M.E./M.Tech. DEGREE EXAMINATION, JUNE 2011.

M.E. – Communication Systems

First Semester

251101 — ADVANCED RADIATION SYSTEMS

(Regulation 2010)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

1. State reciprocity theorem.

2. What are the disadvantages of loop direction finder?

3. Define directivity of an horn antenna.

4. List out the various feeding mechanisms of reflector type antenna.

5. List out the differences between end fire array and broad side array.

6. Define Half Power beam width of an antenna.

7. What are the various excitation techniques of the microstrip antenna?

8. What are the applications of microstrip array antenna?

9. Which antenna is called as frequency independent antenna and why?

10. Define characteristic impedance of the biconical antenna.

PART B — (5 ´ 16 = 80 marks)

11. (a) (i) Derive radiated power and radiation resistance of a half wave

dipole antenna. (12)

(ii) Calculate the effective length of an l 2 antenna. Given Rr = 73W,

( ) 2 Ae max = 0.13l and h = 120p . (4)

Or

(b) Derive reciprocity theorem for antennas. Show that the transmitting and

receiving radiation patterns of an antennas are equal.

12. (a) (i) Calculate the angular aperture for a paraboloid reflector antenna

for which aperture number is (1) 0.25 (2) 0.50 (3) 0.60. Given

diometer of reflector mouth is 10 m, calculate the position of the

focal point with reference to the reflection mouth in each case. (8)

(ii) Describe the methods of feeding a paraboloid reflector in which

primary antenna is located at focal point. (8)

Or

(b) Describe the construction and basic principle of operation of a slot

antenna with neat sketch. (16)

13. (a) (i) What is meant by dolph-chebyshev distribution for a linear array?

Show that such a distribution gives a minimum side lobe level for a

given beem width of major lobe? (8)

(ii) Explain the principle of pattern multiplication and find the array

factor of a two element array. (8)

Or

(b) (i) A broadside array operating at 100 cm wavelength consists of four

half wave dipole spaced 50 cm. Each element carries radio

frequency current in the same phase and of magnitude 0.5 amp.

Calculate (6)

(1) Radiated power

(2) Half width of the major lobe.

(ii) Derive an expression for the far field pattern of an array of

n-identical isotropic point sources arranged in a line and spaced a

distance ‘d’ apart. (10)

14. (a) Explain in detail about the radiation mechanism from microstrip

antenna and also discuss about its excitation techniques. (16)

Or

(b) (i) Explain in detail about ring antenna construction, operation and

analyse radiation from cavity model with neat sketch. (8)

(ii) Derive input impedance of rectangular and circular patch antenna

with neat diagram. (8)

15. (a) What are the two types of antenna measurements, and explain

impedance measurement bridge method for low frequency and slotted

line method for high frequency. (16)

Or

(b) (i) Explain in detail about gain measurement by direct comparison

method. (8)

(ii) Explain in detail about antenna test range design. (8)