Reconfigurable contour beam-reflector antenna synthesis using a mechanical finite-element description of the adjustable surface

A synthesis technique based on a mechanical finite-element (FEM) surface description of dual-offset reflector (DOSR) surfaces is described. This technique is used to implement a reconfigurable contour beam for a geostationary satellite application. The mechanical finite-element description of the surface takes into account the mechanical properties of the reflector surfaces and the effect of a finite number of forces applied at control points on the surface. Mechanical adjustment is achieved using high-deflection stacked piezoelectric actuators attached to the rear of a lightweight flexible subreflector surface. Both the main and subreflector surfaces are shaped for an initial required geographical coverage zone and then the main reflector surface is assumed to be fixed in shape. The variable shape subreflector is then synthesized to achieve the desired illumination for different geographical regions and different geostationary positions. Based on a study of the effect of the mechanical properties of the subreflector surface and actuator number and placement, a practical design has been completed and the ability to reconfigure the beam has been verified.

I. Introduction

Contour beam antennas are used on geostationary satellites to increase antenna efficiency and reduce interference in geographical areas adjacent to the service area. As satellites become more reliable and their expected service life increases, the probability that the satellite service area and/or satellite operator will change also increases. In this case, the ability to reconfigure the contour beam will be a definite advantage. In addition, one may want to correct for surface distortions or atmospheric conditions. The Ku-band attenuation due to atmospheric water vapor, for example, may be compensated for by increasing the gain to areas currently receiving precipitation and decreasing the gain to dryer areas. Reconfigurable contour beams can be implemented in a number of ways including large aperture arrays, multiple feed reflector antennas, and reflector antennas with adjustable main and/or subreflector surfaces. The contour beam reflector antenna (CBRA) is widely used because of its versatility and low cost per unit aperture. The disadvantage of using the array fed offset reflector antenna is that the beam-forming network is heavy, lossy, and expensive. The same disadvantage applies to phased array antennas. In addition, both of these antennas have complex components that need to be space qualified. Piecewise adjustable subreflectors have been used in the past to correct for gravitational distortion in large axially symmetric dual-reflector radio telescope antennas [1], [2]. More recently, they have been proposed as a way to correct for main reflector distortion in dual-offset reflector (DOSR) antennas [3]. A reconfigurable CBRA has also been implemented using an adjustable mesh main reflector and a cluster-feed arrangement [4].