R. Tascone

Synthesis of multiple-ring-resonator filters for optical systems

A method for the synthesis of optical filters consisting of a cascade of N-coupled rings is presented. The procedure is based on the definition of a polynomial whose roots are the zeros of the channel-dropping transmittance characteristic and provides directly the ring electrical lengths and the mutual coupling coefficients. A design example of a Chebyshev-type 6-ring bandpass filter is presented.

Antenna Pattern Verification System Based on a Micro Unmanned Aerial Vehicle (UAV)

This letter presents a radiation pattern verification system for low-frequency antennas in their operative conditions, e.g., on the ground, next to other elements, etc. It is a far-field setup using a properly equipped micro unmanned aerial vehicle (UAV) as a test source. The micro UAV can perform an autonomous flight. Its absolute position is measured with a remote topographic instrument. By data processing, the received power pattern along the UAV flying path is reconstructed. The proposed setup has been validated on two standard wire antennas at 150 and 408 MHz with an estimated accuracy of 1 dB.

A fast reduced-order model for the full-wave FEM analysis of lossy inhomogeneous anisotropic waveguides

The evaluation of the frequency response of waveguiding structures by means of the full-wave finite-element method requires solving a large generalized eigenvalue problem for each frequency. This paper describes a novel approach, based on the singular-value decomposition, which drastically reduces the order of the eigenvalue problem. By inspection of the singular values, the accuracy level of the procedure may be controlled. The technique is applied to the analysis of open and closed waveguides with arbitrary cross section, lossy conductors, and anisotropic dielectric layers, by means of vector elements of generic order; higher order elements are shown to allow the accurate evaluation of fields inside lossy conductors with fewer unknowns, besides exactly modeling normal field discontinuities at material interfaces. Examples of application of the reduced-order technique are shown concerning both non-TEM and quasi-TEM structures.

A novel design tool for waveguide polarizers

This paper presents a novel method for the design of broad-band waveguide polarizers. It consists of an interactive procedure where the designer places the zeros of the reflection coefficient for one polarization, simultaneously also controlling the frequency response of the other one and vice versa. In this way, the best matching condition for both polarizations can be found. This design tool is based on an automated phase control procedure and on an algorithmic characterization of the relationship between the two frequency responses. The spurious effects of multimodal interactions, frequency dispersion, and losses are taken into account and compensated by characterizing them with suitable transfer functions. Designs of iris-loaded polarizers in square and circular waveguides are described, with operative bandwidths up to 30%. Measurements on a 10% bandwidth Ka-band prototype show reflection and cross-polarization levels of approximately -50 dB, with a phase error of approximately 0.4/spl deg/.

A Unified Formulation for the Analysis of General Frequency Selective Surfaces

ABSTRACT In this paper we solve the problem of the scattering of an arbitrary field from a general Frequency Selective Surface (FSS). The keypoint of our approach is a functional equation in the spectral domain, which is solved numerically by the Calrkin Method of Moments. Two approaches are possible, according to whether one assumes as unknown the induced current on the metalilc patches or the, electric field in the complcnentpry aperatures. The former Is convenient when the patches have a simple shape (e.g. strips, rings,discs), the latter in the case of a perforatec screen (e.g. round or rectangular apertures). The formulation Is then extended to treat the case where the patches are not metallic, but constituted by an anysotropic imoodance surfacf. The computer program AHPA is based on this formulation and car. perform a spectral charecterization of multiple grid FSS, with metallic patches described as a collection of scrips. Sample results relative to tripoles and square loops are presented and discussed.

The Sky Polarization Observatory

Abstract The Sky Polarization Observatory (SPOrt) is an ASI-funded experiment specifically designed to measure the sky polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be flown on the International Space Station. Starting in 2006 and for at least 18 months, it will be taking direct and simultaneous measurements of the Stokes parameters Q and U at 660 sky pixels, with FWHM=7°. Due to development efforts over the past few years, the design specifications have been significantly improved with respect to the first proposal. Here we present an up-to-date description of the instrument, which now warrants a pixel sensitivity of 1.7 μK for the polarization of the cosmic background radiation, assuming two years of observations. We discuss SPOrt scientific goals in the light of WMAP results, in particular in connection with the emerging double-reionization cosmological scenario.

Reduced-order optimized mode-matching CAD of microwave waveguide components

The optimum designs of microwave devices require highly accurate and efficient computer-aided-design systems. This paper describes a novel reduced-order model for the mode-matching technique, which is derived from the application of the Krylov subspace concept and of the singular-value-decomposition algorithm to the coupled integral equations solved by the mode-matching technique. The design example of a high performance 12-cavity Ka-band ridged-filter confirms the accuracy and the numerical efficiency of the proposed model. In particular, the presented method also enables to accurately control the metal losses of the devices.

Problem-matched basis functions for moment method analysis-an application to reflection gratings

In the evaluation of the frequency response of a scattering object by the integral equation technique, generally a large linear system of equations has to be solved for each frequency point. This paper deals with a technique that drastically reduces the size of the linear system without loss of accuracy, The key point is the definition of a set of problem-matched basis functions. These basis functions are extremely efficient in the representation of the unknown in the parameter range of interest. In this way, the central processing unit (CPU) time required in the response evaluation is drastically reduced. Examples of application concerning reflection gratings are reported.

Orthomode transducer for millimeter-wave correlation receivers

This paper presents a novel orthomode-transducer (OMT) architecture,which is particularly suitable for correlation receivers at millimeter waves. By exploiting an on-axis reverse-coupling structure, a compact OMT configuration is obtained, which provides high levels of channel equalization. The Ka-band prototypes exhibit very good electric performances in terms of isolation, cross-polarization, return loss, and channel equalization.

A microwave measurement procedure for a full characterization of ortho-mode transducers

Ortho-mode transducers (OMTs) are key components in both dual-polarized antenna feed systems for telecommunication and radioastronomy applications. The evaluation of the overall system performance requires the measurement of the return loss, isolation, and cross-coupling levels of the OMTs. In this paper, a novel technique for the microwave measurements of the full 4/spl times/4 scattering matrix of such devices is reported, which is based on different measurements at the single-polarized ports.