Design of the Complex Permittivity Measurement System Based on the Waveguide Six-Port Reflectometer

This article proposes a simple and cheap complex permittivity measurement system at the frequency of 2450 MHz based on a waveguide six-port reflectometer (SPR) and a ridge waveguide. The SPR composed of a waveguide-stripline-coaxial directional coupler and three SubMiniature version A (SMA) probes is designed. The general theoretical model, simulation, and implementation of the waveguide SPR with an optimal accuracy are given. Within the dynamic measurement range of the power meters, the designed SPR can accurately measure the reflection coefficient and have high measurement stability at different power levels. The ridge waveguide is used as the carrier of the material to obtain good monotonicity of the complex permittivity, and a backpropagation neural network (BPNN) is established for the relationship between the complex permittivity and the reflection coefficient. Compared with the reference values in the literature, it can be found that the error of the whole system in measuring the complex permittivity is also within the acceptable range. The SPR based on rectangular waveguide provides a basis for the measurement while heating with high-power microwave energy.