Superconducting 4-8-GHz Hybrid Assembly for 2SB Cryogenic THz Receivers

We present here the design and characterization of an intermediate frequency (IF) assembly comprising a compact 90 hybrid chip (coupled line coupler - Lange coupler- coupled line coupler), two bias-T circuits for biasing the superconductor-insulator-superconductor (SIS) mixers, and two transmission-line circuits. Specifically, the miniaturized three-section hybrid chip fabricated using thin-film technology utilizes superconducting Niobium (Nb) transmission lines, air bridges to connect the fingers of the Lange coupler (middle section), and is complemented with two bias-T circuits with integrated MIM capacitors. The assembly was designed to ensure amplitude and phase imbalances better than 0.6 dB and +/- 2 degrees, respectively. Experimental verification of the assembly at 4 K shows good agreement between the measurements and simulations with amplitude imbalance of 0.5 dB and maximum phase imbalance of +/- 2 degrees. The ALMA band-5 (163-211 GHz) receiver will include such assembly. The receiver tests shows sideband rejection ratio better than 15 dB over the entire RF band, i.e., a systematic improvement of 3-9 dB as compared with the previously reported results

Terahertz components packaging using integrated waveguide technology

We present an integrated waveguide based packaging solution compatible with different THz component technologies, both for room temperature and cryogenic operations, employing space-qualified wire-bonding for electrical contacts. The proposed waveguide packaging relies on the combination of all-metal micro-machined THz waveguide and active component chip layouts suitable for the realization of systems from 200 up to 5000 GHz. It provides possibility of making 3-dimensional structures via facilitating of multi-level (layered) designs. The surface roughness of the fabricated THz waveguide structure was demonstrated to be 20 nm, while a 2 μm alignment accuracy of the active component chip was verified. \ua9 2011 IEEE

A Technology Demonstrator for 1.6–2.0 THz Waveguide HEB Receiver with a Novel Mixer Layout

In this paper, we present our studies on a technology demonstrator for a balanced waveguide hot-electron bolometer (HEB) mixer operating in the 1.6–2.0 THz band. The design employs a novel layout for the HEB mixer combining several key technologies: all-metal THz waveguide micromachining, ultra-thin NbN film deposition and a micromachining of a silicon-on-insulator (SOI) substrate to manufacture the HEB mixer. In this paper, we present a novel mixer layout that greatly facilitates handling and mounting of the mixer chip via self-aligning as well as provides easy electrical interfacing. In our opinion, this opens up a real prospective for building multi-pixel waveguide THz receivers. Such receivers could be of interest for SOFIA, possible follow up of the Herschel HIFI, and even for ground based telescopes yet over limited periods of time with extremely dry weather (PWV less than 0.1 mm)

Ultra-thin film NbN depositions for HEB heterodyne mixer on Si-substrates

The key of improving hot-electron bolometer (HEB) mixer performance lies inevitably in the quality of ultra-thin NbN films itself. This work presents a thorough investigation of crucial process parameters of NbN films deposited by means of reactive DC-sputtering on Si-substrates at elevated temperatures up to 750°C. The polycrystalline NbN films with thickness of 4 to 10nm were characterized by DC resistivity measurements, ellipsometry and high resolution transmission electron microscopy (HRTEM) in order to confirm thickness and film structure. Since the macroscopic properties such as critical temperature, thickness as well as the transition width to the superconducting state are directly linked to HEB mixer noise temperature and IF bandwidth, a set of experiments were conducted to enhance aforementioned properties. We considered deposition temperature, RF biasing, nitrogen and argon partial and total pressure during deposition as major process variable parameters. Careful optimization of the deposition conditions allowed setting up a process resulting in high-quality NbN ultra-thin films with thickness of 5.5nm exhibiting Tc of 10.5K. Moreover, the transition width could be kept as low as 1.4K. The produced films were stored at ambient conditions and re-characterized over a period of 4 month without measurable degradation

Waveguide-to-substrate transition based on unilateral substrateless finline structure: Design, fabrication, and characterization

We report on a novel waveguide-to-substrate transition with prospective use for broadband mixer design. The transition employs a substrateless finline, i.e., a unilateral finline structure with the substrate removed between the fins. This distinctive feature diminishes the overall insertion loss and facilitates matching with the waveguide. The transition is designed on a thin silicon substrate covered by a superconducting niobium thin layer. An auxiliary Au layer situated on top of the Nb layer provides grounding for the fins and facilitates the mounting process in the split-block waveguide mount. Aiming to compare simulations with measurements, a back-to-back transition arrangement for the 211-373 GHz frequency band was designed, fabricated, and characterized at cryogenic temperatures. The simulation results for the back-to-back structure show an insertion loss of less than 0.6 dB in the whole band, i.e., 0.3 dB per transition. Furthermore, a remarkable fractional bandwidth of 55% with a return loss better than 15 dB is predicted. Experimental verification shows consistent results with simulations

