Rajiv Gandhi Proudyogiki Vishwavidyalaya 2008 B.E Electronics & Tele-Communication Engineering 6th Sem Antenna & Wave Propagation - Question Paper
6th Sem Electronics & Communication, June 2008
Antenna & Wave Propagation
4. (a) Show that input impedance of an antenna is equal to
internal impedance of the same antenna when used as receiver. State the theorems used by you for this.
(b) Two identical antennas arc placed to have a mutual impedance of (7-33 + j 3 6) ohms between them. The combination radiates a total power of 5(X) watts when excited by equal inphase currents of 2 Amp. in each antenna. Calculate the power radiated by one antenna alone if other antenna is open circuited.
5. (a) State and explain the rule of pattern multiplication.
Explain broadside array of two half wave dipoles.
(b) Explain the working and properties of any two of the following :
(i) Parabolic reflector \(ii) Horn antenna (in) Log periodic antenna
6. (a) Explain effective aperture of an antenna. Deterrmre
effective aperture of a half wave dipo:>. approximations made.
(b) Explain the properties ot >posphere for duct propagation.
7. (a)" Explain Ionosphere. Derive th . ki-k on for critical
frequency of an ionospheric la . - *.
(b) Explain skip distance and MU I.
8. Write short notes on any two of the follow 1:1 (i) Bapinets principle for aperture antenna (H) Non-uniform amplitude distributions (iii) Eiiect of earth surfaco on venical pattern
9,050
B. E. (Sixth Semester) EXAMINATION, June, 2008 (Electronics & Communication Engg.)
ANTENNA AND WAVE PROPAGATION (EC -602)
Time : Three Hours Maximum Marks : 100 Minimum Pass Marks : 35
Note : Answer any jive questions. All questions carry equal marks.
1. Derive the expressions for electric and magnetic fields due to an oscillating current element Idl directed in Z-direction at origin in free space. Determine the phasor ratio of electric and magnetic fields at distance of 2 km in X-Y plane if the frequency of oscillation is 10 kHz.
2, Explain radiation resistance and directivity of an antenna.
A short dipole of physical length equal to 75 m is centre
fed by an r. m. s. current of 10 Amp. at frequency of 800 kHz in free space. Calculate the total power radiated by the antenna giving derivation-of the formula used.
3. (a) Explain how the direction of main beam can be
controlled by varying excitation phases in isotropic elements in a uniform array.
(b) A line array of 21 isotropic elements is fed by equal currents with progressive phase shift of 60 degrees. Calculate the maximum interelement distance without appearance of grating lobe at frequency of 6 GHz.
P. T. C .
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