Antenna Fundamentals: Principles, Parameters, and Types

Principles of Antennas

The antenna: an electrical conductor to which an alternating electrical current is applied, converting it into an electromagnetic wave.

Tank circuit: Parallel combination of a capacitor and a coil.

Resonant frequency: Frequency at which the reactive components cancel each other out, so that there is optimum radiation.
Bandwidth: Frequency range that an antenna can emit or receive with sufficient gain.
Electrical Length: Relationship between physical length and the wavelength being transmitted.
Impedance: Opposition shown by the antenna to the applied signal.
Resistance losses: Amount of power lost by the heating of the antenna.
Radiation resistance: Makes the most of the applied current, issuing it.
Standing wave ratio: Factor that measures the mismatch between the transmitter, cable, and antenna.
Directivity: Demarcated area in which there is further radiation from the antenna.
Directive gain: Increased capacity of an antenna to emit or receive power, depending on the angle of incidence.
S opening: Angle in which the antenna emits or receives signals with a difference of less than 3dB with respect to the maximum value.
Polarization: Position of the electric field that is generated or received.
Performance: Efficiency of the work of the antenna, with respect to the ideal.
Wind load: Strength of an antenna mounted on the mast and the wind.

Simple dipole: Antenna consisting of two equal rods that resonates with λ/2.
Folded dipole: The outer ends of a dipole are joined, resulting in λ/2 with a single bent rod open at its lower end. Impedance is increased to 300 Ohms.
Marconi antenna: Dipole formed by a single rod, plus a ground plane. Usually resonates at λ/4.
Log-periodic antenna: Association of λ/2 dipoles with spacing increasing gradually.
Yagi antenna: Simple dipole with a set of passive elements to modify its characteristics.
Phased dipole antennas: Group of dipoles associated in a simple way, amending its gain and directivity.

Reflections on the vertical plane: Common in urban environments. To fix this, one antenna is placed above the other, narrowing the beam vertically.
Reflections on the horizontal plane: Occur when there is a large, smooth surface between the sender and receiver. The solution is to put two equal and phased antennas, thus reducing the horizontal opening angle.

Horn antenna: Widening of a waveguide to capture or output signals.
Prime focus antenna: Satellite dish that has its focal point on the axis of the reflector.
Cassegrain antenna: Satellite dish that has its focal point in the center of it and consists of a cooling system in which the wave reaches the parabola, the spotlight falls on the focus toward the focal point.
Offset antenna: Satellite dish that has its focal point shifted from the axis of the reflector.
Planar antenna: Set of phased dipoles placed in the same plane to receive electromagnetic waves.
Multisatellite antennas: Antenna that can capture signals from several satellites simultaneously.