Adaptor calibration using a matched load and an adjustable shorter without specified phases

The vector network analyzer (VNA) has been widely applied in the measurement of microwave devices with wide frequency bandwidths. Particularly, the measurement of the complex reflection coefficients of waveguide devices is its important applications. Due to connecting the devices to be measured to the VNA with a coaxial-to-waveguide adaptor, the systemic error caused by the defect of the coaxial-to-waveguide adaptor will be introduced. For solving the problem, the calibration of the coaxial-to-waveguide adaptor is needed by connecting a series of known standard components to the measurement system. Subsequently, the systemic error can be obtained by analyzing the measurement results of the known standard components. The traditional calibration method uses three standard components, i.e., a load, a short circuit, and an offset short with known phase. However, with the traditional calibration method, the exact location of the short plane is difficult to be determined at the range of millimeter wave frequencies. In this paper, a novel calibration procedure using a matched load and an adjustable shorter with several unspecified phases is proposed to reduce the systemic error caused by the adaptor. The advantage of this method is only to define one shorter plane as reference plane. During the calibration process, the position of the piston is unnecessary to be recorded. More offset shorts are used; more accurate de-embedding effect can be get. The proposed calibration method is especially fitted to the system calibration at the range of millimeter wave frequencies, where the accuracy of the system calibration is very sensitive to the position of standard short plane. The measured results show that the module of corrected S₁₁ of a shorter is less than 0.1dB with linear phase delay and the corrected S₁₁ of a matched load is below -40 dB. The results are much more accurate than the raw readings, 1.3 dB and -15dB respectively, before the adaptor calibration. It is also shown that the technique is resistant to the error of the adjustable shorter position and is easy to implement.