# Why can radio telescopes use wire mesh as their parabolic dish?

Radio telescopes use wire mesh to save cost. How does that work? Won't the waves go through the gaps?

• It is also to save on mass, reduce air drag, and a solid surface is not necessary when the wavelengths are meters but your mesh gaps are centimeters. – honeste_vivere Mar 13 '18 at 14:48

Depending on the source, radio waves are said to have frequencies from as low as 3 kHz up to 300 GHz. The corresponding wavelength $\lambda$ can be calculated via $$\lambda = c / f$$ where $c$ is the speed of light and $f$ is the frequency. This gives us $\lambda = 3 \mathrm{m}$ for $f=100 \mathrm{MHz}$, a typical FM radio frequency. If a wave encounters a material with holes in it, like wire mesh, it doesn't necessarily "see" those holes. Because they are much smaller than the wave itself, the dish might as well be solid to the wave.