LOFAR consists of an interferometric array of dipole antenna stations distributed throughout the Netherlands and in several countries in Europe. These stations have no moving parts and, due to the effective all-sky coverage of the component dipoles, give LOFAR a large field-of-view.
At station level the signals from individual dipoles are combined digitally into a phased array. Electronic beam-forming techniques make the system agile and allow for rapid re-pointing of the telescope as well as simultaneous observations of multiple, independent areas of the sky.
The following gives a summary overview of the characteristics of the system.
Number of operational stations:
The number of operational stations in January 2015 are:
- 24 Core Stations
- 14 Remote Stations
- 9 International Stations
- Number of stations available for LBA observations: 47
- Number of stations available for HBA (Dual) observations: 71
Note that 3 new international stations are being built in Poland and should become part of the array by the end of 2015.
Observers can choose between the following frequency ranges:
- LBA: 10-90 MHz (200 MHz clock)
- LBA: 30-90 MHz (200 MHz clock)
- HBA: 110-190 MHz (200 MHz clock)
- HBA: 210-250 MHz (200 MHz clock)
Another frequency range in which observations can be performed exists (HBA: 170-230 MHz - 160 MHz clock). However, note that such a frequency range is not supported for full automated operations in Cycle 5. If available by the start of the Cycle, this mode will be offered as a commissioning mode, to be requested by following the instructions concerning 'Commissioning Proposals' given here.
Up to 488 subbands of 0.195 MHz (195.312 kHz at 200 MHz clock) and 0.156 MHz (156.250 kHz at 160MHz clock).
This gives a total bandwidth of 95.16 MHz (200 MHz clock) or 76.13 MHz (160 MHz clock).
As the sensitivity of station beams drops significantly for targets below ~30 degrees elevation, targets with declinations below -5 degrees are not recommended for interferometric observation with LOFAR. Proposers wishing to image low-declination targets will need to justify that the required sensitivity and/or u-v coverage can be attained with their proposed observing programme. More details are given here.