ABSTRACT: The Heterodyne Instrument for the Far-Infrared (HIFI) is a
high-resolution (>300.000), spectrometer for ESA's Herschel Space
Observatory. The instrument is designed to provide a wide and continuous
frequency coverage with velocity resolved resolution and high
sensitivity. The instrument comprises 5 frequency bands covering
480-1150 GHz with SIS mixers and a sixth dual frequency band for the
1410-1910 GHz range with Hot Electron Bolometer Mixers (HEBM). One
frequency band is operating at a time with a single sky-pixel. The Local
Oscillator (LO) subsystem consists of a Ka-band synthesiser followed by
14 chains of frequency multipliers, 2 chains for each frequency band.
Each frequency band has two mixers operating on orthogonal
polarisations. All mixers are designed to have noise performance close
to the quantum noise limit. A pair of Auto-Correlators and a pair of
Acousto-Optic spectrometers process the two IF signals from the
dual-polarisation front-ends and provide instantaneous frequency
coverage of 4 GHz, with a set of resolutions (140 KHz to 1 MHz), better
than < 0.1 Km/s. We will present the design and the first results of
the pre-flight testing and characterization of the instrument.
ABSTRACT: Heterodyne submillimeter detection techniques represent an important development in the field of remote sensing of atmospheric composition. The disclosure of this wavelength region by new low-noise detectors and multichannel high-resolution spectrometers leads to expectations of improved accuracy and vertical resolution of the vertical composition profiles derived from these measurements. Because of the low-noise levels of newly developed receivers, special care is required to ensure that fundamental limitations of the components used do not contribute to systematic errors exceeding the random errors. Operated in an upward-looking geometry, the sensitivity of the retrieval algorithm to noise and instrumental errors can be rather high, and hence instrumental limitations could induce large uncertainties in the derived atmospheric information. Instrumental uncertainties typical for a passive heterodyne sounder are quantified, and their effects on the accuracy of the derived vertical mixing ratio profiles are presented.
Applied Optics 11/2000; 39(30):5518-30. · 1.41 Impact Factor
ABSTRACT: There are great interests in developing Nb SIS mixers because of the extremely low noise temperatures and because of the need of low local oscillator (LO) power. Several groups have demonstrated experimentally that Nb SIS mixers with integrated tuning elements can perform near the quantum noise limit up to the Nb gap frequency (~700 GHz). Beyond this frequency, a major loss will take place in the tuning elements, which are Nb-SiO<sub>2</sub>-Nb micro-striplines, because the incoming photons can break the Cooper-pairs, thus increasing the surface resistance of the Nb strips. Applying highly conductive Al instead of Nb for a stripline can reduce the loss since the former has a lower surface resistance at higher frequencies. In this work, we report the fabrication of waveguide Nb SIS mixers with Al striplines and heterodyne measurement results around 1 THz
Millimeter Wave and Far Infrared Science and Technology, 1996. Proceedings. 4th International Conference on; 09/1996
ABSTRACT: This article gives an overview of the tests performed on the HIFI instrument before and after integration in the Herschel satellite. The test results are compared to the performance requirements. Overall, HIFI complies well with the original requirements. As an example of unexpected test results the effect of unwanted feedback in the amplification circuit on the data quality is discussed.
Astronomy and Astrophysics, v.518 (2010).