Diffraction of radio waves
The phenomenon of bending of waves around the corners of an obstacle or opening placed in its path is called diffraction.The phenomenon is found to be prominent when wavelength of the waves is comparable with the size of the obstacle or opening.
Radio waves are of large wavelengths and the size of obstacles and openings of the buildings are comparable with the wavelengths of the radio waves.But the wavelengths of the light waves are much shorter as compared to the size of the obstacles and openings.That is why radio waves diffract around the buildings while light waves do not.
Difference between interference and diffraction
Diffraction of light