Jawaharlal Nehru Technological University Kakinada 2008 B.Tech Electronics and Communications Engineering ANTENNAS AND WAVE PROPAGATION - Question Paper

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Code No: R05310403 Set No. 3
III B.Tech I Semester Supplimentary Examinations, February 2008
ANTENNAS AND WAVE PROPAGATION
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
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1. (a) As related to Antennas, describe and discuss the subsequent terms:
i. Directivity
ii. Radiation Resistance
iii. Beam Width
iv. Band Width.
(b) Evaluate the directivity of
i. An Isotropic Source
ii. Source with Bi-Directional cos ? power trend. [8+8]
2. (a) What is Retarded Potential? discuss various approaches to solve radiation
Problems.
(b) discuss the Lorentz Gauge Condition and show that
? ?. ¯A/j?µe-j? ¯A = one / j?µe (?*?*¯A)
where ¯A is magnetic vector potential. [8+8]
3. (a) discuss the principle of trend multiplication.What is the effect of earth on
the radiation trend of antennas.
(b) A uniform linear array consists of 16 isotropic point source with a spacing of
?/4 if the phase difference a=-900. obtain
i. HPBW.
ii. Directivity.
iii. Effective aperture. [8+8]
4. (a) discuss the construction and radiation characteristics of Helical Antenna.
(b) What is a ‘V’ antenna. discuss its characteristics. [8+8]
5. (a) discuss how the radiation trend of folded dipole will be replaced with the
addition of a reflector and 2 directors parasitic elements.
(b) Bring out the differences ranging from Active and Passive Corner Reflectors. What
are Retro Reflectors? [8+8]
6. (a) discuss the principle of operation of Dielectric Lens Antenna.
(b) Write short notes on “Radiation from Sectoral Horn”. [8+8]
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Code No: R05310403 Set No. 3
7. (a) elaborate various mechanisms of propagation of electromagnetic waves? Ex-
plain.
(b) What is Critical Frequency? What is Virtual Height? obtain the maximum
distance that can be covered if the virtual height of the ionospheric layer is
250kms. [8+8]
8. (a) Write short notes on “M Curves and their characteristics”.
(b) Show that the radius of curvature of ray path is provided by 2/(der/dh) for
tropospheric waves. [8+8]
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Code No: R05310403 Set No. 4
III B.Tech I Semester Supplimentary Examinations, February 2008
ANTENNAS AND WAVE PROPAGATION
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
? ? ? ? ?
1. (a) discuss the terms “Isotropic”, “Directional” and “Omni directional pattern”,
“Radiation Intensity”.
(b) describe Effective Aperture and compute the effective aperture of a 0.25 ? di-
pole. [8+8]
2. (a) State the Reciprocity Theorem for Antennas? Prove that the Self Impedance
of an Antenna in transmitting and receiving mode is identical.
(b) describe Directivity. find the Directivity of an Isotropic Antenna, Short
Dipole and Half-Wave Dipole. [8+8]
3. (a) elaborate the different differences ranging from binomial and linear arrays.
(b) Design a eight element broadside array of isotropic sources of ?/2 spacing ranging from
elements. The trend is to be optimum with a side lobe level 26db down the
mainlobe maximum. [8+8]
4. (a) Distinguish ranging from
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 fire
antenna with a sharp null along the direction of extension of the wire. [8+8]
5. (a) A Paraboloid reflector of 1.8m diameter is used at 6GHz. compute the beam
width ranging from the nulls and gains in dBs.
(b) Design Yagi Uda antenna of 6 elements to give a again of 12dB if the
operating frequency is 200MHz. [8+8]
6. (a) Distinguish ranging from Sectoral, Pyramidal and Conical horns. discuss their
utility.
(b) With a neat setup, discuss the absolute method of measuring the gain of an
antenna. [8+8]
7. (a) define the salient features of Ground wave propagation. explain the effect of
frequency earth constants and curvature of earth on ground wave propagation.
(b) Communication by ionosphere propagation is needed for a distance of 200kms.
height of the layer is 220kms and the critical frequency is 5MHz. obtain MUF.
[8+8]
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Code No: R05310403 Set No. 4
8. (a) Write explanatory notes on
i. Selective fading and Interference fading.
ii. Field Strength computation for radio AM broadcast waves.
(b) A communication link is to be established ranging from 2 stations using half
length antenna for maximum distance gain. Transmitter power is 1KW, dis-
tance ranging from transmitter and receiver is 100km. What is the maximum power
received by receiver? Frequency of operation is 100MHz. [8+8]
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Earning:   Approval pending.