Diffraction

Waves spread out after passing through a gap or round an obstacle.The narrower the gap, the more waves spread out.The longer the wavelength, the more waves spread out.According to Huygens theory, each point on a wavefront is a secondary source of waves.The wavelets travel in the direction of the wave and combine to form new wavefronts and so spread beyond the gap.
Satellite TV dishes in Europe point south.Satellites orbit the Earth directly above the equator.A bigger dish diffracts less so needs to be aligned more carefully than a smaller dish.