Question

how to deflect Radio waves?

Answer 1

Some electrically conductive material will definitely interfere with radio wave transmissions (aluminum foil, copper wire, etc.) by blocking (absorbing) or reflecting radio waves.  Radio frequency (Rf) waves are a form of electromagnetic energy, and electromagnetic shielding, made specifically for this purpose of blocking EM radiation, is often made of sheet metal, metal screens, or metal foam.  If it is a screen, the holes in the screen should be smaller than the wavelength of the EM (radio) waves you are trying to block. Copper is used a lot because it will also absorb magnetic energy as well as radio waves.  Most thin amounts of non-conductive materials (paper, cotton, rubber) will not affect Rf waves, but the thicker the material, the more chance it has to actually absorb the radio wave energy (and therefore block it).  One reason why mountains, tunnels and deep bridges play havoc on radio reception, especially AM radio.  As Steven Wright said: "I have a friend who is a radio announcer.  When you drive under a bridge with him you can't hear him speak."

Also considering for refracting (really reflecting), the ionosphere itself reflects certain types of radio waves quite well, especially AM and shortwave radio signals, which is why I could pick up the Cubs game on the radio in Philly when I was growing up. This effect is more pronounced at night. Sometime distant stations are clearer than nearby stations due to this "skywave" effect.