Design of Subarrayed Linear and Planar Array Antennas With SLL Control Based on an Excitation Matching Approach

In this paper, the synthesis of subarrayed antennas with subarrays having different weights and dimensions is considered. The problem is formulated as the definition of the element clustering into spatially contiguous subarrays and the corresponding weights to obtain a pattern with the lowest (i.e., minimum achievable) sidelobe level (SLL). The problem is addressed with an unconstrained approach based on an excitation matching method where the synthesis of subarray weights and sizes is simultaneously carried out. Successively, a hybrid version of such an approach is proposed to directly enforce into the optimization procedure the SLL constraints. A set of representative results concerned with both sum and difference patterns are shown. Furthermore, some comparisons with state-of-the-art hybrid evolutionary-based techniques are reported, as well.

I. Introduction

The definition of suitable tradeoff solutions between antenna performance and costs is a problem still actual and of interest in the scientific community involved in array antenna synthesis. On one hand, the need to design radiating systems that satisfy specific and ever tightened user requirements (e.g., long range and high quality connectivity or/and fine angular resolution) and, on the other hand, the limited available budget motivate researchers in studying innovative and low cost approaches. As a matter of fact, ideal antenna devices should generate patterns with conflicting features such as high directivity, low sidelobe level (SLL), narrow beamwidth, and high efficiency. At the same time, simple beam forming networks are needed to reduce the manufacturing complexity allowing a large scale production. To properly address these issues, different approaches have been proposed to design efficient and cheaper antenna systems (see, for example, [1]– [4] and the references cited therein). In such a framework, the use of quantized excitations where either the number of elements on a uniform grid through a statistical thinning procedure [1] or the distance between an a-priori fixed number of radiating elements [3] have been optimized. Another interesting approach considers the grouping of the array elements into contiguous subarrays. This methodology has shown to work properly in the case of linear [5]– [7] as well as planar [8]– [10] arrays. The subarraying method is aimed at breaking the periodic errors in the aperture illumination function that generate unwanted grating lobes [11]. Towards this purpose, different strategies have been proposed. As regards to linear geometries, in [5] the amplitude taper is used at both the element ports and the subarray ports. Subarrays of random sizes have been considered in [6], while the optimization of both the number of elements within each subarray and the subarray weighting has been dealt with in [7] by means of a hybrid approach. Other techniques based on the sequential rotation of groups of elements of different dimensions [8], on the arrangement of a-periodically spaced subarrays [9], and on properly shaping the subarrays [10] have been proposed to deal with planar structures. Moreover, some general considerations and the results from representative experiments have been reported in [12] to show/evaluate the effects of amplitude and phase quantization when using contiguous subarrays.