Topology Optimization of a Wideband Planar Phased Array Element Using Periodic Level Set Functions

Adding complexity to the radiating surface of a planar phased array has the potential to extend the bandwidth of economical array designs, while allowing relative trade-offs between broadside gain, scan volume, and polarization purity to be more fully explored. This work introduces the use of the periodic level set function (p- Lsf)for antenna arrays, an approach which can describe complex material distributions through only a few continuously variable parameters, and applies it to the optimization of a broadband, single polarization, and unbalanced phased array element. The optimization and resulting element are compared against similar prior optimizations of a fragmented aperture antenna with equivalent bandwidth requirements. Finally, the scan performance of an 18x18 finite array (16x16 driven) with the optimized element is modeled and shown.

I. Introduction

Choice of element is a crucial step in the development of a phased array system; while the element may not occupy the majority of the size, weight, or cost of any system, it plays an outsized role in defining system performance. After all, no level of quality in array electronics can overcome an element with a poor element factor and an imperfect match. A variety of element topologies have been proposed to enhance the bandwidth and scan performance of phased array systems, including the planar ultrawideband modular antenna (PUMA) array [1], the balanced antipodal Vivaldi antenna (BAVA) ar-ray, the frequency-scaled ultrawide spectrum element (FUSE) array [2], fully-planar inverted-L monopole (FILM) array [3], and the interwoven spiral array (ISPA) [4]. A common feature of these antenna types is increased mutual coupling between adjacent array elements, which provides a wide bandwidth by producing an approximately uniform current sheet on a plane, rather than by exciting currents in isolated resonant elements.