Eric Mokole

• Doctor of Philosophy
• Retired

It is well-known that an iterative time-reversal (TR) process, applied via a distributed sensing system, can be used to produce a space-time waveform that maximizes the energy scattered from a stationary target back to the sensors. The TR process accomplishes this by automatically focusing energy, both spatially and spectrally, on the stationary ta...

IEEE Standard 1502 recommends standardized practices for radar cross-section (RCS) measurements. This document—geared toward test-range operators and managers as well as users of the acquired data—outlines suggested measurement processes, measurement techniques, imaging concepts, and documentation practices. Consequently, there is a need to revisit...

The articles in this special section focus on ultra wideband technologies and applications. Over the last three decades, ultrawideband (UWB) radars have been designed for military and civilian applications, such as ground-penetrating radar for detecting and imaging antipersonnel and antivehicular mines, sensing through canopies for opposing forces,...

It is our great pleasure and honor to introduce the second of two special issues of the IEEE Aerospace and Electronic Systems Magazine on Waveform Diversity. The first paper,"Application of Waveform Weighting for a Frequency-Invariant Transmit Beampattern,"by Uysal et al. discusses a proposed method for implementing wideband beamforming in wideband...

One of the objectives of this paper is to outline the differences between the internal and external resonances of an electromagnetic structure. At an internal resonance of an object there is a component of the resonant current on the structure which is real and that current does not radiate nor does it couple to the incident field. The external res...

Radar waveform diversity has received considerable attention in recent years due to increasing spectral congestion and the burgeoning capabilities of digital waveform generation. The promise of waveform diversity is far greater utilization of available degrees of freedom to enhance sensing performance and to even facilitate new operating modes. Thi...

This review paper is a sequel to an earlier paper [1] dealing with parametric methods in the context of the principle of analytic continuation and provided its relationship to reduced rank modelling using the total least squares based singular value decomposition methodology. The problem with a parametric method is that the quality of the solution...

This paper considers a distributed wave-based sensing system that probes a scene consisting of multiple interacting idealized targets. Each sensor is a collocated transmit-receive pair that is capable of transmitting arbitrary wideband waveforms. We address the problem of finding the space-time transmit waveform that provides the best target detect...

In this article, we provide a brief history of the evolution of radar across the various regions where the technology's development occurred, often simultaneously and independently. (Note that the original term RADAR, representing "RAdio Detection And Ranging," was devised by the U.S. Navy in 1940.) We cover in detail the years from the late 19th c...

It is our great pleasure and honor to introduce this first of two special issues of the IEEE Aerospace and Electronic Systems Magazine on waveform diversity (WD). WD has been an area of significant scientific and technological endeavor in the last decade or so. The objective of these special issues is to provide a mix of tutorial-like articles and...

Current research on wireless radio frequency (RF) systems often makes unphysical simplifying assumptions and treats the associated signal processing and electromagnetic (EM) analyses independently, resulting in improper inclusion of the underlying physics (EM theory) of such systems and consequently leading to inaccurate and erroneous performance p...

The objective of this review paper is to illustrate the principle of analytic continuation and provide its relationship to reduced rank modelling using the total least squares based singular value decomposition methodology. The principles are illustrated in the different domains using the Matrix Pencil Method and the Cauchy Method for various reduc...

This short expository paper provides a brief introduction to ultrawideband (UWB) theory, technology, applications, and systems with a focus on radar and brief observations on communications. The definition of UWB radar is discussed, and an experimental UWB radar (Microwave Microscope) is considered to illustrate system properties and the imaging ef...

Conventionally, the design of antennas is narrowband and little attention is paid to the phase responses of the devices as functions of frequency. Even the use of the term broadband is misleading as one essentially takes a narrow band signal and sweeps it across the band of interest. In fact, it is not necessary to pay too much attention to the pha...

