Jawaharlal Nehru Technological University Kakinada 2007 B.Tech Electronics and Communications Engineering ANTENNAS AND WAVE PROPAGATION - Question Paper

Telematics)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
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1. (a) describe the terms:
i. Beam Width
ii. Side Lobe Level
iii. Polarization
iv. Effective Aperture Area.
(b) What is the effective length of an antenna. Determine the effective length of
a half wave dipole antenna. [8+8]
2. (a) Show that the radiation resistance of a small loop is equal to 320p 4(A/?2)
ohms where A is loop area.
(b) What is Folded Dipole ? obtain its Radiation Resistance. [8+8]
3. (a) discuss the procedure for measuring the radiation trend of a half wave
dipole.
(b) What is the requirement for tapering of arrays.
(c) State the applications of arrays. [8+4+4]
4. (a) State the advantages and disadvantages of Rhombic Antenna.
(b) Draw the radiation trend for traveling wave antenna for L=?/2,?,2 ?,4? and
8 ?. [8+8]
5. (a) What is a Parasitic Element? define the use of various kinds of parasites
in TV receiving antennas.
(b) Derive an expression for aperture field distribution of a parabolidal reflector.
[8+8]
6. (a) define the method of measuring the gain and radiation trend of an an-
tenna.
(b) A standard gain horn antenna with a power gain of 12.5, is used to measure the
gain of a large directional antenna by comparison method. The test antenna
is connected to the receiver and an attenuator adjusted to 23dB in order to
have the identical receiver output. obtain out the gain of the large antenna. [8+8]
7. It is described to establish short wave communication ranging from 2 points on earths
surface(assumed flat) separated by 1200km. compute MUF and angle of take off
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Code No: R05310403 Set No. 3
of the transmitted wave from the following: Highest signal frequency returned to
earth after vertically upward propagation=7.2MHz. Virtual height of the ionized
layer=200kms. Deduce the working formula. [16]
8. (a) Distinguish ranging from Radio and Optical horizons. provide the reasons.
(b) Write short notes on M-Curves. [8+8]
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Code No: R05310403 Set No. 4
III B.Tech I Semester Regular Examinations, November 2007
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) describe antenna beam width and directivity and find the relation ranging from
them.
(b) compute the electric field (Erms) due to an isotropic radiator radiating 3KW
power at a distance of two Km from it. [8+8]
2. (a) State the subsequent antenna theorems and bring out their importance in an-
tenna measurements :
i. Reciprocity theorem.
ii. Maximum power transfer theorem.
(b) A half wave transmitting antenna radiates 10KW of power at 100MHz.If the
heights of transmitting and receiving antennas are 100m and 9m, compute the
power received at a distance of 10kms from the transmitting antenna. [8+8]
3. (a) compute
i. HPBW
ii. Solid Angle if a linear array having 10 isotropic point source with ?/2
spacing and phase difference d=900.
(b) Write short notes on Hansen-Wood yard end fire array. [8+8]
4. (a) Distinguish ranging from Traveling wave and Standing wave antennas.
(b) Compare Resonant and Non Resonant antennas.
(c) discuss the working of Rhombic antenna. [4+4+8]
5. (a) calculate the gain, principle beam width and HPBW of a 10m diameter par-
abolic dish with a half wave length dipole feed in focus at 10GHz.
(b) discuss the Cassegrain mechanism in transmission mode. List out the advan-
tages and disadvantages of Cassegrain feed. [8+8]
6. (a) What is an electromagnetic horn antenna? elaborate its applications? The
length of an E-plane sectoral horn is 15cms. Design the horn dimensions such
that it is optimum at 10GHz.
(b) compute the minimum distance needed to measure the field trend of an
antenna of diameter 2m at a frequency of 3GHz. Derive the necessary equa-
tion. [8+8]
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Code No: R05310403 Set No. 4
7. (a) Show that Ionosphere act as a variable refractive index medium.
(b) A radio link has to be established ranging from 2 earth station at a distance of
25000kms. If the height of ionosphere is 200kms and its critical frequency is
5MHz. compute the MUF for the provided path. Also compute the electron
density in the ionosphere layer. [8+8]
8. (a) define the troposphere and discuss how tropospheric ducts can be used for
microwave propagation.
(b) Derive the expression for space wave electric field produced by an antenna at
a distance point, assuming a flat earth. [8+8]
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Earning:   Approval pending.