On the cross-polarization characteristics of crooked wire antennas designed by genetic algorithms

Genetic algorithms (GA) have found numerous applications in the design and optimization of antennas. E.E. Altshuler and D.S. Linden have presented a crooked wire antenna made up of a few straight segments above a ground plane and fed by a coaxial line at the base (see Altshuler and Linden, "Electromagnetic Optimization by Genetic Algorithms", John Wiley & Sons, Inc., p.211-48, 1999; Altshuler, IEEE Trans. on Antennas and Propag., vol.48, p.968-72, 2000). The design of such an antenna was facilitated by the use of a GA optimization. However, the cross polarization level was not specified in the cost function and it was not discussed in the analytical or experimental pattern data of the antennas. In many modern communication applications, there is a need for simple circularly polarized antennas for hemispherical coverage with a good axial ratio or low value of cross polarization. We revisited the crooked wire antenna because of its simplicity. It was found that with a few straight segments it was not possible to produce circular polarization with a low value of cross polarization over a wide angular region. If the number of segments is increased to a large value, the antenna shape approaches that of a spiral or curl antenna.