A radiation pattern is a plot of how strongly an antenna sends and receives radio energy in each direction around it. An antenna behaves the same way when receiving as when transmitting, so the radiation pattern describes reception as well. Radiation patterns are the clearest way to compare how two antennas will behave once installed.

Antenna datasheets show the radiation pattern as two polar plots. The azimuth plot is the pattern seen from above, and the elevation plot is the pattern seen from the side. Each plot has the antenna at its centre: the outer ring marks the direction of strongest signal, and each ring inwards shows the signal a set number of dB lower.

An omnidirectional antenna shows a near-circle on its azimuth plot and a flattened shape on its elevation plot, strong around the horizon and weak straight up and down. A directional antenna shows one main lobe in the direction it points, smaller side lobes either side and a back lobe behind. The difference between the main lobe and the back lobe is the front-to-back ratio, quoted in dB, and a higher figure means the antenna rejects more signal from behind.

A radiation pattern also shows nulls, the deep dips where the antenna receives little signal. If a mast sits in a null, signal will be poor even with a high-gain antenna. The width of the main lobe at its half-power points is the antenna's beamwidth, and its peak is the antenna gain.

Radiation patterns change with frequency, so a wideband cellular antenna has a different pair of plots for each band. Mounting changes the pattern too: a metal surface, a nearby wall or an equipment cabinet reshapes it. A published radiation pattern shows what the antenna does under test conditions, not what it will do on every site.