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Radiation of Nonsinusoidal Electromagnetic Waves
... Such criticism of the unrestricted deployment of Fourier transform methods for solving electromagnetic wave propagation problems has lead to the revival of the controversy about how best to define signal propagation speed (inadequacy of the group velocity concept [14]). The climax, however, was the proposed correction of Maxwell's equations given in [11], [12] and further elaborated in [15]. † Other writers have also voiced similar skepticism regarding the unhinged use of frequency-domain methods to infer data and information about the time-domain behaviour of electromagnetic waves, e.g., see the recent book [16] and the papers [17][18][19][20]. ...
... It is derived here rigorously from the more general causal integral (11). In order to compute the time-domain received signal, we re-express (15) in terms of the convolution operation * J(r p , t) =α F (r p ; t) * E in,t (r p , t). ...
We provide a conceptual and theoretical analysis of nonsinusoidal antennas with emphasis on how electromagnetics and communication theories can be integrated to propose ideas for near-field (NF) communications systems utilizing future antennas. It is shown through rigorous analysis that in nonsinusoidal antennas it is possible to derive and solve ordinary differential equations giving specialized time-domain excitation signals that lead to exact cancellation of the near field at specific radiation spheres. This opens the door to building NF communications systems with far-field-like communication receiver infrastructures utilized if the receive antenna is placed at the special sphere where the NF component is made to vanish.
... Such criticism of the unrestricted deployment of Fourier transform methods for solving electromagnetic wave propagation problems has lead to the revival of the controversy about how best to define signal propagation speed (inadequacy of the group velocity concept [14]). The climax, however, was the proposed correction of Maxwell's equations given in [11], [12] and further elaborated in [15]. † Other writers have also voiced similar skepticism regarding the unhinged use of frequency-domain methods to infer data and information about the time-domain behaviour of electromagnetic waves, e.g., see the recent book [16] and the papers [17][18][19][20]. ...
... It is derived here rigorously from the more general causal integral (11). In order to compute the time-domain received signal, we re-express (15) in terms of the convolution operation * J(r p , t) =α F (r p ; t) * E in,t (r p , t). ...
We provide a conceptual and theoretical analysis of nonsinusoidal antennas with emphasis on how electromagnetics and communication theories can be integrated to propose ideas for near-field (NF) communications systems utilizing future antennas. It is shown through rigorous analysis that in nonsinusoidal antennas it is possible to derive and solve ordinary differential equations giving specialized time-domain excitation signals that lead to exact cancellation of the near field at specific radiation spheres. This opens the door to building NF communications systems with far-field-like communication receiver infrastructures utilized if the receive antenna is placed at the special sphere where the NF component is made to vanish.
... Such criticism of the unrestricted deployment of Fourier transform methods for solving electromagnetic wave propagation problems has led to the revival of the controversy about how to best define signal propagation speed (inadequacy of the group velocity concept [14]). The climax, however, was the proposed correction of Maxwell's equations given in [11,12] and further elaborated in [15]. † Other writers have also voiced similar skepticism regarding the unhinged use of frequency-domain methods to infer data and information about the time-domain behaviour of electromagnetic waves, e.g., see the recent book [16] and papers [17][18][19]. ...
... It is derived here rigorously from the more general causal integral of Eq. (11). In order to compute the time-domain received signal, we reexpress Eq. (15) in terms of the convolution operation * J(r p , t) =αF (r p ; t) * E in,t (r p , t). ...
... This antenna [43,44] is made of a rectangular metal sheet which is connected via triangular section of metal sheet to a wire through which source voltage is applied. Absorbing material is also placed in an appropriate manner so that the radiation from this wire does not interfere with that from the rectangular plate. ...
... Note that the expression(43) and other relations based on it do not depend on the small cone approximation.LARGE CONE APPROXIMATION (i.e. ka > > 1)Let us assume -1 < /t, ^ ^ < 1, then we have from [Ref.46] the following relation.Noting also that lim [$ t {ka)] = i + O then finds from (38a) and(45), that lim [aJa.] ...
