Using low microwave frequencies (up to 2 GHz) through a monostatic analysis, the signature of a metallic target behind a thick brick wall is detected and resolved. An alternative approach using cepstral analysis is introduced for resolving the target's signature from that of the wall, which is particularly beneficial at close proximity when both signatures merge in the time domain. The use of lower frequencies combined with the monostatic analysis provides for greater flexibility in operational requirements, frequency spectrum constraints, and cost of transceivers, as well as a better wall penetration of the electromagnetic waves. Additionally, the introduction of the cepstrum-domain analysis opens a new window for detection and identification research in the field of through-wall remote sensing.

A method of enhancing the performance of a numerical FM discriminator in specific receive signal conditions, using frequency feedback techniques, is developed and evaluated. The receive signal conditions of interest are: (1) frequency deviations that are large relative to the bandwidth of the message signal; (2) a low-uniform (complex) sample rate commensurate with the bandwidth; and (3) noise strengths that yield values of input carrier-to-noise ratio of the order of 10 dB or more. Through computer simulation, observed phase cycle-slip counts and phase noise variance estimation are used to compare the enhanced demodulator to the performance of a numerical FM discriminator baseline. Based upon the theoretical analyses and simulation results, the presented method of numerical FM demodulation is shown to be a viable technique for enhancing the performance of numerical FM discriminators under the given modulation conditions.

J.C. Bose, a physicist from India, developed a semiconductor receiver for the detection of millimeter waves (60 GHz) during 1894-1896. Interestingly, Bose's galena receiver, for which he received a patent (application filed September 30, 1901, issued March 29, 1904), is the forerunner of semiconductor diode detectors. This paper reviews the pioneering work of Bose in the area of millimeter waves and appraises the circumstances leading to the development and construction of such a device.

This paper proposes two alternative techniques for the Direction-of-Arrival (DOA) estimation. Both techniques utilize the respective modifications of the conjugate gradient method (CGM) for iteratively finding the weight vector which is orthogonal to the signal subspace. In the first method, an eigenvector corresponding to the smallest eigenvalue is computed by minimizing the Rayleigh quotient of the full complex-valued autocovariance matrix. In the second method, a vector which is orthogonal to the signal subspace is computed directly from the signal matrix by finding a set of weights that minimizes the signal power at the array output. The performances of the proposed techniques are compared to that of the conventional eigen-decomposition (ED) method in terms of angle resolution for a given signal-to-noise ratio (SNR) with a preset number of snapshots in an observation interval. The standard deviation of angle dispersions is also encountered in measuring the array performance when a large number of inseparable signal components are involved in each cluster of the array inputs. From our computer simulations, we found that the proposed techniques in general result in comparable performances to the conventional ED method. The superiority of the suggested procedures becomes evident in adverse signal environments where the detection of the number of array inputs cannot be obtained successfully, for the proposed techniques are performed independently of the detection procedure. Dieser Aufsatz stellt zwei alternative Verfahren zur Schätzung der Einfallsrichtung (DOA) vor. Beide Methoden verwenden die jeweiligen Modifikationen der Methode der konjugierten Gradienten (CGM) zur iterativen Berechnung eines orthogonal auf dem Signal-Unterraum stehenden Gewichtsvektors. Im ersten Verfahren wird der zum kleinsten Eigenwert gehörende Eigenvektor durch Minimierung des Rayleigh-Quotienten der voll komplexwertigen Autokovarianzmatrix berechnet. Im zweiten Verfahren erhält man einen zum Signal-Unterraum orthogonalen Vektor direkt aus der Signalmatrix, durch Berechnung der Gewichte, die die Signalleistung am Ausgang des Sensorfeldes minimieren. Die Ergebnisse der vorgestellten Methoden werden mit den Ergebnissen einer konventionellen Eigenwertmethode (ED-Methode) anhand von Winkelauflösungen für einen vorgegebenen Signal-zu-Rausch-Abstand (SNR) und eine vorgegebene Anzahl an Abtastwerten innerhalb eines Beobachtungsintervalls verglichen. Die Standardabweichung der Winkelstreuung wird ebenfalls betrachtet, wenn eine groβe Anzahl von untrennbaren Signalkomponenten in jeden Satz der Eingangsdaten des Sensorfeldes eingehen. Unsere Computersimulationen zeigten, daβ die hier vorgestellten Methoden im allgemeinen eine mit herkömmlichen ED-Methoden vergleichbare Leistungsfähigkeit aufweisen. Die Überlegenheit der vorgeschlagenen Verfahren wird in ungünstigen Signalumgebungen deutlich, wenn die Entdeckung der Anzahl der Signalkomponenten in den Eingangsdaten des Arrays nicht mehr zuverlässig ist, denn die vorgestellten Methoden arbeiten unabhängig von den Detektionsalgorithmen. Cet article propose deux techniques alternatives pour l'estimation de la Direction-d'Arrivée (DA). Les deux méthodes utilisent les modifications respectives de la méthode du gradient conjugué (MGC) pour trouver itérativement le vecteur de pondération qui est orthogonal au sous-espace du signal. Dans la première méthode, un vecteur propre, correspondant à la valeur propre la plus petite, est calculé en minimisant le quotient de Rayleigh de la matrice d'autocovariance complexe. Dans la seconde méthode, un vecteur orthogonal au sous-espace du signal est calculé directement à partir de la matrice du signal en trouvant un ensemble de pondérations qui minimise la puissance du signal à la sortie du réseau. Les performances des techniques proposées sont comparées à celles de la méthode conventionelle par décomposition en valeurs singulières (DVS) en termes de résolution d'angle pour un rapport signal-sur-bruit donné et un nombre prédéfini d'instantanés dans un intervalle d'observation. La déviation standard des dispersions d'angle est également considérée en mesurant la performance du réseau lorsqu'un nombre conséquent de composantes inséparables du signal entrent en jeu dans chaque noeud des entrées du réseau. Les simulations informatiques ont montré que les techniques proposées ont en général des performances comparables à celles de la DVS conventionelle. La supériorité des procédures présentées devient évidente dans des environnements adverses, ou la détection du nombre d'entrées dans le réseau ne peut pas être réalisée avec succès, car les procédures décrites sont effectuées indépendamment de la procédure de détection.

