We present the design and results of characterization of a new sideband separating (2SB) mixer for 800-950 GHz, based on superconductor-insulator-superconductor (SIS) junctions. This is the first waveguide 2SB SIS mixer demonstrated at such a high frequency. The design is following the classical quadrature hybrid architecture, meanwhile additional attention was put on the reduction of reflections in the RF structure in order to minimize the RF imbalance, to achieve a high image rejection ratio (IRR). The RF waveguide block was manufactured by micromilling and populated by single-ended SIS mixers developed earlier for upgrade of the CHAMP+ high-band array on the APEX telescope. These SIS mixers have double-sideband (DSB) noise temperatures from 210 to 400 K. The assembled 2SB mixer yields a SSB noise temperature from 450 to 900 K, with an IRR above 15 dB in 95% of the band. Comparing the DSB and the SSB sensitivities, we find that the waveguide losses are as low as expected and do not exceed 0.6 dB. The presented mixer is a prototype for use in a 2SB

Traditionally, corrugated conical horn antennas have been the main choice for use in astronomical receivers in the range of millimeter and submillimeter waves. They present low cross-polar level and high coupling efficiency into the fundamental Gaussian mode. However, this type of antenna is difficult to manufacture, inevitably increasing its price and extending the production process. In this article, we present two kinds of feed horn antennas, aimed for use in a frequency range equivalent to atacama large millimeter/submillimeter array (ALMA) Band 6 (211-275 GHz), which can be fabricated in a much simpler way with the conventional machining tools. Specifically, we present the design and performance comparison of smooth-walled spline-profile horns in two geometries, diagonal, and conical. Optimization of the designs has been made by means of an algorithm that allowed us to obtain models whose electrical and mechanical characteristics make them competitive when compared with corrugated horns. In particular, they are 40% shorter than the conventional corrugated horns suited for this band, representing an advantage given the stringent space constraints of most astronomical receivers. We also demonstrate that they can be coupled efficiently to an astronomical-grade optical system, using ALMA Band-6 receiver as an example. Furthermore, we have constructed the diagonal horn and characterized it thoroughly. Experimental results of the radiation pattern at room temperature show a good cross-polar performance with levels below −20 dB and Gaussicity above 96%. Our calculations show a good antenna-efficiency level with losses less than 1%. All these properties demonstrate the feasibility of this type of horns to become the main option at the time of choosing a feed system for cutting-edge astronomical applications.

In this work, we report the design, construction, and characterization of two free-standing single-layer frequencyselective 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 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 flowertype 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.

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