Alexey Pavolotsky

A Swedish heterodyne facility instrument for the APEX telescope

Aims. In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. Methods. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K. Results. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.

Waveguide-to-microstrip transition with integrated bias-T

A novel device, a waveguide-to-microstrip transition with an integrated bias-T, is presented. The substrate-based planar structure comprises a waveguide E-probe, shaped as a radial line. The probe couples the RF field of a full-height waveguide to a microstrip line or directly to an active component, e.g., a transistor or diode in a mixer or direct detector. The radial probe is connected on its wide side to another port via a specially shaped high impedance line that provides RF/DC isolation. This port can then be used to inject DC and/or extract IF signals. The design of the presented structure was done using CAD (3-D EM simulation) and an X-band device was produced and fully characterized. The measured performance is in excellent agreement with the simulations; the device has return loss better than -20 dB, insertion loss less or equal to -0.15 dB and isolation for the bias-T line better than -20 dB. RF bandwidth for the transition is 30% of the central frequency.

A 1.3-THz Balanced Waveguide HEB Mixer for the APEX Telescope

In this paper, we report about the development, fabrication, and characterization of a balanced waveguide hot electron bolometer (HEB) receiver for the Atacama Pathfinder EXperiment telescope covering the frequency band of 1.25-1.39 THz. The receiver uses a quadrature balanced scheme and two HEB mixers, fabricated from 4- to 5-nm-thick NbN film deposited on crystalline quartz substrate with an MgO buffer layer in between. We employed a novel micromachining method to produce all-metal waveguide parts at submicrometer accuracy (the main-mode waveguide dimensions are 90 times 180 mum ). We present details on the mixer design and measurement results, including receiver noise performance, stability and ldquofirst-lightrdquo at the telescope site. The receiver yields a double-sideband noise temperature averaged over the RF band below 1200 K, and outstanding stability with a spectroscopic Allan time more than 200 s.

Performance of the First ALMA Band 5 Production Cartridge

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.

Micromachining Approach in Fabricating of THz Waveguide Components

In this paper, we describe our progress in micromachining of submillimeter waveguide structures such as a quadrature waveguide coupler which is a part of a THz balanced heterodyne receiver. We have set up and developed pilot testing of the micromachining process with required high quality of structure.

All-metal micromachining for the fabrication of sub-millimetre and THz waveguide components and circuits

A novel technology for the manufacturing of micromachined all-metal waveguide circuits and structures for frequency bands ranging from 200 up to 7000 GHz (sub-millimetre and THz) is presented. The waveguide circuits are formed by using metal electroplating with preceding sputtering of a thin metal film seed layer over a photo-lithographically patterned thick SU-8 photoresist. The process provides the possibility of making three-dimensional structures via facilitating multi-level (layered) designs. The surface roughness of the THz waveguide structure was demonstrated to be as low as 30 nm. This technology was used to build a state-of-the-art waveguide balanced 1.3 THz hot electron bolometer mixer and other applications for radio astronomy instrumentation.

Design and Characterization of a 211–275 GHz Sideband Separating Mixer for the APEX Telescope

We present the final results of the development and characterization of the sideband separating superconductor-insulator-superconductor (SIS) mixer for the APEX telescope band 1 (211-275 GHz). The sideband separation is achieved by using a quadrature scheme where the radio frequency (RF) and a local oscillator (LO) power are applied to two identical double sideband SIS mixers. All mixer components, including the LO and RF distribution circuitry, are integrated into a single mixer block. To achieve a compact design we developed a superconducting Lange coupler, based on Nb thin film, which is used as an intermediate frequency hybrid. Typical single sideband noise temperature of 100 K and sideband rejection ratio of about 12 dB and are measured.

Aging- and annealing-induced variations in Nb/Al–AlOx/Nb tunnel junction properties

In this paper, we present studies of room temperature aging and annealing of Nb/Al–AlOx/Nb tunnel junctions with the size of 2–3 μm2. We observed a noticeable drop of junction normal resistance Rn unusually combined with increase in subgap resistance Rj as a result of aging. Variation in both Rn and Rj are subject to the junction size effect. An effect of aging history on the junction degradation after consequent annealing was discovered. Discussion and interpretation of the observed phenomena are presented in terms of structural ordering and reconstruction in the AlOx layer, driven by diffusion flows enhanced due to stress relaxation processes in the Al layer interfacing the AlOx layer.

Facility heterodyne receiver for the Atacama Pathfinder Experiment Telescope

APEX, the Atacama PAthflnder Experiment (APEX) Telescope, is a partnership between Max Planck Institut fur Radioastronomie (in collaboration with Astronomisches Institut Ruhr Universitat Bochum (AIRUB)), Onsala Space Observatory and the European Southern Observatory. The telescope antenna, supplied by VERTEX Antennentechnik, is a 12 m antenna with a 17 mum rms surface accuracy operating at the Atacama Desert in the Chilean Andes at a 5100 m altitude. The APEX heterodyne facility receiver is placed in the telescope Nasmyth Cabin A. The receivers are coupled to the antenna via relay optics allowing the operation of two different Pi-type instruments and a 6-channel facility heterodyne receiver to cover approximately 210 - 1500 GHz frequency range while providing frequency independent illumination of the secondary. In this report, we present details on the optics for the APEX facility heterodyne receiver and details of its design. The report includes a very brief review of the APEX Band 1, 211 - 270 GHz, Band 2, 270 - 370 GHz, Band 3, 385 - 500 GHz, all based on sideband separation SIS mixer technology and Band T2, 1250 - 1390 GHz, a balanced waveguide HEB mixer, all developed by GARD.

A sideband separating mixer for 85-115 GHz

This paper presents the results of development and tests of a sideband separating heterodyne receiver for the 85-115 GHz band with superconducting tunnel junctions (SIS) as frequency down converters. Sideband separation is achieved by using a quadrature scheme where two identical mixer junctions are pumped by a local oscillator (LO) with 90/spl deg/ phase difference. We used an innovative mixer layout where the quadrature scheme is implemented using waveguide-based and integrated on-chip components. We employed an additional pair of SIS junctions as terminations for LO-injection directional couplers.