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Both FID technology and NFC technology developed based on RFID belong to the category of near field communication and have great applications in the field of Internet of Things. Both are based on the principle of electromagnetic induction, using radio frequency signals to identify and communicate with targets. The read-write distance is an important indicator for evaluating their system, and the tag’s resonance frequency is a key parameter that affects this indicator.
After the passive tags of RFID and NFC are packaged, only the non-contact method can be used to measure their resonant frequency. The principle of the non-contact measurement method is reflection measurement. By measuring the S11 of the reflection parameter and observing the frequency value corresponding to the maximum negative peak of S11, the resonant frequency of the tag can be obtained.
Test instrument selection
In order to ensure the reliability and credibility of the non-contact measurement method, we have adopted two measurement methods for measurement:
method one
Use SSA3000X spectrum analyzer, TG tracking source, reflection bridge, reflection measurement software for measurement
Method Two
Use SVA1000X spectrum & vector network analyzer, mechanical calibration kit, VNA (vector network measurement software option) for measurement
Both SSA3000X and SVA1000X devices have reflection measurement functions, which can measure reflection coefficient (ρ), return loss (Return Loss), and voltage standing wave ratio (VSWR) and other indicators. SVA1000X has a built-in reflection bridge, while SSA3000X has been calibrated at the TG Source side without mechanical calibration parts. At the same time, an Agilent network analyzer is used to verify the above two solutions.
RFID tag actual test
The following test uses RFID passive tags that follow the ISO/IEC 14443 TypeA standard, with a calibration frequency of 13.56MHz, and a near-field probe instead of the 13.56MHz measurement loop antenna. When measuring, keep the measuring distance between the near-field probe and the REID tag at 1cm, and use the Marker to read the negative peak value.
SSA3000X settings
1. First connect the reflection bridge:
IN (TG) port: signal input terminal, used to connect the bridge and the spectrum analyzer tracking source TG Source output port
OUT (RF) port: the signal output terminal, used to connect the bridge and the RF Input of the spectrum analyzer
DUT port: used to connect the bridge and the device under test, in this case, connect a near-field probe
2. Press the Mode button to select the reflection measurement function.
Calibrate the open-circuit load. The device under test needs to be disconnected before calibrating the open-circuit load. After the calibration is completed, you can see the return loss, reflection coefficient, voltage standing wave ratio, etc. at the bottom of the screen
Choose the appropriate scale and reference level. In this example, the scale is 1dB and the reference level is 6dB
Select the frequency, set the start frequency to 11MHz, and the stop frequency to 15MHz
SSA3000X test result: SSA3000X tested RFID resonance frequency is about 13.85MHz, return loss is 1.44dB, voltage standing wave ratio is about 12.13
SVA1000X settings
Press the Mode key to enter the vector network measurement function, select S11 parameter measurement
Perform mechanical calibration. Follow the instructions on the screen and connect the three calibration components OPEN, SHORT, and LOAD to the TG Source interface to complete the calibration.
After the calibration is completed, connect the near-field probe and select the test scale as 1dB and the reference level as 0dB
Select the start frequency to be 11MHz, and the stop frequency to be 15MHz
SVA1000X test results: The tested RFID tag resonant frequency is about 13.83MHz, the return loss is 1.38dB, and the voltage standing wave ratio is about 13.27
Comparative verification
The resonant frequency measured by the Agilent E5071C network analyzer is about 13.82MHz, the return loss is 1.74dB, and the voltage standing wave ratio is about 12.52
Conclusion analysis
For the above two measurement methods, the resonant frequencies are 13.85MHz and 13.83MHz, the return loss is 1.44dB and 1.38dB, and the standing wave ratio is 12.13 and 13.27 respectively. Compared with the resonant frequency measured by the Agilent network analyzer, the result is 13.82MHz, The return loss of 1.74dB and the standing wave ratio of 12.52 are very close. Compared with network analyzers, not only these two solutions are cheaper, but also have the functions of a spectrum analyzer. In this test, SSA3000X directly selects the reflection measurement option and the reflection bridge solution, which is more convenient to operate and the test results are more intuitive, but SVA1000X has both spectrum analyzer, vector network analyzer, cable tester and other functions, which can be applied For more test scenarios.
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