Abstract: A modular fast Fourier transform processor which employs identical processor cards, each of which has a butterfly, memory units which send and receive data to and from the butterfly and a pair of input ports and a pair of output ports. The cards are interconnected through these ports to execute a fast Fourier transform decomposition in accord with Singleton's algorithm. The speed and capacity of the processor may be increased in a gradual manner by employing more of the processor cards.