Open-ended rectangular waveguides as antennas for measuring high loss dielectric materials at MM band

Open-ended rectangular waveguides, potentially useful as microwave antennas for measuring high-loss dielectric materials at millimeter band, are described. Reflection coefficients have been measured using a six-port automatic reflectometer for a waveguide filled with standard flanges in contact with the tested materials. The formula for solving for the dielectric constant is derived, and a six-port reflectometer which satisfies the optimum criteria is introduced. Several materials, including distilled water, alcohol, and a type of high-loss solid material, have been measured at 8-mm band (f=36.2 GHz). It is concluded that the proposed measurement technique is convenient, relatively accurate, and of practical usefulness, especially at millimeter and submillimeter wavebands.<>