YAGI-UDA arrays of shaped dipoles for increased directivity

It has been demonstrated by approximate calculations and by experiments [1]-[3] that, for elements longer than a wavelength, shaped dipoles could give a higher directivity than straight dipoles because the distance differentials in the far zone for the various parts of a properly shaped dipole could compensate the phase reversals of the current distribution on the dipole. It is natural to extend this method for increasing directivity to Yagi-Uda arrays. This paper presents a procedure for maximizing the directivity of a Yagi-Uda array of shaped conducting elements. The method of moments is used to obtain a matrix representation of the array problem. The radius of the array elements is taken into consideration, and sinusoidal current distributions over the elements are not assumed. The parameters that determine the shape and the relative positions of the array elements for maximum directivity are found by applying the simplex method for function minimization [4].