Antenna Definitions and Terms
"A", "B", "C", "D", "E", "F", "G"/"H", "I" to "L", "M"/"N"/"O",
"P"/"Q", "R", "S", "T", "U" to "Z"

Image Antenna: A hypothetical mirror-image, a virtual-image, of an antenna, an antenna element, considered to extend as far below the ground plane, as the actual antenna is above the ground plane.

Impedance: The total opposition offered by a circuit or component to the flow of alternating current.

Impedance match: The condition where the load impedance equals the characteristic impedance of a transmission line.

Indirect Wave: A reflected wave.

Indoor Antenna: An antenna designed to operate inside a structure. A TV antenna designed to pick up TV stations inside a house: Note a TV antenna located outside will always function better than an indoor antenna by picking up more TV stations or providing better reception.

Indoor TV Antenna
InDoor Antenna

Inductance: The natural property of an electrical circuit which opposes the rate of change or current, i.e., electrical intertia.

In phase: Two or more signals of the same frequency passing through their maximum and minimum values of like polarity at the same instant.

Insertion Loss: The decrease in power delivered to a load when a device is inserted between the source and the load.

Insulator: A device or material that has a high electrical resistance; a non-conductor of electricity.

Interference: A degradation of a received signal caused by another transmitter, a noise source, or the desired signal propagation over two or more different routes.

Inverted Cone Antenna: A vertically polarized omnidirectional antenna used for broadband communications. Refer to the drawing in the lower right.

Inverted L Antenna: A half-wave dipole fed by a one-quarter wavelength long vertical section.

Inverted Vee Antenna: A half-wave dipole erected in the form of an upside-down V, with the feed point at the apex. It is essentially omnidirectional, and is sometimes called a dropping doublet.

Ionization: The process where radiation and particles from the Sun make some of the Earths atmosphere partially conductive.

Ionosphere: A partially conducting region of the Earths atmosphere between 50 kms and 400 kms high.

Ionospheric Scatter: The propagation of radio waves by scattering as a result of irregularities or discontinuities in the ionization of the ionosphere.

Isotropic Antenna: A hypothetical antenna that radiates or receives equally in all directions.

J-Antenna: A half-wave antenna.

Lambda: Used to represent a wavelength with reference to electrical dimensions in antenna work. Represented by the Greek lower case, 11th letter.

L-Antenna: A horizontal wire and a vertical wire attached together to form an L shaped antenna.

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

Lens Antenna: A microwave antenna that concentrates radiated energy using a dielectric lens.

Linearly Polarized Antenna: Antennas that produce only one polarization.

Line of sight: [LOS]. The transmission path of a wave that travels directly from the transmitting antenna to the receiving antenna.

Load: A device that consumes electrical power.

Loading: Providing or connecting an electrical device capable of accepting power to match the impedance of an antenna to a transmitter so that maximum power is radiated from a generating device, such as a transmitter.

Lobe: A bulge on an antenna radiation pattern which indicates the direction in which radiated power is concentrated. An area of greater signal strength in the transmission pattern of an antenna. An identifiable segment of an antenna radiation pattern.

Log-Periodic Antenna: [LPA] Also called an LP Antenna. A broadband, multi-element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency.

Log-Periodic Dipole Antenna: [LPDA] A type of directional antenna. See the graphic to the right.


Long-wire antenna: An antenna that is a wavelength or more long at its operating frequency. An end fed single wire antenna usually one wavelength or longer. An area of a radiation pattern plotted on a polar-coordinate graph that represents maximum radiation.

Loop Antenna: A style of antenna used for UHF reception [TV]. The shape of the antenna is in the form of a wire loop. A loop antenna is sometime found in combination with Rabbit Ears which are used to receive VHF channels. A type of antenna, in the form of a circle or rectangle, usually used in direction-finding equipment and in UHF reception.

Table-top UHF Loop Antenna
Loop Antenna

Loopstick Antenna: See Ferrite Rod.

Lowest usable frequency: [LUF]. The lowest frequency that will not be absorbed by the ionosphere or smothered by atmospheric noise.

LPDA: Log Periodic Dipole Antenna. A type of directional antenna. Refer to the graphic in the right side-bar.

LP Antenna: See Log-Periodic Antenna.

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