Osmania University (OU) 2006-2nd Sem B.E Electronics & Tele-Communication Engineering 3/4 (E.C.E)(ESTER)SUPPLEMENTARY ,IL, Antennas and propagation - Question Paper
B.E 3/4 (E.C.E)(II-SEMESTER)SUPPLEMENTARY EXAMINATION,APRIL,2006
Antennas and propagation
Code No. 10393
FACULTY OF ENGINEERING B.E. 3/4 (ECE) II Semester Main Examination, April 2006 ANTENNAS AND PROPAGATION
Time : Three Hours] [Maximum Marks : 75
Note: Answer ail questions of Part A and answer five questions from Part B.
PARTA (Marks : 25)
1. An antenna has a field pattern given by E(8) = cos2 8 for 0 < 0 < 90. Find the directivity.
. 3
2. What is broadside array ? 2
3. What is the length of the longest element of a log-periodic antenna operating at frequencies from 100 to 500 MHz ? 3
4. What is a frequency independent antenna ? 2
5. What is the radiation resistance of an infinitesimaUy small dipole whose overall length is L = A/50 ? 3
6. What is an atmospheric duct ? 2
7. Define antenna polarization. 2
8. Find the relative ratio of the two lengths of a rectangular aperture antenna with total quality factor Q, = 14.14. 3
9. Write two important applications of loop antenna and helical antena. 2
10. In ionospheric propagation employing 8 MHz critical frequency with 100 km virtual height for a particular layer, 200 km skip distance has been noticed. Calculate the angle of incidence. 3
PARTB (Marks : 5x10=50)
11. (a) Derive the Friis Transmission formula. 4
(b) A radio link has a 15-W transmitter connected to an antenna of 2.5 m2 effective aperture
at 5 GHz. The receiving antenna has an effective aperture of 0.5m2 and is located at a 15 km iine-of-sight distance from the transmitting antenna. Assuming lossless, matched antennas, find the power delivered to the receiver. 6
12. (a) Determine the electromagnetic fields for an infinitesimal electric current element. 4 (b) Show that in the near field region there is no time average power flow associated with the
field components. 6
13. (a) Derive expression for radiated electric field of an-element array with uniform excitation
(magnitude and phase) and inter-element spacing A/2. . 4
(b) Consider an array of two identical infinitesimal dipolg separated by a distance A/4 with same magnitude excitation but a phase excitation difference P between the elements. Find the nulls of the total field for p = 0; P = tc/2. 6
14. (a) Derive expression for far field patterns of a circular loop antenna with uniform current. 6 (b) Find the radiation resistance of a single turn and 6-tum small circular loop. The radius of
the loop is A/30 and the medium free space. 4
15. (a) Explain the measurement technique of the impedance pattern of an antenna. 5 (b) In the measurement of the antenna gain using three antenna method, three horn antennas A,
B and C are measured in pairs at 12 GHz. The separation of antennas is 8 m. The transmitted power is +3 dBm. The received powers are -31 dBm, -36 dBm and -28 dBm for antenna pairs AB, AC and BC,; respectively. Find the gains of the antennas. 5
16. (a) In what respect binomial array is advantageous when compared to uniform linear array ?
Explain with an example. 1 6
(b) Explain the effect of inter-element phase shift on beam scanning of an array antenna. 4
17. Write short notes on:
(a) Line of sight propagation 3
(b) Travelling wave antennas 3
(c) Yagi Uda array 4
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