Dictionary of Antenna Terms

Fading: A periodic decrease or increase in the received signal strength. Variations in signal strength by atmospheric conditions.

Fan Beam Antenna: A directional antenna producing a main beam having a large ratio of major to minor dimension at any transverse cross section. The picture shows a Soviet era Fan Beam Radar station.

Fan Beam Antenna

Far-field Radiation Pattern: A radiation pattern measured at the far field of an antenna or other emitter.

Feed: A coupling device between an antenna and its transmission line. To supply a signal to the input of a system, subsystem, equipment, or component, such as a transmission line or antenna.

Feeder: A transmission line that carries energy to the antenna.

Feedpoint impedance: Impedance that is measured at the input terminals of an electrical device such as an antenna.

Ferrite Loop Antenna: See Ferrite Rod Antenna.

Ferrite Rod Antenna: An antenna formed by wrapping a wire around a ferrite rod, normally found in AM receivers. Normally placed in parallel with a tuning capacitor.

Fields: Regions in which each point has a value of a physical quantity (voltage, magnetic force, velocity, mass, etc.).

Flat Antenna: A type of antenna with a flat shape. One style of indoor antenna used to receive digital TV signals.

Flexible Coaxial Line: A coaxial line made with a flexible inner conductor insulated from the outer conductor by a solid, continuous insulating material. Also refer to the related terms; Definition of Coaxial Cable, Coax [located within the Dictionary of Radar terms].

Flush Mount: A style of antenna that mounts to a flat surface.

FM Antenna: See Dipole Antenna. An antenna designed to receive signals in the FM band, ranging between 88.5MHz to 108MHz [FM Radio].

FM Discriminator: A device that operates as a frequency to voltage converter.

Folded Dipole: An ordinary half-wave antenna (dipole) that has one or more additional conductors connected across the ends parallel to each other.

Four-Element Array: An array with three parasitic elements and one driven element.

Free space: The absence of matter.

Free space loss: The loss of energy of a radio wave because of the spreading of the wavefront as it travels from the transmitter.

Frequency: The rate at which a process repeats itself. In radio communications, frequency is expressed in Hz.

Frequency hopping: A method of jumping from frequency to frequency in synchronization with one another in a random order at a rate of up to 100 times per second.

Frequency Modulation: [FM] The process of varying the frequency of a carrier wave, usually with an audio frequency, in order to convey intelligence.

Frequency of optimum transmission: 85 percent of the Maximum Usable Frequency (MUF). A practical frequency selection which allows for MUF variations.

Front-to-Back Ratio: The gain of an antenna, in a specified direction.

Full-Wave Dipole: See dipole.