What is the key part in RFID design?

There are three key blocks in RFID passive tag design:
1. The rectifier that powers the circuit. It is the process that mainly defines its performance;
2. The antenna and the matching issue with the integrated circuit;
3. The backscattering modulator that is responsible for the communication tag-to-reader. Here, the impedance that you choose to modulate have a high impact.

A good starting point is the book from Finkenzeller " RFID Handbook".

I would say is the antenna. Depending of the frequency and
the size of the design, the matching of the antenna can be a
nightmare.

The isolation between transmit and receive ports has a very significant impact
on the read range for passive RFID systems.

Hi,

how can we isolate the transmit and receive ports of an RFId system.
plz help guys

-r

Do you mean tag or reader? For the tag, there is no problem of isolation. For the reader, the transmit RF power leaking into receive path may degrade the sensitivity of the receiver.