General approach to solving the problem of synthesis of frequency-independent phased antenna arrays

In a number of applications of phased antenna arrays, it is necessary to form constant directional characteristics (beam width, side lobe level) within a frequency range with several octaves width. One approach to solving the problem of synthesizing a frequency-dependent amplitude-phase distribution that ensures the formation of constant directional characteristics of antenna arrays is to divide the operating frequency band into a number of sub-ranges and calculate the amplitude-phase distribution at the average frequency of each sub-range. When implementing this approach, the issues of choosing the number and bandwidth of the sub-ranges within which the deviation of the directional characteristics does not exceed the permissible values remain open. The known solution to the synthesis problem using sub-ranges with a constant bandwidth leads to irrational costs of computing resources and directly affects the complexity of constructing a scheme for forming an amplitude-phase distribution. In this regard, the issues of determining the relationship between the number of sub-ranges and the permissible change in the directional characteristics within each sub-range are relevant. The article presents a synthesis technique developed using progressive expansion of the frequency sub-range bands. Using the example of solving the problem of synthesizing a linear antenna array operating in a four-fold frequency band, it has been shown that using the developed technique, the operating frequency range of the linear array under study is covered by thirteen sub-ranges, the relative overlap of each of which is 1.11, while the standard deviation between the specified and formed directional patterns at the boundaries of the sub-ranges does not exceed 0.01. As a result of modeling, it has been found that as the frequency increases, the relative excitation amplitude of the outer radiators decreases to zero and the size of the effectively excited aperture decreases. In this case, the effective aperture size remains constant in wavelengths with in-phase excitation of the radiators. The reduction of the effective aperture size and the low level of excitation amplitude of the array radiators outside it correspond to the principles of constructing aperture antennas and antenna arrays with frequency-independent directivity characteristics – the scale principle and the current cutoff principle. The use of the proposed approach and the synthesis technique developed on its basis allows to reduce the cost of computing resources by reducing the number of iterations during the synthesis procedure by 2.3 times and to simplify the construction of schemes for forming the amplitude-phase distribution in the aperture of antenna arrays with frequency-independent directivity characteristics.