Impedance matching a phased-array antenna over wide scan angles by connecting circuits

Abstract

In a phased-array steerable-beam antenna, the active impedance of the radiating elements exhibits considerable change with scan angle. Because of this change, it is ordinarily possible to match the active impedance at only one angle. However, by the addition of lossless circuits which interconnect the element lines, good impedance match over a wide range of scan angles may be obtained. The effects of connecting circuits are easily analyzed in terms of simple equivalent circuits when the array is infinite. For this reason, and because no change is required in the radiating element, the connecting-circuit method is well suited for application to phased arrays containing a large number of regularly-spaced elements. As an example of the use of connecting circuits for wide-angle matching of an array, calculations are made for an infinite planar array of dipoles. Scanning the beam of this array within a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">120\deg</tex> cone is assumed to cause a mismatch as great as 14-db SWR at some angles when no connecting circuits are used. With the addition of a set of connecting circuits in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> plane of the array and another set in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> plane, this limit is reduced to 4.5-db SWR. The improvement in this impedance match corresponds to a 2.3-db increase of gain realized by the antenna.