ABSTRACT
This chapter examines electromagnetic diffraction from a circular hole in a perfectly conducting spherical shell. It analyses the full-wave solution developed accurately a large spherical reflector antenna, of aperture size some hundreds of wavelengths. Even the simplest problem describes of excitation of an open spherical cavity by vertical dipole differs from any conceivable acoustical analogy. In an analogous way enforcement of the mixed boundary conditions produces a pair of coupled dual series equations relatively for the rescaled coefficients in the form. The chapter focuses on an accurate study within the spherical reflector antenna near-field zone of the normalised electromagnetic energy density measured in decibels. It concludes that a single point source is a very ineffective feed, with dramatically reduced aperture efficiency over the larger range of electrical sizes.
