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We propose a new approach to the mask‐constrained power synthesis of reconfigurable circular‐ring array antennas for monopulse radar applications. By resorting to Orbital Angular Momentum vortex beams, and without increasing either the complexity of the beam forming network or the signal processing times with respect to the state‐of‐art solutions, the proposed method allows improving the precision pointing with respect to usual techniques. The overall synthesis is cast as a Convex Programming optimization problem aimed at reducing as much as possible the number of control points of the array, and it is tested in relevant application scenarios. Plain Language Summary: A new antenna‐design method is presented in order to enhance the target localization accuracy of monopulse radars. The synthesis procedure is cast as a Convex Programming problem in the case of reconfigurable circular arrays. Key Points: Phase‐only reconfigurable circular‐ring arrays can be exploited as effective monopulse antennasOrbital Angular Momentum vortex beams increase precision pointingConvex Programming can maximize performance of reconfigurable arrays [ABSTRACT FROM AUTHOR]

The exploitation of Orbital Angular Momentum (OAM) is proposed to design circular‐support continuous aperture distributions and concentric‐ring arrays for target‐localization applications. The proposed approach allows generating a single isolated null of the field in the target direction, which is of interest with respect to common techniques leading to a line (or perpendicular lines) of power‐pattern zeroes in the spectral plane. In the presented design procedure, the optimal continuous aperture source is first identified by resorting to the most suitable OAM vortex and effective tools such as the Singular Value Decomposition of the involved operator and a smart Convex Programming optimization. Then, by exploiting fast deterministic algorithms, this continuous source is discretized into circular‐ring arrays emulating it at best. Relevant applications including equispaced arrays, sum‐difference reconfigurable arrays, and isophoric sparse arrays are presented. The proposed approach is also compared with the state‐of‐the‐art techniques and assessed through full‐wave electromagnetic simulations. Plain Language Summary: The addressed problem is the synthesis of power patterns for target localization. The present work provides an original and relevant contribution to the research community by introducing a new method to design circularly‐symmetric continuous aperture distributions as well as circular‐ring arrays able to maximize the localization accuracy while keeping under control both the beamwidth and the sidelobe level of the power pattern. By virtue of the powerful tools that are jointly exploited, which include the Orbital Angular Momentum beam modes, the Singular Value Decomposition of the corresponding operator, and a Convex Programming optimization of the problem's unknowns, the proposed approach results deeply different from those available in the literature and can overcome a number of intrinsic limitations of the latter. Hence, the achieved results are relevant and original from both the methodological and application points of view. With respect to the available solutions, the introduced paradigm will provide a number of advantages in terms of both application range and technological impact. Key Points: Orbital Angular Momentum of radio waves can be used to improve precision pointingLow‐sidelobe vortex beams can be seen as difference patterns of monopulse radarsExploiting at best Convex Programming and Singular Value Decomposition allows outperforming classical synthesis techniques [ABSTRACT FROM AUTHOR]

A new approach to the bandwidth maximization of reconfigurable antenna arrays for monopulse radar applications is proposed and tested. The provided radiating systems allow switching the radiation behavior from sum to difference patterns (and vice versa) while sharing the excitation amplitudes of a user-decided set of radiating elements. Furthermore, the proposed design procedure guarantees the maximum possible bandwidth performance once the overall antenna size, the desired beamwidth, sidelobe level, and slope in the target direction of the generated power patterns are fixed. The synthesis problem is cast and solved as a sequence of convex programming optimizations, and hence the maximization of performances is attained with advantages in terms of computational times as well as convergence to the global optimum. The given theory is supported by numerical experiments including arrays with ultra-wideband performances. [ABSTRACT FROM AUTHOR]

With reference to the mask-constrained power synthesis of shaped beams through fixedgeometry antenna arrays, we elaborate a recently proposed approach and introduce an innovative effective technique. In particular, the proposed formulation, which can take into account mutual coupling and mounting platform effects, relies on a nested optimization where the external global optimization acts on the field's phase shifts over a minimal number of 'control points' located into the target region whereas the internal optimization acts instead on excitations. As the internal optimization of the ripple is shown to result in a Convex Programming problem and the external optimization deals with a reduced number of unknowns, a full control of the shaped beam's ripple and sidelobe level is achieved even in the case of arrays having a large size and aimed at generating large-footprint patterns. Examples involving comparisons with benchmark approaches as well as full-wave simulated realistic antennas are provided. [ABSTRACT FROM AUTHOR]

We propose a new approach to the mask-constrained synthesis of shaped beams through generic array antennas having arbitrary layouts and element patterns. The introduced general methodology allows casting the design problem as a finite number of Convex Programming optimizations and can generate different excitation solutions all fulfilling the required specifications. Numerical examples, including planar arrays and the full-wave synthesis of an aperiodic array, are provided in support of the given theory. [ABSTRACT FROM AUTHOR]

With reference to the mask-constrained power synthesis of shaped beams, we extend the spectral factorization method to both uniformly and nonuniformly spaced linear arrays wherein mutual coupling and mounting-platform effects are present. The overall design procedure does not rely on any restriction on the nature and the shape of the fields, and it is cast as a couple of convex optimizations plus a polynomial factorization. Moreover, it allows one to ascertain the actual feasibility of the radiating system before performing the synthesis, and it is able to identify very many different array-excitation solutions all corresponding to the desired power pattern. The given theory is supported by numerical experiments concerning the full-wave synthesis of realistic arrays affected by mutual coupling and mounting-platform effects. [ABSTRACT FROM AUTHOR]

