Although the primary aim of the book is to present the equivalent-circuit parameters for a large number of microwave structures, a brief but coherent account of the fundamental concepts necessary for their proper utilisation is included. The first three chapters summarise both the field and network theoretic considerations necessary for the derivation and utilisation of the basic transmission line-equivalent-circuit formalism. The mode concept and transmission-line formulation of the field equations are introduced in Chapter 1. This chapter contains an engineering treatment of the transmission-line theory necessary for the description of propagating and nonpropagating modes in the more important types of uniform and nonuniform waveguides. The field-structure, propagation, attenuation, etc., characteristics of the transmission-line modes so described are compiled in Chapter 2, with both quantitive and pictorial detail. The elements of microwave-network theory required for the analysis, representation, and measurement of the equivalent circuits for N-terminal microwave structures are outlined in Chapter 3; also contained in this chapter is a sketch of some of the field theoretic methods employed in the derivation of the equivalent-circuit parameters reported in Chapters 4 to 8. Although most of the above material is written for the impedance-minded microwave engineer, some of the sections should be of interest to the applied mathematician. The remaining chapters contain a compilation of the equivalent-circuit parameters for a variety of nondissipative N-terminal microwave structures. In Chapter 4 a number of two-terminal structures, such as beyondcutoff and radiative waveguide terminations, are treated. Obstacle and aperture discontinuities in waveguides, gratings in free space, etc., are among the four-terminal structures described in Chapter 5. Chapter 6 deals with six-terminal microwave structures and contains the equivalent-circuit parameters for a number of E-and H -plane T- and Y-junctions, bifurcations, etc. Several eight-terminal structures are treated in Chapter 7. Chapter 8 contains the circuit description of a number of typical composite microwave structures; dielectric-filled guides, thick apertures, etc. This edition also contains a new preface by the editor and several pages of errata which he has collected over the past thirty-five years.