Electrical standing waves in the HIFI HEB mixer amplifier chain

The Heterodyne Instrument for the Far-Infrared (HIFI) is one of three instruments to be launched aboard the Herschel Space Observatory (HSO) in 2009. HIFI will provide unprecedented spectral sensitivity and resolution between 490–1250 GHz and 1410–1910 GHz. In this paper, we report on the analysis of electrical standing waves that are present between the hot electron bolometer (HEB) heterodyne mixing element and the first low noise amplifier in the HIFI instrument. We show that the standing wave shape is not a standard sinusoid and difficult to remove from the resulting spectrum using standard fitting methods. We present a method to remove the standing waves based on data taken during the HIFI instrument level test, and anticipate the use of a similar calibration procedure in actual flight. Using the standing wave profile we obtain direct evidence of the complex IF output impedance of the HEB mixer

Low-noise 0.8-0.96- and 0.96-1.12-THz superconductor-insulator-superconductor mixers for the Herschel Space Observatory

Heterodyne mixers incorporating Nb SIS junctions and NbTiN-SiO/sub 2/-Al microstrip tuning circuits offer the lowest reported receiver noise temperatures to date in the 0.8-0.96- and 0.96-1.12-THz frequency bands. In particular, improvements in the quality of the NbTiN ground plane of the SIS devices' on-chip microstrip tuning circuits have yielded significant improvements in the sensitivity of the 0.96-1.12-THz mixers relative to previously presented results. Additionally, an optimized RF design incorporating a reduced-height waveguide and suspended stripline RF choke filter offers significantly larger operating bandwidths than were obtained with mixers that incorporated full-height waveguides near 1 THz. Finally, the impact of junction current density and quality on the performance of the 0.8-0.96-THz mixers is discussed and compared with measured mixer sensitivities, as are the relative sensitivities of the 0.8-0.96- and 0.96-1.12-THz mixers

Electrical standing waves in the HIFI HEB mixer amplifier chain

The Heterodyne Instrument for the Far-Infrared (HIFI) is one of three instruments to be launched aboard the Herschel Space Observatory (HSO) in 2009. HIFI will provide unprecedented spectral sensitivity and resolution between 490-1250 GHz and 1410-1910 GHz. In this paper, we report on the analysis of electrical standing waves that are present between the hot electron bolometer (HEB) heterodyne mixing element and the first low noise amplifier in the HIFI instrument. We show that the standing wave shape is not a standard sinusoid and difficult to remove from the resulting spectrum using standard fitting methods. We present a method to remove the standing waves based on data taken during the HIFI instrument level test, and anticipate the use of a similar calibration procedure in actual flight. Using the standing wave profile we obtain direct evidence of the complex IF output impedance of the HEB mixer

A 275–425-GHz Tunerless Waveguide Receiver Based on AlN-Barrier SIS Technology

We report on a 275–425-GHz tunerless waveguide receiver with a 3.5–8-GHz IF. As the mixing element, we employ a high-current-density Nb–AlN–Nb superconducting–insulating– superconducting (SIS) tunnel junction. Thanks to the combined use of AlN-barrier SIS technology and a broad bandwidth waveguide to thin-film microstrip transition, we are able to achieve an unprecedented 43% instantaneous bandwidth, limited by the receiver's corrugated feedhorn. The measured double-sideband (DSB) receiver noise temperature, uncorrected for optics loss, ranges from 55 K at 275 GHz, 48 K at 345 GHz, to 72 K at 425 GHz. In this frequency range, the mixer has a DSB conversion loss of 2.3 1 dB. The intrinsic mixer noise is found to vary between 17–19 K, of which 9 K is attributed to shot noise associated with leakage current below the gap. To improve reliability, the IF circuit and bias injection are entirely planar by design. The instrument was successfully installed at the Caltech Submillimeter Observatory (CSO), Mauna Kea, HI, in October 2006

A 850-GHz waveguide receiver employing a niobium SIS junction fabricated on a 1-μm Si_3N_4 membrane