This paper proposes an alternative method of synthesizing a two-dimensional antenna array of which the pattern can be controlled as a function of arrival angle of array input. The new technique includes a procedure of extending a Tseng window in two dimensions by means of rotation. The beam maximum and pattern null can arbitrarily be steered to the direction of desired signal and jamming interferences, respectively. This paper shows how to select one-dimensional Tseng window properly, extend it to two dimensions maintaining the circular symmetry, and finally apply the two-dimensional window to array synthesis. The resultant array is employed for detecting AM signal in the presence of strong jammers which are up to 100 dB above the signal level. Der Beitrag stellt eine Methode zur Synthese einer zweidimensionalen Belegungsfunktion einer Gruppenantenne vor, bei der die Richtcharakteristik in Abha¨ngigkeit von der Richtung der einfallenden Wellen vera¨ndert wird. Die neue Methode umfaßt ein Konzept zur Erweiterung des ‘Tseng window’ auf zwei Dimensionen, so daß Hauptstrahlrichtung und Nullstellen auf beliebige Einfallsrichtungen des erwu¨nschten bzw. des sto¨renden Signals ausgerichtet werden ko¨nnen. Im Beitrag wird darauf eingegangen, wie das eindimensionale ‘Tseng window’ geeignet ausgewa¨hlt und auf die zweidimensionale Antennenbelegungu¨bertragen wird. In einer Simulation wird die Anwendung der derartig synthetisierten Gruppenantenne auf den Fall des Empfang eines AM-Signals in Gegenwart eines bis zu 100 dB sta¨rkeren Sto¨rsignals gezeigt. Cet article propose une me´thode alternative pour synthe´tiser un tableau d'antennea`deux dimensions pour lequel lese´le´ments peuventeˆtre controˆles comme une fonction de l'angle d'arrive´e du tableau d'entre´e. Cette nouvelle technique inclut une proce´dure d'extension de la feneˆtre de Tseng en deux dimensions au moyen de la rotation. Le rayon maximum et lese´le´ment nuls peuventeˆtre respectivement dirige´s vers la direction du signal de´sire´et le brouillage d'interfe´rences. Cet article montre comment se´lectionner correctement une feneˆtre de Tseng unidimensionnelle, l'e´tendrea`deux dimensions tout en maintenant la syme´trie circulaire, et finallement appliquer la feneˆtre bi-dimensionnellea`la synthe`se de tableaux. Le ableau ainsi obtenu est alors utilise´pour la de´tection du signal AM en pre´sence d'un fort brouillage de 100 dB au-dessus du niveau du signal.

