On the radiation properties of array of skewed stacked dipoles

Antenna arrays located on airplanes or other mobile platforms for satellite communication applications are typically required to support very large scan angles (close to end-_re). How- ever, planar antenna arrays are typically characterized by scan loss. To increase the scan range conformal arrays and multi-panel configuration can be found in literature, but the height of the structures is still too large to be installed on airplanes without significant impact on the aircraft drag. To obtain wide-scan capability while still maintaining a low antenna profile, hybrid scanning mechanism are currently implemented (F. Tiezzi et al., Eu- CAP, 2010). The idea is to scan the beam electronically from broadside to a positive, as high as possible, angle and then to achieve the full coverage by mechanical rotation of the array along the azimuth. In this work we present a study to determine the parameters affecting the power radiated in specific directions by antenna arrays with tilted elements. We developed an efficient Method of Moments (MoM) for the analysis of linear arrays with arbitrarily tilted dipole elements, in free space or in the presence of a backing reflector. By using this analysis method, we study the radiation characteristics of arrays of stacked dipoles over a ground plane, highlighting the variation of the patterns as a function of the inter-element distance and the angle of inclination of the element. For half wavelength inter-element distance the array pattern is rather symmetric even for tilted elements, as expected from the Floquet theory (A.K. Bhattacharyya et al., IEEE TAP, 51, 1572-1581, 2003). However, when the elements are tilted by positive angles and for inter-element distance larger than half wavelength, a null and a reduction in directivity in the radiation pattern is achieved for negative scanning angles. Grating lobes in the visible region are weighted by element pattern. The minimum of the radiation pattern is not necessarily aligned with the dipole axis but, due to mutual coupling, it can move to different angles depending on the combination of inclination angle and distance. The array directivity is almost at for positive angles up to very large scanning directions, and decreases rapidly at specific negative angles that change with the inter-element distance. Moreover, it is shown that, for large arrays (i.e. with more than 10 elements), the shape of the active element pattern does not change significantly as a function of the number of elements. At the conference considerations concerning the effects on the active element pattern of mutual coupling and of the onset of grating lobes for a given grid size/tilt angle will be presented. Moreover, a linear array design with selective pattern characteristics will be presented.Tera-Hertz Sensin

Theory and design of an array of skewed stacked dipoles

We propose a systematic approach to describe planar slot antennas, embedded in generic stratified media. An equivalent transmission line model for the slot is proposed, based on a spectral domain analysis. First, we introduce a method of moments solution to model semi-infinite slots, fed by a deltagap excitation. The solution entails only two basis functions, one located at the feed and the other at the termination. The latter basis function is chosen to properly account for the field diffractive behavior at the antenna end point. An approximate circuit model is then introduced, which describes the main mode propagating along the slot as an equivalent transmission line. Lumped impedances are extracted to accurately describe the source and the end point. This procedure can be used to derive the input impedance of planar antennas with arbitrary length in generic layered media or the interaction between multiple feeds within the same slot.Tera-Hertz Sensin

Angularly Stable Frequency Selective Surface Combined with a Wide-Scan Phased Array

A five-layer frequency selective surface (FSS) composed of subwavelength elements with large harmonic rejection bandwidth is presented. The FSS design is based on an equivalent circuit model, where the interlayer interaction is only described with a single transmission line representing the fundamental Floquet wave. A prototype of the designed FSS is fabricated, and the measured response exhibits good stability over a wide conical incidence range up to 45°. The FSS is combined with a wide-scanning connected array of dipoles to implement a phased array with integrated filtering properties. A dispersion analysis is performed to define the distance between the array and the FSS that avoids the propagation of surface waves between the combined structures, allowing to maximize the radiation efficiency. The performance of the array combined with the FSS is experimentally characterized, showing high-order harmonic rejection better than 17 dB over a large bandwidth.Accepted Author ManuscriptTera-Hertz Sensin

An Array of Tilted Dipoles Loaded with Artificial Dielectrics with an Asymmetric Pattern

We present the design of an array of tilted dipoles loaded with artificial dielectrics, to achieve asymmetric radiation patterns. First, a simplified array element consisting of skewed stacked dipoles in the presence of a backing reflector is studied, by means of a dedicated spectral periodic method of moments (MoM). The analysis of the stacked dipoles provides guidelines to design arrays with certain radiation characteristics, by varying the tilt angle and the inter-element spacing. Based on the findings of numerical analysis, we then propose a tilted dipole element design with artificial dielectric loading to implement the pattern asymmetry. The design includes the feeding structure and the balun transition to a 50-Ohm coaxial line.Tera-Hertz Sensin

3D Array Element Design for Pattern Shaping

In this work, antenna arrays with tilted dipoles are investigated in terms of radiation and impedance properties. A spectral method of moments (MoM) was developed for the analysis of doubly-periodic arrays (i.e. periodic in both x and ydirections)with arbitrarily tilted dipole elements, in free space or in the presence of a backing reflector. By the aid of this analysis method, the radiation characteristics of arrays of stacked dipoles over a ground plane are studied, highlighting the variation of thepatterns as a function of the inter-element distance and the angle of inclination of the elements.Tera-Hertz Sensin