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Code No: R05310403
Set No. 1
III B.Tech I Semester Regular Examinations, November 2008
ANTENNAS AND WAVE PROPAGATION
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks

1. (a) De ne and Explain: Directivity and power gain for an antenna. What is the
relation between the two? Prove that the directivity of a /2 aerial is 0.39 db
more than that of short dipole.
(b) What are principal planes? How the antenna beam width is de ned in such
planes? [10+6]

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2. (a) Derive an expression for the Radiation Resistance of a Loop Antenna.
(b) Find the E ective Length of a Half Wave Dipole.

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(c) A Small current element at 10MHz produces a radiated eld in a direction
making angle with the element. Assuming that the current is 10 Amp.
Calculate the power radiated and radiation resistance of the Antenna.[6+6+4]

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3. (a) Derive an expression for radiated power(Rp)of a BSA with ‘n’ vertical dipoles.
Plot the Rp in vertical and horizontal planars for a BSA of 4 dipoles.
(b) Show the directivity of EFA(with increased directivity) is given by 1.789[4(L/ )].
[8+8]
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4. (a) Derive an expression for electric eld of a Non Resonant antenna of length ‘l’
carrying current.
(b) Sketch and explain the constructional features of a Helical Antenna. [10+6]
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5. (a) Describe the performance of paraboloids with respect to aperture blocking.
(b) Describe the constructional details of cassegrain antennas and sketch its radi-
ation characteristics. [8+8]
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6. (a) What is an Optimum Horn? Sketch and Explain its characteristics along with
dimensional relations.
(b) Explain the rst transmission formula and its applicability for antenna gain
measurements. [8+8]
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7. (a) Explain the following :
i. Ground Wave
ii. Space Wave
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iii. Surface Wave.
(b) Discuss the characteristics of ionospheric layers. [8+8]
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Code No: R05310403
Set No. 1
8. (a) Space wave propagates between transmitting and receiving stations of heights
‘h1’ and ‘h2’ respectively. Derive the expression for eld strength.
(b) What are the di erent paths used for propagating radio waves from 300KHz
and 300MHz. [8+8]

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Code No: R05310403
Set No. 2
Telematics)

1. (a) The Directivity
i. equal to number of point surfaces in the sky that the antenna can resolve.
Justify this statement.
(b) The eld pattern of an antenna is given by En=(Sin ) (Sin )

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i. Plot the Normalized power pattern.
ii. Estimate the main beam e ciency of the antenna. [8+8]

2. (a) Explain the terms ‘Radiation Field’, ‘Induction Field’ and ‘Electrostatic Field’

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by deriving the E Field of a current element through vector potential.
(b) What is Polarization? How many types of Polarizations are used in Antennas?

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Explain. [8+8]

3. (a) Find the radiation Pattern of 4 isotropic elements fed in phase, spaced /2
apart by using pattern multiplication.
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(b) What is uniform linear array? Discuss the application of linear array. [8+8]

4. (a) Write short notes on “Helical Antenna”.
(b) Derive an expression for radiated electric eld strength of a traveling wave
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radiation of length ‘l’. [8+8]

5. (a) What is a parabolic element. How does a parasitic element act when length
is greater than and smaller than /2.
(b) Distinguish between Spherical and Cylindrical paraboloids. Comment on their
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aperture e ciency and applications. [8+8]

6. (a) What is the principle of equality of path length? How is it applicable to horn
antenna?
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(b) Discuss how the directivity of horn antenna can be measured. [8+8]

7. (a) What are di erent mechanisms of propagation of electromagnetic waves? Ex-
plain.
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(b) What is Critical Frequency? What is Virtual Height? Find the maximum
distance that can be covered if the virtual height of the ionospheric layer is
250kms. [8+8]

8. (a) Establish the mathematical relation for
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Code No: R05310403
Set No. 2
i. Radio Horizon
ii. Radius of curvature of array path for LOS waves.
(b) Show that the eld strength due to space wave given by
E = (2E0 d)sin(2 hthr d) [8+8]

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Code No: R05310403
Set No. 3
Telematics)

1. (a) Explain the following :
i. Normalized Field Pattern
ii. Beam Solid Angle
iii. Beam E ciency
iv. Directivity.

