help in my rfid design (antenna)

sir. I need an rfid solution, with a custom antenna. How can i do this in a simple and cheap manner. All the rfid modules in the market here is with antenna. I need a big antenna. I need to detect the bus going under this and to identify the bus. Still the problem is the bus contain peoples with the rfid cards. My question is
1, how the rfid used to detect a bus like huge structure ?
2, is there any interfearance occur when the bus and the peoples contain same wave length rfid cards ?

Implementing RFID without knowing what you are doing may result in disaster. Just a bigger antenna may not fulfil your needs and/or may cause interference in other systems.

When this is an application with few readers, large number of tags and relative large distance (say above 1m), you may consider UHF as this gives longest reading range with reasonably prices hardware (both reader and antennas).

When 13.56 MHz is your only option, connecting a larger antenna to a low power reader will lead to a reduction in reading range beyond certain antenna size. To overcome this, you need more power.

I would recommend you to get a good book on RFID (for example: "RFID Handbook, Fundamentals and Applications in Contactless Smart Cards and Identification", or "the RF in RFID" [focus on UHF]).

thanks brother. I'll refer these books and post my ideas