# Antenna and Propagation Dec.09-Jan.10

Set-B

Note: Answer any FIVE full questions.

b.  Explain the following terms with respect to an antenna:

ii) Effective height

iii) Directivity

iv) Beam area

c.   Two space crafts A and B are separated by a distance 100xl06m each has an antenna with D^IOOO, operating at 2.5GHZ. If craft ‘A’s receiver required 20dB over 1 Pico watt, what transmitter power is required on craft ‘B’ to achieve this signal power,

2 a. Find the directivity for a pattern under unidirectional operation with radial component of the average Poynting Vector S =Sm Sin20 Sin3<j>.

b.  Explain the principle of pattern multiplication with an example.

c.   For linear uniform array of N-isotropic point sources, derive an equation for resultant field and obtain the equation for FWBW for Broadside operation.

3  a. Calculate the radiation resistance of ^ dipole antenna.

b.  Derive an expression for the far field components of thin linear antenna.

c.   Derive an expression for the far field patterns of loop antenna for general case and extend it for small loop.

4  a. Explain the main design parameters of Monofilar axial mode helical antenna.

b.  Obtain relation for relative phase velocity of Axial mode helical antenna for the case of ordinary end fire operation.

c.   Design Yagi-uda six element antenna for operation at 400 MHZ with a folded dipole feed. Calculate the length of:

i) Reflector

ii) Driven element

iii) Four director element

iv) Spacing between reflector and driven element

v) Spacing between director element

5 a. Explain the comer reflector antenna and mention its application.

b.  Calculate BWFN and gain of a 2m paraboloid reflector operating at 6 GHZ.

c.   Explain different types of Horn antenna and mention its application. Write design equation for rectangular horn antenna.

6.(a) What is surface wave tilting obtain an equation for tilt angle of the wave?

b. For normal refraction of tropospheric waves, derive the relation between the radius of curvature of the path and the change of dielectric constant with height. Obtain the modified earth’s radius of curvature.

C- The antenna of a TV transmitter is located at a height of 152mts above ground level. Calculate the distance upto which the line of right communication is possible if the height of receiving antenna is to be 9 mts.

7 a. Explain the mechanism by which the radio waves are returned to earth in ionospheric propagation.

b.  Calculate the value of the skip distance given that the height of the ionospheric layer is 50kmt, MUF is 29 MHZ and its critical frequency is 4 MHZ. Derive the formula used.

c.   In Radio wave propagation, what is meant by signal fading? Explain various types of signal fading.

8 Write short notes on :

a.  Cross field effect

b.  Bare Station Antennas for terrestrial mobile communication

c.   Embedded and Plasma Antenna