We present the design, fabrication, and characterization of a broadband vacuum window and infrared filter based on ultra-high molecular weight polyethylene (UHMWPE) for millimeter-wave receivers operating across ALMA Band 6 and 7 (211-373 GHz). The window incorporates pyramidal anti-reflection structures, machined directly into the polyethylene using computer numerical control (CNC) machining, which provide impedance matching over a broad frequency range. The structured UHMWPE method is implemented in two distinct components: a vacuum window and a cryogenic infrared filter. This surface-structuring approach provides mechanical robustness, cryogenic compatibility, and low insertion loss. We characterize the transmission properties using terahertz (THz) time-domain spectroscopy, which demonstrates reflection below 5% across the full band. Complementary heterodyne measurements confirm improved receiver noise performance. These results establish 3D-structured UHMWPE as a promising platform for broadband cryogenic optics in high-sensitivity THz instrumentation.

This article presents the design, simulation, microfabrication, and characterization of broadband waveguide terminations intended as drop-in components in waveguide blocks. Two types of terminations were developed, fabricated, and characterized. The first type employs a quartz-based E-probe to couple to a waveguide, integrating an on-substrate titanium nitride (Ti-N) alloy resistive absorber with broadband tuning circuitry. This design achieves a return loss of better than 20 dB over the 260-375 GHz frequency range. The second type features a finline to slotline transition, constructed from a 30 mu m thick Si membrane covered with high resistivity Ti-N alloy. This load demonstrates a return loss of better than 20 dB across the 210-380 GHz band. In order to ensure the required performance of the loads at cryogenic temperatures, the sheet resistance of the employed Ti-N resistive film was characterized from room temperature to 4K employing a closed-cycle cryostat and a four-probe measurement system. For comparative purposes, the room temperature performance of terminations employing a traditional Eccosorb material was measured and compared with the proposed waveguide terminations. Furthermore, the sideband rejection ratio of a 2SB superconductor-insulator-superconductor mixer was evaluated at cryogenic temperatures using the proposed finline-based terminations for LO directional couplers and 90 degrees RF hybrids in comparison with the Eccosorb made terminations. The measurements showed that the performance of the proposed terminations outperforms those achieved with Eccosorb absorbers at room temperature and is comparable at cryogenic temperatures.

In this article, we present the design of a wideband orthomode transducer (OMT) that aims for the frequency band 210-373 GHz. The OMT employs a modified B empty set ifot layout and is optimized to fit into the tight spatial constraints, e.g., of the ALMA cartridge. The OMT layout harmonizes the receiver cartridge components for both polarizations by allowing the use of the same configuration and components in both polarization chains because of the OMT outputs' colinear positioning. The OMT features a built-in novel broadband 90 degrees waveguide twist, which minimizes the insertion RF loss by removing the H-split waveguide while eases receiver component integration with the 2SB mixers in the ALMA cartridge. The manufactured OMT was characterized by direct measurements with a VNA employing frequency extension modules. The waveguide adapters were used accommodating the OMT waveguide ports having dimensions 760 x 760 mu m for the input port and 380 x 760 mu m for the output ports to the VNA extension modules. The OMT demonstrated the cross pol better than -25 dB across 95% of the frequency band, the output reflections better than 15 dB, and the RF insertion loss better than 0.8 dB.

In mm-wave and THz radio astronomy receivers, key components such as mixers, hybrids etc., needs to be fully characterized individually to ensure they fulfill requirement and specifications of various types. In this paper, we present details of a new measurement setup, built in the labs of the Group for Advanced Receiver Development (GARD) and a new underlaying software back-end for measuring, characterization and monitor any of the receiver’s components. This software, called GMS GARD Measurement System, does allow several frontend graphical user interfaces (GUI) being written in different programming languages to connect and interact with the measurement setup simultaneously.