We report on a 850-GHz superconducting-insulator-superconducting (SIS) heterodyne receiver employing an RF-tuned niobium tunnel junction with a current density of 14 kA/cm^2, fabricated on a 1-µm Si_3N_4 supporting membrane. Since the mixer is designed to be operated well above the superconducting gap frequency of niobium (2Δ/h ≈ 690 GHz), special care has been taken to minimize niobium transmission-line losses. Both Fourier transform spectrometer (FTS) measurements of the direct detection performance and calculations of the IF output noise with the mixer operating in heterodyne mode, indicate an absorption loss in the niobium film of about 6.8 dB at 822 GHz. These results are in reasonably good agreement with the loss predicted by the Mattis-Bardeen theory in the extreme anomalous limit. From 800 to 830 GHz, we report uncorrected receiver noise temperatures of 518 or 514 K when we use Callen and Welton's law to calculate the input load temperatures. Over the same frequency range, the mixer has a 4-dB conversion loss and 265 K ± 10 K noise temperature. At 890 GHz, the sensitivity of the receiver has degraded to 900 K, which is primarily the result of increased niobium film loss in the RF matching network. When the mixer was cooled from 4.2 to 1.9 K, the receiver noise temperature improved about 20% 409-K double sideband (DSB). Approximately half of the receiver noise temperature improvement can be attributed to a lower mixer conversion loss, while the remainder is due to a reduction in the niobium film absorption loss. At 982 GHz, we measured a receiver noise temperature of 1916 K

Sideband separating mixer for 600-720 GHz

The ALMA Band 9 receiver cartridge (600-720 GHz) based on Dual Sideband (DSB) superconductor-insulatorsuperconductor (SIS) mixer is currently in full production. In the case of spectral line observations, the integration time to reach a certain signal-to-noise level can be reduced by about a factor of two by rejecting an unused sideband. The goal is to upgrade the current ALMA band 9 cartridge to a full dual-polarization sideband separating (2SB) capability, with minimal-cost upgrade path. A new compact and modular sideband separating mixer was designed, and a prototype manufactured. The individual SIS mixer devices in the 2SB block are implemented as conventional Band 9 DSB mixers, so that existing devices can be reused and tested individually. Any ALMA DSB developments contribute to the 2SB upgrade. The first experimental results demonstrate noise temperature from 300K to 500K over 80% of the band, which will be improved to fit the ALMA requirements. Nevertheless, the frequency response for 2SB is the same as for DSB, showing that the RF design is still valid, even with different SIS mixer devices. The quality of the RF and IF design is confirmed by a sideband rejection ratio of about 15 dB, which is within the ALMA spec (>10dB )

The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO)

AST/RO, a 1.7 m diameter telescope for astronomy and aeronomy studies at wavelengths between 200 and 2000 microns, was installed at the South Pole during the 1994-1995 Austral summer. The telescope operates continuously through the Austral winter, and is being used primarily for spectroscopic studies of neutral atomic carbon and carbon monoxide in the interstellar medium of the Milky Way and the Magellanic Clouds. The South Pole environment is unique among observatory sites for unusually low wind speeds, low absolute humidity, and the consistent clarity of the submillimeter sky. Four heterodyne receivers, an array receiver, three acousto-optical spectrometers, and an array spectrometer are installed. A Fabry-Perot spectrometer using a bolometric array and a Terahertz receiver are in development. Telescope pointing, focus, and calibration methods as well as the unique working environment and logistical requirements of the South Pole are described.Comment: 57 pages, 15 figures. Submitted to PAS

The Kilopixel Array Pathfinder Project (KAPPa), a 16 pixel integrated heterodyne focal plane array

KAPPa (the Kilopixel Array Pathfinder Project) is developing key technologies to enable the construction of heterodyne focal plane arrays in the terahertz frequency regime with ~1000 pixels. The leap to ~1000 pixels requires solutions to several key technological problems before the construction of such a focal plane is possible. The KAPPa project will develop a small (16-pixel) 2D integrated heterodyne focal plane array for the 660 GHz atmospheric window as a technological pathfinder towards future kilopixel heterodyne focal plane arrays