Some array applications of the curl antenna

The curl antenna is a single-turn horizontal spiral fed by a monopole-like feed. The spiral and monopole dimensions are usually optimized to improve i ts radiation field and axial ratio for broadside radiation. It is shown in this study that the axial ratio can be optimized in certain regions of the radiation zone. In addition, the radiation pattern can be tilted off its ax is on one side, which may be used to improve the array pattern scanning in small arrays. The concept is used for design of small planar arrays for mob ile satellite communications. The axial ratio and array gain enhancements, in an off-axis coverage zone, are initially investigated numerically. The a rray is placed over an infinite ground plane. Experimental prototypes are, however, implemented and tested over a finite 4.5 lambda X 4.5 lambda groun d plane. The axial ratio performance appears to remain satisfactory, but th e array gain reduces slightly, due to the back radiation. The curl antenna configuration, in dual inverted form, is also used for wide-angle axial rat io improvement. It provides a compact high-gain antenna with excellent circ ular polarization over most of the hemispherical region.