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.

中文翻译：

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用于低频和宽带吸收率测量的校准平行板波导技术

提出了一种基于平行板波导(PPW)的法向入射吸收率宽带测量技术。该方法非常适用于基于频率选择表面 (FSS) 的吸收器。通过采用 PPW 结构，测量只需要小样本量，即 FSS 的一维阵列。实施直通反射线 (TRL) 校准以消除基于 PPW 的传统方法中的时间门控歧义。工作频率高达 6 GHz 的测量系统的设计使其长度可调，以确保可以在单个设备中执行所有三个校准标准（直通、反射和线路）。此外，PPW 的高度也是可调的，以允许测量具有不同 FSS 周期的吸收体。制造和测量了两个具有不同周期性的单层基于 FSS 的吸收器。结果与传统的自由空间测量系统非常吻合，验证了所提出的方法。