This paper considers a distributed wave-based sensing system that probes a scene consisting of multiple interacting idealized targets. Each sensor is a collocated transmit-receive pair that is capable of transmitting arbitrary wideband waveforms. We address the problem of finding the space-time transmit waveform that provides the best target detect...

The tutorial is split into 2 components: broadband theory/technology/systems and radar-communication interaction. For the broadband component, we will discuss the underlying theory, component technology, and some systems, with a focus on the two ultrawideband (UWB) application areas (radar and communication systems) in light of recent interest in U...

A precis of spectrum congestion among RF users is given, with a focus on radar-communication co-existence. In particular, some recent efforts to mitigate this interference are briefly discussed, and intimations of requisite research and possible ways to achieve spectral harmony are provided.

The radio-frequency (RF) electromagnetic spectrum, extending from below 1 MHz to above 100 GHz, represents a precious resource. It is used for a wide range of purposes, including communications, radio and television broadcasting, radionavigation, and sensing. Radar represents a fundamentally important use of the electromagnetic (EM) spectrum, in ap...

This paper addresses polyphase code optimization with respect to the nonlinear frequency modulation waveform generated by the continuous phase modulation implementation. A greedy search leveraging the complementary metrics of peak sidelobe level, integrated sidelobe level, and spectral content yield extremely low range sidelobes relative to wavefor...

This paper develops a data model and corresponding imaging operation for multistatic polarimetric radar. The mathematical model describes the processes of radiation from a transmitting antenna, scattering from a moving target, and reception at a receiving antenna. A bistatic scattering matrix based on physical optics and the fast-time Doppler effec...

For many years, Electromagnetic Spectrum has been treated as a commodity within the United States, with allocation shared between Government and private sector interests. Government spectrum managers, working with their industry counterparts, carved out slices of spectrum under the governance of the Federal Communications Commission (FCC) and the N...

Multistatic and polarimetric radars are two active areas of research. Polarimetric radar systems collect more information about an environment than if a single polarization is used, despite the historically prohibitive cost of these systems. Similarly, multistatic systems have a number of theoretical advantages, including 1) the ability to transmit...

A through-dielectric switched-antenna-array radar imaging system is shown that produces near real-time imagery of targets on the opposite side of a lossy dielectric slab. This system operates at S-band, provides a frame rate of 0.5 Hz, and operates at a stand-off range of 6 m or greater. The antenna array synthesizes 44 effective phase centers in a...

Through-lossy-slab radar imaging will be shown at stand-off ranges using a low-power, ultrawideband (UWB), frequency modulated continuous wave (FMCW) radar system. FMCW is desirable for through-slab applications because of the signal gain resulting from pulse compression of long transmit pulses (1.926-4.069 GHz chirp in 10 ms). The difficulty in ut...

In the above titled paper (ibid., vol. 46, pp. 181-193, Feb. 98), there were four typographical errors. The corrections are presented here.

The objective of this chapter is to illustrate that the influence of diversity in the regeneration of species is quite different from the effect of diversity in a vector wireless environment. Diversity in a regenerative environment is always welcome and often provides variety, the often desired spice of life. However, diversity from an electrical e...

In the last fifteen years, the development of ultrawideband (UWB) electromagnetic (EM) systems in communications, radar, and high-power directed energy has been on the rise. In particular, the significant developments in the commercial sector of UWB communications systems and UWB radar for humanitarian de-mining have fueled strong interest in UWB s...

This is the first book to discuss current and future applications of waveform diversity and design in subjects such as radar and sonar, communications systems, passive sensing, and many other technologies. Waveform diversity allows researchers and system designers to optimize electromagnetic and acoustic systems for sensing, communications, electro...

Time reversal can play a significant role in improving the performance of current sky-wave high-frequency over-the-horizon-radar (HF OTHR), especially with respect to real-time monitoring and compensation of ionospheric turbulence. Also, multipath interference arising from an HF OTHR environment can significantly increase resolution and the signal-...

