This book was written more than 35 years ago, so it's hard to emphasize the "Modern" in the book. The transmission line equations and their solutions, the device analyses, the S parameter network theory, etc., of course have not changed, so this book is for most topics still current.
The book was written in the 1970s, before the era of powerful personal computers and very inexpensive computer memory. The numerical analyses of transmission line parameters were written in 1970s Fortran and use only the very limited memory available at the time. These programs will still run on any computer with a Fortran compiler installed, but the user interested in these programs would do much better looking to a current book such as the Introduction To Numerical Electrostatics described on this website.
From The Jacket-Leaf
This book covers the latest methods for properly considering transmission line effects, and the calculation of transmission line properties as a function of materials and geometries. Emphasizing the properties of stripline and microstrip circuits, the author explans that, at high enough frequencies, almost ever interconnection in a circuit exhibits transmission line properties and that, if these circuits are to be well deisgned, the transmission lines in the circuit must be appropriately treated as part of the circuit.... and the it is no longer possible to separate the transmission line user from the transmission line designer - not only are the lines present, but their properties are functions of the circuit layout itself.
The book begins with a review of the underlying foundations of conventional transmission line theory; basic equations are derived and terms are defined. Following is a discussion of scattering (S) parameters - the only convenient method for measuring transmission line parameters at high frequencies...
The next two chapters discuss properties of various transmission line structures relevant to circuit design. Chapter 7 then shows how the skin effect - a primary loss mechanism in transmission lines - can be evaluated for almost any structure. Chapter 8 introduces coupled transmission line devices, while chapters 9 and 10 treat several approaches to finding single and coupled line parameters..... In chapter 11, the treatment of a broad class of transmission line devices used to match impedances, ..... And finally, chapter 12 presents various useful tricks for building practical circuits.
Section 6.4 is an incorrect conformal transformation analysis.