Radar target identification using a combined early-time/late-timeE-pulse technique

The E-pulse technique has been applied in the past to both the early- and the late-time components of a transient radar response. While the late-time E-pulse technique uses aspect-independent waveforms, the early-time E-pulse technique requires a separate waveform for each target aspect angle and thus significantly more storage and processing time. This paper discusses a combination of the two techniques that employs the early-time technique to remove ambiguities generated from application of the late-time method. By narrowing the possible range of aspect angles of the potential targets, the early-time technique can be employed more efficiently     

Subsectional-polynomial E-pulse synthesis and application to radartarget discrimination

A new family of extinction-pulses (E-pulses), called subsectional-polynomial E-pulses, is presented. This new type of E-pulse is constructed by choosing polynomials of degree Q as subsectional basis-functions in the E-pulse expansion. The main feature of this family of E-pulses is that the waveforms are continuous and smooth. Several topics concerning the E-pulse technique are investigated, such as: insensitivity to the exact number of natural modes present in the target response; aspect-angle independence; and effects of additive white Gaussian noise. Numerical results, using the response of a thin cylinder and a sphere, show that the subsectional-polynomial E-pulses improve the results obtained using subsectional-rectangular E-pulses     

Optimization method versus E-pulse method in the context of targetdiscrimination

The performances of the optimization method and the extinction pulse method are evaluated for idealized data as well as experimental data from scaled-model targets. Although both methods use the late-time response to discriminate targets, the discriminant waveform is synthesized differently; from the target pole singularities in the E-pulse method, and from an energy maximization in the optimization method. Responses from waveforms synthesized using calculated wire data and laboratory measured data are presented, and the early-time energy confinements produced by the two methods are found to be generally comparable. The robustness of the optimization and E-pulse methods in the presence of noise is demonstrated by results for calculated and measured data     

一种修正的渐近无偏E脉冲雷达目标识别方法

为了进一步改善低信噪比条件下E脉冲目标识别方法的性能,该文理论分析了渐近无偏E脉冲目标识别方法,指出其存在E脉冲二次滤波使其能量识别数失效和回波中不同极点互藕产生新极点分量从而降低目标识别概率等缺陷,在此基础上提出了一种先互相关再E脉冲滤波的修正渐近无偏E脉冲雷达目标识别新方法,并对其渐近无偏性进行了理论证明。基于三种不同尺寸有限长细导线目标理论计算后时响应的仿真实验表明,该文提出方法的性能大大优于传统E脉冲和渐近无偏E脉冲雷达目标识别方法。     

Use of minimum phase signals to establish the time reference intransient radar target identification schemes

The minimum phase representation of the transient scattered field response of aircraft targets is used to establish the time origin of a measured signal in reference to a stored target library. This allows time-shift-sensitive schemes such as the E-pulse method and neural networks to be used effectively. An example in which the wavelet spectra of unknown and library target responses are correlated demonstrates the viability of the technique     

Performance analysis of an automated E-pulse target discriminationscheme

An automated E-pulse scheme for target discrimination was initially presented by Ilavarasan et al. (1993) without an analytic performance evaluation. Assuming that target responses are contaminated with white Gaussian noise, an automated E-pulse scheme is rigorously analyzed to yield a reliable measure of performance. The discrimination performance of this automated E-pulse scheme is determined quantitatively through the use of energy discrimination numbers (EDNs). Statistics of the EDNs are evaluated analytically to derive the probability of correct identification. The probability of identification as a function of signal-to-noise ratio (SNR) is evaluated using the theoretical scattering data for all potential targets to predict the performance of the automated E-pulse scheme. These theoretical results are corroborated by direct simulation of the discrimination scheme. In addition, the probability density functions of the EDNs are presented providing new physical insights into E-pulse performance as a function of target geometries and SNR     

Measurement of electromagnetic fields near a monopole antennaexcited by a pulse

To observe transient radiation fields, a technique for reconstructing electromagnetic (EM) waveforms using the complex antenna factor (CAF) have been developed. However, the CAF is originally defined assuming plane wave incidence, while the waveforms are measured in a vicinity of the radiating source. In order to examine the reconstruction technique using the CAF in the near-field measurements, the EM fields radiated from a monopole antenna excited by pulsed input voltage was reconstructed and compared with calculated results. For the geometry of the experiment, the waveforms of the reconstructed and calculated EM fields have shown good agreement. Therefore, the reconstruction technique using the CAF can be used for similar dimensions or at a greater distance when sufficient sensitivity is provided     

Application of the matrix pencil method for estimating the SEM(singularity expansion method) poles of source-free transient responsesfrom multiple look directions

The matrix pencil method has been utilized for estimating the natural resonances from different transient responses recorded along multiple look directions as a function of time after the incident field has passed the structure. The novelty of this article is that a single estimate for all the poles are done utilizing multiple transient waveforms emanating from the structure along multiple look directions. The SEM poles are independent of the angle at which the transient response is recorded. The only difference between the various waveforms are that the residues at the various poles are of different magnitudes. Some of the residues may even be zero for some of the poles indicating that the contribution from certain SEM poles may not be significant along that look direction. Here all the waveforms are utilized providing a single estimate for the poles without performing an arithmetic mean of the various waveforms     

Transient and impulse response approximations

Electromagnetic field waveforms produced by scattering of transient plane waves from finite objects are related to those produced by an impulsive plane wave. Properties of the impulse response waveforms at great distances from the target, particularly in the backscattering direction, are discussed. Various methods for approximation of impulse response waveforms using time and frequency domain concepts are suggested and illustrated. Other applications of response waveforms to target identification and to prediction of radar echo pulse waveforms are suggested.     

