Free-Space Transmission Dielectric Properties Measurement Based on Six-Port Technology

Abstract

A six-port technology operating in transmission mode was developed for accurate determination of dielectric properties of low-loss materials from space measurements. The transmission coefficient was obtained by using the ratio of incident waves at ports 1 and 2 of the six-port network, while the power readings were performed at ports 3-6 simultaneously. The incident wave at port 1 originated from a forward propagating electromagnetic wave passing through the material sample. The incident wave at port 2 was the reference signal related to the incident wave at port 1 before or after propagating through the material. The calibration function is developed. The proposed six-port measurement technique was demonstrated at 5.8 GHz for purpose of verification. The material sample was placed between transmitting and receiving antennas. The microwave signal from the oscillator was fed to the transmitting antenna. The receiving antenna collected the signal and sent it to port 1. Two configurations were set up at port 2, either connected to the microwave signal from the oscillator or terminated with an electrical load. Magnitude and phase measurement results for various thicknesses of dielectric slabs compared well with those obtained with a commercial automatic vector network analyzer (ANA). Similarly, dielectric properties measurements on polypropylene, acrylic, and acetal spheres also agreed well with those obtained by the ANA.