Generating given 3-D field intensity distributions in a non-homogeneous scenario is a canonical problem which is of interest in many applications. On the other side, due to its very challenging nature, very few methods have been proposed up to now in the literature. In this communication, starting from the well-known time reversal (TR) technique, a simple innovative approach, the so-called optimized multi-target TR (O-mt-TR), is presented. The strategy is based on the optimization of the phase shifts between the time-reversed fields in a number of control points within the target region. In doing so, the proposed method outperforms the simple juxtaposition of time-reversed fields pursued by the so-called mt-TR, or even succeed in cases in which the latter fails completely. This capability of the proposed method is assessed through a numerical analysis concerned with a 3-D inhomogeneous scenario, in which the results are quantitatively appraised in terms of coverage of the target areas. [ABSTRACT FROM AUTHOR]

Due to the plethora of possible applicative fallouts, in the recent years several efforts have been made to develop three-dimensional (3-D) field intensity shaping methods. While many approaches able to focus a wave-field into a target point are available, few strategies have been instead developed to generate a field having a given intensity spatial distribution. This is probably due to the higher challenging nature of such a problem. In this letter, with reference to scalar fields, we present an innovative 3-D shaping procedure, which casts the problem as the solution of a finite number of convex programming problems. An example of the performance of the proposed procedure in a 3-D inhomogeneous scenario is given to show the capability of ensuring uniform field intensity within a target area while keeping it arbitrarily bounded elsewhere. [ABSTRACT FROM AUTHOR]

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 FROM PUBLISHER]

A rigorous deterministic approach is proposed for the mask-constrained power pattern synthesis of shaped beams through one-dimensional sparse arrays having uniform-amplitude excitations (and variable phases). The approach includes the well known density taper procedure as a special case. The corresponding technique, which exploits an analytical formulation of the problem and convex programming routines, results in fast computation and is able to achieve optimal solutions without recurring to any global optimization. Numerical results assessing the capabilities of the proposed design method are provided, opening the way to the development of an effective approach for the synthesis of circularly symmetric shaped beams via uniformly-excited circular ring arrays. [ABSTRACT FROM PUBLISHER]

Uniform amplitude sparse arrays have recently gained a renewed interest and a number of synthesis techniques, mainly based on global optimization algorithms, have been presented. In this paper, after a discussion about the expected characteristics of such arrays, a simple deterministic approach for the case of pencil beams patterns is proposed and discussed. The approach, which outperforms previous synthesis techniques, takes inspiration from existing (not well-known) density taper procedures to develop a two stages synthesis where the first step is solved in a new closed analytical form, while the second one just requires local refinements or fast 1-D optimizations. As a consequence, the proposed approach avoids the need of multidimensional global optimization procedures and the inherent possibly prohibitive computational costs. Notably the first step, which also exhibits an improved flexibility with respect to other analytical techniques, already outperforms previous approaches in a number of cases of interest. Several numerical results confirm the effectiveness and usefulness of the proposed tools. [ABSTRACT FROM AUTHOR]

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The problem of synthesizing "optimal" sum and difference patterns subject to arbitrary sidelobe bounds by means of a simple feeding network is dealt with. It is shown how a hybrid optimization procedure properly acting on both clustering into subarrays and excitations of these latter greatly improves performances of known feeding architectures with respect to existing procedures. Results of the proposed technique, which significantly outperform existing methods, renew the interest of these simple feeding architectures, and emphasize the effectiveness of this kind of hybrid procedures exploiting the convexity of the problem with respect to a part of the unknowns. [ABSTRACT FROM AUTHOR]

Most global optimization based synthesis procedures act in essentially the same way on all the involved variables. In this paper, it is theoretically discussed and numerically emphasized how explicit exploitation of the convexity of the problem with respect to a part of the degrees of freedom (when available) allows to achieve increased performances with respect to previous results, and to develop new interesting design solutions. Examples are presented for the synthesis of both sum and difference patterns by using nonuniformly spaced arrays and for the so called "optimal compromise amongst sum and difference patterns." Finally, the proposed approach is exploited in developing effective design solutions (based on the concept of interleaved arrays) to the problem of achieving very flexible antennas while using simple feeding networks. As an example, array antennas capable to radiate two different beams with individually steerable patterns, or to perform jammer rejection at the physical layer or even to realize a "flat-top" beam pattern are synthesized and presented [ABSTRACT FROM PUBLISHER]

A new approach providing new theoretical results to the optimal far-field focusing of uniformly spaced arrays, subject to a completely arbitrary mask for sidelobe bounds, is presented and discussed. In both cases of linear or planar arrays (with rectangular boundaries), it is first shown that the problem can be formulated, without any loss to performances on the maximum, as a linear programming one, guaranteeing a globally optimal solution. Second, a sufficient uniqueness criterion for the solution of the overall problem is also developed, which shows how the solution may not be unique (as is actually the case) when planar arrays are considered. In addition, further globally effective optimization procedures are proposed for the latter case in order to optimize directivity, smoothness of excitations, or other performance parameters in the set of equivalent solutions. Last, an extension to planar arrays with a nonrectangular boundary is also given. A thorough numerical analysis confirms the effectiveness of the approach proposed and of the solution codes developed. [ABSTRACT FROM AUTHOR]