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Several electrically large phased array feed (PAF) reflector systems are modeled to examine the mechanism of multiple reflections between parabolic reflectors and low- and high-scattering feeds giving rise to frequency-dependent patterns and impedance ripples. The PAF current is expanded in physics-based macro domain basis functions (CBFs), while the reflector employs the physical optics (POs) equivalent current. The reflector-feed coupling is systematically accounted for through a multiscattering Jacobi approach. An FFT expands the reflector radiated field in only a few plane waves, and the reflector PO current is computed rapidly through a near-field interpolation technique. The FEKO software is used for several cross validations, and the convergence properties of the hybrid method are studied for several representative examples showing excellent numerical performance. The measured and simulated results for a 121-element Vivaldi PAF, which is installed on the Westerbork Synthesis Radio Telescope, are in very good agreement. [ABSTRACT FROM PUBLISHER]

Calibrating for the radiation pattern of a multi-beam Phased array feed (PAF) based radio telescope largely depends on the accuracy of the pattern model, and the availability of suitable reference sources to solve for the unknown parameters in the pattern model. It is shown how the efficiency of this pattern calibration for PAF antennas can be improved by conforming the beamformed far field patterns to a two-parameter physics-based analytic reference model through the use of a linearly constrained minimum variance (LCMV) beamformer. Through this approach, which requires only a few calibration measurements, an accurate and simple pattern model is obtained. The effects of the model parameters on the directivity and sidelobe levels of multiple scanned beams are investigated, and these results are used in an example PAF beamformer design for the proposed MeerKAT antenna. Compared to a typically used maximum directivity (MaxDir) beamformer, the proposed constrained beamforming method is able to produce beam patterns over a wide Field-of-View (FoV) that are modeled with a higher degree of accuracy and result in a significant reduction in pattern calibration complexity. [ABSTRACT FROM PUBLISHER]

A novel beam expansion method is presented that requires employing only a few Characteristic Basis Function Patterns (CBFPs) for the accurate prediction of antenna beam patterns. The method is applied to a proposed design of the MeerKAT/SKA radio telescope, whose antenna geometry is subject to small deformations caused by mechanical or gravitational forces. The resulting deformed pattern, which is affected in a nonlinear fashion by these deformations is then sampled in a few directions only after which the interpolatory CBFPs accurately predict the entire beam shape (beam calibration). The procedure for generating a set of CBFPs—and determining their expansion coefficients using a few reference point sources in the sky—is explained, and the error of the final predicted pattern relative to the actual pattern is examined. The proposed method shows excellent beam prediction capabilities, which is an important step forward towards the development of efficient beam calibration methods for future imaging antenna systems. [ABSTRACT FROM PUBLISHER]