Abstract: A digital filter for generating a frequency domain output signal in response to an incoming signal arriving in successive receiving cycles whenever the incoming signal has any frequency component lying within the passband of the filter. A means for generating a timing signal is provided. An analog-to-digital converter responsive to the timing signal converts the incoming analog signal into a series of digital input pulses during each range gate interval. A reference generator responsive to the timing signal provides a train of digital reference pulses for each of the successive receiving cycles. A predetermined number of successive receiving cycles constitutes a single correlation frame. The amplitude of each train of digital reference pulses is determined by a composite correlation function. A multiplier multiplies each digital reference pulse with each digital input pulse to generate a train of discrete digital output pulses for each receiving cycle.