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

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. obtain the effective length of a ?/2 dipole and ?/4 monopole. Hence compute their
directivities, using the improper radiation resistances. [16]
2. (a) Derive expressions for the electric and magnetic fields radiated by a half wave
length dipole antenna.
(b) A grounded vertical antenna has an effective height of 111.3 mts and operates
at a wavelength of 18.8kms,with base current of 725 amps, obtain the E and H
fields at a distance of 150kms and power radiated by it. [8+8]
3. (a) What is the necessity of an Array? discuss the 3 various kinds of arrays
with regard to beam pointing direction.
(b) 64 isotropic elements are to be organizes in a binomial array form. Determine
the current ratios and obtain polar plot of the array. [8+8]
4. (a) define the construction and properties of Rhombic Antenna.
(b) define the characteristics of long wire traveling wave antenna. Sketch their
trend for lengths of
i. ?/2
ii. five ?
iii. 20 ?. [10+6]
5. (a) With reference to paraboloids,explain the following:
i. Aperture Efficiency
ii. Front toBack Ratio
iii. kinds of Feeds.
(b) Design Yagi-Uda antenna of 6 elements to give a gain of 12dB if the
operating frequency is 200MHz. [8+8]
6. (a) What is the principle of equality of path length? How is it applicable to horn
antenna?
(b) explain how the directivity of horn antenna can be measured. [8+8]
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]
1 of 2
Code No: R05310403 Set No. 2
8. (a) Prove that the radio horizon distance ranging from transmitting and receiving an-
tennas is provided by dmiles=p2ht+p2hr.
(b) Write short notes on “Troposcatter”. [8+8]

Earning:   Approval pending.