In this work, we report on the design and characterization of an all-metal, wideband single-layer dichroic filter operating at non-normal beam incidence. The dichroic filter consists of a perforated metal plate with an angular offset of the perforated channels equal to the beam incidence angle onto the dichroic surface. The fabricated filter is characterized using an especially designed quasi-optical test system. The filter demonstrates 96% transmission of the incoming electromagnetic radiation averaged in the signal band about 37-50 GHz for both polarizations while simultaneously achieving a rejection better than 20 dB for frequencies lower than 26 GHz at the designed beam incidence of 13 degrees. The cross-polarization level for each polarization is better than 30 dB in the passband. The experimental results of the transmission measurements are in very good agreement with electromagnetic simulations confirming the feasibility and benefits of our proposed design concept even at THz frequencies. The simulations of the dichroic scaled version demonstrate that, for instance, it can be employed in the Event Horizon Telescope project, where the 230 GHz and the 345 GHz receiver channels could be operating simultaneously.

We present the design of a novel orthomode transducer, OMT, suitable for scaling up to Terahertz frequencies. The current design aims for the frequency band 270-380 GHz. The OMT combines waveguide components made with conventional milling with substrate-based parts fabricated using microfabrication techniques. This allows critical dimensions of the OMT conventionally to be mechanically machined parts being replaced by photolithographically defined and microfabricated structures. The paper provides details on the OMT layout, simulations, fabrication and tests. The two fabricated and tested prototype OMTs show similar performance providing better than 30 dB cross-pol suppression. The OMTs also demonstrated broadband performance with an operational band of 260-385 GHz corresponding to a 38,8% fractional bandwidth. With the microfabricated polarization splitting junction and relatively simple waveguide circuitry, the OMT has very good potential to be scaled up to higher frequencies, probably up to 1.5 THz.

This article describes the design and performance of a vacuum-seal waveguide feedthrough with ultrawide RF band 67–116 GHz. We describe first the initial drivers behind the chosen design, then we present the results of the numerical simulations and optimization and provide thereafter the results of the RF and vacuum tests of the fabricated devices. The demonstrated RF performance is very close to the one expected from the simulation with an insertion loss less than 0.3 dB and a return loss better than 20 dB. Simultaneously, the feedthrough shows excellent vacuum isolation, Helium gas leak rate of < 2x10 −8 mbar·L/s is demonstrated, which allows using such a device in various space and ground applications.

In this article, we present a novel dielectrically loaded quad-ridge flared horn (QRFH) as a reflector feed with beyond-decade ultrawideband performance. The dielectric is machined in a low-loss, space-grade polyimide specified with low outgassing for a vacuum environment. The feed covers 1–20 GHz bandwidth with a measured band-average input reflection of −13.6 and 41.5 dB isolation between two orthogonal polarized ports. Predicted performance in a paraboloidal reflector with a 60° half-subtended angle is 62% aperture efficiency average over the band. The ridges of the horn are designed with analytic-spline-hybrid 3-D profiles with thickness flaring outwards toward the feed aperture, improving low-frequency polarization properties. The QRFH was manufactured in four quarters for accurate ridge-to-ridge alignment and a reduced number of interfaces for good thermal properties in cryogenic applications. A prototype feed has been installed and tested with promising results in one of the 6 m offset Gregorian reflectors of the Allen Telescope Array (ATA) located at the Hat Creek Observatory, Hat Creek, CA, USA.

Context. We describe the new SEPIA345 heterodyne receiver channel installed at the Atacama Pathfinder EXperiment (APEX) telescope, including details of its configuration, characteristics, and test results on sky. SEPIA345 is designed and built to be a part of the Swedish ESO PI Instrument for the APEX telescope (SEPIA). This new receiver channel is suitable for very high-resolution spectroscopy and covers the frequency range 272–376 GHz. It utilizes a dual polarization sideband separating (2SB) receiver architecture, employing superconductor-isolator-superconductor mixers (SIS), and provides an intermediate frequency (IF) band of 4–12 GHz for each sideband and polarization, thus covering a total instantaneous IF bandwidth of 4 × 8 = 32 GHz. Aims. This paper provides a description of the new receiver in terms of its hardware design, performance, and commissioning results. Methods. The methods of design, construction, and testing of the new receiver are presented. Results. The achieved receiver performance in terms of noise temperature, sideband rejection, stability, and other parameters are described. Conclusions. SEPIA345 is a commissioned APEX facility instrument with state-of-the-art wideband IF performance. It has been available on the APEX telescope for science observations since July 2021.