This paper addresses a multipath fading problem occurring in mobile communications. At each antenna element, there arrives a number of clusters of signals each of which consists of a large number of signal components with their own arrival angles. The clusters are distinguished from each other by distinct group delays. This paper suggests a new efficient method of eliminating the multipath fading that can be used regardless of modulation technique. Since the problem is formulated independently from the arrival angle of each signal component, the array can resolve the multipath effects with a reasonable number of antenna elements even when there exist a large number of signal components. The angles of arrival may be distributed very closely to each other. In fact, the array designed in this paper can reduce the multipath effects once the number of antenna elements is equal to the number of distinct clusters. The new method utilizes a modified conjugate gradient method (CGM) for iteratively computing the optimal weights of the antenna elements. To generate the excitation vector which is required by the CGM, it is assumed that a set of known symbols are sent at each frame. This paper includes many practical examples of various PSKs and 16QAM, and the array performances are shown in many different signal environments in terms of bit-error-rate (BER) performance. From the extensive analysis and various computer simulations, we conclude that the CGM shown in this paper is suitable to adapt for an antenna array in an efficient way for mobile communication. Diese Arbeit behandelt ein Mehrwege-Fading-Problem, das in der mobilen Kommunikation auftritt. An jedem Antennenelement erscheint eine Anzahl von Signal-Clustern, wobei jedes von ihnen aus einer groβen Anzahl von Signalkomponenten mit eigenen Empfangsphasen besteht. Die Cluster sind untereinander aufgrund ihrer spezifischen Gruppenlaufzeiten zu unterscheiden. In der vorliegenden Arbeit wird eine neue effiziente Methode zur Beseitigung von Mehrwege-Fading vorgeschlagen, die unabhängig von der jeweiligen Modulationsform angewendet werden kann. Da das Problem unabhängig von den Empfangsphasen der einzelnen Signalkomponenten formuliert wird, kann das Array die Mehrwege-Effekte mit einer vernünftigen Anzahl von Antennenelementen lösen, selbst wenn eine groβe Anzahl von Signalkomponenten vorliegt. Die Empfangsphasen können dabei sehr eng zusammenliegen. Praktisch können die Mehrwege-Effekte durch das vorgeschlagene Array beseitigt werden, sobald die Anzahl von Antennenelementen gleich der Anzahl der Signal-Cluster ist. Die neue Methode verwendet ein modifiziertes konjugiertes Gradientenverfahren (CGM) für die iterative Berechnung der optimalen Gewichte für die Antennenelemente. Um einen Erregungsvektor zu generieren, der für das CGM benötigt wird, ist anzunehmen, daβ in jedem Rahmen eine Folge bekannter Symbole übertragen wird. Die Arbeit enthält viele praktische Beispiele für PSK und 16QAM; die Funktion des Arrays wird für viele verschiedene Übertragungsbedingungen anhand der Bitfehlerrate (BER) demonstriert. Aufgrund der ausführlichen Analyse und einer Vielzahl von Computer-Simulationen kann geschlossen werden, daβ der in dieser Arbeit eingeführte CGM zur effizienten Adaption von Antennen-Arrays geeignet ist. Ce papier traite du problème d'évanouissement à plusieurs voies, qui a lieu dans les communications mobiles. A chaque élément d'antenne, il arrive un certain nombre de groupes de signaux dont chacun consiste en un grand nombre de composantes du signal, avec leur propre angle d'arrivée. Les groupes de signaux se distinguent les uns des autres par des retards de groupes différents. Cet article suggère une nouvelle méthode efficace pour éliminer l'évanouissement à plusieurs voies, qui peut être utilisé quelle que soit la technique de modulation. Comme le problème est formulé indépendamment de l'angle d'arrivée de chaque composante du signal, la rangée peut résoudre les effets à chemin multiple avec un nombre raisonnable d'éléments d'antennes, même s'il existe un grand nombre de composantes de signaux. Les angles d'arrivée peuvent être distribués très proches les uns des autres. En fait, la rangée élaborée dans cet article peut réduire les effets multi-chemin dès que le nombre d'éléments d'antennes est égal au nombre de groupes de signaux distincts. La nouvelle méthode utilise une méthode de gradient conjugué modifié pour calculer itérativement les poids optimum des éléments d'antennes. Pour générer le vecteur d'excitation qui est nécessité par la méthode du gradient conjugué, il est admis qu'un ensemble de symboles connus est transmis dans chaque trame. Cet article comprend plusieurs exemples pratiques de modulations de phase discrète et d'amplitude en quadrature à 16 niveaux. Les performances des rangées sont montrées dans différentes environnements des signaux en termes de cadence d'erreur de bits. De l'analyse extensive de simulation sur ordinateur varié, nous concluons que la méthode de gradient conjugué, montrée dans cet article, convient pour adapter une rangée d'antennes pour les communications mobiles d'une façon très efficace.

