Beamforming and imaging with the BYU/NRAO L-band 19-element phased array feed

An experimental 19-element L-band phased array feed was installed on the Green Bank 20-Meter Telescope in October 2007 and July 2008 to measure sensitivity and effciency and demonstrate signal processing algorithms for array calibration, multiple beam formation, imaging, and adaptive spatial filtering methods for interference mitigation. System noise performance was characterized using a warm absorber/cold sky Y-factor setup. The peak beam aperture effciency was 69% and the minimum beam equivalent system temperature was 66K. With a single reflector pointing, a high sensitivity image of a field of view approximately two half-power beamwidths in diameter can be produced. Measured figures of merit compare well to numerical simulations, indicating that complicating effects such as mutual coupling are understood well enough to enable the next phase of array feed development to proceed on firm grounds.