ON THE NEAR-FIELD SAMPLING AND TRUNCATION ERRORS IN PLANAR TIME-DOMAIN NEAR-FIELD TO FAR-FIELD TRANSFORMATION

International audienceThis paper studies the effect of three important parameters in planar time-domain (TD) near-field (NF) to far-field (FF) transformation. These parameters are the NF spatial sampling, NF measurement distance and scan surface truncation. The effect of these parameters over the TD FF accuracy are difficult to predict for Ultra Wide Band antennas. In this paper we aim to choose the optimum NF measurement parameters guaranteeing accurate calculation of the time-domain far-field. This allows the optimization of the computation time and memory requirements. Computations using analytic array of elementary dipoles radiation pattern are used to study the impact of each parameter in time-domain near-field antenna measurement. The comparison of the far-field results are presented in time and frequency domains. In particular, it is shown that the choice of the measurement distance and the size of the scan surface decide predominantly on the frequency band of accurate FF calculation. The used formalism in this paper for the NF to FF transformation is based on the Green's function

A Low-Profile Cavity-Backed Dual-Polarized Spiral Antenna Array

International audienceA low-profile cavity-backed dual-polarized printed spiral antenna array is presented. This spiral array is composed of four center-fed Archimedean spiral antennas printed on FR4 substrate backed by a low-profile cavity without absorbing material. The dual polarization is generated using monopolarized spirals in an alternating configuration right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP). These spirals are connected allowing the current to flow from the excited spirals arms into the arms of the neighboring ones. The proposed spiral array provides unidirectional beam while being dual-polarized (LHCP or RHCP) for a wide bandwidth. The dual polarization of the proposed spiral array is extended to low frequencies, and the gain varies up to 13 dBi in the antenna bandwidth. The antenna array performances are presented and validated using electromagnetic simulations and radiation pattern measurements

MATRIX METHOD FOR ANTENNA PLANE WAVE SPECTRUM CALCULATION USING IRREGULARLY DISTRIBUTED NEAR-FIELD DATA : APPLICATION TO FAR-FIELD ASSESSMENT

International audience—The matrix method for the calculation of antenna far-field using irregularly distributed near-field measurement data is presented. The matrix method is based on the determination of the plane wave expansion (PWE) coefficients from the irregular near-field samples using a matrix form that connects the radiated field with the corresponding plane wave spectrum. The plane wave spectrum is used to determine the far-field of the antenna under test (AUT). The matrix method has been implemented, and its potentialities are presented. The validations using analytical radiating model (dipoles array) and experimental measurement (X band standard gain horn antenna) results have demonstrated the efficiency and stability of the proposed method

Near Field Probe Correction using Least Squares Filtering Algorithm

International audienceThe deconvolution technique is widely used for probe correction in the near field technique measurement. However, the measurement noise makes the result obtained by this method inefficient and requires the use of a very low noise measurement facility. In this paper, we present a method to improve the probe correction accuracy by an inverse filtering approach that takes into account the statistical characteristics of the measurement noise using the constrained least squares filtering algorithm (CLSF). Computations with EM software data of two different structures illustrate the reliability of the method

Antenna Modeling Based on a Multiple Spherical Wave Expansion Method: Application to an Antenna Array

WOSInternational audienceA method to derive an equivalent radiation source for planar antennas is presented. This method is based on spherical near-field (NF) data (measured or computed) to ascertain an equivalent set of infinitesimal dipoles placed over the main antenna aperture. These produce the same antenna radiation field, both inside and outside the minimum sphere enclosing the antenna. A spherical wave expansion (SWE) of the NF data is written in terms of infinitesimal dipoles using a transition matrix. This matrix expresses the linear relations between the transmission coefficients of the antenna and the transmission coefficients of each dipole. The antenna a priori information are used to set the spatial distribution of the equivalent dipoles. The translational and rotational addition theorems are exploited to derive the transmission coefficients of the dipoles. Once the excitation of each dipole is known, the field at any aspect angle and distance from the antenna is rapidly calculated. Computations with EM simulation data of an antenna array illustrate the reliability of the method

