Apparatus and method for improving signal-to-jamming ratio in a spread

Abstract

A jamming signal cancellation method and apparatus for removing an undesired in-band CW jamming signal from a desired spread spectrum signal. The jamming cancellation apparatus includes a limiter, a summer, and a feedback loop. The feedback loop includes the summer, a harmonic filter, a mixer, a loop/filter amplifier, and an adjustable gain control (AGC). The limiter limits the waveform of the input signal and issues a limited signal to the AGC and the mixer. The AGC controls the amplitude of the limited signal and passes a controlled amplitude signal to the summer. The summer takes a difference between the input signal and the controlled amplitude signal and passes a difference signal to the filter. The filter filters the harmonics that were created by the limiter and passes an output signal to the mixer. The mixer multiplies the filtered signal by the limited signal to provide an error signal that is proportional to the amplitude of the fundamental frequency in the difference signal. The error signal is then passed through the loop/filter amplifier and used in the AGC to drive the amplitude of the controlled amplitude signal to equal the amplitude of the waveform of the input signal, effectively eliminating the CW jamming signal from the output signal, and thereby improving the signal-to-jamming ratio of the output signal with respect to the input signal.