Reduced sidelobes for Butler-matrix-fed linear arrays

Abstract

It is shown that simple transposition of the elements of a linear array fed by a Butler matrix can be used to improve the sidelobe level without significant degradation of the other characteristics of the array. The beams remain collimated with gain equal to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> times element gain, where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> is the number of elements in the array. The beam crossover level is lowered slightly but not so much as would be the case for a conventionally tapered aperture distribution. Improved sidelobes are obtained for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N \geq 14</tex> , and data are presented for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> as high as 50. Specifically, sidelobe levels of 15.54, 16.54, 17.86, and 18.56 dB are obtained for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N = 18, 31, 37</tex> , and 44, respectively. Although the improvement is modest for low <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> , it appears that the available improvement increases directly with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> .