Agilent / HP / Keysight 4286A

This unit offers accurate and reliable measurements in order to improve the quality and performance of your electronic components or circuit design.

It employs direct-current voltage-measurement technique, as opposed to the reflectionmeasurement technique, for more accurate impedance measurements over wide impedance range.

Also, Q measurement can be much improved due to advanced calibration technique (typical Q accuracy: 6% at 100MHz, Q=100).

So you can reduce the design uncertainty by measuring your device's true impedance values at RF range.