VTU Previous Exam Paper BE EC 6th Sem Antenna and Propagation July 06

Note: 1. Answer any FIVE full questions.

2. Assume any missing data suitably.

1 a. Explain the following parameters of an Antenna:

i) Beam solid angle            ii) Directivity

iii) Effective height           iv) Half power beam width.

b.  Derive Friis transmission formula for an antenna:

c.   A radio link has 100 W transmitter connected to an antenna of 2.5 m2 effective aperture at 5 GHz. The receiving antenna has an effective aperture of 0.5 m2 and is located at a 15 km LOS distance. Find the power delivered to the receiver. (03 Marks)

2 a. State and explain Power Theorem and its applications to an isotropic source.

b.  Derive an expression and draw the field pattern for two isotropic point sources of the same amplitude but opposite phase.

c.   Show that the width of the principle lobe of a uniform end — fire array is greater than that of a uniform broad-side array of the same space.

3 a. Derive an expression for Radiation-Resistance of a short electric dipole.

b.  Considering both general and special cases, derive an expression for Far-Field patterns for a loop antenna.

c.   Find the radiation efficiency of a 1 m diameter loop [C = it m] of 10 mm – diameter copper wire at 10 MHz.

4 a. Explain the practical design considerations for the monofilar axial mode Helical Antenna.

b.  A 16-tum helical beam antenna has a circumference of X, and turn spacing of A/4. What is i) HPBW ii) axial ratio iii) gain and iv) power pattern?

c.   Design a Yagi – Uda Six element antenna for operation at 300 MHz with a folded dipole feed. Calculate the length of i) Reflector ii) Driven element iii) Four director elernent iv) Spacing between reflector and driven element v) Spacing between director element.

5 a. Explain with examples the different types of rectangular and circular horn antennas. What are their advantages over the other antennas?

b.  State and explain Rumsey’s principle for frequency-independent antenna.

c.   Write a brief note on Embedded and Plasma antennas.

6 a. Discuss the antennas used for terrestrial mobile communication system.

b.  Explain with suitable expression and diagrams the need of UWB antennas for digital applications.

7 a. Explain with a neat diagram some of the possible propagation paths.

b.  Find the approximate formula for the field strength in VHF propagation,

8 a. What is the procedure for experimental determination of critical frequencies and virtual heights?

b.  Define and find the expression to calculate maximum usable frequency (MUF).

c.  Explain the phenomenon of Faraday Rotation and how measurement of total electron content is done for an ionospheric propagation.