Beamforming the Station (Empty)

Beamforming is the process by which the station electronics collect the antenna signals, delay them and coherently summed to point at a certain point in the sky. Depending on your bit-mode, you can control between 244 and 976 of these beams, each of which can take on a unique frequency and pointing direction.

Typically, all beams are pointed in the same direction, with the same antenna-set, and only differ in the selected frequencies. While other pages will discuss why/how we can deviate from that choice, this page will focus on observing a single mode, in bit-mode 8 (to use most of the available bandwidth in a given mode).

LBAs

The LBAs allow for beams to be configured 

HBAs

Unlike the LBAs, the HBAs have an analogue beamformer to combine each of the 16 antenna in each tile into a coherent beam prior to any digitisation and electron beamforming. As a result, the HBAs require an extra configuration parameter, --anadir, and the chosen beams must be kept close to each other to prevent signal loss due to falloff  in the analogue beam. 

It is best to think of beaming for HBAs as a two step process. Firstly, the analogue beamformer limits our field of view to that of a single tile (~15deg.), and then the digital beamformer further limits the field of view to that of the selected tiles in the array (~0.5-2deg for the entire array). If the digital beam is not in the main lobe of the analogue beam, there will be a signfiicant degradation in signal quality.

The HBAs currently do not have any extra RFI filtering modes (potentially will be present in LOFAR2.0 to reduce the effects of DAB radio), though have three observing modes: HBALo (mode 5, band '110_190'), HBAHi (mode 7, band '210_250')