Frequency Multiplier Based on Distributed Superconducting Tunnel Junctions: Theory, Design, and Characterization

In this paper, we present the analysis, design, and characterization of the first frequency multiplier using distributed superconductor–insulator–superconductor (SIS) junctions. We derived analytical expressions describing the properties of the distributed SIS junction as a frequency multiplier. The modeling of the distributed SIS junctions shows that high conversion efficiency can be achieved when used as the multiplier. The measured output power generated by such multiplier employing the distributed SIS junction at the second harmonic of the input frequency is in good agreement with the model. Furthermore, the frequency multiplier based on the distributed SIS junction for the first time was able to pump an SIS mixer. The multiplication efficiency of the distributed SIS junction is 15–30% for a fractional bandwidth of 10% with excellent spectral line purity. The –3 dB line width of the multiplied signal is 1 Hz, which was limited by the resolution bandwidth of the spectrum analyzer. The results attained in this paper show that the distributed SIS junction frequency multiplier has considerable future potential, and could possibly be used in LO source in single-end and multipixel SIS mixer receivers

Millimeter-Wave Wideband Waveguide Power Divider with Improved Isolation between Output Ports

We present a novel compact wideband waveguide T-junction power divider especially suited for mm-wave and THz frequencies. It incorporates substrate-based elements into a waveguide structure to provide the output port\u27s isolation and matching. The internal port is introduced at the apex of the T-junction formed as an E-probe on a substrate. This facilitates efficient coupling of the reflected energy from the output port to a novel thin-film-based resistive termination integrated with the E-probe onto the same substrate and fabricated by means of thin-film technology. A power divider was designed, simulated, and fabricated for the frequency band 150-220 GHz, to experimentally verify the theoretical and simulated performance. The results showed excellent agreement between the simulations and measurements with the devices demonstrating a remarkable return loss of 20 dB for both the input and output ports for a three-port device with equal split and isolation better than 17 dB between the output ports. Furthermore, the measured insertion loss is less than 0.3 dB and the amplitude and phase imbalance are 0.15 dB and 0\ub0, respectively. Moreover, the divider\u27s remarkable tolerance to the dimensions and sheet resistance of the resistive material of the built-in absorbing load, makes the device a very practical component for mm-wave and THz systems, in particular radio-astronomy receivers

Wideband Slotline-to-Microstrip Transition for 210-375 GHz based on Marchand Baluns

This paper describes the design and cryogenic measurement of a novel slotline-to-microstrip transition based on Marchand baluns. The proposed transition is an attractive solution for numerous THz applications due to its remarkable broadband performance and compactness. For instance, such transition could be considered for wideband devices covering the frequency band 210-375 GHz. The suggested transition is designed on a thin silicon substrate and employs superconducting Nb as the electrode for the slotline and microstrip lines. In order to verify the performance of the designed transition, we fabricated a dedicated test structure consisting of two transitions connected back-to-back and integrated with E-probes at the waveguide interfaces. Due to the inherent bandwidth limitation of the E-probes, two different test structures for 210-295 GHz and 295-375 GHz were employed to characterize the proposed transition over the whole frequency band. The experimental verification performed at cryogenic temperatures showed results consistent with the simulation. Moreover, the cryogenic measurements indicated a remarkable 56% fractional bandwidth with an insertion loss as low as 0.3 dB for the fabricated slotline-to-microstrip transition

A map of OMC-1 in CO 9-8

The distribution of 12C16O J=9-8 (1.037 THz) emission has been mapped in OMC-1 at 35 points with 84" resolution. This is the first map of this source in this transition and only the second velocity-resolved ground-based observation of a line in the terahertz frequency band. There is emission present at all points in the map, a region roughly 4' by 6' in size, with peak antenna temperature dropping only near the edges. Away from the Orion KL outflow, the velocity structure suggests that most of the emission comes from the OMC-1 photon-dominated region, with a typical linewidthof 3-6 km/s. Large velocity gradient modeling of the emission in J=9-8 and six lower transitions suggests that the lines originate in regions with temperatures around 120 K and densities of at least 10^(3.5) cm^(-3) near theta^(1) C Ori and at the Orion Bar, and from 70 K gas at around 10^(4) cm^(-3) southeast and west of the bar. These observations are among the first made with the 0.8 m Smithsonian Astrophysical Observatory Receiver Lab Telescope, a new instrument designed to observe at frequencies above 1 THz from an extremely high and dry site in northern Chile.Comment: Minor changes to references, text to match ApJ versio

SEPIA345: A 345 GHz dual polarization heterodyne receiver channel for SEPIA at the APEX telescope

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 \uc3\uc2 - 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