Andrea Vallecchi

Design of dual-polarized series-fed microstrip arrays with low losses and high polarization purity

The design of a dual-polarized microstrip series-fed linear traveling-wave array is described in this paper. The array is composed of two identical subarrays formed by cascading an equal number of four-port aperture-coupled cross-patch elements and terminated on a two-port radiating matched load. By properly exciting the array, dual linear or circular polarization can be accomplished and by virtue of the symmetric arrangement of the antenna cross-polarization is annihilated. A straightforward design strategy is proposed for the synthesis of a desired current distribution along the array antenna. Some proof-of-concept linear arrays are developed and the corresponding numerical results, obtained through a full-wave approach based on the method of moments (MoM), are provided. As an independent validation, supplementary analyses by the finite integration technique (FIT) are also reported. Very close agreement is found between prescribed and synthesized array performance, which qualifies the proposed design approach as an accurate and effective tool for the synthesis of series-fed aperture-coupled patch arrays.

Dual-band dual polarization microstrip antenna

This paper describes the development of a multilayer dual-band dual-polarized antenna operating at L and C bands with a common aperture. Unlike earlier approaches, slot coupled patches are employed at both bands to reach cross-polarization suppression better than 30 dB. The antenna has been conceived to be used as a basic module in large series-fed arrays featuring light weight, high efficiency and beam scanning. Moreover, by properly scaling the geometry, the antenna can operate at any else pairs of frequencies with a ratio between 3.5-4.5.

Skew incidence diffraction by an anisotropic impedance half plane with a PEC face and arbitrarily oriented anisotropy axes

High-frequency expressions for the field scattered by a half-plane with a perfectly conducting and an anisotropic impedance face are provided in the format of the uniform geometrical theory of diffraction (UTD), when the half-plane is illuminated by an arbitrarily polarized plane wave obliquely incident on its edge. The loaded face is characterized by a tensor surface impedance with principal anisotropy axes arbitrarily oriented with respect to the edge; a vanishing surface impedance is exhibited in one of the principal directions. This kind of tensor surface impedance can be suitably applied for analyzing the effects on the scattered field of corrugated surfaces or grounded dielectric slabs periodically loaded by metallic strips. This solution extends previous high-frequency formulations valid in those cases in which the direction of corrugations or strips is either parallel or perpendicular to the edge. The analysis is performed by resorting to the Sommerfeld-Maliuzhinets method. To determine the spectral solution, a special function is needed that differs from the standard Maliuzhinets one and was originally introduced to study the electromagnetic scattering by a wedge embedded in a gyroelectric medium.

A Low-Cost Shaped-Beam Hybrid-Feed Microstrip Planar Array Antenna for X-Band Polarimetric Radar Systems

A novel dual-polarized microstrip patch array with a low-loss hybrid feed network suitable for X-band polarimetric airport surveillance radars (ASRs) is presented. A waveguide is used to excite a number of linear subarrays consisting of aperture-coupled microstrip cross-patch elements connected in series. The microstrip radiating part implements the dual polarization capability with low cross polarization, while the very reduced transmission line runs implied in the series-type feeding keeps ohmic and dielectric losses at a minimum. As a further major advantage of this antenna, the radiation pattern can be independently shaped in the two principal planes. In particular, the microstrip subarray is designed to produce a cosecant-squared pattern, whereas the waveguide provides a Taylor-like illumination distribution to have low side lobes in the longitudinal plane. As a result, the proposed array antenna is expected to stand out for high efficiency, polarization purity, simplicity of fabrication, light weight and compactness

AN APPROXIMATE SOLUTION FOR SKEW INCIDENCE DIFFRACTION BY AN INTERIOR RIGHT-ANGLED ANISOTROPIC IMPEDANCE WEDGE

The scattering by an anisotropic impedance interior rightangled wedge is analyzed when the principal anisotropy directions on the two faces are parallel and perpendicular to the edge. The problem is first approached by directly applying geometrical optics (GO); this allows us to identify the conditions under which the edge diffracted contribution vanishes. For those configurations not satisfying the above conditions, a perturbative technique, based on the Sommerfeld-Maliuzhinets method, is developed to determine an approximate edge diffracted field solution, valid when the normalized surface impedances on the anisotropic faces assume small values. The perturbative corrections to the field are asymptotically evaluated in the context of the Uniform Geometrical Theory of Diffraction (UTD).

Investigation of microstrip-fed slot antennas backed by shallow cavities

A low-profile cavity-backed slot (CBS) antenna is demonstrated by operating the slot about its second resonance. The cavity thickness of this slot antenna is ten times smaller than conventional one-quarter wavelength cavities, which allows the antenna to be constructed with standard cost-effective printed circuit techniques. The high gain and fairly wideband operation are additional advantages of the proposed configuration.

Rigorous closed-form formulas for the scattering from plane angular sectors with conical-section boundaries

Closed-form representations of the physical optics (PO) field scattered in the far zone by penetrable dielectric or metallic plane angular sectors of arbitrary opening angle with a conical-section boundary are derived in terms of incomplete cylindrical functions. The proposed expressions in combination with PO formulas for the scattering from polygonal plates can constitute a powerful tool to evaluate the scattering from flat surfaces with curved edges in a very computationally efficient manner. In order to check the accuracy and numerical effectiveness of the proposed scattered field solutions, comparisons with the results obtained by an accurate completely numerical PO approach are provided.

Multi-objective optimization of wideband spiral arrays

A challenging task in array design is to synthesize an array working at multiple frequencies within a large frequency band, with constraints imposed to the radiation pattern in terms of side lobe level (SLL). This kind of array synthesis requires a multi-objective approach since there is no single solution which can be considered the best at the multiple investigated frequencies for all the compulsory requirements. Therefore this class of problems, instead of a single one, is characterized by an ideal set of solutions, the Pareto front (PF), which comprises solutions over which no other solution of the population dominates [1]. This set provides a range of solutions for which no one can simultaneously satisfy the required performance but represents a tradeoff of the design requirements. Multi-objective genetic algorithms (MOAs) can be a useful tool for determining the Pareto front. They perform similarly to conventional genetic algorithms but they search for the set of solution which belongs to the PF, rather than providing only a single optimal solution. In particular, we have adopted a multi-objective genetic algorithm, called Non-dominated Sorting Genetic Algorithm (NSGA-II) [2] to optimize the array factor of a Spiral Array.

Diffraction by two classes of anisotropic impedance half-planes with nonaxial anisotropy tensors

The three-dimensional plane wave scattering from anisotropic impedance half-planes having their principal anisotropy axes arbitrarily oriented with respect to the diffracting edge is analyzed. Two classes of exactly solvable half-plane configurations are identified and the corresponding rigorous analytical expressions for the total scattered field are derived in terms of a generalization of the Maliuzhinets special function. Then, explicit uniform asymptotic field expressions are provided along with samples of numerical results proving their validity.

Planar square and diamond microstrip patch array antennas for dual-polarization operation

Two compact low-cost planar microstrip array antennas devised to achieve dual-polarization capability are presented. The arrays are composed of five square patches with a central aperture-coupled element feeding the outer patches through a straightforward network of resonant microstrip lines. Dual-edge and dual-corner feeding arrangements for the external patches are considered as alternatives. By appropriately driving the two antennas at their input ports, dual-linear as well as circular polarization of the radiated field can be accomplished. Preliminary numerical investigations of the proposed antenna configurations are reported and the relevant performance is comparatively assessed.