Giovanni Toso

Deterministic Synthesis of Uniform Amplitude Sparse Arrays via New Density Taper Techniques

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.

Scanning Performances of Wideband Connected Arrays in the Presence of a Backing Reflector

In this paper, the scanning performances of connected arrays that include backing reflectors are investigated. The comparison between connected dipoles and slots is based on the properties of the corresponding Greens functions (GFs). The investigation reveals that connected arrays of dipoles are better suited to scan to wide angles (45deg), retaining the minimal number of transmit/receive (T/R) modules. This paper quantifies and motivates this preference. Eventually, the theoretical design of a fully efficient, 40% bandwidth (BW), planar array with the lowest possible cross polarization is presented.

Sunflower Array Antenna with Adjustable Density Taper

A deterministic procedure to design a nonperiodic planar array radiating a rotationally symmetric pencil beam pattern with an adjustable sidelobe level is proposed. The elements positions are derived by modifying the peculiar locations of the sunflower seeds in such a way that the corresponding spatial density fits a Taylor amplitude tapering law which guarantees the pattern requirements in terms of beamwidth and sidelobe level. Different configurations, based on a Voronoi cell spatial tessellation of the radiative aperture, are presented, having as a benchmark the requirements for a typical multibeam satellite antenna.

Array Antennas With Jointly Optimized Elements Positions and Dimensions Part II: Planar Circular Arrays

The paper describes a deterministic algorithm based on simple analytical equations for designing planar circular sparse array antennas where the positions and the dimensions of the radiating elements are jointly exploited and optimized. The proposed solution permits addressing one of the main limitations associated to sparse arrays, i.e., their poor aperture efficiency especially when patterns with low sidelobe levels are obtained using only the density of the elements avoiding any amplitude tapering. The accuracy of the method is guaranteed by the fact that the achieved directivity differs from the target value, associated to a continuous reference aperture distribution, by a quantity asymptotically equal to the factor π/4 (corresponding to about -1.05 dB) representing the filling factor of a circular planar array organized in concentric rings populated by circular apertures. As required for several applications, the method includes the possibility to add a constraint on the maximum scanning angle with respect to the boresight direction.

Aperiodic Arrays for Spaceborne SAR Applications

An innovative three-step procedure for the synthesis of linear phased arrays with nonuniformly spaced elements is presented. The main objective is to obtain an array with a minimal number of elements and an optimal efficiency of the amplifiers driving the elements. The procedure consists of three steps. First of all, a periodic array with a single-amplitude tapering and as much phase tapering as there are required shaped patterns is derived. Then, starting from the results of the first step, an equiamplitude nonperiodic array, with a number of phase tapering equal to the number of required patterns and with a minimum number of radiators is synthesized. Finally, a numerical optimization permits refining the results so as to satisfy the design constraints.

A hybrid perturbative technique to characterize the coupling between a corrugated horn and a reflector dish

In this paper the electromagnetic coupling between a corrugated horn and a reflector dish is analyzed with a new hybrid perturbative technique. This coupling may produce significant modifications especially in the return loss and in the cross-polar pattern of the feed. The hybrid perturbative approach combines three different techniques: a mode matching (MM) technique for the propagation inside the horn, a method of moments (MoM) technique for the radiation of the horn taking into account the external part of the horn itself, and a fast Gaussian beam asymptotic physical optics (FGBAPO) technique for the interactions between the feed and the reflector. Some measurements and the comparison with rigorous numerical results demonstrate the accuracy of the new hybrid technique and the effects of this electromagnetic coupling on the feed performance.

PO near-field expression of a penetrable planar structure in terms of a line integral

An exact line integral representation of the physical optics (PO) field scattered in the near zone by a penetrable planar structure illuminated by a plane wave is discussed.

HEURISTIC DIFFRACTION COEFFICIENT FOR PLANE-WAVE SCATTERING FROM EDGES IN PERIODIC PLANAR SURFACES

A uniform heuristic high-frequency solution is obtained for plane-wave scattering from edges in periodic planar surfaces. The case of a wedge with periodic impedance boundary conditions on its faces and that of a truncated strip grating are analyzed. Numerical results are presented and compared with reference solutions to validate the heuristic expressions proposed.

Electromagnetic scattering by nonplanar junctions of resistive sheets

Approximate uniform asymptotic expressions are provided to determine the field scattered by a penetrable wedge illuminated at normal incidence. The wedge is formed by two resistive sheets or two thin dielectric slabs definable as resistive sheets having identical geometric and electromagnetic characteristics. The solution is limited to wedge angles and source positions where internal reflections cannot occur. It is obtained by using a geometrical optics (GO) approximation for the field internal to the slabs and by performing a uniform asymptotic evaluation of the physical optics (PO) radiation integral in the hypothesis that a resistive sheet condition is valid. Samples of numerical results so obtained are presented and compared with other methods to demonstrate the effectiveness of the proposed technique.

A boundary element approach to the scattering from inhomogeneous dielectric bodies

A boundary element method (BEM) for the analysis of the electromagnetic scattering from inhomogeneous dielectric structures is presented. The problem is formulated in terms of a single integral equation reducing by half the number of unknowns required with respect to a conventional approach based on two coupled integral equations.