A preliminary investigation is conducted on the selection of antenna configurations which have potential to be ultrawideband (UWB). Each configuration is summarized. This includes discussions of new results that are byproducts of the study, conclusions that are drawn from the survey, and recommendations that are made which are predicated on the research. With regard to approaches for characterizing UWB antennas, two overriding conclusions emerged from this effort: (1) the philosophical maxim, 'the proof of the UWB antenna is in its short pulse behavior,' should be implicit in any study, and (2) each campaign should be a synergistic merging of theoretical, numerical, and experimental methods. Based on the capability to enhance existing knowledge and understanding of the performance of UWB antennas, this study recommends the following topics be studied in greater detail: loaded dipoles, flared and notch antennas, helixes and spirals, fat antennas, arrays with mutual coupling, the possible reduction of phase variation in log periodic antennas, wide-angle biconical antennas, and antennas that are suitable for impulse radiation.
... In the late 1960s, Tektronix and Hewlett Packard developed oscilloscopes for UWB signals [44]; they also produced the first time domain instruments for diagnos- With the conference held at W.J. Schafer Associates [47] and one at Los Alamos National Laboratory in 1991 [48], there have been numerous meetings held on impulse radar/radio [49,50,51,52,53,54,55,56]. ...
L’objectif de cette thèse est la classification automatique des cibles (ATC) en utilisant les signaux rétrodiffusés par un radar ultra large bande (UWB). La classification des cibles est réalisée en comparant les signatures des cibles et les signatures stockées dans une base de données. Premièrement, une étude sur la théorie de diffusion nous a permis de comprendre le sens physique des paramètres extraits et de les exprimer mathématiquement. Deuxièmement, des méthodes d’extraction de paramètres sont appliquées afin de déterminer les signatures des cibles. Un bon choix des paramètres est important afin de distinguer les différentes cibles. Différentes méthodes d’extraction de paramètres sont comparées notamment : méthode de Prony, Racine-classification des signaux multiples (Root-MUSIC), l’estimation des paramètres des signaux par des techniques d’invariances rotationnels (ESPRIT), et la méthode Matrix Pencil (MPM). Troisièmement, une méthode efficace de classification supervisée est nécessaire afin de classer les cibles inconnues par l’utilisation de leurs signatures extraites. Différentes méthodes de classification sont comparées notamment : Classification par la distance de Mahalanobis (MDC), Naïve Bayes (NB), k-plus proches voisins (k-NN), Machines à Vecteurs de Support (SVM). Une bonne technique de classification doit avoir une bonne précision en présence de signaux bruités et quelques soit l’angle d’émission. Les différents algorithmes ont été validés en utilisant les simulations des données rétrodiffusées par des objets canoniques et des cibles de géométries complexes modélisées par des fils minces et parfaitement conducteurs. Une méthode de classification automatique de cibles basée sur l’utilisation de la méthode Matrix Pencil dans le domaine fréquentiel (MPMFD) pour l’extraction des paramètres et la classification par la distance de Mahalanobis est proposée. Les résultats de simulation montrent que les paramètres extraits par MPMFD présentent une solution plausible pour la classification automatique des cibles. En outre, nous avons prouvé que la méthode proposée a une bonne tolérance aux bruits lors de la classification des cibles. Enfin, les différents algorithmes sont validés sur des données expérimentales et cibles réelles.
... that virtually any frequency-coded pulse could be generated by a step function (cf.Ross, 1986, p. 11). This is a method also long studied and reported byHarmuth (cf., 1981, p. 48-54, 77;1990, Preface and section 1.7-A Guide to Reading, p. 52). ...
... However inherent distortion of signal waveform is principal moment for electromagnetic pulse (EMP) simulators, high-resolution radars, spread-spectrum communications, electromagnetic compatibility (EMC) issue, VLSI and printed board design and so on. Generally each element of such system effects on signal waveform passing through it (Harmuth, 1990). Resulted signal is not rather simple replica of input waveform like in case of narrow-band or sinusoidal signal. ...
Time-domain interpretation of non-stationary electromagnetic events, including nearrange effects, which is not enough shown
in literature, is discussed here. Generally the results obtained with time domain simulations demonstrate more physical meaning
and are more clearly dependent on the influence of problem parameters than those in frequency-domain.
All presented above regularities are important for UWB or transient antenna design. Inherent transformation of signal waveform
passing through components of UWB system especially its antennas should be carefully treated. The last is ordinary achieved
with complex numerical computing. In this sense the benefits of proposed physically meaningful straightforward technique with
easy Matlab, Maple etc. simulation seems valuable for research and engineering practice as well for academic goals. Generally
the presented above approach allows the next steps in research when time-domain antenna arrays can be considered that are
in progress now.
