Research On Calibration System Of Open-Ended Rectangular Waveguide Probe From1GHz To26.5GHz

With the development of microwave technology, near-field measurement has been widely used, as one of core components of near-field measurement system, open-ended rectangular waveguide probe (OEWG) has a critical influence on measurement accuracy. Foreign institutions already have the ability of OEWG calibration below Ka-band with high accuracy, compared with which China has a wide gap in the relevant fields. Both for scientific research and national defense, traceability of OEWG is imminently needed.The subject involved in this paper is from National Institute of Metrology, which aims to establish a calibration system for OWEG working from1GHz-26.5GHz, solve traceability issues of absolute gain and pattern of these OWEG and establish national standard of waveguide calibration so as to meet the urgent needs of economic development and national defense, improve service levels of related industries as well as promote the development of microwave measurement technique.This paper makes some theoretical analysis for the characteristics of OWEG, several commonly used formulas to estimate the gain of OWEG are given. Simulation are made for the OWEG, whose results show that OWEG has a full radiation pattern with a wide3dB bandwidth, H-plane pattern is much narrower than E-plane pattern; the gain value of OWEG is low and increases with the frequency;there are no nulls at the boreside gain over the usable bandwidth.On the basis of analysis from theory and simulation, this paper elaborates the principle, site, process and other aspects of the OWEG calibration system. Minimum measurement distances at different frequencies and the size of anechoic chamber as well as the formulas for calculating the gain of OWEG are given. To estimate the accuracy of the calibration system, the measurement gains of WR284are compared with the simulation ones, and the results show that over the whole bandwidth, there are good agreements between the measurement and simulation, among which the maximum deviation is0.25dB.At the end of this paper, basic concepts and assessment principles of uncertainty are introduced, all possible factors are analyzed. A mathematical uncertainty model has been established and analyzed based on the measurement data of WR284OWEG at3GHz. Finally the standard and expanded uncertainties as well as the uncertainty budget of the system are given, which show that at this frequency the major contributions to uncertainty result from the mutual coupling between the probes and mismatch error at the port.