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Abstract

A radio antenna that comprises a half-wave dipole as the detecting element, with one or more rods placed behind and in front of it. The additional rods are made of a conducting material but are not electrically connected to the dipole (they are thus ‘parasitic’ leading to the alternative name ‘parasitic aerial’ for the device). The rods behind the dipole reflect radiation onto it and screen it from radio sources behind it. The rods in front of the dipole act to concentrate the radiation, and are called directors. The Yagi antenna is very familiar as the domestic TV aerial. In radio telescopes it may be used as the feed of a large radio dish, or many Yagis may be combined into an array.