Description:DT This book provides a strong mathematical grounding in the use of variational principles to analyse distributed electromagnetic structures such as generalised transmission lines. It establishes the link between variational principles and well known analysis methods that are frequently cited in the literature but seldom explained (reaction concept, methods of moments, perturbation method, transmission line matrix, finite difference and finite element methods). It also demonstrates a variety of situations and technologies including microwave and millimetre wave circuits, radiating structures and travelling wave photodetectors. Applications include planar substrates, semiconducting substrates and bioliquids. This book presents a new generalised principle with a number of potential future applications in the fields of distributed circuits and electromagnetics. Numerical simulation, the basic tool for the design of generalised distributed circuits, can be optimised in terms of complexity and computational time by using a variational formulation of the problem. This book describes the application of variational principles to the analysis of multilayered generalised circuits.