... [19], [26], [27]. Antenna radiation characteristics when non-sinusoidal electromagnetic waves are driven and the propagation characteristics thereof were also analysed by Harmuth [18]–[24] . From the above description, Harmuth's results appear to be connected to present-day code division multiple access (CDMA) technology. ...
A baseband transmission scheme for wireless communications has been proposed and examined using a pair of discone antennas for transmission and reception. The wireless baseband transmission scheme radiates a baseband signal stream, such as non-return-to-zero (NRZ), return-to-zero (RZ), or Manchester encoded signals, directly from an antenna. Namely, a carrier in terms of a sinusoidal radio wave or light wave is not used in the transmission. In experiments, baseband pulses generated with a data generator were radiated directly from the discone antenna, and received waveforms were observed with a digital storage oscilloscope. The experiments showed that wireless baseband transmission is realisable when using antennas with a flat amplitude spectrum and a linear phase characteristic, such as discone antennas, over a given band. Manchester encoding is promising for this wireless baseband transmission.
... The radiated waveform from a bow-tie dipole antenna with a nominal centre frequency of 1.5 GHz is shown in Fig. 2, with the direct wave on the left and the received wavelet reflected through air from a steel sheet shown on the right. The received signal is a complex combination of non-sinusoidal wavelets [3,4], with multiple reflections from feed points and dipole ends [5], and displaying multi-lobed frequency spectra characteristics. ...
Übersicht Das Reflexions- und Transmissionsverhalten einer ebenen Grenzfläche zwischen einem Isolator und einem verlustbehafteten Halbraum wird für senkrecht einfallende ebene TEM-Wellen mit beliebiger Wellenformfunktion analytisch im Zeitbereich untersucht. Die reflektierten und durchgehenden Teilwellen werden danach für eine impulsförmige Wellenformfunktion der einfallenden Welle spezialisiert. Aufgrund der Verluste entstehen kontinuierliche Feldanteile. Für die Aufteilung und Ausbreitung der impulsförmigen Feldanteile gelten ganz elementare Zusammenhänge. Durch geeignete Normierungen lassen sich die Feldlösungen sehr allgemein verwenden und auch auf leitungsgebundene Wellen anwenden.
Considerable nontrivial contributions that have been done by Henning F. Harmuth to electromagnetic signal theory and UWB radar and Communication systems are briefly described in the paper. An interesting historical analogy in scientific life of Henning Harmuth and Oliver Heaviside is traced.
Dissipation of electromagnetic energy in conducting media takes place not only because of its absorption due to acceleration of charged particles by the electric field and their inelastic collisions with atoms, but also due to interaction of the wavepsilas magnetic field with magnetic dipole current induced by those collisions in the atoms. The simplest way to describe this phenomenon is to use Ohmpsilas law for magnet dipole current as H. Harmuth suggested in his modified Maxwell equations.
IntroductionThe Maxwell Postulates: Microphysics and ContinuaPolarizability Dyadics of Small Homogeneous ParticlesPolarizability Dyadics of MoleculesThe Equivalent ContinuumElectromagnetic Fields in the ContinuumOne-Dimensional Field Variations in the Equivalent ContinuumClosing Remarks
Ultra wide band (UWB) radio has recently attracted in-creased attention due to its expected unlicensed operation, and po-tential to provide very high data rates at relatively short ranges. In this article we briefly describe some main candidate multiple access and modulation schemes for UWB communications, followed with their power spectral density calculation and properties. We also present some illustrative capacity results, and provide a discussion of the impact of network topology on multiple access capacity.
Dissipation of electromagnetic energy in conducting media takes place not only because of its absorption due to acceleration of charged particles by the electric field and their inelastic collisions with atoms, but also due to interaction of the wave's magnetic field with magnetic and electric dipole currents induced by those collisions in the atoms. The simplest way to describe this phenomenon is to use Ohm's law for magnetic dipole current as H. Harmuth suggested in his Modified Maxwell's equations.
