The study of the origin and transport of water in the universe is an important part of the scientific program of the Millimetron space observatory. This will be made possible by observations conducted in single-dish mode using an onboard instrument-the high-resolution spectrometer (HRS). This instrument incorporates heterodyne array receivers operating within the range 0.5 -2.7 THz, comprising 3-pixel arrays of superconductor-insulator-superconductor mixers operating at frequencies below 1.3 THz and 7-pixel matrix receivers based on NbN HEB mixers observing above 1.3 THz. This article presents the current status of development for a mixers planned for use in the HRS instrument of the Millimetron space observatory.

The Cherenkov Telescope Array Observatory (CTAO) will include telescopes of three different sizes, the smallest of which are the Small-Sized Telescopes (SSTs). In particular, the SSTs will be installed at the southern site of CTAO, on the Chilean Andes, and will cover the highest energy range of CTAO (up to similar to 300 TeV). The SSTs are developed by an international consortium of institutes that will provide them as an in-kind contribution to CTAO. The optical design of the SSTs is based on a Schwarzschild-Couder-like dual-mirror polynomial configuration, with a primary aperture of 4.3m diameter. They are equipped with a focal plane camera based on SiPM detectors covering a field of view of similar to 9 degrees. The preliminary design of the SST telescopes was evaluated and approved during the Product Review (PR) organised with CTAO in February 2023. The SST project is now going through a consolidation phase leading to the finalisation and submission of the final design to the Critical Design Review (CDR), expected to occur late 2024, after which the production and construction of the telescopes will begin leading to a delivery of the telescopes to CTAO southern site starting at the end of 2025-early 2026 onward. In this contribution we will present the progress of the SST programme, including the results of the PDR, the consolidation phase of the project and the plan up to the on-site integration of the telescopes.

The Africa Millimetre Telescope (AMT) is a project to realize the first millimeter-wave telescope in Namibia desert to participate in the Event Horizon Telescope (EHT) network and make higher-resolution pictures of black holes possible. We made a preliminary design of the optics to combine the beams of the first light receivers that will enable simultaneous observations of the same area of the sky in four frequency bands. The system is based on the use of dichroics and it has been designed following a geometrical optics approximation to guarantee that all beams will follow the same optical path.

The Millimetron Space Observatory will be equipped with the cryogenically cooled instrument for a Space-Earth Very Large Baseline Interferometry (S-E VLBI). It will be a multi-channel heterodyne receiver with 7mm, 3mm, 1.3mm and 0.8mm channels. The VLBI instrument will have a multi-frequency capability, provided by signal splitting in the input optics and by back-end functionalities. The optical design is shown in this report.

In this work we have measured the frequency response of a heterodyne receiver based on a mixer at the Superconductor-Insulator-Superconductor (SIS) tunnel junction for the frequency range 211–275 GHz. The measurement was done with a Fourier spectrometer using two methods of reading the detector signal: by direct current and by the power of the intermediate frequency output signal. The reason for studying these methods is that intermediate frequency (IF) measurements give a better signal-to-noise ratio than direct current (DC) measurements. It is found that the spectrograms obtained by these methods are different up to the degree of squaring, also for IF measurements the appearance of artefacts in the microwave range, which coincide with the bandwidth of the IF system, is found. Modelling of the spectrometer operation for both methods is carried out, explaining the reason of 'artefacts' occurrence at measurements in the intermediate frequency reading mode and describing the nature and size of the convolution of the receiver spectrum in comparison with direct current measurements.

We present the results of a study on the feasibility of upgrading the existing ALMA Band 9 receivers (602-720 GHz). In the current configuration, each receiver is a dual channel heterodyne system capable of detecting orthogonally polarized signals through the use of a wire grid and a compact arrangement of mirrors. The main goals of the study are the upgrade of the mixer architecture from Double-Sideband (DSB) to Sideband-separating (2SB), the extension of the IF and RF bandwidth, and the analysis of the possibilities of improving the polarimetric performance. We demonstrate the performance of 2SB mixers both in the lab and on-sky with the SEPIA660 receiver at APEX, which shows image rejection ratios exceeding 20 dB and can perform successful observations of several spectral lines close to the band edges. The same architecture in ALMA Band 9 would lead to an increase in the effective spectral sensitivity and a gain of a factor two in observation time. We set up also an electromagnetic model of the optics to simulate the polarization performance of the receivers, which is currently limited by the cross-polar level and the beam squint, i.e. pointing mismatch between the two polarizations. We present the results of the simulations compared to the measurements and we conclude that the use of a polarizing grid is the main responsible of the limitations.

In some practical applications, devices based on superconducting electronics, due to their unique set of parameters, are far superior to those based on conventional technologies, being in some cases the only viable option. One of the most advanced areas is the development of ultra-sensitive terahertz-range receivers: their operating frequency has reached 1 THz, and the noise temperature is only limited by quantum or photon noise.

