ANTE NNAS & WAVE PROPAGATION BSC EXAM Time: 3 Hours Jan 2016 MANSOURA UNIVERSITY FACULTYOF ENGINEERING DEPARTMENT OF ELECTRONICS & ELECTRICALCOMMUNICATIONS Attempt all questions. Full Mark: 100 All questions carry equal marks. Q1: (a) Write definitions of: i- Radiation power intensity ii- Beam solid angle iii- Directivity of an antenna iv- radiation resistance of an antenna v- Polarization of an antenna. (b) The radiation field of a small single turn circular loop antenna of radius a and uniform current of rms value I amperes in free space is given by: E, = 30TT (~a)2 I sineS) e-i13r/r. (E, 0, Ee= 0.) i- Determine the radiation resistance, the beam solid angle, and the directivity of the antenna. What would be these parameters if the loop is made of n turns? ii- What is the type of polarization of the small loop antenna? = 02: (a) Two antennas are separated by a distance r in free space. Write expression relating the power at output the terminals of the receiving antenna to the input power delivered to the transmitting antenna. (b) Discuss the principle of working of Parabolic Reflectors. What factors do degrade the directivity of parabolic reflector antennas? (c) A satellite transmits electromagnetic waves at 12 GHz via an antenna of gain 56 dB. The input power to the satellite antenna is 20 W. Determine the magnitude of the electric field at a point A on the earth distant 37000 km from the satellite. The receiving antenna at A is a parabolic dish of aperture diameter 6 m, aperture efficiency 90%, and radiation efficiency 80%. What is the gain of this antenna in dB and what is the power at its output terminals? 03: (a) Give three examples of broad-band wire antennas and explain briefly why they are broad-band. (b) Outline the radiation mechanism of microstrip patch antennas What are the main advantages and limitations of these antennas? What are the effects of substrate thickness and dielectric constant on the impedance bandwidth of the antenna? 04: (a)What are the reasons for using antenna arrays? (b) Determine the main beam-width and the level of the first side lobe relative to the main beam of an n = 6 elements uniform forward endfire array with element spacing M2. Vvhat would be these parameters if n is made very large? (c) A 3-elel1'ent linear array is made up of equally spaced parallel short elect ic dipole" oriented in free space in the z direction. The element currents are such that 11 : b : I~ = 1. : 2 : 1. If the array is placed at height h above a perfectly ground plane, what would be the far zone electric field? (Hint: make use of the principal of pattern multiplication) Q5: Write short notes on: i- Ground wave propagation ii- Propagation in the ionosphere iii- Line of sight communication. v- Diversity reception.