Here are some of the preparation books for GATE ECE given below you can prefer:

General Aptitude: By CAT by Arun Sharma, Quantitative Aptitude by R.S Agarwal

Control System: by Nagarath and Gopal

Network: by Alexander Sadiku

Electronic Devices:  by Millman & Halkias

Signal Systems:   by S.K Mitra

Analog Circuits : By Donald A Neaman

Digital System : by M.Morris Mano

Electromagnetics : by Matthew N.O. Sadiku

Communication System : by Simon Haykin

MCQ book : Gate ECE by R.K Kanodia

Maths : by R. K. Jain

To check complete detail about the books you can go through with given below link.

GATE ECE Syllabus

Good Luck!