Montoya (Sigma),

You did not give any indication of the frequency you use, and commercial
RFID tags range from somewhere around 125 kHz to over 5 Ghz. Makes just
a little bit of difference.

This can't be part of a legitimate commercial project or else the
company would already be bankrupt for lack of adequate staffing.
Assuming it is a student project the recommendation would be to contact
your professors and fellow students to learn more about RF.

For some specific ideas check out some of the voluminous documentation
available from RFID manufacturers. For example, Texas Instruments has a
lot of RFID documents available for downloading, including a 47 page
technical note on antennas for RFID. The high level site address is
www.ti.com/rfid

73,
Gene
W4SZ


Montoya wrote:
Hi, all,
I am new to RF, but (un)fortunately i am handling a transferred
project on RFID. Some of the rf concepts i am not not so sure, and
seek for assitance here.
Let me give a bit more on the original designs first. They are tags
that talk to each other unlike the passive tag. This design is already
working with a quarter wave-length antenna. My task is to modify it
to a smaller (shorter) one.
The design is like :
antenna----matching circuit----transceiver----mcu

Now comes the questions:
1. when we talk about the load impedance, where should it start
counting? From transceiver down left or from the matching circuit down
left?
2. the original matching circuit is working for the quarter wave
length antenna. Do i need to adjust the value (C and L) if i replace
them with other forms of antennas(e.g chip antenna, loop antenna)?
3. How am i going to measure the load impedance? What equipment is
needed?

thanks. Any advice is favorable.
Sigma