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HF characteristic impedance

(mechanical dimensions of coaxial impedance standards)

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For the determination of the characteristic impedance of coaxial HF reference impedance standards ("air lines"), the diameter of both inner and outer conductor must be precisely known. Additionally, in case of air lines used as HF phase standards, their length must be precisely determined as well.

These diameters are determined by using a commercial diameter measuring setup ("air gauge") with analog voltage output and a commercial lasermicrometer system (for inner conductor diameter measurements). By relative measurement the diameter of the device under test is compared with the diameter of three diameter standards (precise cylindrical bolts or rings) which are traced back to PTB length standards. To increase the measurement resolution down to 0.1 µm, the measured voltages are A/D-converted with high resolution and acquired by a PC for data processing. Simultaneously, the position of the device under test is measured by a commercial length measuring system with digital output to the PC.

A commercial length measuring system with digital display used to determine the axial dimensions of the air lines. The length of both inner and outer conductor is compared with the length of gauge blocks which are traced back to PTB length standards.

With these measuring setups, coaxial HF impedance standards in the coaxial line systems 7 mm (connectors PC-7 and N), 3.5 mm (PC-3.5), 2.92 mm (PC-2.92), 2.4 mm (PC-2.4), 1.85 mm (PC-1.85) and 1.0 mm (PC-1.0) can be mechanically characterized.

Measurement Setup for the caracteristic impedance.
Length measurement, Lasermikrometer and Air-Gauge system (from left to right).

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Research/Development

The setups for calibration of coaxial impedance standards are continuously enhanced.

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