The Large Adaptive Reflector concept

Cost effective, new antenna technology is required to build the large collecting area being planned for the next generation of radio telescopes. The Large Adaptive Reflector (LAR) is a novel concept being developed in Canada to meet this challenge. A prototype with a 200-350m diameter reflector, operating up to 2 GHz with a bandwidth of 750 MHz is planned. With a collecting area up to ∼ 10% of the planned SKA, and an array feed capable of imaging a 0.3 deg 2 field-of-view, the prototype would address a number of the most compelling questions in modern astrophysics. The LAR is a concept for a large diameter, large f/D parabolic reflector that requires an airborne platform to support the prime focus receiver system. The active reflector surface has a very flat profile, supported over a large area, to reduce significantly the cost per unit area compared to traditional designs. A large field-of-view across a wide band-width is attained through the use of a focal plane phased array (Dewdney et al. 2002; Carlson et al. 2000). As the LAR reflector has a focal length of several hundred metres, the Focal Point Apparatus (FPA) needs to be supported by a " sky-crane " , for which we have chosen a helium-filled aerostat (Fig. 1). The aerostat is attached to the FPA via a leash, isolating the FPA from balloon motions, and the position of the FPA is controlled by six computer-controlled winches. This system is being evaluated using a 1/3-scale prototype (Fig. 1) to verify a computer simulation of the system. Once verified, the computer model becomes an extremely powerful design tool for the full-scale system. Recent tests on the prototype reveal that this system can work down to a zenith angle of 60 • , while maintaining the position of the FPA to within a few centimetres, adequate for the focus design we propose (Sec. 1.3). The LAR reflector is a large diameter, faceted approximation to an offset parabolic reflector with a long focal length (f/D∼2.5). Each of the 20-m triangular facets is supported on actuated legs that extend up to 12m. These actuators maintain the parabolic shape of the reflector as the pointing Figure 1. The Large Adaptive Reflector Concept. The top figure shows a cartoon of the system configuration. The lower figure shows the aerostat being used currently in the 1/3-scale prototype of the tethered aerostat system.