ANTENNA TERMS IEEE STD-145
Antenna Factor That quality by which the voltage developed across this impedance must be multiplied to obtain the incident field strength in which the antenna is immersed......usually refers to 50 ohms output
Aperture iIIumination The field over the aperture as described by amplitude, phase, and polarization distribution.
Axial Ratio The ratio of the major axis to the minor axis of the polarization ellipse defines the magnitude of the axial ratio. The tilt angle describes the orientation of the ellipse in space.
Circular Polarization It may be either right hand circular polarization (RHCP) or left hand circular polarization (LHCP). The sense of polarization id determined by observation of the direction of the rotation of the electric field vector from a point behind the source.
Co-Polarized The polarization which the antenna is intended to radiate or receive. Also "like polarized".
Cross Polarization In a specific plane containing the reference polarization ellipse, the polarization that is orthogonal to a specified polarization. NOTE: The reference polarization is the co-polarization.
Directive Gain In a given direction, 4 pie times the ratio of the radiation intensity in that direction to the total power radiated by the antenna.
Directivity The value of the directive gain in the direction of its maximum value, as represented by the distribution in space of the power radiated by the antenna. The directivity is defined as 4 pie times the ratio of the maximum radiation intensity ( power radiated per unit solid angle) to the total power radiated by the antenna. The directivity of an antenna is independent of its radiation efficiency and its impedance match to the connected transmission line.
Effective Area of an Antenna In a given direction, the ratio of power available at the terminals of a receiving antenna to the power per unit area of a plane wave incident on the antenna from that direction, polarized coincident with the polarization that the antenna would radiate.
Far Field Region That region of the field of an antenna where the angular field distribution is essentially independent of the distance from a specified point in the antenna region. NOTE: In free space, if the antenna has a maximum dimension, D, which is large compared to the wavelength, the far field region is commonly taken to exist at distances greater that 2D sq / Lambda from the antenna, Lambda being the wavelength. The far field pattern of certain antennas, such as multi-beam reflector antennas, are sensitive to variations in phase over their apertures. For these antennas the above equation may be inadequate.
Front-to-Back Ratio The ratio of the maximum directivity of an antenna to its directivity in a specified rearward direction.
Gain dBi The gain expressed in decibels relative to an isotropic radiator.
Gain dBic The gain expressed in decibels relative to an isotropic radiator that is circularly polarized.
Gain dBil The gain expressed in decibels relative to an isotropic radiator that is linearly polarized.
Half -Power Beam width In a plane containing the direction of the maximum of a beam, the angle between the two directions in which the radiation intensity is one half the maximum value of the beam. NOTE: The half power beam width is equal to the 3dB beam width or the 0.707 voltage beam width.
Input Impedance Input impedance is the parameter which relates the antenna to its transmission line. It is of primary importance in determining the transfer of power from the transmission line to the antenna and visa versa. The impedance match between the antenna and the transmission line is usually expressed in terms of voltage standing wave ratio (VSWR) or the reflective coefficient of the antenna when connected to a transmission line of a given impedance. The reflection coefficient expressed in decibels is return loss.
Isotropic Radiator A hypothetical antenna having equal radiation intensity in all directions. NOTE: An isotropic radiator represents a convenient reference for expressing the directive properties of actual antennas. It may have any polarization.
Near-Field Region The part space between the antenna and the far field region.
Null That region of a radiation pattern, either computed or measured, where the amplitude goes through a minimum value.