Electronic counter measures in radar

Abstract

Apparatus and method for eliminating an interference signal from a desired signal where a difference of polarization exists or can be made to exist. The desired signal is received on a first antenna of appropriate polarization and the interference signal is received via another port of the same antenna or a second antenna polarized ninety degrees away from the first. The signal received via the other polarization is adjusted for amplitude and phase so that all interference will be cancelled when both signals are subtracted in a summing junction. In the case where the interference and desired signals do not have polarization differences, provision is made to change the polarization of the desired signal.

We claim:  
     
       1. Apparatus for receiving a wanted radio frequency signal in the presence of interference comprising: 
       a first antenna polarized in the same mode as the wanted radio frequency signal;  
       a second antenna polarized orthoginally with respect to said first antenna;  
       means coupling said first antenna substantially directly to a radio receiver for receiving said wanted radio frequency signal;  
       a signal controller coupled to said second antenna for varying the amplitude and phase of any signal received by said second antenna;  
       means subtractively combining the output of said signal controller with the signals present in said first antenna to radio receiver coupling means;  
       means for sampling the signals present between said subtractively combining means and said radio receiver;  
       a signal processor coupled to said sampling means and to said signal controller to receive signal samples in the polarization of said first and second antennas;  
       said signal processor including means for comparing the phase of signals derived from said first and second antennas, said means for comparing the phase of signals deriving phase correction constants;  
       said signal processor including means for comparing the amplitude of signals derived from said first and second antennas, said means for comparing the amplitude of signals deriving amplitude correction constants;  
       said signal processor including means for deriving the amplitude and phase correction constants for said signal controller from said comparing means;  and  
       means coupling the output of said signal processor to said signal controller for controlling the amount of phase and amplitude variation of said signal controller to produce a minimum interference signal at said sampling means.  
     
     
       2. Apparatus for receiving a wanted radio frequency signal in the presence of interference comprising; 
       a first antenna polarized in the same mode as the wanted radio frequency signal;  
       a second antenna polarized orthoginally with respect to said first antenna;  
       means coupling said first antenna substantially directly to a radio receiver for receiving said wanted radio frequency signal;  
       a signal controller coupled to said second antenna for varying the amplitude and phase of any signal received by said second antenna;  
       means subtractively combining the output of said signal controller with the signals present in said first antenna to radio receiver coupling means;  
       first and second sampling means, said first sampling means sampling first signals present between said subtractively combining means and said radio receiver;  
       a local oscillator;  
       a first mixer coupled to said local oscillator;  
       means introducing the output of said first sampling means into said first mixer whereby the signals sampled thereby are converted to an intermediate frequency;  
       said second sampling means sampling signals from said second antenna, a second mixer coupled to said local oscillator;  
       said second sampling means coupled to said second mixer to convert signals sampled from said second antenna to the same intermediate frequency as the output of said first sampling means;  
       a signal processor coupled to said first and second mixers and to said signal controller to receive signal samples in the polarization of said first and second antennas;  
       said signal processor including means for comparing the phase of signals derived from said first and second antennas;  
       said signal processor including means for comparing the amplitude of signals derived from said first and second antennas at said intermediate frequency.