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… Click to show full abstract
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.
