Abstract
In this study, a novel multi-parameter overall situation optimisation method and mathematical model has been developed for use with terrestrial and space reflector antenna electro-mechanical systems and other metallic and polymer composite civil engineering structures. To satisfy extremely high design requirements, the proposed approach incorporates the objectives from various structural and electromagnetic (EM) performances of the system such as structural frequency, weight, stiffness, strength, reflector surface accuracy, antenna EM efficiency (gain), and radiation patterns at many working/loading cases simultaneously. The optimisation involves geometric and material design variables, and integrated design of composites and structural systems. Various terrestrial, launch and orbital working environments and loading cases which affect antenna performances have been included in the optimisation. These involve self-weight at different elevation attitudes, wind loading, random/dynamic loads and temperature distributions. Both truss and sandwich parabolic reflector panels with honeycomb core and carbon fibre laminate skins stiffened with composite ribs have been optimised. The effects of structural deformation on antenna EM performances have been investigated, modelled and repeatedly analysed in the iterative optimum-seeking procedure. Optical ray tracing, spline function aperture field interpolation, geometric optics aperture integration, Zernike modes analysis and FFT techniques have been used to analyse the EM performances of distorted reflector antennas. An important aspect of the work was the establishment of evaluation criteria in optimising engineering systems. A new method is presented, which can be used as a design review tool to assess the design quality of engineering systems. This systematic method quantitatively evaluates a design from multi-discipline and numerous points of view simultaneously for Pareto optimisation. A general purpose optimisation program MOST (Multifactor Optimisation of Structures Technique) has been developed to implement the proposed approach. MOST has the ability to utilise ABAQUS as an analysis routine for linear and non-linear, static and dynamic structural analysis in the optimisation procedures. Examples are presented to demonstrate the capabilities of the optimisation methodology and MOST program system. These examples are: an 8m Cassegrain antenna system, a 3.6x2.6m composite space deployable reflector antenna structure, and two 4m low side-lobe off-set antenna systems (with composite structures). The optimisation results for these antennas show that the optimisation procedures succeed in that at all the working/loading cases the antenna performances have been greatly improved.