Conference Paper

Extending the capabilities of the GRASP and CAESAR software to analyze and optimize active beamforming array feeds for reflector systems

Netherlands Inst. for Radio Astron. (ASTRON), Dwingeloo, Netherlands
DOI: 10.1109/ICEAA.2010.5652962 Conference: Electromagnetics in Advanced Applications (ICEAA), 2010 International Conference on
Source: IEEE Xplore


This paper describes a numerical approach for the analysis of a reflector antenna system which is fed by a Phased Array Feed. This approach takes mutual interaction effects into account between the antenna array and the low noise amplifiers in the evaluation of the system sensitivity and optimization of the beamformer weights, and can be used when several signal and noise sources are present on the sky, ground, and inside the system itself. The described methodology has been applied to a practical PAF (comprising 144 tapered slot antennas operating from 1 to 1.75 GHz) which is installed at a 25-m reflector antenna. Comparison of numerical and experimental results shows a good agreement.

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    • "This design features a very short transmission line between the antenna and the LNA, since the circular slotline cavity has been moved sideways. More details on the array design and the numerical approach used for the EM-analysis of the antenna can be found in [7] and [6] [8], respectively. The simulations of the antenna have been carried out using CAESAR software that is an array system simulator, developed at ASTRON [9]. "
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    ABSTRACT: The purpose of this report is to document the noise performance of a complex beamforming array antenna system and to characterize the recently developed noise measurement facility called THACO, which was developed at ASTRON. The receiver system includes the array antenna of strongly coupled 144 TSA elements, 144 Low Noise Amplifiers (LNAs) (Tmin =35-40K) and the data recording/storing facilities of the initial test station that allow for off-line digital beamforming. The primary goal of this study is to compare the measured receiver noise temperatures with the simulated values for several practical beamformers, and to predict the associated receiver noise coupling contribution, antenna thermal noise and ground noise pick-up (due to the back radiation).
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    • "The following results pertain to the APERTIF prototype system which includes a phased array feed consisting of 144 tapered slot antenna elements, 144 low noise amplifiers and an active (digital) beamforming network. The entire receiving system has been modeled by an enhanced version of the method of moments used as the electromagnetic simulation software, combined with a microwave circuit simulator (CAESAR), and the high frequency electromagnetic solver GRASP for modeling the reflector antenna [5] [6] "
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    ABSTRACT: The results of four recently introduced beamforming schemes for phased array systems are discussed, each of which is capable to provide high sensitivity and accurate polarimetric performance of array-based radio telescopes. Ideally, a radio polarimeter should recover the actual polarization state of the celestial source, and thus compensate for unwanted polarization degradation effects which are intrinsic to the instrument. In this paper, we compare the proposed beamforming schemes through an example of a practical phased array system (APERTIF prototype) and demonstrate that the optimal beamformer, the max-SLNR beamformer, the eigenvector beamformer, and the bi-scalar beamformer are sensitivity equivalent but lead to different polarization state solutions, some of which are sub-optimal.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
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    • "This section describes a procedure to simulate PAF receiving systems, and to optimize their beamformer weights. For this purpose, CAESAR's combined MoM and circuit solver as presented in [21] has been extended and interfaced with GRASP [33]. Fig. 2 illustrates the general diagram of the implemented algorithm, where the first block lists the required input parameters: 1) the simulated or measured impedance matrix and the embedded element patterns of the considered antenna array. "
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    ABSTRACT: An optimal beamforming strategy is proposed for performing large-field surveys with dual-polarized phased-array-fed reflector antennas. This strategy uses signal-processing algorithms that maximize the beam sensitivity and the continuity of a field of view (FOV) that is formed by multiple closely overlapping beams. A mathematical framework and a newly developed numerical approach are described to analyze and optimize a phased array feed (PAF) system. The modeling approach has been applied to an experimental PAF system (APERTIF prototype) that is installed on the Westerbork Synthesis Radio Telescope. The resulting beam shapes, sensitivity, and polarization diversity characteristics (such as the beam orthogonality and the intrinsic cross-polarization ratio) are examined over a large FOV and frequency bandwidth. We consider weighting schemes to achieve a conjugate-field matched situation (max. received power), maximum signal-to-noise ratio (SNR), and a reduced SNR scenario but with constraints on the beam shape. The latter improves the rotational symmetry of the beam and reduces the sensitivity ripple, at a modest maximum sensitivity penalty. The obtained numerical results demonstrate a very good agreement with the measurements performed at the telescope.
    IEEE Transactions on Antennas and Propagation 07/2011; 59(6-59):1864 - 1875. DOI:10.1109/TAP.2011.2123865 · 2.18 Impact Factor
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