R. Shavit

Optimal Adaptive Waveform Design for Cognitive MIMO Radar

This paper addresses the problem of adaptive waveform design for estimation of parameters of linear systems. This problem arises in several applications such as radar, sonar, or tomography. In the proposed technique, the transmit/input signal waveform is optimally determined at each step based on the observations in the previous steps. The waveform is determined to minimize the Bayesian Cramér-Rao bound (BCRB) or the Reuven-Messer bound (RMB) for estimation of the unknown system parameters at each step. The algorithms are tested for spatial transmit waveform design in multiple-input multiple-output radar target angle estimation at very low signal-to-noise ratio. The proposed techniques allow to automatically focusing the transmit beam toward the target direction. The simulations show that the proposed adaptive waveform design methods achieve significantly higher rate of performance improvement as a function of the pulse index, compared to other signal transmission methods, in terms of estimation accuracy.

An efficient vector sensor configuration for source localization

An electromagnetic vector-sensor enables estimation of the direction of arrival (DOA) and polarization of an incident electromagnetic wave with arbitrary polarization. In this letter, an efficient vector-sensor configuration is proposed. This configuration includes the minimal number of sensors, which enables DOA estimation of an arbitrary polarized signal from any direction except two opposite directions on the z-axis. The configuration is obtained by analyzing the Cramer-Rao lower bound (CRLB) for source localization using a single vector-sensor. The resulting vector-sensor configuration consists of two electric and two magnetic sensors. It is shown that this quadrature configuration satisfies the necessary and sufficient conditions for the DOA estimation problem. The CRLB for DOA estimation of signals in the azimuth plane is identical for the quadrature and the complete vector-sensor configurations.

Dielectric cover effect on rectangular microstrip antenna array

A theoretical model to analyze a covered rectangular antenna with an arbitrary dielectric constant superstrate is developed. The antenna is simulated by the radiation of two magnetic dipoles located at the radiating edges of the patch. The Greens function of an elementary magnetic dipole in a superstrate-substrate structure, utilizing spectral-domain analysis, is formulated, and the surface-wave and radiation field are computed. An improved transmission line model, which considers the stored energy near the radiating edges and the external mutual coupling, is used to compute the input impedances and radiation efficiency. Design considerations on the superstrate thickness and its dielectric constant are discussed. Experimental data for a single element and a 4/spl times/4 microstrip array is presented to validate the theory. >

Direction of Arrival Estimation in the Presence of Noise Coupling in Antenna Arrays

The direction of arrival (DOA) estimation problem in the presence of signal and noise coupling in antenna arrays is addressed. In many applications, such as smart antenna, radar and navigation systems, the noise coupling between different antenna array elements is often neglected in the antenna modeling and thus, may significantly degrade the system performance. Utilizing the exact noise covariance matrix enables to achieve high-performance source localization by taking into account the colored properties of the array noise. The noise covariance matrix of the antenna array consists of both the external noise sources from sky, ground and interference, and the internal noise sources from amplifiers and loads. Computation of the internal noise covariance matrix is implemented using the theory of noisy linear networks combined with the method of moments (MoM). Based on this noise statistical analysis, a new four-port antenna element consisting of two orthogonal loops is proposed with enhanced source localization performance. The maximum likelihood (ML) estimator and the Cramer-Rao lower bound (CRLB) for DOA estimation in the presence of noise coupling is derived. Simulation results show that the noise coupling in antenna arrays may substantially alter the source localization performance. The performance of a mismatched ML estimator based on a model which ignores the noise coupling shows significant performance degradation due to noise coupling. These results demonstrate the importance of the noise coupling modeling in the DOA estimation algorithms.

