Analysis of Contactless Measurement Accuracy of RFID Transponder Resonant Frequency and Quality Factor

The article analyses the accuracy of contactless measurement of resonant frequency and quality factor of RFID transponders in a simplified measuring circuit that does not use an impedance meter nor vector network analyser. The described measurement does not use compensation for the influence of the measuring circuit on the results. This creates a systematic measurement error, the value of which is analysed. Such simplified measuring circuit is used for fast testing of the finalized RFID transponders in the factory when contact measurement is no longer possible. The measuring circuit works like a band-stop (notch) filter, and to measure the parameters of RFID transponders, it is sufficient to measure the absolute value of the transfer function, e.g. using a signal generator and a voltage level meter, but a spectrum analyser with a tracking generator can be faster alternative. The results of the analysis show the influence of individual parameters of the measuring circuit, including the parasitic ones, on the accuracy of the resonant frequency and quality factor measurement.