In this work, we report the design, construction, and characterization of two free-standing single-layer frequency-selective surface structures to be used as dichroic filters in the THz range. Their spectral responses are aimed to fulfill a stringent band-pass performance in the atmospheric window between $600\; \text{and } 725$ GHz. Specifically, the dichroics have been required to allow a transmission of electromagnetic radiation of at least 90%, achieve a rejection in the stop-band lower than $-25$ dB, and have cross-polarization levels below $-30$ dB. All these specifications were demanded to be satisfied at normal and nonnormal beam incidence. We have studied dichroic filters with hexagonal patterns of two different apertures, a well-known single-hole geometry and, in order to enhance the spectral performance, a novel aperture geometry that we call the flower type. Their transmission characteristics were measured using a Fourier transform spectrometer. The electromagnetic simulations and experimental results not only show a good agreement but they demonstrate that the flower-type geometry can greatly outperform its single-hole counterpart achieving all the desired requirements. In this way, we demonstrate the feasibility of implementing single-layer systems at (sub)-THz frequencies suitable for low-noise astronomical applications.

中文翻译：

---

用于 THz 频率多频接收器的单层二向色滤波器

在这项工作中，我们报告了在太赫兹范围内用作二向色滤波器的两个独立式单层频率选择表面结构的设计、构造和表征。它们的光谱响应旨在满足大气窗口中严格的带通性能$600\; \text{和} 725$ 吉赫兹。具体而言，要求二向色镜允许至少 90% 的电磁辐射传输，在阻带中实现低于$-25$ dB，并且交叉极化水平低于 $-30$ D b。要求在垂直和非垂直光束入射时满足所有这些规格。我们研究了具有两种不同孔径的六边形图案的二向色滤光片、一种众所周知的单孔几何形状，以及为了提高光谱性能，我们称之为花型的新型孔径几何形状。使用傅立叶变换光谱仪测量它们的传输特性。电磁模拟和实验结果不仅显示出良好的一致性，而且还表明花型几何形状可以大大优于其单孔几何形状，实现所有所需的要求。通过这种方式，我们证明了在适合低噪声天文应用的（亚）太赫兹频率下实现单层系统的可行性。