A practical hands-on description on how to build a prototype of an ultra wideband (UWB) radar is presented. UWB radar, and UWB communication as well, are quite hot topics these days both in the industry and in the academia. Nevertheless many people would like to have working schematics to start prototyping, just to see the "magic" in it. To this end the topic is kept to a very didactic and popular level without boring people, or even frightening, with lots of theory. As a matter of fact, many engineers and scientists already went deep into UWB theory but they were unfortunately unable to start working. Therefore, practicing with UWB is exactly the purpose of this lecture. Although UWB theory has been described in a series of books [1][2][3][4] published as early as the 80's, the actual electronic circuits presented here are mainly based on what was disclosed in a few US patents [5][6][7][8][9][10], along with direct experience of the author [11][12][13]. The author itself is aware that some patents filed by the US Lawrence Livermore National Laboratory (LLNL) were questioned and reexamined by the United States Patents & Trademarks Office (USPTO) and eventually declared as "anticipated" by other patents filed before by Mr. Larry W. Fullerton and Time Domain Inc.. Apart from any patent litigation, it is the aim of the paper to present a working prototype of a UWB radar from a purely didactic and "amateur" point of view, avoiding infringing any other party rights nor unauthorized disclosing of any other data. Anyway the reader should remember that industrial production and/or sale of the systems presented here might infringe other parties' patent rights. Eventually it is the final responsibility of the reader to use the following information in all but unlawful way. A UWB radar prototype of the "noise" kind will be detailed with the schematics, a bit of rationale for the various technical solutions adopted, the testing procedures and even how to have fun with it.
This paper treats the Green's functions of transient plane waves in lossy media for finite and infinite regions. For infinite regions they are given by two essentially different infinite series, one converging extremely rapidly for small times, one for large times. In the limit of infinite light velocity one obtains diffusing fields in terms of -functions, discussed in a preceding paper [1]. They can also be represented by two essentially different infinite series related to one another by Jacobi-transformations. So the present paper generalises the results of the earlier one.In der vorliegenden Arbeit werden die Green'schen Funktionen transienter ebener Wellen in endlichen und unendlichen verlustbehafteten Medien behandelt. Im Fall endlicher Medien knnen diese durch zwei wesentlich verschiedene unendliche Reihen dargestellt werden, deren eine fr kleine, Zeiten, deren andere fr groe Zeiten extrem rasch konvergiert. In der Grenze unendlicher Lichtgeschwindigkeit ergeben sich diffundierende elektromagnetische Felder, die in einer vorhergehenden Arbeit behandelt wurden [1]. In diesem Spezialfall sind die Felder durch -Funktionen gegeben, deren unterschiedliche Reihendarstellungen ber die Jacobi-Transformationen miteinander zusammenhngen. Die Ergebnisse der vorliegenden Arbeit verallgemeinern diese Zusammenhnge.
Die Maxwellgleichungen werden fr eindimensionale ebene TEM-Wellen in verlustbehafteten, homogenen und linearen Medien mit der Riemannschen Integrations methode analytisch im Zeitbereich gelst. Die so gewonnenen Basislsungen fr elektrische und magnetische Feldgren besitzen gegenber den bekannten Frequenzbereichslsungen den Vorteil, da sie fr beliebige Wellenformen bis hin zu Impulswellen geschlossen darstellbar sind und das physikalische Verstndnis der Wellenausbreitung in Medien mit nichtverschwindender Leitfhigkeit vertiefen. Da die Basislsungen als Lsung eines charakteristischen Anfangswertproblems gewonnen werden und somit ihre Freiheitsgrade eine ganz spezifische Form aufweisen, liefern sie in idealer Weise Feldanstze zur Untersuchung der Reflexions- und Transmissionseigenschaften geschichteter, verlustbehafteter Medien im Zeitbereich.Maxwell's equations are analytically solved in time domain for one-dimensional plane TEM-waves in lossy, homogeneous and linear media with Riemann's method. The calculated closed form fundamental solutions for both electric and magnetic fields are formulated for arbitrary wave shapes, up to impulse waves, which is one advantage over the well known frequency domain solutions. In addition to this they give more insight to the physical understanding of wave propagation in lossy media. These fundamental solutions are very well suited to examine the reflection and transmission properties of layered lossy media in time domain, because they are solutions of a characteristic initial value problem.