Extinction pulses synthesis for radar target discrimination using /spl beta/-splines, new E-pulse conditions

The extinction pulse method has been proven to be a suitable method for radar target discrimination using the natural resonance annihilation concept. The standard procedure for extinction pulse (E-pulse) construction is based on an expansion on subsectional polynomials. In this paper it is proposed a new formalism for E-pulse construction using /spl beta/-splines. This formalism allows the E-pulse polynomial basis expansion to be treated in a unified theoretical framework and leads to a simplification of the original problem due to the linear nature of all the involved parameters. This new formulation has been also used to impose new conditions over the spectral contents of the E-pulses. These E-pulses constructed using the new conditions annihilate better the natural modes in the late-time radar target response, and provide a better discrimination rates than the classical scheme.     

The K-pulse and E-pulse

The relationship between the K-pulse and the E-pulse is considered. Conditions are derived whereby the two waveforms differ, at most, by a multiplicative constant.     

A general E-pulse scheme arising from the dual early-time/late-timebehavior of radar scatterers

A duality between the temporal late-time response and the spectral early-time response of a radar target is used to form the basis for a general E-pulse technique. Examples, using the ultrawide-band measurements of an aircraft model, reveal that E-pulse cancellation is possible both in the time domain for the late-time component and in the frequency domain for the early-time component. Applications to radar target discrimination and clutter cancellation are described, and the aspect dependence of early-time discrimination is investigated     

一种基于傅里叶级数的E脉冲识别波形综合方法

为了直接发射E脉冲进行雷达目标识别,本文从理论上推导了产生特定矩形基编码脉冲信号傅里叶级数系数的一般性表达式;提出了一种基于傅里叶级数的E脉冲目标识别波形综合方法;给出了参数设计原则以及综合E脉冲波形的系统组成框图;并利用细导线散射场数据仿真了理论E脉冲和综合E脉冲目标识别性能;验证了本文提出的方法的可行性。     

Detection of Depth Changes of a Metallic Target Buried in a Frequency-Dependent Lossy Halfspace Using the E-Pulse Technique

The extinction pulse (E-pulse) technique has been widely applied to the problem of free-space radar target identification. In this paper, the possibility of applying the same E-pulse technique to a subsurface target recognition scheme is investigated. In particular, the detection of depth changes of a metallic target is considered with numerical examples that determine the depth of a hip prosthesis model buried inside representative human tissue.     

An asymptotically unbiased E-pulse-based scheme for radar target discrimination

This communication proposes an E-pulse-based scheme for radar target discrimination that provides asymptotically correct results for any level of additive white noise contaminating the radar signal. After multiple sampling of the signal dispersed by the target, it is analytically shown that the cross correlation between the output signals of the E-pulse designed for the standard target, corresponding to two different sampling periods, is asymptotically , regardless of the amount of contaminating noise. The results obtained by simulation have allowed us to propose a discrimination criterion that produces better results than the original E-pulse technique at very low signal-to-noise ratio (SNR) levels.     

Transient coupling analysis using the singularity expansion method

The problem of electromagnetic coupling between objects has been extensively studied within the context of continuous-wave (CW) signals. The problem of coupling between objects for transient excitation has not received as much attention. This paper addresses the problem of transient coupling using the singularity expansion method (SEM). Specifically, the proper physical interpretation of the SEM modes of a system of objects is discussed within the context of observed transient surface currents and scattered fields. It is seen that the SEM modes of the system of objects are global quantities and hence have no clear physical interpretation prior to times when global modes can be established. It is also apparent that the early-time response of the system can be expressed using the SEM modes of the individual objects for some time periods. These observations are important for the effective use of target identification schemes based on natural resonance phenomena in multiple target situations as well as the proper use of SEM in EMC coupling analyses     

Natural Mode Series Representation of the Transient Field Reflected From an N-Layer Lossy Medium

The conditions under which the plane-wave transient field reflected from a layered medium can be represented as a natural mode series are determined. It is shown that if each of the layers has frequency constant permittivity, permeability, and conductivity, then the late-time reflected field has a pure natural mode representation if the backing region is either lossless or a perfect electric conductor. This result, along with a decomposition of the temporal response into subregion responses, is used to determine periods of the early-time response which are also composed of pure natural mode series. Examples for structures with two and three layers are used to demonstrate the validity of the representation. The natural mode representation allows the use of existing techniques, such as the E-pulse method, to diagnose changes in the properties of the various material layers under the established conditions.      

Radar-Target Identification via Exponential Extinction-Pulse Synthesis

New contributions to noncooperative radar-target discrimination using only the scattered response of conductive objects are presented in this paper. The technique studied is the extinction-pulse (E-pulse), which makes use of natural resonances as discrimination features. The E-pulse expansion using complex exponential functions as basis functions is proposed, obtaining new E-pulses with characteristics completely different from those in the literature. Specifically, a weighting factor is added to modulate the exponential frequency, providing E-pulses with better discrimination capability. Numerical results achieved in the discrimination between thin straight wires of different lengths show that the proposed exponential E-pulses improve the discrimination results with respect to other types of E-pulses in the literature.     

A Review of Numerical Models for Predicting the Energy Deposition and Resultant Thermal Response of Humans Exposed to Electromagnetic Fields

For humans exposed to electromagnetic (EM) radiation, the resulting thermophysiologic response is not well understood. Because it is unlikely that this information will be determined from quantitative experimentation, it is necessary to develop theoretical models which predict the resultant thermal response after exposure to EM fields. These calculations are difficult and involved because the human thermoregulatory system is very complex. In this paper, the important numerical models are reviewed and possibilities for future development are discussed.