Frequency multiplexers for the frequency-dependent fan-in of n individual signals of bandwidth (B) sampled at the frequency fa/n, which are subjected to a Fourier transform FFT, the complex output signals of which are weighted by equal-paired factors and fed into a chain of delay and summing components, where the output signals from said chains are time-multiplexed at the sampling frequency fa into the complex frequency multiplex output signal. A delay component is derived from the chain of delay and summing components, the corresponding part of the complex output signals of the Fourier transform is delayed thereby, and then the delayed and undelayed part of the complex output signals of the Fourier transform FFT are weighted by the various factors, combined correspondingly in pairs and fed into the remaining chains of delay and summing components. Used in the formation and separation of frequency multiplex signals by digital filter banks, especially in satellite communication, the invention provides considerable advantages by reducing costs by smaller chip areas and lower chip power. An additional advantage is that the frequency multiplexer or demultiplexer has a linear phase, i.e. an exactly constant group delay.