G. Di Massa

A novel hybrid approach for far-field characterization from near-field amplitude-only measurements on arbitrary scanning surfaces

A novel hybrid procedure is proposed in this paper for far-field reconstruction from phaseless near-field data. A basically interferometric approach is adopted to retrieve the near-field phase from amplitude-only measurements, which are collected by a simple microstrip circuit used in conjunction with two identical probes moving on the scanning surface. A certain number of sets of complex near-field data is obtained, apart from constant phase-shifts to be computed, one for each set. A nonredundant representation based on the introduction of the reduced field is then adopted to evaluate these shifts, with an accurate and fast convergence to the solution. In order to validate the proposed technique, an X-band prototype using two flanged WR-90 waveguides is successfully designed and tested on a cylindrical geometry for a standard pyramidal horn.

The truncation error in the application of sampling series to electromagnetic problems

Truncation error interpolation methods used in the evaluation and representation of scattered fields are discussed. Three main points are considered: the choice of the sampling point lattice: the choice of the type of sampling expansion: and the determination of the number of terms of the sampling series that must be retained to insure a negligible truncation error. The aim is to provide a clear reference frame for the applications which allow the optimal choice for the reconstruction algorithm. The cases of bounded and square integrable band-limited functions are separately dealt with in order to exploit the properties of each method. A general analysis of the multidimensional truncation error is carried out. No particular assumption on the sampling expansion is made, except for that concerning the use of a rectangular sampling lattice. Simple and effective expressions relating the multidimensional error to the corresponding one-dimensional bounds are derived. The one-dimensional error is then analyzed in detail with reference to the most relevant case of central interpolation. By very simple methods, error bounds for all the sampling expansions explicitly considered in the literature are derived in a systematic way. Expressions providing the values of the sampling rate and number of retained samples which minimize the overall computer time and memory requirement are derived. Some numerical examples are presented and briefly discussed. >

Design and Validation of a Reconfigurable Single Varactor-Tuned Reflectarray

An aperture-coupled reflectarray element giving a full phase tuning range with a single varactor diode is proposed in this paper for pattern reconfigurability applications. The full phase agility is achieved by a proper optimization of the phase tuning line, thus providing an alternate inductive/capacitive effect able to avoid the use of two varactor diodes, usually adopted in similar existing configurations. The proposed active element structure is adopted to design a demonstrative reflectarray prototype of 3 × 15 radiators. Furthermore, an own synthesis procedure is applied to obtain the proper biasing voltages giving the prescribed H-plane field. Test examples of beam-scanning, multibeam, and shaped-beam patterns are discussed to demonstrate the effectiveness of the approach.

Control of reflector antennas performance by rim loading

An analysis of the behavior of reflector antennas loaded by a surface impedance along a peripherical rim is carried out in order to ascertain the possibility of improving their performance by such a loading technique. Both single and dual (Cassegrain) reflector antennas are considered. It is shown that an effective control of the radiated field can be achieved by the proper choice of the loading characteristics. In the case of Cassegrain antennas, subreflector loading is sufficient to enhance copolar or crosspolar overall performance.

Multiband software defined radar for soil discontinuities detection

A multiband Software Defined Radar based on orthogonal frequency-division multiplexing technique is proposed in this work for an accurate soil discontinuities detection, taking into account also the dispersive behavior of media. A multilayer soil structure is assumed as a validation test to demonstrate the effectiveness of the proposed approach, by accurately retrieving the unknown thicknesses and permittivities of the soil layers.

Radar array diagnosis from undersampled data using a compressed sensing/sparse recovery technique

A Compressed Sensing/Sparse Recovery approach is adopted in this paper for the accurate diagnosis of fault array elements from undersampled data. Experimental validations on a slotted waveguide test array are discussed to demonstrate the effectiveness of the proposed procedure in the failures retrieval froma small set of measurements with respect to the number of radiating elements. Due to the sparsity feature of the proposed formulation, the method is particularly appealing for the diagnostics of large arrays, typically adopted for radar applications.

Use of characteristic modes in multiple-scattering problems

It is proposed that a convenient choice of basis functions for applying the moment method to the analysis of scattering and/or mutual coupling between metallic bodies impinged upon by an electromagnetic field is that of the characteristic modes of a single scatterer. Due to the resonant behaviour of such modes, only a small number of them are required for an accurate representation of the current distribution even in the presence of mutual coupling. Results for the case of two-dimensional strips are reported and compared with those obtained with the conventional, direct application of the moment method.

Tunable reflectarray cell for wide angle beam-steering radar applications

An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radar applications. A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilities within a wider angular region. The radiating structure is accurately optimized to provide a full phase tuning range by adopting a single varactor load as phase shifter element. A 0.46λ-reflectarray cell is designed at the frequency of 11.5GHz, obtaining a phase agility of about 330°. The cell is successfully adopted for the design of a 21 × 21 reconfigurable reflectarray. The antenna is numerically tested for different configurations of the varactors capacitance values, and good beam-steering performances are demonstrated with in a wide angular range.

Dielectric waveguide with non-linear permittivity

The dispersion relation for TE polarized waves guided by a non-linear dielectric slab with intensity-dependent refractive index, surrounded on one side by linear media and on the other side by a metallic surface, is found. The dependence of the propagation constant from the energy flux is also investigated. Some examples are investigated in detail.

Fast computation of radiation integral for reflector antennas

A FORTRAN IV program to compute the field scattered by parabolic reflector antennas in a prescribed plane cut is presented. This program was executed on the UNIVAC 1100/80 at the University of Naples. A flowchart of the main program is provided