Edward J. Rothwell

The singularity expansion method and its application to target identification

The singularity expansion method (SEM) for quantifying the transient electromagnetic (EM) scattering from targets illuminated by pulsed EM radiation is reviewed. SEM representations for both induced currents and scattered fields are presented. Natural-resonance-based target identification schemes, based upon the SEM, are described. Various techniques for the extraction of natural-resonance modes from measured transient response waveforms are reviewed. Particular attention is given to the aspect-independent (extinction) E-pulse and (single-mode) S-pulse discriminant waveforms which, when convolved with the late-time pulse response of a matched target, produce null or mono-mode responses, respectively, through natural-mode annihilation. Extensive experiment results for practical target models are included to validate the E-pulse target discrimination technique. Finally, anticipated future extensions and areas requiring additional research are identified. >

Radar target discrimination using the extinction-pulse technique

An aspect independent radar target discrimination scheme based on the natural frequencies of the target is considered. An extinction-pulse waveform upon excitation of a particular conducting target results in the elimination of specified natural modal content of the scattered field. Excitation of a dissimilar target produces a noticeably different late-time response. Construction of appropriate extinction-pulse waveforms is discussed, as well as the effects of random noise on their application to thin cylinder targets. Also presented is experimental verification of this discrimination concept using simplified aircraft models.

Investigation of Simulated annealing, ant-colony optimization, and genetic algorithms for self-structuring antennas

A self-structuring antenna (SSA) is capable of arranging itself into a large number of configurations. Because the properties of the configurations are generally unknown at the onset of operation, efficient search algorithms are required to find suitable configurations for a given set of environmental and operational conditions. This paper investigates the use of ant-colony optimization, simulated annealing, and genetic algorithms for finding suitable antenna states. The implementation of each algorithm for SSA searches is described, and the performance of each algorithm is compared to a random search.

Radar target discrimination by convolution of radar return with extinction-pulses and single-mode extraction signals

A new method of radar target discrimination and identification is presented. This new method is based on the natural frequencies of the target. It consists of synthesizing aspect-independent discriminant signals, called extinction-pulses (E-pulses) and single-mode extraction signals which, when convolved numerically with the late-time transient response of an expected target, lead to zero or single-mode responses. When the synthesized, discriminant signals for an expected target are convolved with the radar return from a different target, the resulting signal will be significantly different from the expected zero or single-mode responses, thus, the differing targets can be discriminated. Theoretical synthesis of discriminant signals from known target natural frequencies and experimental synthesis of them for a complex target from its measured pulse response are presented. The scheme has been tested with measured responses of various targets in the laboratory.

Frequency domain E-pulse synthesis and target discrimination

A frequency domain approach to the E -pulse radar target discrimination scheme is introduced. This approach is shown to allow easier interpretation of E -pulse convolutions via the E -pulse spectrum, and leads to a simplified calculation of pulse basis function amplitudes in the E -pulse expansion. Experimental evidence obtained using aircraft models verifies the single-mode discrimination scheme, as well as the aspect-independent nature of the E -pulse technique. This leads to an integrated technique for target discrimination combining the E -pulse with single mode extraction waveforms.

Miniaturization of Patch Antennas Using a Metamaterial-Inspired Technique

A new design methodology for producing highly miniaturized patch antennas is introduced. The methodology uses complementary split-ring resonators placed horizontally between the patch and the ground plane. By optimizing the geometry of the split rings, sub-wavelength resonance of the patch antenna can be achieved with a good impedance match and radiation characteristics comparable to those of a traditional patch antenna on a finite ground plane. Construction of the optimized antenna is straightforward, requiring only the sandwiching of two etched circuit boards. High levels of miniaturization are demonstrated through simulations and experiments, with reductions of a factor of more than four in transverse dimension achieved for a circular patch resonant at 2.45 GHz. Although miniaturization is accompanied by a decrease in antenna radiation efficiency and a loss of fractional bandwidth, antenna performance remains acceptable even for a 1/16 reduction in patch area.

Extraction of the natural frequencies of a radar target from a measured response using E-pulse techniques

A new scheme is introduced for extracting the natural resonance frequencies of a radar target from a measured response. The method is based on the E -pulse technique and is shown to be relatively insensitive to random noise and to estimates of modal content. Verification of the technique is accomplished by comparing the natural frequencies extracted from the measured responses of a thin cylinder and a circular loop with those obtained from theory. The applicability of the technique to low- Q targets is also demonstrated, using the measured response of a scale model aircraft.

Performance of an automated radar target discrimination scheme using E pulses and S pulses

Previous studies have demonstrated the viability of natural resonance based target discrimination using extinction pulses (E pulses) and single-mode pulses (S pulses). These studies qualitatively demonstrated the principles of resonance annihilation by forcing the interrogating pulse to have zeros at the complex natural resonance frequencies of the target. Here a quantitative scheme for evaluating discrimination using the E pulse and the S pulse is given. The performance of an automated E-pulse and S-pulse discrimination scheme is evaluated using numerically derived scattering data with varying amounts of noise. >

Scattering center analysis of radar targets using fitting scheme and genetic algorithm

Development of successful radar target discrimination schemes using ultrawideband signatures hinges on an accurate understanding of the scattering behavior of complex radar targets. Since it is very difficult to calculate the scattered field of complex targets theoretically, a mathematical model (Altes (1976) model) representing scattering center impulse response has been developed to describe the scattered field. The extraction of temporal positions, pulse responses, and transfer functions of target scattering centers is demonstrated using artificially created and measured responses. Two different scale aircraft models (B-58 and B-52) are utilized. The fitting scheme based on the least squares method is quite satisfactory but its accuracy deteriorates when the overlapping of scattering-center pulse responses is severe. To overcome this problem a genetic algorithm is used to improve the results. While the genetic algorithm gives much better accuracy, it consumes much more computer time due to its global nature and lack of derivative information. The purpose of this analysis is to provide a method to reduce data storage for ultrawideband signatures in target discrimination.

Self-structuring antennas

This paper introduces a new class of antennas, called self-structuring antennas (SSAs). An SSA has the ability to alter its electrical shape in response to changes in its environment. This property makes an SSA suitable for use in a number of traditionally difficult antenna situations. The basic principles of the SSA are introduced, and a number of potential applications are highlighted. Details of a simple prototype antenna are provided. Computer tools capable of analyzing the SSA are described, and results of both numerical and experimental investigations of the SSA are presented.