The design of SEPIA (Swedish ESO PI Instrument for APEX) was driven by the idea of using ALMA receiver cartridges on the APEX telescope. SEPIA was installed at the guest position of the Naismith cabin A, APEX telescope in early 2015. The SEPIA cryostat and optics was designed to accommodate up to 3 ALMA cartridges. In 2017, the APEX facility instrument SHeFI was decommissioned and SEPIA was accepted as its successor. Moving SEPIA from its PI into Facility Instrument position brought additional constrains due to the severe limitations of the available space. That had led to the necessity of complete redesigning of the SEPIA tertiary optics. During February-March 2019, the new tertiary optics was installed in the APEX Cabin A and SEPIA was placed at its final Facility Instrument position. Here, we present the details of the optical design, layout of the optical component placement, the beam alignment technique, the results of the alignment and SEPIA technical commissioning results at the APEX telescope.

Context: We describe the new SEPIA (Swedish-ESO PI Instrument for APEX) receiver, which was designed and built by the Group for Advanced Receiver Development (GARD), at Onsala Space Observatory (OSO) in collaboration with ESO. It was installed and commissioned at the APEX telescope during 2015 with an ALMA Band 5 receiver channel and updated with a new frequency channel (ALMA Band 9) in February 2016. Aims: This manuscript aims to provide, for observers who use the SEPIA receiver, a reference in terms of the hardware description, optics and performance as well as the commissioning results. Methods: Out of three available receiver cartridge positions in SEPIA, the two current frequency channels, corresponding to ALMA Band 5, the RF band 158--211 GHz, and Band 9, the RF band 600--722 GHz, provide state-of-the-art dual polarization receivers. The Band 5 frequency channel uses 2SB SIS mixers with an average SSB noise temperature around 45K with IF (intermediate frequency) band 4--8 GHz for each sideband providing total 4x4 GHz IF band. The Band 9 frequency channel uses DSB SIS mixers with a noise temperature of 75--125K with IF band 4--12 GHz for each polarization. Results: Both current SEPIA receiver channels are available to all APEX observers.

We describe the design, performance, and commissioning results for the new ALMA Band 5 receiver channel, 163–211 GHz, which is in the final stage of full deployment and expected to be available for observations in 2018. This manuscript provides the description of the new ALMA Band 5 receiver cartridge and serves as a reference for observers using the ALMA Band 5 receiver for observations. At the time of writing this paper, the ALMA Band 5 Production Consortium consisting of NOVA Instrumentation group, based in Groningen, NL, and GARD in Sweden have produced and delivered to ALMA Observatory over 60 receiver cartridges. All 60 cartridges fulfil the new more stringent specifications for Band 5 and demonstrate excellent noise temperatures, typically below 45 K single sideband (SSB) at 4 K detector physical temperature and below 35 K SSB at 3.5 K (typical for operation at the ALMA Frontend), providing the average sideband rejection better than 15 dB, and the integrated cross-polarization level better than –25 dB. The 70 warm cartridge assemblies, hosting Band 5 local oscillator and DC bias electronics, have been produced and delivered to ALMA by NRAO. The commissioning results confirm the excellent performance of the receivers.

In this paper, we discuss a “broken step” phenomenon in an SIS mixer. This phenomena was observed in the production version of the SIS mixers, designed for the 159-211 GHz RF band,being used for the construction of the ALMA Band 5 receiver The broken step typically appears at LO frequencies above 180 GHz and manifests itself as a sharp onset in the DC current at the middle of the quasiparticle step. Correspondingly, this affects the mixer IF response in a way that is similar to the Josephson step but is however of a different nature. Such behaviour affects the SIS mixer dynamic range and complicates the tuning of the 2SB mixer to optimize its performance, for both the receiver noise as well as the sideband rejection. In this paper, we describe results of a few experiments which were performed to understand this undesirable phenomenon.

