Andrew J. Terzuoli

Bistatic scattering characterization of complex objects

Although much of the radar development over the past fifty years has been focused in the monostatic domain, a bistatic detection approach offers several key benefits. Without proper understanding of the bistatic scattering mechanisms, utilization of these benefits may not be fully realized This paper addresses some phenomenological aspects of bistatic scattering from a complex object with an emphasis on specular, shadowing, dihedral and cavity effects. Both ray tracing and scattering center approaches are used to describe the bistatic mechanisms. An appraisal of the effectiveness and utility of the bistatic equivalence theorems and several commercial scattering prediction codes are also accomplished. Finally some rules of thumb are proposed to help guide the reader in evaluating the bistatic scattering of complex shapes in general.

An investigation of bistatic calibration objects

Several popular metallic bistatic calibration objects are investigated, including a sphere, long and short cylinders, dihedral, trihedral, circular disk and wire mesh. Comparisons are made between the advantages and disadvantages of various objects for calibration. The analysis addresses sensitivity to object alignment error, availability of accurate radar cross section (RCS) calculations and bistatic RCS levels. Both theoretical concepts and practical considerations are discussed based on measurements accomplished at the European Microwave Signature Laboratory (EMSL) of the EC Joint Research Center (JRC) in Ispra, Italy. This facility has the capability to produce far-field fully polarimetric precision bistatic measurements in a 30 cm diameter quiet zone, suitable for comparing different calibration objects.

FDTD analysis of a new leaky traveling wave antenna

A new antenna is proposed based on a structure first constructed by Menzel (1979) that utilizes the leaky wave phenomena of the first higher order mode. This work seeks to determine the effect on performance of the antenna due to varying geometries. Standard antenna range far-field and near-field measurements are not sensitive enough to extract the propagation constant. A numerical simulation was thus developed using the finite difference time domain (FDTD) method to extract the propagation constant. The simulation was validated with published analytical data as well as measured data.

An investigation of bistatic calibration techniques

Several popular bistatic calibration techniques are investigated and comparisons made between the relative merits of the various techniques. The analysis addresses sensitivity to object alignment error, sensitivity to polarization impurity, and ease of implementation. Both theoretical concepts and practical considerations are discussed based on measurements accomplished at the European Microwave Signature Laboratory of the European Commission Joint Research Center, Ispra, Italy. This facility has the capability to produce far-field fully polarimetric precision bistatic measurements in a 30-cm-diameter quiet zone, suitable for comparing different calibration methods.

On the concept of near field radar cross section

The notion of far field radar cross section (RCS) is intuitively pleasing in that it provides a measure of the scattering characteristics of an object independent of antenna orientation or range to the object. When the transmitting or receiving antenna of a radar move into the near field, the assumptions made to calculate far field RCS are no longer valid. This paper presents two definitions of near field RCS developed by Lee, Wang, and Labarre (1991), based on variations of the radar range equation: RCS1 and RCS2. Results of numerical simulations of a sphere and a square flat plate within the near field showed that these definitions failed to achieve the antenna orientation and range independence observed in far field RCS. The final conclusion drawn from this work is that the only physically meaningful quantity measured in a near field radar scenario is the ratio of the power received to the power transmitted called the power return ratio.

Evaluation of a Near-Field Monostatic-to-Bistatic Equivalence Theorem

This paper presents the results of an investigation to quantitatively determine the limits of Falconers monostatic-to-bistatic equivalence theorem (MBET). Falconer developed two extensions to Kells MBET: one that is applicable to near-zone data and one that is valid in both the near- and far-zone regions. This paper encompassed collecting and analyzing both monostatic and bistatic radar cross-section data for perfect electrically conducting objects. Specifically, the authors analyzed the effects of varying the transmission frequency, scattering object complexity, and receiver bistatic angle. Objects ranged in geometric complexity from simple canonical objects to multifaceted shapes that produce multiple reflections. Empirical data collected in the far zone were compared with the analytical predictions produced by a commercially available method-of-moment (MoM) code. The code was run at X-band through K-band frequencies for a comparison with the measured data. The empirical bistatic data were then compared with the estimate produced by the MBET to ascertain the region in which the MBET approximation is applicable. Finally, the MoM code was used to produce near-field scattering predictions to facilitate the evaluation of Falconers near-field MBET. It is shown that the complexity of the scatterer restricts the region of validity for the MBET, where shadowing and multipath interactions prevail. The disparity between the MBET accuracies for the different test objects used clearly illustrates this point.

