A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si3N4/SiO2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. The gain bandwidth of the HEB mixers on Si3N4/SiO2 membranes was found to be 0.7÷0.9 GHz, which is much smaller than for similar devices on silicon. Application of buffer layers and use of alternative types of membranes (e.g. silicon-on-insulator) is under investigation.
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 Si3N4/SiO2 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.
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 μm2 junctions current density
ranges from 4 to 13 kA/cm2, 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.