10: Antennas and Radiation
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- 10.1: Radiation from charges and currents
- This page provides an overview of antenna interaction with electromagnetic waves and electric fields from static charges. It covers characteristics of antennas, computation of static electric potential from charge distributions, and magnetic fields from static currents. The text delves into the derivation of Helmholtz equations from electromagnetic theory, discussing vector fields, their divergence, and the relation of potentials to source distributions.
- 10.2: Short Dipole Antennas
- This page covers the radiation emitted by Hertzian dipoles, including the derivation of electromagnetic fields using Maxwell’s equations and the Biot-Savart law. It emphasizes the behavior of far-field and near-field radiation, detailing the donut-shaped radiation pattern and the conversion of electromagnetic waves to circuit voltages by antennas. The analysis includes θ-polarized plane waves, focusing on intensity and total power radiated, with dependencies on antenna efficiency and wavelength.
- 10.3: Antenna gain, effective area, and circuit properties
- This page covers the fundamentals of antenna directivity, gain, and impedance, focusing on short dipole antennas. It defines key relationships between gain, radiation resistance, and the effective area, employing Thevenin equivalents to analyze antenna circuits. The reciprocity principle is emphasized, detailing how transmitted power impacts received power across distances.
- 10.4: Antenna Arrays
- This page discusses enhancements in dipole antenna arrays, including increased gain, beam steering, and simultaneous transmissions through configurations and effective area adjustments. It highlights the use of mirrors to improve short dipole antenna gain and analysis of uniform dipole arrays, focusing on element factors and phase variations affecting radiation patterns.
Thumbnail: Animation of a half-wave dipole antenna transmitting radio waves, showing the electric field lines. (Public Domain; Chetvorno via Wikipedia)