DESIGN OF NULLS IN ANTENNA FRESNEL ZONES FOR POSSIBLE RFI REDUCTION APPLICATIONS,

摘要

The rather unconventional concept of designing a null into the Fresnel Zone of an antenna is considered. A method is given that makes it possible to produce a null at some specific position. A possible application is the reduction of radio frequency interference. It is shown that,by proper antenna aperture blocking, a deep minimum can be located at the specific position in the Fresnel Zone. If the size of the blocked part of the antenna is much smaller than the aperture itself there is no significant influence on the main beam. However,side lobe levels become higher as more of the aperture is blocked. A wider and deeper minimum is obtained at the position more distant from the main beam axis. The results of this study indicate that the position rather than the size of the blocked area on the aperture is the more important factor in determining a deep minimum at the desired position. As the side lobe levels becomes higher the purpose of acquiring a minimum in the Fresnel region will be compensated by more power radiated in the directions other than that of the main beam. The area covered by the deep minimum is small as compared with the dimensions of the antenna aperture. (Author)