MTI-Filter in a trackding radar receiver

Claim 1

In a receiver unit of a tracking radar whose transmitting unit transmits series of M radar pulses having a given pulse repetition frequency f PRF wherein each pulse in the series has a different carrier frequency and the series are repeated with a given frequency repetition frequency f FRF which is a function of the range of the target being tracked, a MTI-filter comprising: means for processing the received echo pulses to analog pulse signals; analog to digital conversion means for converting the analog pulse signals to digital values represented by coded combinations of pulse signals; digital filtering means including a plurality of serially connected digital delay means each having a delay equal to 1/f PRF and corresponding to the number of carrier frequencies used by the transmitting unit when transmitting; a digital differentiator means having a first input connected to the output of the analog to digital converter means, a second input and an output which is the output of the MTI-filter; controllable switching means having a plurality of inputs each connected to an output of a different one of digital delay means and an output connected to the second input of said digital differentiator means for connecting the output of a selected one of said digital delay means to the digital differentiator in accordance with the number of radar pulses in the transmitted series.