Simultaneous nulling in sum and difference patterns by amplitude control

A method is discussed of suppressing jammers simultaneously in the sum and the difference patterns of a linear antenna array by either using complex weights or controlling the current amplitudes only, with special emphasis on the latter method. For a given array size, the total number of jammers that can be nulled is doubled if complex weights are used instead of real weights. However, the amplitude-only technique has many attractions. It is shown that because the resulting current amplitude distribution has a double symmetry, the number of attenuators required for simultaneous nulling can be as low as a quarter of the total number of elements in the array. This means a much faster computing speed as well as a considerable saving in hardware. The method also allows the main beam of the antenna to be scanned by using phase-shifters while nulls are placed in directions of known jammers in both the sum and difference patterns by using attenuators. As a result, the maximization of the signal-to-jammer ratio can be achieved with relative ease, because the stronger a jammer is, the easier it is to locate it and hence to suppress it.