Kd Prasad Antenna And Wave Propagation [upd] Jun 2026

Unit I: Antenna Fundamentals This section establishes the mathematical and physical basis for understanding how antennas work. 1.1 Basic Concepts

Definition: An antenna is a transducer that converts guided electromagnetic waves (from transmission lines) into free-space electromagnetic waves (and vice versa). Radiation Mechanism: Radiation occurs due to time-varying currents. A static charge produces an electric field, and a uniformly moving charge produces a magnetic field, but an accelerated charge (time-varying current) produces radiation. Retarded Potentials: The concept that changes in the field propagate at the speed of light. The potentials at a point are determined by the current at an earlier time ($t - r/c$).

1.2 Antenna Parameters (Crucial for Exams) K.D. Prasad emphasizes these definitions heavily:

Radiation Intensity ($U$): Power radiated per unit solid angle. Directivity ($D$): The ratio of the maximum radiation intensity to the average radiation intensity. It measures how "focused" the antenna is. Gain ($G$): Directivity multiplied by efficiency ($\eta$). It accounts for losses in the antenna material. Radiation Pattern: A graphical representation of radiation properties (Field strength or Power density) as a function of angular coordinates. kd prasad antenna and wave propagation

Types: Field pattern, Power pattern, E-plane pattern, H-plane pattern.

Beamwidth:

Half-Power Beamwidth (HPBW): The angle between points where power drops to half (-3dB) the maximum. First Null Beamwidth (FNBW): Angular width between the first nulls on either side of the main lobe. Unit I: Antenna Fundamentals This section establishes the

Polarization: The orientation of the electric field vector (Linear, Circular, Elliptical). Effective Aperture ($A_e$): The ratio of power received to the power density of the incident wave. Relationship: $D = \frac{4\pi A_e}{\lambda^2}$. Impedance: Input impedance is the ratio of voltage to current at the feed point. For maximum power transfer, input impedance must match the characteristic impedance of the transmission line.

1.3 Antenna Theorems

Reciprocity Theorem: The properties of an antenna are identical whether it is used for transmitting or receiving (e.g., the radiation pattern is the same). Maximum Power Transfer Theorem: Applied to match the antenna impedance with the source/load. A static charge produces an electric field, and

Unit II: Point Sources and Arrays This section moves from single ideal sources to practical arrays used to increase directivity. 2.1 Point Sources

Defined as a hypothetical antenna with no physical dimensions. Isotropic Radiator: Radiates equally in all directions. Used as a reference for calculating directivity. Directional Point Source: Radiates in specific directions.