0z and 2%% :0zc= 2 +0z and 2%% :0z d= 2(0z and 2% (0z$$. ? wave length of $ meter can be e9pected in

a= -F b= (F c= 0F d= 0F

$2. (edium wave radio broadcast is done in a= 0orizontal polarization b= ertical polarizationc= 4ircular polarization d= Elliptical polarization

$ .The main difference between the operation of transmission lines and waveguides is thata= the latter are not distributed, li+e transmission linesb= the former can use stubs and quarterHwave transformers, unli+e the latter

c= transmission lines use the principal mode of propagation, and therefore do not suffer from lowHfrequency cutoff d= terms such as impedance matching and standingHwave ratio cannot be applied to

waveguides$3. Bonosphere propagation fails beyond

a= % :0z b= %%:0z c= %%%:0z d= %,%%%:0z$". For the ground wave propagation the antenna should be polarized

a= 0orizontally b= ertically c= circularly d= None$@. ?s one moves away from transmitter, ground wave eventually disappears because

a= +y wave interfaces with ground waveb= Gf tilit in wave front

c= Gf loss of line of sightd= Gf limitation of single hop distance$!. The shortest distance form the transmitter along the surface of the earth at which s+y

wave of fi9ed frequency < more than critical frequency= is returned to the earth is +nownas a= lip distance b= +ip distance c= dead zone d= virtual distance

$&. The principal propagation agency for propagating signals in the frequency range %%:0zH (0z is bya= pace wave b= grounded wave c= s+y wave d= None

$ . (ost of the absorption suffered by an electromagnetic wave passing through theionosphere ta+es place in a= 4ircular b= vertical c= horizontal d= mi9ed

2%. (ost of the absorption suffered by an electromagnetic wave passing through theionosphere ta+es place in a= F2layer b= EHlayer c= F $ layer d= F 2 layer

2$. )eception of commercial radio broadcast is better during the cloudy weather becauseof the absence of the following


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a= E layer b= 7 layer c= F $ layer d= F 2 layer 22. The absorption of radio waves by the atmosphere increases with the increase of

a= 7istance b= Frequency c= height d= None2 . The highest components of atmosphere responsible for absorption of E( waves are

a= 4ritical frequencyb= (IF c= useful frequency d= None

23. The main components of atmosphere responsible for absorption of E( waves are a= nitrogen and o9ygen b= nitrogen and hydrogenc= o9ygen and water vapor d= nitrogen and water vapor

2". To increase the radar range of ground and surface targets to see well beyond thenormal radar horizon, the electromagnetic wave propagation adopted is a= ionospheric scatter b= troposcatter c= ground wave vapour d= duct

2@. The (IF for an angle of incidence of @% % and a critical frequency of @% (0z will bea= 3" (0z b= $$$.!(0z c= $2% (0z d= $"% (0z

2!. The amplifiers which are inserted at intervals to amplify the signal and compensate for

transmission loss on the cable are calleda= line amplifiers b= equalizing amplifiersc= compandors d= repeaters

2&. Transmission of signals in a terrestrial micro wave system is achieved througha= reflection from the ionosphere b= line of sight mode.c= reflection from the ground d= differation from the stratosphere

2 .? )adio wave is incident on a layer of ionosphere at an angle of % % with the vertical. Bfthe critical frequency is $.2 (0z .The ma9imum usable frequency is a= $.2 (0z b= 2.3(0z c= %.@ (0z d= $. &@ (0z

%. For a short wave radio lin+ between two stations via the ionosphere, the ratio of thema9imum usable frequency to the critical frequencya= is always less than $ b= is always greater than $c= may be $ depending upon the distance between the two stationsd= does not depend on the distance between the two stations.

$. (edium wave radio signals may be received at far off distance at night times becausea= radio waves travel faster at night b= grounded wave alternation is low at night

c= the s+y wave is stronger at night d= these is no fading at night2. 8hen electromagnetic waves are propagated in a waveguide

a= They travel along the broader walls of the guideb= /round wave attamation is low at night

c= They travel through the dielectric without touching the wallsd= They travel along all four walls of the waveguide

. 7 layer roughly e9tends froma= "" to % +m b= 2% to 3% +m c= % to $$% +m d= beyond $$% + m

3. 8aveguides are used mainly for microwave signals becausea= They depend on straightHline propagation which applies to microwaves onlyb= -osses would be too heavy at lower frequencies


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c= There are no generators powerful enough to e9cite them at lower frequenciesd= They would be too bul+y at lower frequencies.

". For a given ionipheric layer, the highest frequency that will be reflected bac+ for verticalincidence isa= f c &$Nma9 b= f c &$N2 ma9 c= max81 N f c = d= max81 N f c =

@. ? cho+e flange may be used to couple two waveguidesa= To help in the alignment of the waveguidesb= Cecause it is simpler than any other Aoinc= to compensate for discontinuities at the Aoind= to increase the bandwidth of the system

!. The dominant mode of propagation is preferred with rectangular waveguides because< Bndicate false statement=a= Bt leads to the smallest waveguide dimensionsb= The resulting impedance can be matched directly to coa9ial linesc= Bt is easier to e9cite than the other modesd= 1ropagation of it without any spurious generation can be ensured

&. ? signal propagated in a waveguide has a full wave of electric intensity changebetween the two further walls, and no component of the electric field in the direction ofpropagation. The mode isa= TE $.$ b= TE$.% c= T( 2.2 d= TE2.%

. For very high frequencies earth acts as aa= 4onductor b= dielectric c= resistor d= uper conductor

3%. The ionosphere plays a significant role in radio wave propagation ata= Gptical frequencies b= microwave frequenciesc= high frequency d= medium frequency

3$. Bndicate the false statement .8hen the freeHspace wavelength of a signal equals thecutoff wavelength of the guidea= The group velocity of the signal becomes zerob= The phase velocity of the signal becomes zeroc= The characteristic impedance of the guide becomes infinited= The wavelength within the waveguide becomes infinite

32. ?s a result of reflections from a plane conducting wall, electromagnetic waves acquirean apparent velocity greater than the velocity of light in space This is called thea= elocity of propagation b= normal velocityc= group velocity d= phase velocity

3 . This layer of the ionosphere vanishes during night timea= CHlayer b= 7Hlayer c= EHlayer d= FHlayer

33. 8hen electromagnetic waves are reflected at an angle from a wall, their waveHlengthalong the wall isa= The same as in free spaceb= The same as the wavelength perpendicular to the wallc= hortened because of the 7oppler Effect


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d= /reater than in the actual direction of propagation3". %%H %%%(0z frequency range is +nows as

a= 0F b= (F c= 0F d= I0F

3@. 4ompared with equivalent transmission lines, H/0z waveguides

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Wave Propagation Ec