Every radio signal, Wi-Fi included, is built from sine waves. Change the amplitude, frequency, wavelength and phase to see what each one means, then add a second wave to see how two waves add up or cancel out. Radio, light and X-rays are the same kind of wave, only a different length: use the presets to travel across the spectrum.
Each step on this scale is ten times the frequency. Drag the marker, or click anywhere, to move the wave; the arrow keys move it too. Band edges are approximate: the names describe how the waves are made and used, not a physical boundary.
A second wave with the same frequency, shifted by a phase. Where the two waves line up they add together (constructive); where one is up while the other is down they cancel (destructive). Radio waves meet like this whenever a signal arrives by two paths, such as a direct path and a reflection.
Each wave as an arrow: its length is the amplitude and its angle is the phase. Put the arrows tip to tail and the black arrow is the sum.
How tall the wave is: the peak strength of the signal. Power goes with the square of the amplitude, so halving the amplitude leaves a quarter of the power, which is 6 dB less.
Frequency is how many complete cycles pass a point each second. Wavelength is the distance from one crest to the next. Radio waves all travel at the speed of light, so the two are locked together: λ = c ÷ f. Double the frequency and the wavelength halves. That's why a 2.4 GHz wave is about 12.5 cm long and a 5 GHz wave only about 6 cm.
Where a wave is in its cycle, measured in degrees: 360° is one full cycle. Phase only means something when you compare two waves. A wave that has travelled one extra half-wavelength arrives 180° out of phase; one extra whole wavelength brings it back to 0°.
Radio, Wi-Fi, infrared, visible light, ultraviolet, X-rays and gamma rays are all electromagnetic waves travelling at the speed of light. They differ only in frequency, and so in wavelength: an AM radio wave is hundreds of metres long, green light about 550 nm, a gamma ray smaller than an atom. How a wave behaves depends on its size compared with what it meets: a 12 cm Wi-Fi wave passes through a plasterboard wall that stops light completely, while X-rays pass through the soft tissue that blocks light.
Each wave is carried as photons, and one photon's energy is E = h × f (h is Planck's constant). From about 10 eV (far ultraviolet, shorter than roughly 124 nm) a single photon can knock an electron off an atom: that is ionising radiation, and X-rays and gamma rays carry thousands to millions of eV, which is why exposure to them is limited. The UV in sunlight (about 3 to 4 eV) is not ionising, but it can still break chemical bonds in DNA directly, which is why it causes sunburn. A 2.4 GHz Wi-Fi photon carries about 0.00001 eV, around a million times too little to ionise anything, so radio can only warm things.
In the Wi-Fi Glossary: electromagnetic spectrum ↗, photon energy ↗, ionising radiation ↗
Multipath: indoors, the signal reaches the receiver directly and by reflections off walls, floors and furniture. Each copy arrives with a different phase. Moving a phone a few centimetres (a fraction of a wavelength) can turn a strong spot into a weak one.
Beamforming: an access point with several antennas adjusts the phase of each one so the copies arrive in phase at the client, adding up. See the Beamforming Simulator.
Modulation: Wi-Fi sends data by changing the amplitude and phase of its waves. See the Wi-Fi Modulation Simulator.
Real waves cycle millions (AM radio) to billions of billions (gamma rays) of times a second, far too fast to see. The animation is slowed down by the factor shown on the first chart. Between 1 and 10 GHz the chart keeps a fixed 60 cm ruler, so a higher frequency visibly cycles faster and every wave travels at the same speed. Outside that range the ruler grows or shrinks with the wave so that about five wavelengths always fit, and the label under the chart gives its real length.