Robust antenna diagnostics method using equivalent elemental dipoles and the spherical wave expansion

International audienceA robust method for antenna diagnostics that can provide the reconstruction of the aperture field from spherical near- or far-field measurements, is presented. This method is based on the equivalence principle which consists in the rewriting of the spherical wave expansion of the radiated field in terms of infinitesimal electric and magnetic dipoles distributed over the antenna main surface. This method presents the advantage of being very stable and extremely robust beside the measurement noise. Synthesized data (simulated antenna) used with different level of noise will show the viability of this technique for antenna diagnostics purpose

The use of infinitesimal dipoles and the spherical wave expansion for planar antennas modeling

International audienceIn this paper, a method to derive an equivalent radiation model for planar antennas is presented. This method uses the spherical near-field (NF) data (measured or computed) to ascertain an equivalent set of infinitesimal dipoles placed over the main antenna surface. The spherical wave expansion (SWE) of the NF data is written in terms of infinitesimal dipoles using a transition matrix. This matrix expresses the linear relations between the spherical wave coefficients of the antenna and the spherical wave coefficients of each dipole. Once the excitation of each dipole is known, the field at any angle and distance from the antenna is rapidly calculated even inside the minimum sphere. Computations with EM simulation data of an antenna array illustrate the reliability of the method

Conception et optimisation d'antennes large bande destinées au radar à pénétration de sol dans la bande fréquentielle [0.6GHz, 3GHz]

National audienceNous proposons dans cet article deux prototypes d'antennes large-bande que nous avons optimisé pour la réalisation d'un radar à pénétration de sol fonctionnant dans la bande [0.6GHz 3GHz]. Le choix de cette plage fréquentielle découle de notre objectif qui est d'assurer une profondeur de pénétration de l'ordre du mètre et atteindre une résolution centimétrique. Le premier prototype est une antenne spirale imprimée sur FR4 (εr=4.2). Le caractère large bande et la facilité de conception des antennes spirales sont des atouts justifiant notre choix. Néanmoins, ces antennes sont dispersives et caractérisées par un rayonnement bidirectionnel. L'antenne spirale retenue permet de contrecarrer ces inconvénients. Le deuxième prototype est une antenne Vivaldi. Elle est caractérisée par une transition progressive de son ouverture assurant une bonne adaptation sur une large bande fréquentielle. La difficulté majeure rencontrée dans la conception des antennes Vivaldi réside dans l'optimisation du système d'excitation assurant à la fois une adaptation de l'antenne en basses comme en hautes fréquences

Aperture antenna modelling by a finite number of elemental dipoles from truncated spherical field measurement: Experimental investigation

International audienceA method to determine a distribution of a finite number of elementary dipoles that reproduce the radiation behaviour of the antenna under test (AUT) from truncated spherical field measurements is proposed. It is based on the substitution of the actual antenna by a finite number of equivalent infinitesimal dipoles (electric and magnetic), distributed over the antenna aperture. This equivalent set of elementary dipoles is optimized using the transmission coefficient involving the spherical wave expansion of the measured field and using an appropriate matching method. Once the current excitation of each dipole is known, the radiated field of the antenna at different distances can be rapidly determined. The reliability and the accuracy of the method are shown using experimental data issued from the measurement of an X-band horn antenna, in two different measurement setups

Transient UWB Antenna Near-Field and Far-Field Assessment From Time Domain Planar Near-Field Characterization: Simulation and Measurement Investigations

International audience— In this paper we present the experimental validation of Time-Domain (TD) Near-Field to Near-Field (NFNF) and Near-Field to Far-Field (NFFF) transformations for UWB antenna transient characterization. The used computation schemes for near-field to near-or far-field transformations are based on the Green's function representation of the radiated field where NF and FF are directly calculated in the time domain. The first step of the validation process comprises the electromagnetic simulation results dedicated to evaluate the accuracy of NFFF and NFNF transformations. The second step uses near-field measurement data of a Vivaldi antenna to validate the developed computation schemes whereas the measurement and calibration procedures are fully described. The measured NF data using Supelec planar and cylindrical near-field facilities are also compared with the electromagnetic simulation transient results of the Vivaldi antenna