G. Delisle

Moving target imaging and trajectory computation using ISAR

Novel algorithms for moving target imaging and trajectory computation using a two-receiver radar are presented. The range-bin alignment is implemented with an adaptive method using the envelope correlation feature of different returns and the angular trajectory equation is solved using a linear least squares method combined with a unique phase-unwrapping technique. The angular positions of the synthetic array elements are determined from the trajectory computation. Three target models moving along a perturbed straight line are used to verify the proposed algorithms. >

Lens-fed multiple beam array for millimeter wave indoor communications

This article shows a printed circuit lens fed multiple beam antenna array designed for millimeter wave indoor personal communication systems, which is formed by using of a linear array of equally spaced elements, fed with an improved printed circuit Rotman lens. Both the lens and the array are designed and built on the same dielectric substrate. The antenna operates in frequency range of 27-30 GHz and covers an angular sector near 120 degrees with 11 beams. A full azimuth coverage can be obtained through a set of three antenna arrays. Simulation results of phase and amplitude distributions, radiation pattern prediction as well as application considerations are given.

Method of admittance matrix measurement of an antenna array

A method is described for measuring the admittance matrix of an antenna array considered as an N-port network. The method utilizes the properties of hybrid junctions to apply at the antenna ports, taken two at a time, with all other ports short-circuited, two pairs of incident voltages of known amplitudes and phases. Measurements are obtained of the reflections coefficients ( \Gamma ) and of the input admittances ( Y_{in} ) at the pair of antenna ports under test for both modes of excitations. The desired admittance parameters are then easily determined from the measured quantities as shown in the formulation given below. The proposed method applies to arbitrary arrays and is gererally easier to implement than those that are now available [1-4].

Generalized multiple scatterer algorithm for ISAR phase compensation

In inverse synthetic aperture radar (ISAR) imaging, the random phase errors of the inverse synthetic aperture must be compensated. This paper presents a generalized multiple scatterer algorithm (GMSA) for ISAR phase compensation. Experimental data processing and simulations show that the image noise can be reduced significantly with the proposed method.

Phase Control in Multibeam Arrays

The phases of the radiation fields in a multibeam antenna are analyzed and their relations to the feed network are established. A method of phase control is proposed and applied to the case of cophasal beams radiated from an array for which the feed network is a lossless Butler matrix.

Using directive antennas to reduce multipath fading in indoor PCN systems

There is a growing need for indoor wireless PCN systems to provide high speed digital transmission between computer terminals and peripherals. Millimeter-waves were selected to implement this new system application, because of the capability to allow easy frequency re-use and the development of MMIC technology. This paper focuses on the characteristics of the MM-waves propagation with particular emphasis on the utilization of antenna directivity to combat multipath fading. Experimental results were conducted at 37.2 GHz under line-of-sight conditions. CW recordings are analyzed in terms of small-scale fading and path loss.

Phase behavior of radar cross-sections. Theoretical and experimental results

The radar cross section (RCS) of any object is a complex quantity that possesses both an amplitude and a phase. While the former is fairly widely documented in the literature, the latter is conspicuous by its almost total absence. An attempt is made to introduce some of the distinguishing characteristics of the phase, the factors that govern its behaviour and its utility in recognizing targets. Comparisons between theory and practice are presented.<<ETX>>

Signal-to-noise ratios of array receiving systems with internal losses

A formulation of the signal-to-noise ratio (SNR) for a typical antenna array receiving system that is more complete than those now available in the literature is presented. In addition to the external noise accepted by the array, it includes all forms of internal noise generated by the lossy components of the system. Distinct measurable factors account for distinct noise sources. For the analysis, it is shown that the actual lossy system can be replaced by an equivalent lossless system with appropriate attenuators. The formulation is used to design the combining network that will optimize the receiving system SNR for signals incident from a given direction in the presence of a known external noise distribution. The theory is applied to a specific array antenna receiving system operating under a variety of noise conditions, internal as well as external. A discussion of some typical results is presented.

Modélisation d’une antenne-réseau et traitement optimal

AnalyseLes auteurs modélisent une antenne-réseau par un filtre linéaire multipolaire dont une des entrées correspond à une source à grande distance dans une direction donnée, ce filtre est caractérisé par sa matrice d’admittance. L’exemple des antennes électromagnétiques formées de conducteurs filiformes parallèles sert à montrer comment cette matrice peut être calculée numériquement, par des équations discrètes de propagation (méthode des moments de Harrington). La formulation des traitements optimaux à rémission (maximalisation du gain avec ou sans contrainte) et à la réception (maximalisation du rapport signal à bruit), au moyen de la matrice d’admittance, permet d’inclure dans l’optimalisation, un modèle de propagation réaliste tenant compte des pertes dans l’antenne, du couplage entre ses éléments et du bruit engendré par le système de réception. On peut ainsi procéder à une optimalisation géométrique de l’antenne et étudier les phénomènes de superdirectivité.AbstractAn array antenna is modeled after a linear multipole filter, one part of which is connected to a distant source, radiating in a specified direction, while the relations between the other parts are characterized by the antenna admittance matrix.This modeling technique is applied to an array of parallel linear wire antennas. It is shown how the array admittance matrix can be evaluated numerically by a discrete quantization of the Maxwell’s equations with the proper boundary conditions (Harrington’s method of moments). The admittance matrix is then used to formulate the optimum signal processing for transmission (maximization of antenna gain, with or without constraints) and for reception (maximization of signalto-noise ratio). Along with the model of the array antenna that is submitted, a method of signal processing is developed in which accurate estimates are included of the losses that occur within the array elements as well as of the coupling between elements and of the noise arising in the receiving system. The antenna designer can thus optimize the geometric configuration of the array and study the phenomenon of superdirectivity with a more realistic approach than was hitherto possible.