Theoretical design data are presented for short Yagi aerials. The arrays considered are (a) equi-spaced linear arrays with one driven half-wave dipole and from one to four identical parasitic radiators; (b) an equi-spaced linear array of two unequal parasitic radiators placed in front of a driven half-wave dipole; (c) an equi-spaced linear array of two unequal parasitic radiators placed one on each side of a driven half-wave dipole; and (d) an array of two driven dipoles at half-wavelength spacing each having a parasitic radiator behind it.Polar diagrams, power gain and input resistance curves, as a function of the self-reactance of the parasitic radiators, are provided for each array. On the basis of transmission-line theory of aerials, the above reactance is − 120 cot (πl/λ) logz (l/a) ohms, for a cylindrical wire radius a and length l.