Comparison of Compact Range Quiet Zone Performances as Predicted by Asymptotic methods vs. Method of Moments

Authors: Mark. Ingerson, and Vince Rodriguez
Publication: AMTA 2025
Copyright Owner: NSI-MI Technologies

There are many antennas and microwave analysis and modeling software packages available, each with its preferred computational approach. Sometimes some of the available packages can use different numerical techniques. It is always gratifying if the solutions are consistent.

Conventionally at NSI-MI compact range (CR) performance is evaluated with a proprietary software tool that drives two different approaches depending on the type of edge treatment. Serrated edge reflectors are handled using a well-known commercial package based on Asymptotic methods such as Geometrical (GO), Physical Optics (PO) and Geometrical Theory of Diffraction (GTD). For rolled blended-edge reflectors, the tool calls on a GO and modified unified theory of diffraction (UTD) introduced by Ellingson, Gupta and Burnside [1]. UTD used the method introduced by.

Recently, NSI-MI has been using a commercial package based on the Method of Moments (MoM) using higher order basis functions. This tool showed correlation with the GO and m-UTD approach introduced in [1]. The results were presented in [2]. While the Asymptotic methods are faster and can be used for quick optimization of the design, they are not suited for analysis of the feed fence interaction, the reflector absorber skirt that hides the support structure or the interaction with the antenna under test (AUT) positioner. The MoM based approach allows for these types of analysis [3,4]. The MoM package leverages techniques like highorder basis functions (HOBFs), and sophisticated reduction methods. In this software a CR dish is modeled though the import of a CAD file that is used in the manufacture of the CR dish or is modeled within the software package GUI using its native CAD functionality.

In this paper the quiet zone (QZ) performances predicted by the commercial package using asymptotic techniques and those predicted by the MoM-HOBF package are compared for a typical serrated CR dish. The QZ performance is determined by a set of metrics driven by amplitude and phase flatness along onedimensional cuts across two lateral and orthogonal axes centered at the center of the QZ as recommended in [5]. The results show that with the proper meshing constraints the performances modeled by the asymptotic approach and the MoM-HOBF are consistent and comparable for the cases presented in this. The long history of predictions that match the measured results upon implementation on the field of reflector designed by the asymptotic technique means that the MoM results can be used to accurately predict the performance of ranges while analyzing the effects of fences, skirts and the absorber on the AUT positioners that the MoM tool allows.

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