Mainlobe

Mainlobe refers to the region of an antenna’s radiation pattern that contains the maximum radiated power or gain. It is the dominant lobe of the pattern and is distinct from sidelobes and the backlobe, which contain less energy. The mainlobe points in the direction of greatest radiation, and its centerline defines the beam direction.

The angular width of the mainlobe is described by the beamwidth, commonly defined as the angular separation between points where the radiated power falls to half its peak value, i.e., the -3 decibel points. The peak of the pattern corresponds to the maximum gain, measured in a reference such as dBi.

In practice, the shape and direction of the mainlobe are determined by the antenna’s aperture distribution or the arrangement and excitation of its elements. In array antennas, the mainlobe can be steered by adjusting element phases and amplitudes, enabling beam scanning without moving the structure. Signal performance is often optimized by reducing sidelobes relative to the mainlobe to minimize interference and undesired reception.

The backlobe lies opposite the mainlobe and contains radiation toward the rear, while sidelobes are secondary maxima at other angles. Although named for its dominance, the mainlobe can be accompanied by multiple sidelobes of varying amplitude, depending on the design and operating frequency. The concept is used across radio, radar, and acoustics to describe the primary direction of energy and its angular extent.