A simple method for extreme impedances measurement

The paper describes a new method for measurement of extreme impedances — impedances with a magnitude of the corresponding reflection coefficient approaching unity. The proposed method employs a common vector network analyzer (VNA) with a reference impedance of 50 Ω or 75Ω The method is based on subtracting a reference reflection coefficient from a reflection coefficient of the device under test (DUT) by a 180-deg 3dB hybrid coupler. This difference is then amplified and measured by the VNA as a transmission coefficient. The method was experimentally verified in frequency band from 1.5 to 3 GHz. A corresponding calibration and correction method is suggested. Applications of the method can be expected in measurements of emerging novel microwave and THz devices based on carbon nanotubes, whose impedances are in orders of tens or hundreds of kΩ.