Antenna terms, and definitions

Rabbit Ears Antenna: A style of antenna used for VHF reception [TV]. Rabbit Ears may also be used in combination with a UHF Loop Antenna VHF UHF Antenna

Rabbit Ears Antenna

Radiate: To transmit RF energy.

Radiation: Energy that moves through space as electromagnetic waves.

Radiation Field: The electromagnetic field that radiates from an antenna and travels through space.

Radiation Loss: The part of the transmission loss because of radiation of radio frequency power.

Radiation Pattern: A chart of relative radiation intensity (or power) versus direction. A plot of the radiated energy from an antenna. The variation of the field intensity of an antenna as an angular function with respect to the axis. See the graphic in the side-bar.

Radiation Resistance: The resistance that, if inserted in place of an antenna, would consume the same amount of power that is radiated by the antenna.

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

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. The locus of points at which direct rays from an antenna are tangential to the surface of the Earth.

Radio Range. The distance from a transmitter at which the signal strength remains above the minimum usable level for a particular antenna and receiver combination.

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

Random Wire Antenna: A wire antenna with a wire length which does not necessarily match the wavelength being used.

Received Noise Power. The calculated or measured noise power, within the bandwidth being used, at the receive end of a circuit, channel, link, or system.

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

Receiving Antenna. The device used to pick up the RF signal from space. Also refer to Antenna Manufacturers.

Reception: The process of recovering transmitted information; the process of converting electro-magnetic fields to current in wires. The instant when an electromagnetic wave passes through a receiver antenna and induces a voltage in that antenna.

Reciprocity: The various properties of an antenna apply equally whether the antenna is transmitting or receiving. The property of interchangeability of the same antenna for transmitting and 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.

Reference Dipole: A dipole used as a reference antenna.

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

Reflecting Layer: In the ionosphere, a layer that has a free-electron density sufficient to reflect radio waves.

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: In an antenna, one or more conducting elements or surfaces that reflect incident radiant energy. The parasitic element of an array that causes maximum energy radiation in a direction toward the driven element.

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.

Right-Hand Polarized Wave: An elliptically polarized electromagnetic wave in which the rotation of the electric field is clockwise when looking in the direction of propagation.

Relay: A radio station used for the reception and retransmission of signals from another radio station.

Repeater Station: An intermediate point in a transmission system where signals are received, amplified, reshaped and retransmitted.

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 Antenna: See periodic antenna.

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

RF Bandwidth. The width in frequency at a level of 6dB below the peak, which may include a minor lobe which exceeds the -6dB level. Refer to the graphic in the right side-bar.

RFID Antenna: An antenna designed to receive signals from a Radio Frequency Identification [RFID] chip.

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. As part of the dictionary of Radar terms; Coaxial Cable Defined.

Rotary Beam Antenna: A directional antenna used with Short Wave communication which is mounted on a mast that can be rotated so that the antenna may point in another direction.