ANALYSIS OF PARABOLIC SHAPED REFLECTOROF AN ANTENNA

Abstract

Large self-deployable, reflector antennas are needed for a variety of space-based applications. The potential applications include mobile communications, earth observation radiometry, active microwaves sensing, orbiting very-long-baseline interferometry, space-based radar and micro spacecraft. Inflatable structures have been a subject of renewed interest in recent years for space applications such as communication antennas, solar thermal propulsion, and entry/landing systems. This is because inflatable structures are very lightweight and on-orbit deployable. In addition, they have high strength-to-mass ratio and require minimal stowage volume, which makes them especially suitable for cost-effective large space structures. For these structures to give signal accurately, their vibration must be controlled while keeping the weight low. Piezoelectric materials have become ' strong candidates for actuator and sensor applications in the active vibration control of such structures due to their lightweight, conformability to the host structure, and distributed nature. Several papers on static structural analysis and dynamic analysis of inflated cylinders and toroidal structures have been written, describing different techniques such as linear shell theory, and nonlinear and variational methods, but very little work had been done in dynamics of complete structures of inflatable antenna reflector with torus and struts. It is well known from the theory of shells that classical solutions of shells subjected to different types of loads involves tedious calculations and is extremely difficult especially for shells of arbitrary shapes. The finite element method is very much suitable for the analysis of shells of general shape. In these modem days, number of software are available for finite element analysis, ANSYS is one of such software. The present work is aimed to analyze static and dynamic behavior of a large 5-meter thin film inflatable reflector, and determination of different mode shape and natural frequencies. In static analysis pressure is applied on reflector and the point of maximum & minimum stress has been found out. The change in shape of torus and reflector has been presented. In dynamic analysis, a free vibration analysis of a complete inflated antenna reflector with torus is performed and the different natural frequencies and mode III shapes has been determined. The effect of different parameters such as aspect ratio, internal pressure, and wall-thickness of the inflated antenna on the natural frequencies and mode shapes of the structures has been studied. Then patches of PVDF are attached on the reflector and the passive effect of piezopolymer on the dynamics of inflatable space-based structures has been studied and trend in natural frequencies for various patch areas and thicknesses has been explored.