# Antennas and Propagation May/June 2010

PART-A

1 a.  Define the following with respect to antenna:

ii)    Directivity

iv)   Polarization.

b. Antenna of gain G radiates Wt. Watts. Show that the free space intensity’  at a distance of r meter is given by e

c. Derive an expression for antenna efficiency in terms of radiation resistance.

2 a. Find the directivity and beam width of the following :

i)         U – Um sin

ii)       cos2 0

iii)    U = Um cos § sin20.

b. State and prove the power theorem.

c. Prove that D=2 (n+1) for a unidirectional pattern given by U = Um cosn 0.

3 a. Derive an expression for field intensity for two isotropic point sources with equal amplitude and equal phase.

b. Draw the polar diagram of a broadside array with number of elements = 5 and spacing = A./2.

4 a. Derive an expression for radiation resistance of a short electric dipole, b. Write short notes on :

(i) Folded dipole antenna ;   (ii) Thin linear antenna.

PART-B ,

5 a. Discuss the features of a loop antenna. Derive an expression for far field components of a loop antenna,

b. Write notes on : i) Horn antenna ; ii) Slot antenna.

6 a. Discuss the features of an helical antenna. Give the construction details of the helical antenna.

b. What are parabolic reflectors? Where these antennas are used?

c.  Draw the construction details of an embedded antenna.

7 a. Discuss the different forms of radio wave propagation.

b. Derive an expression for wave tilt of surface wave.

8 a. Explain different layers of ionosphere in detail.

b. Define the following with respect to wave propagation :

(i) Critical frequency                       (ii) MUF

(iii) Virtual height                           (iv) Skip distance.