Improving the Calibration Efficiency of an Array Fed Reflector Antenna Through Constrained Beamforming

Abstract

Calibrating for the radiation pattern of a multibeam 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 twoparameter 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.

An adaptive calibration and beamforming technique for a GEO satellite data relay

“…However, even if a well defined setup is simulated this becomes challenging. The offset configuration of the array‐fed reflector introduces geometrical phase shifts between the array elements which can only be approximated by analytical formulas as shown in Young et al …”

“…As it is not possible to accurately describe the radiation pattern of a reflector antenna analytically, some approximations must be made. A good approximation of the copolarized radiation pattern in the near‐boresight direction that already accounts for effects of reflector underillumination, coma aberration, and phase variation for scanned beams can be found in Young et al : where k is the free space wavenumber, s ⩽1 is a scaling parameter which accounts for underillumination of the reflector aperture or coma aberration when scanning, a is the radius of the reflector, ( θ , ϕ ) define the local coordinate system, Ψ is a constant that determines the phase gradient, and ϕ 0 defines the direction of the phase‐center shift.…”

“…A, Simulated and analytically calculated radiation patterns for the reflector antenna used in the experimental setup. The curves show an uncalibrated sample radiation pattern obtained with random phases (dashed), a radiation pattern that was obtained using calibration and beamforming (solid), and an analytically calculated array‐fed reflector pattern (dash‐dotted) . B, The 3D pattern of the calibrated array‐fed reflector antenna [Colour figure can be viewed at wileyonlinelibrary.com]…”

The SKA and the MeerKAT precursor — Extreme antenna engineering

“…EMBRACE can generate two entirely independent beams. (By comparison, PAFs are generally used to effectively broaden the field of view, by overlapping the individual beams; see, for example [19]). …”

Model-Switched Beamformer with Large Dynamic Range

“…Generally, array errors are overcome through two methods, namely, array calibration and robust adaptive beamforming. The literatures [8,9] introduce some calibration methodologies to deal with the deterministic error, such as amplitude and phase errors in RF front-end. Furthermore, numerous robust beamformers are studied to combat the stochastic error.…”