Radar technology has a number of self-competing interests. For example, a radar must be able to search and track targets by resolving their spatial locations in range and azimuth. Transmitted short-duration pulses, with associated desirable broad bandwidths, allow radars to achieve the high range resolutions necessary to resolve multiple targets in...

The allowable transmission spectrum of US Navy radars is being heavily utilized by other services like telecommunication systems which is causing many interference problems between the radars and the non-radar services when the radars operate in a littoral environment. In addition, many Navy radars are being operated in close proximity thereby caus...

The purpose of this chapter is to provide a contextual setting for the waveform diversity (WD) activities of the past several years (2002-2009), as well as to provide a summary of the history of WD and its evolution over this short period. Also, the authors wish to apologize in advance for the radar-centricity of the ensuing discussion, as radar is...

A low-cost ultrawideband (UWB), 1.926-4.069 GHz, phased array radar system is developed that requires only one exciter and digital receiver that is time-division-multiplexed (TDM) across 8 receive elements and 13 transmit elements, synthesizing a fully populated 2.24 m long (λ/2 element-to-element spacing) linear phased array. A 2.24 m linear phase...

Through-lossy-slab radar imaging will be shown at stand-off ranges using a low-power, ultrawideband (UWB), frequency modulated continuous wave (FMCW) radar system. FMCW is desirable for through-slab applications because of the signal gain resulting from pulse compression of long transmit pulses (1.926-4.069 GHz chirp in 10 ms). The difficulty in ut...

Let us begin by stating that it is difficult to provide an adequate response that will enlighten the audience if the correspondent neither provides the necessary references nor the details of his computations that are in disagreement with the authors. Since science is evidence based, it is difficult to respond intelligently where evidence of a disa...

The wide-angle bicone antenna terminated by a spherical cap is investigated. The antenna radiation patterns have been observed for various values of ka where k represents the phase constant and a represents the conical length. It is seen that for large values of ka the radiation pattern is limited within an angular sector bounded by the cones of th...

The wide-angle discone antenna terminated by a truncated spherical cap is investigated. The antenna is simulated in both the time and the frequency domains. The radiation pattern has been observed for various values of ka signifying all the ranges of operation of the antenna. It is seen that for large values of ka the radiation pattern is limited w...

Wireless communication is an active area of current research in communication technology. To assess the performance of a wireless system, one needs to quantify its ability to handle information. Typically, the performance of such systems is characterized in terms of the channel capacity. In this article, we look at the various mathematical represen...

For radars operating with medium to high pulse repetition frequency (PRF), a loss in detection performance can result when the arrival of return echoes coincides with the transmission of a pulse, during which time the receiver is turned off. This so-called ldquoeclipsing lossrdquo is due to the partial reception of the reflected waveform correspond...

Summary Introduction Formulation of the New Direct Data Domain Least Squares Approach Approximately Compensating for the Effects of Mutual Coupling Using the In Situ Element Patterns Simulation Results Reason for a Decline in the Performance of the Algorithm When the Intensity of the Jammer Is Increased Conclusion References

Summary Introduction Signal Enhancement Methodology Through Adaptivity on Transmit Exploitation of the Polarization Properties in the Proposed Methodology Numerical Simulations Conclusion References

Summary Historical Overview of Maxwell's Equations Review of Maxwell-Heaviside-Hertz Equations Solution of Maxwell's Equations Radiation and Reception Properties of a Point Source Antenna in Frequency and in Time Domain Radiation and Reception Properties of Finite-Sized Dipole-Like Structures in Frequency and in Time Conclusion References

Summary Introduction Formulation of a Direct Data Domain Least Squares Approach Using Real Weights Simulation Results for Adaptive Processsing Formulation of an Amplitude-only Direct Data Domain Least Squares Space-Time Adaptive Processing Simulation Results Conclusion References

Summary Introduction Review of the Direct Data Domain Least Squares Approach Review of Space-Time Adaptive Processing Based on the D3LS Method Minimum Norm Property of the Adaptive Weights at the DOA of the SOI for the 1-D Case and at Doppler Frequency and DOA for STAP Numerical Examples Conclusion References

