Let’s get something clear straight from the beginning: this book discusses advanced topics, so its target audience consists of graduate students and specialists working in the electrical engineering field.
You should buy "RF Circuit Design: Theory and Applications" if you want to deepen your understanding of transmission lines, oscillators, filters, mixers, and so much more.
I especially liked the authors’ ability to dissect highly technical material by making use of intuitive diagrams and step-by-step explanations of real-world examples.
The book tries (and succeeds) to keep readers up to date with the latest discoveries in the industry by covering RF MEMS and RFICs, discussing simulation software, modern design tools, and so on.
Don’t buy this book if you are an absolute beginner. Or buy it if you really want to, but start your RF circuit design journey using one of the other books recommended on this site.