В работе рассмотрены научные и технические перспективы и возможные направления развития субтерагерцовой астрономии в Российской Федерации. Предложена концепция создания субтерагерцовых инструментов в виде универсальной компактной антенной решетки для размещения на территории России. На базе концепции такой антенной решетки возможна реализация нескольких космических проектов субтерагерцового диапазона нового поколения – космического интерферометра и телескопа, расположенного на поверхности Луны. Наземные антенные решетки смогут выступить в качестве поддержки режима интерферометра со сверхдлинной базой обсерватории «Миллиметрон».

This paper addresses the scientific and technical prospects and potential directions for the development of subterahertz astronomy in the Russian Federation. The concept of creating subterahertz instruments in the form of a universal compact antenna array for placement on the territory of the Russian Federation is proposed. It is possible to implement several space projects in the subterahertz range using such an antenna array, including a space interferometer and a telescope on the surface of the Moon. Ground-based compact antenna arrays will be able to act as a support for the very long baseline interferometer mode of the Millimetron observatory.

Within this proceeding, we introduce the U-Board platform, a versatile platform for signal generation, acquisition and processing, based on a heterogenous processing architecture. Based on this platform we present a readout for Microwave Kinetic Inductance Detectors (MKIDs) for the A-MKID camera for APEX. In addition to the implementation of the readout on this heterogenous architecture, we also present a first comparison of the performance of the readout compared to the currently used readout of the A-MKID camera. Last but not least, we discuss how we plan to miniaturize the current prototype, which is based on commercial off the shelf components.

Characterization of wide-field optics in the Terahertz regime imposes new and demanding requirements for testing systems. Basic optical parameters can be determined from scalar planar characterization, obtained using monochromatic or thermal sources located in the instrument focal plane. In contrast, important features, such as the spillover efficiency, wave front error, or aperture efficiency cannot be easily measured by such approaches. Moreover, when instruments have a curved focal plane, designed to match the hosting telescope, even basic parameters are difficult to extract from scalar planar measurements. In such cases, the use of phase and amplitude information is mandatory. From a complex planar measurement, the complete information of the optical system can be obtained, allowing the estimation of all relevant optical parameters. In this work, we present and demonstrate experimentally a technique to perform such measurement based on the use of continuous wave photonic terahertz sources. Here, we present our results at 350 GHz and 850 GHz, demonstrating the feasibility of performing measurements at different submillimeter frequencies using a single experimental setup. The proposed system was implemented to fully characterize a wide-field submillimeter camera based on kinetic inductance detectors designed to be deployed at the APEX Telescope in Chile.

We present an analysis of a waveguide structure for a 211–275 GHz sideband separating (2SB) mixer based on superconductor–insulator–superconductor (SIS) tunnel junctions. A general analytical model describing the quality of the sideband rejection ratio (SRR) is developed. It shows a crucial influence of reflections from single-ended mixers, reference frequency (RF) load, and the RF hybrid on the SRR level. Due to the intrinsic asymmetry of the 2SB waveguide structure, the reflections strongly affect both the balance of the observed signal and the balance of the local oscillator (LO) pumping signal. The model is verified and confirmed by 3-D electromagnetic simulations showing good qualitative and quantitative agreement. The developed theory gives a practical tool to design 2SB waveguide mixers with a required SRR level. Based on the presented theory, the waveguide structure of the 211–275 GHz 2SB SIS mixer is designed. It is predicted a degradation of the SRR level from 26 dB to about 18 dB due to reflections. The developed model explains some experimental data measured for 2SB SIS mixers developed earlier.

We present and compare the design and performance of two 850 GHz radial probe fed superconductor-insulator-superconductor mixers, where the antenna is aligned perpendicular to the E-Plane of the input full-height rectangular waveguide connected to a multiple flare-angles smooth-walled horn. Both designs are comprised of 0.5 mu m(2) hybrid niobium/aluminium-nitride/niobium-nitride tunnel junction, fabricated on top of a niobium titanium nitride ground plane with an Al wiring layer. The entire superconducting circuit is supported with a 40 mu m thick quartz substrate. The major difference between the two designs is the method used to cancel out the parasitic junction capacitance for broadband performance. The first design utilises two identical junctions connected in parallel with a short transmission line to convert the capacitance of one junction into the equivalent inductance of the other junction, commonly known as the twin-junction tuning scheme; whilst the second design employs an end-loaded scheme with only one tunnel junction. We found that both methods offer similar radio frequency performances, with close to 2x the double sideband quantum noise temperature, but the twin-junction design is more resilient to fabrication tolerances. However, the end-loaded design offers a much better intermediate frequency (IF) bandwidth performance, made possible by the sub-micron and high current density tunnel junction technology. The improved IF performance is important for many millimetre (mm) and sub-mm observatories, such as future upgrades of Atacama Large Millimetre/sub-mm Array receivers, as well as forthcoming space-borne far-infrared missions. Therefore, we conclude that the single-junction mixer design is the preferred option for THz applications, as long as the fabrication error can be minimised within a certain limit.

Millimetron space observatory will be equipped with the cryogenically cooled instruments for a Space-Earth Very Large Baseline Interferometry (S-E VLBI). It will be a heterodyne multichannel receiver including 7mm, 3mm, 1.3mm and (presumably) 0.8mm channel. Two low frequency channels will be based on HEMT amplifiers, while for the high frequencies superconductor-insulator-superconductor (SIS) receivers will be utilized. The VLBI instrument will have a multi frequency capability allowing simultaneous observation using several channels. This mode has a high potential for improving of black hole event horizon observations due to phase transferring capabilities. The multi frequency observation will be provided by a signal split in the input optics and by back-end capabilities.

The Cherenkov Telescope Array Observatory (CTAO) consists of three types of telescopes: large-sized (LST), mediumsized (MST), and small-sized (SST), distributed in two observing sites (North and South). For the CTA South “Alpha Configuration” the construction and installation of 37 (+5) SST telescopes (a number that could increase up to 70 in future upgrades) are planned. The SSTs are developed by an international consortium of institutes that will provide them as an in-kind contribution to CTAO. The SSTs rely on a Schwarzschild-Couder-like dual-mirror polynomial optical design, with a primary mirror of 4 m diameter, and are equipped with a focal plane camera based on SiPM detectors covering a field of view of ~9°. The current SST concept was validated by developing the prototype dual-mirror ASTRI-Horn Cherenkov telescope and the CHEC-S SiPM focal plane camera. In this contribution, we will present an overview of the SST key technologies, the current status of the SST project, and the planned schedule.

We present the quality measurements of thick (thicker than London penetration depth) NbTiN superconducting films at Terahertz frequencies using a Dispersive Fourier Transform Spectrometer (DFTS). The reflected RF signal from the tested film was measured in time domain, allowing us to separate it from other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in superconducting state (film temperature below $Tc$ ) with that of the normal state (film temperature above $Tc$ ), we characterized the film quality at terahertz frequencies, and directly probed the energy of the superconducting gap of the tested film. The experimental results were fitted using the extended Mattis-Bardeen theory and th obtained film parameters show a good agreement with the literature. In addition to the DFTS, we have also measured the properties of NbTiN film using Time Domain Spectroscopy (TDS). It is shown that both TDS and DFTS provide similar results, and both techniques can be used for the quality control of thick NbTiN films. The superconducting gap determined from the measurements by both DFTS and TDS are in good agreement for both solid and meshed films showing that there is no remarkable degradation in the film quality due to technological processes of lift-off or ion etching.

The ALMA Band 9 (600–720 GHz) receiver is a dual channel heterodyne system capable of detecting orthogonally polarized signals using a wire grid. The light entering the front end is refocused with a compact arrangement of mirrors, which is fully contained within the cartridge. The cross–polar performance of existing Band 9 receivers does not meet the requirements specified for the ALMA channels, i.e. a cross-polar level lower than -23 dB. Moreover, this channel shows a relatively large beam squint, which makes this channel not suitable for extended-source polarimetry. Within the framework of ESO “Advanced Study for Upgrades of the Atacama Large Millimeter/sub-millimeter Array (ALMA)”, we analyze the possibility of improving cross-polarization performance by removing the grid and using an OMT to separate the two orthogonal polarizations. We set up the electromagnetic model of the optics to simulate its performance with and without the grid. The results of the simulations are compared with measurements. Another limiting factor for polarimetric observations in ALMA is the beam squint, which translates directly into a gradient of Stokes Q error across the field of view. The OMT-based ALMA bands show a beam squint within 2% of the FWHM, whereas band with wire grids show a much larger scatter. We investigate what causes the scatter in Band 9, trying to understand if it could be improved by reducing tolerances of the grid mounting or if it is a limiting factor related to aberrations in the current optics.

Imaging of the shadow around supermassive black hole (SMBH) horizon with a very long baseline interferometry (VLBI) is recognized recently as a powerful tool for experimental testing of Einstein’s General relativity. The Event Horizon Telescope (EHT) has demonstrated that an Earth-extended VLBI with the maximum long base (D = 10, 700 km) can provide a sufficient angular resolution θ ∼ 20 μas at λ = 1.3 mm (ν = 230 GHz) for imaging the shadow around SMBH located in the galaxy M87. However, the accuracy of critically important characteristics, such as the asymmetry of the crescent-shaped bright structure around the shadow and the sharpness of a transition zone between the shadow floor and the bright crescent silhouette, both of order Δθ ∼ 4 μas, is still to be improved. In our previous paper we have shown that Space-Earth VLBI observation within a joint Millimetron and EHT configuration at the near-Earth high elliptical orbit (HEO) can considerably improve the image quality. Even more solid grounds for firm experimental validation of General relativity can be obtained with a higher resolution available within the joint Millimetron and EHT program at the Lagrangian point L2 in the Sun-Earth system with an expected resolution of Δθ ∼ 0.1 μas. In this paper we argue that in spite of limitations of L2 orbit an adequate sparse (u, v) coverage can be achieved and the imaging of the shadows around Sgr A∗ and M87∗ can be performed with a reasonable quality.