Tolerance Study of Reflector Antenna Systems (Random Surface Errors, Retrodirective Array, Focal Shift)

100 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1986.The tolerance issue is one of the most important problems in the design and construction of high performance antenna systems. This problem becomes more acute due to the large antenna size, the high operating frequency, and the hostile antenna operating environment. In this thesis, three topics related to the tolerance problem in reflector antenna systems are addressed.First, the effect of axial feed displacement is studied. Depending on the nature of the feed, it is found that higher directivity can sometimes be obtained as the result of feed movement either toward or away from the reflector. This result is similar to an optical phenomenon called the focal shift. A unified view is presented to explain the focal shift in parabolic reflectors in terms of spillover, aperture illumination efficiency and phase asynchronism. For a system with optimum aperture edge taper, no focal shift can exist.Second, the degradation in the sidelobe level of a reflector antenna subject to some random surface errors is investigated. Specifically, the random pattern function is considered and its sidelobe level studied using the level-upcrossing theory. Both the degradation of the peak sidelobe and the degradation of the sidelobe region with respect to certain CCIR sidelobe envelopes are obtained. The theoretical results are found in excellent agreement with those obtained by Monte Carlo simulations. Finally, extensive tolerance charts are presented. They should be useful to the antenna designers in specifying the required surface tolerance for achieving a desired sidelobe performance.Third, an experiment involving a seven-element array of open-ended waveguides is carried out to demonstrate the feasibility of near-field focusing for hyperthermia applications. A novel conjugate field matching scheme is used to adjust the phase of each radiating element in order to achieve constructive interference of fields in the focal region. This simple scheme readily lends itself to an adaptive implementation and shows promise as a viable method of reflector surface error compensation by a focal plane array.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD