Testing UHF RFID Antenna Radiating Pattern and Gain with Voyantic Tagformance

Application Note

Published 1/2015
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1 Introduction

This application note describes how the Voyantic Tagformance can be used for testing the UHF RFID reader antenna’s radiating pattern and gain.

2 System and Components Used in the Testing

The following system components are used in the described test:

  • Tagformance lite Measurement Unit (TF-HW-TFL)
  • Tag Designer Suite (TDS) software package (TF-SW-TDS)
  • Connectorized tag (delivered as a part of the Readformance system), separately part TF-AC-CTA
  • Large RFID Measurement Cabinet (LC-HW-SR) with rotation system (LC-HW-ROT).

3 Testing the Radiating Pattern

The antenna can be tested with the Tagformance lite using a connectorized tag. The connectorized tag is attached to the antenna port. In the combination the UHF antenna works as tag’s antenna, and antenna – tag combination can be tested.

When a rotation test is made for tag + antenna, the result is a radiating pattern with the set frequency and power.

The results can be used for comparing antennas.

4 Testing the Antenna Gain

Measuring the antenna gain is based on the accurately known characterization of the Voyantic Tagformance Reference Tag and Patch Antenna used in the Tagformance system.

The threshold power required to power up the tag is constant (power on tag forward). The transmit power required to reach the threshold power on tag forward varies depending on the reader’s output power, losses from the cables and the antenna gain. When the threshold transmit power is measured with both the Voyantic antenna and the antenna to be tested in same surroundings, the difference in the transmit power is caused by the difference in the antenna gain. The antenna gain can be calculated from this difference.

4.1 Test Procedure

Create the setup using the Voyantic antenna; use a measured setup. Verify with the Reference Tag that the setup is correct: measure the Voyantic Reference Tag and check that the result corresponds with the saved reference tag curve (quick button with green tag image). The difference should be less than 1dB.

Replace the Voyantic antenna with the antenna to be tested, without changing the setup.

Measure the frequency response (threshold sweep) with the Voyantic Reference Tag with the antenna to be tested.

Take the measurement result, the Reference Tag data and the gain curve of the Voyantic antenna to Excel and calculate the gain (antenna factor) of the antenna to be tested as a function of frequency.

For each frequency point:
G2 = G1 + Pt1 – Pt2

G2 is the gain of the antenna to be tested in dB
G1 is the gain of the Voyantic antenna in dB, values are in Appendix 1
Pt1 is the threshold transmitted power of the Reference Tag measured with the Voyantic antenna in dBm
Pt2 is the threshold transmitted power of the Reference Tag measured with the antenna to be tested in dBm.

Appendix 1 – Voyantic Standard Patch Antenna Gain