Linear Ensemble Antennas Resulting from the Optimization of Log Periodic Dipole Arrays Using Genetic Algorithms

Optimization with genetic algorithms (GAs) has become both popular and realistic in the electromagnetic community with the growth in computers and precise electromagnetic computer programs. Intuition is often required for antenna design but GAs can instead define and search a large design space. Using this method results in a non-intuitive and yet very effective antenna architectures. This paper presents an integrated technique to optimize antennas whose basis is Log Periodic Dipole Arrays (LPDA). We use an aggregated fitness function in a multi-objective GA, the NSGA-II, and the optimization software package iSIGHT, along with the Graphical Numerical Electromagnetics Code (GNEC), a method of moments program for antenna design. The results of this design technique compare excellently to Yagi-Uda designs as well as produce acceptable antenna designs based on LPDAs.

1-D feature extraction using a dispersive scattering center parametric model

Automatic object recognition, the ability for a machine to classify an object it has detected, is an area of continual interest. The classification of objects requires extraction of discriminatory information, and this process is called feature extraction. The extractable features are inextricably tied to the type of sensor used, and this work addresses one-dimensional, high resolution radar (HRR). Several approaches have been proposed for feature extraction in HRR. One approach is based on finding sinusoids in noise by a sum-of-damped exponentials (DE) model. The features of the DE-based scattering models, range and amplitude, have been used for feature extraction, but the DE model simplistically assumes that all scattering centers on the object have the frequency response of an ideal point scatterer. The high potential improvement to the damped exponential model lies in estimating the frequency response of each scattering center uniquely. This improvement is based on the geometric theory of diffraction of (GTD) and the uniform theory of diffraction (UTD) and includes electromagnetic scattering theory as a basis for scattering center modeling. Research in adapting the DE models to include GTD/UTD has been performed, but has had limited implementation in object recognition problems. This work provides an analysis and a proof-of-concept for implementing the GTD/UTD-based dispersive scattering center (DSC) model to perform object recognition. The DSC model presented is based directly upon Potters (see IEEE Trans. Antennas Progagat., vol.43, p.1058-67, 1995) work at the Ohio State University.

Validation of near-field monostatic to bistatic equivalence theorem

The purpose of this research is to quantitatively determine the limits of Falconers monostatic to bistatic equivalence theorem (MBET). Falconer developed two extensions to Kells MBET, one applicable to near zone data and one valid in the far zone region. This work encompassed collecting and analyzing both monostatic and bistatic radar cross section (RCS) data for perfect electric conducting (PEC) objects. Specifically, this research analyzes the effects of varying the parameters of transmission frequency, object shape complexity, and receiver bistatic angle. Objects range in geometric complexity from canonical objects comprised of simple scatterers to multifaceted composites that sustain numerous interactions. Empirical data collected in the far zone are compared to analytical predictions produced by commercially available electromagnetic computer codes, both a method of moments (MoM) code and a near-field physical optics code. The codes ran at X-band through K-band frequencies for a comparison with object data. Further, the empirical bistatic data are compared to the estimate produced by the MBET, to ascertain the region in which the MBET approximation is applicable. Finally, electromagnetic computer codes are used to produce near-field scartering predictions to facilitate validation of Falconers near-field MBET.

A parallelized search strategy for solving a multicriteria aircraft routing problem

Currently, aircraft fighter pilots use some type of computer system to plot courses and determine fuel consumption. Even with a computer this is a time consuming tsak. The traditional auterouting problem is further complicated when the aircraft in question is considered to be one of “stealth” or lowobservable design. Research is being conducted irtto the use of supercomputers as aids to pilots in performing real-time mission routing. This paper presents the software engineering synthesis of an automated software tool, based on a parallelized search slgonthm, to determine mission routes from a real-time perspective. This investigation studies various areas of the mission routing problem in conjunction the efficient usage of a supercomputer system.