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A Note on Antipodal Focussing

James R. Wait

出版	U.S. Department of Commerce, National Bureau of Standards, 1963
URL	http://books.google.com.hk/books?id=Awzkooen1OkC&hl=&source=gbs_api
EBook	FULL_PUBLIC_DOMAIN

註釋

There has been some interest shown recently in the practical significance of the antipodal focussing in VLF propagation. If the earth and the ionosphere were perfectly concentric spherical surfaces, theory indicates that the amplitude of the field should build up to a maximum at the geographic antipodal point of the transmitter. In the language of optice, this point may be called an axial caustic. It is the purpose of the present paper to discuss this matter further. To shed some light on the subject, a very simple perturbation of the ideal model is considered. Essentially, it is assumed that the illumination of the antipodal region is non-uniform.