JNTU B.Tech III ANTENNAS AND PROPAGATION Previous Question Paper (February/March - 2022 - R18)

The beam area (Ω_A) of an antenna is defined as the integral of the normalized radiation intensity over a sphere of 4π steradians. It represents the solid angle through which all the power radiated by the antenna would stream if its radiation intensity were constant and equal to the maximum value over the beam area.

Beam efficiency (ε_M) is the ratio of the beam area of the main lobe to the total beam area of the antenna. It indicates how much of the total radiated power is concentrated within the main beam.

Where Ω_M is the beam area of the main lobe. Since the total beam area Ω_A is the sum of the main lobe area and the side lobe area (Ω_S), the efficiency can also be expressed as ε_M = Ω_M / (Ω_M + Ω_S).

Effective area (A_e) is a measure of the antenna's ability to intercept electromagnetic energy from an incident plane wave. It is defined as the ratio of the power delivered to the load (P_L) to the incident power density (S) of the wave.

For a lossless antenna, the maximum effective area is related to the directivity (D) by the formula A_em = (λ² / 4π)D. It represents the equivalent physical area that would capture the same amount of power as the antenna.

Effective height (h_e) is a parameter used primarily for linear wire antennas to relate the voltage induced at the terminals (V) to the incident electric field strength (E) of the wave. It is defined as the ratio of the open-circuit voltage to the electric field intensity.

For a thin linear antenna of physical length L, the effective height depends on the current distribution along the wire. For a short dipole, h_e is half the physical length (L/2), whereas for a half-wave dipole, it is λ/π. It effectively quantifies the antenna's capability to convert an incident electric field into a terminal voltage.