The polyphase decomposition is dividing an Nth order filter into L – sections of sub – filters that can be realized in parallel. In this decomposition the sub – filters will differ only in phase characteristics and so they are called polyphase filters. Therefore, the process of dividing the filter into sub – filters is called polyphase decomposition.
The polyphase decomposition of filters leads to a realization structure for filters with reduced computations. Hence, the polyphase decomposition can be applied to (anti – aliasing) filters used for decimators and (anti – imagine) filters used for interpolators in order to realize computationally efficient multirate digital signal processing systems.