The material of this book chapter covers the topics presented within the corresponding IEEE ISCAS 2006 tutorial, and in particular it focuses on the following items: the UWB radio signal and its spectral characteristics, power issues and current standardization trends, multi user interference in impulse radio UWB networks, ranging and positioning with UWB, medium access control for UWB networks, location-aware UWB routing algorithms and metrics, and finally introducing cognitive principles in UWB networks
Tuning spectra by pulse shaping is feasible in both impulse radio (IR) and continuous radio transmissions, since, as well known, the impulse response of the pulse shaper affects the spectral properties of radiated signals. What is peculiar to IR-UWB, and makes pulse shaping particularly appealing, is the impulsive nature of the carrier. Given their very short duration, transmitted pulses in different intervals overlap neither on clock beats nor in between two clock beats. Spectrum matching in IR can thus be restricted with reasonable approximation to a single inter-pulse interval, and as such be redirected in a rather straightforward way into a waveform representation problem.This paper analyzes the above problem of tuning radiated IR-UWB signals to reference spectral patterns by pulse shaping, and shows the correspondence between spectrum and waveform matching problems. Examples of application include three case studies: matching the FCC emission masks, mitigating interference in the ISM bands, and reducing inter-system interference for two coexisting UWB networks. The proposed approach goes beyond the signal processing analysis to tentatively propose a procedure and related protocol for integrating spectral adaptation mechanisms into network operating principles.
Ultra-wideband (UWB) signals as implemented in our localizers provide a foundation for highly accurate methods of 3D position determination using precise ranging between any two nodes. In a large, distributed network of nodes, the time required for all nodes to acquire each other is of paramount importance. We have developed a method of rapid acquisition that allows two nodes to acquire each other in a fraction of the time afforded by other methods. We utilize a beacon/listener technique using Kasami sequences and divide-and-conquer algorithms to effect acquisitions in less than a second. We discuss our rapid acquisition process in this paper.
We present results of our investigations on the propagation of EM signals through interstellar medium that is supposed to be formed by neutral atomic hydrogen gas with rather low density. We describe the model under consideration and obtain the partial differential equation for one of the EM field components, as well as formulation of the initial-boundary value problem for that equation and the method for its solution in the time domain. EM signals propagation over billions light years distance through such medium is studied for various combinations of its parameters
To investigate the propagation of nonsinusoidal signal in a bounded attenuating medium, it is generally required to solve the 2nd order hyperbolic partial differential equation (PDE) with specified initial-boundary conditions (IBCs). Because of the lack of well-posed conditions of such PDE system, some problems aroused in such system, referred to as Harmuth's (1986) problem, relating to the validity of Maxwell's equations for signal propagation in attenuating media. Previous investigations on the equivalence between the magnetic and electric sources in attenuating medium shows that similar problem arises. Mathematically, the problem is essentially restricted to the case whether we can give a complete solutions, including the associated magnetic (electric) propagation for electric (magnetic) excitation, for some specified signal such as the step function signal or the exponential ramp signal since for many other excitations, the equations with corresponding IBCs can be solved successfully. The lack of well-posed conditions baffles a comprehensive solving of the problem and has led to different solving techniques to give a unique and causal solution in practice. By investigating the restrictions on the IBCs due to the causality requirement, supplement requirements on the IBCs of the 2nd order hyperbolic PDE, though does not mean the well-posed IBCs, can be offered to help the evaluation of Harmuth's modification to Maxwell's equations
Propagation of the transient electromagnetic field in a waveguide
with the perfectly conducting surface of arbitrary cross-section and
filled with a lossy medium is considered. The time domain method of
waveguide evolutionary equations has been used, and original
initial-boundary value vector problem for Maxwell's equations has been
reduced to integrating of the one-dimensional Klein-Gordon scalar
equation. Its solution is obtained as an expansion in terms of a
suitable for time domain method basic set. The expansion coefficients
are readily derived through the same decomposition of the input signal.
Analytical forms of early- and late-time approximations for propagating
electromagnetic signal are presented, and the validity conditions for
the explicit formulas are discussed
Summary form only given, as follows. In connection with the deforming plasma systems these questions are raised: Can the general nature of the behavior of the deforming electromagnetic radiation systems be investigated without quantum statics with the help of qualitative theory of second-order linear differential equations so that the results are true with respect to classes of fast-changing or singular deformations? Or, what are the new radiation and deformation laws?
