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Reg. No. :

Iv'{2131

B.E./B. ech.

DEGREEEXAMINATION.

APRIL/IVIAY 008.

Seventh Semester

Electronics and Communication

Engineering

EC 431

-

ANTENNAS

AND PROPAGATION

Time

: Three hours

Maximum

: 100 marks

Answer ALL

questions.

PART A

-

(10

x2

=

2Omarks)

1.

Define

antenna

efficiency.

2. What are end

fire arrays?

3. Mention two

important advantagesof folded

dipole antenna.

4. What are

the frequency independent antennas?

5. What is ERP of an antenna?

6. What is an aperture

number of

paraboloidal reflector?

7. Calculate

the

power

gain

of an optimum

horn antenna

approximately

with a

square aperture of 10) on a side.

8. What

is the relation between directivity

(D)

and beam solid

angle

(Oo

)

or

Beam area

(B)

in

antenna?

9. What is short wave

propagation?

10. Calculate

the critical frequency for

reflection

at vertical

incidence

if the

maximum value

of

electronsdensitv is

81 m-3.

PARTB- (5x16=80marks )

11.

(a)

(i)

What is

the

effective aperture

of an antenna

and how

does

t relate

to the

gain?

(10)

(ii)

Explain directive

gain

and directivity

of

antenna.

(6)

Or

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(b )

(i)

Explain

antenna

impedance

and

polarizalion.

(ii)

Sketch

the

horizontal

and

vertical

plane radiation

fed

vertical

dipole

of

I

ainote

and

2) dipole.

Derive

a uniformly

spaced

linear

array

of

z isotropic

uniform

phase difference

between

consecutive

elements.

side array

and

end

fire

array.

Or

What

are

electromagnetic

horn

antennas?

What

are

horns?

What

are their

practical applications?

How

compare

with

paraboloidal

reflector

antennas?

(6)

pattern ofcentre

(10)

elements with

Compare

broad

(16)

the

various

types

of

do

these

antennas

(16)

M 2131

12.

(a )

Or

Using

the

pattern multiplication

principle, sketch

the

horizontal

pattern

of

four vertical

antennas.

(i)

Spaced

one

half

wavelength

apart

and

fed

with

equal

currents

but

with 180 phasing between he adjacent

elements.

(8)

(ii)

Spaced

one

quarter wavelength

apart

and having

progressive

phase

shift

of 90o

between

he

elements'

(8)

18.

(a)

What

is

radiation

resistance

of

an

antenna?

Show

that

the

radiation

resistance

of

a half

wave dipole

is

73 ohms.

Also

calculate

the

radiation

resistance

offolded

diPole.

(16)

L4.

(a)

Or

Write

short

notes

on the

following

:

(i)

Helical

antenna

(ii)

Small

loop

antenna

(iii)

Half wave

dipole

Describe

and explain

the operations

(i) Yagi uda antenna

(ii)

Log

periodic

antenna.

of the

following

antennas

:

(b)

(b )

(6)

(o/

(5)

(8)

(8)

(b )

2

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15.

(a)

(i)

Explain MUF and

give

one

method of calculating

it

(10)

(6)

the

part

(L2)

(4)

(ii)

A high frequency

radio link has to be established

between

two

points

at a distance

of 2500

km

on

earth's

surface.

Considering

he

ionospheric height to be

200 km and its criticai

frequency 5

MHz,

calculate the

MUF for the

given path.

(b)

(i )

(ii)

Or

Describe the structure of

the ionosphere. Also discuss

played

by the

ionosphere n radio

wave

propagation.

Explain Faraday

rotation.

M 2131

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