What is a reference antenna that all other antennas with gain are compared to?

A reference antenna that all other antennas with gain are compared to is the dipole antenna. The dipole antenna is considered a standard for establishing a reference level of gain because it has well-defined radiation characteristics and a consistent performance. It is isotropic in a theoretical sense, meaning it radiates equally in all directions in the horizontal plane, and it typically has a gain of about 2.15 dBi (decibels relative to an isotropic radiator).

In antenna theory, the dipole serves as a benchmark to determine how much more efficient or directional another antenna is compared to this baseline. For instance, when engineers assess a new antenna design, they often express its gain in relation to the dipole to understand its performance capabilities. This makes the dipole a fundamental tool in antenna design and evaluation, establishing a clear point of comparison for understanding various antenna types and configurations.