Method and means for providing enhanced main beam nulling in antijamming antenna

Abstract

In a microwave communications link, an antijamming antenna system with enhanced main beam nulling is realized by providing gain in the difference port output of a monopulse antenna compared to the sum port. As a consequence interference signals are nulled out at much closer angles to the desired signal than is the case when the gain is the same in both channels. The gain is introduced when a dominant jammer is detected. Detection of a dominant jammer is identified for the conditions in which the monopulse sum channel power level exceeds the sum of the difference channel power levels and the system processor output signal/noise ratio is unsatisfactory.

What is claimed is:  
     
       1. In an antijamming antenna system having a main antenna, an omnidirectional antenna, a monopulse antenna with azimuth and elevation difference beam ports each having gain and a sum beam port, and a processor receiving signals therefrom and providing a processed output, the method of enhancing main beam nulling comprising the step of 
       increasing gain in said difference beam ports.  
     
     
       2. In an antijamming antenna system having a main antenna, an omnidirectional antenna, a monopulse antenna with azimuth and elevation difference beam ports each having gain and a sum beam port, and a processor receiving signals therefrom and providing a processed output, the method of enhancing main beam nulling comprising the steps of 
       detecting the presence of a dominant jamming signal from the power levels in said monopulse antenna sum and difference beam ports and the signal/noise ratio of said processed output, and  
       increasing gain in said difference beam ports in response thereto.  
     
     
       3. In an antijamming antenna system having a main antenna, an omnidirectional antenna, a monopulse antenna with azimuth and elevation difference beam ports each having gain and a sum beam port, and a processor receiving signals therefrom and providing a processed output, the method of enhancing main beam nulling defined in  claim 2  wherein the presence of a dominant jamming signal is detected by the steps of 
       sensing the power level in said monopulse antenna sum beam port,  
       sensing the power levels in said monopulse antenna difference beam ports,  
       determining if the signal/noise ratio of said processed output is satisfactory or unsatisfactory, and  
       identifying the presence of a dominant jamming signal for the condition that the power in the sum beam port exceeds the power in both difference beam ports and the signal/noise ratio of said processed output is unsatisfactory.  
     
     
       4. In an antijamming antenna system having a main antenna, an omnidirectional antenna, a monopulse antenna with azimuth and elevation difference beam ports each having gain and a sum beam port, and a processor receiving signal therefrom and providing a processed output, the method of enhancing main beam nulling defined in  claim 3  wherein gain in said difference beam ports is increased by an amount in a range between 3dB and 9dB. 
     
     
       5. In a microwave communications link, an aritijamming antenna system comprising 
       a main antenna,  
       an omnidirectional antenna,  
       a monopulse antenna outputting azimuth and elevation difference signals and sum signals,  
       processor means receiving and processing the outputs of said main antennas, said omnidirectional antenna and said monopulse antenna azimuth and elevation difference signals and sum signals, and providing a processed output therefrom,  
       jamming signal detecting means for detecting and outputting a signal in response to the presence of a dominant jamming signal, said jamming signal detecting means detecting jamming signals from the power levels of said monopulse antenna azimuth and elevation difference signals and sum signals and the signal/noise ratio of said processed output, and  
       gain control means for increasing the gain of said moncpulse antenna azimuth and elevation difference signals in response to the jamming signal detecting means output signal.  
     
     
       6. In a microwave communications link, an antijamming antenna as defined in  claim 5  wherein said gain control means increases the gain of said monopulse antenna azimuth and elevation difference signals in response to the conditions in which the power level of said sum signal is greater than the total power of said azimuth and elevation difference signals and the signal/noise ratio of said processed output is less than a preselected threshold. 
     
     
       7. In a microwave communications link, an antijamming antenna as defined in  claim 6  wherein said gain control means increases the gain of said monopulse azimuth and elevation difference signals by an amount in a range between 3dB and 9dB.