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Measuring Impedance of Integral Antennas

Antennas integral to electronic products often have to be impedance matched via a simple network to the radio transceiver chip-sets that they are connected to.

In order to do this, the complex impedance at the input of the antenna has to be known in order to calculate the values of the components used in this network.

As this impedance is effected by the proximity of the antenna to the product casework and the dimensions of the product etc, this impedance has to be measured.

This can often be done by connecting a thin flexible short 50 ohm length of low loss coaxial cable between the WE-2705P and the antenna. The reference plane is moved to the point of measurement, and the complex impedance (R + jX) directly measured.

To avoid significant changes in the electrical properties of the product structure due to the connection of the WE-2705P and coax, it is recommended to fit several ferrite beads over the outside of the coaxial cable at the point of measurement. This helps to isolate the grounding of the testing system from the ground of the device under test.