We present in this paper the front-end design and the results of RF simulations, carried out with Microwave Studio (CST) and HFSS for SHAHIRA (Submillimeter Heterodyne Array for High-speed Radio Astronomy), a 4x4 heterodyne array at 2.5 THz and 4.7 THz. One can then observe 16 spatial positions at 2 frequencies. The design has been chosen to be quasi-optic, because of its simplicity, novelty and multi-pixels applicability. Pixels are made of Niobium Nitride HEB mixers with double-slot antennas, processed on 1 μm thick stress-less Si<sub>3</sub>N<sub>4</sub>/SiO<sub>2</sub> membrane. The use of the membrane shows numerous advantages: for instance the use of the mixers at higher RF frequencies, a better power coupling efficiency or a solution for avoiding dielectric modes, losses and reflections. This work is supported by ESA and is a collaboration between LERMA, CHALMERS and LAAS. The Camera is expected to find applications, for SOFIA or CIDRE.
We report in this paper a new concept for 2.7 THz superconducting Niobium nitride (NbN) Hot-Electron Bolometer mixer (HEB). The membrane process was developped for space telecommnunication applications a few years ago and the HEB mixer concept is now considered as the best choice for low-noise submillimeter-wave frequency heterodyne receivers. The idea is then to join these two technologies. The novel fabrication scheme is to fabricate a NbN HEB mixer on a 1 μm thick stress-less Si<sub>3</sub>N<sub>4</sub>/SiO<sub>2</sub> membrane. This seems to present numerous improvements concerning : use at higher RF frequencies, power coupling efficiency, HEB mixer sensitivity, noise temperature, and space applications. This work is to be continued within the framework of an ESA TRP project, a 2.7 THz heterodyne camera with numerous applications including a SOFIA airborne receiver. This paper presents the whole fabrication process, the validation tests and preliminary results. Membrane-based HEB mixer theory is currently being investigated and further tests such as heterodyne and Fourier transform spectrometry measurement are planed shortly.
Observation and analysis of submillimeter-wave radiation
(300GHz-3THz) in astronomy and atmospheric sciences requires
increasingly performant receivers. The most sensitive receivers
working in this range of electromagnetic spectrum use
superconductor-insolator-superconductor (SIS) junctions.
In order to increase the bandwidth and the sensitivity, we are
developing a quantum-noise limited heterodyne receiver
based on several parallel SIS junctions with broad
(larger than 30%) fixed tuned bandwidth. These circuits can be
viewed as passband filters which have been optimized by
varying the spacings between junctions.
We have designed such 5-junction arrays for operation in the
range 480-640 GHz. Fabrication and heterodyne characterization
of these devices has been done. The 1 μm<sup>2</sup> junctions current density
ranges from 4 to 13 kA/cm<sup>2</sup>, using optical lithography and
Nb/Al2Nb5/Nb trilayer sputtering technology. The fabrication
process and yield are presented in this paper, along with
We report on the status of the development of a 30% bandwidth tunerless SIS double-sideband mixer for the “Band 1” (480 GHz-630 GHz) channel of the heterodyne instrument (HIFI) of ESA’s Herschel Space Observatory, scheduled for launch in 2007. After exposing the main features of our mixer design, we present the performance achieved by the demonstration mixer, measured via Fourier Transform Spectroscopy and heterodyne Y factor calibrations. We infer from a preliminary mixer analysis that the mixer has very low, quantum-limited noise and low conversion loss. We also report on some pre-qualification tests, as we currently start to manufacture the qualification models and design the last iteration of masks for SIS junction production.
Corrugated feedhorns are commonly used with reflector antennas, either for emission or reception purposes, because of their very low side lobe beam patterns, their very good E-H plane symmetry and their important bandwidth. Unfortunately, the electroforming technique that is generally used to fabricate them requires the machining of single-use mandrel. Direct milling of the horn is also possible, either in a single block or in a split block, but this also requires to machine each desired horn. At submillimeter frequencies, machining of small corrugations in a mandrel or in a block is costly. We present in this paper a cost-effective technique to fabricate helicoidal corrugated feed horns, which consists in machining one reusable mandrel and to mold as many horns as needed.
We describe the preliminary design of the proposed Heterodyne Instrument for FIRST (HIFI). The instrument will have a continuous frequency coverage over the range from 480 to 1250 GHz in five bands, while a sixth band will provide coverage for 1410 - 1910 GHz and 2400 - 2700 GHz. The first five bands will use SIS mixers and varactor frequency multipliers while in the sixth band a laser photomixer local oscillator will pump HEB mixers. HIFI will have an instantaneous bandwidth of 4 GHz, analyzed in parallel by two types of spectrometers: a pair of wide-band spectrometers (WBS), and a pair of high- resolution spectrometer (HRS). The wide-band spectrometer will use acousto-optic technology with a frequency resolution of 1 MHz and a bandwidth of 4 GHz for each of the two polarizations. The HRS will provide two combinations of bandwidth and resolution: 1 GHz bandwidth at 200 kHz resolution, and at least 500 MHz at 100 kHz resolution. The HRS will be divided into 4 or 5 sub-bands, each of which can be placed anywhere within the full 4 GHz IF band. The instrument will be able to perform rapid and complete spectral line surveys with resolving powers from 10<SUP>3</SUP> up to 10<SUP>7</SUP> (300 - 0.03 km/s) and deep line observations.