Phased array feeds (PAFs) for reflector antennas offer the potential for increased reflector field of view and faster survey speeds. To address some of the development challenges that remain for scientifically useful PAFs, including calibration and beamforming algorithms, sensitivity optimization, and demonstration of wide field of view imaging, we report experimental results from a 19 element room temperature L-band PAF mounted on the Green Bank 20-Meter Telescope. Formed beams achieved an aperture efficiency of 69% and system noise temperature of 66 K. Radio camera images of several sky regions are presented. We investigate the noise performance and sensitivity of the system as a function of elevation angle with statistically optimal beamforming and demonstrate cancelation of radio frequency interference sources with adaptive spatial filtering.

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A major emphasis in current radio astronomy instrumentation research is the use of phased array feeds (PAF) to provide radio telescopes with larger fields of view. One of the challenges of PAF systems is the design of beamformers that provide sufficient sensitivity and known, stable beam pattern structure. High sensitivity has been achieved with the maximum sensitivity beamformer without regard to beam pattern shape. Deterministic beamformers provide the desired pattern shape control, but suffer from a significant reduction in sensitivity. We present a hybrid beamforming method, which balances the tradeoff between high sensitivity and precise beam pattern shape control. A comparison of each of these beamforming methods, using measured data, confirms the advantage of the hybrid approach. The pattern distortions introduced by modeled beamformers can be mitigated with a transformation step, but ultimately it is shown that PAF beamformer design is best done using measured calibrators. A PAF calibration vector quality metric based on minimum description length is also introduced.Index Terms-Antenna array feeds, array signal processing, phased arrays, radio astronomy.

A major research emphasis in current radio astronomy instrument development is the use of phased array feeds (PAF) to provide radio telescopes with larger fields of view. Statistically optimal beamformers have been shown to provide high sensitivity for PAFs, however, inability to precisely control beampattern details (even in sidelobes) is problematic. Enforcing beampattern structure with a deterministic beamformer is useful. A hybrid beamforming approach is presented in this paper, which offers the best in sensitivity for a desired amount of beampattern control. Designing any beamformer with simulated calibration data is inadequate for PAF operation and introduces distortion in the final beampattern. A transformation step is required to reduce such effects.

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