New Optimisation Approach for Log-periodic Array Antenna Applied to Eleven Feed Design

Jian Yang and Per-Simon Kildal

One way of achieving antennas with one or more octaves bandwidths is to use log-periodic arrays of dipole elements. Chalmers University of Technology has been recently developing a new dual polarized antenna with more than one decade bandwidth, i.e. the Eleven antenna. It has over the bandwidth nearly constant beam width with 11 dBi directivity and the phase centre has the same location all over the band. In addition, the Eleven antenna has low profile. It can therefore find several applications in radio astronomy and other wideband systems. Due to the large size of the geometry in terms of wavelengths at the highest frequency, optimisation of the performance of the Eleven antenna is a large challenge. Previously we had achieved a reflection coefficient of -8 dB over 1 - 13 GHz by using a simple one-by-one parameter optimisation scheme. In the present paper we will present a new method: full optimisation by using Genetic Algorithm on a single element embedded in an infinite log-periodic array. Using the new method, the reflection coefficient can be reduced to - 12 dB over the whole 1 - 13 GHz range.