Summary form only given, as follows. A highly overmoded, Ka-band, phase-coherent, harmonic-multiplying, inverted, gyrotwystron (phigtron) experiment is described. The phigtron was composed of the following parts: a fundamental gyro-TWT as prebunching input section; a short buncher cavity (1.5λ); and, a long output cavity (12λ), with both cavities operating at the second harmonic of the electron cyclotron frequency. Phase locking, amplification and mode selection have been studied and compared with performance in a previous one-cavity phigtron. Enhanced amplifier efficiency of 25% and improved frequency response characteristics are obtained with the new two-cavity version, further demonstrating that the phigtron has the potential of becoming a high average power, millimeter wave generator with good efficiency, high gain, compact driver, and medium bandwidth for radar and other advanced applications
Summary form only given, as follows. Recently, a series of experiments conducted in the Naval Research Laboratory's Space Physics Simulation Chamber (SPSC) have shown ion energization in a weakly ionized argon plasma in the presence of large amplitude ion cyclotron waves and a DC electric field. The SPSC is a 1.8 m diameter by 5 m long cylinder equipped with a microwave discharge plasma source, an external magnetic field, and a variable background pressure. Wave and bulk parameters are measured with heatable Langmuir probes, emissive probes, and a perpendicular ion energy analyzer. DC electric fields are created within the SPSC plasma column by modifying the plasma potential tranverse to the external magnetic field. The experimental observations indicate that the argon ion perpendicular temperature can be increased at least by a factor of 2 in the presence of 1-10% plasma density fluctuations, a inhomogeneous DC electric field, and large amplitude ion cyclotron fluctuations. The ion collision frequency is composed of both ion-neutral and ion-electron contributions and can be varied to be much less than or greater than the ambient ion cyclotron frequency. We have computed the expected ion energization in the SPSC using several approaches, i.e., particle-in-cell simulations, quasilinear heating, large amplitude trapping, and ion collisional heating. We will present the results of these analyses and compare with the experimental observations
Summary form only given. A very large amount of money was spent on the controlled thermonuclear fusion in quasi-neutral plasmas. Unfortunately no real positive and remarkable results have been achieved in this way. These unsuccessful or partly successful attempts call for essentially new approaches. This presentation gives an unusual arrangement for the establishment of a controlled thermonuclear reactor using non-neutral plasma, and discusses some possible applications
Summary form only given, as follows. Present paper shows up that the deforming electromagnetic radiation fields (photon gas) or deforming ionized plasma cannot be described in the usual way based on the equilibrium states. Namely, in deforming systems, the quantum structure of the fields collapses generally because then a magnetic current density appears in the Maxwell equations. But these completed Maxwell equations have a non-sinusoidal solutions in general. Therefore, changing topology quantum radiation fields or quantum plasmas cannot inherit their boundary states structures
Summary form only given, as follows. The present paper shows that
the deforming electromagnetic radiation fields (photon gas) or deforming
ionized plasma cannot be quantized, in general. Namely, in deforming
systems, the quantum structure of the fields collapses generally because
then a magnetic current density appears in the Maxwell equations. But
these completed Maxwell equations have a nonsinusoidal solutions in
general. Therefore, changing topology of quantum radiation fields or
quantum plasmas cannot exist. In connection with these systems this
question is raised: can the general nature of the behaviour of the
deforming electromagnetic radiation systems be investigated without
quantum physics with the help of qualitative theory of second-order
linear differential equations so that the results are true with respect
to classes of fast-changing or singular deformations?
Transient solutions for a class of waveforms in a general lossy
medium have been published recently (H.F. Harmuth, 1986). These
solutions are expressed in terms of improper integrals and are functions
of the conductivity of the medium. Numerical evaluation of these
integrals for the case of seawater results in ill-conditioned problems
giving rise to computational overflows. An approximate closed-form
transient solution valid for propagation of signals in seawater is
developed. An electromagnetic signal with the initial time variation of
a rectangular pulse with a given width is assumed. This solution is used
for the computation of the absorption losses in seawater as a function
of propagation distance
The problem of propagation in linear dispersive medium with
initial conditions is a problem that is incompletely treated. The
authors discuss five different methods for solving this problem using a
linear system approach. It is shown that the Fourier transform is not a
proper tool for solving this problem. The Laplace transform is then
shown to work for one type of linear system
One of the most important tasks for the practical use of
nonsinusoidal waves in radar is the design of radiators. Just like
resonating radiators for sinusoidal waves, they must efficiently
transform a driving current and voltage into electromagnetic waves.
