code no: rt31045 r13 set - 1 iii b. tech i semester...

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Code No: RT31045

III B. Tech I Semester Regular/Supplementary Examinations, October/November - 2016

ANTENNAS AND WAVE PROPAGATION (Electronics and Communication Engineering)

Time: 3 hours Max. Marks: 70

Note: 1. Question Paper consists of two parts (Part-A and Part-B)

2. Answering the question in Part-A is compulsory

3. Answer any THREE Questions from Part-B

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PART –A

1 a) Define the terms radiation intensity and directivity. [4M]

b) Compare the different types of wire antenna. [4M]

c) Given a linear broadside uniform array of isotropic elements, (N=∞) with a separation

of λ/4 (d= λ/4) between the elements. Find the directivity of an array.

[3M]

d) What are the advantages of Microstrip antennas? [3M]

e) Describe the cassegrain method of feeding a parabolic reflector. [4M]

f) Define the terms MUF and Skip Distance [4M]

PART -B

2 a) Explain the current distribution on a thin-wire antenna. [10M]

b) For an infinitesimal dipole excited by a constant RF current I, determine radiation

intensity U, maximum value of U and directivity.

[6M]

3 a) Explain the concept of Retarded Potentials. [10M]

b) A thin dipole is λ/15 long. If it has loss resistances of 1.5Ω, calculate its directivity

and gain

[6M]

4 a) With a neat sketch explain the operation of Yagi-Uda array. [8M]

b) Deduce an expression for the radiation pattern of an end-fire array with N vertical

dipoles.

[8M]

5 a) Find the directivity of 10 turn helix antenna having pitch angle 100, circumference C

equal to λ.

[4M]

b) Explain the radiation mechanism of microstrip antenna. [8M]

c) Describe the different types of microstrip antennas [4M]

6 a) Briefly explain about Flat Sheet Reflectors. [10M]

b) A paraboloid reflector of circular cross-sectional area 8000 sq.cm is uniformly

excited at 5GHz. Calculate the HPBW and the gain.

[6M]

7 a) Explain in detail about Ground wave propagation. [10M]

b) A television transmitter antenna has a height of 169 metres and the receiving antenna

has a height of 16 metres. What is the maximum distance through which the TV

signal could be received by space propagation? What is the radio horizon in this case.

[6M]

*****

R13 SET - 1

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Code No: RT31045







~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PART –A

1 a) Define the terms beam efficiency and half-power beam width of an antenna. [4M]

b) Find the radiation resistance of a 20 turn, 1m diameter small loop antenna operating

at 10 MHz. If the loss resistance of 1-turn loop is 1Ω, find its radiation efficiency?

[3M]

c) Discuss the characteristics of folded dipoles. [4M]

d) Describe the significance of Helical antennas. [4M]

e) List the features of Lens antennas. [3M]

f) Write a brief note on Radio Horizon. [4M]

PART -B

2 a) Explain the radiation mechanism in a single wire. [6M]

b) The radiation intensity of an antenna is given by U(θ) = cos4θ; (0≤ θ≤90

0, 0≤

φ≤3600). Find the half-power beam width (HPBW).

[4M]

c) Discuss the different field regions of an antenna.

[6M]

3 a) Derive an expression for the radiation resistance of a short electric dipole element. [8M]

b) What is meant by the effective area of an antenna? How is it related to the gain? [4M]

c) Calculate the radiation resistance of a single-turn small circular loop having mean

radius of λ/20 and radiating in free space.

[4M]

4 a) Explain in detail about Broadside and End-fire arrays. [12M]

b) A broadside array operating at 100 cm wavelength consists of four half wave dipoles

spaced 50 cm. Each element carries radio frequency current in the same phase and

magnitude 0.5 Amp. Calculate the radiated power.

[4M]

5 a) Describe the construction and operation of helical antenna under normal mode [8M]

b) Explain the features and radiation properties of rectangular patch antennas.