Design of a new dual-frequency and dual-polarization microstrip element

A new type of a dual-frequency and dual-linear-polarization multilayer stacked microstrip antenna element is presented. The feeding mechanism of the element is aperture coupling for one polarization and direct feeding for the orthogonal polarization. The microstrip element exhibits a wide band of operation, high isolation between ports, and high radiation efficiency for both polarizations compared to other types of elements. A parametric study was conducted using a commercial software based on a method of moments (MoM) algorithm and is presented. A prototype with dimensions based on the simulations was built and tested. The agreement between the measured and numerical results is good.

Scattering analysis of high performance large sandwich radomes

Large radomes are assembled from many panels connected together forming joints or seams. When the panels are type A sandwiches that are optimized for minimum transmission loss over moderately narrow bandwidths, the seams and joints introduce scattering effects that can degrade the overall electromagnetic performance. Tuning the dielectric seams with conductive wires and optimizing their geometry is, therefore, crucial to enhancing the electromagnetic performance of the radome. The authors address the problem of systematically tuning the dielectric seams and present both numerical and experimental results to illustrate the tuning procedure. Included are results showing the effect of the tuning of the radome on the radiation of an enclosed aperture of circular or elliptic shape. >

Novel microwave near-field sensors for material characterization, biology, and nanotechnology

The wide range of interesting electromagnetic behavior of contemporary materials requires that experimentalists working in this field master many diverse measurement techniques and have a broad understanding of condensed matter physics and biophysics. Measurement of the electromagnetic response of materials at microwave frequencies is important for both fundamental and practical reasons. In this paper, we propose a novel near-field microwave sensor with application to material characterization, biology, and nanotechnology. The sensor is based on a subwavelength ferrite-disk resonator with magnetic-dipolar-mode (MDM) oscillations. Strong energy concentration and unique topological structures of the near fields originated from the MDM resonators allow effective measuring material parameters in microwaves, both for ordinary structures and objects with chiral properties.

Design of transverse slot arrays fed by a boxed stripline

A design procedure is described whereby the lengths and offsets of an array of transverse slots can be determined, in the presence of mutual coupling, when the slots are excited by a boxed stripline and when pattern and input impedance are specified. The design is based on two sets of simultaneous equations. One set relates the TEM scattering off each slot to the field distribution in the slot, in the manner of Stevenson. The other set relates the stripline-fed slot array to an equivalent, properly loaded slot array, center-fed by two-wire lines, whose mutual impedance terms are easily calculated. The procedure is illustrated by the design of an eight element linear array. Experimental data in support of the theory will be presented.

Errata to “Dual Frequency and Dual Circular Polarization Microstrip Nonresonant Array Pin-Fed From a Radial Line”

A new type of a dual frequency and dual circular polarization multilayer microstrip nonresonant antenna array for satellite communication is presented. The microstrip radiating elements in the array are arranged in concentric circles and fed through pins embedded in a radial line. The radial line is excited through a probe at its center. The microstrip array exhibits a dual frequency band of operation, low side-lobes in the radiation pattern, and high radiation efficiency (more than 65%) for both polarizations. The microstrip element has been designed using commercial software based on the method of finite integral time domain algorithm, and the feed network has been designed by a theoretical analysis. A prototype of the array has been built and tested. The agreement between the measured and numerical results is satisfactory.

Tellegen particles and magnetoelectric metamaterials

In 1948 Tellegen [Philips Res. Rep. 3, 81 (1948)] suggested that an assembly of the lined up electric-magnetic dipole twins can construct a new type of an electromagnetic material. Until now, however, the problem of creation of the Tellegen medium is a subject of strong discussions. An elementary symmetry analysis makes questionable an idea of a simple combination of two (electric and magnetic) dipoles to realize local materials with the Tellegen particles as structural elements. In this paper we show that in search of sources with local junctions of the electrical and magnetic properties one cannot rely on the induced parameters of small electromagnetic scatterers. No near-field electromagnetic structures and no classical motion equations for point charges give a physical basis for realization of sources with a local junction of the electrical and magnetic properties. We advance a hypothesis that local magnetoelectric (ME) particles should be physical objects with eigenmode oscillation spectra and noncla...