# Arrays of Sub-Terahertz Cryogenic Metamaterial
###### Abstract  
Integrated quasi-optical cryogenic terahertz receivers contain arrays of detectors, quasi-optical filters, interferometers, and other metamaterials. Matrices of quasi-optical band-pass, low-pass, and high-pass filters, Fabry-Perot grid interferometers, and arrays of half-wave and electrically small antennas with superconductor-insulator-normal metal-insulator-superconductor (SINIS) sub-terahertz wavelength range detectors were fabricated and experimentally studied on the same computational, technological, and experimental platform. For the design of the filters, we used the periodic frequency-selective surfaces (FSS) approach, contrary to detector arrays that can be presented in a model of distributed absorbers. The structures were fabricated using direct electron beam lithography, thermal shadow evaporation, lift-off, alternatively magnetron sputtering, and chemical and plasma etching. The numerical simulation methods of such structures are sufficiently different: for the reactive matrices with low losses, the approximation of an infinite structure with periodic boundary conditions is applicable, and for the arrays of detectors with dissipative elements of absorbers, a complete analysis of the finite structure with hundreds of interacting ports is applicable. The difference is determined by the presence of dissipation in the detector arrays, the phase of the reflected or re-emitted signal turned out to be undefined and the Floquet periodic boundary conditions are correct only for a phased array antenna. The spectral characteristics of the created filters, interferometers, and antenna arrays were measured in the frequency range 50-600 GHz.  
f 1 (2021)  
Bolometer-type detecting devices are intrinsically wideband and are affected by incoming background radiation in the wide frequency range. Usually, bolometers are integrated into antennas (antenna arrays) designed for this specific frequency range to match impedances and receive the incoming signal with the detector in the required frequency band. Additional quasi-optical beam guides with band-pass, low-pass, and high-pass filter elements eliminate or reduce out-of-band background overheating. In the sub-THz wavelength range, it is effective to use frequency-selective surfaces approach, on the basis of which both receiving antenna arrays and various filters (band-pass, low-pass, and high-pass filters) can be created.  
Both matrices of bolometers and mesh filters can be viewed as a sort of metamaterial or metasurface. Metamaterial [7] and metasurface [8], as its specific option, can be applied for receiving, filtering, and conversion of electromagnetic radiation in a wide range of spectra. In this paper, we present simulation and experimental studies of mesh filters with half-wave and electrically small unit cells, as well as matrices of half-wave and electrically small ring antennas with bolometers. Structures with half-wave unit cell is suitable for narrow-band applications, and matrices with electrically small unit cell are advantageous for broad-bang applications. Simulation approaches for these two families of metasurfaces are quite different. In Section 2, we present frequency-selective surface modelling, Section 3 describes matrices of various filters, simulation, fabrication, and experimental studies. Section 4 is devoted to matrices of annular ring antennas with bolometers, also simulation, fabrication, and experimental studies.