J. Cummins

Internal noise in the SNR optimization of receiving arrays

The problem of obtaining the maximum signal-to-noise ratio (SNR) of a receiving array is considered. The formulation includes noise due to internal as well as external sources. The concept of a mean spatial noise temperature is introduced for the purpose of defining the normalized SNR of an array as a useful criterion for evaluating its performance with respect to signal and noise. The theory is applied to a specific array and a discussion of the results is presented.

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].

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.

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.