I don't know whether you focus on radio frequency or microwave. Both of them have classic works, but most of them are foreign, but they are all written in Chinese. What is said upstairs are all undergraduate textbooks, but I still recommend reading those classic foreign textbooks. For radio frequency, it is "design and application of radio frequency system", and for microwave, it is of course "microwave engineering". Their greatest advantage is that it is not difficult, but it will start from the most basic, but undergraduate. I majored in electricity and electromagnetic field. Good luck!