Calibrated Parallel-Plate Waveguide Technique for Low-Frequency and Broadband Absorptivity Measurement

Abstract

A broadband measurement technique for the normal-incidence absorptivity based on parallel-plate waveguide (PPW) is proposed. The method is well suited for frequency-selective surface (FSS)-based absorbers. By employing the PPW structure, only a small sample size, i.e., 1-D array of FSS, is required for the measurement. The thru-reflect-line (TRL) calibration is implemented to remove the time-gating ambiguity in the conventional PPW-based method. A measurement system working up to 6 GHz is designed such that its length is adjustable to ensure all three calibration standards (thru, reflect, and line) can be carried out in a single device. Moreover, the height of the PPW is also adjustable to allow the measurement of absorbers with a different periodicity of FSSs. Two single-layer FSS-based absorbers with different periodicity are fabricated and measured. The results agree well with the conventional free-space measurement system, which validates the proposed method.