However, in addition, the distortions caused by the buildup and decay of
the energy stored in the near zone must be avoided, a task not required
of the radiators of steady-state sinusoidal waves
Discusses two letters by Wait concerning signal solutions to the
Maxwell equations: Wait (1993, IEEE Trans. Electromagn. Comp., vol.35,
no.4, p.486-8) and Wait (1993, IEEE Trans. Electromagn. Comp., vol.34,
no.4, p.491-2)
It has been previously reported that a general electric field
solution and its initial condition, Eg(z,t) and
Eg(z,0), respectively, are not causal when formed by a
superposition of time-harmonic waves in an attenuating medium. However,
this is not the case. Further, the relationship between attenuation and
phase velocity as well as their dependence on frequency arise simply
from the form chosen for the time harmonic particular solutions. Even
though causality is not introduced during the solution to the wave
equation, the general solution can subsequently be shown to be a time
convolution of a causal boundary condition (time history of the electric
field as it crosses the z=0 plane, Eg(0,t)), and the medium's
impulse response g(z,t), which can be shown to be causal. Hence, the
general solution is also causal. The initial condition occurs at the
instant, t=0, when the electric field arrives at the z=0 plane, and it
has been previously reported that the initial condition depends on the
boundary condition for times after the initial time thereby violating
causality. A re-examination shows that the initial condition does not
depend on times after the initial time. Hence, the initial condition
obeys causality, and it can also be shown to be properly determined (E
g(z,0)=0 for z>0) even when the boundary condition is not
zero. It has also been reported that limiting expressions for the
boundary and initial conditions, Eg(0,t→0) and E<sub>g
</sub>(z→0,0), respectively, are not equal. However, a
re-examination reveals that
Eg(0,t→0)=Eg(z→0,0)
A target recognition method that utilizes both target length
determined from target signature duration for target classification and
target shape determined from target signature amplitude variation for
target identification is presented. The transformation of the target
axes coordinate system into a rotated coordinate system enables target
recognition at any aspect angle. The information obtained about target
shape and size, in addition to the velocity information supplied by the
Doppler effect, can be used to generalize Woodward's ambiguity function
to a range-velocity-shape resolution function. Thumbtack
range-velocity-shape resolution functions are easily obtained by
increasing the number of pulses in the transmitted radar signal
It is shown that H.F. Harmuth's magnetic conductivity term is not
needed to predict the transient response for plane-wave transmission in
a homogeneous lossy medium. Thus, his repeated harsh criticisms of S.A.
Stratton's classic analysis using Laplace transforms are not justified
In 1986 H.F. Harmuth introduced a modification of Maxwell's
equations to study the propagation of transient electric and magnetic
field strengths in lossy media. Opponents of this modification of
Maxwell's equations have claimed and attempted to demonstrate that
Maxwell's equations in their known forms can correctly be solved, for
example by the Laplace transformation method, to obtain solutions of
transient electric and associated magnetic field strengths in lossy
media without encountering any difficulties. This work presents detailed
computer plots of Harmuth's transient solutions of the modified
Maxwell's equations and that of Maxwell's equations solved by the
Laplace transformation characteristic for the two solutions, which
indicate that they are not the same. It is shown that Harmuth's
procedure results in physically more plausible solutions
In response to the arguments of J.R. Wait (ibid., vol.34, no.2, p.139, 1992), the commenter gives four different reasons for not neglecting magnetic sources.< >
The commenter clarifies the physics of magnetic dipole currents.
