USN 06F,.C64

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Sixth Semester B.E. Degree Examination, Dec.2013 lJan.20l4Antennas aflrd Propagation

Time: 3 hrs. Max. Marks:100Note: Answer FIVE full questions, selecting

at leust TWO epuestions from each part.

PART _ ADelqe the following:D Isotropic radiator ii) Direc'ivity iii) Radiation int€nsityiv) Beam width v) Radiation ef1iciency (10 Marks)

Anantenflahas a fieldpattern given br E(0)=cosr0 for 0<e<90'. Findthe beamareaand the directivity. (06 Marks)

c. Calculate the maximum Dower received at a distance of 1 km over a free space fbr a radiolink operating at 1 GHz fiequencv and consisting of transrnitting antenna with 25 dB gainand a receiving antenna of 20 dB gain. ,tssume the transmitting antenna input is 200 Watts.

(04 Marks)1

2 a. For a ! dipole antenna derive the maximum eflbctive aperture and determine directivity.2 ' ,06 Marks)

b. Derive an expression for total fleld ,r case of two isotropic point sources with same

amplitude and opposite phase. Plot the relative tield pattern when these two isotropicA

sources are soaced I aoart. And also determine the directions of maximum field and nulls.,2(08 Marks)

c. Calculate the directivity lbr the sources having the tbilowing patterns:

i) U=U,,sin0sin20 ii) LI .=T,,cos$sinr0where0<e<nand0<0<n

3 a. State and explain the principle of paiterrr rrultiplication. Plot tna defO pattern of an array of

twonon'isotropic dissimilar sources:E1 :cos$ and Ez: sin$ Zyt,wherc V =](cosO+f).

with reference to the sourcel as showrr il

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I

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F'ig. Q3 (a). (06 Marks)

k- --JI c:=YU I

Fie. Q3 (a)

What is an array fbctor? Obtain thc; arr:., t'actor for: a linear array of n isotropic point sourcesof equal amplitude and same displacen',ei-rl. (06 Marks)

A linear array of four isotropic sources rrzith equal displacement of I and same amplitude2

but a phase diffbrence of -d.. Plot lhe firlC pattern and determine half power beam width and

b.

directions of nulls. (08 Marks)

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068C64

a. Derive an expression fbr the ratliation re sistance of a shofi electric dipole. (08 Marks)

b. Obtainthefieldpatternof-thinlinearirltennaoflengihD L:: ii) L:1. (06Marks)22

c. Write shofi notes on:i) Rhombic antenna

5a.b.

c.

ii) Fclce;c dipoie antenna.

EAE-tsConsidering the general case derive the tbr-freld equations lbr loop antenna.

State and explain the Batrinet's prinr;iplc.

(06 Marks)

.:(08 Marks)(04 Marks)

(08 Marks)Write shofi notes on:i) Patch antenna ii) R;:iangular horn antenna.

6a.b.

c.

Discuss the features of lieiical antenna" iiive :he construciional details of helical antenna.

Explain the corner reflector antennas. [8:ilil[]Write shorl notes on:i) Log-periodic antennas ii) Antennas for ground penetrating radar. (08 Marks)

Explain the space wave propagation anC obtain the expression for modified refractive index.(10 Marks)

Mention the conditions fbr sub-refractron, super refraction and duct propagation and draw asuitable diagram to depict these regions above the earth surface. (06 Marks)

c. An antenna located at tl-ie surfbce of the ear:th is used to receive the signals transmitted byanother antenna located at a height ot'60 m from the spherical surfbce of the earth (mean

radius :6370km). Calculate the optical and radio horizons tt H = 49lkm. (04 Marks)

8 a. Define the lollowing with respect to \va\epropagation: ir CriticaI lrequency ii) Maximumusable frequency (MUF) iii) Virtual height iv) Skip distance (06 Marks)

b. Derive the expression for critical frecliiency in terms of maximum electron density,N,ffu*.rl

c. An electromagnetic \vave at fiequency,' f is propagating through a lossy medium havingconductivity g, permittir,'itv e=eoe, and permeability p : Iro. Derive an expression for the

attenuation per unit length of the nilrl.illm. if o/(ro e) << 1. Show that the attenuation is

given by 60no/./e , . (06 Marks)

7a.b.

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