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(b) An antenna has a eld pattern given by E ( ) =cos cos 2 for 00 =
= 900.
Find

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i. the HPBW

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ii. Beam Width between rst nulls. (FNBW) [8+8]

2. (a) Show that for a slot in a conducting plane, the impedance Zslot is given by
Zdipole Zslot=Z0 2 4 where Z0 is the impedance of free space.

Calculate the directivity of the antenna.
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(b) The radiation intensity of a particular antenna is given by Ø( Ø) = sin2 .

(c) De ne the e ective aperture and calculate the e ective aperture of 0.25 di-
pole. [8+4+4]
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3. (a) Enumerate the advantages and disadvantages of linear arrays.
(b) Find the phasing required to steer a beam zenith to -400 for a 5 element array
with 0.4 inter element spacing. [8+8]
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4. (a) What is meant by Non Resonant antenna? Derive from the rst principle, the
eld due to such antenna and sketch the eld pattern for lengths and 2 .
(b) Mention the merits and demerits of a traveling wave antenna. [8+8]
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5. (a) A Paraboloid re ector of 1.8m diameter is used at 6GHz. Calculate the beam
width between the nulls and gains in dBs.
(b) Design Yagi Uda antenna of six elements to provide a again of 12dB if the
operating frequency is 200MHz. [8+8]
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6. (a) How is the eld pattern of a receiving antenna experimentally determined.
Explain with a neat diagram.
(b) Distinguish between Curved Surface Zoning and Plane Surface Zoning of lens
antenna. Discuss their merits and demerits. [8+8]
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Code No: R05310403
Set No. 3
7. (a) What is Angle of Tilt? How does it a ect the eld strength at a distance from
the transmitter?
(b) A 150m antenna transmitting at 1.2MHz by ground wave has an antenna
current of 8A. What voltage is received by a receiving antenna 40kms away,
with a height of 2meters? [8+8]

8. (a) A police radio transmitter operating at a frequency 1.69GHz is required to
provide a ground wave having a strength of 0.5mv/m at a distance of 16km.
The transmitter antenna, having an e ciency of 50% pro duces a radiating
eld proportional of cos . The ground wave has = 5 × 10-5 mho/cm and r
= 15. Calculate the power transmitted.
(b) Derive the fundamental equation for free space propagation. [8+8]

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Code No: R05310403
Set No. 4
Telematics)

1. (a) De ne and account for the presence of
i. Radial Power Flow
ii. Radiation resistance for a short dipole
iii. Uniform Current Distribution.

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(b) Calculate the following for an antenna carrying 50A (rms) at 480 kHz having
e ective length of 60.96metres. Take loss resistance of the antenna= 5 .
i. Radiation resistance

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ii. Power radiated
iii. Antenna e ciency

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iv. Directivity and power gain
v. HPBW and BWFN. [6+10]

2. (a) De ne the following terms:
i. Directivity
ii. Gain
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iii. E ective Aperture of Antennas.
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(b) Show that the Directivity of an elementary Dipole (Current Element) is 1.5
or 1.76dB.
(c) Calculate the power gain of a half wave Dipole whose ohmic losses and Direc-
tive gain are 7.0 Ohms and 1.64 respectively. [6+6+4]
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3. (a) Explain the concept of scanning arrays.
(b) Show that Dolph-Tchebyshelf distributions gives optimum distribution and
minimum side lobe level for a given beam width of major lobe. [8+8]
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4. (a) Distinguish between
i. Resonant and Non Resonant antennas.
ii. Narrow Band and Wide Band antennas.
(b) Show that a single wire excited with a traveling wave current is an end re
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antenna with a sharp null along the direction of extension of the wire. [8+8]

5. (a) A paraboloid re ector has radiation characteristics whose HPBW is 50. Find
out its null to null beam width and power gain.
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Code No: R05310403
Set No. 4
(b) Discuss the conditions under which a parasitic dipole placed near and parallel
to a driven dipole can act as a re ector. [8+8]

6. (a) With a neat setup, explain the method of measurement of the beam width of
pyramidal horn antennas in E-plane. How does it di er from H-plane mea-
surement?
(b) Explain the basic principle of operation of lens antenna. [8+8]

7. (a) Discuss the propagation characteristics of EM wave.
(b) Mention the salient features of Ground wave propagation. [8+8]

8. (a) Derive an expression for the curvature of the ray path due to the changing
refractive index in the troposphere.
(b) Explain the phenomenon of duct propagation. [8+8]

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