He then discusses J.R. Wait's contention (ibid., vol.34, no.2, p.139,
1992) that one can make magnetic dipole currents disappear by a
mathematical transformation
The problem of detecting an electromagnetic signal with the
initial time variation of a rectangular pulse is presented. The medium
between the transmitter and the receiver is assumed to introduce ohmic
losses. The implication of additive thermal noise on the error
probability and the detectable propagation velocity is investigated. The
results are shown for a synchronous binary communications model in which
the receiver has knowledge of the starting time of each observation
interval. A correlator receiver is assumed for optimal signal detection
in the mean-square-error sense. It is shown that the observable
propagation velocity of the signal is a function of the receiver
characteristics and the parameters of the signal used. Formulas relating
the pulse width, signal-to-noise ratio, propagation distance, error
probability, and the observed propagation velocity are derived. Plots
for specific examples are presented
The commenter maintains that the claims made by H.F. Harmuth in
the above-titled paper (ibid., vol.EMC-28, p.250-8, Nov. 1986) that a
satisfactory condition for the existence of solutions for transients in
lossy media is the modification of Maxwell's equations by the addition
of a magnetic current density is not valid. In his reply, Harmuth states
that if the commenter's claim holds true regardless of the method of
solution, he will have contributed an important simplification to the
problem of transient solutions of Maxwell's equations. He provides
further discussion of the commenter's point
A beamforming method for nonsinusoidal waves using parabolic
arrays is described. Antenna patterns for rectangular and sinusoidal
pulses are given. Patterns for radiated signals with arbitrary time
variations are shown to be derivable through function approximation by
sums of linear ramp functions. In addition, the related far-field
transient of signals that are zero for t <0 and have an
arbitrary time variation for t ⩾0 is described. A number of
computer simulations are also given
In commenting on the above-named work by O.R. Asfar (see ibid., vol.EMC-32, no.3, p.228-31, Aug. 1990), the commenter notes that one can write infinitely many solutions for the associated magnetic field strength that will all satisfy Maxwell's equations, but Maxwell's equations cannot tell which one of these infinitely many solutions is the right one. It is further pointed out that the physical significance of the magnetic current density term used became clear when transients in lossy media were investigated with Lorentz's equations of electron theory, which allow for the fact that electric charges are always connected with particles having a mass, whereas Maxwell's original equations do not contain the concept of mass. A physical explanation for this is offered, and attention is given to the creation of the singularity in Maxwell's equations that make sit impossible to obtain the associated magnetic field strength without some limit process
Additional comments on an ongoing controversy on Maxwell's equations are presented. Kuester's (see ibid., vol.EMC-29, no.2, p.187, 1987), relation for the magnitude of the electric field strength for a planar TEM wave with any polarisation excited by an electric step function is discussed
The well-known radar equation for sinusoidal waves is extended to
apply to nonsinusoidal waves, in particular to binary waves with the two
values ± E and ± H for the electric- and
magnetic-field strength during signal transmission. Three major
modifications have to be made: the concept of radar cross section is
changed; the gain of the radiating antenna and the resolution angle of
the receiving antenna are different from the values holding for
sinusoidal waves; and the effect of noise is modified, primarily due to
the absence of a rectifier
J.E. Gray and S.P. Bowen (see ibid., vol.30, no.4, p.586-9, Nov.
1988) use a modification of Maxwell's equations by substituting
distributions for functions differentiable in the sense of Leibnitz and
Newton. The commenter notes that the work of Gray and Bowen confirms
what he has claimed previously, i.e. that Maxwell's equations must be
modified. The commenter then considers which modification(s) can explain
all the experimental results that the current theory cannot
explain
It is well known that the usual frequency filters based on sine-cosine functions do not require synchronization. Furthermore, sinusoidal electromagnetic waves of different frequency can be separated in mobile communication without any synchronization between the various transmitters and receivers. It is widely believed that this is a result of certain shift invariant features of sinusoidal functions that do not exist for other functions. The purpose of this report is to show by means of simple examples that there are infinitely many systems of functions on which one may base asynchronous filters and mobile radio communication. The difference in the usefulness of these systems of functions depends on the state of technology, no system is inherently better than others. (Author)
There is a class of antennas whose pattern as well as impedance is practically independent of frequency for all frequencies above a certain value. The general formula for their shape is r = e^{a}(varpi+varpi_{0})F(theta) where r theta varpi are the usual spherical coordinates, a and varpi_{0} are constants and F(theta) is any function of theta . Assuming a to be positive, varpi ranges from - infty to some finite value which determines the low frequency limit. For such antennas a change of frequency is equivalent to a rotation of the antenna about theta=0 . It appears that the pattern converges to the characteristic pattern as the frequency is raised, if a is not infty , and that the impedance converges to the characteristic impedance for all a .
It is well known that the usual frequency filters based on sine-cosine functions do not require synchronization. Furthermore, sinusoidal electromagnetic waves of different frequency can be separated in mobile communication without any synchronization between the various transmitters and receivers, It is widely believed that this is a result of certain shift invariant features of sinusoidal functions that do not exist for other functions, The purpose of this paper is to show by means of simple examples that there are infinitely many systems of functions on which one may base asynchronous filters and mobile radio commnuication. The difference in the usefulness of these systems of functions depends only on the state of technology, no system is inherently better than others.
Elements of electromagnetic waves
- L A Ware
- LA Ware
Radiation patterns for antennas with Walsh current inputs
- J Perlman
Electromagnetic Walsh waves in communication
- H Harmuth
Grundlagen und mögliche Anwendungen der Sequenztechnik
- H Harmuth