Angelo Freni

A Circularly-Polarized Isoflux Antenna Based on Anisotropic Metasurface

Theory, design, realization and measurements of an X-band isoflux circularly polarized antenna for LEO satellite platforms are presented. The antenna is based on a metasurface composed by a dense texture of sub-wavelength metal patches on a grounded dielectric slab, excited by a surface wave generated by a coplanar feeder. The antenna is extremely flat (1.57 mm) and light (less than 1 Kg) and represents a competitive solution for space-to-ground data link applications.

Twenty-four-hour spectral analysis of heart rate variability in congestive heart failure secondary to coronary artery disease

Abstract It is well known that heart rate (HR) fluctuates in time and that this variation is closely related to changes in the neural activity to the heart. 1,2 Therefore, HR variability represents a noninvasive parameter for studying the autonomic control to the heart. Recently, it has been shown that HR variability is a powerful independent prognostic factor in patients with coronary artery disease 3 and a low HR variability count has been found to be related to sudden death. 4 Spectrum analysis of HR may provide further information, since HR variability possesses 2 major components that have been shown to relate to different patterns of neural control to the heart. 5,6 Patients with congestive heart failure (CHF) have a complex abnormality of the autonomic control to the heart 7 that also affects some HR characteristics. 8 These abnormalities may be determined either by a selective reduction of the vagal outflow to the heart or by a more complex abnormality. This investigation was undertaken to evaluate the components of HR variability in normal persons and patients with CHF, and their 24-hour behavior.

Progress in Antenna Coupled Kinetic Inductance Detectors

This paper describes the combined Dutch efforts toward the development of large wideband focal plane array receivers based on kinetic inductance detectors (KIDs). Taking into account strict electromagnetic and detector sensitivity requirements for future ground and space based observatories, this work has led to the identification of well-suited coupling strategies based on the use of lens antenna and the demonstration of their feasibility. Moreover, some specific antenna design difficulties that characterize KIDs-based designs have been investigated, and innovative feeds for the focal plane array which could allow the receivers to be sensitive over a decade of Bandwidth have been proposed.

Automatic Design of CP-RLSA Antennas

In this paper a procedure is presented, allowing the automatic design of circular polarized radial line slot antennas, with either pencil or shaped beam patterns. The antenna slot layout is refined by an optimization scheme based on the physical picture behind the working mechanism of the array. The validity of the approach has been proved by designing very efficient pencil beam antennas, either with maximum directivity or with controlled side lobe levels, and a shaped isoflux beam antenna.

An efficient full-wave method of moments analysis for RLSA antennas

Here a computationally efficient method of moments (MoM) formulation is presented for the full-wave analysis and design of radial line slot antennas (RLSAs). The method efficiency is based on an ad-hoc representation of the internal problem (electrically large circular cavity) Greens function, which is split into the sum of a parallel plate waveguide contribution and a rim effect contribution, expanded in terms of radial modes. The convergence rate of the proposed Greens function expansion is investigated both analytically and numerically with the aid of some examples. Furthermore, comparisons with a commercial general purpose MoM software were performed on a complete RLSA to demonstrate the accuracy and the efficiency of our approach

Design, Manufacture and Test of a Low-Cost Shaped-Beam Reflectarray Using a Single Layer of Varying-Sized Printed Dipoles

This paper presents the design, manufacture and test of a low-cost reflectarray antenna that provides a sectored-cosecant squared beam. The bandwidth limitation of single-layer reflectarrays is overcome by using three parallel dipoles in each cell. First, the relative length of the three dipoles is chosen to improve the element bandwidth. Then, the dipole dimensions are adjusted to generate a sectored beam in azimuth and cosecant squared in elevation. A prototype has been manufactured and tested. The measured radiation pattern has been compared with the results of approximate and full-wave numerical methods. The influence of the grounded substrate used to fix the antenna structure has also been investigated. Both experimental and simulation results demonstrate the capabilities of the proposed single-layer configuration to provide a shaped-beam on a 10% bandwidth and low losses. This antenna can be a low-cost alternative to multilayer configurations for communication and radar applications.

Asymptotic Approximation of Mutual Admittance Involved in MoM Analysis of RLSA Antennas

In this paper, a computationally efficient method of moments (MoM) formulation is presented that makes use of an approximate asymptotic formula for the slot mutual admittance. The formula accuracy to the asymptotic order O(r - 3/2) gives sufficient precision for moderate slot distance (1.5-2 wavelengths). In a typical radial line slot array analysis, this permits avoiding the numerical integration in more than 90% of the slot pairs with a savings of CPU time of the same order.

Large Depth of Field Pseudo-Bessel Beam Generation With a RLSA Antenna

The paper discusses the possibility of generating a pseudo-Bessel beam, with a propagation distance of several hundreds of wavelengths in microwave and millimeter frequency band, by using a radial line slot array (RLSA). A specific application for non-contact microwave detection of buried mines has been considered as test case. The design benefits of a holographic approach to assure the required aperture field distribution and makes use of an ad hoc optimization tool to control the antenna slot layout. The predicted and measured antenna behaviors show that high efficiency and polarization purity can be obtained by such a compact and flat antenna, achieving at the same time both manufacturing and setup simplicity.

Analysis, Design and Realization of a Novel Directive Ultrawideband Antenna

In this paper, we present a simple log-periodic-dipole-array (LPDA) solution that allows us to achieve good ultrawideband (UWB) performances. The antenna has been manufactured and the measurements agree well with the theoretical predictions. The antenna presents an average gain of 8 dB and a return loss better than -10 dB over the band from 4.2 to 10.6 GHz. Both the measured antenna transfer function and the computed effect on pulse transmission show good performances in comparison with already known UWB antennas.

Design of a Low Loss Metallo-Dielectric EBG Waveguide at Submillimeter Wavelengths

In this letter we show the viability of using concentric cylindrically-periodic (CP) dielectrics to realize low-loss propagation at submillimeter wavelengths. Most of the power in the CP Waveguide (WG) is confined to an air core propagating a TE01 mode. The TM11 mode degeneracy is removed over a very wide bandwidth by a series of periodically spaced dielectric rings that are optimized in thickness and spacing. The new waveguide differs from classical Bragg fibers in that we use only a small number of dielectric layers (2-4), and terminate the outer layer with an external metal coating. We include several designs and describe the optimization procedure that was used to realize structures with low propagation and bend loss.