[8M]

6 a) Briefly explain about Corner Reflectors. [10M]

b) The diameter of a parabolic reflector is 2m. For operation at 6 GHz, find the beam

width between first nulls and the gain

[6M]

7 a) Explain the following terms: (i) Critical frequency (ii) MUF

(iii) Skip Distance (iv) Virtual height

[12M]

b) Find the range of LOS system when the receive and transmit antenna heights are

10m and 100m respectively. Take the effective earth’s radius into consideration

[4M]

*****

R13 SET - 2

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Code No: RT31045


ANTENNAS AND WAVE PROPAGATION (Electronics and Communication Engineering )





~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PART –A

1 a) What are the factors that contribute to the efficiency of antenna? [3M]

b) Find the radiation resistance and directivity of long wire resonant antenna of length

l=λ?

[4M]

c) Describe the concept of Scanning Arrays. [4M]

d) Give the comparison between axial mode and normal mode of helical antenna. [3M]

e) Write a brief note on Zoning. [4M]

f) List the characteristics of Sky wave propagation. [4M]

PART -B

2 a) Explain the radiation mechanism in dipole. [6M]

b) An antenna has a radiation resistance of 72 Ω, a loss resistance of 8Ω and a power

gain of 12 dB. Determine the antenna efficiency

[4M]

c) Explain the isotropic, directional and omnidirectional patterns.

[6M]

3 a) A half-wave dipole antenna is radiating 1KW and has a gain of 2.15dBi. Find the

input power to the isotropic antenna which will radiate same field strength of the

dipole

[8M]

b) Explain the concept of short magnetic dipole

[8M]

4 a) Explain in detail about Binomial arrays. [10M]

b) Discuss the radiation pattern of a linear array of the three isotropic sources spaced λ/2

apart. The excitation of the sources is in-phase and have amplitude ratio 1:2:1.

[6M]

5 a) Describe the construction and operation of helical antenna under axial mode. [8M]

b) Explain the radiation mechanism in travelling wave radiator.

[8M]

6 a) Explain the important design parameters of parabolic reflector antenna [10M]

b) Give the comparison between horn antenna and paraboloidal reflector antenna.

[6M]

7 a) A HF radio link has to be established between two points at a distance of 2500 Km on

earth’s surface considering the ionospheric height to be 200 Km and its critical

frequency 5 MHz. Calculate the MUF for the given path.

[6M]

b) Explain in detail about sky wave propagation. [10M]

*****

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Code No: RT31045







~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PART –A

1 a) Define the terms gain and resolution of an antenna. [4M]

b) Give the comparison of far fields of small loop and short dipole. [3M]

c) Explain the principle of Pattern multiplication. [4M]

d) What are the limitations of Microstrip antennas? [3M]

e) Write a brief note on F/D ratio. [4M]

f) Explain the mechanism of reflection and refraction. [4M]

PART -B

2 a) Briefly explain about principal pattern. [6M]

b) A lossless antenna has input impedance of 73Ω. It is fed by a 50 Ω transmission line

If the radiation power pattern of the antenna is given by U=4 sin3θ, find the maximum

absolute gain of the antenna and its overall efficiency .

[8M]

c) Give the classification of polarization

[2M]

3 a) Derive expressions for the components of the radiated field of a short dipole element. [8M]

b) The mean radius of a small circular loop of constant current is λ/10. Find the physical

area of the loop

[4M]

c) Explain how a loop antenna is used for determining the field strength in a medium.

[4M]

4 a) For a 6-element Yagi array for operation of 500 MHz with a folded dipole, find the

length of reflector element and driven element.

[4M]

b) For an N-element uniform linear array, derive an expression for the array factor. [6M]

c) Write a brief note on Parasitic elements.

[6M]

5 a) Explain the design considerations for monofilar helical antennas in different modes. [10M]

b) Discuss the basic properties of helical antennas.

[6M]

6 a) Find the BWFN and power gain of a 2m paraboloid reflector operating at 6000 MHz. [4M]

b) Describe the directivity and gain measurements of an antenna.

[12M]

7 a) What is the critical frequency for reflection at vertical incidence, if the maximum

value of electron density is 1.24x106 per cm

3.

