Antenna terms, and definitions

Radiate: To transmit RF energy.

Radiation: Energy that moves through space as electromagnetic waves.

Radiation patterns: A chart of relative radiation intensity (or power) versus direction.

Radio frequency: Any frequency of electrical energy capable of propagation into space (usually above 20 kHz). Also called RF.

Radio horizon: The greatest distance on the Earth at which a transmitted wave can be received by the direct path from a transmitter located on the Earth.

Radio waves: Electromagnetic waves at a frequency lower than 3,000 GHz and propagated through space without and artificial guide.

Receiver: Amplifying and selecting equipment that receives radio frequencies and delivers a duplicate of the information impressed on the transmitter.

Reception: The process of recovering transmitted information; the process of converting electro-magnetic fields to current in wires.

Reciprocity: The various properties of an antenna apply equally whether the antenna is transmitting or receiving.

Reference Antenna: An antenna that may be real, virtual, or theoretical, and has a radiation pattern that can be used as a basis of comparison with other antenna radiation patterns.

Reflected waves: Waves that change their direction of propagation after striking a surface that is either a conductor or an insulator.

Reflection: The turning back of a radio wave from an object or the surface of the Earth.

Reflective Array Antenna: An antenna, such as a billboard antenna, in which the driven elements are situated at a predetermined distance from a surface designed to reflect the signal in a desired direction.

Reflector type antenna: An antenna placed in front of a conducting surface (reflector) for the purpose of increasing radiation in one direction, at the expense of radiation in other directions.

Refraction: The bending, or changing direction, of a radio wave passing into or through layers of the atmosphere or the ionosphere that have different density (dielectric constant).

Refractive index: A measure of the degree by which the speed of an electromagnetic wave is slowed as it propagates through a given material.

Resistance: The property of a material or substance to oppose the passage of current through it, thus causing electrical energy to be converted into heat energy.

Resonance: The state or frequency of vibration, electrical or mechanical, in which forces that impede the motion are minimum.

Resonant length: The proper length of an antenna to render it resonant

Rhombic antenna: An antenna made of four wires of equal length connected together in the shape of a rhombus. A directional antenna that is composed of long-wire radiators that form the sides of a rhombus, the two halves of which are fed equally in opposite phase at one apex.

Rigid Coaxial Line: A coaxial line consisting of a central, insulated wire (inner conductor) mounted inside a tubular outer conductor.

Antenna "S" Terms and definitions