An optimization technique for sum and difference array factors [radar array signal processing]

Modern high-resolution radars often employ planar phased array antennas. The patterns for these arrays are usually designed to have narrow mainbeams and low sidelobes. This is best achieved by minimizing the total sidelobe energy in the array factor, rather than setting a sidelobe threshold level as is usually done. A method to achieve the minimizing patterns is described here for both sum and difference array factors. We define the optimum array factor for a linear array as minimizing the total array factor energy outside of a specified angular range about the peak of the mainbeam. This optimization technique is at least as easy to apply as the older techniques and is superior for many applications. In addition, the optimization technique has far fewer restrictions on the placement of the elements and is, therefore, more general. We can easily generalize the method to include nonuniform array designs, however an initial look into the performance of nonuniform arrays gave disappointing results for the sum array factor.

I. Introduction

Modern high-resolution radars often employ planar phased array antennas. The patterns for these antennas are usually designed to have narrow mainbeams and low sidelobes. These designs are often based on either the Dolph-Chebyshev [1], [2, p. 537], or the Taylor line source [2, p. 543], [3], [4] methods that work well in general but are not optimized for any applications. Recently, additional techniques have been introduced that attempt some form of optimization [5], [6]. It should also be noted that there are windowing techniques in the signal processing literature [7]–[9] that can be applied almost directly to pattern design. Difference pattern designs, used for finer resolution of target position than can be obtained from the sum patterns, are often based on the Bayliss technique [10]. Here too, there are recently introduced techniques [11]–[13]. We present here an alternative approach that provides sidelobes with minimum energy content.