Contactless measurement method

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5

Contactless measurement method

This section describes a contactless verification method of antenna coil prototypes. The

results presented here are based on a short-range (SR) tag antenna initially designed to

have the following characteristics:

●

Antenna dimensions: 38 mm × 38 mm (A3)

●

Tuning frequency: 14.4 MHz

5.1

Antenna coil prototype verification with an analyzer

Equipment needed:

●

Impedance analyzer

●

Prototype antenna coil

●

Reference capacitor

The equivalent circuit of the antenna coil can be determined using the appropriate

measuring instruments (see Figure 12) and following the instructions described in

Section 5.1.2.

5.1.1

Preparing the equipment and connections

The reference capacitor is used to simulate the presence of the chip on the prototype coil.

Connect it to the coil using an appropriate test fixture (to have as little interference as

possible). The coil is now ready for measurements.

This example measurement uses the 7405-901 Eaton/Alitech (singer) 6 cm loop probe

connected to the reflection interface of the Hp 8712ET network analyzer.

Figure 12.

Measurement equipment

5.1.2

Instructions

The network analyzer must be in reflection mode.

Measurement conditions (case of a short-range RFID tag):

●

Start frequency: 10 MHz

End frequency: 15 MHz

●

Power: –10 dB (which is the minimum detection level, the lowest field required to power

the chip)

The coil must be in the field generated by the network analyzer via the loop probe

(measurements made at about 0.5 cm from the probe).

Network analyser

Loop probe

Antenna coil prototype

+ reference capacitor

ai15816