Method for testing the pattern and gain of UHF RFID antenna

1 Introduction

Antenna pattern is also called radiation pattern and far-field pattern. The so-called antenna pattern refers to the graph of the relative field strength of the radiation field changing with the direction at a certain distance from the antenna. It is usually represented by two mutually perpendicular plane patterns in the maximum radiation direction of the antenna. The antenna pattern is An important graph to measure antenna performance; antenna gain is the degree to which the antenna radiates the input power (energy). From a communication point of view, it is the ability to generate signals in a certain direction and within a certain range. This article describes how to use a Finnish tag performance tester to test the pattern and gain of an UHF RFID Reader antenna.

2. The system and components used in the test

In the test, the Finnish UHF tag performance test host, tag design kit software package, gold tag (connected tag in the reader performance test system), large RFID test black box and turntable system will be used.

3. Test antenna pattern

Here, the Finnish UHF tag performance tester is used together with the gold tag to test the antenna pattern. First, connect the gold tag to the port of the UHF antenna, and let the Finnish UHF antenna work as the antenna of the gold tag, as follows As shown in the figure:

The test environment is a large-scale RFID test black box and a turntable system. After connecting the gold tag and the UHF antenna, place it on the turntable in the dark box. Fully automated testing is possible, as shown in the figure below:

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4. Test antenna gain

Using this method to test the gain of the antenna needs to know the detailed parameter indicators of the Finnish reference tag and the panel antenna. In terms of software, use the threshold test function in the tag design kit software package. The threshold test function will use the reader’s transmit power threshold. That is, how much power can be sent by the reader to activate the tag; the power threshold for activating the tag is also used, that is, the power at the tag is the tag activation sensitivity. In the same environment, use a tag performance tester with a Finnish flat-panel antenna and the antenna under test to test the tag activation sensitivity and the reader's transmit power threshold. The transmit power threshold will have different test results due to different antenna gains. Through this The difference allows the calculation of the gain of the antenna under test.

Test process: first build a system with a tag performance tester and a Finnish antenna, use this system for testing, and then use a reference tag to verify the correctness of the system. How to verify it? That is, test the sensitivity power threshold of the Finnish reference tag, and then Import the curve of the reference label (click the button with the green label), and the verification is passed if the difference is less than 1dB. Then use the tested antenna instead of the Finnish antenna, and keep the other connections unchanged. At this time, use the antenna under test to test the threshold of the reference tag.

According to the gain of the Finnish antenna, the results of testing the reference tag with the Finnish antenna, and the results of testing the reference tag with the antenna under test, the gain of the antenna under test is calculated. The gain calculation formula for each frequency point is as follows:

G2 = G1 + Pt1 – Pt2

Here, G2 is the gain of the antenna under test, in dB;

G1 is the gain of the Finnish antenna in dB, see Annex 1 for details;

Pt1 is the transmit power threshold of the reference tag tested by the Finnish antenna, the unit is dBm;

Pt2 is the transmit power threshold for testing the reference tag with the antenna under test, and the unit is dBm.

  5 Conclusion

The antenna pattern test and the antenna gain test can be completed through the UHF tag performance tester of the Voyantic company of Finland in conjunction with the test software, black box, turntable, etc. The operation is simple and the accuracy is high.