Measurements of millimeter wave reflection coefficients over wide frequency range by using a special T-junction

This paper reports a method for wideband measurement without adjustment. It is an extension of the T-junction method in which reflection coefficients can be measured with a simple circuit. In the T-junction method, it is necessary to reposition the movable short at each frequency for measuring a characteristic quantity of the system. This makes wideband measurement difficult. A method has been developed that enables wideband measurement by using a special T-junction in which the width of the E-plane of the waveguide connecting the load is narrowed. In accordance with the theoretical study, a T-junction was designed and fabricated. The experiment at 29-39 GHz indicated that wideband measurement is possible. The estimated error of the absolute value of the reflection coefficient of the load at 34.0 GHz is determined.