S. Costanzo

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.

Far-Field Reconstruction from Phaseless Near-Field Data on a Cylindrical Helix

An efficient procedure is developed for far-field reconstruction from phaseless near-field data on a circular helix. The application of an integrated probe is considered for collecting amplitude data to be used in the near-field phase retrieval. This is performed along the single line given bythe helicoidal curve, thus reducing computation time as compared with planar and plane-polar geometries. Antenna far-field pattern is directlyevaluated from complex near-field helicoidal data by a Fast Fourier Transform based algorithm, so anyintermediate interpolation on a cylindrical surface is avoided. Numerical simulations on arrays of Huyghens sources are presented for assessing the effectiveness of the proposed approach.

Reduction of Patch Antenna Coupling by Using a Compact EBG Formed by Shorted Strips With Interlocked Branch-Stubs

This letter presents a new type of planar electromagnetic band-gap (EBG) surface composed of short-circuited microstrips densely coupled with each other through interlocked branch stubs. With respect to a conventional mushroom surface, this structure exhibits a better space-wave decoupling performance due to the soft nature of the surface. With respect to other soft surfaces, like shorted strip already introduced in the literature, the present solution possesses better miniaturization properties, thus allowing the use of lower permittivity and consequent improvements when integrated in planar dense arrays. The experimental results demonstrate a decoupling until 38 dB in both planes for patches separated by only one half free-space wavelength.

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.

Aperture-Coupled Reflectarrays with Enhanced Bandwidth Features

An extensive analysis is performed on the aperture-coupled reflectarray configuration to highlight and quantify the bandwidth enhancement due to the use of reduced inter-element spacings. Bandwidth extension is directly evaluated on the phase curves relative to the reflection coefficient against frequency for different lengths of the tuning line. The operating frequency range computed with the proposed approach is numerically validated on the gain patterns of synthesized reflectarrays and a strong broadband behavior is demonstrated for reflectarrays of moderate aperture dimensions and reduced unit cell size.

Direct Far-Field Computation from Bi-Polar Near-Field Samples

The problem of fast data processing for the bi-polar near-field measurement technique is addressed in this paper. A computing algorithm is developed to perform direct far-field transformation from near-field samples acquired on the bi-polar scanning surface. Radiation integral is efficiently evaluated by taking advantages of the convolution property leading to use the Fast Fourier Transform and the related shift theorem. The accuracy of the proposed transformation procedure is numerically demonstrated on arrays of infinitesimal dipoles. Results for a measured reflector antenna are also included.

An improved synthesis algorithm for reflectarrays design

An improved synthesis procedure is presented in this letter for the design of microstrip reflectarray antennas. The iterative projection based algorithm is modified to include the effect of different incidence angles on the reflectarray elements in the evaluation of the design curve. Experimental results on an X-band prototype of unequal microstrip patch elements are reported.

High resolution software defined radar system for target detection

The Universal Software Radio Peripheral USRP NI2920, a software defined transceiver so far mainly used in Software Defined Radio applications, is adopted in this work to design a high resolution L-Band Software Defined Radar system. The enhanced available bandwidth, due to the Gigabit Ethernet interface, is exploited to obtain a higher slant-range resolution with respect to the existing Software Defined Radar implementations. A specific Lab VIEW application, performing radar operations, is discussed, and successful validations are presented to demonstrate the accurate target detection capability of the proposed software radar architecture. In particular, outdoor and indoor test are performed by adopting a metal plate as reference structure located at different distances from the designed radar system, and results obtained from the measured echo are successfully processed to accurately reveal the correct target position, with the predicted slant-range resolution equal to 6m.

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.

POTENTIALITIES OF USRP-BASED SOFTWARE DEFINED RADAR SYSTEMS

Software Deflned Radar is the latest trend in radar development. To handle enhanced radar signal processing techniques, advanced radars need to be able of generating various types of waveforms, such as frequency modulated or phase coded, and to perform multiple functions. The adoption of a Software Deflned Radio system makes easier all these abilities. In this work, the implementation of a Software Deflned Radar system for target tracking using the Universal Software Radio Peripheral platform is discussed. For the flrst time, an experimental characterization in terms of radar application is performed on the latest Universal Software Radio Peripheral NI2920, demonstrating a strongly improved target resolution with respect to the flrst generation platform.