Parabolic reflectors for microwaves differ from mirrors due to their rough surfaces, which cause diffuse reflection, scattering light in multiple directions rather than reflecting it smoothly. In contrast, smoother surfaces like spoons achieve specular reflection, effectively reflecting light at the same angle of incidence. The scattering of light does not affect microwaves because their wavelengths are much larger, allowing the dish's surface roughness to remain insignificant. Additionally, materials can reflect different wavelengths differently, with some transparent to visible light being effective in the infrared spectrum. The reflective properties at specific frequencies can be described using the index of refraction and Fresnel equations.