[6M]

b) Explain in detail about Tropospheric wave propagation.. [10M]

*****

R13 SET - 4

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Code No: RT31045

III B. Tech I Semester Supplementary Examinations, May -2016






*****

PART –A

1 a) Distinguish between isotropic and directional radiators. [3M]

b) What is a retarded potential? [3M]

c) Why array antennas are preferred over a single radiator? [4M]

d) Distinguish between resonant and non-resonant radiators. [4M]

e) What are the applications of reflector antennas? [4M]

f) What is the effect of earth’s curvature on radio wave propagation? [4M]

PART -B

2 a) Explain antenna radiation mechanism with a two wire line. [8M]

b) The radial component of the radiated power density of an infinitesimal linear dipole

is given by Wav = A0 sin2 / r

2 ar W/m

2. Find its maximum directivity.

[8M]

3 a) Derive the expressions for field components of an alternating current element

located at the origin?

[12M]

b) What are Radiative, inductive and electrostatic field components derived in the

above expressions?

[4M]

4 a) Prove that maximum of the first minor lobe is 13.46 db down from the maximum at

the major lobe of an N-element linear array.

[8M]

b) What is broadside array and derive the expression for angles of nulls, maxima and

half power points?

[8M]

5 a) Give the construction details and radiation pattern of travelling wave antenna. [8M]

b) Explain the working of helical antenna in axial mode? [8M]

6 a) What is aperture blocking and how to avoid it with cassegrain feed mechanism? [8M]

b) Explain in detail about pyramidal horn antenna. [8M]

7 a) Write the expression for field strength of ground wave and explain all the terms. [8M]

b) How earth’s surface reflects radio waves? [8M]

*****

R13 SET - 1

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Code No: RT31045

III B. Tech I Semester Regular Examinations, November - 2015






*****

PART –A

1 a) What is the radiation resistance of half wave dipole antenna? [3M]

b) What are the far field conditions for an antenna? [3M]

c) Discuss the merits and demerits of zoned antennas. [4M]

d) Calculate PLF (dB) when polarization of incoming wave is perfectly matched to

polarization of Rx antenna.

[4M]

e) Name the parasitic elements used in Yagi uda array. Explain their significance in

array.

[4M]

f) In which frequency band Tropospheric scattering is used. [4M]

PART -B

2 a) With the help of neat diagrams explain the principle of radiation mechanism in

antennas.

[8M]

b) A source has a constant power pattern limited to top half of the hemisphere only.

Find its directivity and effective area.

[8M]

3 a) The normalized radiation intensity of an antenna is rotationally symmetric in φ and

it is represented by

<≤

<≤

<≤

<≤

=

00

00

00

0

180900

90601.0

60305.0

3001

θ

θ

θ

θ

U

What is the directivity (above isotropic) of antenna in dB?

[8M]

b) Derive the relationship between effective aperture area and gain of antenna.

[8M]

4 a) Write short notes on:

i) Collinear arrays

ii) Binomial arrays and

iii) Scanning arrays.

[8M]

b) Draw the radiation pattern of 8 – isotropic elements fed in phase, spaced λ/2 apart

with the principle of pattern multiplication.

1 of 2

[8M]

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Code No: RT31045

5 a) Derive the expression for pitch angle to get circularly polarized radiation pattern

for a helical antenna, operating in broadside mode and sketch its pattern.

[8M]

b) Compare the requirements and radiation characteristics of resonant and non-

resonant radiators?

[8M]

6 a) List out the differences between active and passive corner reflectors. [8M]

b) With reference to paraboloids, explain the following:

i) f/D ratio

ii) Spill over and aperture efficiency

iii) Front to back ratio

iv) Types of feeds.

[8M]

7 a) Describe briefly the salient features of ground wave propagation. [6M]

b) What should be the polarization of EM wave for the ground wave propagation?

Justify.

