There are three kinds of LOFAR station layouts with individual characteristics which, according to their distance from the centre of the array, are classified as Core, Remote or International stations. The three kinds of stations have different antenna field configurations and underlying electronics.
The operating frequency range of LOFAR is 10 MHz to 240 MHz, while the antennas are optimized for the ranges of 30-80 MHz and 120-240 MHz. Because the optimized bandwidth of the operating frequency range spans 8 octaves, at least two types of antenna are necessary: the Low Band Antenna (LBA) and the High Band Antenna (HBA).
The fundamental receiving elements of LOFAR are two types of small, relatively low-cost antennas that together cover the 10–240 MHz operating bandpass. These antennas are grouped together into 52 separate stations distributed over the northeastern part of the Netherlands as well as in Germany, France, the UK, Sweden, Poland, Ireland, and Latvia.
A number of different types of beam are used when dealing with the LOFAR telescope. LOFAR beam-forming is hierarchical in nature - forming first beams at HBA tile level, then station level, and then array level - so the picture can be confusing if one is not completely clear on what `beam' is meant in a particular situation.
The combination of analogue and digital signal processing both at station level and at the Central Processing facility allows for a flexible definiton of the total frequency range, subband selection, and spectral channel width.
This section provides a brief overview of the LOFAR system and introduces some of the technical (and hardware) terms used throughout the rest of the documentation.
One of the great strengths of the LOFAR system is its capacity for enhancement. It is of course common for astronomical facilities to increase their capabilities through continued software development.