This shows the elevation radiation pattern of a half-wave horizontal dipole antenna — how strongly it radiates at each elevation angle above the horizon — and, more importantly, why that pattern has the shape it does: it's produced by the direct wave from the antenna interfering with the wave reflected off the ground below it. The white pulsing sphere is the antenna itself, current oscillating along its length, viewed end-on from one tip of the wire looking straight down its axis.
Brighter arcs mean stronger signal in that direction — a lobe. Dimmer, darker arcs mean weaker signal — a null. This is the single most important thing to read on screen: follow the brightness outward in any direction and you're reading the antenna's actual gain in that direction.
The direct wave and the ground-reflected wave are each drawn in the color you choose for them in the controls below. Orange and sky blue are the defaults, chosen to remain clearly distinguishable for colorblind viewers; magenta, cyan, and yellow are also available. Small yellow dots travel outward along the ground line — each one marks the exact spot where an expanding direct wavefront reaches the earth. That's the bounce point; the reflected wave arcs are mathematically what a real reflection from that point produces, everywhere above ground.
A solid ring marks a wave crest (peak); a dashed ring marks a trough (the opposite extreme). Both are equally strong when reinforcing — solid vs. dashed only tells you which part of the wave cycle you're looking at, not how strong it is. Strength is brightness alone.
Since brightness fades gradually, it can be hard to pin down an exact pattern shape at a glance. The white outline solves that: it's a single continuous curve where the distance from center is directly proportional to signal strength in that direction, scaled so the strongest lobe reaches the outer edge — the same style used in classic printed antenna-pattern charts. It updates only when you change height or frequency, not continuously with the animated waves. Toggle it off any time you want an unobstructed view of the wave interference itself.
These mark the directions where the direct and reflected waves are perfectly in phase — where they reinforce each other as strongly as physically possible. These are the true lobe directions, and you should see them running right through the brightest, most consistent arcs on screen.
Slide height all the way to the right, past 3λ, and the ground disappears entirely — this is free space, the antenna floating with nothing to reflect off of. With no reflected wave to interfere with the direct one, there's nothing left to create lobes or nulls: you'll see plain circular wavefronts expanding equally in every direction. That's not a simplification — a horizontal dipole's true 3-D pattern is a donut shape centered on the wire, and this particular viewing angle (looking straight down the wire's own axis) happens to be exactly the cross-section where that donut is at its widest and most uniform, so it renders as a perfect circle. All the lobing you see at every other height slider position is entirely a product of the ground reflection — remove the ground, and the pattern goes uniform.
Frequency sets the operating frequency (and therefore the wavelength). Height above ground is the dipole's physical height above the earth, expressed in wavelengths, up to 3λ before reaching the free-space position — this is the key variable that reshapes the whole pattern. Zoom just adjusts your viewing distance.
Drag the height slider and watch the lobes reshape in real time. At very low heights (around 1/8 to 1/4 λ), a significant amount of energy is directed at steep upward angles, with the pattern fairly broad and close to omnidirectional overhead — this is the NVIS effect (Near Vertical Incidence Skywave), useful for regional contacts where the signal needs to come back down from the ionosphere at a steep angle. As you raise the antenna, that broad high-angle lobe narrows and tilts down toward the horizon. At 0.5λ — a common, practical all-around height — you get one clean, well-formed lobe at a moderate angle (around 30°), a solid general-purpose compromise between local and long-distance coverage. Push the height higher, toward a full wavelength, and the main lobe keeps dropping toward the horizon (down toward 14° or lower) for the longest possible skip distance — though a second, higher-angle lobe also appears at those greater heights. Keep going past 1λ, up toward 3λ, and you'll see the pattern split into progressively more numerous, narrower lobes as height increases — a real effect, though most practical amateur installations stay well under 1λ.