Elimination of infinities in equivalent edge currents, Part II: Physical optics components

A solution finite for all directions of illumination and observation is derived for the physical optics (PO) components of equivalent edge currents. The solution is based on the uniform asymptotic theory of endpoint evaluation of integrals. An extension taking into account the variation of the surface metric with the distance from the edge is presented, and a similar extension for including slope diffraction is indicated. The expressions derived complement the results of our previous work on elimination of infinities from the fringe components of equivalent currents.     

Uniform physical theory of diffraction equivalent edge currents fortruncated wedge strips

New uniform closed-form expressions for physical theory of diffraction equivalent edge currents are derived for truncated incremental wedge strips. In contrast to previously reported expressions, the new expressions are well behaved for all directions of incidence and observation and take a finite value for zero strip length. This means that the expressions are well suited for implementation in general computer codes. The new expressions are expressed as the difference between two terms. The first term is obtained by integrating the exact fringe wave current on a wedge along an untruncated incremental strip extending from the leading edge of the structure under consideration. The second term is calculated from an integration of the asymptotic fringe wave (FW) current along another untruncated incremental strip extending from the trailing edge of the structure. The new expressions are tested numerically on a triangular cylinder and the results are compared with those obtained using the method of moments and the previously reported expressions     

Transients in dispersive media, part I: Theory

The asymptotic evaluation of complex frequency integrals arising in the theory of radiation from transient sources in dispersive media is reviewed and extended to accommodate phenomena observed at distant observation points at any observation time. Helpful graphical methods are emphasized and illustrated for a plasma medium discussed in detail in Part II of this paper. Results are interpreted in terms of space-time rays whose properties are reviewed, and these rays, together with the (k, omega) dispersion surfaces for the medium, are utilized for the study of reflection and refraction processes at an interface.     

Tutorial 15: control theory, part I

Control theory is the branch of engineering that tries to answer questions like "given a system configured in a particular fashion, will the system behave reasonably?" That is, control theory deals with analyzing systems. Control theory also tries to answer the question "given a system with (negative) feedback, what can I add to my system to see to it that my system will meet its specifications?" That is, control theory deals with designing systems, too.     

Lumped equivalent circuits of magnetic components: thegyrator-capacitor approach

In place of the conventional reluctance-resistance analogy for forming lumped equivalent circuits of inductive components, a permeance-capacitance analogy is advocated. In this approach, magnetic paths are modeled by capacitive circuits and windings are represented by gyrator two-ports. The technique is applied to the integrated magnetics of a zero-ripple isolated Cuk DC-DC converter allowing its electrical and magnetic circuits to be simultaneously simulated with SPICE     

Elimination of emitter edge dislocations in silicon planar n-p-n transistors

It is shown that the conventional method for elimination of emitter edge dislocations, which consists of a low concentration emitter phosphorus diffusion, has two disadvantages: it increases reverse emitter-base current and reduces current gain at low currents. Also, it is shown that the mentioned disadvantages can be successfully avoided by a new method for elimination of emitter edge dislocations, which consists of a high concentration emitter phosphorus diffusion followed by an additional shallow boron diffusion.     

Weapons systems analysis,part I: System effectiveness

Often, a weapon system may be approved based on a particular required military capability without due consideration given to other missions which it might or might not be able to perform. This paper puts forward a methodology for the analysis of weapons systems, and examines various criteria and attributes that relate to system effectiveness. Criteria and attributes included are system performance, operational readiness, life cycle costing, design to cost, reliability, availability, maintainability, producibility, operability, capability, adequacy and logistics.     

Elimination of water peak in optical fibre taper components

A water peak of typically 0.4 dB at 1380 nm is apparent in the loss spectra of single-mode fibre taper components make with conventional water-producing flames. The loss peak is avoided entirely by using a water-free heat source, such as a carbon monoxide flame.<>     

The near field of dipole antennas, part I: Theory

The theoretical and experimental evaluation of the electromagnetic fields in the immediate vicinity of resonant dipole antennas is presented. This type of antenna is widely used with portable and mobile radio transmitters. The work presented herein has been motivated by the concern that future Radio Frequency Protection Guides with respect to human exposure to nonionizing electromagnetic radiation might be expressed strictly in terms of the intensity squared of the electric or magnetic fields. It is shown in the results that it is possible to detect relatively high intensity electromagnetic (EM) fields in close proximity to resonant dipoles even for very low levels of radiated power (1 mW and less). The paper is divided into a theoretical section and an experimental section because its goals are twofold. First, the formulas for the correct evaluation of the EM fields in the close proximity to dipole antennas are established. Second, it is shown that such EM fields, which can be theoretically predicted and experimentally verified with satisfactory accuracy, are indeed strong enough to violate proposed Radio Frequency Protection Guides even for very low levels of radiated power. Thus portable radios are rendered virtually useless, although the same guides permit exposures to much higher levels of power in the far field. Part I of the paper is essentially theoretical and expresses the fields near dipole antennas in terms of cylindrical waves, which lend themselves to closed form integration. The asymptotic expressions of some components of the field are particularly simple for close distances (in terms of wavelength) from the antenna. The correctness of the solution is checked by evaluating how closely boundary conditions are satisfied. Results have shown that previously used formulas for evaluating field intensity very near dipole antennas can give incorrect values.     

Dielectric lens shaping and coma-correction zoning, part I: Analysis

Shaping techniques are applied to the design of dielectric lens antennas. By shaping the lens to serve as an optical transformer for aperture distribution control, many special antenna patterns can be achieved. For multiple beam applications, the cubic phase error for off-axis beams can be significantly reduced by a unique method of coma-correction zoning. Such shaped lenses are excellent candidates for low-cost, lightweight and high-performance antennas for extremely high frequency (EHF) systems. In this communication, the design principles and numerical techniques are given. Examples with parametric trade-offs are also discussed.     

