EFFECT OF SUBREFLECTOR AND FEED SCATTERING IN DUAL-SHAPED REFLECTOR SINGLE-CHAMBER COMPACT RANGES

The effects of feed interference and diffraction scattering from the s ubreflector in dual-shaped reflector single-chamber compact ranges are investigated. These effects are manifested as undesirable ripple of t he fields in the quiet or measurement zone of the compact range. Reduc tion of this ripple can be accomplished, without any deleterious effec ts on range performance, by serrating or rolling the edges of the subr eflector, and/or, as investigated herein and earlier, by substantial r eduction of the shaped subreflector edge fields. In an earlier work, t he feed spillover fields and the diffraction from the subreflector rad iating directly into the measurement zone was not accounted for in the single chamber geometry. We intend, in this paper, to show the effect s of this scattering on the measurements zone ripple. Three dual shape d models are considered - a -30 dB subreflector edge taper, a -20 dB t aper, and a -10 dB taper. In general, the -20 dB and -30 dB edge taper s prove sufficient to result in virtually no direct interference rippl e by the feed or subreflector fields anywhere in the measurement zone. The -10 dB subreflector edge taper does result in moderately extra ri pple effect close to the main reflector region of the measurement zone . Since the field scattered from the subreflector as well as the feed radiation generally decay approximately as 1/R from their respective c austic source regions, and whereas the field scattered from the main r eflector is focussed into a planar wave, the ripple due to these extra neous scattering effects (subreflector and feed radiated fields) dimin ishes rapidly with distance from the main reflector.