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In previous work, the authors derived a closed-form expression from which the maximum quantization error and scan range in the visible region could be calculated for dense regular arrays. This is a continuation of the previous work in which a more advanced beamforming algorithm is investigated. It will be shown that a significant improvement on the array factor pointing accuracy is achieved. Quantization...
The Characteristic Basis Function Method (CBFM)-enhanced Jacobi method has been introduced as an improvement to the standard iterative Jacobi method for finite array analysis. This technique is a domain decomposition approach based on the Method of Moments (MoM) formulation. In some cases, e.g. array environments with a low degree of mutual coupling, the runtime benefit of the CBFM-enhanced Jacobi...
The analysis of sparse, disjoint finite antenna array structures is considered in this work. The Method-of-Moments (MoM) based CBFM-enhanced Jacobi technique is presented, and offers an improvement over the standard iterative Jacobi method in terms of convergence and accuracy. By applying the Characteristic Basis Function Method (CBFM) during each iteration the effect of mutual coupling between the...
This paper presents a method with which to calculate the maximum scan error due to phase quantization in the visible region of dense phased arrays. The scan error is expressed as a function of the density ratio and the number of bits being used for digitization. A closed-form expression is derived with which the maximum scan error as well as the maximum scan range in the visible region of the array...
Radio frequency (RF) metrology using unmanned aerial vehicles (UAV's) is adding a new dimension to Electromagnetic Compatibility (EMC) investigations. However, the self-induced radio frequency interference (RFI) has limited its applications. We investigate the feasibility of an RFI-quiet multicopter, designed from inception with electromagnetic shielding in mind. This work discusses and tests the...
Near-field scanning using multi-copter based artificial sources could aid calibration of elemental patterns on large Mid Frequency Aperture Array (MFAA) stations, planned for phase 2 of the Square Kilometre Array (SKA) project. Current high-end positioning systems used on multi-copters have an accuracy in the order of centimetres. This study investigates the extent of errors caused by uncertainties...
This paper considers the characteristic mode analysis (CMA) of finite antenna arrays, specifically for the design of the array element. The approach incorporates the Domain Greens Function Method (DGFM), i.e. a method-of-moments (MoM) based approach, to extract an active impedance matrix for each array element. The impedance matrices model the array environment for each antenna element and serve as...
The purpose of this work is to compare two iterative techniques that may be used for the analysis of large, disjoint finite antenna arrays, viz. the iterative Jacobi method and the iterative Domain Green's Function Method. These methods are conceptually similar, in that they offer alternative ways to improve non-local current distributions during the iterative process. The error convergence of each...
This work considers a combined structural-electromagnetic analysis of large dish reflector antennas typically used in radio astronomy. The effect of gravitational deformation on the radio telescope is quantified by a structural analysis conducted with a finite element solver. The deformed geometry is then analysed using a computational electromagnetic package from which the performance degradation...
The purpose of this work Is to Introduce the Iterative Domain Green's Function Method (DGFM) that may be used for the analysis of large, disjoint finite antenna arrays. The iterative DGFM presents an improvement over the conventional DGFM in terms of accuracy. The convergence rate of the technique will be illustrated at the hand of an example.
The South African Square Kilometre Array (SKA-SA) precursor instrument (MeerKAT) is being realized in the semi-desert Karoo region of the Northern Cape. Thus far, much has been achieved in terms of electromagnetic compatibility (EMC) interventions. However, recent surveys have shown that signal propagation ought to be examined in greater detail, ultimately leading to a site evaluation of the SKA-SA...
The indoor antenna range at Stellenbosch University was substantially modernised during a recent upgrade. Now, this antenna range contains five automated motion stages, plus one manual stage, that facilitate redundant planar and spherical near-field measurements using an integrated system. In this paper, this capability is used to investigate the effect of potential sources of reflection in the range.
The two dimensional formalism of the measurement equation was developed for radio synthesis telescopes that are coplanar and that have small fields of view. However, radio telescopes are being constructed that are spread over a continent and that have fields of view that cover a hemisphere. For such cases, a novel formalism of the measurement equation is developed to image a polarised sky.
Current and future interferometric imaging arrays in radio astronomy may be limited by the accuracy with which various direction-dependent effects, such as the antenna gain patterns, can be corrected. Doing this in an efficient manner during the calibration and imaging process is especially difficult due to these effects often being also baseline-dependent. A newly proposed method, called A-stacking,...
We consider the application of the Characteristic Basis Function Pattern (CBFP) method to calibrate for direction-dependent gain effects of the LOFAR Low Band Antenna (LBA) array. The use of array-based calibration models, as opposed to element-based calibration models, is proposed in order to reduce the number of solvable beam model parameters.
A review of full-wave and reduced-order modelling techniques for large, dense antenna arrays as proposed for the Square Kilometre Array is presented. A reduced-order method of modelling microstrip-fed Vivaldi Arrays, the Infinite Array Approximation as well as the Domain Green's Function method are discussed with specific reference made to runtime, memory usage and solution accuracy as compared to...
The purpose of this work is to present a quantitative comparison between three Method-of-Moments based domain decomposition techniques that are used for the analysis of large, disjoint finite antenna arrays. The methods considered are the Characteristic Basis Function Method, the Domain Green's Function Method, and a newly proposed improved version of the DGFM, i.e., the i-DGFM. The computational...
A number of new radio telescope designs, operating in the low-GHz regime, are currently under construction or in the pre-construction phase, in particular SKA precursor instruments and now SKA1-mid. This paper demonstrates the application of full wave computational electromagnetic analysis techniques — in particular the MLFMM — to the modelling of radio telescope dishes in this frequency band. Results...
This paper considers the efficient numerical analysis of large, finite antenna arrays comprising of disjoint subarrays by using the Domain Green's Function Method (DGFM) [1] in conjunction with the Characteristic Basis Function Method (CBFM) [2]. In the CBFM-enhanced DGFM we consider large arrays consisting of multiple disjoint subarrays and impose the infinite array type assumption, i.e. that the...
This paper considers the efficient numerical analysis of arbitrary finite antenna array structures using the Domain Green's Function Method (DGFM). The DGFM is implemented in the comprehensive 3D electromagnetic field solver, FEKO [1], and uses the Method-of-Moments (MoM) formulation. The technique is based on that initially presented in [2] and is a perturbation approach where mutual coupling between...
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