Resolution enhancement in equivalent currents reconstruction by means of prior discrete fourier transform

Use of a plane wave spectrum in the equivalent currents reconstruction of an antenna causes a poor resolution in the spatial domain. This is because the spectrum is band limited and therefore its discrete Fourier transform offers a limited resolution (l). The use of prior discrete Fourier transform for the equivalent current reconstruction is proposed. This technique is able to obtain, by incorporating information of the antenna to the transformation, the best approximation to the ideal currents by means of the minimum weighted norm estimation.     

Weakly dispersive spectral theory of transients, part I: Formulation and interpretation

Dispersive effects in transient propagation and scattering are usually negligible over the high frequency portion of the signal spectrum, and for certain configurations, they may be neglected altogether. The source-excited field may then be expressed as a continuous spatial spectrum of nondispersive time-harmonic local plane waves, which can be inverted in closed form into the time domain to yield a fundamental field representation in terms of a spatial spectrum of transient local plane waves. By exploiting its analytic properties, one may evaluate the basic spectral integral in terms of its singularities-real and complex, time dependent and time independent-in the complex spectral plane. These singularities describe distinct features of the propagation and scattering process appropriate to a given environment. The theory is developed in detail for the generic local plane wave spectra representative of a broad class of two-dimensional propagation and diffraction problems, with emphasis on physical interpretation of the various spectral contributions. Moreover, the theory is compared with a similar approach that restricts all spectra to be real, thereby forcing certain wave processes into a spectral mold less natural than that admitting complex spectra. Finally, application of the theory is illustrated by specific examples. The presentation is divided into three parts. Part I, in this paper, deals with the formulation of the theory and the classification of the singularities. Parts II and III, to appear subsequently, contain the evaluation and interpretation of the spectral integral and the applications, respectively.     

The design of a slot array in nonradiating dielectric waveguide, part I: Theory

A set of theoretical design equations for a slot array fed by nonradiating dielectric (NRD) waveguide is developed. Mutual coupling between the slots cut into one of the metal walls of the waveguide is taken into consideration for a design that can have a predetermined radiation pattern. The theoretical development follows that of Elliott.     

Leakage currents, surface current and 1/f noise in planar bipolar transistors

Using arguments based on the d.c. equivalent circuit of a planar bipolar transistor, it is shown that the ratio ICEO/ICBO is a measure of the significance of surface recombination current. Measurements of 1/f noise and ICEO/ICBO for a variety of transistors provide new evidence that the 1/f noise is due to the surface recombination current.     

Improvement of resolution in equivalent currents reconstruction using Papoulis-Gerchberg algorithm and replicas of the spectrum

A new algorithm to increase the resolution in the reconstruction of equivalent currents from spherical near-field measurements is proposed. The algorithm obtains the non-visible part of the plane- wave spectrum used for the reconstruction. This is achieved by means of a band-limited extrapolation method, the Papoulis-Gerchberg algorithm, and the replication of the known part of the spectrum. The gain in resolution is from llambda in the method without the algorithm proposed, to 0.4-0.51 with this new algorithm. Results with real measurements are shown.     

Quantum-dot lasers: Principal components of the threshold current density

Injection heterolasers based on quantum dots grown by molecular-beam epitaxy have been investigated. It is shown that the room-temperature threshold current density can be lowered to 15 A/cm² by decreasing the nonradiative recombination and increasing the degree of carrier localization. The density of states in structures with vertically coupled quantum dots was investigated by the electroabsorption method. Fiz. Tekh. Poluprovodn. 31, 1106–1108 (September 1997)     

Resonance and radiation of the elliptic disk microstrip structure, part I: Formulation

The analysis of resonance, input impedance, and radiation of the elliptic disk microstrip structure is rigorously formulated, using the scalar and vector Mathieu transforms. With the help of these transforms, the resonance frequencies of the structure can be derived exactly using Galerkin's method and approximately using a perturbational approach. Expressions for the input impedance and the radiation pattern are also obtained.     

Effects of densensitization on mobile radio system performance, part I: Qualitative analysis

Densensitization, or the blocking of the receiver portion of the communications system, is one of the principal causes limiting receiver operation, especially in mobile networks under cositing situations. A clear understanding of this nonlinear effect is thus essential when attempting to improve the reliability of mobile radio communication systems so as to prevent severe interferences. A thorough qualitative analysis of desensitization effects on receiver parameters is provided and semi-empirical and statistical relationships useful for performing quantitative computations are developed. The developed analysis initially treats the computation of desensitization effects on radio communication system scenarios for both a single interfering transmitter and several simultaneous interfering transmitters. The results of this qualitative analysis then allow us to compute quantitatively the desensitization effects of a typical mobile radio system which are presented in a second paper.     

Control of distributed generation systems-Part I: Voltages and currents control

This paper discusses a digital control strategy for three-phase pulse-width modulation voltage inverters used in a single stand-alone ac distributed generation system. The proposed control strategy utilizes the perfect robust servomechanism problem control theory to allow elimination of specified unwanted voltage harmonics from the output voltages under severe nonlinear load and to achieve fast recovery performance on load transient. This technique is combined with a discrete sliding mode current controller that provides fast current limiting capability necessary under overload or short circuit conditions. The proposed control strategy has been implemented on a digital signal processor system and experimentally tested on an 80-kVA prototype unit. The results showed the effectiveness of the proposed control algorithm.