Mumbai University Previous year question papers
VI Sem Electronics Examination Dec 2005
Antena and Wave Propogation
(1) Question No.1 is cOlTpUlsory.
(2) Attempt any four from che rema1ning six questions.
(3) Figure to the right indicate full marks.
(4) As.sumeany suitable data Wh~112Verrequired.
1.a) Expain isotropic antenna, omnidirectional antenna and directional antenna.
b) Define directivity and gain of an antenna: Derive the relation between the two.
c) Explain the different types of antenna los-es.
d) What is a magnetic dipole? Compare it with electric dipole.
e) An antenna having a gain of 6 db over a reference antenna is radiating 700 watts. Calculate the power the reference antenna must radiate in order to be equally effectiveinmostpreferreddirection.
f) Compare traveling wave and standing wave antennas.
2. a) Derive the wave equation in terms of vector potential from Me :well’s equations. Also sqlve the wave equation for infinitesimal current source 01 current. density Jz.
b) Find the expression for far electric field of a infinitesimal electric dipole placed vertically at a height ‘h’ over a perfect electric conducting plane. Draw the field patt~r~ for h= O.
3. a) Define beam solid angle, beam efficiency and resolution of an antenna. Find the number of radio transmitters distributed uniformly over the sky whieh an antenna can resolve in terms of directivity.
b) Normalised radiation intensity of an antenna is given’ by .
F sine sin<1> 0 :s e :s n & 0 :s <1>:s n0 elsewhere.
jj)Azimuthand elevationplaneHPBWin degrees.
4. a) Explain Friis transmission formula. A series of microwave repeater links operating at 10 Ghz are used to relay TV signals into a valley that is surrounded by steep mountain ranges. Each repeater consists of a receiver, a transmitter, antennas and associated equipment. The transmitting and receiving antennas are identical horns having a gain of 15 db. The repeaters are separated by 10 kms.
For acceptable SIN ratio the power received at receiver must be greater than 10’nwatts. Lossdueto polarization mismatch is 3db.Assumematched loadsand free space propagation condi~ions. Determine the minimum transmitter power that should be used.
b) Derive the relation between the maximum effective aperture and maximum directivity of an antenna.
S. a) List the parameters that decide the overall pattern of an antenna array.
b) A broadside array consists of 4 isotropic SOJ.lrceswith a distance 00J2 between them. .
Find – i)’The array factor.
ii) Directions of major lobe and minor lobe maxima.
iii}Directions of minima.
‘iv) HPBW and FNBW.
v) First minor.lobe level.
vi) Plot the pattern.
6. a) Explain the different types of feed systems for paraboloidal reflectors. Find FNSW and gain of paraboloidal reflector antenna of mouth diameter of 2 mts and operating at 6000mhz.
b) What is a folded dipole? Find its radiation resistance. D,iscuss its applications.
7. a) Explain the mechanism of ionospheric propagation. Define critical frequency, MUF and OWF. ‘
b) A high frequency radiolink has to be established between two points at a di,stanceof2500kms on earth’s surface. Considering the ionospheric height of200kms andcritical frequencyof 5mhz,calculateMUF for given path. Derive the formula used.