GrdBi

GrdBi is a term occasionally encountered in RF literature and product datasheets, but it is not a standard unit in antenna engineering. Its exact meaning can vary between sources, which can lead to confusion. In general, GrdBi is used to convey antenna gain with some form of ground reference, such as a ground plane or a ground environment, rather than a purely free-space isotropic reference. Because there is no universally agreed definition, it is important to consult the specific source to understand the reference conditions used to derive GrdBi.

By comparison, standard antenna gain is typically expressed in dBi (gain relative to an isotropic radiator in free space) or in dBd (gain relative to a half-wave dipole). When GrdBi is mentioned, it is often described as a variant of dBi that incorporates the effects of a ground plane or ground environment into the measurement or model. The presence of a ground plane can significantly affect impedance, radiation patterns, and efficiency, particularly at lower frequencies, so the GrdBi value can reflect conditions that are not equivalent to free-space dBi.

Measurement considerations for GrdBi should specify several factors: the frequency, the direction of measurement (boresight), the test setup (anechoic chamber or real-world environment), height above ground, ground material properties, whether a real ground plane is used, polarization, and the method used to determine the gain.

In summary, GrdBi is not standardized and can be ambiguous. When encountered, verify the reference conditions from the source, and prefer standard dBi or dBd values for clear comparisons.