Antenna terms, and definitions

Gain: The increase in signal strength that is produced by an amplifier. The ratio between the amount of energy propagated from an antenna that is directional compared to the energy from the same antenna that would be propagated if the antenna were not directional. The gain of an antenna is the same regardless of if the antenna is used to transmit or receive.

Generator: A device that changes mechanical energy into electrical energy.

Grid Antenna: An antenna with a reflector produced by a wire grid or mesh.

Ground: A reference source. A very large semiconductive surface (the Earth) or a smaller highly conductive surface. A return path.

Ground Plane: An electrically conductive surface that serves as the near-field reflection point for an antenna.

Ground-Plane Antenna: A type of antenna that uses a ground plane as a simulated ground to produce low-angle radiation.

Ground Radials: Wires on or in the earth to improve its conductivity near the antenna.

Ground Reflective Wave: A radio frequency wave that reaches the receiving antenna after being reflective off the ground after leaving the transmitting antenna.

Ground screen: A wire mesh ground plane or metal screen placed on the ground to set the height of the antenna and decrease the ground absorption losses [grounded antenna theory].

Ground wave: A radio wave that travels along the Earths surface rather than through the upper atmosphere. A ground wave includes the direct wave, the ground reflective wave and the surface wave. Ground waves are composed of two separate waves, a surface wave and a space wave.

Guard Band. The unused frequency space between subcarriers in FDM systems and between RF carriers, used to guard against interference.

Guy Wire: A high tension cable used to provide support to an antenna tower or mast. Read more on Antenna Guy Wires [companion site].

Half-Wave Antenna: An antenna whose electrical length is half the wavelength of the transmitter or received signal.

Half-Wave Dipole Antenna: A center-fed antenna whose electrical length is half the wavelength of the transmitter or received signal. An antenna consisting of two rods (1/4 wavelength each) in a straight line, that radiates electromagnetic energy.

Half-wave Vertical Dipole Antenna: A half-wave dipole constructed vertical to the Earths surface.

Harmonic Antenna. An antenna with an electrical length that is an integral multiple of a half wavelength.

H-Bend: A smooth change in the direction of the axis of a waveguide, throughout which the axis remains in a plane parallel to the direction of magnetic H-field (transverse) polarization.

Height, Antenna: The distance from the top of the antenna to the ground. Technical note; Most antenna structures that are taller than 60.96 meters (200 feet) above ground level or that may interfere with the flight path of a nearby airport must be cleared by the Federal Aviation Administration (FAA) and registered with the FCC.

Height Gain: For a given propagation mode of an electromagnetic wave, the ratio of the field strength at a specified height to the field strength at the surface of the Earth.

Helical Antenna: An antenna with a spiral conductor wound around a cross section. An antenna that has the form of a helix. Note: When the helix circumference is much smaller than one wavelength, the antenna radiates at right angles to the axis of the helix. When the helix circumference is one wavelength, maximum radiation is along the helix axis. A Helical Beam Antenna.

Hertz: One cycle per second.

Hertz antenna: A half-wave antenna installed some distance above ground and positioned either vertically or horizontally.

High frequency: Frequencies between 3 and 30 MHz.

Hop: A single reflection of the wave back to Earth at a point beyond the horizon.

Dipole Antenna

Horizon Angle: Of a directional antenna, the angle, in a vertical plane, subtended by the lines extending from the antenna to the radio horizon and from the antenna in its direction of maximum radiation.

Horizontal dipole: A dipole constructed parallel to the surface of the earth.

Horizontal pattern: The horizontal cross-section of an antennas three-dimensional radiation pattern.

Horizontal polarization: Transmission of radio waves in such a way that the electric lines of force are horizontal (parallel to the Earths surface). Waves that are radiated with their E field component parallel to the Earths surface.

Horn. A funnel-shaped section of waveguide used as a termination device and as a radiating antenna.

Horn Antenna. Horn Radiator. [Antenna Systems]. A waveguide antenna that is wider at the open end.

Horn Radiator. A tapered, tubular or rectangular microwave antenna that is widest at the open end. Also refer to the Radar Dictionary section of the site.

Hybrid Modulation. A combination of modulation methods used to impress information on a carrier.