A technique for estimating the spatial and temporal parameters of multiple transient signals impinging on a uniform linear array is proposed. Each transient signal is assumed to be the sum of complex exponentials arriving at the array from a different direction. The technique is based on the subspace decomposition and matrix pencil (SDMP) approach which can be implemented by solving for eigenvectors and eigenvalues. Simulations show that the subspace-decomposition and matrix-pencil method can achieve the Cramer-Rao bound.>

An E-field integral equation for the computation of the radar cross section of finite composite conducting and lossy inhomogeneous dielectric bodies is presented. The equivalence principle is used to replace all conducting bodies by an equivalent surface electric current, and the dielectric is replaced by an equivalent volume polarization current. The respective boundary conditions on the dielectric and the conductor are utilized to solve for the electric current on the entire structure. Also the augmented conjugate gradient method is presented for the solution of extremely large systems of equations that arise in the present problem. Finally, typical results are presented to illustrate the potential of this method.>

A novel method called matrix pencil method for estimating poles or frequencies from exponentially damped or undamped sinusoidal sequences is presented as an alternative to either the ESPRIT or pencil-of-functions method. A singular generalized eigenvalue problem in this method is solved in several different ways. First-order perturbation analysis reveals many fundamental perturbation properties of the new method. It is found consistently from both theoretical and simulation results that it performs better than the high-performance polynomial method of R. Kumaresan and D.W. Tufts (1982).>

The three methods (Prony's, Pisarenko's and Pencil-of-Function Methods) used for wave direction estimation based on one snapshot outputs of uniform linear array are studied for high SNR case.

Hankel matrix systems often arise in many problems of signal analysis. Toeplitz matrix systems is a special case of a Hankel matrix equations. Both the auto-correlation and the covariance matrix equations are different forms of the Hankel matrix equations. Trench has developed a direct method that can solve Hankel matrix equations in θ(N2) operations. In this paper, we propose an alternate algorithm. This new method is a combination of the FFT and the conjugate gradient method. The advantage of this new approach is that it is computationally robust to highly ill-conditioned and even singular matrix equations. Preliminary results indicated that for very large complex Toeplitz matrix equations, the CPU time is proportional to N as the number of unknowns as increased, as opposed to N2for conventional methods.

Evaluation of the time-domain response of multiconductor transmission lines is of great importance in the analysis of the crosstalk in fast digital circuit interconnections, as well as in the analysis of power lines. Several techniques for the computation of the line response, starting from the known circuit-theory parameters, are presented and evaluated. These methods are: time-stepping solution of the telegrapher equations, modal analysis in the time domain, model analysis in the frequency domain, and a convolution technique which uses line Green's functions. The last method can treat the most general case of lossy transmission lines with nonlinear terminal networks. Numerical and experimental results are presented to illustrate these techniques and to give insight into the crosstalk problems in fast digital circuits.

In this paper we discuss the Half Fourier Transform (HFT) and explore its application to radar-return signals with specular components. It is shown that this transform enables separation of the desired part from the specular impulsive components. The effectiveness of this technique and the computer program developed, is demonstrated by simulation examples. Our program uses an optimization package which performs minimization of a nonlinear sum-of-squares functional with a model trust region strategy.

