Extending the Capabilities of the GRASP and CAESAR Software to Analyze and Optimize Active Beamforming Array Feeds for Reflector Systems M.V. Ivashina 1 , O. Iupikov 2 , and W. van Cappellen 1 1 Netherlands Institute for Radio Astronomy (ASTRON), P.O. Box 2, 7990 AA Dwingeloo, The Netherlands Dwingeloo, The Netherlands. e-mail: ivashina@astron.nl , cappellen@astron.nl tel.: +31 521 595 100, fax: +39 011 5644099. 2 Sevastopol National Technical University, Radio Engineering Dept., Sevastopol, 99053, Ukraine Abstract − 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. 1 MOTIVATION AND OBJECTIVES An important limitation of conventional single-beam radio telescopes is that they can observe only a small region of the sky for each beam pointing. This problem can be surmounted by novel Phased Array Feeds (PAFs) of many electrically small antenna elements that are capable to provide closely overlapping beams on the sky in one snapshot and, hence, can greatly improve the size and continuity of the Field Of View (FOV) [1, 2]. However, the design of a PAF system represents a great challenge, as it requires an accurate analysis of the interaction between array element mutual coupling, receiver noise and beamformer weights to maximize the system sensitivity. Strong mutual coupling between the array elements is essential for achieving a wide frequency bandwidth and large FOV, but results in a strong correlation between the signal/noise waves, which propagate through the antenna-receiver system. These waves are then complex weighted and combined in a digital beamforming network to realize multiple beams [3-4]. Consequently, optimization of beamforming FPA systems is no longer an antenna or LNA problem alone, but it becomes a combined antenna – LNA and signal processing problem. In this paper we will present a numeral approach for the analysis and the optimization of PAF systems. This approach has been implemented in a newly developed toolbox for the CAESAR software [5] which interfaces the combined EM and Microwave Circuit solver with GRASP9 [6] to be able to perform the PAF system analysis in its entirety. The developed toolbox has been tailored to compute the overall (reflector-array-receiver) system noise-wave correlation matrix and the signal-wave vectors due to several signal and noise sources on the sky and inside the system itself. Based on these results, the optimum beamformer weights can be calculated for the specified observation directions and selected performance criteria [7-8]. The modeling approach has been applied to an experimental PAF system (APERTIF prototype) which is installed on the Westerbork Synthesis Radio Telescope. The numerical results have been obtained for the PAF prototype comprising 144 dual-polarized tapered slot antenna elements and demonstrate a very good agreement with the measurements performed at one of the telescope’s reflector. 2 MODELING APPROACH First, we will summarize the capabilities of two existing state-of-the-art software tools (GRASP and CAESAR) that can be used to analyze/design reflector antennas and array-receiver systems. Afterwards, it is descried how the underlying methodology can be extended for the analysis and optimization of PAF receiving systems. The CAESAR (Computationally Advanced and Efficient Simulator for ARrays) software is a customized numerical tool for radio astronomy that has been developed at ASTRON. The CAESAR ElectroMagnetic (EM) MoM solver has been tailored to compute the antenna radiation and impedance 978-1-4244-7368-7/10/$26.00 ©2010 IEEE 197