Antennas

Question 1

Describe the types of antenna employed in satellite communications.

Answer 1

1. Horn antenna;
2. Helical (end-fire) antenna;
3. Reflector (parabolic) antenna;
4. Phased array antenna;

Question 2

Describe design and performance of the phase array antenna. What are the
advantages and disadvantages of this type of antenna?

Answer 2

Advantage: can produce several beams
simultaneously by single antenna.
Drawback: complexity of associated equipment.

Question 3

Explain terms used for an antenna: (i) effective isotropic radiated power (EIRP);

Answer 3

the power that an omnidirectional antenna would need to radiate to give the same radiated power P as a directional antenna of gain G.

Question 4

Explain terms used for an antenna:(ii)
antenna gain;

Answer 4

Antenna gain G is the ratio of power radiated by the antenna into the beam direction to the power produced by a hypothetical isotropic antenna feeding by the same power source.

Question 5

Explain terms used for an antenna:(iii) antenna beam width;

Answer 5

The beam width θ3dB is the angle between the half-power (-3dB) points of the main lobe.

Question 6

Explain terms used for an antenna:(iv) free space propagation path loss.

Answer 6

Free-space path loss, LFS, is the loss in signal strength of an EM wave that would result from a line-of-sight path through free space, with no obstacles nearby to cause reflection or diffraction

Question 7

Why is the free-space propagation path loss model used in satellite communications?

Answer 7

it provides a simple and accurate way to predict the signal loss between a satellite and its receiver.

it takes into account factors such as atmospheric absorption and scattering, and can be used to accurately predict the received signal power

Question 8

Explain the parabolic approximation of the antenna beam.

Answer 8

a method used to approximate the radiation pattern of an antenna.

It is based on the assumption that the antenna is a parabolic reflector with a narrow beamwidth and that the field radiated by the antenna can be approximated by a parabolic function.

This approximation simplifies the design and analysis of antennas, as it allows for the calculation of the antenna gain and directivity without the need for a detailed analysis of the antenna radiation pattern.