arrays of parabolic dishes (e.g. the One-Mile Telescope or the Very Large Array), arrays of one-dimensional antennas (e.g. the Molonglo Observatory Synthesis Telescope) or two-dimensional arrays of omnidirectional antennas (e.g. Antony Hewish's Interplanetary Scintillation Array). LOFAR combines aspects of many of these earlier telescopes; in particular, it uses omnidirectional dipole antennas as elements of a phased array at individual stations, and combines those phased arrays using the aperture synthesis technique developed in the 1950s. Like the earlier Cambridge Low Frequency Synthesis Telescope (CLFST) low-frequency radio telescope, the design of LOFAR has concentrated on the use of large numbers of relatively cheap antennas without any moving parts, concentrated in stations, with the mapping performed using aperture synthesis software. The direction of observation ("beam") of the stations is chosen electronically by phase delays between the antennas. LOFAR can observe in several directions simultaneously, as long as the aggregated data rate remains under its cap. This in principle allows a multi-user operation. LOFAR makes observations in the 10 MHz to 240 MHz frequency range with two types of antennas: Low Band Antenna (LBA) and High Band Antenna (HBA), optimized for 10-80 MHz and 120-240 MHz respectively. The electric signals from the LOFAR stations are digitised, transported to a central digital processor, and combined in software in order to map the sky. Therefore, LOFAR is a "software telescope". The cost of such telescopes is dominated by the cost of electronics and will therefore mostly follow Moore's law, becoming cheaper with time and allowing increasingly large telescopes to be built. Each antenna is fairly simple- but there are about 20,000 of them in the LOFAR array. LOFAR stations To make radio surveys of the sky with adequate resolution, the antennas are arranged in clusters that are spread out over an area of more than 1000 km in diameter. The LOFAR stations in the Netherlands reach baselines of about 100 km. LOFAR currently receives data from 24 core stations (in Exloo), 14 'remote' stations in The Netherlands, and 14 international stations. Each of the core and remote stations has 48 HBAs and 96 LBAs and a total of 48 digital Receiver Units (RCUs). International stations have 96 LBAs and 96 HBAs and a total of 96 digital Receiver Units (RCUs). The locations of the international LOFAR stations are: Germany Effelsberg - run by Max Planck Institute for Radio Astronomy, at the site of the Effelsberg Radio