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

摘要

The effects of feed interference and diffraction scattering from the subreflector in dual-shaped reflector single-chamber compact ranges are investigated. These effects are manifested as undesirable ripple of the fields in the quiet or measurement zone of the compact range. Reduction of this ripple can be accomplished, without any deleterious effects on range performance, by serrating or rolling the edges of the subreflector, and/or, as investigated herein and earlier, by substantial reduction of the shaped subreflector edge fields. In an earlier work, the feed spillover fields and the diffraction from the subrefiector radiating directly into the measurement zone was not accounted for in the single chamber geometry. We intend, in this paper, to show the effects of this scattering on the measurements zone ripple. Three dual shaped models are considered — a -30 dB subreflector edge taper; a -20 dB taper, and a -10 dB taper. In general, the -20 dB and -30 dB edge tapers prove sufficient to result in virtually no direct interference ripple by the feed or subreflector fields anywhere in the measurement zone. The -10 dB subreflector edge taper does result in moderately extra ripple 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 caustic source regions, and whereas the field scattered from the main reflector is fbcussed into a planar wave, the ripple due to these extraneous scattering effects (subreflector and feed radiated fields) diminishes rapidly with distance from the main reflector.