It’s a point source that occupies a negligible space. X-Pol Isotropic antenna It’s an hypothetic antenna, i.e., it does not exist in real life, yet it’s used as a measuring bar for real antenna characteristics.
X-Pol Antenna parameters Solid angle, WA and Radiation intensity, U Radiation pattern, Pn, sidelobes, HPBW Far field zone, rff Directivity, D or Gain, G Antenna radiation impedance, Rrad Effective Area, Ae All of these parameters are expressed in terms of a transmission antenna, but are identically applicable to a receiving antenna. Spatial filter directionally-dependent sensitivity Polarization filter polarization-dependent sensitivity Impedance transformer (50 Ω to 377Ω) transition between free space and transmission line Propagation mode adapter from free-space fields to guided waves (e.g., transmission line, waveguide)ħ Antenna types Helical antenna Horn antenna Parabolic reflector antennaĨ Antenna parameters Solid angle, WA and Radiation intensity, Uĭr. Converts Electrons to Photons of EM energy It is a transducer which interfaces a circuit and freespaceĥ Only accelerated (or decelerated) charges radiate EM waves.Ī current with a time-harmonic variation (AC current) satisfies this requirement.Ħ The role of antennas Antennas serve four primary functions: An antenna is a passive structure that serves as transition between a transmission line and air used to transmit and/or receive electromagnetic waves. Hertz ( ) First aerial propagation (German) Marconi ( ) Transatlantic transmission (Italian) DeForest (Triode tube 1920) Signal generators (American) World War II ( ) Intense war-driven developmentĤ What is an Antenna? An antenna is a way of converting the guided waves present in a waveguide, feeder cable or transmission line into radiating waves travelling in free space, or vice versa. Folded dipole, Yagi array.ģ Antenna Background Maxwell (1831-79) Fundamental equations.
Matching – Baluns, Polarization mismatch, Antenna noise temperature, Radiation from oscillating dipole, Half wave dipole. Definition of antenna parameters : Gain, Directivity, Effective aperture, Radiation Resistance, Band width, Beam width, Input Impedance.
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