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.
Note: Reflective array antennas (a) usually have many driven elements working in conjunction with an electrically large reflecting surface to produce a unidirectional beam, (b) may be used to increase… (Read More →)

The reflectance at the surface of a material so thick that the reflectance does not change with increasing thickness, i.e., the intrinsic reflectance of the surface, irrespective of other parameters such as the reflectance of the rear surface.
Note: The term "reflectivity" is no longer in common use. See reflectance.

1. In an rf antenna, one or more conducting elements or surfaces that reflect incident radiant energy.
Note: A reflector may consist of a large surface, as in a dish antenna, or a linear element, as in a Yagi antenna.
2. See mail reflector.

1. A ray that undergoes a change of velocity, or in the general case, both velocity and direction, as a result of interaction with the material medium in which it travels.
2. In an optical fiber, a ray that is refracted from the core into the cladding. Specifically a ray having direction such that where r is the radial distance… (Read More →)

Retardation, and--in the general case--redirection, of a wavefront passing through (a) a boundary between two dissimilar media or (b) a medium having a refractive index that is a continuous function of position, e.g., a graded-index optical fiber.
Note: For two media of different refractive indices, the angle of refraction is closely approximated by Snell's Law.

Synonym refractive index profile.

Of a medium, the ratio of the velocity of propagation of an electromagnetic wave in vacuum to its velocity in the medium. Synonym index of refraction.
Note: When the Greek character eta is unavailable, the letter n is used to represent the refractive index.

In an optical fiber, a measure of the relative difference in refractive index of the core and cladding.
Note: Refractive index contrast, , is given by = (n12- n 22)/(2n12), where n1 is the maximum refractive index in the core and n2 is the refractive index of the homogeneous cladding.

Of the cross section of an optical fiber, the description, i.e., plot, of the value of the refractive index as a function of distance from the fiber axis along a diameter. Synonyms index profile, refraction profile.

The time interval between the instant at which a valid frame-alignment signal is available at the receiving data terminal equipment and the instant at which frame alignment is established.
Note: The reframing time includes the time required for replicated verification of the validity of the frame-alignment signal. Synonym frame-alignment recovery time.