The HIFI instrument provides continuous frequency coverage over the range 480-1250 GHz (625-240 microns) in five bands with approximately equal tuning range. An additional pair of bands provide coverage of the frequency range 1410-1910 GHz (213-157 microns). The instrument operates at only one local oscillator frequency at a time.
In all mixer bands two independent mixers receive both horizontal and vertical polarizations of the astronomical signal, although in some cases reduced bandwidth or use of a single polarization is required to stay within the data rate available to the instrument.
The user has the choice of using only a single polarization if he/she chooses.
The first 5 mixer bands use SIS (superconductor-insulator-superconductor) mixers; bands 6 and 7, use Hot-Electron Bolometers (HEBs).
The instantaneous bandwidth of the instrument will be 4 GHz. The frequency coverage of the instrument is summarised in Table 3.1, “HIFI frequency coverage”.
Table 3.1. HIFI frequency coverage and band allocation. Note that the values presented are Local Oscillator frequencies. Each band is further split in two ("a" and "b") due to the use of two Local Oscillator chains for the lower and upper portions of the frequency range for each band. A further 8GHz is available at each end of the frequency range due to the frequency placement of the upper and lower sidebands in HIFI in bands 1 to 5. This is only a further 4.8GHz in bands 6 and 7.
Band | Mixer type | LO Lower freq. | LO Upper freq. | Beam Size (HPBW) | IF Bandwidth |
|---|---|---|---|---|---|
1 | SIS | 488.1 GHz | 628.4 GHz | 39" | 4.0 GHz |
2 | SIS | 642.1 GHz | 793.9 GHz | 30" | 4.0 GHz |
3 | SIS | 807.1 GHz | 952.9 GHz | 25" | 4.0 GHz |
4 | SIS | 957.2 GHz | 1113.8 GHz | 21" | 4.0 GHz |
5 | SIS | 1116.2 GHz | 1271.8 GHz | 19" | 4.0 GHz |
6 + 7 | HEB | 1430.2 GHz | 1901.8 GHz | 13" | 2.4 GHz |