ECE Department
Question Bank
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Subject Name : ANTENNAS
AND WAVE PROPAGATION Branch:ECE
Subject Code : 10144EC604 Year
/ Sem. : III/VI
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Unit – I
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Part - A
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1
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Define retarded vector
potential.
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2
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Define radiation resistance of
an antenna.
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3
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Calculate the radiation
resistance of a λ/10 wire dipole in free space.
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4
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An antenna whose radiation resistance is 300 ohm operates at a frequency
of 1 GHz
and with a current of 3Amp.Find
the radiated Power.
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5
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What is meant by oscillating
electric dipole?
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6
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Distinguish between induction
field and radiation field.
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7
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State the differences between half wave
dipole and quarter wave monopole.
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8
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Define: Electric vector potential.
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9
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A short vertical transmitting antenna erected on the surface of a
perfectly
conducting earth produce an rms field strength Eө=100sinӨ mv/m at a distance of 1km from the antenna.calculate the total power radiated by the antenna. |
10
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Define antenna efficiency
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11
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Define Hertzian dipole.
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Part - B
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11
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a)Derive an expression for the
power radiated and radiation resistance of a small
current element. (8)
b) At what distance in
wavelength, is the radiation component of magnetic field
be equal and twice the induction component. (8) |
12
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a)When the amplitude of the magnetic field
in a plane wave is 2A/m.
i)
Determine the magnitude of the electric field for the plane wave in free
space.
ii) Determine the magnitude of the electric field when the wave
propagates in a medium which is characterized by σ =0, µ= µ0 and ε
= ε0
(8)
b) Derive
an expression for the radiation field from an infinitesimal Dipole
and also write the expressions for far
field and near field regions (8)
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13
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a)Derive an expression for the radiation field from a half
wave dipole (10)
b) A dipole antenna with length equal to 10cm and carrying
a current of 1A at a
frequency
of 108 /2π hertz radiates into free space. Calculate the electric
field
intensity at a distance of r=10km from
the antenna, where the induction field is
negligible. (6)
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14
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a)
Explain retarded vector potential.
(4)
b)
A plane electromagnetic wave having a frequency of 100 MHz has an
averaging pointing vector of 1 W/m2.If the medium is lossless with
relative permeability 2 and relative permittivity 3. Find i) velocity of
propagation. ii) Wavelength. (12)
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15
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a)
Derive an expression for the radiation field from a
small current element (8)
b)
A half wave dipole is radiating into free space. The
co-ordinate system is defined so that the origin is at the center of the
dipole and the Z axis is aligned with the dipole. Input power to the diploe
is 100W.Assuming an overall efficiency of 50%, find the power density (in w/m2)
at r=500m, θ=60,φ=0.
(8)
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16
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a)An antenna
whose radiation resistance is 300 ohm operates at a frequency of 1 GHz and
with a current of 3 amps. Find the radiated power.
(3)
b)A half wave dipole with a
total loss resistance of 1Ω, is connected to a generator whose internal
impedance is 50+j25 Ω. Assuming that the peak voltage of the generator is 2 V
and the impedance of the dipole excluding the loss resistance is 73+j42.5 Ω,
find the power supplied by the source.
(3)
c) What do you mean by
induction field and radiation field? (5)
d) Find the radiation
resistance of a hertizian dipole of length λ/40, λ/60, and λ/80. (5)
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Unit – II
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Part - A
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1
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Distinguish between broadside
array and end fire array.
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2
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Define Ferrite loop.
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3
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An antenna has
a radiation resistance of 72 ohm. A loss resistance of 8 ohm and power
gain of 12 db. Determine the antenna
efficiency and directivity.
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4
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What is the maximum effective
aperture of a microwave antenna with a directivity of 900?
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5
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A linear broadside array
consists of 4 equal isotropic in phase, point source with λ /3 spacing. Calculate the directivity, beam width and HPBW.
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6
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State the reciprocity theorem
for two antennas.
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7
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Define array factor.
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8
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What are grating lobes?
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9
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An antenna with omni
directional amplitude pattern with a half power beam width of 90 degrees has
radiation intensity of U=sinnq.Determine the value of
‘n’
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10
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State pattern multiplication
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11
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Define radiation intensity
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12
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Mention the two important
advantages of folded dipole antenna
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13
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Give the significance of Friss
transmission formula.
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Part - B
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1
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a. Calculate the field for an
array of two isotropic sources of same amplitude
and phase for d=3l/4. (8)
b. The radiation intensity of an antenna is
given by
U (q,F) =
{B0 sinq
sin2F , where 0£F£p, 0£F£p
0 , elsewhere. (8)
Determine the maximum directivity
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2
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a. Derive an expression for radiated field due
to small circular loop
antenna. (10)
b. Derive an expression relating
directivity, gain and effective length. (6)
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3
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a. Show that the
relative E (F)
pattern of an array of two identical isotropic in
phase point sources are arranged in fig 1.is given by E (F) = cos [dr/2 sin F where dr=2pd/l. (8)
b. In a microwave communication
link, two identical antennas operating at 10
GHz are used with power gain of 40 db. If the transmitted power is 1 W. Find the received power, if the range of the link is 30 km. (8) |
4
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. a. Explain the
operation of helical antenna in normal mode of operation. (8)
b. A uniform linear array
consists of 16 isotropic point sources with a spacing of
l/4, if the phase difference d= -90 degrees. Calculate i) HPBW ii) Beam solid Angle iii) Effective aperture iv) Directivity. (8) |
5
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a) For an array of 2 isotropic
point sources, fed with currents of same magnitude but, in phase quadrature,
determine the radiation pattern. Evaluate the null directions and directions
of maxima and draw the pattern. (10)
b) Explain the principle of
pattern multiplication with an example. (6)
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6
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Derive the formula to find the maxima, null points
and half power points of an N element broadside array and show that the first minor lobe is
13.46 dB down from the major lobe.(16)
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