Can anyone help me in designing Active RFID reader (2.4GHz) circuit for my project? Any relevent information such as schematic or circuit diagram will help me a lot. Thank you.

There are RFID shields IIRC and RFID readers that have a serial interface (cable) so what is your goal, What are you trying to build? Where do you use the RFID's for.

have you checked - http://shieldlist.org -?