Hello Aspirant,

I am enlisting down some best books for preparation of IES and GATE 2021especially for ECE branch :-

@IES

For General studies & Engineering Aptitude :-

• General Studies & Engineering Aptitude 2020-IES Master Publication
• ESE 2020 Prelims: General Studies & Engineering Aptitude-ACE Engineering Publications
• ESE 2020 General Studies & Engineering Aptitude Practice Book-Made Easy Publications
• General Studies & Engineering Aptitude-R.K. Jain

For Electronics and Telecommunication part :-

• Network Analysis-a) Van Valkenburg b) Chakrabarti
• Electromagnetic Waves & Radiating Systems-a) Jardon & Balmain b) JD Kraus
• Integrated Circuits-K.R. Botkar
• Op. Amps & Linear Integrated Circuit-Gayakwad
• Digital Logic & Computer Design-Morris Mano
• Automatic Control System-a)Benjamin C. Kuo b) B.S Manke
• Control System Engg.-Nagrath & Gopal
• Principle of Communication System-a) Taub & Schilling b) J.B Gupta) c) A. Bruu Carlson
• Integrated Electronics-a) Jacob Milman & C. Halkias b) Millman & Grabel
• Network and Systems-D. Roy Choudhary
• Signals and System-a) Oppehum, Willsky & Nacob b) Sanjay Sharma
• Electronics & Communication Engineering-Arihant Publication
• Detailed Solutions in Electronics & Communication for Competitions-S. K. Karna
• Electronics Engineering Handout-Made Easy Publication

For more details kindly check out the link given below :-

https://competition.careers360.com/articles/upsc-ese-books

@GATE

• Wiley Acing the GATE: Electronics and Communication Engineering, 2ed, 2020-Varsha Agrawal, Nakul Maini Anil K. Maini
• GATE Electronics and Communication Engineering-Pearson
• GATE 2020: Electronics Engineering 33 Years’ Topic-Wise Previous Solved Papers-GK Publications
• GATE Tutor 2020 For Electronics and Communication Engineering-Arihant Experts
• GATE-2020 Electronics & Communication Engineering Previous GATE Questions with Solutions-ACE Engineering Academy
• Network Analysis and Synthesis-Franklin F. Kuo
• Circuits and Networks-A. Sudhakar, Shyammohan S. Palli
• Circuit Theory-A Chakravarthy
• Signals and Systems-Simon Haykin and Bang Vanveen
• Electronic Devices and Circuits-Millman, Halkias
• Fundamentals of Digital Circuits-Kumar A. Anand
• Control Systems Engineering-IJ Nagrath, M Gopal
• Microprocessors and Its Interfacing-Douglas V Hall
• Communication Systems-Simon Haykins
• Elements of Electromagnetics-N. O. Sadiku

For more details kindly check out the link given below :-

https://engineering.careers360.com/articles/gate-preparation-books-for-ece

I hope this information helps you.

Good Luck!!