Summary Introduction UWB Input Pulse Travelling-Wave Antenna Reciprocity Relation Between Antennas Antenna Simulations Loaded Antennas Conventional Wideband Antennas Experimental Verification of the Wideband Responses from Antennas Conclusion References

Summary Various Forms of the Optimum Filters Direct Data Domain Least Squares Approaches to Adaptive Processing Based on a Single Snapshot of Data Direct Data Domain Least Squares Approach to Space-Time Adaptive Processing Application of the Direct Data Domain Least Squares Techniques to Airborne Radar for Space-Time Adaptive Processing Conclusion...

Summary Introduction EIRP Degradation of Array Antennas Due to Random Position Errors Example of EIRP Degradation in Antenna Arrays Simulation Results Conclusion References

Summary Introduction History of Entropy and Its Evolution Different Formulations for the Channel Capacity Information Content of a Waveform Numerical Examples Illustrating the Relevance of the Maxwellian Physics in Characterizing the Channel Capacity Conclusion Appendix: History of Entropy and Its Evolution References

Summary Introduction Formulation of a Direct Data Domain Least Squares Method for Adaptive Processing of Finite Bandwidth Signals Having Different Frequencies Numerical Simulation Results Conclusion References

Summary Introduction Description of the Various Signals of Interest Statistical-Based STAP Algorithms Direct Data Domain Least Squares STAP Algorithms Channel Mismatch Simulation Results Conclusion References

Summary Introduction DOA Estimation Using a Realistic Antenna Array Cramer-Rao Bound for DOA Estimation DOA Estimation Using 0.1 λ Long Antennas DOA Estimation Using Different Antenna Array Configurations Conclusion References

Summary Introduction Formulation of a Direct Data Domain Approach for Multiple Beamforming Simulation Results Formulation of a Direct Data Domain Least Squares Approach for Multiple Beamforming in Space-Time Adaptive Processing Simulation Results Conclusion References

Summary Introduction Brief Overview of the Matrix Pencil Method Problem Formulation for Simultaneous Estimation of DOA and the Frequency of the Signal Cramer-Rao Bound for the Direction of Arrival and Frequency of the Signal Example Using Isotropic Point Sources Example Using Realistic Antenna Elements Conclusion References

Summary Field Produced by a Hertzian Dipole Concept of Near and Far Fields Field Radiated by a Small Circular Loop Field Produced by a Finite-Sized Dipole Radiation Field from a Linear Antenna Near-and Far-Field Properties of Antennas The Mathematics and Physics of an Antenna Array Propagation Modeling in the Frequency Domain Conclusion References

Summary Introduction Formulation of the Direct Data Domain Least Squares Solution for a Phase-Only Adaptive System Simulation Results Formulation of a Phase-Only Direct Data Domain Least Squares Space-Time Adaptive Processing Simulation Results Conclusion References

To understand the target-like artifacts in radar returns called sea spikes 1 that are induced by ocean scatter,2 the WIPL-D3 and WIPL-DP4 electromagnetics codes are used to calculate monostatic and bistatic radar cross sections (RCSs) of a trihedral comer reflector at 1.5, 3.8, and 7 GHz for vertically and horizontally polarized fields. These compu...

Broadband antennas are very useful in many applications because they operate over a wide range of frequencies. The objective of this paper is to study the transient responses of various well-known antennas over broad frequency ranges. As such, the phase responses of these antennas as a function of frequency are of great interest. In the ensuing ana...

In traditional, adaptive signal processing algorithms one change both the amplitude and phase of the weight vectors associated with an array at each of the antenna elements. The use of complex weights offers greater control over the array response at the expense of system complexity. However, it is easier if one requires only amplitude variation wi...

One commonly used way to classify signals and devices is based on frequency coverage or bandwidth. Three somewhat similar, but significantly different, ultra-wideband (UWB) classification schemes from the open literature are presented. These classification schemes differ in how they define bandwidth and categorization criteria. A comparison of the...

