A generalized hybrid algorithm for the synthesis of uniform amplitude ring-arrays is introduced. The method exploits the analytical properties of the field radiated by a circular array in order to get advantages from the use of convex programming techniques. The method, aimed to the synthesis of circularly symmetric patterns, is very flexible and allows the use of different kind of feeds as well as stepped excitations. The synthesis procedure is demonstrated in the case of high-directivity pencil beam patterns

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Non-periodic, sparse Direct Radiating Arrays employing equi-amplitude (isophoric) radiators represent an appealing solution to meet the requirements of next satellite services. In this work we address the synthesis of isophoric sparse arrays capable of radiating highly steerable pencil beams, in order to meet the requirement of full Earth coverage from GEO orbits. To this aim, we first of all perform an analytical study that allows assessing the geometrical constraints that the desired beam steerability puts on the design of the array layout. Starting from such results, in the second part of the work we address the actual synthesis of the sparse array. The proposed strategy consists in the synthesis of the optimal radiating feed followed by the synthesis of the array layout capable of taking into account the aforementioned geometrical constraints as well as the feeds' pattern, in such a way to guarantee satisfaction of the side lobe level constraint for every steered beam. Numerical examples demonstrate the effectiveness of the proposed synthesis strategy

Abstract:The aim of this paper is to analyze the array synthesis for 5 G massive MIMO systems in the line-of-sight working condition. The main result of the numerical investigation performed is that non-uniform arrays are the natural choice in this kind of application. In particular, by using non-equispaced arrays, we show that it is possible to achieve a better average condition number of the channel matrix and a significantly higher spectral efficiency. Furthermore, we verify that increasing the array size is beneficial also for circular arrays, and we provide some useful rules-of-thumb for antenna array design for massive MIMO applications. These results are in contrast to the widely-accepted idea in the 5 G massive MIMO literature, in which the half-wavelength linear uniform array is universally adopted.

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We present some modifications to the deterministic approach (DA) recently proposed for fast design of aperiodic concentric ring arrays. Such modifications are aimed at improving the array performances in terms of directivity, side lobe level (SLL) and number of control points. In particular, an easy implementation of the size-tapering concept is provided within the processing scheme of the DA procedure; moreover, an improved collocation criterion is presented. Finally, a local optimization procedure, tailored to the concentric ring array case, is addressed