[6M]

c) Explain the term” wave tilt of surface waves”. [4M]

*****

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Code No: RT31045







*****

PART –A

1 a) What is the difference between directive gain and gain of antenna? [4M]

b) A transmitting antenna radiates 251W isotropically. A receiving antenna, located

100m away from the transmitting antenna, has an effective aperture of 500cm2.

Determine the total power received by the antenna.

[4M]

c) For an 8ft (2.4m) parabolic dish antenna operating at 4GHz, What is the minimum

distance required for far field measurement?

[4M]

d) A wave traveling normally out of the page (toward the reader) has two linearly

polarized components tEx ωcos2=

( )o90cos3 += tE y ω

What is the axial ratio of the resultant wave?

[4M]

e) What is the skip zone of a radio wave? [3M]

f) How do raindrops affect radio waves? [3M]

PART -B

2 a) What are the differences between transmission line and dipole antenna? [4M]

b) Sketch and comment on the current distributions and radiation patterns of vertical

antennas of length λ/2, λ, 3λ/2, 2λ.

[8M]

c) Write short notes on antenna field zones. [4M]

3 a) The power radiated by a lossless antenna is 10W. The directional characteristics of

the Antenna are represented by the radiation intensity of

πφπ

θθ 20;2

0cos3

0 ≤≤≤≤

=

anglesolidunit

WBU .

Find 0B , Maximum radiation intensity and Maximum power density (W/m2) at a

distance of 1000m (assume far field distance).

[8M]

b) A short antenna of height 2/lh = is mounted on a conducting plane. Show that its

radiation resistance is one-half that of a short dipole antenna of length l and

carrying the same current.

1 of 2

[8M]

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Code No: RT31045

4 a) Explain the need and configuration of a folded dipole antenna. Sketch its radiation

pattern and compare its characteristics with those of a simple half wave dipole.

[8M]

b) Obtain the expression for the beam width of broadside and end-fire array and

compare them.

[8M]

5 a) Explain the salient features of Microstrip Antennas. [8M]

b) What are the advantages and limitations of Microstrip antennas?

[8M]

6 a) Explain the principle of formation of images in an active corner reflector antenna.

Hence sketch the image formation for a 90o corner reflector. Obtain array factor for

90o

corner reflector.

[8M]

b) What is the principle of equality of path length? How is it applicable to Horn

antennas? Obtain an expression for the directivity of a pyramidal horn in terms of

its aperture dimensions.

[8M]

7 a) List out the modes of propagation and their frequency ranges for radio waves.

Show that an approximate estimate for the magnitude of electric field strength at

VHF and above is given by

2

21240

d

hhI

λ

π

where I - current in the λ/2 transmitting aerial

h1, h2 - heights of Tx and Rx antennas

d - direct distance between aerials

λ - wavelength.

Specify the assumptions made for the validity of the above expression.

[8M]

b) Write a short notes on:

i) MUF

ii) Virtual Height

iii) Wave tilt

iv) Multihop Transmission.

[8M]

*****

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SET - 2 R13

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Code No: RT31045







****

PART –A

1 a) What is the effect of antenna’s sidelobes and backlobes on its gain? [3M]

b) Calculate half power beamwidth for a hertzian dipole. [4M]

c) What is the directivity of isotropic antenna? [3M]

d) What are the advantages of cassegrain feed in parabolic antenna? [4M]

e) In which frequency range ground wave propagation is effective. Why? [4M]

f) What is the difference between broad-side array and end-fire array? [4M]

PART -B

2 a) An infinitesimal electric dipole is centered at the origin and lies along z-axis. Find

the far–zone electric and magnetic fields radiated.

[8M]

b) An infinitesimal electric dipole is centered at the origin and lies on the x-y plane

along a line which is at an angle of 450 with respect to the x-axis. Find the far –zone

electric and magnetic fields radiated.

[4M]

c) Compare monopole antennas and dipole antennas. [4M]

3 a) The normalized radiation intensity of a given antenna is given by φθ sinsin=U .

The intensity exists only in the region πφπθ ≤≤≤≤ 0,0 and it is zero elsewhere.

Find azimuthal and elevation plane half power beam widths (in degrees).

