The following text evolved out of a series of courses on radio frequency (RF) engineering to undergraduates, postgraduates, government and industry. It was designed to meet the needs of such groups and, in particular, the needs of working engineers attempting to upgrade their skills. Thirty years ago, it appeared as if the fibre optics revolution would relegate wireless to a niche discipline, and universities accordingly downgraded their offerings in RF. In the past 10 years, however, there has been a renaissance in wireless and to a point where it is now a key technology. This has been made possible by the developments in very large-scale integration (VLSI) and CMOS technology in particular. In order to meet the manpower requirements of the wireless industry, there has been a need to upgrade the status of RF training in universities and to provide courses suitable for in-service training. The applications of wireless systems have changed greatly over the past 30 years, as has the available technology. In particular, there is a greater use of digital technologies, and antenna systems can often be of the array variety. The current text has been written with these changes in mind and there has been a culling of some traditional material that is of limited utility in the current age (graphical design methods for example). Material in the book has been carefully chosen to provide a basic training in RF and a springboard for more advanced study.