| Four significant factors have led us to update this text. The first is the breathtaking progress in technology, especially in receiver and digital techniques. The second is the advance of radio astronomy to shorter wavelengths, and the increased availability of astronomical satellites. The third is a need to reorganize some of the chapters in order to separate the basic theory, that seldom changes, from practical aspects that change often. Finally, it is our desire to enhance the text by including problem sets for each chapter. In view of this ambitious plan, we have expanded the number of authors.
In the reorganization of this edition, we have divided Chap. 4 of the 4th edition into two Chaps. 4 and 5. The first remains Chap. 4, with a slightly different title, Signal Processing and Receivers: Theory. This was expanded to include digital processing and components including samplers and digitizers. In Chap. 5, Practical Receiver Systems. we have relegated the presentations of maser and parametric amplifier front ends, which are no longer commonly used as microwave receivers in radio astronomy, to a short section on “historical developments” and We have retained and improved the presentations of current state-of-the-art devices, cooled transistor and superconducting front ends. We have also included descriptions of local oscillators and phase lock loops. Chapters 5 and 6 in the 4th edition has now become Chap. 6, Fundamentals of Antenna Theory and Chap. 7, Practical Aspects of Filled Aperture Antennas. Our goal is to have an exposition of the rather mathematical theory, in Chap. 6 followed by a treatment of the practical aspects of antennas. Chapter 7 in the 4th edition is now Chap. 8, titled Single Dish Observational Methods. Chapter 9 deals with Interferometers and Aperture Synthesis. Aperture synthesis has become the most important imaging technique in radio astronomy; this provides the only general method available for obtaining images of extremely high resolution and quality, so the discussion has been extended and improved with material pertenant to interferometers such as the Atacama Large Millimeter Array (ALMA) and the Square Kilometer Array (SKA). Chapters 10 to 14 of this edition have been updated to include recent observational results. Chapter 15 of the 4th edition, Molecules in Interstellar Space, has been divided into two Chapters, Overview of Molecular Basics and Chap. 16, Molecules in the Interstellar Medium. Chapters 15 and 16 have been updated to take new developments into account. |
