PURPOSE: To prevent the deterioration of functions of a sleeve as a Spertopf and a half-wavelength dipole antenna by covering the exposed part of a core wire and the outer surface of the sleeve with a covering material made of a dielectric or magnetic substance. ;CONSTITUTION: The cylindrical space formed between a sleeve 2 and a coaxial cable 1 is filled with a dielectric cylinder 7 of 'Teflon (R)', etc., and a magnetic cylinder 8 of ferrite, etc. Then a core wire exposed part 1a and the outer surface of the sleeve 2 are covered with covering materials 5, 6 made of a dielectric or magnetic substance respectively. In such a constitution, the wavelength is reduced like the inside of the sleeve 2. In this respect, the dielectric constants, the magnetic permeability, and the thickness of the materials 5 and 6 are properly selected. Thus it is possible to secure the coincidence of shortening degrees of wavelength between the inside and the outside of the sleeve 2 and to reduce the inside and outside wavelengths of the sleeve 2 less than the resonance wavelength. In other words, the sleeve 2 can ensure the satisfactory function as a Spertopf without deteriorating the function an antenna with regard to the radiation of radio waves, etc.;COPYRIGHT: (C)1994,JPO&Japio
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