Open Electromagnetic Waveguides
This book provides an extensive introduction to the practical use of spectral methods in solving real engineering problems in an open electromagnetic waveguide environment.
Inspec keywords: waveguide theory; waveguides; electromagnetism
Other keywords: approximate methods; open electromagnetic waveguides; electromagnetic theory; bound modes; planar dielectric waveguides; discontinuities; transverse resonance diffraction
Subjects: Waveguide and cavity theory; Waveguides and microwave transmission lines; Electric and magnetic fields
 Book DOI: 10.1049/PBEW043E
 Chapter DOI: 10.1049/PBEW043E
 ISBN: 9780852968963
 eISBN: 9781849191838
 Page count: 400
 Format: PDF

Front Matter
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1 Introduction to open electromagneticwaveguides
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An open waveguide may be defined as any physical device, with longitudinal axial symmetry and unbounded crosssection, capable of guiding electromagnetic waves. In contrast to closed waveguides, the electromagnetic field in the crosssection is not confined to a limited region of space, thus extending up to infinity. Examples of closed waveguides are wellknown from basic electromagnetic courses; they include coaxial cables, metallic waveguides (with rectangular or circular cross section), etc. Their spectrum is also wellknown, being made by an infinite, discrete set of modes, orthogonal and complete over the waveguide crosssection. On the other hand, any waveguide not entirely enclosed in a metal shielding, may be taken as an example of an open waveguide. It is also worth noting that, by cutting a slot parallel to the longitudinal axis in the metal enclosure of a closed waveguide, again an open waveguide is obtained. An open waveguide possesses a spectrum which is no longer discrete, but is constituted by a few bound modes, when present, plus a continuum of modes.
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2 Electromagnetic theory
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This chapter provides both an overview of classical concepts in electromagnetic theory and a reference with respect to some concepts frequently used throughout the following chapters.
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3 Planar dielectric waveguides
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This chapter deals with planar dielectric waveguides, also called slab waveguides, which are possibly the most simple and yet practically useful open waveguides. In this introduction we briefly recall how a bound mode can occur; we also discuss why it is natural to look for the complete spectrum of slab waveguides and what features it should possess.
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4 Bound modes by approximate methods
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The method used for optical waveguides is the EDC and will be illustrated in the first section of this chapter. Not surprisingly the accuracy of the results obtained by this method improves as the frequency increases. It will be observed also that the results relative to the propagation constant are fairly accurate. Open waveguides operating in the microwave frequency range are often investigated by a different approximate method, i.e. by conformal mapping. The latter is introduced by referring to the example of a microstrip line in the last section of this chapter.
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5 Discontinuities in planar dielectricwaveguides
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In this chapter we begin to examine some simple discontinuity problems by using the example of the slab waveguide. The known modal structure of this waveguide and its onedimensional crosssection allows us to concentrate on the discontinuity problem itself. From a practical viewpoint the problems dealt with in this chapter are relevant in integrated optics and millimetrics as the slab waveguide may be considered a good approximation of the guides used in common practice.
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6 Bound modes by transverse resonancediffraction
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In this chapter we study, in a rigorous manner, the bound modes of several transmission lines which find applications in both the microwave and millimetre wave frequency ranges, as well as in integrated optics. The bound modes of these transmission lines play a fundamental role in circuit design. As noted in previous chapters, in several instances it is possible to derive their properties by using suitable approximations, e.g. the effective dielectric constant method. However, when propagation constants must be known with greater accuracy, or when the approximations break down, or when the field shape is of interest as in discontinuity problems, it becomes necessary to employ rigorous procedures such as those described hereafter. Note also that, as new structures are considered, it is sometimes unclear what approximations are feasible; in these cases a prudent approach suggests using rigorous fullwave analyses.
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7 Complete spectra of open waveguides
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The continuum of an open waveguide describes radiation as simply, in principle, as the discrete spectrum of a classical guide describes any physical field in it. In fact, the knowledge of the modal spectra for open waveguides allows us to apply to discontinuity problems in open environments the same techniques originally developed for closed waveguides. However, this part of the spectrum, the continuum, has received little attention for most open guides. Therefore, this chapter is devoted to an introduction of the continuum. The chapter can be considered to be divided into two parts. In the first part we introduce the main characteristics of this part of the spectrum. In the second part we exemplify the procedure by deriving the continuum for some practical transmission lines such as coplanar, rib and inset waveguides.
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8 Some examples and applications
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This chapter is divided into two parts: the first part deals with somewhat simpler structures and is used to introduce the methodology. In the second part we provide some examples of applications to practical problems such as the characterization of airbridges in coplanar waveguides, of viaholes in microstrip lines and of step discontinuities in dielectric rib waveguides.
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Back Matter
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