[3M]

b) Derive the relation between directivity and beam solid angle. [8M]

c) The Electric field of a linearly polarized electromagnetic wave given by zkj

xi eyxEaE−= ),(0

is incident upon a linearly polarized antenna whose electric

field polarization can be expressed as ),,()( φθrEaaE yxa += . Find polarization

loss factor (PLF).

[5M]

4 a) Explain the effects of uniform and non-uniform amplitude distributions in array? [8M]

b) Explain how to select current excitations in an array to avoid sidelobes in radiation

pattern?

1 of 2

[8M]

R13 SET - 3

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Code No: RT31045

5 a) Describe the characteristics of long wire travelling wave antennas and sketch their

patterns for different lengths.

[8M]

b) What are the advantages of Rhombic antenna over a single wire antenna? List out

the design equations associated with a Rhombic antenna.

[8M]

6 a) With neat set up, explain the absolute method of measuring the gain of an antenna. [8M]

b) Discuss about Dielectric and metal Lens Antennas and their applications. [8M]

7 a) Derive the relationship between MUF and critical frequency.

[8M]

b) Discuss experimental determination of virtual heights and critical frequencies. [8M]

*****

2 of 2

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Code No: RT31045







*****

PART –A

1 a) What kind of antenna polarizations must be selected to avoid probability of

interference between 2 co-channel radio links?

[3M]

b) What is the advantage of using helical antenna over straight wire antenna? [4M]

c) In a uniform linear array, four isotropic radiating elements are spaced λ/2 apart.

What is the required progressive phase shift between the elements for forming the

main beam at 600

off the end-fire?

[4M]

d) Calculate PLF (dB) when polarization of incoming wave is orthogonal to

polarization of Rx antenna.

[4M]

e) What three main factors determine the amount of refraction in the ionosphere? [3M]

f) After the radiation field leaves an antenna, what is the relationship between the E

and H fields with respect to (a) phase and (b) physical displacement in space?

[4M]

PART -B

2 a) Define the terms:

i) Effective length

ii) Effective aperture area.

[4M]

b) Calculate effective length and effective aperture area of antenna whose radiation

resistance is 73 ohms.

[6M]

c) Derive the expression for power radiated and find the radiation resistance of a half

wave dipole?

[6M]

3 a) Calculate half power beam width when

[ ]πθ

θπ

≤≤=−+

0cos

4

)1cos(

r

eE

rkj

[3M]

b) Define reciprocity theorem and prove it in case of antenna system. [8M]

c) What is the maximum effective aperture of a microwave antenna which has a

directivity of 900?

[5M]

4 a) Derive the expression for the far field pattern of an array of 2 – isotropic point

sources of

i) Equal amplitude and phase

ii) Equal amplitude and opposite phase

iii) Unequal amplitude and any phase.

1 of 2

[8M]

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Code No: RT31045

b) Find the radiation pattern of linear array of 4 isotropic sources spaced 2

λ apart.

And sketch it. The excitations of sources are in phase and amplitude ratio 1:3:3:1.

[8M]

5 a) Sketch the typical geometry of a helical antenna radiating in axial mode. List out

all its parameters and basic characteristics. Write the expressions for HPBW,

BWFN, directivity and axial ratio.

[8M]

b) Compare the characteristics of Hertzian dipole and Hertzian Loop antenna.

[8M]

6 a) What is radio horizon and optical horizon? Show that radio horizon is about 1.33

times the optical horizon.

[8M]

b) What is the density of free electrons in the ionospheric layer at critical frequency

of 1.3 MHz?

[4M]

c) Explain the Gain comparison method for measuring the gain of an antenna.

[4M]

7 a) Describe any two types of fading normally encountered in radio wave propagation.

How are the problems of fading overcome?

[8M]

b) Determine the change in the electron density of E-layer when the critical

frequency changes from 4 MHz to 1 MHz between mid - day and sun-set.

[8M]

*****

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R13 SET - 4

code no: rt31045 r13 set - 1 iii b. tech i semester...

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