Reference

How to read a radiation pattern

Every antenna page shows a radiation-pattern diagram. Here is what those plots mean — and why the same antenna can look omnidirectional in one view and like a figure-eight in another.

It's really a 3D shape

An antenna radiates into three dimensions. The true pattern is a 3D "balloon" showing signal strength in every direction. Because 3D is hard to draw, we show a flat slice through it — called a cut or plane. The polar plot is that slice: distance from the centre = relative strength in that direction, marked in decibels (dB), with the outer ring being the strongest.

The dipole donut

Take a simple half-wave dipole. Its 3D pattern is a donut (toroid) wrapped around the wire: strongest broadside to the wire, with deep nulls off the two ends. Nothing about the antenna changes — but the slice you choose does:

So the rule of thumb: a figure-eight appears whenever the slice passes through the plane that contains the wire (the E-plane); a circle appears in the plane perpendicular to it (the H-plane). That is exactly why a vertical antenna is "omnidirectional" — from above you are looking at its circular H-plane cut.

Planes you'll see on this site

• Azimuth (H-plane): the horizontal, map-like view — "which compass directions get the signal."
• Elevation (E-plane): the vertical, side view — "how high or low the energy goes," e.g. toward the horizon vs. overhead.
• E-plane / H-plane: named after the electric (E) and magnetic (H) fields; the E-plane contains the wire/driven element.

Reading the diagrams here

Each antenna's diagram shows a small orientation icon (how the antenna is positioned) and a label for which plane the cut represents. Directional antennas (Yagi, dish) show one strong forward main lobe — point the antenna that way. Verticals show a circle. Beams and apertures get narrower (higher gain) as they focus energy into a tighter lobe.