Navy radar operations are being curtailed in a littoral environment. This is due to two factors: the encroachment of cell phone systems into the naval radar bands; in-band interference from other radars. The spectral width of most pulsed radars is significantly wider than necessary with present modulation schemes. Most radars utilize some form of c...

If the signal is constrained to last only for a single baud, the optimum signal is the well-known “Prolate Spheroidal Wave Function”1. However, for signals of more than one baud time duration, it is necessary to remove intersymbol interference. There are two common constraints that are used to remove intersymbol interference. The first constraint i...

Beam based phase-space formulations are an important tool in wave theory since they provide a systematic framework for ray-based construction of spectrally uniform local solutions in complex configurations. An important property of these formulations is that the spectrum of beam propagators is overcomplete and thus may be a priori discretized as, f...

In recent years, electromagnetic characterization of subsurface targets and its application to detection and identification using ultra-wideband (UWB) ground penetrating radar (GPR) have attracted great interest from the research community.1–6 The targets are stationary and located in clutter environments with large false-alarm rates as a universal...

Techniques like high power microwaves (HPM), pulse scattering, EMP, ESD and transient radar still lack reliable electric field monitors. One of the main obstacles to develop such field sensors are the enormous difficulties to miniaturize the sensor head providing simultaneously sufficient sensitivity, dynamic range and electrical isolation. This pa...

One-dimensional propagation of a normally incident, pulsed electromagnetic plane wave upon an isotropic, spatially homogeneous, Lorentz half-space is investigated analytically. Fourier integral representations of the time-dependent reflected and transmitted fields are obtained for an arbitrary incident pulse, and detailed examinations of these fiel...

The intent of this work is to ascertain through analytical means whether a circularly polarized radiated field is possible for some antenna configuration with an ultrawideband (UWB) source. Consequently, the behavior of the radiated electric field from identical, thin, half-wave, electromagnetically uncoupled, orthogonal dipoles in free space that...

The problem of radiation and reception of electromagnetic waves associated with a spherically capped biconical antenna having unequal cone angles ψ₁ and ψ₂ is investigated. Both cones that comprise a bicone are excited symmetrically at the apices by a voltage source so that the only higher order modes are TM. A variational exp...

The mathematical model of the resistively loaded dipole, introduced by Wu and King (1965) for obtaining the current distribution along the dipole and the radiated electric field in the frequency domain, is used here to study the corresponding time-dependent current and field. In addition, the characteristics of the open-circuit voltage of a similar...

The purpose of this paper is to present in a tutorial fashion some of the fundamental properties and characteristics of antenna elements that are responsible for very broadband or ultrawideband (UWB) behavior. Before selecting, designing, or analyzing UWB radiators, one must understand the how and the why of the broadband nature of antenna elements...

This paper discusses general issues concerning ultrawideband (UWB) arrays and specifically analyzes time-delay scanning linear arrays of thin dipoles that are excited by a single-cycle sine, when the effects of mutual coupling are neglected. In particular, when the array consists of eleven equally spaced and equally weighted dipoles, the time-domai...

An estimate of the impact of very severe ionospheric conditions on the coherent and noncoherent integration process from a two-way, transionospheric, propagation path is obtained for a specific type of frequency-diverse waveform. A bound on the total integration loss that would result from using this waveform during such ionospheric conditions is o...

WIPL-D is being used to compute monostatic and bistatic radar cross sections of a trihedral corner reflector over the frequency range of 1-12 GHz. Initial results are discussed for vertically and horizontally polarized fields at two frequencies (1.5 and 3.8 GHz). These computations are being used to provide a benchmark against which the performance...

Broadband characterisations are very useful in many applications as they operate over a wide range of frequencies. The objective of this paper is to study the transient response of a century bandwidth antenna. As such, the phase response of this antenna as a function of frequency is of great interest, as it is an inherently broadband, up to a 100:1...