Adaptive sinusoidal interference filter

An adaptive filtering system for filtering a sinusoidal interference signal contained within the useful bandwidth of a desired wide-band signal, said system comprising:

• an input terminal and an output terminal;
• means for phase-tracking the interfering signal contained within the wide-band signal by the use of a phase-lock loop circuit including an oscillator, said means being connected to said input terminal of said system;
• means for generating two synchronous square wave signals in phase quadrature, synchronous with said interfering signal, said means for generating two synchronous square wave signals being driven by said oscillator in said phase-lock loop circuit;
• means for filtering and limiting the said two synchronous square wave signals;
• means for generating two weighted signals including filter means connected to said output terminal, two multipliers connected to said filter means and said means for filtering and limiting, and two intergrators connected to said two multipliers to produce said two weighted signals
• weighting second multiplier means coupled to said two integrators and said means for generating two synchronous square wave signals for generating two weighted square wave signals;
• mixing means for combining said weighted square wave signals for producing a combined weighted signal;
• an output filter connected to said mixing means to produce a signal which is an estimate of the interference in said input signal;
• an output combiner connected to said input terminal and said output filter for receiving said estimate signal to cancel the interfering signal in said input signal and produce an output signal substantially free of sinusoidal interference at said output terminal.