Method and apparatus for reducing electromagnetic interference and jamming in GPS equipment operating in rolling environments

Abstract

A method and apparatus for reducing electromagnetic interference (EMI) and jamming in Global Positioning System (GPS) receivers operating on rolling or spinning platforms and/or environments is provided. An antenna system having a pair of diametrically-mounted elements provides interferometric cancellation for spatial and polarization nulling of interference signals. The antenna system, operating in conjunction with multiplexing and anti-jamming electronics, provides interference suppression for a GPS receiver connected thereto. Interference cancellation is provided in jamming and non-jamming environments by selectively employing spatial or polarization nulling of the interference signal.

What is claimed is:  
     
         1 . A method for reducing interference and jamming in a receiver operating on a moving platform comprising: 
 receiving a radio signal with an antenna system mounted on the platform;    sensing interference or jamming in the radio signal;    determining platform roll;    implementing a polarization nulling technique to cancel interference or jamming where there is no roll or slow roll; and    implementing a spatial nulling technique to cancel interference or jamming where roll exceeds slow roll.    
     
     
         2 . The method of  claim 1 , further comprising synchronizing the nulling technique with a source of interference without using external references.  
     
     
         3 . The method of  claim 1 , further comprising switching from spatial nulling to polarization nulling when platform roll changes from a fast roll to a slow roll.  
     
     
         4 . The method of  claim 1 , further comprising switching from polarization nulling to spatial nulling when platform roll changes from a slow roll to a fast roll.  
     
     
         5 . The method of  claim 1 , further comprising wrap calibrating the polarization nulling technique to produce an optimal polarization null pattern.  
     
     
         6 . The method of  claim 1 , further comprising wrap calibrating the spatial nulling technique to produce an optimal spatial null pattern.  
     
     
         7 . An apparatus for reducing interference in a receiver operating on a rolling platform comprising: 
 a pair of diametrically-mounted antennas mounted on the rolling platform;    means for determining interference levels of radio signals received by the antennas;    means for determining roll rates of the rolling platform;    a modulator for generating a spatial null pattern and a polarization null pattern; and    means for selecting between the spatial null pattern and the polarization null pattern based upon the roll rates.    
     
     
         8 . The apparatus of  claim 7 , further comprising means for combining the pair of antennas to produce a receive signal when no interference or jamming is present.  
     
     
         9 . The apparatus of  claim 7 , further comprising a multiplexer connected to the antennas.  
     
     
         10 . The apparatus of  claim 9 , wherein the multiplexer switches the antennas between spatial and polarization nulling modes.  
     
     
         11 . The apparatus of  claim 7 , wherein the modulator modulates phases and amplitudes of radio signals received by the antennas to generate the spatial null pattern and the polarization null pattern.  
     
     
         12 . The apparatus of  claim 7 , further comprising a controller for controlling the modulator.  
     
     
         13 . The apparatus of  claim 12 , wherein the controller controls the modulator in response to sensed interference levels.  
     
     
         14 . A method for reducing interference in a receiver operating on a moving platform comprising: 
 detecting interference or jamming in a radio signal received by the receiver;    creating a spatial null pattern if platform roll exceeds slow roll;    calibrating and maintaining the spatial null pattern with a downhill gradient process if interference levels exceed predetermined thresholds and platform roll exceeds slow roll;    creating a polarization null pattern if the platform has no roll or slow roll; and    calibrating and maintaining the polarization null pattern with a downhill gradient process if interference is present and the platform has no roll or slow roll.    
     
     
         15 . The method of  claim 14 , wherein the steps of calibrating and maintaining the spatial and polarization null patterns comprises: 
 monitoring relative phases and amplitudes of the radio signal using a tracking loop;    determining the best null in response to the monitored phases and amplitudes; and    creating the best null by adjusting the phases and amplitudes of the radio signal.    
     
     
         16 . The method of  claim 14 , further comprising removing the null patterns when interference is not present.