Waveguide is typically used:

A waveguide is essentially a hollow metal pipe used to carry radio frequency energy. Because the physical dimensions of a waveguide must be strictly proportional to the wavelength of the signal it carries, utilizing them for lower frequencies would require impractically massive pipes. To keep the size manageable for manufacturing and installation, waveguides are restricted to microwave frequencies. Therefore, they are most commonly used at frequencies above 3000 MHz (3 GHz), where the wavelengths are short enough that the waveguide cross-section only needs to be a few centimeters wide.