rfid signal strength
How difficult is it to measure signal strength of an RFID tag with a given code in presence of other tags? If there an existing signal structure where it would be easy to do? I would appreciate any references on this subject.
Thank you,
- Nick
The question possibly has to be answered different depending on the involved RFID standard.
I assume, that you are refering to any RFID standard with passive RFID tags. Field strength of tag-to-interrogator communication must be described in terms of modulation ratio or differential field strength rather than absolute quantities as with active transmitters. They have to be measured in presence of an interrogators CW field.
Test and measurement specifications exist for common RFID standards and have usually a defined method to measure tag transmission performance. To distinguish between multiple tags, the respective test receiver or analyzer must have capabilities to follow the communication protocol and display measured quantities related to individual tags.
I know of spezialized analyzers for the 13.56 MHz domain, but I guess, they exist for others as well. A test system can be assembled also from general communication meassurement equipment, but at least a standard specific protocol decoder is needed. Alternatively, selective field monitoring near the tag under test can be a means.
That's what I thought. Looking for a comparison table of standards...
I'm free to choose any existing standard, or create my own as long as I stay within mechanical and tight cost constraints.
I possibly misunderstood the question. I thought it was about performance test of a given RFID system. If this isn't the case, what's your purpose of "measure signal strength of an RFID tag". Which information do you want to get from it? Generally, most RFID interrogators don't provide received signal strength information. They are trying to identify any receivable tag, up to the receivers noise limit, usually.
Because neither interrogator nor tag have omnidirectional antennas respectively coupler coils, field strength isn't clearly related to distance, which is probably the information you're looking for. From theory, circular polarized UHF antennas should operate nearly omnidirectional, but you also have to deal with multipath transmission in any real enviroment. So n-channel diversity would be needed for a reliable distance estimation.
Some practical info in this parallel thread, which I've started on RFID yahoo group. http://finance.groups.yahoo.com/grou...e/message/2527
FYI