Digitally reconfigurable approach to compact antenna test range design

Abstract

The efficiency of use of the parabolic reflector of a single offset reflector compact antenna test range (CATR) is affected largely by the illumination provided by the range feed and the reflector edge treatment. Thus, when these factors are taken together it is commonly found that the realized quiet zone (QZ) diameter is typically as little as 30% of the diameter of the reflector for the commonly encountered case of a single offset CATR. Furthermore, single offset CATR performance is known to degrade as the wavelength of the illuminating fields becomes more comparable with the physical dimensions of the reflector because the physical optics (PO) assumption needed for collimation of the reflected field becomes less effective. Different reflector edge treatments such as rolled or serrated edges are commonly employed to taper the intensity of the reflected fields at the reflector aperture boundary, seeking to minimize the level of diffracted fields in the quiet-zone (QZ). Such strategies mean that at higher frequencies the transverse dimensions of the QZ are unnecessarily reduced thereby decreasing the spatial efficiency of the CATR and limiting the effective bandwidth of the antenna test system. In this paper we report preliminary results that begin to investigate the alternative strategy for controlling the signal illuminating the CATR reflector by utilising a shaped beam feed antenna. Building on our previously reported work of efficient CATR computational electromagnetic simulation, we report the use of an array feed whose excitation is optimized to achieve maximum QZ size for a given reflector dimension thereby minimising the cost of a new test system or increasing the capacity of an existing one. We illustrate the concept by employing the technique with a sector-shaped, single offset reflector CATR by examining the impact that this has on the amplitude taper and the amplitude and phase peak-to-peak ripple. We demonstrate that a 9-element array feeding an un-serrated rim reflector can attain a useable QZ size approaching 50% the size of the 80λ diameter main reflector.