Hello Aspirant,

Here are the some preparation books given below:

Maths by B.S. Grewal

General Aptitude by R.S. AGGARWAL

Network theory by Alexander Sadiku

Digital electronics by Morris mano

Signals & Systems By Alan V. Oppenheim

Automatic Control Systems – Benjamin C Kuo

Analog and Digital Communication System by Simon Haykin

most important question bank Gate ECE by R.K Kanodia

You can also go through with the given below link to check the books.

https://engineering.careers360.com/articles/what-are-best-books-for-gate-ec

Good Luck!