The Swedish-ESO PI receiver for APEX (SEPIA) was installed at the APEX telescope in 2015. This instrument currently contains ALMA Band 5 (157-212 GHz) and Band 9 (600-722 GHz) receivers. Commissioning and science verification for Band 5 have been successfully completed but are still ongoing for Band 9. The SEPIA instrument is briefly described and the commissioning of the Band 5 receiver and results from the first science observations are presented.

A new receiver for the Onsala 20 m antenna with the possibility of being equipped with 3 mm and 4 mm bands has been built and the 3 mm channel has been commissioned during the Spring 2014. For single-dish operation, the receiver uses an innovative on-source/off-source optical switch. In combination with additional optical components and within the same optical layout, the switch provides two calibration loads (for the 3 mm and 4 mm channels), sideband rejection measurement, and tuning possibilities. The optical layout of the receiver employs all cold (4 K) offset elliptical mirrors for both channels, whereas the on-off switch employs flat mirrors only. The 3 mm channel employs a sideband separation (2SB) dual polarization receiver with orthomode transducer (OMT), 4-8 GHz intermediate frequency (IF), x? 2pol x? upper and lower sidebands (USB? +? LSB). The cryostat has four optical windows made of high density polyethylene (HDPE) with anti-reflection corrugations, two for the signal and two for each frequency band cold load. The cryostat uses a two-stage cryocooler produced by Sumitomo HI? RDK? 408D2 with anti-vibration suspension of the cold-head to minimize impact of the vibrations on the receiver stability. The local oscillator (LO) system is based on a Gunn oscillator with aphase lock loop (PLL) and four mechanical tuners for broadband operation, providing independently tunable LO power for each polarization. This paper provides a technical description of the receiver and its technology and could be useful for instrumentation engineers and observers using the Onsala 20 m telescope.

We present the design and the first light results for the new dual band receiver (4 mm and 3 mm bands) for Onsala Observatory 20 m antenna. For single dish operation, the receiver uses innovative on-source/off-source optical switch. Within the same optical layout, the switch, in combination with additional optical components, provides 2 calibration loads and sideband measurements possibilities. The optics layout of the receiver uses offset elliptical cold mirrors for both channels whereas the on-off switch employs flat mirrors only. The 3 mm channel employs 2SB dual polarization receiver with OMT, 4-8 GHz IF, x 2pol x (USB+LSB). The cryostat has 4 optical widows made of HDPE with anti-reflection corrugations, two for the signal and two for each frequency band cold load. The cryostat employs a two stage cryocooler RDK 408D2 and uses anti-vibration suspension of the cold-head to minimize impact of the vibrations on the receiver stability. The LO system is based on Gunn oscillator with PLL and two mechanical tuners for broadband operation, providing independently tunable LO power for each polarization. At the conference, we will present details on the receiver optics, cryostat design and the result of the first on-sky observations.

We present performance of the first ALMA Band 5 production cartridge, covering frequencies from 163 to 211 GHz. Atacama Large Millimeter/sub-millimeter Array (ALMA) Band 5 is a dual polarization, sideband separation (2SB) receiver based on all Niobium (Nb) superconductor-insulator-superconductor (SIS) tunnel junction mixers, providing 16 GHz of instantaneous RF bandwidth for astronomy observations. The 2SB mixer for each polarization employs a quadrature configuration. The sideband separation occurs at the output of the IF hybrid that has integrated bias-T for biasing the mixers, and is produced using superconducting thin-film technology. Experimental verification of the Band 5 cold cartridge performed together with warm cartridge assembly, confirms that the system noise temperature is below 45 K over most of the RF band, which is less than 5 photon noise (5 hf/k). This is to our knowledge, the best results reported at these frequencies. The measurement of the sideband rejection indicates that the sideband rejection is better than 10 dB over 90% of the observational band.