Pisarenko's harmonic retrieval method provides unbiased spectral estimates of a signal consisting of the sum of n sinusoidal signals in additive white noise. Recently, a few adaptive versions based on Pisarenko's method have been developed. In this paper we propose an alternative technique for adaptive spectral estimation based on the method of conjugate gradient, which is used for iteratively finding the eigenvector corresponding to the minimum eigenvalue of the covariance matrix. The new method is an exact adaptive version of Pisarenko's method and converges in finite steps for any initial guesses. Simulations have been performed to compare the new method with the existing ones. It is seen that the new method improves the CPU time by a factor of 40. Also, the technique performs very well for both narrow band and wide band signals.

Since it is practically difficult to generate and propagate an impulse, often a system is excited by a narrow time domain pulse. The output is recorded and then a numerical deconvolution is often done to extract the impulse response of the object. Classically, the fast Fourier transform technique has been applied with much success to the above deconvolution problem. However, when the signal to noise ratio becomes small, sometimes one encounters instability with the FFT approach. In this paper, the method of conjugate gradient is applied to the deconvolution problem entirely in the time domain. The method converges for any initial guess in a finite number of steps. Also for the application of the conjugate gradient method the time samples need not be uniform like FFT. Computed impulse response utilizing this technique has been presented for measured incident and scattered fields from a sphere and a cylinder.

An adaptive spectral analysis technique is presented for estimating complex frequencies in colored noise. It is assumed that the noise covariance matrix of the colored noise is known. The method presented in this paper is similar to Thompson's technique of an on line estimation of the eigenvector of the covariance matrix corresponding to the minimum eigenvalue, without explicitly evaluating the covariance matrix. The method of conjugate gradient has been utilized to obtain the eigenvector corresponding to the minimum eigenvalue. The advantages of this technique over the method of steepest descent is that it is a finite step iterative method and secondly there is no arbitrary constants in the expression which dictates the overall rate of convergence. In the proposed method, the spread of the eigenvalues has no significant effect on the overall rate of convergence. The disadvantage of this technique is that one has to store a matrix of data instead of one row only, as is conventionally done. The proposed method however yields unbiased estimates for the frequencies in colored noise.

Resolution of two sinusoidal signals of frequencies f1and f2requires a time record of length at least1/|f_{1}-f_{2}|. Resolution of two decaying exponentials of complex frequencies s1= σ1+jω1and s2= σ2+jω2, with\sigma_{2} \leq \sigma_{1}, by correlation coefficient is independent of the ratios σ2/σ1, and (ω1- ω2)/σ1for a time record of length greater than3/|\sigma_{1}|. This is also the condition for near-orthogonalization of a set of complex exponentials, with small error.

The paper describes very recent and promising results on a new approach to noise correction for pole-zero modeling of signals by the pencil-of-functions method. In contradistinction to spectral subtraction techniques where only amplitude information is emphasized (and phase is ignored), we propose a method that (a) estimates the noise spectral density for the frame, and then (b) performs the subtraction of the noise correlation matrix from the correlation matrix of the information signals. The information signals are, of course, generated by processing the test signal by a cascade of first-order low pass signals, as described in earlier papers. Improvement resulting from this noise correction technique is particularly remarkable when judged by the pole-estimation accuracy, A comparison of the poles for multiple noise runs for three methods, namely, (a) Prony method, (b) Pencil-of-functions method, and (c) Pencil-of-functions method with noise correction, is given. The signal considered was the impulse response of a third order rational filter H(z), masked by noise with an SNR=12 dB.

Pole-zero modeling of low-pass signals, such as an electromagnetic-scatterer response, is considered in this paper. It is shown by use of pencil-of-functions theorem that (a) the true parameters can be recovered in the ideal case (where the signal is the impulse response of a rational function H(z)), and (b) the parameters are optimal in the generalized least-squares sense when the observed data are corrupted by additive noise or by systematic error. Although the computations are more involved than in all-pole modeling, they are considerably less than those required in iterative schemes of pole-zero modeling. The advantages of the method are demonstrated by simulation example and through application to the electromagnetic response ofa scatterer. The paper also includes very recent and tantalizing results on a new approach to noise correction. In contradistinction with spectral subtraction techniques, where only amplitude information is emphasized (and phase is ignored), we propose a method that (a) estimates the sample variance for the particular data frame, and then performs the subtraction from the Gram matrix.