Reference no: EM132546765

ELEC 20009 Antenna Theory and Communication System - Middle East College

Learning Outcome 1: Critically evaluate antennas parameters used in communication links; and

Learning Outcome 2: Explain the propagation effects on radio wave propagation.

Question 1.

a. As communication engineer you have been requested to design radio communication system using parabolic antenna of 120 cm diameter operates on 1800 MHz frequency with input power of 1 KW, radiated power of 62-W and radiation resistance is 18.75Ω. Obtain:
i. Efficiency of the antenna;
ii. Gain of the antenna;
iii. The Loss resistance RL ;
iv. Suggest ways to increase the gain at the same operating frequency.

b. An isotropic antenna is radiating in free space. Consider a far field distance of 250 m from the antenna where the total Magnetic field Intensity H is 30 mA/m. Calculate the power radiated.

Question 2.
a. A Wi-Fi access point radiates a signal using dipole antenna at frequency of 2.4 GHz with the current (IRMS) of 8 A. It is given in the antenna manual specification that the antenna Gain G=16.98 dB and Directivity D=17.78 dB. Assume that the loss resistance is 10 Ω. For the same antenna determine the following:

i. Radiation resistance;
ii. Radiated power;
iii. Total input Power fed to the antenna

b. For an antenna the radiation resistance and loss resistance are 72 ohms and 1.5 ohms respectively. The radiation intensity of antenna is given by U = A₀ sin² θ W/dΩ, where A₀ is the peak value of power density; with 0 ≤ θ ≤ Π; and 0 ≤ Φ ≤ 2Π, determine the following:
i. Maximum directivity of antenna;
ii. Maximum gain of antenna (in dB)

Question 3.
a. For the sky wave propagation link is shown in figure 1, calculate the following:
i. The maximum usable frequency
ii. The optimum frequency of operation
iii. Angle of incidence of the transmitted signal

b. Assume that reflection takes place at a height of 400 km in a sky wave communication link and that maximum density in the ionosphere corresponds to a 0.9 refractive index at 10 MHz. What will be the range for which optimum frequency is 7.65 MHz?

Question 4.
a. Give reasons for the following:
i. Reception of signals is better during night than day time;
ii. Fading is more in sky waves
b. With a suitable diagram discuss the concept of skip distance occur in the radio wave propagation and list minimum of three factors that the skip distance depends upon.

Question 5.
a. An antenna receiving a signal of 500 MHz has the specifications of radiated power Prad = 3.25 kW; effective area of antenna Aeff = 3.5 m2; total efficiency of antennae0 = 42%; radiation efficiency of antennae??d = 65%; tilt angle of the received signal Ψ = 350.
Determine
i. Gain of the antenna (in dB);
ii. Maximum radiation intensity of the antenna (in dB);
iii. If the power radiated from the antenna is doubled, discuss how it affects the directivity of the antenna using necessary equations.

b. A VHF communication is to be established with a transmitter at 100 MHz. If the height of the transmitting antenna is 20 m and the maximum distance to achieve line of sight (LoS) connection is 40Km. Obtain the minimum height of receiving antenna.