Fourier transform of RF signal with a "prism"? We can use a prism to decompose visible light into components of different frequencies. This is a Fourier transform by nature. For an ideal prism, the energy is conserved in the process. How about RF signals? There is no fundamental difference between an RF signal and visible light -- they are both EM waves. Is there a device/circuit that can separate the RF signal into different frequencies spatially just like a prism to visible light? Thanks.